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AFTAC ltr 25 Jan 1972

BEST AVAILABLE COPY

TECHNICAL REPORT NO. 70-1

OPERATION OF THE TONTO FOREST SEISMOLOGICAL OBSERVATORY

Final Report, Project VT/9702 Contract F33657-69-C-0803

1 January through 51 December 1969

Sponsored by

Advanced Research Projects Agency Nuclear Test Detection Office

ARPA Order No. 624

NOTICE

THIS DOCUMENT IS SUBJECT TO SPECIAL EXPORT CONTROLS AND EACH TRANS- MITTAL TO FOREIGN GOVERNMENTS OR FOREIGN NATIONALS MAY BE MADE ONLY WITH PRIOR APPROVAL OF CHIEF, AFTAC.

TELE DYNE GEOTEQi 5401 Shi loh Road Garland, Texas

15 February 1970

I

IDENTIFICATION

AFTAC Project No: Project Title: ARPA Order No: ARPA Program Code No: Name of Contractor:

Contract Number: Effective Date of Contract Amount of Contract: Contract Expiration Date: Program Manager:

VELA T/9702 Operation of TFSO 624 8F10 Teledyne Industries, Geotech Division Garland, Texas F33657-69-C-0803 1 January 1969 $441,976 31 December 1969 B. B. Leichliter, BR1-2561, ext. 222

TR 70-1

CONTENTS

ABSTRACT

-i-

Page

1. INTRODUCTION j 1.1 Authority 1 1.2 History 1 1.3 Work of Project VT/9702 1

2. SUMMARY 3

3. OPERATION OF THE TONTO FOREST SEISMOLOGICAL OBSERVATORY 4 3.1 General 4

3.1.1 Security inspection 4 3.1.2 Government property inspections 4 3.1.3 Routine calibration of test equipment 4 3.1.4 Quality control 4

3.2 Seismograph systems operated during Project VT/9702 6 3.2.1 Crossed-linear array b 3.2.2 Thirty-seven element array 6 3.2.3 Seven-element array of three-component 6

long-period seismographs 3.2.4 Broad-band seismograph b

3.3 Standard seismograph operating parameters 9 3.4 Data channel assignments 9 3.5 Operation of the Astrodata Seismic Data Acquisition System 9 3.6 Shipment of data to SDL 20 3.7 Facilities and equipment 20

3.7.1 Facilities maintenance 20 3.7.2 Equipment maintenance 20

3.8 Emergency power generator 29

4. MAINTENANCE AND MODIFICATION OF TFSO INSTRUMENTATION 32 4.1 Short-period array 32

4.1.1 Lightning protection 32 4.1.2 Spike noise 32 4.1.3 Solid-state amplifiers 32

4.2 Long-period array 32 4.2.1 Lightning protection 32 4.2.2 Solid-state amplifier 39 4.2.3 Calibration circuit transients 39 4.2.4 Tone-controlled calibration circuit 39 4.2.5 Horizontal seismometer case seals 41

TR 70-1

CONTEXTS, Continued

Page

3. ROUTINE .ANALYSIS 42 5.1 Introduction 42 5.2 Analysis procedures 42

5.2.1 Preliminary analysis 42 5.2.2 Checking and finalization of preliminary 42

analysis 5.2.5 Daily reporting to the ESSA-C^GS 45

b. INSTRUMENT EVALUATION 44 0.1 High-frequency seismograpli 44 6.2 Experimental Develocorder Pump, Model 50Ü82 44 b.5 Multichannel filter system (MCF) 4b b.4 Extended long-period seismographs 52 b.5 Evacuated LP horizontal seismographs 52

b.5.1 Evacuated seismometer 52 6.5.2 Evacuated tank vault 52 b.5.3 Discussion of results 58

b.b Nitrogen-filled LP tank vaults 58 b.7 Flag traces b7 b.8 Lightning protection b7 b.9 Multiconductor cable b7

7. ASSISTANCE PROVIDED TO OTHER GROUPS b8 7.1 Telemetry to Massachusetts Institute of Technology b8 7.2 The University of Utah b8 7.3 Texas Instruments Inc. b8 7.4 University of California, San Diego b8 7.5 National Aeronautics and Space Administration b8 7.b University of California, Los Angeles b9 7.7 Visitors b9

7.7.1 Visits by VELA seismological center personnel 69 7.7.2 Teledyne visitors 69 7.7.5 Visits by school groups b9 7.7.4 Others 70

8. REPORTS AND DOCUMENTS PUBLISHED UNDER PROJECT VT/97Ü2 71 8.1 Technical reports 71 8.2 Letter reports 71

APPENDIX 1 - Statement of work to be done

APPENDIX 2 - Letter report on "Flag traces at TFSO"

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TR 7Ü-1

ILLUSTRATIONS

Figure Page

1 Configuration of the crossed-linear array of 7 short-period seismographs at TFSO

2 Vault locations in the 57-element, short-period 8 array, the 7-element, long-period array, and the crossed-linear array at TFSO

3 Response characteristics of TFSO standard seismographs 10 normalized at a period of one second

4 TFSO ^hort-period seismograms exhibiting spikes on Z66, 33 a solid-state system with data and power on the same pair. (X1Ü enlargement of 16-millimeter film)

5 TFSO short-period seismograms of solid-state systems 34 having power on one pair and calibrations and data on the other pair. Note the absence of spikes as compared to Z66 on DT 10 at same tin.e interval. (212 noisy, cause unknown) (X10 enlargement of 16- millimeter film)

6 TFSO short-period seismograms of solid-state systems 35 having power on one pair and data and calibration on other pair. Note the absence of spikes as compared to Z66 on DT 10 at same time interval. (Z16 noisy, cause unknown) (X10 enlargement of 16-millimeter film)

7 TFSO short-period seismograms of solid-state systems 36 having power on one pair and calibration and data on other pair. Note the absence of spikes as compared to Z66 on DT 10 at same time interval. (XIO enlargement of 16-millimeter film)

8 New lightning protection for LP power circuits at sites 37 1, 2, 3, 4, and 5

9 Lightning protection circuit for DC power to Hoffman 38 boxes at TFSO sites LP6 and LP7

10 Amplifiers mounted in Hoffman box at LP3 40

11 View of Hoffman box at LP3 with insulated lid in place 40

12 Frequency response of TFSO high frequency seismograph 45 ZHF8

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TK 70-1

ILLUSTRAT1ÜXS. Continued

Figure Page

13 Frequency response for MCF using BS-5 (55 point) filter. 47

This was used with data from TFSO channel Z4.

14 MCF seismograms exhibiting the response of BS traces to 48 a low level teleseismic event, epicenter unknown. (X1Ü enlargement of lb-millimeter film)

15 TFSO short-period seismograms exhibiting response 50 of MCF1, MCF2, and MCFPR to a high frequency signal of a near regional event, epicenter unknown. (X1Ü enlargement of lb-millimeter film)

16 TFSO short-period seismograms exhibiting response of 51 MCF1, MCF2, and MCFPR to low frequency signal of a teleseismic event, epicenter unknown. (X10 enlarge- ment of lb-millimeter film)

17 Frequency response of TFSO experimental long-period 55 seismograph ZXLP

18 Frequency response of TFSO experimental long-period 54 seismograph ZYLP

19 Long-period seismogram showing responses of ZXLP, 55 ZVLP, and Z1LP to typical seismic background noise during a quiet period

20 Long-period seismogram showing responses of ZXLP, 5b ZYLP, and Z1LP seismographs to the PP phase of an event having an epicenter located approximately 150 degrees WSW of TFSO

21 Long-period seismogram showing response of ZXLP, ZVLP, 57 and Z1LP to Rayleigh waves from an event of unknown epicenter

22 , Long-period seismogram showing responses of EXLP and 59 E1LP to typical night background when operating at normal magnifications. HXLP vault was evacuated. (XIO enlargement of lb-millimeter film)

23 Long-period seis gram showing responses of EXLP and 60 E1LP to a group of surface waves. Epicenter is unknown. EXLP vault was evacuated. (X10 enlargement of lb- millimeter film)

24 Long-period seismogram showing responses of EXLP and E1LP bl to a group of surface waves. Hpicenter is unknown. EXLP vault was evacuated. (X10 enlargement of 16- millimeter film)

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TR 70-1

ILLUSTRATIONS, Continued

Figure Page

25 Long-period seismogram showing responses of EXLP and 62 E1LP to atmospheric pressure changes. EXLP vault was evacuated. (X1Ü enlargement of lb-millimeter film)

26 Long-period seismogram showing responses of EXLP and 63 E1LP to wind. EXLP vault was evacuated. (X10 enlarge- ment of 16-millimeter film)

27 Long-period seismogram showing response of EXLP and 64 E1LP to typical night background with EXLP operating at 140K magnification. EXLP vault was evacuated. (XiÜ enlargement of 16-millimeter film)

28 Long-period seismogram showing response of EXLP and 65 E1LP to surface wave train. Epicenter is unknown. EXLP vault was evacuated. (X10 enlargement of 16- millimeter film)

29 Dry nitrogen tank, controls and gauges mounted in box 66 prior to installation at LP7, 1FS0

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TR 70-1

TABLES

Table

Operating parameters and tolerances of standard seismographs at TFSÜ

Page

11

:

5

5

6

7

8

9

10

11

TFS^ frequency response norms and tolerances

Data channel assignments for TFSO lb-millimeter film seismograms made during Project VT/97Ü2. Dates without asterisks are start dates; dates with asterisks are stop dates

Data channel assignment for TFSO FM magnetic-tape seismograms made during Project VT/9702. Dates without asterisks are start dates; dates with asterisks are stop dates

Key to the designations used in the data format assignments at TFSO

ASDAS recording format used at TFSO

Summary of Spiral-4 cable replacements in 1969

Summary of Spiral-4 cable splices in 1969

1969 annual 57-element short-period array and 7-element 3-component long-period array seismometer motor consr^nt checks

Local (L) , near regional (N) , regional (R) , and teleseismic (T) events reported to the C5GS by TFSO from 1 January through 51 December 1969

MCF recording formats from 1 January through 31 March 1969

12

15

18

19

21

27

28

29

43

49

TR 70-1

-VI-

mm^mmmmmmtm - j[l!tfMi.

