INTERPRETATION OF VIBROSEIS REFLECTIONS Jeanne L. Brennan · INTERPRETATION OF VIBROSEIS...
Transcript of INTERPRETATION OF VIBROSEIS REFLECTIONS Jeanne L. Brennan · INTERPRETATION OF VIBROSEIS...
INTERPRETATION OF VIBROSEIS REFLECTIONS
FROM WITHIN THE CATOCTIN FORMATION OF CENTRAL VIRGINIA
by
Jeanne L. Brennan
Thesis submitted to the Faculty of the
Virginia Polytechnic Institute and State University
in partial fulfillment of the requirements for the degree of
Master of Science
in
Geophysics
APPROVED:
John K. Costain, Chairman
G. A. Bollfnger 17 Eynn Glover, III
September 1985
Blacksburg, Virginia
INTERPRETATION OF VIBROSEIS REFLECTIONS
FROM WITHIN THE CATOCTIN FORMATION OF CENTRAL VIRGINIA
by
Jeanne L. Brennan
John K. Costain, Chairman
Geophysics
(ABSTRACT)
Large amplitude seismic reflections from within the
Catoctin Formation of central Virginia are interpreted to
originate from acoustically thin beds of interlayered
metabasal ts and metasediments. Large acoustic impedance
contrasts exist between epidotised layers ( epidosi tes and
volcanic breccia) and non-epidotised layers (greenstones and
phyllites) within the Catoctin Formation. Acoustic impedance
contrasts also exist between greenstones (metabasalts) and
phyllites (metasediments). Constructive interference of
small amplitude reflections from thin beds result in large
amplitude, reverberating reflections.
Thin bed reflections that approximate the first deriva-
tive of the source wavelet constructively interfere to give
even larger amplitude reflections than those originating by
conventional tuning. Computer modeling based on two geologic
sections of thin beds of epidosites interlayered with
greenstones and of greenstones interlayered with phyllites
and epidosi tes indicates that large amplitude reflections
result from constructive interference of thin bed re-
flections.
ACKNOWLEDGEMENTS
This research was supported by ARCO and CONOCO Fellowships
through the department of Geological Sciences, and by NRC
Contract #NRC-04-75-237 to L. Glover, III and J. K. Costain,
Principal Investigators.
I express great appreciation to my major advisor, Dr.
John Costain, for bringing geologists and geophysicists to-
gether to solve this interpretation problem. Dr. Lynn
Glover, III, provided extremely valuable comments concerning
presentation and analysis of the data and was instrumental
in relating geophysical and geological studies. Revisions
suggested by Dr. Gil Bollinger will hopefully make this paper
more meaningful to members of the science community in dis-
ciplines outside of reflection seismology and geology.
Graduate student organized and guided one of the
field trips that resulted in sample collection and provided
preliminary geologic sections used in the modeling. The ul-
trasonic velocity data would not have been obtained without
the patience and ingenuity of of the
Geophysical Instrumentation Laboratory. I am grateful to
for the petrographic modal analysis of the
Catoctin Formation which he did for us on a very rushed
schedule.
Acknowledgements iv
I express my deep love and appreciation to my brother
and sisters, and to my good friend , for their
support and encouragement during the last two years. I owe
everything to my parents, and , who have made many
sacrifices for me during my life but have never reminded me
of it. I dedicate this paper to my father, who has an en-
thusiasm for science from which I have always benefited.
Acknowledgements v
TABLE OF CONTENTS
INTRODUCTION AND PURPOSE OF STUDY
OVERVIEW OF GEOLOGIC FRAMEWORK
REFLECTIVITY OF CATOCTIN FORMATION
Modal Analyses
Velocity Determinations
Density Determinations
Reflection Coefficients
THIN BED THEORETICAL MODELS
Results
CONCLUSIONS
REFERENCES
APPENDIX A. CALIBRATION CURVES
APPENDIX B. REFLECTION COEFFICIENTS
VITA
Table of Contents
1
6
12
12
12
21
24
29
46
57
58
60
64
95
vi
LIST OF ILLUSTRATIONS
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
1. Central Virginia study area . . . 2. Stacked section of line NSF-2
3. Schematic geologic cross-section of Eastern Blue Ridge . . . . . . . . . . . . . . . .
4. Catoctin Formation section and core sample lo-cations. . . . . . . . . . . . . . . . .
5. Stratigraphic sections of Catoctin Formation
6. Modal analyses of 12 Catoctin Fm and 1 Chilhowee Fm sample . . . . . . . . . .
7. Velocity versus pressure of Catoctin greenstones . . . . . . . . . . . .
8. Velocity versus pressure of Catoctin epidosites . . . . . . . . . . . .
9. Velocity versus density of Catoctin greens tones . . . . . . . . . . . . . . .
10. Velocity versus density of Catoctin epidosites
11. Acoustic impedance versus pressure of Catoctin greens tones . . . . . . . . . . . . . . . .
12. Acoustic impedance versus pressure of Catoctin epidosites . . . . . . . . . . .
Figure 13. Synthetic 14-56 Hz Klauder wavelet
Figure 14. Resolution limit of 14-56 Hz wavelet
Figure 15. Tuning thickness
Figure 16. Tuning of reflections for two dipoles of same polarity . . . . . . .
Figure 17. Tuning of reflections from two dipoles of same polarity . . . . . . . . . . . . . .
Figure 18. Tuning of reflections from two dipoles of op-posite polarity . . . . . . . . . .
List of Illustrations
2
5
7
8
9
13
19
20
22
23
25
26
30
32
33
34
36
37
vii
Figure 19. Tuning of reflections from two dipoles of op-posite polarity . . . 38
Figure 20. Thin bed models 40
Figure 21. Multiple thin bed model 42
Figure 22. Simplified thin bed model . . . 43
Figure 23. Multiple thin bed model for i:::T/2 44
Figure 24. Catoctin thin bed model constructed from sec-tion A . . . . . . . . . . . . 48
Figure 25. Section A without beds <l ms and with beds replaced . . . . . . . . . . . 49
Figure 26. Section A - previous figure without layer JB4-4G . . . . . . . . . . . . . . 50
Figure 27. Section A - previous figure with layers re-peated and replaced . . . . . . . . . 51
Figure 28. Section A - previous figure with layers re-peated . . . . . . . 52
Figure 29. Catoctin thin bed model constructed from sec-tion B . . . 54
Figure 30. Section B - layers replaced and removed 55
Figure 31. Section B - two layers removed 56
Figure 32. Steel calibration curve for 200 atm 61
Figure 33. Steel calibration curve for 400 atm 62
Figure 34. Steel calibration curve for 600 atm . . . 63
List of Illustrations viii
LIST OF TABLES
Table 1. P-Velocities and Densities of Catoctin
Samples 15
Table 2. Anisotropy of Catoctin Formation 28
Table 3. Catoctin Reflection Coefficients(600atm) 65
List of Tables ix
INTRODUCTION AND PURPOSE OF STUDY
The Catoctin Formation of central Virginia is a rift
volcanic sequence of metabasalts interlayered with
metasediments. Seismic reflections from within syn- and
post-rift sediments are commonly observed along passive mar-
gins, including the Bay of Biscay and the U.S. Atlantic mar-
gin (Brun and Choukroune, 1983; Bally, 1981). In central
Virginia, it is primarily the reflectivity of metamorphosed
basalts that allow an interpretation of the subsurface thrust
geometry using reflection seismology.
The record of rifting in the southern Appalachians is
incomplete due to erosion, deformation, and metamorphism
(Wehr and Glover, 1985). An interpretation of the origin of
the reflections from the Catoctin Formation provides further
information about the tectonic architecture in central
Virginia. Such information may be used to constrain geologic
and tectonic models. An interpretation of the reflections
is possible in large part because of the acoustic impedance
contrast between thin layers of epidotised and non-epidotised
rift basal ts and sediments. On a broader scale, an inter-
pretation of the reflections may be used to help identify the
seismic signature of thin bed sequences from other geologic
settings as well as along passive continental margins.
Introduction and Purpose of Study 1
0 co C
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ure
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inia
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Vibroseis reflection data collected and processed by the
Regional Geophysics Laboratory (RGL) along the James River
in central Virginia (Figure 1) include segment NSF-2 of
seismic profile JRT-1 extending from Richmond to the crest
of the Blue Ridge. NSF-2, which has particularly good re-
flection quality and excellent signal to noise ratio, con-
tains large amplitude, east-dipping reflections (Figure 2)
with a reverberating nature. Reflections are defined as
reverberating when successive reflections blend together into
a steady oscillation (Sheriff, 1973). The reverberating re-
flections present on NSF-2 are interpreted to have developed
from within the Catoctin Formation.
Velocity analyses of the reflections indicate that these
reflections are primary reflections ( Coruh and others, in
review). The seismic signature of the reflections from
within the Catoctin Formation have been characterized as
parallel reflections from the tops and bottoms of thick beds
(Coruh and others, in review). The purpose of this study is
to determine the origin of these reflections from the
Catoctin formation in the crystalline Blue Ridge terrane of
central Virginia. The author hopes to show that large am-
plitude, reverberating reflections result from constructive
interference of reflections from a series of thin beds rather
than thick beds. This hypothesis is substantiated by
reflectivity data (velocity and density), stratigraphic
Introduction and Purpose of Study 3
sections, and synthetic seismograms of the Catoctin Forma-
tion.
Introduction and Purpose of Study 4
A c;;) c;;)
Figure 2.
·-o -0 w N I
c;;) g (J1 (Si Eil -i
D -i
Stacked section of line NSF-2: Reflections from the Catoctin Formation along the James River traverse in central Virginia.
Introduction and Purpose of Study 5
OVERVIEW OF GEOLOGIC FRAMEWORK
The Catoctin Formation of central Virginia is composed
of metamorphosed basalts and sandstones that are believed to
represent part of the Eocambrian rift facies of the eastern
continental margin of North America (Wehr and Glover, 1985).
Rifting and crustal attenuation occurred predominantly during
the Precambrian, although there is some evidence of rifting
continuing into the Eocambrian. The axial zone of the Blue
Ridge anticlinorium in central Virginia is believed to be a
reactivated hinge zone separating attenuated crust to the
east from normal continental crust to the west (Wehr and
Glover, 1985).
On the west side of the Blue Ridge near line NSF-2 and
the study area, granuli te facies grani toid rocks of 1 Ga
Grenville basement are overlain nonconformably by a thin unit
of Eocambrian (?) Swift Run shallow-water elastics and non-
marine Catoctin volcanics metamorphosed to greenschist facies
(Figure 3). These formations were probably deposited
subaerially in rift basins which developed landward of the
hinge zone (Wehr and Glover, 1985). Nonconformably overlying
the Catoctin Formation in the adjacent Valley and Ridge are
shallow marine and alluvial elastics of the Cambrian
Chilhowee Group (Wehr and Glover, 1985). Preliminary
stratigraphic sections of the Catoctin Formation (Figure 5)
Overview of Geologic Framework 6
NW AXIS Of
BLUE RIDGE ANTICLINORIUM
ROCK FISH VALLEY
FAULT
SE
C/§f?C'.t;;~=~~~-;~~L~~-;:~~~!/{(\Utmnx\:Y! ~~ 1l 11 ;;;~-~~~:;;; '~;'~~~ l 1 :;:,:,:.:,:,:::::::::::<.Fm.::::./: Lynchburi;i ·Gp.
,,,,, .. ,, .. v L
.._.__,..___...____,_--'-'-~--=-"-~~~~-'-~
11 11 .., I 1 .. -
. (Wehr and Glover, 1985) Schematic restored cross sections across the Blue Ridge (not to scale) showing
relations among earty PaJeozoic-late Proterozoic units. Patterns as in Figure l: d2l"k stipple represents volcanic rocks; random dashes represent Crossnore plutons.
