Outline

1
Outline

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
Building a Las Vegas Seismic Model
3
Model Rendered as Amplification Map

• Geology, Basin Depth, Geotech, Geophysical data
  into ModelAssembler

Deep Volcanic Rifts
Las Vegas Basin
Little Skull Mtn.
4
Max. Ground Motion Computed 0.1 Hz

• E3D elastic finite-difference solution, by Shawn
  Larsen, LLNL

5
Detailed Model Makes a Difference- even at 0.1 Hz

• Max. ground motion ratio, models with and without
  geotechnical model

6
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
Max. Ground Motion Computed 0.5 Hz

• E3D elastic finite-difference solution, by Shawn
  Larsen, LLNL

8
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
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 Vs300.5 km/s Constant
10
Detailed Model Makes a Difference at 0.5 Hz

• Max. ground motion ratio, models with and without
  geotechnical model

11
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
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.