ABSTRACT

This is a report of the work accomplished on Project VT/9702 from 1 January through 51 December 1969. Project VT/9702 includes the operation, evaluation, and improvement of the Tonto Forest Seismological Observatory (TFSO) located near Payson, Arizona. It also includes special research and test functions carried out at TFSO and research and development tasks performed by the Garland, Texas, staff using TFSO data.

TR 7Ü-1

I

OPERATION OF THE TONTO FOREST SEISMOLOGICAL OBSERVATORY

Final Report, Project VT/9702 Contract F33657-69-C-0803

1 January through 51 December 1969

INTRODUCTION

1.1 AUTHORITY

The research described in this report was supported by the Advanced Research Projects Agency, Nuclear Test Detection Office, and was monitored by the Air Force Technical Applications Center (AFTAC) under Contract AF 33657-69-C-0803, dated 1 January 1969. The statement of work for Project VT/9702 is included as appendix 1 to this report.

1.2 HISTORY

The Tonto Forest Seismological Observatory (TFSO), located near Payson, Arizona, was constructed by the United States Corps of Engineers in 1963. TFSO was de- signed to record seismic events and to be used as a laboratory for testing, comparing, and evaluating advanced seismograph equipment and recording tech- niques. The instrumentation was assembled, installed, and operated until 30 April 1965 by United Electrodynamics (UED) - now Earth Sciences, A Teledyne Company - under Contract AF 33(657)-7747. In March 1964, the Long-Range Seismic Measurements (LRSM) Program provided eight mobile seismic recording vans to extend the existing instrument arrays at TFSO. On 1 May 1965, Geotech ascumed the responsibility for operating TFSO. The LRSM vans were phased out of the TFSO operation on 3 October 1965. During the 20-month period from 1 May 1965 through 31 December 1966, the operation of TFSO under Project VT/5055 was closely allied with the work performed at the Blue Mountains, Uinta Basin, and Wichita Mountains Seismological Observatories, under Projects VT/1124, VT/4054, and VT/5054. When reasonable, operating procedural changes, observatory instrumen- tation improvements, and special research investigations were accomplished simultaneously at all observatories. In other instances, improvements, modifi- cations, and/or procedures that had been developed and proven at another obser- vatory were incorporated into the TFSO operation. During 1967, under Contract AF 33657-67-C-0091, Project VT/7702, a 37-element, short-period array and a 7-element, long-period array were designed and installed.

1.3 WORK OF PROJECT VT/9702

The work of Project VT/9702 was to some degree a continuation of the work of earlier TFSO projects, and was similar to much of the work conducted at the Uinta Basin Seismological Observatory under Project VT/6705. The work of this project can be divided into the following general categories:

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TR 70-1

mm

a. Continued operation of TFSO;

b. Evaluation and improvement of the standard instrumentation to provide a more efficient and effective observatory;

c. Field testing of newly developed and experimental instrumentation;

d. Analysis of resulting seismometric data;

e. Evaluation of the capabilities of the 37-element short-period and 7-element long-period arrays;

f. Short-period and long-period noise studies.

-2-

TR 70-1

"—** Wtlllil

SUMMARY

Work at the Tonto Forest Seismological Observatory was directed primarily toward the continuous operation of four seismograph systems; the 'ST-element short-period array, the seven-element, three-component, long-period array, the broad-band vertical seismograph, and the cr^jsed-linear, short-period array. Operating parameters of each seismograph system were maintained within specified tolerances and repairs were performed as required. All magnetic- tape and Develocorder film seismograms were shipped to the Seismic Data Laboratory, Alexandria, Virginia. Most were shipped directly, but unselected samples were routed through the Geotech laboratories at Garland, Texas, for quality control inspection.

Data taken during 1969 indicated that modifications made to the short-period array during 1968 caused a reduction of 60 percent in the lightning damage. Modifications made in June 1969 to the long-period array circuits reduced remote power supply damage to zero.

Seismometric data were routinely analyzed and earthquake phase arrival data were transmitted daily to the Environmental Science Services Administrations Coast and Geodetic Survey.

Operational tests and evaluation work was conducted with a high-frequency seismograph, an experimental Develocorder pump, a multichannel filter, and two high-magnification long-period seismographs. Nitrogen-fil'ed long-period tank vaults were established and tested, and alternate arrangements of summed data for flag traces were studied.

Assistance was provided to personnel from four universities, one industrial organization, and one government agency who visited TFSO to test geophysical instrumentation,

TR 70-1

:>. OPERATION OF THE TONTO FOREST SEISMOLOGICAL OBSERVATORY

5.1 GENERAL

5.1.1 Security Inspection

Mr. K. G. Ozbolt, Industrial Security Inspector from the Phoenix, Arizona, office of the Los Angeles Defense Contract Adminstration Services Region (DCASR), conducted a routine security inspection during January 1969.

Mr. M. L. Craig, Industrial Security Chief, conducted routine inspections during May 1969 and September 1969. During each of these visits, the observatory pro- cedures, methods, and facilities were found to be substantially in conformance with the requirements of the Department of Defense Industrial Security Manual.

5.1.2 Government Property Inspections

During August 1969, Mr. D. Peebles, Chief of the Production Division, and Mr. E. Friedman, Property Officer, both of the Phoenix office of Los Angeles DCASR, conducted a utilization survey of industrial plant equipment located at TFSO. This inspection was made at the request of DCASR, Dallas, Texas.

Several items were found that did not conform to DCASR standards. These dis- crepancies concerned methods for storage of materials and property, and the maintenance of Government vehicles. These discrepancies were corrected by

changing TFSO procedures.

Mr. E. Friedman and Mr. W. Moore, newly assigned property officer for TFSO, made an orientation visit during early October.

In November, Mr. Friedman visited TFSO with Mr. Ray Madden in order to introduce Mr. Madden as the new TFSO property administrator, replacing Mr. Moore.

5.1.5 Routine Calibration of Test Equipment

Test instruments were routinely calibrated at TFSO during the year and calibra- tion logs were maintained for all such instruments.

All calibrations are referred to Eppley standard cells which, in turn, are periodically certified to deviate less than 0.001 percent from standards main- tained by the National Bureau of Standards.

5.1.4 Quality Control

5.1.4.1 Quality Control of 16-Millimeter Film Seismograms

Quality control checks of randomly selected 16-millimeter film seismograms from data trunks 1, 2, and 8, and the associated operation logs were made in Garland. Items that were routinely checked by the quality control analyst include:

a. Film boxes - neatness and completeness of box markings;

b. Develocorder logs - completeness, accuracy, and legibility of logs;

TR 70-1

■ '■ "■ ■■"' ■ ""

c. Film:

(1) Quality of the overall appearance of the record (for example,

trace spacing and trace intensity) ;

(2) Quality of film processing;

d. Analysis - completeness, legibility, and accuracy of the analysis sheets.

Results of these evaluations are sent to the observatory for their review and

comment.

3.1.4.2 Quality Control of FM Magnetic-Tape Seismograms

Routine quality control checks of randomly selected magnetic-tape seismograms were made in Garland and at TFSO to assure that recordings met specified stand- ards. The following are among the items that were checked during quality control

analysis:

a. Tape and box labeling;

b. Accuracy, completeness, and neatness of logs;

c. Adequate documentation of logs by voice comments on tape where applicable;

d. Seismograph polarity;

e. Level of calibration signals;

f. Relative phase shift between array seismographs;

g. Level of the microseismic background noise;

h. Level of the system noise;

i. PTA dc balance;

j. Oscillator alignment;

k. Quality of the recorded WWV signal where applicable;

1. Time-pulse carrier;

m. Binary coded digital time marks.

Discrepancies noted during quality-control analysis resulted in the adjustment of tape soeed on four FM magnetic-tape recorders during the year.

3.1.4.3 Qrality Control of Digital Magnetic-Tape Seismograms

Because of difficulties encountered in recovering data from some of the digital magnetic-tape seismograms we began routine checking of the quality of the Astro- data seismogram- during June. Initially, one tape per day was checked, alter- nating between tapes recorded on transports 1 and 2; however, later we found

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TR 70-1

I that checking of two or three seismograms each week was adequate to maintain good quality data. U'e found that routine quality conv.rol analysis of digital seismograms was valuable in helping to detect Astrodata system malfunctions, format errors, and systematic operator errors which might otherwise have gone undetected for extended periods. Also, quality control efforts were successful in improving the accuracy of the operating logs and in delineating areas where system modifications could improve the system performance.

Among those characteristics of the digital seismograms that we routinely check are:

a. Presence or absence of parity errors;

b. Recording sensitivity;

c. Fidelity of reproductions;

d. Quality of x-y plots of short intervals of data from each channel;

e. Presence of header record and correct record length;

f. Accuracy, completeness, and neatness of the associated logs.

3.2 SEISMOGRAPH SYSTEMS OPERATED DURING PROJECT VT/9702

3.2.1 Crossed-Linear Array

The crossed-linear array, consisting of 12 short-period three-component elements spaced at intervals of about 2 kilometers was operated throughout Project VT/9702, A summation of eight of the vertical components of elements of this array was used as a flag trace during routine on-line seismogram analysis. The configura- tion of this array is shown in figure 1 and its orientation in relation to the other TFSO arrays is shown in figure 2.

3.2.2 Thirty-Seven Element Array

A 37-element array of short-period vertical seismographs (figure 2) was installed under Project VT/7702. Under Project VT/8702, this array was evaluated from the standpoint of reliability, beam-steering capability, and detection capability. Operation of this array continued under VT/9702.

3.2.3 Seven-Element Array of Three-Component Long-Period Seismographs

A seven-element array of three-component long-period seismographs was installed during Project VT/7702. Under Project VT/8702, operational difficulties were experienced with seismographs in this array and the major efforts were directed toward solving these problems. Some modifications and changes were made to the seismographs and its operation was continued during Project VT/9702. The con- figyration of this array is also shown in figure 2.

3.2.4 Broad-Band Seismograph

Operation of the vertical broad-band seismograph was resumed on 21 May 1969.

TR 70-1

■■■ii -I, ——-— ———

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A T79 R80

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% SHORT-PERIOD VERTICAL SF.ISMOGRAPH

A THREE COMPONENT SHORT-PERIOD SEISMOGRAPH

O EXPERIMENTAL VAULT

□ LONG-PERIOD VAULT

X///\ CENTRAL RECORDING BUILDING

SCALE

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T

KILOMETERS

Figure 1. Configuration of the crossed-linear array of short period seismographs at TFSO

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TR 70-1

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Figure 2. Vault locations in the 37-element, short-period array, the 7-element, long-period array, and the crossed-linear array at TFSO

0 4699

-8-

TR 70-1

I ■II "I

This seismograph uses a seismometer installed in the LP1 vault and a phototube amplifier installed in the CRB, and has the frequency response shown in figure 3,

3.3 STANDARD SEISMOGRAPH OPERATING PARAMETERS

The operating parameters and tolerances for the TFSO standard seismographs are shown in table 1. Frequency response tests are made monthly, and the parameters of seismograph systems not conforming to the tolerances shown in table 2 are reset.