Figure 3. Schematic geologic cross-section of Eastern Blue Ridge: central Virginia Precambrian to Paleozoic sediments (Glover and Wehr, 1985).
Overview of Geologic Framework 7
8
a.Io::> pu-e
-. '
/
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SCHISTOSE BASALT
EPIDOTISED SANDSTONE SCHISTOSE BASALT
PHYLLITE SCHISTOSE BASALT
PHYLtrTE SCHISTOSE BASALT
PHYLLITE SCHISTOSE BASALT
EPIDOTISED SCHISTOSE BASALT
SCHISTOSE BASALT
PHYLLITE EPIDOTISED SCHISTOSE BASALT
PHYLLITE SCHISTOSE BASALT
PHYLLITE
0
"' '::! ... 0 Q 0..
"'
SCHISTOSE BASALT
AMYGDALOIDAL
METASANDSTONE 60
VOLCANIC BRECCIA . SCHISTOSE
~PHYLLITE
DSCHIST
SECTION A
-
/' //, /,// //Jfi/@,/
-
-
SCHISTOSE BASALT
AMYGOALOIDAL EPIDOTISED BASALT
SCHISTOSE BASALT
EPIDOTISED BASAL TS AND AMYGDALOIDAL
VOLCANIC BRECCIA
SCHISTOSE BASALT
EPIDOTISED BASALT AND VOLCANIC BRECCIA
PHYLLITE
SCHISTOSE BASALT
SECTION B
: 0 •• ' ••••••••• • : • ••• • • • •• 0 . . ...... ·.· .. . . . . . . . . . . • 0 • • •••• ' •••
•• • ••••••• 0 ••
. . . . ... '• '•'a 111 .' , 0 • ' 0 1' . · ... · ....... . ,o•''.o•o•'•o
• • • • 0. • • ••• . "... .
Figure 5. Stratigraphic Formation: (a) Section B.
sections Section A
of Catoctin on Figure 4; (b)
Overview of Geologic Framework 9
at two locations (Figure 4) include thin beds ( <30 meters
thick). Section B consists of thin beds of metamorphosed,
epidotised basal ts and sandstones interlayered with non-
epidotised, foliated metabasalts and
Figure 5, (R. Badger, pers. comm., 1985).
zones are flow breccias or highly altered
and quartz (R. Badger, pers. comm., 1985).
metasediments,
The epidotised
zones of epidote
Gathright (1976)
refers to these zones as epidote-amygdaloidal breccia.
Basalt flows and rift sediments are also commonly interlay-
ered within the Catoctin Formation ( R. Badger, pers. comm.,
1985) as in section A, Figure 5.
East of the Blue Ridge, Grenville age basement and Late
Precambrian intrusives are overlain nonconformably by east-
dipping Eocambrian shallow to deep marine elastic rocks of
the Lynchburg Group deposited in large rift basins (Wehr and
Glover, 1985) . Overlying the Lynchburg Formation are ap-
proximately 2 km of Catoctin greenschist-facies metamorphosed
basal ts interbedded with metasediments. This sequence is
believed to have been deposited in a submarine environment
because of the presence of interlayered turbidite sandstone
beds, pillows, and volcanic breccia (Wehr and Glover, 1985).
Coarse epidote amygdules are also present in outcrop (Wehr
and Glover, 1985). The Evington deep-water sequence, a pos-
sible equivalent of the Cambre-Ordovician Valley and Ridge
Chilhowee shelf sequence, stratigraphically overlies the
Overview of Geologic Framework 10
Catoctin on the east side of the Blue Ridge (Wehr and Glover,
1985) .
A geologic interpretation of seismic reflection profile
NSF-2 places the Catoctin Formation above the Lynchburg For-
mation and below the Evington Group (Coruh and others, in
review). This stratigraphy corresponds to the east side of
the Blue Ridge. The seismic reflections originating from
within the Catoctin Formation on NSF-2 are therefore origi-
nating from within a rift sequence believed to have been de-
posited in a submarine environment.
Stratigraphic sections, Figure 5, and sample collection
locations, Figure 4, are located on the west side of the Blue
Ridge. The Catoctin Formation outcrop on the east side of
the Blue Ridge is more heavily foliated than Catoctin Forma-
tion outcrop on the west side of the Blue Ridge, making it
more easily waethered than Catoctin outcrops on the west side
of the Blue Ridge. Rock samples were not collected at the
Catoctin Formation outcrop on the east side of the Blue Ridge
because of the poorer sample quality of the heavily foliated
section.
Overview of Geologic Framework 11
REFLECTIVITY OF CATOCTIN FORMATION
MODAL ANALYSES
Modal analyses of 12 samples of Catoctin Formation and
1 sample of the Chilhowee Formation were done by Russell Guy
on a 1000 point grid (Figure 6). Zircon was seen in each thin
section, although it did not appear in the count grid. Min-
ute traces of calcite and chlorite were seen in many samples,
al though in insufficient amounts to be counted. Only one
sample had more than 10% plagioclase (JB4-4D); several other
samples had minor amounts. The small grain size and lack of
twinning in the fine-grained samples made the distinction of
quartz from feldspar very difficult (Russell Guy, pers.
comm., 1985). For this reason, percentages of quartz and
feldspar were combined for sample descriptions.
VELOCITY DETERMINATIONS
Compressional wave velocities parallel and perpendic-
ular to the dominant foliation (when present) in 12 Catoctin
Formation samples and one Chilhowee Formation sample were
determined in a pressure cell in the Regional Geophysics
Laboratory at Virginia Tech using the method described by
Kolich ( 1974). Samples were collected at central Virginia
Reflectivity of Catoctin Formation 12
Percentage Minerals Sample Q Feld Ep Op Cc Chl Act Sph Bio z Total% ------------------------------------------------------------------------JB4·1 36.8 o. 7 8.6 15. 3 37. 6 0.6 0.4 100 (Chilhowee phyllite)
JB4·3B 21. 7 9. 1 37.9 1. 8 25.6 3.9 100 (Phyllite)
JB4·3C 42.9 1. 8 45. 2 10. 1 100 (Epidosite)
JB4·3D 13.5 46. 8 5. 7 6. 1 27.9 100 (Greenstone)
JB4·4A 17. 1 0.2 49.8 7.5 8.0 17.4 100 (Epidosite)
JB4·4D 1. 5 12. 6 18. 1 18. 9 5. 1 38.0 5.8 100 (Greenstone)
JB4·4G 2. 7 1. 2 21. 3 45.4 3. 9 25.5 100 (Greenstone)
JBS·SD 28.8 0.4 (Volcanic breccia)
37.8 22.6 10.4 100
JBS·SF 15. 6 1. 6 6.2 13. 6 5.2 42. 7 lS. 1 100 (Greenstone)
JBS·lOC 21. 3 12.6 21. 9 4.4 39.8 100 (Greens tone)
JBS·lOD 14. 1 1. 5 44. 7 33.6 6. 1 100 (Volcanic breccia)
JBS·llA 2S.4 0. 6 42.0 31. 7 0. 3 100 (Epidosite)
JBS·12A 3S.O 19. 7 4S.3 100 (Epidosite)
Figure 6. Modal analyses of 12 Catoctin Fm and 1 Chilhowee Fm sample: Q=quartz; Feld=albite; Ep=epidote; Op=opaques; Cc=carbonates; Chl=chlorite; Act=actinolite; Sph=sphene; Bio=biotite; Z=zircon; (Russell Guy, pers. comm., 1985). Lithologic names in parentheses are from R. Badger (pers. comm., 1985).
Reflectivity of Catoctin Formation 13
locations shown in Figure 4 and at Luck Stone Quarry in cen-
tral Virginia. Compressional velocities were determined at
pressures of 200, 400, and 600 atm, corresponding to depths
of approximately 0.75, 1.5, and 2.25 km respectively, assum-
ing a geopressure gradient of 266 atm/km (Dobrin, 1976).
Velocities determined at 600 atm range from 5. 13 km/sec to
6.47 km/sec for samples of the Catoctin epidosites,
greenstones, phyllites, and volcanic breccia (Table 1).
Reflectivity of Catoctin Formation 14
Table 1 (Part 1 of 4) · P-Veloci ties and Densities of Catoctin Samples
CORE P-VELOCITY DATA (KM/SEC)
SAMPLE PROP DESCRIPTION PRESSURE(ATM DIR Zoo L!oo (,00
JB4-l ..Ls1 Chilhowee 5.29 5.29 5.29 phylli te km/s km/s km/s 38%Chl,38%Q+F, 15%0p,9%Ep ( Phylli te)
JB4-3B __l_ s 1 Phyllite 38%0p, 5.13 5.14 5.13 26%Chl,22%Q,9%Ep 4%Sph,2%Cc (Phyllite)
JB4-3C no Meta sandstone 5. 72 5.73 5. 71 S1 45%Ep,45%Q+F,
10%0p (Epidosite)
JB4-3D II s1 Schist 6.26 6.25 6.28 4 7%Ep, 28%Chl I
14%Q,6%Cc,5%0p (Greenstone)
JB4-3D __L S1 Schist 5.95 5.98 5.97 47%Ep, 28%Chl, 14%Q,6%Cc,5%0p (Greenstone)
S1 REFERS TO PRIMARY FOLIATION
~S 1 =VELOCITY MEASURED 11s1
-L S 1=VELOCITY MEASURED _LS 1
PROP DIR=PROPAGATION DIRECTION
Reflectivity of Catoctin Formation
DENSITY
GM/CM 1
2.79
J. l~ 5
2.80
2.99
2.95
15
Table 1 (Part 2 of 4). P-Velocities and Densities of Catoctin Samples
CORE P-VELOCITY DATA (KM/SEC)
SAMPLE PROP DESCRIPTION PP1"<:;SUREIATM DIR 1..00 'iOO (:,(0
JB4-4A no Metabasalt 6.22 6.23 6.24 S1 50%Ep, 1 7%Chl,
17%Q+F,8%Cc,8%0p (Epidosite)
JB4-4D is 1 Schist 38%Chl, 6.30 6.38 6.39 19%0p,18%Ep,5%Cc 14%Q+F,6%Sph (Greenstone)
JB4-4D _l_s1 Schist 38%Chl, 5.81 5.80 5.80 19%0p,18%0p,5%Cc 14%Q+F,6%Sph (Greenstone)
JB4-4G __Ls1 Schist 45%Chl, 5.84 5.90 5.92 26%Sph,21%Ep, 4%Q+ F, 4/'oAct (Greens tone)
JB4-4G i S1 Schist 45%Chl, 6.42 6.48 6.47 26%Sph,21%Ep, 4%Q+F,4%Act (Greenstone)
S1 REFERS TO PRIMARY FOLIATION
II S1 =VELOCITY MEASURED II s I _l_ S 1 =VELOCITY MEASURED _J_ S 1
PROP DIR=PROPAGATION DIRECTION
Reflectivity of Catoctin Formation
DENSITY
GM/CM>
3.19
3.02
2.97
3.01
3.01
16
Table 1 (Part 3 of 4). P-Velocities and Densities of Catoctin Samples
CORE P-VELOCITY DATA (KM/SEC}
SAMPLE PROP DESCRIPTION PRESSURE(ATM DIR 200 400 (,,CO
JBS-SD no Metabasalt S.87 S.97 S.98 S1 38%Ep,29%Q+F,
23%0p,10%Cc (Vole Breccia}
JBS-SF _l__s1 Schist 43%Chl, S.24 S.S2 S.68 17%Q+F,1S%Sph, 14%0p,6%Ep,S%Cc (Greenstone}
JBS-lOC !S1 Schist 40%Chl, 6.37 6.41 6.4S 22%0p,21%Q, 13%Ep,4%Cc (Greens tone)
JBS-lOC J_ S1 Schist 40%Chl, S.90 S.99 6.01 22%0p,21%Q, 13%Ep,4%Cc (Greenstone)
JBS-lOD ..l_ S1 Phylli te S.S4 S.6S S.68 4S%Ep,34%0p, 1S%Q+F,6%Cc (Vole Breccia)
S1 REFERS TO PRIMARY FOLIATION
~S 1 =VELOCITY MEASURED II s I _L_ S1 =VELOCITY MEASURED _Ls 1
PROP DIR=PROPAGATION DIRECTION
Reflectivity of Catoctin Formation
DENSITY
GM/CM'
3.03
2.89
2.93
2.91
3 .11
17
Table 1 (Part 4 of 4). P-Veloci ties and Densities of Catoctin Samples
CORE P-VELOCITY DATA (KM/SEC)
SAMPLE PROP DESCRIPTION PRESSURE(ATM DIR Zoo 'ioo ~oo
JBS-lOD I s1 Phyllite 6.22 6.26 6.21 45%Ep,34%0p, 15%Q+F,6%Cc (Vole Breccia)
JB5-llA no Amygdaloidal 6.11 6.14 6.16 S1 metabasalt
42%Ep, 32%0p,26%Q+F (Epidosite)
JB5-12A no Amygdaloidal 5.97 6.16 6.15 S1 metabasalt
45%0p,35%Q,20%Ep (Epidosite)
S1 REFERS TO PRIMARY FOLIATION
~ S1 =VELOCITY MEASURED II S1
_l_ S1 =VELOCITY MEASURED J....s 1
PROP DIR=P.ROPAGATION DIRECTION
DENSITY
GM/CM 2
3.07
3.30
3.15
Velocities parallel to foliation are higher than veloc-
i ty perpendicular to foliation for all of the samples for
which velocities in both directions were available
(greenstones) (Figure 7). Velocities of the epidosites gen-
erally lie between a velocity parallel to foliation and a
velocity perpendicular to foliation of the greenstones (Fig-
Reflectivity of Catoctin Formation 18
5.2
5.0 200 300 400 500 600
PRESSURE {atm)
Figure 7. Velocity versus pressure of Catoctin greenstones: Sample JBS-lOD is an epidotized, foliated volcanic breccia.
