1. J. Louie 9/5/2005 OutlineOutline 1.Refraction Microtremor for Shallow Vs 2.ReMi-Borehole Comparison 3.Los Angeles Transect 4.Las Vegas Transect 5.Effect of Shallow Vs on Shaking Models 1.Refraction Microtremor for Shallow Vs 2.ReMi-Borehole Comparison 3.Los Angeles Transect 4.Las Vegas Transect 5.Effect of Shallow Vs on Shaking Models

2. J. Louie 9/5/2005 Building a Las Vegas Seismic Model

3. J. Louie 9/5/2005 Model Rendered as Amplification Map  Geology, Basin Depth, Geotech, Geophysical data into ModelAssembler Las Vegas Basin Las Vegas Basin Little Skull Mtn. Little Skull Mtn. Deep Volcanic Rifts Deep Volcanic Rifts

4. J. Louie 9/5/2005 Max. Ground Motion Computed– 0.1 Hz  E3D elastic finite-difference solution, by Shawn Larsen, LLNL Las Vegas Basin Las Vegas Basin Little Skull Mtn. Little Skull Mtn. Deep Volcanic Rifts Deep Volcanic Rifts

5. J. Louie 9/5/2005 Detailed Model Makes a Difference- even at 0.1 Hz  Max. ground motion ratio, models with and without geotechnical model Little Skull Mtn. Las Vegas Basin Las Vegas Basin

6. J. Louie 9/5/2005 Detailed Model Makes a Difference  But not in any way that can be predicted from the model alone– basin geometry, source, and propagation path all matter! 73% predicted for 2-4 Hz 6% computed for 0.1 Hz

7. J. Louie 9/5/2005 Max. Ground Motion Computed– 0.5 Hz  E3D elastic finite-difference solution, by Shawn Larsen, LLNL Las Vegas Basin Las Vegas Basin Little Skull Mtn. Little Skull Mtn. Deep Volcanic Rifts Deep Volcanic Rifts

8. J. Louie 9/5/2005 Comparing Computed GM at 0.5 Hz  At UNLV in the southern part of LVV, there are unexpected waveform differences, even with the similar maximum motions.

9. J. Louie 9/5/2005 Comparing Computed GM at 0.5 Hz  In central Las Vegas Valley, the detailed model has lower velocities (0.35 km/s) than the 0.5 km/s Vs30 assumed for basins. Detailed LVV Model Basin Vs30=0.5 km/s Constant

10. J. Louie 9/5/2005 Detailed Model Makes a Difference at 0.5 Hz  Max. ground motion ratio, models with and without geotechnical model Little Skull Mtn. Las Vegas Basin Las Vegas Basin

11. J. Louie 9/5/2005 Detailed Model Makes a Difference- at 0.5 Hz  In a way that can be partly predicted from the model alone– but basin geometry, source, and propagation path still matter at 0.5 Hz. 73% predicted for 2-4 Hz Up to 213% computed for 0.5 Hz

12. J. Louie 9/5/2005 Conclusions II  In tectonic areas, the regional distribution of basins affects shaking.  We have built a ModelAssembler for Nevada to create 3-d computation grids from geological and geotechnical data.  Surprisingly, geotechnical details affect even 10-sec computations in ways difficult to forecast.  In tectonic areas, the regional distribution of basins affects shaking.  We have built a ModelAssembler for Nevada to create 3-d computation grids from geological and geotechnical data.  Surprisingly, geotechnical details affect even 10-sec computations in ways difficult to forecast.