Normalized response characteristics of TFSO standard seismographs are shown in figure 3. In addition to these standard seismographs, two filtered summation seismographs and a high-frequency seismograph were recorded. A resistive sum- mation of eight selected elements of the crossed-linear array was filtered by each of two band-pass filters having different characteristics. One of the filtered seismographs (ETF) utilized a filter with a high-cut frequency of 1.75 cps and a low-cut frequency of 0.7 cps, both with slopes of 12 dB per octave. The other filtered seismograph (ZTFK) used a filter with the high-cut and low-cut frequencies set at 2.0 cps and 1.0 cps, respectively, with slopes of 24 dB per octave. Both of these seismographs are recorded on 16-millimeter film.

3.4 DATA CHANNEL ASSIGNMENTS

Each data format recorded at TFSO was assigned a number (format number in the case of digital seismograms), and each time a new data format was established a new number was assigned. Data format change notices showing both the new data channel assignments and the previous data channel assignments were submitted to the Project Officer and were distributed to frequent users of TFSO data. The data formats recorded during Project VT/9702 are summarized in tables 3 and 4, and a key to the seismograph designators is given in table 5.

3.5 OPERATION OF THE ASTRODATK SEISMIC DATA ACQUISITION SYSTEM

From 1 January 1969 through 31 December 1969, the Astrodata Seismic Data Acqui- sition System (ASDAS) was operated daily from 00002 to approximately 2200Z. The time from approximately 2200Z to 2400Z was used for system test, adjustment, and maintenance. Emergency maintenance was performed at other times, when parts such as vacuum pump motors failed and stopped operation of the ASDAS. These failures, in general, caused losses of data for short periods of time, usually not more than 2 hours. A more serious failure was caused by a head misalignment on transport #1. This was first detected on 2 December, and was corrected on 11 December, but resulted in the loss of data from 24 November 1969 to 11 Dec- ember 1969. Tape head alignment is now checked monthly or. both ASDAS tape trans- ports.

Some tapes which are received for use on the ASDAS are defective, having been damaged by mishandling or by operation on misaligned transports. To avoid loss of data, all tapes are inspected for wrinkles and scratches before they are used. This procedure has been highly successful. To date, 297 suspect tapes - mostly

TR 70-1

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11-

TR 7U-1

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5.0

Table 2. TFSQ frequency response norms and tolerances

Short period

Relative amplitude f Ups)

0.2

Tolerance (percent)

10

Norm

0.0118

Max

0.013

Min

0.0106

2.5 0.4 7.8 0.0988 0.106 0.0916

1.25 0.8 5.0 0.68 0.714 Ü.646

1.00 1.0 0 1.00 1.00 1.00

0.67 1.5 5.2 1.55 1.63 1.47

0.50 2.0 5.1 1.97 2.07 1.87

0.33 3.0 7.3 2.30 2.47 2.13

0.25 4.0 12.2 2.05 2.30 1.80

0.167 6.0 20.3 1.38 1.66 1.10

100

80

60

SO

40

30

25

20

15

10

0.01

0.0125

0.0167

0.02

0.025

0.033

0.04

0.05

0.0667

0.1

Long period

20

20

15

15

10

10

20

0.135 0.162 0.108

0.278 0.333 0.222

0.485 0.558 0.412

0.644 0.741 0.548

0.874 0.961 0.787

1.03 1.082 0.978

1.00 1.00 1.000

0.825 0.866 0.784

0.470 0.517 0.425

0.110 0.132 0.0879

TR 70-1

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-18-

TR 70-1

Table 5. Key to the designations used in the data format assignments at TFSO

TCDMG Time Code Data Management Generator

Z Amplified vertical seismograph from site identified by number

IT Summation of the crossed-linear array vertical seismographs

ZTF IT filtered (UED filter)

ZTFK ET filtered (Krohn-Hite)

N North-south horizontal seismograph

E East-west horizontal seismograph

SP Short-period seismograph

WWV Radio time from National Bureau of Standards Radio Station WWV (WWV, STS, and Voice on tape)

T Transverse seismograph

R Radial seismograph

BF Seismograph using Benioff seismometer

LL Low, low magnification (short-poriod) or low magnification long-period seismograph

MS Short-period microbarograph

IB Intermediate-band seismograph

V Unamplified (earth-powered) vertical seismograph

SL Low magnification short-period seismograph

WI Wind indicator

BS Beam-steered seismograph. Number refers to azimuth orientation.

HF8 High-frequency seismograph (suffix "1/10" indicates magnification one-tenth that of ZHF8 seismograph)

PT Number of points used in digital filters (beam-steer)

LP Long-period seismograph from site identified by number

BB Broad band seismograph from site identified by number

EB Summation of R-70, -61, -65, -68 seismographs

ZC Summation of T-70, -61, -65, -68 seismographs

COMP Tape recorder wow and flutter compensation channel

-19-

TR 7Ü-1

with wrinkled edges - have been found and removed from use. These were shipped to SDL where they were tested operationally. SDL found two-thirds of the suspect tapes were defective. Table 6 lists the formats in which digital data were re-

corded during 1969.

3.6 SHIPMENT OF DATA TO SDL

Six analog FM magnetic-tape units are used to record data for the AFTAC/VELA Seismological Center (VSC). Tapes from these units are sent weekly to our Garland, Texas, laboratory for quality control, and are shipped from Garland to SDL about IS davr after the end of the month in which they were recorded.

All Develocorder film seismograms except quality control copies are routinely shipped to SDL. One seismogram from each Develocorder is sent each week to the Garland, Texas, laboratory for quality control. These recordings are sent to SDL by the Garland office at a later date.

Until April, all digital magnetic-tape seismograms were held at the observatory until they were requested. If no request was received, the tapes were recycled on a 6-week schedule. During April, we began making daily shipments to SDL of all digital tapes except two per week which were sent to the Garland Laboratory for quality control. These tapes were sent to SDL by the Garland facility at a

later date.

3.7 FACILITIES AND EQUIPMENT

3.7.1 Facilities Maintenance

Lightning storms were severe during July, August, and September 1969. During this interval, two trees within 100 feet of the CRB were struck, a 20,000-volt Arizona Public Service transformer located near the parking lot was damaged, and the CRB was struck. Lightning caused major damage to six starter coils and

six switches in the water well and pump building.

The TFSO facilities were maintained in accordance with sound industrial proce- dures throughout the reporting period. Work in this area included periodic extermination service, semiannual fire extinguisher inspection, routine clean- ing, inspection of all office equipment, and periodic servicing and maintenance

of all air conditioning and heating facilities.

During October the circuit breaker for the standby power generator failed and dropped out whenever the full TFSO load was applied to the generator. For 2 weeks, until a new breaker was installed, the generator was operated only at reduced load and was used only to furnish standby power to the CR3.

3.7.2 Equipment Maintenance

3.7.2.1 Spiral-Four Cable Replacement

During 1969, several lengths of Spiral-4 cable were replaced in the long- and short-period arrays. In general, replacement of the cable was required because

-20-

TR 70-1

Table b. ASDAS recording format used at TFSQ

1 January 1969 through 5 March 1969

Format No. 13

Channel Data Channel

1 Z1LP 25 2 Z2LP 26 3 Z3LP 27 4 Z4LP 28 5 Z5LP 29 6 Z6LP 30 7 Z7LP 31 8 N1LP 32 9 N2LP 33

10 N3LP 34 11 N4LP 35 12 N5LP 36 13 N6LP 37 14 N7LP 38 15 E1LP 39 16 E2LP 40 17 E3LP 41 18 E4LP 42 19 E5LP 43 20 E6LP 44 21 E7LP 45 22 ZILPLo 46 23 Z2LPLO 47 24 Z3LPLO 48

Data

Z4LPLo Z5LPLo Z6LPL0 Z7LPLo NILPLo N2LPLO N3LPLo N4LPLO N5LPLO N6LPL0 N7LPLO ElLPLo E2LPLo E3LPLo E4LPLO E5LPLO E6LPL0 E7LPLo Z60SP N60SP E60SP I LPZ WWV STS

•21-

TR 70-1

Table b. Continued

Channel

1 2 5 4 5 6 7 S 9

10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

b March 19b9 through 2 April 19b9

Format Xo. 12

Data Channel

Z 1 25 Z 2 26 Z 3 27 Z 4 28 Z 5 29 Z 6 30 Z 7 31 Z 8 32 Z 9 33 Z 10 34 Z 11 35 Z 12 36 Z 13 37 Z 14 38 Z 15 39 Z lb 40 Z 17 41 Z 18 42 Z 19 43 Z 20 44 Z 21 45 Z 22 46 Z 23 47 Z 24 48

Data

Z 25 Z 2b Z 27 Z 28 Z 29

30 31 32 53 34 35 36 37

Z1LP Z2LP Z3LP Z4LP Z5LP Z6LP Z7LP I T I LPZ wwv STS

z z z z z z z

■:.2-

TR 70-1

Table 6, Continued

5 April 1969 through 9 April 1969

Format No. 15

Channel Data

1 Z1LP 2 Z2LP 3 Z3LP 4 Z4LP 5 Z5LP 6 Z6LP 7 Z7LP 8 N1LP 9 N2LP

10 N3LP 11 N4LP 12 N5LP 13 N6LP 14 N7LP 15 E1LP 16 E2LP 17 E3LP 18 E4LP 19 E5LP 20 E6LP 21 E7LP 22 Z 1 23 Z 2 24 Z 3

Channel

25 26 27 28 29 30 31 32 55 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48

Data

L 4 - 5 1 6 z 7 z 8 z 9 z It) z 11 z 12 z 13 z 14 z 15 z 16 z 17 -7 6 18 z 19 I T z 60 N60SP E60SP BS 0 BS 1 WWV STS

■23-

TR /O-l

Table 6, Continued

Channel

1 2 5 4 5 6 7 8 9

10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

10 April 1969 through 25 September 1969

Format No. 16 —

Data Ch annel

ZILP 25 Z2LP 26 Z5LP 27 Z4LP 28 Z5LP 29 Z6LP 30 Z7LP 31 N1LP 32 N2LP 33 N3LP 34 N4LP 35 N5LP 36 N6LP 37 N7LP 38 E1LP 39 E2LP 40 E3LP 41 E4LP 42 E5LP 43 E6LP 44 E7LP 45 Z 1 46 Z 2 47 Z 3 48

Data

4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 T 60

N60SP E60SP ZHF-8 BS 1 wwv STS

z z z z z •7 L 7

i 1

.24.