Reflectivity of Catoctin Formation 19
6.4 JB4-4A
6.2
- 6.0 a>
........ E 5.8 ~ JB4-3C - • • • >Q. 5. 6
5.4
5.2
5.0 200 300 400 500 600
PRESSURE (atm)
Figure 8. Velocity versus epidosites
pressure
Reflectivity of Catoctin Formation
of Catoctin
20
ure 8). Variation of velocity with pressure decreases as
pressure increases (Figure 7 and Figure 8). The difference
in velocity from 400 to 600 atm probably represents the pre-
cision of the traveltime measurements (i.e. of a frequency
counter) and inaccuracies of the velocity determinations.
Measurements of core lengths were repeatable to within
1% while travel time measurements were repeatable to within
4% at 600 atm. Velocity is as precise as the least precise
measurement involved in the velocity determination which is
the measurement of travel time. Velocities are therefore
precise to ±4% at 600 atm. Velocities determined at 600 atm
are used to calculate reflection coefficients.
DENSITY DETERMINATIONS
Specific gravities (Mendenhall and others, 1950) of the
Catoctin samples are listed in Table 1. A graph of velocity
versus density for samples with no apparent foliation
(epidosites) (Figure 10) shows that velocity is approximately
a linear function of density (e.g. Birch, 1961).
Reflectivity of Catoctin Formation 21
-"' ........
6.4
6.2
6.0
~ 5.8 -Q.
> 5.6
5.4
5.2
5.0
JBS 10Ce JB4-4G II~, llS, e J64-4 D llS,
JB4-3D e II~, e JD5-10Dl(S,
JB5-10C e JB4-3o..l .;, .Ls, e
e JB4-4G .L'S,
e JB4-4DJ. s,
9 JB5-10DlS1
2.6 2.8 3.0 3.2 3.4 DENSITY (g/cm3 )
Figure 9. Velocity versus density of Catoctin greenstones: Sample JBS-lOD is an epidotized, foliated volcanic breccia.
Reflectivity of Catoctin Formation 22
6.4 JB4-4A
6.2 e
JB5-12A e o · :rns-11A
6.0 -0
' 5.8 E .:.:: - eJB4-3C
Q. > 5.6
5.4
5.2
5.0 2.6 2.8 3.0 3.2 3.4
DENSITY (g/cm3)
Figure 10. Velocity versus epidosites
Reflectivity of Catoctin Formation
density of Catoctin
23
REFLECTION COEFFICIENTS
Normal incidence reflection coefficients were calcu-
lated at 600 atm for various juxtapositions of Catoctin For-
ma ti on li thologies. Results are tabulated in Appendix B.
Most significant is the result that the highly epidotised
metamorphosed basalts and sandstones, samples JB4-4A,
JBS-llA, JBS-3C, and JBS-SD are associated with reflection
coefficients of magnitudes greater than or equal to 0.1. An
absolute value of 0.1 or greater indicates a "good" reflector
(Waters, 1981).
Pressure versus acoustic impedance perpendicular and
parallel to foliation of the greenstones (Figure 11) and
highly epidotized samples (epidosites) (Figure 12) indicate
that maximum constrasts result from the juxtaposition of the
Catoctin greenstones against the epidosites. A large con-
trast exists between acoustic impedance of sample JB4-3C and
acoustic impedance parallel to foliation of the greenstone
samples. Large contrasts occur between the acoustic
impedance of samples JB4-4A, JBS-llA, and JBS-12A and acous-
tic impedance perpendicular to foliation of the greenstone
samples; the reflection coefficient between sample JB4-4A and
sample JBS-lOC _1__S 1 is -0.08. Acoustic impedance constrasts
within the epidosites between sample JB4-3C, a metsandstone,
and samples JB4-4A, JBS-llA, and JBS-12A, the amygdaloidal metabasalts, are the largest observed; the reflection coef-
Reflectivity of Catoctin Formation 24
- 21 "' I ('II
E 20 () ........ ~
JB4-4G fl<;, : <:?-. ,.._, .
0 ~11~,
,... 19 ~ - •JB4-3DllS, i JBS-tOC 11s-;! w (.) z 18 <( JB4-30J.<;, • c S _ JB4-4D.le' w ~5, c.. 17 ~
(.)
~ 16 l ~ 15 __. ____ ....._ __ _._ ____ w
200 300 400 500 600 PRESSURE (atm)
Figure 11. Acoustic impedance versus pressure of Catoctin greenstones
Reflectivity of Catoctin Formation 25
-; 21 I
N. i::s4-4A .JBS-11A • E 0 20 ' E
,.._ <:r>
0 19 ,... -w· 0 z 18 Jss-so __. ~
<t ~ c w Q, 17 :E 0 - 16 JB4-3C t-CJ) :::> 0 0 15 <t 200 300 400 500 600
PRESSURE (atm)
Figure 12. Acoustic impedance versus pressure of Catoctin epidosites
Reflectivity of Catoctin Formation 26
ficient between samples JB4-3C and JB4-4A is 0.12.
Acoustic impedance constrasts resulting in reflection
coefficients also result from anisotropy (Figure 11).
Juxtaposition of acoustic impedance parallel to foliation
against acoustic impedance perpendicular to foliation for
sample JB4-4D gives a reflection coefficient of 0.06.
Anisotropy factors, A, of samples for which velocities were
available parallel and perpendicular to the foliation were
calculated according to the method of Uhrig and Van Melle
(1955). Per cent anisotropy was calculated using the method
of Christensen (1965). Data are listed in Table 2. From the
data given in the reflection coefficient table (Table 3 on
page 65) and the anisotropy table (Table 2), it may be con-
cluded that anisotropy is a secondary effect leading to re-
flections.
Reflectivity of Catoctin Formation 27
Table 2. Anisotropy of Catoctin Formation
PRESSURE 200ATM 400ATM 600ATM
SAMPLE A %ANIS A %ANIS A %ANIS
3D 1.05 5% 1.05 5 1.05 5
4D 1.06 8 1.10 10 1.10 10
4G 1.10 9 1.10 9 1.09 9
lOC 1.08 8 1.07 7 1.07 7
lOD 1.12 12 1.11 10 1.09 9
A=ANISOTROPY FACTOR=Vp II S1/V p.L S1
'1.,ANIS='1.,ANISOTROPY=Vp II S1 -v,J. Si/ { [ vf II S1+Vp.L S1 ]/2)
Reflectivity of Catoctin Formation 28
THIN BED THEORETICAL MODELS
Twenty-four fold NSF-2 data were acquired near
Charlottesville, Virginia using a 10-80 Hz Vibroseis sweep.
A narrower 14-56 Hz Klauder wavelet was chosen for modeling,
however, because the observed frequency content of Catoctin
reflections on NSF-2 data was more band-limited than the
source sweep (Figure 2). Computer modeling of thin bed se-
quences was done to obtain synthetic seismograms which might
simulate the reflection character observed on segment NSF-2.
A thin bed was defined by Marangakis and others (1985)
as one whose two-way time thickness is less than the tuning
thickness, T/2, of the incident wavelet where T is the domi-
nant period of the wavelet. A tapered Vibroseis sweep of
14-56 Hz has a dominant period of 26 ms and a corresponding
dominant frequency (defined as the inverse of the dominant
period) of 38 Hz (Figure 13). The tuning thickness, T/2, for
the chosen Vibrosei s sweep is 13 ms ( Sengbush and others,
1961). A bed with thickness less than T/2 (13 ms) is herein
a thin bed.
At tuning thickness, the reflection begins to take on
the shape of the first derivative of the source wavelet
(Sengbush and others, 1961). Reflections from beds less than
X/8 thick where X is the dominant wavelength in the thin bed,
are essentially first derivatives of the incident wavelet
Thin Bed Theoretical Models 29
2.0
1 . 5
1 . 0 w 0.5 0
~ r-_J 0 .0 Q_ 2 -0.5 <(
-1. 0
- 1 . 5
-2.0 0 40 80 120
TIME (MS)
Figure 13. Synthetic 14-56 Hz Klauder wavelet
Thin Bed Theoretical Models 30
(Widess, 1973). The reflection from a thin bed is thus ei-
ther a first derivative waveform or is beginning to take on
the shape of a first derivative of the incident wavelet.
Generally, for zero-phase incident wavelets, beds less
than tuning thickness are not resolvable into the top re-
flection and the bottom reflection by conventional methods
(Kallweit and Wood, 1982; Widess, 1973). The resolution
limit of the zero-phase Klauder wavelet is defined as = T/2
(Kallwei t and Wood, 1982), Figure 14. Two spikes of equal
magnitude and the same polarity are progressively separated
in time by 2 ms ( 1 sample interval) . At 14 ms separation,
reflections from each spike are resolved, Figure 14(h). At
12 ms, the reflections interfere, Figure 14(g)).
The thin bed model also illustrates the Klauder waveform
resolution limit which corresponds to tuning thickness. Re-
flections from the top and bottom of a thin bed are not re-
solved at tuning thickness, as illustrated in Figure 15. A
dipole is a pair of reflection coefficients of opposite po-
larity and represents a thin bed. Maximum reflection ampli-
tude occurs at approximately 14-16 ms dipole thickness,
Figure lS(g),(h).
