refraction microtremor for shallow shear velocity in urban basins

$: Refraction Microtremor for Shallow Shear Velocity in Urban Basins$
J. Louie 18/8/2005J. Louie 18/8/2005

Refraction MicrotremorRefraction Microtremorfor Shallow Shear Velocityfor Shallow Shear Velocity

in Urban Basinsin Urban Basins

Refraction MicrotremorRefraction Microtremorfor Shallow Shear Velocityfor Shallow Shear Velocity

in Urban Basinsin Urban Basins

John Louie, Nevada Seismological Lab(at GNS & VUW through July 2006– [email protected])UNR students: J. B. Scott, T. Rasmussen, W. Thelen, M. Clark

Collaborators:S. Pullammanappallil & B. Honjas, Optim LLCW. J. Stephenson, R. A. Williams, & J. K. Odum, USGS

Support from:IRIS-PASSCAL Instrument Center at NMT

More details at www.seismo.unr.edu/hazsurv

John Louie, Nevada Seismological Lab(at GNS & VUW through July 2006– [email protected])UNR students: J. B. Scott, T. Rasmussen, W. Thelen, M. Clark

Collaborators:S. Pullammanappallil & B. Honjas, Optim LLCW. J. Stephenson, R. A. Williams, & J. K. Odum, USGS

Support from:IRIS-PASSCAL Instrument Center at NMT

More details at www.seismo.unr.edu/hazsurv

J. Louie 18/8/2005J. Louie 18/8/2005

OutlineOutlineOutlineOutline

1.1. Refraction Microtremor for Shallow VsRefraction Microtremor for Shallow Vs

2.2. ReMi-Borehole ComparisonReMi-Borehole Comparison

3.3. Los Angeles TransectLos Angeles Transect

4.4. Las Vegas TransectLas Vegas Transect

5.5. Effect of Shallow Vs on Shaking ModelsEffect of Shallow Vs on Shaking Models






J. Louie 18/8/2005J. Louie 18/8/2005

ReMi measures Rayleigh dispersion with linear refraction arrays (paper by Louie, April 2001 BSSA).

Refraction Microtremor for Shallow Shear VelocityRefraction Microtremor for Shallow Shear VelocityRefraction Microtremor for Shallow Shear VelocityRefraction Microtremor for Shallow Shear Velocity

100-m depth resolution

Initial funding from SCEC, UNR, VUW, Optim LLC

J. Louie 18/8/2005J. Louie 18/8/2005

Low-frequencies, 1-20 Hz, so bad geophone plants still work.



J. Louie 18/8/2005J. Louie 18/8/2005

Fieldwork is quick and simple; best results in cities.Refraction Microtremor for Shallow Shear VelocityRefraction Microtremor for Shallow Shear VelocityRefraction Microtremor for Shallow Shear VelocityRefraction Microtremor for Shallow Shear Velocity


J. Louie 18/8/2005J. Louie 18/8/2005

ReMi has classified hard and soft sites around the world by measuring V30, average shear velocity to 30 m depth.


J. Louie 18/8/2005J. Louie 18/8/2005












J. Louie 18/8/2005J. Louie 18/8/2005

Four deep suspension logs in Santa Clara Valley

Collaboration with Stephenson, Williams, Odum (USGS), and Pullammanappallil (Optim), BSSA in press

Refraction, MASW, and ReMi at each hole

ReMi-Borehole ReMi-Borehole ComparisonComparison

ReMi-Borehole ReMi-Borehole ComparisonComparison

J. Louie 18/8/2005J. Louie 18/8/2005

No surface method can match log details.ReMi-Borehole ComparisonReMi-Borehole ComparisonReMi-Borehole ComparisonReMi-Borehole Comparison

J. Louie 18/8/2005J. Louie 18/8/2005

Depth-averaged velocities are a good match.But CCOC’s LVZ is a problem.