TR 70-1

Table 6, Continued

26 September 1969 through 3 November 1969

Format No. 17

Channel Data Ch annel Data

1 Z 1 25 Z 25 2 z 2 26 Z 26 3 z 3 27 Z 27 4 z 4 28 Z 28 5 z 5 29 Z 29 6 7 6 30 Z 30 7 z 7 31 Z 31 8 z 8 32 Z 32 9 z 9 33 Z 33

10 z 10 34 Z 34 11 z 11 35 Z 35 12 z 12 36 Z 36 13 z 13 37 Z 37 14 z 14 38 Z1LP 15 z 15 39 Z2LP 16 z 16 40 Z3LP 17 z 17 41 Z4LP 18 z 18 42 Z5LP 19 z 19 43 Z6LP 20 z 20 44 Z7LP 21 z 21 45 ZXLP 22 z 22 46 ZYLP 23 z 23 47 Z T 24 z 24 48 STS

•25-

TR 70-1

Table b, Continued

3 November 19b9 thr ough 51 December 1969

Format No. 18

Channel Data Ch annel

1 - 1 25 2 Z 2 26 5 — - 5 27 4 M 4 28 5 - 5 29 6 _ 0 50 7 - 7 51 8 S 52 9 z 9 55

10 z 10 54 11 it 11 55 12 w 12 56 13 — 13 57 14 w 14 58 15 ^ 15 59 16 M 16 40 17 — 17 41 18 18 42 19 •7 19 45 20 „ 20 44 21 ^ 21 45 22 z 22 46 23 24

z 23 24

47 48

Data

Z 25 Z 26 Z 27 Z 28 Z 29 Z 50 Z 51 Z 52 Z :>5 Z 54 Z 55 Z 5b Z 57 Z1LP Z2LP Z5LP Z4LP Z5LP Z6LP Z7LP ZXLP ZHF-8 I T STS

-2b-

TR 70-1

m

of excessive leakage-to-ground, lightning damage, or vandalism. Spiral-4 cabh replacement history is summarized in table 7.

Table 7. Summary of Spiral-4 cable replacements in 1969

Month

January

February

March

April

May

June

July ^

August

September

October

November

December

TOTAL

Number of reels replaced

(1/4-mile lengths)

17

11

16

4

4

4

4

11

4

16

19

11

Reason for replacement

Line leakage

Line leakage

Line leakage

Line leakage

Line leakage and lightning

Line leakage

Lightning

Line leakage and lightning

Line leakage and lightning

Line leakage and lightning

Line leakage and lightning

Line leakage

121

Spiral-4 cables that were cleanly cut were spliced and sealed rather than re- placed. Spiral-4 cable splice history is summarized in table 8.

Of 9 cables damaged by vandalism, 7 were shot and 2 w re cut with an ax. Although the FBI, Phoenix, Arizona, investigated the shooting of one cable, collected evidence, and instituted prosecution proceedings, the case was dis- missed when the Court ruled that insufficient evidence was available to justify a trial.

Ten cables were damaged by a United States Forest Service subcontractor who was doing rehabilitation work within the 37-element array. Five other cables were damaged by county maintenance equipment.

During December, two thousand reels of Spiral-4 cable were delivered to the observatory. Several sections of cable were used and other sections randomly checked. All cable checked and used was found to be in good condition.

•27-

TR 70-1

_«

Table 8,

Month

January

February

March

April

May

June

July

August

September

October

November

December

Summary of Spiral-4 cable splices in 1969

Number of splices Reason for splices

2 Unknown vehicle

Ü

4

2

Ü

0

11

Unknown vehicle

Road maintenance

Road maintenance S vandalism

Road maintenance ^ fire

Vandalism

Road Maintenance, vandalism, fire, and animal

Road maintenance, vandalism, vehicle, and animal

Road maintenance

TOTAL 34

3.7.2.2 Phase Responses

Th me

e phase responses of all channels in the 37-element short-period array were asured in April, May, June, and December and were maintained to a tolerance

of ±4.5 degrees at 1.0 cps.

3.7.2.3 Seismometer Motor-Constant Checks

The annual motor constant (G) checks of the 37-element, short-period array and 7-element, three-component, long-period array seismometers were made between 17 September and 7 November. The results of these checks and adjustments that

were made are shown in table 9.

3.7.2.4 Tape Speed Checks

The tape speeds on all FM magnetic-tape recorder transports are checked once per month at TFSO and are maintained at 0.3 inch per second ±0.5 percent. In addition, this tape speed is monitored during routine quality control examina-

tions conducted on selected tapes at Garland.

-28-

TR 70-1

3.8 EMERGENCY POWER GENERATOR

The 100 kW generator, Diesel Power Unit, Caterpillar Model 59825, was operated a total of 137.6 hours. It furnished power for 99 hours during lightning storms and commercial power outages, and was operated 38.6 hours for test and preventa- tive maintenance.

Table 9. 1969 annual 37-element short-period array and 7-element 3-component long-period array seismometer motor constant checks

Short-Period Ax^ray

Percent error Initial G from .296 Final G (newtons/ (newtons/ (newtons/

Channel ampere)

0.285

ampere) ampere)

Z 1 3.7 0.291 Z 2 0.289 2.4 0.302 Z 3 0.288 2.7 0.303 Z 4 0.275 7.1 0.296

Z 5 0.303 2.4 0.500 Z 6 0.292 1.3 0.292 Z 7 0.290 2.0 0.295 Z 8 0.300 1.3 0.300 Z 9 0.280 5.4 0.300 Z 10 0.306 3.4 0.296 Z 11 0.298 0.7 0.298 Z 12 0.292 1.3 0.292 Z 13 0.296 0.0 0.296 Z 14 0.298 0.7 0.298 Z 15 0.304 2.7 0.292

Z 16 0.293 1.0 0.293 Z 17 0.298 4.7 0.299 Z 18 0.294 0.7 0.294 Z 19 0.289 2.4 0.290 Z 20 0.291 1.7 0.291 Z 21 0.292 1.3 0.292 Z 22 0.266 10.1 0.305 Z 23 0.294 0.7 0.294 Z 24 0.296 0.0 0.296 Z 25 0.292 1.3 0.292 Z 26 0.296 0.0 0.296 Z 27 0.286 3.4 0.295

Remarks

Degaussed in field Degaussed in field Degaussed in field Degaussed in field and G resistor changed Degaussed in field

Degaussed in field

Adjusted in shop

Degaussed in fieid and G resistor changed

Adjusted in shop

Degaussed in field

G resistor changed

Degaussed in field and G resistor changed

•29-

TR 70-1

Channel

Initial G (newtons/ ampere)

0.285

Table 9, Continued

Short-Period Array

Percent error from .296 (newtons/

ampere)

5.7

Find G (new tons/ ampere)

0.297

Z 29 0.298 0.7 0.298 Z 50 0.291 1.7 0.296 Z 51 0.282 4.7 0.297 Z 52 0.295 1.0 0.295 Z 55 0.298 0.7 0.298 Z 54 0.297 0.5 0.297 Z 55 0.294 0.7 0.294 Z 56 0.280 5.4 0.500 Z 57 0.504 2.7 0.504

Remarks

Degaussed in field and G resistor changed

Degaussed in field

Degaussed in field

Long-Period Array

Percent error Initial G from .0280 Final G (newtons/ (newtons/ (newtons/

Channel

Z1LP

ampere)

0.0289

ampere) ampere)

5.2 0.0289 NILP 0.0277 1.1 0.0277 ExLP 0.0284 1.4 0.0284

Z2LP 0.0276 1.4 0.0276 N2LP 0.0286 2.1 0.0286 E2LP 0.0276 1.4 0.0276

Z5LP 0.0246 12.0 0.0271 \5LP 0.0275 1.8 0.0275 E5LP 0.0260 7.0 0.0284

Z4LP 0.0285 1.1 0.0285 N4LP 0.0276 1.4 0.0276 E4LP 0.0279 0.4 0.0279

Z5LP 0.0246 12.0 0.0286 N5LP 0.0276 1.4 0.0276 E5LP 0.0524 15.7 0.0274

Remarks

Shunts removed

Shunts removed

Installed high Z cal coil Shunts removed Shunts removed

TR 70-1

-50-

>

Table 9, Continued

Long-Period Array

Channel

Percent error Initial G from .0280 Final G (newtons/ (newtons/ (newtons/

Z6LP N6LP E6LP

, * j

0.0274 0.0313 0.0276

c i

2.1 11.8 1.4

0.0274 0.0280 0.0276

Z7LP N7LP E7LP

0.0273 0.0280 0.0280

2.5 0.0 0.0

0.0273 0.0280 0.0280

ZYLP ZXLP EXLP

0.0051 0.0310 0.0276

- 0.0051 0.0310 0.0276

Remarks

Corrected in CRB

■31-

TR 70-1

4. MAINTENANCE AND MODIFICATION OF TFSO INSTRUMENTATION

4.1 SHORT-PERIOD ARRAY

4.1.1 Lightning Protection

No modifications were made to the lightning protection circuits of the short- period array during 1969, but data were collected to permit evaluation of the present circuits.

From 1 January to 31 December 1968, electrical storms occurred during 58 days and damaged 42 amplifiers. During the same time period in 1969, electrical storms occurred during 58 days and damaged 25 amplifiers. With corrections maae for storm incidence, the relative damage during 1969 was 39 percent of that during 1968. This indicates that a substantial improvement in the effectiveness of the lightning protection circuits was realized by modifications undertaken during the latter part of 1968.