Consider the tuning of reflections from two dipoles of
the same polarity, Figure 16 and Figure 17. For an increas-
ing dipole separation and a constant bed thickness of 6 ms,
Figure 16, maximum constructive inter£ erence results when
Thin Bed Theoretical Models 31
.~ D 12'S
FREQUENCY (Hz) o~a~·~.~ 1zs. a 1zs. o 1a
-t i Ill
i ~
0 -
I I
0 -
I ! :
Ca) (b) Cc)
.~ .~ !\/\ 0 125. 0 ,.,Y,';v';,~
FREQUENCY (Hz) 1~ 0 1zs. 0 -
-t i .. i ~
8 -
f I
(f) (g) (h)
0 -
r 8 -
= I
(d)
.~ 0 1.S
F I I
(I)
F=
!
<·~
Figure 14. Resolution limit of 14-56 Hz wavelet: (a) Source wavelet amplitude spectrum, re-flection, and reflectivity series; (b)-(i) amplitude spectrum, reflection and re-flection coefficients of model; spike sepa-ration is 2 ms in (b) and is incremented by 2 ms per figure.
Thin Bed Theoretical Models 32
r-1 ~ /~ ~ /.1~~ 111111~1' 0 '"' 0 L?'S. 0 '"' 0 '"' 0 '"' FREQUENCY (Hz)
a -
i= a - a - a -
a : j. - t -.. I T i Ill
i I !.
I g - !
8 I :i - 8 - 8 -a -
I l a -
l a -
- -
l I - -------
~ - ~ - ~ - ~ - ~ -(a) (b) (c) (d) (e)
~ _,--~ J .... fl~, ~ Cr~ 0 '"' 0 !.:'S
FREQUENCY (Hz) 0 0 ::."'!!. 0 :;";;.
a: ~ a : j, 0: j a - J a -
1= ~ -==7 - 2
=~~~ =· ~ =~- ~.:-::( .. { r - i' I
i i I .. i I !. I
I
i 5 u 8 - il
a -
T T T -i--
I ! t - ;, ~ u ~ - CJ) (I) (g) (h) (I)
Figure 15. Tuning thickness: (a) Source wavelet ampli-tude spectrum, reflection, and reflectivity series; (b )- ( j) amplitude spectrum, re-flection, and reflection coefficients of model; bed thickness is 2 ms in (b) and is incremented by 2 ms per figure.
Thin Bed Theoretical Models 33
.~ a 121> FREQUENCY (Hz)
0 -
-4 i -Ill -
i : !.
0 -
~ 0 IZS
0 -
0 -
- - 8 - -8 -8 - . -0 0
- ~ =--=i= =r= I r I
---= i I I I
I i
I ' i I
I
I i
i N - 8 -I!!
(e) (f)
t '
"' - -
l'l - 8 -(c) (d) Ca) (b)
dj~~~~~~ o ·~ o ia o 1a a 1~ a 1~ o 1~ FREQUENCY (Hz)
0 - 0 -
-4 -i -"' -i : !.
0 -
-8 -
---;-
0 -
- -. 8 - 0 -0
-=t= =i= :----I - -.-
1
~ -
! ; I !
(g) (h)
-"' -l'l
I
!
-"' -l'l
(j)
I I
i !
- -"' - ill -., 0 0
(k) (I)
Figure 16. Tuning of reflections for two dipoles of same polarity: effect of increasing dipole sepa-ration for a constant bed thickness of 6 ms; (a) Source wavelet amplitude, reflection, and reflection coefficient; (b )- ( J) ampli-tude spectrum, reflection, and reflection coefficients of model; bed thickness is 2 ms in (b) and is and is incremented by 2 ms per figure.
Thin Bed Theoretical Models 34
beds are 12 ms, T/2, apart, Figure 16(h). For increasing bed
thickness and a constant dipole separation of 6 ms,
Figure 17, maximum constructive interference results when
each thin bed is at tuning thickness c~ 12 ms).
From Figure 16 and Figure 17, we may conclude that beds
at tuning thickness or tuning thickness apart may tune to
give large amplitude reflections. Maximum amplitude re-
flections result from the constructive interference of beds
at tuning thickness. The composite reflection from two
dipoles of the same polarity has either a first derivative
or ringing waveform, depending on the bed thicknesses and
dipole separation.
Consider now two dipoles of opposite polarity with an
increasing dipole separation and a constant bed thickness of
6 ms thickness, Figure 18. Up to 16 ms thickness, the in-
crease in dipole separation widens the central lobe of the
reflection until resolution is apparent at 18 ms dipole sep-
aration, Figure 18(j). Dipole separations of 2-8 ms lead to
maximum constructive interference of thin bed reflections and
a well-formed Klauder wavelet.
If dipole thickness is increased and dipole separation
is held constant at 6 ms, Figure 19, the central lobe on the
reflection widens as the beds become thicker, as in the pre-
vious example, Figure 18. The composite thin bed reflections
Thin Bed Theoretical Models 35
.~~~ ~ ~~ O l~ O lZS 0 ll'S. 0 !ZS 0 IZS FREQUENCY (Hz)
0 -
... -i "' -i : !.. :
0 -
=
(b)
= I ! I
(c)
-~ -
-8 - 8 -0 -
I r I ! I I I
~ - I ~ -
(d) (e) (f)
JJ~~LAL~~~L a IZS a IZS 0 12S 0 !ZS 0 IZS 0 I~
FREQUENCY (Hz)
... -i -Ill -
i : !.. =
- =r-r I
-~ -
(g)
Figure 17.
0 -
- --c i
-N -
"' 0
(h)
--0 0
___,___
r N -i'i
co
o;t -. -
0 0
r !
-N -i'i
(J)
- -8 - 8 -
~ - ---,
I I= ! I
I I
- -~ - ~ -
(k) (I)
Tuning of reflections from two dipoles of same polarity: effect of increasing bed thickness for constant dipole separation of 6 ms. (a) Source wavelet amplitude spectrum, reflection, and reflectivity series; (b)-(1) amplitude spectrum, reflection, and re-flection coefficients of model; bed thick-ness is 2 ms in (b) and is incremented by 2 ms per figure.
Thin Bed Theoretical Models 36
r-\ 111111~ a 1a
FREQUENCY _(Hz) 0 -
-4 i -"' i ?.
(a)
£.':y~
o~~
lT . - I 8
(b)
. -8 . -
8 . -8
0 -
T -T ~ - ~ -
Cc) (d)
0 -
__ T _ T ~ ~
(e) (f)
Dfl.~ f.W~. J\0~~ ('y~ (\A 0 1"5. 0 :::.-s 0
rl1111~ .-'T •••• ~
FREQUENCY (Hz) IZ':i. 0 •-'!> 0 l<"S 0
0 -
~ 0 - 0 - 0 - 0 -- ~ - .3. __ l __},. 0 -
~ - - --
T - - - --4 ·~, -
i -
~ ~ -
-~~ -
-~ -.. - -:::> "7> - -=--:-~ - f ? -
i -
f - ?
- I f
r ?. - I
I - i I
! I I I i ( ! I - - - i 8 '· i -
8 " 8 ..
g u -" 0
T -l. T l r =+= -- -
i I i
I !
l I .. N •. i.'l " " " " (h) J• ;,; ,, '" (g) (I) 0
(k) 0
(j) (I)
Figure 18. Tuning of reflections from two dipoles of opposite polarity: effect of changing dipole separation for beds of 6 ms thickness. (a) Source wavelet amplitude spectrum, re-flection, and reflectivity series; (b )- ( i) amplitude spectrum, reflection, and re-flection coefficients of model; dipole sepa-ration is 2 ms in (b) and is incremented by 2 ms per figure.
Thin Bed Theoretical Models
1,.,;
37
I~ ~~~~ 0 I~ 0 I~ a I~ 0 I~ a 1~
FREQUENCY (Hz) 0 -
-4 -ii: : m
a = !. -
(a)
0 : ==r= I I
(c)
-N -<D 0
=i= I l
(d)
~~~~~. 0 125 a !LS. 0 lZS a IZS 0
FREQUENCY (Hz)
io~t m -a • -
- I 8 -
~ : ( (f)
-8
-"' -<D 0
(g)
-g
-"' -<D 0
= --i !
(h)
0 0
-
-"' -<D 0
_j=
(I)
-N -<D 0
CJ)
Figure 19. Tuning of reflections from two dipoles of opposite polarity: effect of changing bed thickness for constant dipole separation of 6 ms. (a) Source wavelet amplitude spectrum, reflection, and ref lecti vi ty series; ( b) - ( j) amplitude spectrum, reflection, and re-flection coefficient of model; bed thickness is 2 ms in (b) and is incremented by 2 ms per figure.
Thin Bed Theoretical Models 38
from either increasing dipole separation or increasing bed
thickness have approximately the same well-formed Klauder
waveform reflection for beds less than tuning thickness. The
two-dipole model with dipoles of opposite polarity and dipole
separation of 2 ms is chosen to develop a multiple thin bed
model.
The time series summation of the reflectivity function
for a sequence of thin and thick beds may be found from its
reflectivity expression. Consider an 8 dipole reflectivity
series with 4 dipoles of opposite polarity in the repeating
unit (Figure 20). This 8 dipole reflectivity expansion (16
reflection coefficients) reduces to 7 reflection coefficients
when the separation between dipoles goes to zero
(Figure 20). A thin bed model with 8 thin beds of uniform
thickness has the same time series representation as a a
simplified thin bed model with 6 beds of varying thicknesses.
To a first approximation, the simplified multiple thin
bed model (Figure 20) with dipole separation of zero may be
written as the summation of four series:
<.o I'\ r(t)=!(-1) [(-6(t-4nt)+26(t-(4n+l)t) -26(t-(4n+3)t) ,, "'(;)
+6(t-(4n+4)t)]
where t is the two-way travel time through the bed (dipole
thickness).
Thin Bed Theoretical Models 39
TIME (me) ·
-0.12 -o 8 0 .12 10
2 - ·10 0.24 8 2
-20 20
- 30 -0.24
10 -40
-50
-so
-10
-so
-90
(al (b)
Figure 20. Thin bed models: (a) Multiple thin bed model;(b) Simplified thin bed model with six beds.
Thin Bed Theoretical Models 40
A term by term expansion of this series gives:
r(t)=(-1) 0 [o(t)+26(t-t)-26(t-3t) +6(t-4t)]
+(-1) 1 [-6(t-4t)+26(t-5t)-26(t-7t) +6(t-8t)]
+(-1) 2 [-o(t-81)+2o(t-91) -2o(t-111)+o(t-121)J
+(-1) 3 [-o(t-121) +2o(t-13t)-2o(t-15•)+o(t-16t)J
+ . . .
which is the reflectivity expression for the multiple thin
bed model. Because the thin bed model and the simplified
thin bed model have the same time series expression, they are
convolutionally equivalent.
The series simulating beds of tuning thickness may be
generalized for any wavelet as:
~ n r(t)=E(-1) [(-6((t-4nt)+26(t-((T/2)n+l)•)
n~
-2o(t-((T/2)n+3)t)+o(t-((T/2)n+4)t)]
where T is the dominant period of the wavelet.
