Need for NGA-East: EPRI CEUS Ground Motion Report, Summary and Issues Norm Abrahamson Mar 7, 2008

EPRI 2004 Approach Develop weights for existing ground motion models Median and standard deviation are separated

Regionalization Followed EPRI (1993)

Model Clusters 1Single Corner Stochastic 2Double Corner Stochastic 3Hybrid 4Finite source / Greens Function

Models Grouped by Class ClusterModel TypeModels 1Single Corner Stochastic Hwang and Huo (1997) Silva et al (2002) - SC-CS Silva et al (2002) - SC-CS-Sat Silva et al (2002) - SC-VS Toro et al (1997) Frankel et al (1996) 2Double Corner Stochastic Atkinson and Boore (1995) Silva et al (2002) DC Silva et al (2002) DC - Sat 3HybridAbrahamon & Silva (2002) Atkinson (2001) & Sadigh et al (1997) Campbell (2003) 4Finite Source /Greens Function Somerville et al. (2001)

Candidate Models, Median M5 10 Hz 1 Hz

Candidate Models, Median M6 10 Hz 1 Hz

Candidate Models, Median M7 10 Hz 1 Hz

Candidate Models, Std Dev 1 Hz 10 Hz

Cluster Evaluation Consistency of the cluster median with CEUS ground motion data Strength of the seismological principals used in the model development Degree to which modeling of epistemic uncertainty was considered in developing individual ground motion models

EUS Data Used for Model Evaluations

Consistency with CEUS Data (Weights inversely proportional to variance) ClusterRelative Weight Single Corner Stochastic Double Corner Stochastic Hybrid Finite Source /Greens Function

Cluster Weights Based on Seismological Principles and Uncertainty Treatment Seismological Principles Single Corner Double Corner HybridGF Medium High Explicit modeling of epistemic Only Parametric No consideration 0.0 Final Weight

Weights for Clusters Importance Weights ClusterConsistency with data Seismological /Uncertainty Composite Weight

Model Weights within a Cluster ClusterModel TypeModelsWeights 1Single Corner Stochastic Hwang & Huo (1997) Silva et al (2002) - SC-CS Silva et al (2002) - SC-CS-Sat Silva et al (2002) - SC-VS Toro et al (1997) Frankel et al (1996) Double Corner Stochastic Atkinson & Boore (1995) Silva et al (2002) DC Silva et al (2002) DC - Sat HybridAbrahamon & Silva (2002) Atkinson (2001) & Sadigh et al (1997) Campbell (2003) Finite Source /Greens Function Somerville et al. (2001)1.0

Median by Cluster PGA

Median by Cluster T=1 sec

Cluster 1 Stress drops ModelMedian Stress Drop (Bars) Frankel et al (1996)150 Hwang and Huo (1997)150 Silva (2002) Constant  120 Silva (2002) Constant  with saturation 120 Silva (2002) variable  160 for M<=5.5, 70 for M8.5 Toro et al (1997)120

Adjustments for Epicentral Distance Based PSHA Some PSHA model earthquake as Epicenters Need to allow models to use epicental distance Two corrections needed –Median R JB (R epi,M), R rup (R epi,M) –Increase in standard deviation

Logic Tree

Epistemic: Stress-Drop Median (cluster 1)

Epistemic: Path (cluster 1)

Epistemic Single Corner (cluster 1)

Epistemic Double Corner (cluster 2)

Epistemic Hybrid (cluster 3)

Epistemic GF (cluster 4)

Issues Regionalization –Same two regions as EPRI 1993? –Rift vs non-rift Change in depth distribution If R JB is used, then are different models needed? Depends on scaling with depth

Regionalization Regions Considered by EPRI 1993

Issues Distance Metric –Do we need to consider epicenter distance based models? –RJB models may need to account for average depth

Issues Comparisons with Data –Hybrid models based on WUS models that were not well constrained for M<5, but most CEUS data is for M<5

Issues Finite Source /GF Simulations –Based on a single model (Somerville et al 2001) –MCEER project (1997) used multiple methods and found a large range (factors of 2-3) in the medians for the different simulation methods

Needs for NGA-East Approach Develop new models, with comprehensive evaluations and reviews –Revising weights for existing models is not going to lead to significant improvements Where possible, collect/apply new data to constrain ground motions –Site conditions for GM stations –Geological observations for GM constraints –Ground motions from M>4 stable regions would-wide Coordinated application of different numerical simulation methods