COLLUVIAL WEDGE IMAGING USING X-WELL AND CDP TRAVELTIME TOMOGRAPHY

COLLUVIAL WEDGE COLLUVIAL WEDGE IMAGING USING X-WELL IMAGING USING X-WELL AND CDP TRAVELTIME AND CDP TRAVELTIME

TOMOGRAPHYTOMOGRAPHY

MAIKE-L. BUDDENSIEKMAIKE-L. BUDDENSIEK

GERARD T. SCHUSTERGERARD T. SCHUSTER

RONALD L. BRUHNRONALD L. BRUHN

IntroductionIntroduction Seismic SurveySeismic Survey ResultsResults ConclusionConclusion

• INTRODUCTIONINTRODUCTION

• SEISMIC SURVEY SUMMARYSEISMIC SURVEY SUMMARY

• RESULTS AND INTERPRETATIONRESULTS AND INTERPRETATION

• CONCLUSIONCONCLUSION

OUTLINEOUTLINE

(a)(a)Pre - EarthquakePre - Earthquake

(b)(b)

(c)(c)

EarthquakeEarthquake

1000 years later1000 years laterColluvial WedgeColluvial Wedge


COLLUVIAL WEDGESCOLLUVIAL WEDGES

COLLUVIAL WEDGECOLLUVIAL WEDGE

Seismic SurveySeismic SurveyIntroductionIntroduction ResultsResults ConclusionConclusion

COLLUVIAL WEDGECOLLUVIAL WEDGE

Seismic SurveySeismic Survey ResultsResults ConclusionConclusionIntroductionIntroduction

IntroductionIntroduction Seismic SurveySeismic Survey

SLCSLCSLCSLC SLCSLCSLCSLC

LOCATION: MapletonLOCATION: Mapleton

WFZ, Provo SegmentWFZ, Provo SegmentWFZ, Provo SegmentWFZ, Provo Segment

PROVOPROVOPROVOPROVO

PROVOPROVOPROVOPROVO

Wasatch Fault Wasatch Fault Zone, UtahZone, Utah

ResultsResults ConclusionConclusion

GEOLOGYGEOLOGY

SeismicSeismic SurveySurveyIntroductionIntroduction

Footwall SideFootwall SideHanging Wall SideHanging Wall Side

af1

ResultsResults ConclusionConclusion

SeismicSeismic SurveySurvey

Footwall SideFootwall SideHanging Wall SideHanging Wall Side

Line 3Line 3 HiResHiRes

af1

SEISMIC SURVEY ISEISMIC SURVEY I

IntroductionIntroduction ResultsResults ConclusionConclusion

TrenchTrench

Line 2

Line 2

SURVEY SITESURVEY SITE

SeismicSeismic SurveySurveyIntroductionIntroduction ResultsResults ConclusionConclusion

SURVEY SITESURVEY SITE


Low-ResLow-ResLow-ResLow-Res Hi-ResHi-ResHi-ResHi-Res


GIGA TRENCHGIGA TRENCHdone by Sue Olig, URS Corp.done by Sue Olig, URS Corp.

!!! GROUNDTRUTH !!!!!! GROUNDTRUTH !!!

SEISMIC SURVEY IISEISMIC SURVEY II

SeismicSeismic SurveySurvey ResultsResults ConclusionConclusionIntroductionIntroduction

SHOT POSITIONSSHOT POSITIONS

GEOPHONE LINESGEOPHONE LINES

• 2 geophone lines2 geophone lines

• shot line on surfaceshot line on surface

SEISMIC SURVEY IISEISMIC SURVEY II


• 2 geophone lines2 geophone lines

• 2 shot lines2 shot lines

• 1 vertical profile1 vertical profile

• shot line on benchshot line on bench

SHOT POSITIONSSHOT POSITIONS

GEOPHONE LINESGEOPHONE LINES

REFRACTION VS. REFRACTION VS. CROSSWELLCROSSWELL


SURVEY SUMMARYSURVEY SUMMARY

• Line 1: 83.5 m high-res line (E-W)Line 1: 83.5 m high-res line (E-W)• Line 2: 595 m low-res line (N-S)Line 2: 595 m low-res line (N-S)• Line 3: 595 m low-res line (E-W)Line 3: 595 m low-res line (E-W)• Trench results, preliminary borehole resultsTrench results, preliminary borehole results• X-well 1: Geophones @ Suface, shots @ 1st benchX-well 1: Geophones @ Suface, shots @ 1st bench• X-well 2: Geophones @ 1st bench, shots @ surfaceX-well 2: Geophones @ 1st bench, shots @ surface• 1 vertical profile (12 geophones, 4 shots)1 vertical profile (12 geophones, 4 shots)