Reflections corresponding to the series expansions for
the terms n=O through n=2 for beds 8 ms thick and 2 ms apart,
Figure 21, result from constructive interference of re-
flections from two or more thin beds. This can be seen more
clearly by comparison of the multiple thin bed model with its
convolutional equivalent, the simplified thin bed model,
Thin Bed Theoretical Models 41
I~ ... L 0 12S 125 O IZS: FREQUENCY (Hz)
·-4 -I: -m i -!. -
-8 - -8 - 8 - - - -- 8 - 8 - 8 -
I 0 -
T 0 - -..__ 0 - r= 0 - == 0 - --- - - --, - I - - __,_ - =:/--
I - - -- - -I
i I =r= I - - - == I i I - I
I I
- I N - N -ill <D
(a) 0 (b)
I I I I ! ! i -
N - - I N
- i ~
- - N - -<D <D <D
(c) 0 (d) 0 (e) 0 (f)
Figure 21. Multiple thin bed model: (a) Source wavelet amplitude spectrum, reflection, and reflectivity for a single interface; (b) am-plitude spectrum, reflection, and reflection coefficients of thin bed model-reflection approximates first derivative waveform; ( c) four dipole model - approximation to 3-point model; (d) series expansion for n=O term; (e) n=l; (f) n=2.
Thin Bed Theoretical Models 42
~~ l .. L 0 l~ 0 I~ 125 0 I.ZS FREQUENCY (Hz)
0 - 0 - 0 -
-t -i m -i !. -
0 -
I JT JT Jr JI :T a> m en ~ m
(a) 0 (b) 0 (c) 0 (d) (e) 0 (f) N -
~
Figure 22. Simplified thin bed model: Convolutional equivalent of multiple thin bed model. (a) source wavelet amplitude spectrum, re-flection, and reflectivity for a single interface; (b) amplitude spectrum, re-flection and reflection coefficients of thin bed; (c) three-point model arrived at by re-ducing dipole separation of four-dipole model in multiple thin bed model; (d) n=O term - tuning of two thin bed reflections; (e) n=l term; (f) n=2 term.
Thin Bed Theoretical Models 43
.~~~lfL1.~ ~REQUENCY l~z) a '"" a '"" a '"" o 125
-4 -i -!!! . -3 -!. :
0 0
-0 0
- -8
" I :IT :1 T : T : T 00 ~ ID 00 00
o (a) (b) a (c) o (d) o (e)
Figure 23. Multiple thin bed model for t~T/2: beds at tuning thickness result in very large ampli-tude reflections. (a) Source wavelet ampli-tude spectrum, reflection, and reflectivity series; (b) tuned first derivative waveform; ( c) tuned 3-point model approximation; ( d) n=O term; (e) n=l term. Note that individual reflections in ( d) and ( e) are resolvable into first derivative waveforms from thin beds and Klauder waveform from 3-point model approximation.
Thin Bed Theoretical Models 44
Figure 22. From the simplified thin bed model, Figure 22(d),
we see that the four-dipole model in Figure 2l(d) approxi-
mates two dipoles of the same polarity 20 ms apart. The re-
flections from the two beds constructively interfere to give
a large amplitude reflection with first derivative charac-
teristics (e.g. Figure 16(k)). A two-dipole series approxi-
mates a 3-point reflectivity series which results in a
reflection with a Klauder waveform, Figure 21 ( c) . As more
thin beds are added to the time series, the reflections take
on a reverberating character.
First derivative and Klauder waveforms are distinguish-
able in models for the n=O through n=2 terms of the series
expression of the multiple thin bed model, Figure 22. For
beds of tuning thickness in the multiple thin bed model, the
individual thin bed reflections are resolvable (Figure 23).
Constructive inter£ erence of multiple thin bed reflections
results in large amplitude reflections.
As the spike separation in a dipole decreases, convo-
lution of the wavelet with the dipole results in differen-
tiation of the wavelet and and a shift in the amplitude
spectrum toward high frequencies. Peaks in the amplitude
spectra of the thin bed model reflections occur at f requen-
cies which correspond to the periodicities of the dipoles
used in the models. Dipole periodicity is 1/t where t is the
two-way time thickness (Marangakis and others, 1985). Side
lobes in the amplitude spectra result from complex frequency
Thin Bed Theoretical Models 45
domain addition of amplitude spectra of reflectivity func-
tions. The number of side lobes increases as thin beds are
added to the time series, Figure 21 and Figure 22. Addition
of the complex amplitude spectra of reflectivity functions
of the multiple thin bed model results in amplitude spectra
similar to spectra of reverberations in that they are tuned
at a specific frequency.
RESULTS
Computer modeling of thin beds shows that reflections
from a thin bed slightly less than tuning thickness
Figure 15, approximates the first derivative of the wavelet.
However, these thin bed reflections themselves may construc-
tively interfere to form "tuned'' first derivative reflections
which are larger in amplitude than either the incident
wavelet or the reflection from a single tuned thin bed ,Fig-
ure 13 and Figure 15(c). Modeling of multiple thin beds is
extended to the Catoctin Formation using the reflection co-
efficients determined in this study and stratigraphic infor-
mation supplied by R. Badger (Figure 5).
Exact thin bed models of Catoctin reflectivity are con-
structed based on the stratigraphy of the geologic sections
of R. Badger (pers. comm., 1985), Figure 24 and Figure 29,
and from reflection coefficients determined in this study.
Variations on these models are constructed to illustrate re-
Thin Bed Theoretical Models 46
f lection character of other possible thin bed models for the
Catoctin Formation. Homogeneous layers of the samples chosen
are assumed. Lateral and vertical velocity variations pres-
ent in outcrop and in the subsurface are not represented in
these models.
The beds in the stratigraphic sections shown in
Figure 24 and Figure 29 are acoustically thin beds. For a
dominant frequency of 38 Hz and a compressional velocity of
6000 m/s, the dominant wavelength is approximately 157 m.
The Catoctin model beds are less than 30 m thick or less than
X/4 thick, so they are acoustically thin beds.
The reflection from the exact time model of section A,
Figure 24, is a small amplitude reflection. Individual thin
bed reflections have destructively interfered in this model.
Reflections from models based on variations of section A with
layers removed and replaced, Figure 25, Figure 26,
Figure 27, and Figure 28, are generally smaller amplitude
than the source wavelet also. However, the reflection from
the model in Figure 28 is a well-formed Klauder wavelet of
amplitude slightly less than the source wavelet. Construe-
tive interference of thin bed reflections from this model has
resulted in a waveform similar to the waveform of reflections
from within the Catoctin Formation on seismic profile NSF-2.
The reflection from the exact outcrop model of section
B is a large amplitude reflection with a slighl ty ringy or
reverberating appearance, Figure 29. Variations on section
Thin Bed Theoretical Models 47
OEPTH (m)
o-------- JB5-10C 6010 mis
60
JB4-3C 5710 mis JB4-30 5969 mis JB4-3B 5126mla JB4-30 5969 mis JB4-3B 5128 mis
-"1:.::::::::z::C:::::~ JB5-10C 6010 mis . JB4-3B 5128 mla
JB5-10C 6450 mis
JB5-100 6212 mla
JB5-10C 601<lml1
JB4-3B 5128 mis JB5-10C 6010 mis JB4-38 5128 mis JB4-30 6281 mis JB5'-100 6212 mis
JB5-10C 6010 mis
(a)
-o cC, -,___.~ c15 -0.0'1 0-0'i - 5
-o.O'l o.o'-J -o o'1 0.08
-0-0'1
(b)
-10
-15 o.os
-20
0 -
"" -0 0
0 -
... -.. 0
-=== I '
Figure 24. Catoctin thin bed model constructed from section A: (a) Original depth model; (b) corresponding time series ;(c) amplitude spectrum, reflection, and ref lee ti vi ty se-ries.
Thin Bed Theoretical Models 48
~' 0 IZB
DEPTH (m)
0
50
(a)
JB4-30 5969 mis
JB5-1or. 6212mls
JB4-4G 5924 mis
JB4-3C 5710mls
J84-40 6369 mis
-o.o:; -o.
(b)
·nflo\e(ms) -0
o.o'f -')
r~o o.o
-15
-w
0 -
.. -0 0
0 -
N -.. 0
?
-<=--I I
!
(c)
Figure 25. Section A without beds <l ms and with beds replaced: (a) depth model of A without beds <l ms thick; JBS-lOC and JBS-lOD of Figure 24 replaced by JB4-4G and JB4-3C; (b) corresponding ref lecti vi ty series; ( c) am-plitude spectrum, reflection, and reflectivity series.
Thin Bed Theoretical Models 49
DEPTH (m) 0 ______ .,
40
J84-30 5969 mis
JB5-100 6212 mis
JB4-3C 5710 mis
J84-40 6389 mis
-o.o~
(b)
,~. 0 1~
-o 0 -
o.o'i -5 o.o~
-10
... -8
0 -
N -... 0
(c)
Figure 26. Section A - previous figure without layer JB4-4G: (a) same depth model as Figure 25 without JB4-4G; (b) corresponding reflectivity series; (c) amplitude spectrum, reflection, and reflectivity series.
Thin Bed Theoretical Models 50
DEPTH (m)
JB4-30 5969 mis
JB5-10f"I 6212 mis
J64-3C 5710 m/a
-o.o~
JB5-10C 6010 mis
-o.o'-l JBS-100 6212 mis
-104-30 5969 mis
(a) t'l>J
I\ t-\i;: (Y't"'-J
-o
o.a-1 -~ Q.0'.:
- IO
-1? .o.o··
-'lD
~C~-r-r .. 0
0 -
.. -0 0
0 -
N -,,. 0
12S
1 )
--=-
(c)
Figure 27. Section A - previous figure with layers re-peated and replaced: (a) Same depth model as Figure 26 with JB4-4D replaced by JBS-lOC and with layers JB4-3D and JBS-lOD repeated; (b) corresponding time series; (c) amplitude spectrum, reflection, and reflectivity se-ries.
Thin Bed Theoretical Models 51
DEPTH (m) o-r-----.. JB4-30
rL ii Mt~
I ' I t t 1 t I I 1r;'";\.I
0 ti;
10 5969 m/s
JBS-100 20 6212 mis -o.o9
JB4-3C 5710 m/a
-0 0 -
1 o.o'i -5 0.0) I
-10 30
JB5-10C -o.os - 15 6010 mis
40 .. -0 0
..-...... JB4-JC 5710 m/e
(_~)
0 - -(b) -,
I "' - I .. 0
(<!)
Figure 28. Section A - previous figure with layers re-peated: (a) Sarne depth model as Figure 27 with layer JB4-3C repeated instead of layers JB4-3D and JBS-lOD repeated; (b) correspond-ing time series; (c) amplitude spectrum, re-flection, and reflectivity series.
Thin Bed Theoretical Models 52
DEPTH (m)
0
70
(a)
Figure 29.
JBS-SF
I''hrn S680 mis
JB4-4A 6238 mis TlME:l'.w.s) 0
_o 0 -
JBs-1oc t 6010 mla 0.10 _s -o Oi
JBS-11A o.os- lo I 6TS9mls
I -0.11 JBS-SF o.o? - IS
I -20 ,. -JBS-SO o.o~ 0
5979 mis -o.o8 0
-2~ 0 - ---=-I
JBS-SF 5680 mis
(b) "' -,. 0
Le)
Catoctin thin bed model constructed from section B: (a) Original depth model; (b) corresponding time series; (c) amplitude spectrum, reflection, and ref lecti vi ty se-ries.
126
Thin Bed Theoretical Models 53
DEPTH (m) 0
Figure 30.
(a)
JB4-30 5969 mis
JBS-11A 6159m/s
JBS-SO 5979 mis
-o.ob
-o o5
{b)
0 -
o.o"!_?