4.1.2 Spike Noise

TFSO records have continued to be free of spikes since the circuits were modi- fied to transmit dc power and FM signals over separate cable pairs last Septem- ber and October. However, to reconfirm that spikes occurred when dc power and FM signal were on the same cable pair, Z66, a linear array channel, was connected to instrumentation and circuitry like that used in the 37-element array prior to the modifications made in September and October 1968. Z66 operated under this test condition from 10 January through 13 March 1969. During this time period, Z66 recorded many spikes, whereas the seismographs in the 37-element array were free from spikes during the same interval. Figures 4, 5, 6, and 7 show seismo- grams for Z66 and Zl through Z37 for 1113Z on 14 February. Note the spikes on Z66 and the freedom of spikes on Zl through Z37.

4.1.3 Solid-State Amplifiers

.Amplifier modification work was continued throughout the report period. When- ever an amplifier is brought in from the field, one resistor is changed to in- crease its output carrier level. To date, 32 of the 43 amplifiers have been modified.

4.2 LONG-PERIOD ARRAY

4.2.1 Lightning Protection

Following the frequent failure of fuses in the circuits protecting the remote Lambda power supplies, and following the loss of seven seismic amplifiers due to lightning in May, additional lightning protection was designed and was installed throughout the array during June. Figures 8 and 9 show the circuit modifications that were made. The protection afforded by these circuits has been completely effective. No Lambda power supplies have been damaged since these modifications were made.

-32-

TR 70-1

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TR 70-1

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TR 70-1

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TR 70-1

Modification of solid-state amplifiers was started during August to improve lightning ^protection for the power converter, and involves the removal of a 0.1 mfd feedback capacitor from between the ±10-volt common and the transformer center tap on the "B" board of the power converter. All amplifiers are being modified as the/ come in from the field for repairs. To date, eight amplifiers have czen modified.

I 4.2.2 Solidj-State Amplifier

At the beginning of this report period, all long-period seismic amplifiers except those tat LP1 were installed in tank vaults with seismometers. This required that a vault be opened whenever an amplifier required checking, adjustment, or maintenance. Such a procedure was undesirable, for it disturbed the seismometer, permitted moisture to enter the tank, and required considerable time and effort, as the tanks are buried under several feet of sawdust and earth. This undesirable situation was corrected by relocating the amplifiers in the Hoffman boxes at each site except LP1 and LP4, which are non-standard and do not use Hoffman boxes. The relocation was first tested at LP5 and found to cause no deterioration in seismograph performance, and then was accomplished at other sites. Figures 10 and 11 show the LP3 installation. An insulated wood box is used to cover the Hoffman box and stabilize its interior temperature.

4.2.3 Calibration Circuit Transients

During analysis of LP data recorded on digital magnetic tape, it was noted that frequently a large transient appeared at the beginning of each sinusoidal cali- bration and overloaded the Astrodata system. At times, the overload persisted throughout the calibration and made it valueless. The transient was traced to a small unbalance in the calibration discriminator output and a small shift in the VCO center frequency. Both deviations were within instrument operating specifications but were greatly magnified because the VCO and discriminator were being operated at a very small deviation during calibrations. The routine 12 pA p-p calibration current produced a frequency deviation of only 0.09 per- cent p-p. The frequency deviation of the calibration system was increased by a factor of 10, and the circuit at LP1 was modified and tested. When this was found to reduce calibration transients to acceptable values, calibration circuits at all LP sites were modified.

4.2.4 Tone-Controlled Calibration Circuit

Some of the noise in the long-period data has been traced co spurious operation of the calibration discriminators at the field sites. Normally, these dis- criminators will be disabled unless they receive a calibration carrier from the central recording building. However, it was found that they can be triggered momentarily into an operational state by transmission system noise. An auxiliary, tone-controlled circuit that completely disconnects the discriminator output from the seismometer calibration coil when no tone is received was built and was tested at LP4. The concept was proven sound, but the equipment used was easily damaged by lightning and required frequent maintenance. LP4 calibration circuits were restored to their original configuration in order to keep the site operational without excessive maintenance effort.

■39-

TR 70-1

__„ . 1 ———— ■' -n -. . ■.,.iM»-M^—,«..„,■..«■,. mmm — "" •' ■ ■ " " ' '.'

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G4972

-40-

TR 70-1

4.2,5 Horizontal Seismometer Case Seals

Plugs were removed from the cases of all long-period horizontal seismometers, and breather assemblies were installed after tests at LP1 and LP4 showed that this modification reduced seismograph noise. It is believed that this modi- fication prevents mechanical distortion of seismometer bases due to pressure and temperature changes.

■41-

TR 7U-1

5. ROUTINE ANALYSIS

5.1 INTRODUCTION

Seismometric data were recorded at TFSO continuously throughout this reporting period. The recorded data were routinely analyzed, the analyses checked, and a daily tabulation of arrival times of P phases and selected later phases of earthquake signals were transmitted to the Environmental Science Services Administration's Coast and Geodetic Survey (ESSA-C^GS).

Sixteen-millimeter film seismograms and associated preliminary analysis data were routinely selected ^n a random basis by our Garland laboratory personnel for review by a quality-ccntrol analyst. Recorded data were also used to evaluate routine and special seismograph systems operated at TFSO and to obtain data for research studies.

5.2 .ANALYSIS PROCEDURES

5.2.1 Preliminary Analysis

Film seismograms were analyzed during each 24-hour period. Preliminary analysi: was conducted on an "on-line" basis and the analysis data were recorded on worksheets compatible to both observatory use and direct transcription of data to IBM cards. Data recorded during preliminary analysis consist of:

a. Phase arrival time;

b. Period and peak amplitude of each phase arrival;

c. Preliminary phase identification when possible;

d. Classification of events by general type (for example, local, near regional);

e. Estimated station-to-epicenter distance and/or azimuth (when possible);

f. Seismograph system and component.

5.2.2 Checking and Finalization of Preliminary Analysis

The seismograms were reviewed by a second analyst who checked the arrival time, period, and amplitude data recorded on the work sheets, and reviewed portions of the seismogram classified as "possible signal" by the preliminary analyst. Data from the analysis sheets were used for compilation of information for ESSA-C^GS.

-42-

TR 70-1

'■'-*

5.2. 3 Daily Reporting to the ESSA-CflGS

Throughout the reporting period, the arrival time, signal period sienal

ampUtude. and estimates of epicentral locations when estima es'uere' possible) of even s recorded at TFSO were reported daily to the ESSA-C^GS in hashing on^ D.C. Daily messages, sent by TWX. were relayed to Washington, D.C bv the General Services Administration in Phoenix on week days, and were s^nt directlv to ivashington, D.C, on weekends and holidays, Data ar^ used bTtl e C^GS in ' their hypocenter location program. 7

Table 10 shows the number of events of each type reported by TFSO.

Table 10. Local (L), teleseismic TFSO from 1

L

5

near reg (T) evei January

N

140

ional (N), regional (R), its reported to the C^GS through 31 December 1969

and bv

Total

795

Month R

10

T

January 1969 640

February- 2 482 15 644 1143

March i 568 10 771 1350

April 1 135 17 846 999

May 1 111 7 781 900

June 0 76 17 1048 . 1141

July 2 83 16 996 1097

August 1 76 79 1706 1862

September 0 94 23 1381 1498

October 2 68 61 1148 1279

November 1 64 43 944 1052

December 5 80 17 1186 1288

■43-

TR 7U-1

b. INSTRUMENT EVALUATION

6.1 HIGH-FREQUENCY SEISMOGRAPH

The high-frequency seismograph, ZHF8, was operated routinely and was occasion- ally maintained from 1 January until 1Ü August, when lightning damaged the seismometer signal coils and substantially reduced the charges of some of the seismometer magnetic assemblies. By 29 October, the damaged signal coils were replaced, the magnets were recharged, resistor/diode lightning protector circuits were installed in the seismometer to protect the signal and calibration circuits, and the seismograph was returned to routine operation. During the remainder of the report period, the seismograph was operated routinely except for one time period during which isolation amplifier mainten ce was performed.

ZHF8 data were recorded continuously on the ASDAS magnetic tape with two exceptions: (1) They were not recorded during periods of maintenance; [2) They were not recorded from 24 September to 3 November 1969, when the ASDAS channel was useu to record other data. Figure 12 shows the frequency response of the ZHF8 seismograph.

6.2 EXPERIMENTAL DEVELOCORDER PUMP, MODEL 50082

Testing was started during September 1968 to determine the long-time operational characteristics of the experimental Develocorder Pump, Model 30082, and was continued throughout the report period. The pump was operated routinely on Develocorder No. 9 under normal observatory operating conditions. The following observations have been made during these tests:

a. The hose failure rate (4 per year) on the new pump is approximately the same as the average failure rate on the 11 standard pumps operated during the same time period.

b. Rollers in the new pump seized and stopped turning soon after the pump was put into operation. This is not unusual - rollers in 5 of the 11 standard pumps have seized and stopped turning.

c. The new -jump was easier to inspect than the old one.

d. Hose replacement on the new pump was easier and quicker (10 vs 60 minutes) than on the standard pump.

Operation of the experimental pump will be continued on a routine basis.

-44.

TR 70-1

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FREQUENCY (Hz)

Figure 12. Frequency response of TFSO high frequency seismograph ZHF8

45-

G 5487

TR 70-1

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6.3 MULTICHANNEL FILTER SYSTEM (MCF)

Comparison tests of the 19-point and 35-point filter programs, which were started on 22 December 1968, were terminated on 24 January. The MCF was made available to TI personnel until 27 January. On 27 January, a new format was established with five beam-steer traces using a new 55-point filter routine with different input instruments. The six omitted seismographs are Z6, Z9, Z12,^Z15, Z24, and Z55. Prior to 24 January, the omitted seismographs were Z3, Z5, 17, Z8, Z12, and Z16. The change in inputs was made to eliminate those traces that exhibit the highest level of cultural noise, which we attribute to vehicle traffic and construction of highway, pipeline, and subdivisions. Figure 15 shows a frequency response of the MCF output of beam steer No. 5, which includes the 55-point filter and the inputs as revised on 27 January.' Figure 14 shows the response of this and other outputs. Table 11 lists the recording formats.

At the request of the Project Officer, changes in the auxiliary processor were begun 24 January so that a special format could be recorded for TI.

TI personnel installed additional circuits in the auxiliary processor and a program was put in MCF 1 and MCF 2. MCF 1 responds to low-frequency signals and MCF 2 responds to high-frequency signals. Thf output of the auxiliary processor is the difference between the squared values of these two MCF channels. The new output is designated MCFPR and responds to higher frequency energy with a positive deflection and to lower frequency energy with a negative deflection. Figures 15 and 16 show the responses of these outputs to signals of various frequencies.