ReMi-Borehole ComparisonReMi-Borehole ComparisonReMi-Borehole ComparisonReMi-Borehole Comparison

J. Louie 18/8/2005J. Louie 18/8/2005

Joyner et al. (1981) quarter-wavelength spectra similar at important frequencies.ReMi-Borehole ComparisonReMi-Borehole ComparisonReMi-Borehole ComparisonReMi-Borehole Comparison

J. Louie 18/8/2005J. Louie 18/8/2005












J. Louie 18/8/2005J. Louie 18/8/2005

Los Angeles TransectLos Angeles TransectLos Angeles TransectLos Angeles Transect

J. Louie 18/8/2005J. Louie 18/8/2005

We Follow Field’s (2001) Amplification-Mapping StrategyWe Follow Field’s (2001) Amplification-Mapping StrategyWe Follow Field’s (2001) Amplification-Mapping StrategyWe Follow Field’s (2001) Amplification-Mapping Strategy

Two Inputs for Microzonation: V30 and Basin Depth (Z1.5?)

J. Louie 18/8/2005J. Louie 18/8/2005

July 2003 San Gabriel Valley & Los AngelesShallow Shear-Velocity TransectsShallow Shear-Velocity TransectsShallow Shear-Velocity TransectsShallow Shear-Velocity Transects

B-C

C-D

D

D-E

Transect mapped on NEHRP hazard class map by Wills, from SCEC Phase 3 Report

Supported by USGS, NEHRP ERP and IRIS-PASSCAL

J. Louie 18/8/2005J. Louie 18/8/2005

Los Angeles Transect: V30 ResultsLos Angeles Transect: V30 ResultsLos Angeles Transect: V30 ResultsLos Angeles Transect: V30 Results

J. Louie 18/8/2005J. Louie 18/8/2005

Los Angeles Transect: Full SectionLos Angeles Transect: Full SectionLos Angeles Transect: Full SectionLos Angeles Transect: Full Section

• Fast bouldery alluvium near ranges

• Low-velocity near-surface layers

thicken toward sea

• Vs constraint to 200 m depth

• Z1.0 only constrained over 1/3 of

transect– deep basin

SG MtsSG MtsWhittierNarrowsWhittierNarrows Seal BeachSeal Beach

J. Louie 18/8/2005J. Louie 18/8/2005

Boreholes in Open-File ReportsBoreholes in Open-File ReportsBoreholes in Open-File ReportsBoreholes in Open-File Reports

Four within 1 Four within 1 km of transectkm of transect

Also an Also an incomplete incomplete posting at posting at ROSRINE, ROSRINE, Pico Rivera 2Pico Rivera 2

Borehole Database Comparison—Data points within 1 km of transect

Source, Transect Array Number

Distance from Borehole

30-m Shear Velocity

% Difference NEHRP Class

Gibbs et al. (2000) ----------------- 226.9 m/s ---------------- D

This study, 186 850 m 309 m/s 36.18% D

This study, 187 269 m 301 m/s 32.66% D

This study, 188 345 m 284 m/s 25.17% D

This study, 189 930 m 251 m/s 10.62% D

Gibbs et al. (2001) ----------------- 298.7 m/s ---------------- D

This study, 140 661 m 401 m/s 34.25% C

This study, 141 442 m 338 m/s 13.15% D

This study, 142 955 m 424 m/s 41.95% C

Gibbs et al. (2001) ----------------- 544.7 m/s ---------------- C

This study, 121 870 m 580 m/s 6.48% C

This study, 122 673 m 538 m/s -1.23% C

This study, 123 997 m 498 m/s -8.57% C

Wills and Silva (1998)

----------------- 339.06 m/s ---------------- D

This study, 158 939 m 317 m/s -6.51% D

This study, 159 973 m 306 m/s -9.75% D

ROSRINE Borehole ----------------- 241.54 m/s ---------------- D

This study, 153 492 m 425 m/s 75.95% C

This study, 154 221 m 381 m/s 57.74% C

This study, 155 775 m 337 m/s 39.52% D

J. Louie 18/8/2005J. Louie 18/8/2005

Rosrine/USGS Pico Rivera 2Rosrine/USGS Pico Rivera 2Rosrine/USGS Pico Rivera 2Rosrine/USGS Pico Rivera 2 Good correlation with transect below 8 m depth.Good correlation with transect below 8 m depth.

