Ground-Motion Attenuation Relationships for Cascadia Subduction Zone Megathrust Earthquakes Based on

a Stochastic Finite-Fault Model

Nick GregorNick Gregor11, Walter Silva, Walter Silva11, Ivan Wong, Ivan Wong22, and Bob Youngs, and Bob Youngs33

11 Pacific Engineering and Analysis Pacific Engineering and Analysis22 URS Corporation URS Corporation

33 Geomatrix Consultants Geomatrix Consultants

Pacific Northwest Workshop for USGS Hazard MapsPacific Northwest Workshop for USGS Hazard Maps

Seattle Washington, March 28-29, 2006Seattle Washington, March 28-29, 2006

Outline

Stochastic Finite-Fault ModelStochastic Finite-Fault Model Model ValidationModel Validation Rock and Soil ProfilesRock and Soil Profiles Ground Motion ComparisonsGround Motion Comparisons Model UpdatesModel Updates

Stochastic Finite-Fault Model

Model Validation

1985 Michoacan, Mexico Earthquake (M8.0):1985 Michoacan, Mexico Earthquake (M8.0): 14 rock sites14 rock sites Distances 15 - 251 kmDistances 15 - 251 km

1985 Valpariso, Chile Earthquake (M7.9):1985 Valpariso, Chile Earthquake (M7.9): 6 rock sites6 rock sites Distances 39 - 119 kmDistances 39 - 119 km

Michoacan Earthquake

Michoacan Earthquake

Michoacan Earthquake

Valpariso Earthquake

Valpariso Earthquake

Modeling Bias

Cascadia Finite-Fault Model M 8.0, 8.5, 9.0M 8.0, 8.5, 9.0 Fault lengths = 150, 450, and 1,100 kmFault lengths = 150, 450, and 1,100 km Fault Width = 90 kmFault Width = 90 km Dip Angle = 9Dip Angle = 9oo

16 Site Locations (Center limb, South limb)16 Site Locations (Center limb, South limb) Rock (Columbia River Basalt), Soil site Rock (Columbia River Basalt), Soil site

ConditionsConditions Q(f) = 380fQ(f) = 380f0.39 0.39 (Atkinson, 1995)(Atkinson, 1995) Crustal Model (Crustal Model (Trehu et al., 1994; Cohee et al., 1991; Trehu et al., 1994; Cohee et al., 1991;

Ludwin et al., 1991Ludwin et al., 1991))

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Fault Plane

Zone of Randomized points of Rupture Initiation

East Limb

South Limb

W

50020010050200

10

-45

L

Distance (km)

¬ <= Randomized hypocenter location

Attenuation Model Update

Non-linear Site Response Model from Non-linear Site Response Model from PEER NGA PEER NGA (Walling and Abrahamson, 2006)(Walling and Abrahamson, 2006)

Reference “Rock” VsReference “Rock” Vs30m30m=1,100 m/sec=1,100 m/sec

VsVs30m30m range: 270 - 2,830 m/sec range: 270 - 2,830 m/sec

Depth range: 30 - 1,000 feetDepth range: 30 - 1,000 feet EPRI and Penisular Soil CurvesEPRI and Penisular Soil Curves Input Rock PGA range: 0.01 - 1.5 gInput Rock PGA range: 0.01 - 1.5 g

0.1

1

10

0.001 0.01 0.1 1 10

PGArock (g)

Amp.f(V274)/Amp.f(V750)

Peninsular Model

Epri Model

Boore 1997

Choi & Stewart, 2005

PGA

T=0.3 sec

0.1

1

10

0.001 0.01 0.1 1 10

PGArock (g)

Amp.f(V274)/Amp.f(V750)

Peninsular Model

Epri Model

Boore, 1997

Choi & Stewart, 2005

T=1.0 sec

0.1

1

10

0.001 0.01 0.1 1 10

PGArock (g)

Amp.f(V274)/Amp.f(V750)

Peninsular Model

Epri Model

Boore 1997

Choi & Stewart, 2005