On 7 February, the TI MCF programs were received and the Kurile Islands Program installed. Recording in this format has continued with the designa- tions MCF 1, MCF 2, av.d MCFPR on Data Trunk 7, Data Group 7280. The recordings of this data trunk have been sent to TI on a weekly basis.

On 2 April 1969, the format was changed by deleting MCF 1, MCF 2, and MCFPR, and using a new trace, MCFLP, in place of MCF 1. MCFLP is a recording of LP data that has been routed through a modified channel of the MCF and recorded on Develocorder No. 5, Data Trunk No. 7. The MCF channel was modified to accommodate LP data without distortion. Two capacitors were removed to provide a flat frequency response from dc to 0.5 cps.

During July, noise that appeared intermittently at the beam-steered outputs was traced to temperature rise caused by dirt-clogged filters in the MCF forced- air cooling system. Cleaning the filters appears to have eliminated the noise. Later, lightning caused a fuse to fail in the ac regulator.

On 21 July, the MCF format was restored to its previous configuration. MCFLP was removed and MCF 1, MCF 2, and MCFPR were again made active channels.

Several attempts were made, during late November and throughout December, to set up the MCF auxiliary processor so that Fisher processing of data could be performed. The attempts were unsuccessful, as insufficient historical and instructional information about the MCF was available to permit establishment and testing of the required circuits.

-46-

TR 70-1

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PERIOD (seconds)

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G4974

■47-

TR 70-1

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Azimuth Distance Channel Beam- steer from from Apparent

No. output

22 December

TFSO

1968 through

TFSO velocity

24 January 1969

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28 January through 31 March 1969

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6.4 EXTENDED LONG-PERIOD SEISMOGRAPHS

Work was started late in July to set up and operate two high-magnification vertical, 3ong-period seismographs at TFSO. These were designated ZXLP and ZYLP and used 25-second seismometers, 115-second Harris galvanometers and phototube amplifiers. Their frequency responses, shown in figures 17 and U, were closely matched and peaked at 40 seconds. Seismograms have been made on 16-millimeter film, analog FM tape, Helicorder paper, and digital tape, and have been sent routinely to SDL with other data shipments. Magnifications on film and paper were originally set to approximately 200K to permit viewing of small magnitude events but have been reduced to approximately 130K so that magnification at 25 seconds would equal that on Z1LP.

The seismometers and phototube amplifiers used with ZXLP and ZYLP were installed on the pier next to LP1 in the east underground vault.

Typical seismograms showing data ZXLP, ZYLP and other channels are included in this report. Figure 19 shows background noise recorded during a seismically quiet period. Figures 20 and 21 show phases received from small events.

6.5 EVACUATED LP HORIZONTAL SEISMOGRAPHS

The following tests were conducted using materials and equipment on hand to determine if there were immediately apparent advantages to operating LP horizontal seismometers in a partial vacuum.

6.5.1 Evacuated Seismometer

A horizontal LP seismograph, designated EXLP, was installed in the east walk- in vault during April 1969. It used a seismometer, Geotech Model 870ÜC instal ed nex^to'the LP1 seismometers, and signal transmission and conditioning equipment that made its magnification and frequency response equivalent to the standard LP array seismograph channel. The seismometer was oriented in an east-west direction, and ail joints in its case were sealed with RTV sil cone rubber or DC-4 silicone grease until a leak time constant of W^Xl»^/ 4400 hours was realized. The seismograph was operated ^^J^lJitL with the case evacuated to 2 mm of mercury and was operated for 6 days with the case unsealed. Seismograms for these time periods showed very close agreement between EXLP traces and UU» traces except for infrequent, inter- mittent, large-amplitude spikes th.t appeared on the EXLP trace during its operation with an evacuated case.

6.5.2 Evacuated Tank Vault

While operational tests were being conducted using a seismometer with an evacuated case work was undertaken to seal the experimental surface tank vlultthatt located approximately 1/4 mile from both the CRB and LP1 vault. Bv reolacing the cable entry condulet with a hermetically sealed header, nLring a nfw low-porosity concrete floor, painting both the interior and exterior of the tank with epoxy, and pouring a new RTV-30 gasket in the tank Ud he ?ime constant of the tank was raised from less than 8 hours to

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approximately 1200 hours. The HXLP seismometer was removed from the underground vault and was installed in the newly sealed experimental tank vault, Its amplifier was installed nearby in an insulated box, and this seismograph, still designated '^XLP, was adjusted to have the standard LP array magnification and frequency response. The Seismograph was operated routinely for several weeks with the tank vault evacuated to 1 mm of Hg. Seismograms for this time- period showed very close agreement between HXLP and ülLP during quiet periods and a greater increase in noise on the EXLP trace than on the L1LP trace when winds were blowing. Figures 22 through 28 show typical seismograms from these tests.

AdditionaJ recordings were made under the following conditions of operation:

a. With the tank vault sealed but not evacuated;

b. With the vacuum pump operating and a motor generator set running near the tank vault;

c. With the vacuum pump operating and a motor generator set running 200 feet from the tank vault.

The test results were inconclusive. Although all data showed that noise was introduced when the motor generator set operated near the tank vault and was lessened when it was moved 200 feet from the vault, only some data showed that stopping the vacuum pump reduced the recorded LP noise. Other data showed that operating the vacuum pump apparently introduced no noise.

6.5.3 Discussion of Results

The test results indicate there is no advantage to operating a horizontal LP seismometer in a partial (1-2 mm of Hg) vacuum, and furthermore, showed that neither the seismometer case nor the tank vault are suitable for evacuated operation. Neithei" was designed for such service, and lacks the mechanical strength and the seals retired. It is recommended that further tests of evacuated seismographs be conducted using equipment designed specifically for that purpose.

6.6 NITROGEN-FILLED LP TANK VAULTS

On 22 November, equipment was installed at LP7 to determine the performance improvements that will be derived and the problems that will be encountered from operating LP seismometers in tank vaults pressurized with 1 psi dry nitrogen. It is believed that pressurizing the tanks with dry nitrogen will exclude moisture and will prevent the condensation which now causes electrical leakage paths and increases the system noise. A standard commercial nitrogen tank, a pressure regulator, three gauges and three shutoff valves were inter- connected and installed in a lockable wooden box, as shown in figure 29, and the entire assembly was transported to LP7. Each tank vault was connected to the nitrogen tank through a separate cutoff valve and a separate low-pressure line. Tank vault pressure was measured by one gauge, nitrogen tank pressure by the second, and nitrogen tank contents by the third. Upon completing the

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installation, each tank vault was pressurized to 5 psi of nitrogen and its seal broken to release this pressure and purge the tank vault interior. The tank vault seal was then restored and the tank was pressurized with 1 psi of nitrogen.

From 22 November to 18 December, 160 cu ft, the entire contents of the (partially full) supply tank were used. As this rate of usage, 6.4 cu ft per day, was much greater than anticipated, all seals were retested and a defective one was repaired. Our objective was to reduce the nitrogen usage to about 1.5 cu ft per day, so that a 300 cu ft tank would furnish gas for 6 months. Long-term testing of this installation is continuing.

6.7 FLAG TRACES

Three high-magnification seismogramL, routinely recorded at TFSO, serve as flag traces and are used in analysis work to detect low-amplitude arrivals. As these seismograms are produced by summing and filtering data from eight seismographs in the crossed linear array, and that array is used for no other purpose, a study was undertaken to determine if suitable flag traces could be produced using data from the 37-element short-Period array. In general, the study results indicated that flag traces using 37-element array data would be quite inferior to chose using crossed linear array data. A copy of the letter report on this subject submitted to the Project Officer on 4 November 1969 is included in appendix 2.

6.8 LIGHTNING PROTECTION

Annual tests of all AEI lightning protectors in service at TFSO were con- ducted between March and August of this year. Of 232 units tested, 100 (43 percent) were found defective and were replaced. By comparispn, 77 per- cent of the units tested during 1968 were found defective and were replaced.

6.9 MULTICONDUCTOR CABLE

During December 1968, a S000-foot length of shielded 12-conductor cable was substituted for Spiral-4 cable in each of two cable runs in the short-period array. Both lengths were installed in areas of high lightning activity to compare their field performances with that of Spiral-4 cable. Short-period data from channels Z13, Z28, and Z29 were routed through one section and from channels Zlü, Z23, and Z24 through the other section.

Tho section carrying channels Z13, Z28, and Z29 has operated without failure since its installation. The other section has suffered partial failures. At different times, from 2 to 4 conductors have shorted together. Since February, only the Z10 and Z24 data have passed through the 12-conductor cable. It has been necessary to route Z23 data through a separate Spiral-4 cable, ihe causes of the multiconductor cable failures are unknown. There has been no known lightning in the failure area, and there is no visible damage to the cable exterior.

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ASSISTANCE PROVIDED TO OTHER GROUPS

7.1 TELEMETRY TO MASSACHUSETTS INSTITUTE OF liiCHNOLOGY

Data from seven seismographs were telemetered to the Massachusetts Institute of Technology Lincoln Laboratories throughout the year. The data transmitted were Z60, E60, NbÜ, Z1LP, E47BF, Z47BF, and X47BF. The center frequency of all the circuits was adjusted when requested by MIT.

7.2 THE UNIVERSITY OF UTAH

A copy of each daily event record sent to ESSA-C&GS, was also sent to Dr. Kenneth Cook at the University of Utah.

7.3 TEXAS INSTRUMENTS INC.

Mr. Jack D, Woodham and the Texas Instruments Inc. (TI) digital recording van arrived at TFSO on 22 January 1969. On 24 January 1969, Mr. Leo Heiting arrived and recording of selected MCF processed data from the short-period and long-period arrays was begun. Recording was discontinued on 4 February 19b9, but was resumed on 19 February after TFSO corrected malfunctions in several noisy long-period instruments. TI continued recording TFSO data until 5 March 1969. 9

7.4 UNIVERSITY OF CALIFORNIA, SAN DIEGO

University of California representatives, Mr. Bill Farrell and Mr. Don Miller, arrived on 1Ü February 1969 anH Or. Richard Haubrick arrived on 12 February to collect data for determining the effects of tidal loading in the TFSO area. Since 14 February they have recorded data from a JM seismometer, modified for displacement response; a gravity meter, and intermittently recorded data from several TFSO seismographs. Space for their recorders and instruments was provided in the west walk-in vault. Mr. Farrell and Mr. Miller have visited TFSO periodically throughout this interval to collect data and to maintain their equipment. TFSO personnel have assisted the group by routinely inspecting the recorders and instruments for proper operations.

