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Ground Motion Attenuation for Cascadia Subduction Earthquakes

Explore a stochastic finite-fault model validating ground motion from historic earthquakes, comparing rock and soil profiles, and updating the modeling bias for Cascadia megathrust events. This study covers various rock and soil conditions and includes site-specific attenuation models to predict PGA for different periods.

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Ground Motion Attenuation for Cascadia Subduction Earthquakes

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  1. Ground-Motion Attenuation Relationships for Cascadia Subduction Zone Megathrust Earthquakes Based on a Stochastic Finite-Fault Model Nick Gregor1, Walter Silva1, Ivan Wong2, and Bob Youngs3 1 Pacific Engineering and Analysis 2 URS Corporation 3 Geomatrix Consultants Pacific Northwest Workshop for USGS Hazard Maps Seattle Washington, March 28-29, 2006

  2. Outline • Stochastic Finite-Fault Model • Model Validation • Rock and Soil Profiles • Ground Motion Comparisons • Model Updates

  3. Stochastic Finite-Fault Model

  4. Model Validation • 1985 Michoacan, Mexico Earthquake (M8.0): • 14 rock sites • Distances 15 - 251 km • 1985 Valpariso, Chile Earthquake (M7.9): • 6 rock sites • Distances 39 - 119 km

  5. Michoacan Earthquake

  6. Michoacan Earthquake

  7. Michoacan Earthquake

  8. Valpariso Earthquake

  9. Valpariso Earthquake

  10. Modeling Bias

  11. Cascadia Finite-Fault Model • M 8.0, 8.5, 9.0 • Fault lengths = 150, 450, and 1,100 km • Fault Width = 90 km • Dip Angle = 9o • 16 Site Locations (Center limb, South limb) • Rock (Columbia River Basalt), Soil site Conditions • Q(f) = 380f0.39 (Atkinson, 1995) • Crustal Model (Trehu et al., 1994; Cohee et al., 1991; Ludwin et al., 1991)

  12. Attenuation Model Update • Non-linear Site Response Model from PEER NGA (Walling and Abrahamson, 2006) • Reference “Rock” Vs30m=1,100 m/sec • Vs30m range: 270 - 2,830 m/sec • Depth range: 30 - 1,000 feet • EPRI and Penisular Soil Curves • Input Rock PGA range: 0.01 - 1.5 g

  13. PGA

  14. T=0.3 sec

  15. T=1.0 sec

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