HIGH-RES LINEHIGH-RES LINE


• 6 faults6 faults• 4 colluvial wedges4 colluvial wedges

WEDGE 1WEDGE 1



WEDGE 2WEDGE 2

WEDGE 3WEDGE 3


WEDGE 4WEDGE 4


HI-RES & TRENCH RESULTSHI-RES & TRENCH RESULTS


• Groundtruth agrees approx. with seismicGroundtruth agrees approx. with seismic• Tomogram can do greater depth than Tomogram can do greater depth than trenching, but wedges are subtle and trenching, but wedges are subtle and faults shifted faults shifted

HI-RES & X-WELLHI-RES & X-WELL


• Faults are imaged well in both tomogramsFaults are imaged well in both tomograms• Overall structure is the same Overall structure is the same • No indication of biggest wedge in X-WellNo indication of biggest wedge in X-Well• Velocities in X-Well smaller than in CDP Velocities in X-Well smaller than in CDP tomography. Opening the trench loosened tomography. Opening the trench loosened material. (half data set, no QC yet)material. (half data set, no QC yet)


MIGRATIONMIGRATION

• Small structures are very sensitive to Small structures are very sensitive to schedules of the inversion.schedules of the inversion.

• Colluvial wedges may be very subtle Colluvial wedges may be very subtle or not resolved.or not resolved.

• Faults are resolved well with X-Well Faults are resolved well with X-Well and refraction tomography.and refraction tomography.

• Seismic tomography does not give Seismic tomography does not give as much resolution as trenching, but as much resolution as trenching, but it reaches greater depth.it reaches greater depth.


CONCLUSIONCONCLUSION

CONCLUSIONCONCLUSION


Why is this interesting?Why is this interesting?

This comparison with groundtruth shows, that This comparison with groundtruth shows, that high resolution tomography can achieve such a high resolution tomography can achieve such a good resolution, that ambiguities like in the good resolution, that ambiguities like in the INCO data set could actually be determined.INCO data set could actually be determined.

FUTURE WORKFUTURE WORK


• Process all trench data to find Process all trench data to find velocity of colluvial wedgevelocity of colluvial wedge

• Compare X-Well results with Line 1Compare X-Well results with Line 1

• Synthetic test: What size and velocity Synthetic test: What size and velocity contrast does a coll. wedge need to contrast does a coll. wedge need to be resolved? be resolved?

• Is there a schedule that does resolve Is there a schedule that does resolve small scale features reliably?small scale features reliably?

REFERENCESREFERENCES


• Morey, D., and Schuster, G. T., 1999, Morey, D., and Schuster, G. T., 1999, Paleoseismicity of the Oquirrh fault, Utah from Paleoseismicity of the Oquirrh fault, Utah from shallow seismic tomography: Geophys. J. Int., shallow seismic tomography: Geophys. J. Int., 138,25-35138,25-35

• Nemeth, T., Normark, E., and Qin, F., 1997, Nemeth, T., Normark, E., and Qin, F., 1997, Dynamic smoothing in cross-well traveltime Dynamic smoothing in cross-well traveltime tomography: Geophysics, 62, 168-176tomography: Geophysics, 62, 168-176

• Lund, W.R., Schwartz, D. P., Mulvey, W. E., Lund, W.R., Schwartz, D. P., Mulvey, W. E., Budding, K. E., Black, B. D., 1991, Fault behavior Budding, K. E., Black, B. D., 1991, Fault behavior and earthquake recurrence on the Provo segment and earthquake recurrence on the Provo segment of the Wasatch fault zone at Mapleton, Utah of the Wasatch fault zone at Mapleton, Utah County, Utah, UGMS Special studies 75. County, Utah, UGMS Special studies 75.

THANKS TOTHANKS TO• Susan Olig and URS Corp for their trench resultsSusan Olig and URS Corp for their trench results• Travis Crosby for his experience in the field and Travis Crosby for his experience in the field and

his cheerful attitudehis cheerful attitude• Min Zhou for his experience with PC_GUI and Min Zhou for his experience with PC_GUI and

LINUX_GUILINUX_GUI• The UTAM students for their help in the field and The UTAM students for their help in the field and

their programming experiencetheir programming experience• Ann Mattson for her help in interpreting Ann Mattson for her help in interpreting

tomograms for colluvial wedgestomograms for colluvial wedges• Last spring’s GG5220 class for their help in the Last spring’s GG5220 class for their help in the

fieldfield


COLLUVIAL WEDGE IMAGING USING X-WELL AND CDP TRAVELTIME TOMOGRAPHY

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