-10
-.&. -
8
0 -
( c.}
Section B - layers replaced and removed: (a) Sarne depth model as Figure 29 with layer JBS-lOC replaced by JBS-30, JBS-SF and JBS-lOD removed ( b) corresponding time se-ries; (c) amplitude spectrum, reflection, and reflectivity series.
Thin Bed Theoretical Models S4
DEPTH (m)
0
JB4-4A 6238 mis
JBS-10C 6010 mis
JBS-SF S680 mis
JBS-SO S979 mis
-0
5
D.05'"- lO
o.o:i - l5
fl I I I I I I I I I f I I 0 12!0
0 -
-~
.. -0 c
0 -
JBS-10() ___ _.... .............. _. //l.i l.; m/ s T
Figure 31.
(~) (ti)
N -.. 0
I I
(C)
Section B two layers removed: (a) Same depth model as Figure 29 with JBS-llA removed and JBS-lOD removed (b) corresponding time series; ( c) amplitude spectrum, reflection, and reflectivity series.
Thin Bed Theoretical Models 55
B arrived at by replacing, removing, or repeating layers in
section B result in reflections with a variety of waveforms,
Figure 30 and Figure 31.
Figure 31 is a large
derivative appearance.
The reflection from the model in
amplitude reflection with a first-
This first derivative waveform could
be interpreted as a single thin bed when, in fact, the re-
flection represents several beds.
Models based on the Catoctin outcrop information illus-
trate that constructive interference of reflections from
multiple thin beds results in large amplitude composite re-
flections. These composite reflections are characterized by
first derivative waveforms, Klauder-type waveforms, or ring-
ing signatures.
Thin Bed Theoretical Models 56
CONCLUSIONS
Reflections from within the Catoctin Formation of cen-
tral Virginia are due to constructive interference of re-
flections from acoustically thin, epidotized metabasalts and
metasediments inter layered with non-epidotized metabasal ts
and metasediments. Interbedded thin layers of rift volcanics
and rift sediments also provide acoustic impedance contrasts
from which reflections may originate. Individual thin bed
reflections constructively interfere to form large amplitude,
reverberating reflections similar to those seen on seimsic
reflection data in central Virginia.
Conclusions 57
REFERENCES
Backus, M. M., 1959, Water Reverberations-Their Nature and Elimination, Geophysics, Vol.24, February, p. 233.
Bally, A. W., 1981, Atlantic-Type Continental Margins in Geology of Passive Continental Margins, AAPG Education Course Note Series #19.
Birch, Francis, 1961, The Velocity of Compressional Waves in Rocks to 10 Kilobars, Part 2, Journal of Geophysical Re-search, Vol. 66, No. 7, p. 2199-2224.
Brun, J. P. and P. Choukroune, 1983, Normal Faulting, Block Tilting, and Decollement in a Stretched Crust, Tectonics, V. 2, No. 4, p. 345-356, August.
Christensen, N. I., 1965, Compressional Wave Velocities in Rocks at Pressures to 10 Kilobars, Journal of Geophysical Research, Vol. 70, p. 6147.
Coruh, C., Costain, J. K., Glover, Lynn III, Pratt, T. L., 1985, Sei smici ty and Seismic Reflection, Gravity, and Geology of Central Virginia Seismic Zone, Part 2, Re-flection Seismology.
Dobrin, Milton B., 1976, Introduction to Geophysical Pros-pecting, Third Edition, McGraw-Hill, New York.
Gathright, T. M., II, 1976, Geology of the Shenandoah Na-tional Park, Virginia: Virginia Division of Mineral Re-sources Bulletin 86, 93 p.
Kallweit, R. S. and L. C. Wood, 1982, The limits of resol-ution of zero-phase wavelets, Geophysics, Vol. 47, No. 7, p. 1035-1046.
Kolich, 1974, Master's Thesis, Virginia Polytechnic Institute and State University.
Marangakis, A. , Costain. J. K., and Coruh, C., 1985, Use of integrated energy spectra for thin-layer recognition, Short note, Geophysics, Vol. 50, No. 3, p. 495-500.
Mendenhall, C. E., Eve, A. S., Keys, D. A., and R. M. Sutton, 1950, College Physics, Third Edi ti on, D. C. Heath and Company, Boston.
References 58
Sengbush, R. L., Lawrence, P. L., and McDonal, F. J., 1961, Interpretation of Synthetic Seismograms, Geophysics, Vol. 26, No. 2, p. 138-157.
Sheriff, Robert E., 1973, Encyclopedic Dictionary of Explo-ration Geophysics, Society of Exploration Geophysicists, Tulsa, Oklahoma.
Uhrig, L. F., and F. A. Melle, 1955, Velocity Anisotropy in a Stratified Media, Geophysics, Vol. 20, No. 4, pp. 774-779.
Waters, Kenneth H., 1981, Reflection Seismology, A Tool For Energy Resource Exploration, John Wiley & Sons, New York.
Wehr, Frederick and Lynn Glover, III, 1985, Stratigraphy and tectonics of the Virginia-North Carolina Blue Ridge:Evolution of a late Proterozoic-early Paleozoic hinge zone, Geological Society of America Bulletin, v. 96, p. 285-295, March.
Widess, M. B., How thin is a Thin Bed?, Geophysics, Vol. 38, No. 6 (December 1973), p. 1176-1180.
References 59
APPENDIX A. CALIBRATION CURVES
Calibration curves used to determine the correction for
transit time through the steel and the electronics at pres-
sures of 200, 400, and 600 atmospheres are shown in
Figure 32, Figure 33, and Figure 34 respectively.
60
47 46
0 45 ~ 44 ~ 43 w ~ 42 t-u:: 4 1 > ~ 40 t-
39 38
6.0 7.0 8.0 9.0 10.0 CYLINDER HEIGHT, CM
Figure 32. Steel calibration curve for 200 atm
I I . 0
61
47 46 45
0 w 44 en ~ 43 .. . w :e 42 -I-.J 41 w > 40 < a: I- 39 e
38 6.0 7.0 8.0 9.0 10.0 11 . 0
CYLINDER HEIGHT, CM
Figure 33. Steel calibration curve for 400 atm
62
·47
46 0 45 w 0 44 ~ u.i 43 ! 42 .... w 41 > ~ 40 1-
39 38
6.0 •
7.0 8.0 9.0 10.0 CYLINDER HEIGHT, CM
Figure 34. Steel calibration curve for 600 atrn
11 . 0
63
APPENDIX B. REFLECTION COEFFICIENTS
64
Table 3 (Part 1 of 30). Catoctin Fe~lection Coefficients(600atm)
I
TOP LAYER Description
3B __L S1 Phyllite 38%0p,26%Chl,22%Q, 9%Ep,4%Sph,2%Cc (Phyllite)
BOTTOM LAYER Description R.C.
JB4-3C Meta sandstone -0.01 45%Ep, 45%Q+F,10%0p (Epidosite)
JB4-3D J_ S1 Schist 0.04 47%Ep,28%Chl, 14%Q,6%Cc,5%0p (Greenstone)
JB4-3D 11 s1 Schist 0.08 47%Ep,28%Chl, 14%Q,6%Cc,5%0p (Greenstone)
JB4-4A Metabasalt 0.12 50%Ep,17%Chl,17%Q+F 8%Cc,8%0p (Epidosite)
JB4-4D _L S1 Schist 0.03 38%Chl,19%0p,18%Ep, 14%Q+F,6%Sph,5%Cc (Greenstone)
S1 REFERS TO MAJOR FOLIATION
II S1 =PROPAGATION II TO MAJOR FOLIATION
l_s 1=PROPAGATION _LTO MAJOR FOLIATION
65
Table 3 (Part 2 of 30). Catoctin Reflection Coefficients(600atm)
JB4-4D II S1 Schist 0.09 38%Chl,19%0p,18%Ep, 14%Q+F,6%Sph,5%Cc (Greenstone)
JB4-4G J_ S1 Schist o.os 4S%Chl,26%Sph, 21%Ep,4%Q+F,4%Act (Greenstone)
JB4-4G II S1 Schist 0.09 4S%Chl,26%Sph, 21%Ep,4%Q+F,4%Act (Greenstone)
JBS-SD Metabasalt 0.06 38%Ep,29%Q+F,23%0p, 10%Cc (Volcanic Breccia)
JBS-SF _L S1 Schist 43%Chl, 0.01 17%Q+F,15%Sph, 14%0p,6%Ep,S%Cc (Greenstone)
JBS-lOC _J_ S1 Schist 0.04 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)
JBS-lOC II S1 Schist 0.08 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)
S1 REFERS TO MAJOR FOLIATION
II S1 =PROPAGATION II TO MAJOR FOLIATION
_L_ S1 =PROPAGATION J_ TO MAJOR FOLIATION
66
Table 3 (Part 3 of 30). Catoctin Reflection Coefficients(600atm)
JBS-lOD _l_ S 1 Phyllite 0.05 45%Ep,34%0p,15%Q+F, 6%Cc (Volcanic Breccia)
JBS-lOD II S1 Phyllite 0.08 45%Ep,34%0p,15%Q+F, 6%Cc (Volcanic Breccia)
JBS-llA Amygdaloidal 0.11 metabasalt 42%Ep,32%0p,26%Q+F (Epidosite)
JB5-12A Amygdaloidal 0.09 metabasalt 45%0p,35%Q,20%Ep (Epidosite)
S1 REFERS TO MAJOR FOLIATION
~S 1 =PROPAGATION ~ TO MAJOR FOLIATION
_L_ S1 =PROPAGATION _L TO MAJOR FOLIATION
67
Table 3 (Part 4 of 30). Catoctin Reflection Coefficients(600atm)
TOP LAYER Description
JB4-3C Meta sandstone 45%Ep, 45%Q+F,10%0p (Epidosite)
BOTTOM LAYER Description R.C.
JB4-3D _l_ S 1 Schist 0.05 47%Ep,28%Chl,14%Q, 6%Cc,5%0p (Greenstone)
JB4-3D II S1 Schist 0.08 47%Ep,28%Chl,14%Q, 6%Cc,5%0p (Greenstone)
JB4-4A Metabasalt 0.12 50%Ep I l 7%Chl I 17%Q+F,8%Cc,8%0p (Epidosite)
JB4-4D _J_ S1 Schist 0.04 38%Chl,19%0p,18%Ep, 14%Q+F,6%Sph,5%Cc (Greenstone)
JB4-4D II S1 Schist 0.09 38%Chl,19%0p,18%Ep, 14%Q+F,6%Sph,5%Cc (Greenstone)
S1 REFERS TO MAJOR FOLIATION
II S1 =PROPAGATION II TO MAJOR FOLIATION
J_ S1 =PROPAGATION l_ TO MAJOR FOLIATION
68
Table 3 (Part S of 30). Catoctin Reflection Coefficients(600atm)
JB4-4G -~ S1 Schist o.os 4S%Chl,26%Sph, 21%Ep,4%Q+F,4%Act (Greenstone)
JB4-4G II S1 Schist 0.10 4S%Chl,26%Sph, 21%Ep,4%Q+F,4%Act (Greenstone)
JBS-SD Metabasalt 0.06 38%Ep,29%Q+F, 23%0p,10%Cc (Volcanic Breccia)
JBS-SF _I S1 Schist 43%Chl I 0.01 17%Q+F,1S%Sph, 14%0p,6%Ep,S%Cc (Greenstone)
JBS-lOC J_ Si Schist o.os 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)
JBS-lOC II S1 Schist 0.08 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)
JBS-lOD _J __ S1 Phyllite o.os 4S%Ep,34%0p,1S%Q+F, 6%Cc (Volcanic Breccia)
S1 REFERS TO MAJOR FOLIATION
II S1 =PROPAGATION II TO MAJOR FOLIATION
.J_S 1=PROPAGATION _l_TO MAJOR FOLIATION
69
Table 3 (Part 6 of 30). Catoctin Reflection Coefficients(600atrn)
JBS-lOD II S1 Phyllite 0.09 45%Ep,34%0p,15%Q+F, 6%Cc (Volcanic Breccia)
JBS-llA Arnygdaloidal 0.12 rnetabasalt 42%Ep,32%0p,26%Q+F (Epidosite)
JBS-12A Arnygdaloidal 0.10 rnetabasalt 45%0p,35%Q,20%Ep (Epidosite)
S1 REFERS TO MAJOR FOLIATION
II S1 =PROPAGATION II TO MAJOR FOLIATION I ' ..LS 1 =PROPAGATION ...L TO MAJOR FOLIATION
70
Table 3 (Part 7 of 30). Catoctin Reflection Coefficients(600atm)
TOP LAYER Description I JB4-3D _1_ S1 Schist
47%Ep,28%Chl,14%Q, 6%Cc,5%0p (Greenstone)
BOTTOM LAYER Description R.C.
