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Need for NGA-East: EPRI CEUS Ground Motion Report, Summary and Issues

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.

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Need for NGA-East: EPRI CEUS Ground Motion Report, Summary and Issues

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

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

  3. RegionalizationFollowed EPRI (1993)

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

  5. Models Grouped by Class

  6. Candidate Models, Median M5 10 Hz 1 Hz

  7. Candidate Models, Median M6 10 Hz 1 Hz

  8. Candidate Models, Median M7 10 Hz 1 Hz

  9. Candidate Models, Std Dev 1 Hz 10 Hz

  10. 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

  11. EUS Data Used for Model Evaluations

  12. Consistency with CEUS Data(Weights inversely proportional to variance)

  13. Cluster Weights Based on Seismological Principles and Uncertainty Treatment

  14. Weights for Clusters

  15. Model Weights within a Cluster

  16. Medianby ClusterPGA

  17. Medianby ClusterT=1 sec

  18. Cluster 1 Stress drops

  19. Adjustments for Epicentral Distance Based PSHA • Some PSHA model earthquake as Epicenters • Need to allow models to use epicental distance • Two corrections needed • Median RJB (Repi,M), Rrup (Repi,M) • Increase in standard deviation

  20. Logic Tree

  21. Epistemic:Stress-DropMedian(cluster 1)

  22. Epistemic:Path(cluster 1)

  23. EpistemicSingle Corner(cluster 1)

  24. EpistemicDoubleCorner(cluster 2)

  25. EpistemicHybrid(cluster 3)

  26. EpistemicGF(cluster 4)

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

  28. RegionalizationRegions Considered by EPRI 1993

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

  30. 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

  31. 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

  32. 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

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