Transcript PowerPoint Presentation - Surveying Seismic Microzonation

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
J. Louie 9/5/2005
Building a Las Vegas Seismic Model
J. Louie 9/5/2005
Model Rendered as Amplification Map

Geology, Basin Depth, Geotech, Geophysical data into ModelAssembler
Deep
Volcanic
Rifts
Las Vegas
Basin
Little
Skull Mtn.
J. Louie 9/5/2005
Max. Ground Motion Computed– 0.1 Hz

E3D elastic finite-difference solution, by Shawn Larsen, LLNL
Deep
Volcanic
Rifts
Las Vegas
Basin
Little
Skull Mtn.
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
Las Vegas
Basin
Little
Skull Mtn.
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
J. Louie 9/5/2005
6% computed for 0.1 Hz
Max. Ground Motion Computed– 0.5 Hz

E3D elastic finite-difference solution, by Shawn Larsen, LLNL
Deep
Volcanic
Rifts
Las Vegas
Basin
Little
Skull Mtn.
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.
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
J. Louie 9/5/2005
Basin Vs30=0.5 km/s Constant
Detailed Model Makes a Difference at 0.5 Hz

Max. ground motion ratio, models with and without geotechnical model
Las Vegas
Basin
Little
Skull Mtn.
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
J. Louie 9/5/2005
Up to 213% computed for 0.5 Hz
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.
J. Louie 9/5/2005