1. David von Seggern 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

2. David von Seggern 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. David von Seggern Catalog Location of Earthquakes Used for Inversion (1990-2006)

4. David von Seggern

5. Stations used in the inversion

6. David von Seggern Catalog Magnitudes of Earthquakes

7. David von Seggern Depth Distribution of Catalog Hypocenters

8. David von Seggern Arrival-Time Residuals From Catalog Residuals are computed with respect to 1-dimensional layered model.

9. David von Seggern Catalog Locations of Blasts Used

10. David von Seggern Summary of Input  > 200,000 P and S travel times  > 200,000 cross-correlation times  > 14,000 earthquakes  23 blasts  71 stations

11. David von Seggern 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

12. David von Seggern 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.

13. David von Seggern Checkerboard Test (Vp)

14. David von Seggern Checkerboard Test (Vp) vertical exag. = 3

15. David von Seggern Imaged Depth Section (Vp): -1 km

16. David von Seggern Imaged Depth Section (Vp): 2 km

17. David von Seggern Imaged Depth Section (Vp): 10 km

18. David von Seggern Imaged Cross-section(Vp): 39.55N RenoBasin vertical exag. = 3

19. David von Seggern Imaged Cross-section (Vp): -119.75W vertical exag. = 3

20. David von Seggern Imaged Depth Section (Vp/Vs): -1 km

21. David von Seggern Imaged Cross-section (Vp/Vs): 39.55N vertical exag. = 3

22. David von Seggern Imaged Cross-section (Vp/Vs): 39.25N vertical exag. = 3

23. David von Seggern Imaged Cross-section (Vp/Vs): -119.75W vertical exag. = 3

24. David von Seggern E-W Cross-sections

25. David von Seggern N-S Cross-sections

26. David von Seggern Iso-surface: 6.0 < Vp < 6.5

27. David von Seggern How Do We Compare? 2-DRefractionLineTomography (Louie et al.) 3-DJointInversion (This Study)

28. David von Seggern Original Catalog Epicenters Joint Inversion Epicenters

29. David von Seggern 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.

30. David von Seggern Example of Seismicity Lineation ~ 6 - 10 km north of Kings Beach Carson Range

31. David von Seggern 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.