0

50

100

150

200

250

0 200 400 600 800 1000 1200Shear-wave Velocity, m/s

Depth, m

ROSRINE picoriv2 borehole

SGRiv Survey Station 155A: ReMi



J. Louie 18/8/2005J. Louie 18/8/2005

Los Angeles Transect: V30 ResultsLos Angeles Transect: V30 ResultsLos Angeles Transect: V30 ResultsLos Angeles Transect: V30 Results

Nearby borehole results in red

J. Louie 18/8/2005J. Louie 18/8/2005

Measured VMeasured V3030 vs Wills et al. (2000) vs Wills et al. (2000)Measured VMeasured V3030 vs Wills et al. (2000) vs Wills et al. (2000)

Average Average measurements within measurements within ranges for classes B-ranges for classes B-C, D, and D-EC, D, and D-E

N. San Gabriel Val. N. San Gabriel Val. Measurements Measurements average above average above predicted C-D rangepredicted C-D range

60 new C-D data 60 new C-D data pointspoints

583 580

330

255

100

200

300

400

500

600

700

800

Wills et al. (2000) Predicted Hazard Class

Measured 30-m Shear Velocity

2003 UNR Measurements

Measured Averages

Wills et al. (2000) Averages andRanges

B

B-C

CC-D

D D-EE

J. Louie 18/8/2005J. Louie 18/8/2005

VV3030 vs Geologic Unit vs Geologic UnitVV3030 vs Geologic Unit vs Geologic Unit

Large VLarge V3030 variation inside each unit variation inside each unit

Large VLarge V30 30 variation between units variation between units

J. Louie 18/8/2005J. Louie 18/8/2005

VV3030 vs Soil Type vs Soil TypeVV3030 vs Soil Type vs Soil Type

In general, large VIn general, large V3030 variation within units variation within units Units 2 and 5 may be NEHRP DUnits 2 and 5 may be NEHRP D

Large VLarge V3030 variation between units variation between units

J. Louie 18/8/2005J. Louie 18/8/2005

VV3030 vs Riverbank Elevation vs Riverbank ElevationVV3030 vs Riverbank Elevation vs Riverbank Elevation Fast, bouldery alluvium at higher elevations on River’s alluvial fanFast, bouldery alluvium at higher elevations on River’s alluvial fan

River Profile vs. 30-m Shear Velocity

0

50

100

150

200

250

300

0 10 20 30 40 50 60

Distance from San Gabriel Range Front (km)

Elevation (m)

200

300

400

500

600

700

800

30-m Shear Velocity (m/s)

Levee & Path Elevation Profile

30-m Shear Velocity

J. Louie 18/8/2005J. Louie 18/8/2005

Spatial Statistics on VSpatial Statistics on V3030Spatial Statistics on VSpatial Statistics on V3030 Line in log-log Line in log-log

spectrum means spectrum means fractal spatial fractal spatial distributiondistribution

V30 less V30 less predictable as predictable as distance from distance from measurement measurement increasesincreases

““Noise Floor”- Noise Floor”- minimum minimum variance reached variance reached at 700-m at 700-m separationseparation

Incorporate Incorporate fractal dimension fractal dimension into PSHA?into PSHA?

San Gabriel River Vs30 Transect Spatial Power Spectra

SGRiv: y = 20823x -1.5913

R2 = 0.6705 D=1.70(D=1.78 w/o noise floor)

1.E+03

1.E+04

1.E+05

1.E+06

1.E+07

1.E+08

0.01 0.1 1 10

Spatial Frequency, /km

Power, m^2/s^2/km

NoiseFloor

J. Louie 18/8/2005J. Louie 18/8/2005

Conclusions IConclusions IConclusions IConclusions I

Long ReMi transects can geophysically Long ReMi transects can geophysically

characterize characterize spatial variationsspatial variations in shaking in shaking

hazard.hazard.

Soil and geologic units must be Soil and geologic units must be

specifically specifically mapped for velocitymapped for velocity, to , to

reliably predict measured Vreliably predict measured V3030..

210 measurements in LA 210 measurements in LA match match

predictionspredictions, and add to class C-D data., and add to class C-D data.

Long ReMi transects can geophysically Long ReMi transects can geophysically

characterize characterize spatial variationsspatial variations in shaking in shaking

hazard.hazard.

Soil and geologic units must be Soil and geologic units must be

specifically specifically mapped for velocitymapped for velocity, to , to

reliably predict measured Vreliably predict measured V3030..

210 measurements in LA 210 measurements in LA match match

predictionspredictions, and add to class C-D data., and add to class C-D data.

