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COLLUVIAL WEDGE IMAGING USING X-WELL AND CDP TRAVELTIME TOMOGRAPHY

COLLUVIAL WEDGE IMAGING USING X-WELL AND CDP TRAVELTIME TOMOGRAPHY. MAIKE-L. BUDDENSIEK GERARD T. SCHUSTER RONALD L. BRUHN. OUTLINE. INTRODUCTION SEISMIC SURVEY SUMMARY RESULTS AND INTERPRETATION CONCLUSION. Introduction. Seismic Survey. Results. Conclusion. COLLUVIAL WEDGES. (a).

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COLLUVIAL WEDGE IMAGING USING X-WELL AND CDP TRAVELTIME TOMOGRAPHY

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  1. COLLUVIAL WEDGE IMAGING USING X-WELL AND CDP TRAVELTIME TOMOGRAPHY MAIKE-L. BUDDENSIEK GERARD T. SCHUSTER RONALD L. BRUHN

  2. OUTLINE • INTRODUCTION • SEISMIC SURVEY SUMMARY • RESULTS AND INTERPRETATION • CONCLUSION Introduction Seismic Survey Results Conclusion

  3. COLLUVIAL WEDGES (a) Pre - Earthquake (b) Earthquake (c) 1000 years later Colluvial Wedge Seismic Survey Results Conclusion Introduction

  4. COLLUVIAL WEDGE Seismic Survey Results Conclusion Introduction

  5. COLLUVIAL WEDGE Seismic Survey Results Conclusion Introduction

  6. LOCATION: Mapleton SLC SLC PROVO WFZ, Provo Segment PROVO Wasatch Fault Zone, Utah Seismic Survey Results Conclusion Introduction

  7. GEOLOGY Footwall Side Hanging Wall Side af1 SeismicSurvey Results Conclusion Introduction

  8. Line 3 HiRes Trench Line 2 SEISMIC SURVEY I Footwall Side Hanging Wall Side af1 Introduction SeismicSurvey Results Conclusion

  9. SURVEY SITE Introduction SeismicSurvey Results Conclusion

  10. SURVEY SITE Hi-Res Low-Res Introduction SeismicSurvey Results Conclusion

  11. GIGA TRENCH done by Sue Olig, URS Corp. !!! GROUNDTRUTH !!! Introduction SeismicSurvey Results Conclusion

  12. 2 geophone lines SEISMIC SURVEY II GEOPHONE LINES SHOT POSITIONS • shot line on surface Introduction SeismicSurvey Results Conclusion

  13. 2 geophone lines • 2 shot lines • shot line on bench • 1 vertical profile SEISMIC SURVEY II GEOPHONE LINES SHOT POSITIONS Introduction SeismicSurvey Results Conclusion

  14. REFRACTION VS. CROSSWELL Introduction SeismicSurvey Results Conclusion

  15. SURVEY SUMMARY • Line 1: 83.5 m high-res line (E-W) • Line 2: 595 m low-res line (N-S) • Line 3: 595 m low-res line (E-W) • Trench results, preliminary borehole results • X-well 1: Geophones @ Suface, shots @ 1st bench • X-well 2: Geophones @ 1st bench, shots @ surface • 1 vertical profile (12 geophones, 4 shots) Introduction SeismicSurvey Results Conclusion

  16. HIGH-RES LINE • 6 faults • 4 colluvial wedges Introduction Seismic Survey Results Conclusion

  17. WEDGE 1 Introduction Seismic Survey Results Conclusion

  18. WEDGE 2 Introduction Seismic Survey Results Conclusion

  19. WEDGE 3 Introduction Seismic Survey Results Conclusion

  20. WEDGE 4 Introduction Seismic Survey Results Conclusion

  21. HI-RES & TRENCH RESULTS • Groundtruth agrees approx. with seismic • Tomogram can do greater depth than • trenching, but wedges are subtle and • faults shifted Introduction Seismic Survey Results Conclusion

  22. HI-RES & X-WELL • Faults are imaged well in both tomograms • Overall structure is the same • No indication of biggest wedge in X-Well • Velocities in X-Well smaller than in CDP • tomography. Opening the trench loosened • material. (half data set, no QC yet) Introduction Seismic Survey Results Conclusion

  23. MIGRATION Introduction Seismic Survey Results Conclusion

  24. CONCLUSION • Small structures are very sensitive to schedules of the inversion. • Colluvial wedges may be very subtle or not resolved. • Faults are resolved well with X-Well and refraction tomography. • Seismic tomography does not give as much resolution as trenching, but it reaches greater depth. Introduction Seismic Survey Results Conclusion

  25. CONCLUSION Why is this interesting? This comparison with groundtruth shows, that high resolution tomography can achieve such a good resolution, that ambiguities like in the INCO data set could actually be determined. Introduction Seismic Survey Results Conclusion

  26. FUTURE WORK • Process all trench data to find velocity of colluvial wedge • Compare X-Well results with Line 1 • Synthetic test: What size and velocity contrast does a coll. wedge need to be resolved? • Is there a schedule that does resolve small scale features reliably? Introduction Seismic Survey Results Conclusion

  27. REFERENCES • Morey, D., and Schuster, G. T., 1999, Paleoseismicity of the Oquirrh fault, Utah from shallow seismic tomography: Geophys. J. Int., 138,25-35 • Nemeth, T., Normark, E., and Qin, F., 1997, Dynamic smoothing in cross-well traveltime tomography: Geophysics, 62, 168-176 • Lund, W.R., Schwartz, D. P., Mulvey, W. E., Budding, K. E., Black, B. D., 1991, Fault behavior and earthquake recurrence on the Provo segment of the Wasatch fault zone at Mapleton, Utah County, Utah, UGMS Special studies 75. Introduction Seismic Survey Results Conclusion

  28. THANKS TO • Susan Olig and URS Corp for their trench results • Travis Crosby for his experience in the field and his cheerful attitude • Min Zhou for his experience with PC_GUI and LINUX_GUI • The UTAM students for their help in the field and their programming experience • Ann Mattson for her help in interpreting tomograms for colluvial wedges • Last spring’s GG5220 class for their help in the field Introduction Seismic Survey Results Conclusion

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