JB4-3D II s1 Schist 0.03 47%Ep,28%Chl,14%Q, 6%Cc,5%0p (Greenstone)
JB4-4A Metabasalt 0.07 50%Ep I l 7%Chl I
17%Q+F,8%Cc,8%0p (Epidosite)
JB4-4D J_ S1 Schist -0.01 38%Chl,19%0p,18%Ep, 14%Q+F,6%Sph,5%Cc (Greenstone)
JB4-4D 11 s1 Schist 0.05 38%Chl,19%0p,18%Ep, 14%Q+F,6%Sph,5%Cc (Greenstone)
I JB4-4G _L S1 Schist 0.01 45%Chl,26%Sph, 21%Ep,4%Q+F,4%Act (Greenstone)
S1 REFERS TO MAJOR FOLIATION
II S1 =PROPAGATION II TO MAJOR FOLIATION
.l_S 1=PROPAGATION j_ TO MAJOR FOLIATION
71
Table 3 (Part 8 of 30). Catoctin Reflection Coefficients(600atm)
JB4-4G II S1 Schist o.os 4S%Chl,26%Sph, 21%Ep,4%Q+F,4%Act (Greenstone)
JBS-SD Metabasalt 0.01 38%Ep,29%Q+F,23%0p, 10%Cc (Volcanic Breccia)
JBS-SF J_ S1 Schist 43%Chl, -0.04 17%Q+F,1S%Sph, 14%0p,6%Ep,S%Cc (Greenstone)
JBS-lOC j_ S1 Schist 0.00 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)
JBS-lOC II S1 Schist 0.04 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)
JBS-lOD J_ S1 Phyllite 0.00 4S%Ep,34%0p,1S%Q+F, 6%Cc (Volcanic Breccia)
JBS-lOD II S1 Phyllite 0.04 4S%Ep,34%0p,1S%Q+F, 6%Cc (Volcanic Breccia)
S1 REFERS TO MAJOR FOLIATION
II S1 =PROPAGATION II TO MAJOR FOLIATION
J_ S1 =PROPAGATION j_ TO MAJOR FOLIATION
72
Table 3 (Part 9 of 30). Catoctin Reflection Coefficients(600atrn)
JBS-llA Arnygdaloidal 0.07 rnetabasalt 42%Ep,32%0p,26%Q+F (Epidosite)
JB5-12A Arnygdaloidal 0.05 rnetabasalt 45%0p,35%Q,20%Ep (Epidosite)
S1 REFERS TO MAJOR FOLIATION
II S1 =PROPAGATION II TO MAJOR FOLIATION
J_ S 1 =PROPAGATION j_ TO MAJOR FOLIATION
73
Table 3 (Part 10 of 30). Catoctin Reflection Coefficients(600atrn)
TOP LAYER Description
JB4-3D II S1 Me ta sandstone 45%Ep, 45%Q+F,10%0p (Epidosite)
BOTTOM LAYER Description R.C.
JB4-4A Metabasalt 0.04 50%Ep I 17%Chl I 17%Q+F,8%Cc,8%0p (Epidosite)
JB4-4D _l_ S1 Schist -0.04 38%Chl,19%0p,18%Ep, 14%Q+F,6%Sph,5%Cc (Greenstone)
JB4-4D II S1 Schist 0.01 38%Chl,19%0p,18%Ep, 14%Q+F,6%Sph,5%Cc (Greenstone)
. JB4-4G -L S 1 Schist -0.03
45%Chl,26%Sph, 21%Ep,4%Q+F,4%Act (Greenstone)
JB4-4G II S1 Schist 0.02 45%Chl,26%Sph, 21%Ep,4%Q+F,4%Act (Greenstone)
S1 REFERS TO MAJOR FOLIATION
l!S 1=PROPAGATION II TO MAJOR FOLIATION
_l_ S1 =PROPAGATION J_ TO MAJOR FOLIATION
74
Table 3 (Part 11 of 30). Catoctin Reflection Coefficients(600atm)
JBS-SD Metabasalt -0.02 38%Ep,29%Q+F,23%0p, 10%Cc (Volcanic Breccia)
JBS-SF J_ S1 Schist 43%Chl, -0.07 17%Q+F,1S%Sph, 14%0p,6%Ep,5%Cc (Greenstone)
JBS-lOC _L S1 Schist -0.04 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)
JBS-lOC 11 s1 Schist 0.00 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)
JBS-lOD J_ S1 Phyllite -0.03 45%Ep,34%0p, 1S%Q+F,6%Cc (Volcanic Breccia)
JBS-lOD II S1 Phyllite 0.01 45%Ep,34%0p, 1S%Q+F,6%Cc (Volcanic Breccia)
JBS-llA Amygdaloidal 0.04 metabasalt 42%Ep,32%0p,26%Q+F (Epidosite)
S1 REFERS TO MAJOR FOLIATION
II S1 =PROPAGATION II TO MAJOR FOLIATION
.L S 1 =PROPAGATION J_ TO MAJOR FOLIATION
75
Table 3 (Part 12 of 30). Catoctin Reflection Coefficients(600atrn)
JB5-12A Arnygdaloidal 0.02 rnetabasalt 45%0p,35%Q,20%Ep (Epidosite)
S1 REFERS TO MAJOR FOLIATION
II S1 =PROPAGATION II TO MAJOR FOLIATION
J_ S1 =PROPAGATION J_ TO MAJOR FOLIATION
76
Table 3 (Part 13 of 30). Catoctin Reflection Coefficients(600atrn)
TOP LAYER Description
JB4-4A Metabasalt SO%Ep, 17%Chl,17%Q+F, 8%Cc,8%0p (Epidosite)
BOTTOM LAYER Description R.C.
JB4-4D _;_ S 1 Schist -0.08 38%Chl,19%0p,18%Ep, 14%Q+F,6%Sph,S%Cc (Greenstone)
JB4-4D 11 s1 Schist -0.03 38%Chl,19%0p,18%Ep, 14%Q+F,6%Sph,S%Cc (Greenstone)
JB4-4G J_s1 Schist -0.07 4S%Chl,26%Sph, 21%Ep,4%Q+F,4%Act (Greenstone)
JB4-4G II S1 Schist -0.02 45%Chl,26%Sph, 21%Ep,4%Q+F,4%Act (Greenstone)
JBS-SD Metabasalt -0.06 38%Ep,29%Q+F,23%0p, 10%Cc (Volcanic Breccia)
S1 REFERS TO MAJOR FOLIATION
II s 1 =PROPAGATION II TO MAJOR FOLIATION
_L S1 =PROPAGATION J_ TO MAJOR FOLIATION
77
Table 3 (Part 14 of 30). Catoctin Reflection Coefficients(600atm)
JBS-SF~ S1 Schist 43%Chl, -0.11 17%Q+F,1S%Sph, 14%0p,6%Ep,5%Cc (Greenstone)
JBS-lOC J.. S1 Schist -0.08 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)
JBS-lOC II S1 Schist -0.04 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)
JBS-100 J_ S1 Phyllite -0.07 4S%Ep,34%0p, 1S%Q+F,6%Cc (Volcanic Breccia)
JBS-100 i1S1 Phyllite -0.03 4S%Ep,34%0p, 1S%Q+F,6%Cc (Volcanic Breccia)
JBS-llA Amygdaloidal 0.00 metabasalt 42%Ep,32%0p,26%Q+F (Epidosite)
JBS-12A Amygdaloidal -0.02 metabasalt 4S%0p,35%Q,20%Ep (Epidosite)
S1 REFERS TO MAJOR FOLIATION
ijS 1=PROPAGATION ij TO MAJOR FOLIATION
J_S 1 =PROPAGATION _J_To MAJOR FOLIATION
78
Table 3 (Part lS of 30). Catoctin Reflection Coefficients(600atrn)
TOP LAYER Description
JB4-4D _l S1 Schist 38%Chl,19%0p,18%Ep, 14%Q+F,6%Sph,S%Cc (Greenstone)
BOTTOM LAYER Description R.C.
JB4-4D II S1 Schist 0.06 38%Chl,19%0p,18%Ep, 14%Q+F,6%Sph,S%Cc (Greenstone)
JB4-4G l_ S1 Schist 0.02 4S%Chl,26%Sph, 21%Ep,4%Q+F,47.,Act (Greenstone)
JB4-4G II S1 Schist 0.06 4S%Chl,26%Sph, 21%Ep,4%Q+F,4%Act (Greenstone)
JBS-SD Metabasalt 0.03 38%Ep,29%Q+F,23%0p, 10%Cc (Volcanic Breccia)
JBS-SF J_ S1 Schist 43%Chl, -0.02 17%Q+F,1S%Sph, 14%0p,6%Ep,5%Cc (Greenstone)
S1 REFERS TO MAJOR FOLIATION
II S1 =PROPAGATION II TO MAJOR FOLIATION
J_ S1 =PROPAGATION _l_ TO MAJOR FOLIATION
79
Table 3 (Part 16 of 30). Catoctin Reflection Coefficients(600atrn)
JBS-lOC J_ S1 Schist 0.01 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)
JBS-lOC II S1 Schist 0.05 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)
JBS-lOD J_ S1 Phyllite 0.01 45%Ep,34%0p, 15%Q+F,6%Cc (Volcanic Breccia)
JBS-lOD II S1 Phyllite 0.05 45%Ep,34%0p, 15%Q+F,6%Cc (Volcanic Breccia)
JBS-llA Arnygdaloidal 0.08 rnetabasalt 42%Ep, 32%0p,26%Q+F (Epidosite)
JB5-12A Arnygdaloidal 0.06 rnetabasalt 45%0p,35%Q,20%Ep (Epidosite)
S1 REFERS TO MAJOR FOLIATION
~S 1 =PROPAGATION ~ TO MAJOR FOLIATION
J_ S 1 =PROPAGATION J_ TO MAJOR FOLIATION
80
Table 3 (Part 17 of 30). Catoctin Reflection Coefficients(600atm)
TOP LAYER Description
JB4-4D 11 s1 Schist 38%Chl,19%0p,18%Ep, 14%Q+F,6%Sph,S%Cc (Greenstone)
BOTTOM LAYER Description R.C.