J. Louie 18/8/2005J. Louie 18/8/2005












J. Louie 18/8/2005J. Louie 18/8/2005

Las Vegas TransectLas Vegas TransectLas Vegas TransectLas Vegas Transect

J. Louie 18/8/2005J. Louie 18/8/2005

Las Vegas Shaking Computation, 2-secLas Vegas Shaking Computation, 2-secLas Vegas Shaking Computation, 2-secLas Vegas Shaking Computation, 2-sec

E3D synthetic-seismogram code courtesy of Shawn Larsen, LLNL

J. Louie 18/8/2005J. Louie 18/8/2005

Las Vegas Shaking Computation, 2-secLas Vegas Shaking Computation, 2-secLas Vegas Shaking Computation, 2-secLas Vegas Shaking Computation, 2-sec

33 seconds after Little Skull Mtn. earthquake, as Rayleigh wave enters Las Vegas.

LasVegas

LittleSkullMtn.

LittleSkullMtn.

J. Louie 18/8/2005J. Louie 18/8/2005

Las Vegas TransectLas Vegas TransectLas Vegas TransectLas Vegas Transect

J. Louie 18/8/2005J. Louie 18/8/2005

Most of Strip, Downtown; south side of Basin only

79 sites total

1145 well logs & geologic mapping

Las Vegas Las Vegas TransectTransect

Basin-depth contours in meters

J. Louie 18/8/2005J. Louie 18/8/2005

Some correlation to faulting, soil type?Las Vegas TransectLas Vegas Transect

J. Louie 18/8/2005J. Louie 18/8/2005

Geologic Info to Predict VGeologic Info to Predict Vss

NSL, July ‘03, sponsored by LLNL

Can soil maps predict VCan soil maps predict Vss??

J. Louie 18/8/2005J. Louie 18/8/2005

How to Extrapolate Shallow VHow to Extrapolate Shallow Vss

Correlate Correlate transect transect measurements measurements against Soil against Soil Map.Map.

Correlate 75 Correlate 75 Vs values Vs values against a against a stratigraphic stratigraphic model from model from 1145 water-1145 water-well logs.well logs.

SoilSoil

StratigraphyStratigraphy

Courtesy W. Taylor, UNLV, and J. Wagoner, LLNL

J. Louie 18/8/2005J. Louie 18/8/2005

How to Extrapolate Shallow VHow to Extrapolate Shallow Vss Predictions are good where many measurements exist.Predictions are good where many measurements exist.

Comparison of Las Vegas Vs30 Data and

200

300

400

500

600

700

0 2 4 6 8 10 12 14

Transect Distance South of Cheyenne, km

Vs30, km/s

UNR Transect Vs30 Measurements

Soil-Map Predictions

Stratigraphic-Model Predictions

J. Louie 18/8/2005J. Louie 18/8/2005

How to Extrapolate Shallow VHow to Extrapolate Shallow Vss

Predictions are not Predictions are not good where there good where there only sparse only sparse measurements.measurements.

Soil map Soil map predictions are not predictions are not conservative.conservative.

Stratigraphic model Stratigraphic model predictions are, at predictions are, at least, conservative.least, conservative.

Off-Transect Measurements and Predictions

200

400

600

800

1000

200 400 600 800 1000

Measured Vs30, m/s

Predicted Vs30, m/s

Soil-Map PredictionsStratigraphic-Model PredictionsNot ConservativeConservative

Not

Con

serv

ativ

e

Not

Con

serv

ativ

e

Conservative

Conservative

J. Louie 18/8/2005J. Louie 18/8/2005












J. Louie 18/8/2005J. Louie 18/8/2005

Building a Las Vegas Seismic ModelBuilding a Las Vegas Seismic ModelBuilding a Las Vegas Seismic ModelBuilding a Las Vegas Seismic Model

J. Louie 18/8/2005J. Louie 18/8/2005

Model Rendered as Amplification MapModel Rendered as Amplification Map Geology, Basin Depth, Geotech, Geophysical data into Geology, Basin Depth, Geotech, Geophysical data into ModelAssemblerModelAssembler

Las VegasBasinLas VegasBasin

LittleSkull Mtn.LittleSkull Mtn.

DeepVolcanic

Rifts

DeepVolcanic

Rifts

J. Louie 18/8/2005J. Louie 18/8/2005

Max. Ground Motion Computed– 0.5 HzMax. Ground Motion Computed– 0.5 Hz E3D elastic finite-difference solution, by Shawn Larsen, LLNLE3D elastic finite-difference solution, by Shawn Larsen, LLNL


LittleSkull Mtn.