7.5 NATIONAL AERONAUTICS .AND SPACE ADMINISTRATION

Mr. Keith Westhusing and Mr. Robert Bechtold, both of Lockheed - NASA, Houston, Texas, arrived at TFSO on 29 March with the NASA Mobile Geophysical Laboratory, installed seismic instruments in the east walk-in vault and started operations. Data from several of their instruments and from the TFSO LIU system were recorded until late June. Mr. Bechtold and a co-worker of his, Mr. George Powasnick, visited TFSO alternately during the recording period to monitor instrument performance. All personnel and equipment departed on

26 June 1969.

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Mr. Moyer and Mr. Schmidtt, NASA, Washington, D.C., tested their Mars Seismograph at TFSO on 22 August 1969. Their da-'-.a were recorded simultaneously with data from the TFSO Z47BF seismograph.

7.6 UNIVERSITY OF CALIFORNIA, LOS ANGELES

On 22 and 23 August 1969, Mr. C. L. Hager and Mr. Eric Syrstad, of the University of California at Los Angeles, set up earth tide recording equip- ment in the observatory engineering laboratory and collected data for Dr. Louis B. Slichter, UCLA Space Science Center. The system was operated unattended except for periodic circuit balancing by TFSO personnel, and was removed on 24 September 1969.

7.7 VISITORS

7.7.1 Visits by VELA Seismological Center Personnel

Captain Fred Munzlinger, VSC Project Officer, visited TFSO from 13 through 17 January 1969 to discuss observatory work planned for the contract period.

Captain Fred Munzlinger, departing VSC Project Officer, and Lieutenant John H. Fergus, the new VSC Project Officer, visited the observatory on 10 and 11 April 1969.

Dr. Frank Pilotte, VSC, escorted visitors at TFSO on 13 May 1969. The visitors included Mr. D. C. Clements, ARPA; W. A. Gallif, Hqs./OAR; Major D. D. Young, USAF; M. J. Kerper, USAF/OAR; and Mr. William Best, USAF/OAR.

7.7.2 Teledyne Visitors

Mr. Brad Leichliter, Geotech Program Manager, visited TFSO from 13 through 15 January 1969, to discus.« observatory work planned for the contract period. Mr. Leichliter visited TFSO again 10 and 11 April 1969 while escorting the new Project Officer on an orientation tour.

Mr. R. A. Amett, Geotech President, and Mr. J. L. Wood, Geotech Administrative Vice-President, were visitors at TFSO on 23 June 1969.

Mr. Jack Hamilton, Teledyne, and Mr. R. A. Amett, Geotech President, visited TFSO 26 and 27 October 1969.

Mr. Martin Gudzin, Geotech Program Engineer, visited TFSO 25 through 28 March and 9 through II September 1969, to coordinate engineering work and special tests.

7.7.3 Visits by School Groups

From I January to 31 December 1969, approximately 672 students and instructors from Arizona State University visited TFSO in several groups. During the same time period, four groups of high school students from Phoenix and Payson, Arizona, area visited TFSO. All visitors were given tours of the observatory and brief lectures about seismology.

-69-

TR 70-1

7.7.4 Others

Mr. Lowell DeJong, 5M Company, visited TFSO on 18 Feoruary 1969 to investigate our complaints of unsatisfactory performance of 3M magnetic tape on TFSO recorders.

Mr. Jesse E. King and Miss Linnea Poulsen, Central Intelligence Agency (CIA), toured the observatory and several field sites on 14 July 1969 to collect information to be used in a CIA study.

Mr. C. P. Smith and Mr. Les Jackson, U. S. Forest Service, visited TFSO on 16 May 1969 to coordinate USFS rehabilitation work within the TFSO arrays with station operation.

Dr. R. Biandford, Geotech-SDL, visited TFSO 15 December 1969 to become familiar with and to discuss observatory operations.

Mr. Phillips and Mr. Kiliner, Empire Machinery, visited TFSO 3 December 1969 to discuss the requirements for an automatic switchover emergency power system,

-70-

TR 70-1

8. REPORTS AND DOCUMENTS PUBLISHED UNDER PROJECT VT/9702

8.1 TECHNICAL REPORTS

The following technical reports were published and distributed in accordance with the requirements of Project VT/9702.

a. Technical Report No. 69-2, Preliminary Study of TFSO Short-Period and Long-Period Noise Fields;

b. Technical Report No. 69-16, Operation of the Tonto Forest Seismo- logical Observatory, Quarterly Report. No. 1, Project VT/9702, 1 January through 51 March 1969;

c. Technical Report No. 69-27, Operation of the Tonto Forest Seismo- logical Observatory, Quarterly Report No. 2, Project VT/9702, 1 April through 50 June 1969;

d. Technical Report No. 69-48, Operation of the Tonto Forest Seismo- logical Observatory, Quarterly Report No. 5. Project VT/9702, 1 July through 50 September 1969.

8.2 LETTER REPORTS

The following letter reports were submitted to the Project Officer:

a. "Evacuated Long-Period Seismometer," dated 10 June 1969;

b. "Extended Long-Period Seismographs at TFSO and Garland," dated 22 August 1969;

c. "Effect of Sampling Rate on Digitally Recorded Seismic Signals," dated 25 September 1969;

d. "Flag Traces at TFSO," dated 4 November 1969;

e. "Extended Long-Period Seismographs," dated 1 October 1969.

•71-

TR 70-1

APPENDIX 1 to TECHNICAL REPORT NO. 70-1

STATEMENT OF WORK TO BE DONE

ri

h Oct 1968

OCX 1 i 1968

53080 STAIEMEXT OF WORK TO BE DONE

(AFTAC Project Authorization No. VELA T/9702/S/ASD) (32)

Tasks;

a. Operation:

(1) Continue operation of the Tonto Forest Seismological Observatory (TFSO), normally recording data continuously,

(2) Evaluate the seismic data to determine optimum operational characteristics and make changes in the operating parameters as may be required to provide the most effective observatory possible. Addition and modification of instruments are within the scope of work. However, such instrument modifications and additions, data evaluation, and major parameter changes are subject to the prior approval of the AFTAC project officer.

(3) Conduct routine daily analysis of seismic data at the observatory and transmit daily seismic teletype reports to the Coast and Geodetic Si'rvey, Environmental Science Services Administration, Washington Science Center, Rockville, Maryland, using the established report format and detailed instructions.

(4) Establish quality control procedures and conduct quality control, as necessary, to assure the recording of high-quali :y data on both magnetic tape and film. Ease experience indicates that a quality control review of one magnetic tape per magnetic tape recorder at the observatory during each week is satisfactory unless quality control tolerances have been exceeded and the necessity of additional quality control arises. Quality control of magnetic tape should include, but need not necessarily be limited to, the following items;

(a) Completeness and accuracy of operation logs.

(b) Accuracy of observatory measurements of system noise and equivalent ground motion.

(c) Quality and completeness of voice comments,

(d) Examination of all calibrations to assure that clipping does not occur.

(e) Determination of relative phase shift on all array seismographs.

(f) Measurement of DC unbalance.

(g) Presence and accuracy cf tape calibration and align- ment . ^i

(h) Check of uncompensated noise on eacn channel. sfr

&

&

Atch 1

(i) Check of uncompensated signal-to-noise of channel 7.

(j) Check of general strength and quality of timing data

derived frotr, National Bureau of Standards Station WWV.

(k) Check of time pulse modulated 60 cps on channel 14 for

adequate signal level and for presence of time pulses.

(1) Check of synchronization of digital time encoder with

WWV.

(5) Provide observatory facilities, accompanying technical assistance by observatory personnel, and seismological data to requesting organizations and individuals after approval by the AtTAC

project officer.

(fc) Maintain, repair, protect, and preserve the facilities of TFSO in good physical condition in accordance with sound industrial

practice.

b instrument Evaluation: On approval by the AFTAC project officer evaluate the performance characteristics of experimental or off-the-shelf equipment offering potential improvement in the performance of observatory seismograph systems. Operation and test of such instrumentation under field conditions should normally be preceded by laboratory test and

evaluation.

c. Special Investigationsr

(1) Conduct research investigations as approved or requested by the AFTAC project officer to obtain fundamental information which will lead to improvements in the detection capability of TFSO. These programs should take advantage of geological, meteorological, and seismological

conditions of the observatory.

(2) Investigations may be conducted in, but not necessarily limited to, the following areas of interest: microseismic noise signal cha^cteristics, data presentation, detection threshold, and

array design (surface and shallow borehole).

(3) Prior to commencing any research investigation, AFTAC approval of the proposed investigation and of a comprehensive program

our line of the intended research must be obtained.

4r t?

&

. - ..

APPENDIX 2 to TECHNICAL REPORT NO. 70-1

LETTER REPORT ON "FLAG TRACES AT TFSO"

4 November 1969

HQ USAF (AFTAC/VELA Seismological Center)

Washington, D.C. 20333

Attention: Lt. John H. Fergus

Subject: Flag traces at TFSO

Gentlemen:

Data from selected elements in the crossed-linear short-period (Si ) array at TFSO are routinely summed, filtered and recorded to produce three flag seis- mograms: ST, ITF, and STFK. The simple summation channel, ZT, is normally recorded at a magnification of approximately 1200K, and the filtered summation channels, ZTF and STFK, at magnifications of approximately 6500K at 1 cps. These extra-high magnification channels are used in routine analysis work to detect low-amplitude arrivals which might not be discernible on lower gain seismograms.

Eight seismographs in the crossed-linear array are operated and maintained only to obtain data for the three flag seismograms; these data are not used for any other purpose. If suitable flag seismograms could be produced with data from the 37-element SP array, the crossed-linear array could be deacti- vated, and the work load at TFSO could be reduced. The feasiblity of accom- plishing this was investigated from February to July 1969, when data from selected elements in the 37-element SP array were summed, filtered, and recorded to produce five new flag seismograms. These (ZX, ZXFK, SNWF, SNEF and ZEWF) were studied and compared with the original three flag seismograms to determine if use of the crossed-linear array could be discontinued without reducing the detection capability of TFSO.