JB4-4G J_ S1 Schist -0.04 4S%Chl,26%Sph, 21%Ep,4%Q+F,4%Act (Greenstone)
JB4-4G 11 s1 Schist 0.01 4S%Chl,26%Sph, 21%Ep,4%Q+F,4%Act (Greenstone)
JBS-SD Metabasalt -0.03 38%Ep,29%Q+F,23%0p, 10%Cc (Volcanic Breccia)
JBS-SF _l_ S1 Schist 43%Chl, -0.08 17%Q+F,1S%Sph, 14%0p,6%Ep,S%Cc (Greenstone)
JBS-lOC J_ S1 Schist -0.0S 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)
S1 REFERS TO MAJOR FOLIATION
II S1 =PROPAGATION II TO MAJOR FOLIATION
_l_ S 1 =PROPAGATION _l_ TO MAJOR FOLIATION
81
Table 3 (Part 18 of 30). Catoctin Reflection Coefficients(600atrn)
JBS-lOC II S1 Schist -0.01 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)
JBS-lOD J_ 81 Phyllite -0.04 45%Ep,34%0p, 15%Q+F,6%Cc (Volcanic Breccia)
JBS-lOD 1181 Phyllite -0.01 45%Ep,34%0p, 15%Q+F,6%Cc (Volcanic Breccia)
JBS-llA Arnygdaloidal 0.03 rnetabasalt 42%Ep,32%0p,26%Q+F (Epidosite)
JBS-12A Arnygdaloidal 0.00 rnetabasalt 45%0p,35%Q,20%Ep (Epidosite)
S1 REFERS TO MAJOR FOLIATION
~81=PROPAGATION ~ TO MAJOR FOLIATION
_L S1 =PROPAGATION _L TO MAJOR FOLIATION
82
Table 3 (Part 19 of 30). Catoctin Reflection Coefficients(600atrn)
TOP LAYER Description
JB4-4G_l_ S1 Schist 4S%Chl,26%Sph, 21%Ep,4%Q+F,4%Act (Greenstone)
BOTTOM LAYER Description R.C.
JB4-4G II S1 Schist 0.04 4S%Chl,26%Sph, 21%Ep,4%Q+F,4%Act (Greenstone)
JBS-SD Metabasalt 0.01 38%Ep,29%Q+F,23%0p, 10%Cc (Volcanic Breccia)
JBS-SF J_ S1 Schist 43%Chl, -0.04 17%Q+F,1S%Sph, 14%0p,6%Ep,S%Cc (Greenstone)
JBS-lOC J_ S1 Schist -0.01 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)
JBS-lOC II S1 Schist 0.03 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)
S1 REFERS TO MAJOR FOLIATION
II S1 =PROPAGATION II TO MAJOR FOLIATION
j_ S1 =PROPAGATION J_ TO MAJOR FOLIATION
83
Table 3 (Part 20 of 30). Catoctin Reflection Coefficients(600atm)
JBS-lOD _j_ S1 Phyllite 0.00 45%Ep,34%0p, 15%Q+F,6%Cc (Volcanic Breccia)
JBS-lOD II S1 Phyllite 0.03 45%Ep,34%0p, 15%Q+F,6%Cc (Volcanic Breccia)
JBS-llA Amygdaloidal 0.07 metabasalt 42%Ep,32%0p,26%Q+F (Epidosite)
JBS-12A Amygdaloidal 0.04 metabasalt 45%0p,35%Q,20%Ep (Epidosite)
S1 REFERS TO MAJOR FOLIATION
II s 1 =PROPAGATION II TO MAJOR FOLIATION
_l_ S1 =PROPAGATION _L TO MAJOR FOLIATION
84
Table 3 (Part 21 of 30). Catoctin Reflection Coefficients(600atm)
TOP LAYER Description
JB4-4G II S1 Schist 4S%Chl,26%Sph, 21%Ep,4%Q+F,4roAct (Greenstone)
BOTTOM LAYER Description R.C.
JBS-SD Metabasalt -0.04 38%Ep,29%Q+F,23%0p, 10%Cc (Volcanic Breccia)
JBS-SF _L S1 Schist 43%Chl I -0.09 17%Q+F,1S%Sph, 14%0p,6%Ep,S%Cc (Greenstone)
JBS-lOC J_ S 1 Schist -0.0S 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)
JBS-lOC II S1 Schist -0.02 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)
JBS-lOD _l S1 Phyllite -0.0S 45%Ep,34%0p, 15%Q+F,6%Cc (Volcanic Breccia)
S1 REFERS TO MAJOR FOLIATION
II s 1 =PROPAGATION II TO MAJOR FOLIATION
_J__ S1 =PROPAGATION _J_ TO MAJOR FOLIATION
8S
Table 3 (Part 22 of 30). Catoctin Reflection Coefficients(600atm)
JBS-lOD II S1 Phyllite -0.01 45%Ep,34%0p, 15%Q+F,6%Cc (Volcanic Breccia)
JBS-llA Amygdaloidal 0.02 metabasalt 42%Ep,32%0p,26%Q+F (Epidosite)
JB5-12A Amygdaloidal 0.00 metabasalt 45%0p,35%Q,20%Ep (Epidosite)
S1 REFERS TO MAJOR FOLIATION
II S1 =PROPAGATION II TO MAJOR FOLIATION
_!_S 1 =PROPAGATION _l TO MAJOR FOLIATION
86
Table 3 (Part 23 of 30). Catoctin Reflection Coefficients(600atm)
TOP LAYER Description
JBS-SD Metabasalt 38%Ep,29%Q+F,23%0p, 10%Cc (Volcanic Breccia)
BOTTOM LAYER Description R.C.
JBS-SF J_ S1 Schist 43%Chl, -0.0S 17%Q+F,1S%Sph, 14%0p,6%Ep,S%Cc (Greenstone)
JBS-lOC J_S1 Schist -0.02 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)
JBS-lOC II S1 Schist 0.02 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)
JBS-lOD _J_ S1 Phyllite -0.01 4S%Ep,34%0p, 1S%Q+F,6%Cc (Volcanic Breccia)
JBS-lOD II S1 Phyllite 0.03 4S%Ep,34%0p, 1S%Q+F,6%Cc (Volcanic Breccia)
S1 REFERS TO MAJOR FOLIATION
II S1 =PROPAGATION II TO MAJOR FOLIATION
J_ S 1 =PROPAGATION _l TO MAJOR FOLIATION
87
Table 3 (Part 24 of 30). Catoctin Reflection Coefficients(600atrn)
JBS-llA Arnygdaloidal 0.06 rnetabasalt 42%Ep,32%0p,26%Q+F (Epidosite)
JB5-12A Arnygdaloidal 0.03 rnetabasalt 45%0p,35%Q,20%Ep (Epidosite)
S1 REFERS TO MAJOR FOLIATION
II s 1 =PROPAGATION II TO MAJOR FOLIATION
_l S1 =PROPAGATION j_ TO MAJOR FOLIATION
88
Table 3 (Part 2S of 30). Catoctin Reflection Coefficients(600atm)
TOP LAYER Description I JBS-SF _,_ S1 Schist 43%Chl I
17%Q+F,1S%Sph, 14%0p,6%Ep,S%Cc (Greenstone)
BOTTOM LAYER Description R.C.
JBS-lOC J_ S1 Schist 0.03 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)
JBS-lOC II S1 Schist 0.07 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)
' JBS-lOD ~· S1 Phyllite 0.04 4S%Ep,34%0p, 1S%Q+F,6%Cc (Volcanic Breccia)
JBS-lOD II S1 Phyllite 0.08 4S%Ep,34%0p, 1S%Q+F,6%Cc (Volcanic Breccia)
JBS-llA Amygdaloidal 0.11 metabasalt 42%Ep,32%0p,26%Q+F (Epidosite)
S1 REFERS TO MAJOR FOLIATION
II s 1 =PROPAGATION II TO MAJOR FOLIATION
J __ S 1 =PROPAGATION J_ TO MAJOR FOLIATION
89
Table 3 (Part 26 of 30). Catoctin Reflection Coefficients(600atrn)
JB5-12A Amygdaloidal 0.08 rnetabasalt 45%0p,35%Q,20%Ep (Epidosite)
S1 REFERS TO MAJOR FOLIATION
~S 1 =PROPAGATION ~ TO MAJOR FOLIATION
__L 5 1 =PROPAGATION _l_To MAJOR FOLIATION
90
Table 3 (Part 27 of 30). Catoctin Reflection Coefficients(600atm)
TOP LAYER Description
JBS-lOC _L S 1 Schist 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)
BOTTOM LAYER Description R.C.
JBS-lOC II S1 Schist 0.04 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)
JBS-lOD _l_ S 1 Phyllite 0.01 45%Ep,34%0p, 15%Q+F,6%Cc (Volcanic Breccia)
JBS-lOD II S1 Phyllite 0.04 45%Ep,34%0p, 15%Q+F,6%Cc (Volcanic Breccia)
JBS-llA Amygdaloidal 0.08 metabasalt 42%Ep,32%0p,26%Q+F (Epidosite)
JB5-12A Amygdaloidal 0.05 metabasalt 45%0p,35%Q,20%Ep (Epidosite)
S1 REFERS TO MAJOR FOLIATION
II S1 =PROPAGATION II TO MAJOR FOLIATION
_J_S 1=PROPAGATION j_ TO MAJOR FOLIATION
91
Table 3 (Part 28 of 30). Catoctin Reflection Coefficients(600atrn)
TOP LAYER Description
JBS-lOC II S1 Schist 40%Chl,22%0p, 21%Q,13%Ep,4%Cc (Greenstone)
BOTTOM LAYER Description R.C.
JBS-lOD J_ S1 Phyllite -0.03 45%Ep,34%0p, 15%Q+F,6%Cc (Volcanic Breccia)
JBS-lOD i1S1 Phyllite 0.01 45%Ep,34%0p, 15%Q+F,6%Cc (Volcanic Breccia)
JBS-llA Arnygdaloidal 0.04 rnetabasalt 42%Ep,32%0p,26%Q+F (Epidosite)
JBS-12A Arnygdaloidal 0.01 rnetabasalt 45%0p,35%Q,20%Ep (Epidosite)
S1 REFERS TO MAJOR FOLIATION
II S1 =PROPAGATION II TO MAJOR FOLIATION
_l_S 1 =PROPAGATION j_ TO MAJOR FOLIATION
92
Table 3 (Part 29 of 30). Catoctin Reflection Coefficients(600atrn)
TOP LAYER Description
JBS-lOD l. S1 Phyllite 45%Ep,34%0p, 15%Q+F,6%Cc (Volcanic Breccia)
BOTTOM LAYER Description R.C.
JBS-lOD II S1 Phyllite 0.04 45%Ep,34%0p, 15%Q+F,6%Cc (Volcanic Breccia)
JBS-llA Arnygdaloidal 0.07 rnetabasalt 42%Ep,32%0p,26%Q+F (Epidosite)
JB5-12A Arnygdaloidal 0.05 rnetabasalt 45%0p,35%Q,20%Ep (Epidosite)
S1 REFERS TO MAJOR FOLIATION
II S1 =PROPAGATION II TO MAJOR FOLIATION
_L S1 =PROPAGATION j_ TO MAJOR FOLIATION
93
Table 3 (Part 30 of 30). Catoctin Reflection Coefficients(600atm)
TOP LAYER Description
JBS-lOD II S1 Phyllite 45%Ep,34%0p, 15%Q+F,6%Cc (Volcanic Breccia)
BOTTOM LAYER Description R.C.
JBS-llA Amygdaloidal 0.03 metabasalt 42%Ep,32%0p,26%Q+F (Epidosite)
JB5-12A Amygdaloidal 0.01 metabasalt 45%0p,35%Q,20%Ep (Epidosite)
S1 REFERS TO MAJOR FOLIATION
~S1=PROPAGATION ~ TO MAJOR FOLIATION
_l_s1=PROPAGATION J_To MAJOR FOLIATION
94
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