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Goals

Joint Seismic Tomography/Location Inversion in the Reno/Carson City Area Leiph Preston & David von Seggern Nevada Seismological Laboratory Community Velocity Model Workshop January 14-15, 2008. Goals.

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Goals

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  1. Joint Seismic Tomography/Location Inversion in the Reno/Carson City Area Leiph Preston & David von SeggernNevada Seismological LaboratoryCommunity Velocity Model WorkshopJanuary 14-15, 2008

  2. Goals • Develop a tomographic velocity model in the Reno/Carson City area at kilometer scale to roughly 15 km depth. • Relocate NSL catalog seismicity jointly with tomographic imaging. • Utilize cross-correlation times of P and S waves to constrain the relative hypocenters. • Compare imaging results with other available velocity results.

  3. Catalog Location of EarthquakesUsed for Inversion(1990-2006)

  4. Stations used in the inversion

  5. Catalog Magnitudes of Earthquakes

  6. Depth Distribution of Catalog Hypocenters

  7. Arrival-Time Residuals From Catalog Residuals are computed with respect to 1-dimensional layered model.

  8. Catalog Locations of Blasts Used

  9. Summary of Input • > 200,000 P and S travel times • > 200,000 cross-correlation times • > 14,000 earthquakes • 23 blasts • 71 stations

  10. Image Parameters • horizontal resolution = 2 km (90 x 91 grid) • vertical resolution = 1 km • 42 depths, from -5 to 36 km, relative to MSL • Vp and Vp/Vs images

  11. Establish Resolving Capability Dependence on Starting Model: We ran cases with various reasonable starting models and found no significant dependency of result on starting velocities. Checkerboard Test: We perturb the final model, recompute travel-times, re-image the velocity model, and see if perturbations are recovered.

  12. Checkerboard Test (Vp)

  13. Checkerboard Test (Vp) vertical exag. = 3

  14. Imaged Depth Section (Vp): -1 km

  15. Imaged Depth Section (Vp): 2 km

  16. Imaged Depth Section (Vp): 10 km

  17. Imaged Cross-section(Vp): 39.55N Reno Basin vertical exag. = 3

  18. Imaged Cross-section (Vp): -119.75W vertical exag. = 3

  19. Imaged Depth Section (Vp/Vs): -1 km

  20. Imaged Cross-section (Vp/Vs): 39.55N vertical exag. = 3

  21. Imaged Cross-section (Vp/Vs): 39.25N vertical exag. = 3

  22. Imaged Cross-section (Vp/Vs): -119.75W vertical exag. = 3

  23. E-W Cross-sections

  24. N-S Cross-sections

  25. Iso-surface: 6.0 < Vp < 6.5

  26. How Do We Compare? 2-D Refraction Line Tomography (Louie et al.) 3-D Joint Inversion (This Study)

  27. Original Catalog Epicenters Joint Inversion Epicenters

  28. Caveats With Seismicity Relocation • Many earthquakes are culled out by residual analysis and data requirements during inversion. • Locations trade off with structure in joint inversion. • Nevada seismicity tends to be diffuse, with unclear relation to known fault traces. • Lineations, if present, need to be viewed by zooming plots.

  29. Example of Seismicity Lineation Carson Range ~ 6 - 10 km north of Kings Beach

  30. Summary • A volume in the region 38.5,-121.0 to 40.0,-119.0 down to ~ 15 km depth below MSL was imaged using P and S wave tomography and simultaneous solution for refined hypocenters. • Low velocities exist east of the Sierra Nevada at shallow depths, coinciding with known basins, and especially low in the Reno basin. • The Sierra Nevada crest and westward have high velocities at shallow depth. • Anomalously high Vp/Vs material apparently exists just above the 2003 deep (25-30 km) swarm of earthquakes under north Lake Tahoe.

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