The following is an identification of all flag seismograms used in this study:

ZT - Z61, 262, Z64, Z65, Z68, Z70, Z71, Z72 (unfiltered) ZTF - Z61, Z62, Z64, Z65, Z68, Z70, Z71, Z72 (UED filter) ZTFK - Z61, Z62, Z64, Z65, Z68, Z7Ü, Z71, Z72 (Krohn-Hite filter) ZX - Zl, Z2, Z3, Z4, Z5, Z6, Z7 (unfiltered) ZXFK - Zl, Z2, Z3, Z4, Z5, Z6, Z7 (Krohn-Hite filter) ZNWF - Zl, Z2, Z5, Z8, Z14, Z2Ü, Z29 (TFSO filter) ZNEF - Zl, Z3, Z6, Z10, Z16, Z23, Z32 (TFSO filter) ZEWF - Zl, Z4, Z7, Z12, Z18, Z26, Z3S (TFSO filter)

-1-

TR 7U-1, app 2

a

AFTAC, Lt. John H. Fergus 4 Nover Page 2 4 November 1969

Seismometer locations are shown in figure 1; seismograph frequency responses are shown in figure 2.

Flag seismograms were recorded at magnifications limited only by microseismic background. Channels with filters best able to discriminate against this background (which has a frequency of approximately 0.167 cps) were operated at the highest magnifications. STF, ZTFK, and ZXFK operated at approximately 6500K; ZNWF, ENEF, and EEWF operated at approximately 2500K, and ZT and SF (unfiltered) operated at approximately 1200K.

Figures 3 through 13 show seismograms typical of those made during the recording period. The following is additional information concerning these recordings:

Figure 3. Recording of an event about 70 degrees ENE of TFSO. ZTFK responds to amplitude greater than EXFK by a factor of about 2. Note ZXFK is recording through filter normally used for ZTFK.. and ZTFK is recording through filter normally used for ZXFK.

Figure 4. Recording of an event 130 degrees NE of TFSO. Note equal amplitude response of ZTFK and ZXFK. Also, the linear array summations re- spond equally. ZTFK is recording through filter normally used for ZXFK and ZXFK is recording through filter normally used for ZTFK.

Figure 5. Recording of an event about 79 degrees NW of TFSO. The event amplitude on ZTFK is twice the event amplitude on ZXFK. The signal is broadside to some of the elements composing ZTFK. Note the large amplitude on ZNEF.

Figure 6. Recording of an event about 80 degrees SW of TFSO. ZTFK responds with only slightly higher amplitude than ZXFK. This is due to epicenter being in line with most of the elements composing ZTFK. Note the amplitude recorded on ZNWF.

Figure 7. Recording of an event about 72 degrees SE of TFSO. ZTFK responds to amplitude greater than ZXFK. Note the amplitude of the ZNEF trace.

Figure 8. Recording of an event 46 degrees NW of TFSO. ZTFK responds to signal with amplitude greater than ZXFK by a factor of about 2.

Figure 9. Recording of an event about 27 degrees SE of TFSO. ZTFK responds to signal with amplitude greater than ZXFK by a factor of more

than 3.

Figure 10. Recording of an event about 118 degrees SW of TFSO. Note that ZXFK, ZTFK, and the linear summations recorded this signal with about equal amplitudes.

-2-

TR 70-1, app 2

. .- — 'i .11 I I

AFTAC, Lt. John H. Fergus 4 November 1969 Page 3

Figure 11. Recording of an event 124.5 degrees SW of TFSO. Note equal amplitude response of STFK and ZXFK. ZXFK is not attenuated because array is causing very little cancelling effect due to the apparent velocity (angle of incidence very steep) being so fast. Also note that the linear array summations respond with similar amplitudes due to the steepness of the angle of incidence.

Figure 12. Recording of a teleseismic event with unknown epicenter. Event is probably P (110 degrees or greater) distance since ITFK and ZXFK respond with equal amplitude and also the linear array summations respond with similar amplitudes.

Figure 13. Recording of a teleseismic event with unknown epicenter. IT and ZTFK respond to amplitudes greater than ZX and ZXFK, respectively, by a factor greater than 5.

Data taken from the seismograms indicate that ZX and ZXFK respond as well as do ZT and ZTFK for events approximately 100 or more degrees away, but do not respond as well to closer events. At a distance of 25 degrees, the responses differ by a factor of 4. The seismograms also show that signals from events at all distances, and arriving broadside to the ZNWF, ZNEF and ZEWF arrays are received with amplitudes that are very nearly equal to those received by ZT and ZTFK. These observations indicate that flag traces made by simply sum- ming selected elements of the 37-element SP array are far more limited in their detection capabilities than those made from summing elements of the crossed- linear array.

In order to better understand the parameters involved in establishing a useful flag trace, expressions for array directivity were derived and plots were made. Figure 14 shows the directivity pattern (zero degrees is broadside to the array) for a 7-element linear array like ZNWF, ZNEF, or ZEWF where array elements are spaced 1/2 wavelength. Although the gain at the peaks of the two major lobes is seven times that of a single instrument, the array is sharply directional. Three such arrays, arranged at 60-degree intervals would give very poor azi- muthal coverage, and in addition, would be extremely directional on a three- dimensional basis. Figures 16 and 17 show the directivity patterns for 5-element linear arrays. Note that the major lobes are broader, but still give poor azimuthal coverage. Figure 18 shows the directivity pattern as a function of angle of incidence, for the omnidirectional array ZX. A wave arriving along a path normal to the earth's surface is considered to have a zero degree angle of incidence; one arriving along the earth's surface has 90 degrees. Figure 19 shows relative array gain as a function of incidence angle and figure 20 array gain as a function of great circle distance - based on published information that relates great circle distanc to angle of incidence. Figures 21 through 23 show directivity patterns for the crossed-linear array. Note that it is very nearly omnidirectional for the most useful great circle distances. Also note that the element spacings are either 1/10 or 1/5 wavelength.

TR 70-1, app 2

AFTAC, Lt. John H, Fergus 4 November 1969 Page 4

These data and observations lead to the following conclusions:

1. Simple summations of elements in the 37-element array, whether arranged as linear or omnidirectional arrays, will not produce flag traces as good as summations of elements in the linear array. The element spacing is too great (1/2 wavelength at signal frequencies) and produces a directiv- ity pattern that looks at large areas of the earth with very low gain.

2. The filtered summation of 9 elements within the crossed-linear array (ZTFK) produces the best flag trace that can be made using existing operational sites at TFSO. It has good azimuthal and great circle coverage.

3. A flag trace with better omnidirectional characteristics but slightly less gain than ZTFK could be made by simply summing and filtering the outputs from a 7-element omnidirectional array whose elements are spaced 1/10 wavelength apart. Figure 24 shows the directivity of this array. Note the small gain variation over the great circle distances of interest and note that gain varia- tions with azimuth are insignificant. Contrast this with figure 23.

We hope that this information will be of interest to you, and will be pleased to discuss it further.

Very truly yours,

B. B. Leichliter Department Manager Field Operations

BBL:ma

bcc: R. K. Rasmussen G. M. Stanfill M. G. Gudzin D. R. Phillips J. M. Ward

-4-

TR 70-1, app 2

SCALE

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■ LONG-PERIOD VAULT

DD CENTRAL RECORDING BUILDING

• CONTRIBUTING ELEMENT TO CROSS-LINEAR SUMMATION (FILTERED)

Figure 1. Tonto Forest Seismological Observatory 37-element and cross-linear arrays

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TR 70-1, app 2

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19-

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TR 7U-1, app 2

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-20-

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TR 70-1, app 2

COMPOSITE OF THREE LINEAR ARRAYS ALIGNED 120° APART.

FIVE ELEMENTS PER ARRAY. 1/2 WAVEl ENGTH APART.

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Ilnclassif-i^ ^ecr ntyCIasBification

DOCUMENT CONTROL DATA R&D ^^^y_j]^^j}^ion_olJjtl», body of mbtttmcl and indeMlnj mnnotmtlon mutt b» •ntmnd whin tha ovm^mll fßort I» elmmmllM}

l ORIGINATING ACTIVITY cCorporar« aufhorj

Geotech, A Teledyne Company 3401 Shi loh Road Garland, Texas

3 REPORT TITLE

I». REPORT tCCURITV C L AMI FIC A TION

Unclassified 2b. CROUP

Operation of the Tonto Forest Seismological Observatory Final Report, Project VT/9702, Contract F33657-69-C-0803 1 January through 31 December 1969

4 DESCRIPTIVE NOTES (-7>pe of report and fnclu«<ve daf«*)

9 AUTHOR(Sl (Fifinmma, middlm Inlllml, Utl name)

Geotech Staff

6 REPORT DATE

15 February 1970 8«. CONTRACT OR GRANT NO.

F33657-69-C-0803 b. PROJEC T NO.

VELA T/9702 c.

ARPA Order No. 624 ARPA Program ^ode No. 6F10

7a. TOTAL NO. OF PAGES

114 7b. NO. OF REFS

»a. ORIGINATOR'S REPORT NUMBER!»»

TR 70-1

9b. OTHER REPORT NO(S) (Any othar number* (bar may be a««lana<f rbi» tnpart)

10 DISTRIBUTION STATEMENT

This document is subject to special export controls and each transraittal to foreign governments or foreign nationals may be made only with prior approval of the Chief of AFTAC.

II. SUPPL CMENTARV NOTES

13 ABSTRACT

12 SPONSORING MILITARY ACTIVITY

Advanced Research Projects Agency Nuclear Test Detection Office Washington, D.C.

J'1, . . f Thin is a report of the work accomplished on Project VT/9702 from 1 January through 31 December 1969. Project VT/9702-includes the operation, evaluation, and improvement of the Tonto Forest Seismological Observatory (TFSO) located near Payson, Arizona. It also includes special research and test functions carried out at TFSO and research and development tasks performed by the Garland, Texas, staff using TFSO data.

;

DD ,Fr.,1473 Unclassified Sccuritv Classification

•VWHHMBIMHIBPHIHWI

Unclassified Sscurity Claatlficatlon

14 Ktv woRoa

LINK A

NOWK

Operation of TFSO 37-element short-period array 7-element long-period array Multichannel filter Lightning protection modifications Spiking problems Seismograph operating parameters Short-period array systems modifications Instrument reliability; short-period and long-

period array Flag traces

WT

'.INK • LINK C

HOWS mr WOLB WT

Unclassified Security Clarification

~—• r"''"■■■