LittleSkull Mtn.

DeepVolcanic

Rifts

DeepVolcanic

Rifts

J. Louie 18/8/2005J. Louie 18/8/2005

Max. Ground Motion Computed– 0.1 HzMax. Ground Motion Computed– 0.1 Hz E3D elastic finite-difference solution, by Shawn Larsen, LLNLE3D elastic finite-difference solution, by Shawn Larsen, LLNL


LittleSkull Mtn.LittleSkull Mtn.

DeepVolcanic

Rifts

DeepVolcanic

Rifts

J. Louie 18/8/2005J. Louie 18/8/2005

Detailed Model Makes a DifferenceDetailed Model Makes a Difference Max. ground motion ratio, models with and without geotechnical modelMax. ground motion ratio, models with and without geotechnical model

LittleSkull Mtn.


J. Louie 18/8/2005J. Louie 18/8/2005

Detailed Model Makes a DifferenceDetailed Model Makes a Difference But not in any way that can be predicted from the model alone– basin But not in any way that can be predicted from the model alone– basin

geometry, source, and propagation path all matter!geometry, source, and propagation path all matter!

73% predicted for 2-4 Hz73% predicted for 2-4 Hz 6% computed for 0.1 Hz6% computed for 0.1 Hz

J. Louie 18/8/2005J. Louie 18/8/2005

Conclusions IIConclusions IIConclusions IIConclusions II

In tectonic areas, the regional In tectonic areas, the regional

distribution of distribution of basinsbasins affects shaking. affects shaking.

We have built a We have built a ModelAssemblerModelAssembler for for

Nevada to create 3-d computation grids Nevada to create 3-d computation grids

from geological and geotechnical data.from geological and geotechnical data.

Surprisingly, geotechnical Surprisingly, geotechnical detailsdetails affect affect

even 10-sec computations in ways even 10-sec computations in ways

difficult to forecast.difficult to forecast.

In tectonic areas, the regional In tectonic areas, the regional

distribution of distribution of basinsbasins affects shaking. affects shaking.

We have built a We have built a ModelAssemblerModelAssembler for for

Nevada to create 3-d computation grids Nevada to create 3-d computation grids

from geological and geotechnical data.from geological and geotechnical data.

Surprisingly, geotechnical Surprisingly, geotechnical detailsdetails affect affect

even 10-sec computations in ways even 10-sec computations in ways

difficult to forecast.difficult to forecast.

J. Louie 18/8/2005J. Louie 18/8/2005

Los Angeles TransectLos Angeles TransectLos Angeles TransectLos Angeles Transect

Approximately 60 km in lengthApproximately 60 km in length Followed San Gabriel River Bike PathFollowed San Gabriel River Bike Path 20 m takeout interval, 300 m array, recorded for 30 min20 m takeout interval, 300 m array, recorded for 30 min

4 teams, 3 people each, 4.5 days4 teams, 3 people each, 4.5 days 120 IRIS/PASSCAL “Texan” single-channel recorders 120 IRIS/PASSCAL “Texan” single-channel recorders

mated to a vertical 4.5-Hz geophonemated to a vertical 4.5-Hz geophoneSupported by USGS, NEHRP ERP and IRIS-PASSCAL

J. Louie 18/8/2005J. Louie 18/8/2005

Los Angeles Transect:Los Angeles Transect:Levee EffectsLevee Effects

Los Angeles Transect:Los Angeles Transect:Levee EffectsLevee Effects

VV30 30 levee: 245 m/s levee: 245 m/s

VV30 30 non-levee: 241 non-levee: 241 m/sm/s

J. Louie 18/8/2005J. Louie 18/8/2005

Basin Depth Model from USGS GravityBasin Depth Model from USGS Gravity Includes volcanic rift basins up to 9 km deep.Includes volcanic rift basins up to 9 km deep.


LittleSkull Mtn.

LittleSkull Mtn.

DeepVolcanic

Rifts

DeepVolcanic

Rifts

Death ValleyDeath Valley

refraction microtremor for shallow shear velocity in urban basins

Documents

dthis study

outlinerefraction microtremor

cthis study

remiborehole comparisonjoyner

average shear velocity

pullammanappallil optim

initial funding

optim llcw