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Further Development of Site Response in NGA Models

Further Development of Site Response in NGA Models. PEER Lifelines Program NGA-West2 Project Topic #8 Working Group Meeting. Kickoff Meeting. April 20, 2010. Agenda. 10 am: Welcome/logistics (Stewart/Bozorgnia) 10:10 am: NGA-West2 overview and project objectives (Bozorgnia)

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Further Development of Site Response in NGA Models

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  1. Further Development of Site Response in NGA Models PEER Lifelines Program NGA-West2 Project Topic #8 Working Group Meeting Kickoff Meeting April 20, 2010

  2. Agenda • 10 am: Welcome/logistics (Stewart/Bozorgnia) • 10:10 am: NGA-West2 overview and project objectives (Bozorgnia) • 10:30 am: Background on NEHRP site factors (Borcherdt) • 11:00 am: Results from previous NGA Site Factor Working Group (Power) • 11:30 am: Comparison of NGA-West site terms to NEHRP (Stewart/Seyhan) • Noon: Lunch • 1 pm: Open discussion of project objectives, scope, deliverables, & schedule

  3. Project Management • Yousef Bozorgnia, PEER, NGA-West2 Project Manager • Jonathan P. Stewart, UC Los Angeles (Working Group Chair) • Emel Seyhan, UC Los Angeles (GSR)

  4. Working Group Committee (WGC) • Don Anderson, CH2MHill, Bellevue, WA (Geotechnical engineer, TS3 Member) • Roger Borcherdt, USGS, Menlo Park, CA (Engineering seismology, developer of NEHRP site factors) • C. B. Crouse, URS Corporation, Seattle, WA (Geotechnical engineer, TS3 Chair and PUC Member) • R.W. Graves, URS, Pasadena, CA (Seismologist, ground motion simulation and basin effects) • I.M. Idriss, UC Davis, Santa Fe, NM (Geotechnical engineer, GMPE developer) • Maury Power, AMEC Geomatrix, Oakland, CA (Geotechnical engineer, for TS3 Chair) • Walter Silva, PEA, El Cerrito, CA (Seismologist, NGA database manager, GMPE developer) • Thomas Shantz, Caltrans, Sacrament, CA (Geotechnical engineer)

  5. Working Group Committee (WGC) • Do we need others?

  6. Logistics • Database provided by NGA-West2 (PEA) • Technical work by UCLA researchers • Oversight of work direction/results by WGC • Oversight of WGC by …? • Deliverables: • Check of NGA-W models (trends with Vs30, nonlinearity, sigma) • Evaluate basin depth effects • Develop technical basis for, and consensus behind, revisions to NEHRP site factors

  7. Agenda • 10 am: Welcome/logistics (Stewart/Bozorgnia) • 10:10 am: NGA-West2 overview and project objectives (Bozorgnia) • 10:30 am: Background on NEHRP site factors (Borcherdt) • 11:00 am: Results from previous NGA Site Factor Working Group (Power) • 11:30 am: Comparison of NGA-West site terms to NEHRP (Stewart/Seyhan) • Noon: Lunch • 1 pm: Open discussion of project objectives, scope, deliverables, & schedule

  8. NGA-West2 Overview and Project Objectives Yousef Bozorgnia

  9. Background on NEHRP Site Factors Roger Borcherdt

  10. Results from Previous NGA Site Factor Working Group Maury Power

  11. Agenda • 10 am: Welcome/logistics (Stewart/Bozorgnia) • 10:10 am: NGA-West2 overview and project objectives (Bozorgnia) • 10:30 am: Background on NEHRP site factors (Borcherdt) • 11:00 am: Results from previous NGA Site Factor Working Group (Power) • 11:30 am: Comparison of NGA-West site terms to NEHRP (Stewart/Seyhan) • Noon: Lunch • 1 pm: Open discussion of project objectives, scope, deliverables, & schedule

  12. Outline • Evaluation of Site Factors • Available approaches • Approaches adopted in NEHRP and NGA GMPEs • Input parameters • Comparison of NGA & NEHRP site terms

  13. G/GMax D g Evaluation of Site Factors • Simulation driven: • Computational model, 1D or 3D Output V s Rock Att. Input

  14. Evaluation of Site Factors • Simulation driven: • Computational model, 1D or 3D Day et al. 2008

  15. Evaluation of Site Factors • Simulation driven: • Computational model, 1D or 3D • Randomized soil properties and input motions (1D only) Walling et al. 2008

  16. Evaluation of Site Factors • Simulation driven: • Computational model, 1D or 3D • Randomized soil properties and input motions (1D only) Walling et al. 2008

  17. Evaluation of Site Factors • Simulation driven: • Computational model, 1D or 3D • Randomized soil properties and input motions (1D only) • Site factors from simulation results Walling et al. 2008

  18. Evaluation of Site Factors • Simulation driven: • Computational model, 1D or 3D • Randomized soil properties and input motions (1D only) • Site factors from simulation results Day et al. 2008

  19. Evaluation of Site Factors • Simulation driven: • Computational model, 1D or 3D • Randomized soil properties and input motions (1D only) • Site factors from simulation results Day et al. 2008

  20. Evaluation of Site Factors • Simulation driven: • Not used as “stand alone” factors for active regions • Used to constrain certain aspects of “hybrid” models

  21. Evaluation of Site Factors • Simulation driven • Empirical (reference site approach) • Single event • IMsoil/IMref: evaluate dependence on site condition and PGAref Borcherdt 2002

  22. Evaluation of Site Factors • Simulation driven • Empirical (reference site approach) • Empirical (non-reference site approach) • Multiple events • Analysis of residuals • Evaluate dependence on site condition, PGArock, etc. Choi & Stewart 2005

  23. Evaluation of Site Factors Empirical: Ref. Site Empirical: Non-Ref. Site Simulation

  24. Evaluation of Site Factors NEHRP Factors Nonlinearity Weak Motion Amplification Empirical: Ref. Site Empirical: Non-Ref. Site Simulation

  25. Evaluation of Site Factors NGA: AS, CB Amplification level; Vs30-dependence Nonlinearity Empirical: Ref. Site Empirical: Non-Ref. Site Simulation

  26. Evaluation of Site Factors NGA: BA, CY Nonlinearity; Amplification level; Vs30-dependence Empirical: Ref. Site Empirical: Non-Ref. Site Simulation

  27. Evaluation of Site Factors • Input parameters: • NEHRP: Vs30, Ss, S1 • AS: VS30, Median PGA1100 • BA: VS30, Median PGA760 • CB: VS30, Median PGA1100 • CY: VS30, Median + i (Sa)1130

  28. NGA-NEHRP Comparisons • In natural log units, site term = Fx(Vs30, Ax) • Fx=amplification relative to Vs30=x site condition • Ax=ground motion amplitude for reference site condition of Vs30=x • Use Vs30=150, 270, 560, 760, and 1100 m/s • Evaluate F at T=0.3 and 1.0 sec.

  29. NGA-NEHRP Comparisons • Ax: • A=median PGA for AS, BA, CB • A=Sa at period of interest for CY (median + i); Take Sa(0.3)=2.5×PGA and Sa(1.0)=1.0×PGA • Adopt reference condition of 760 m/s • F760(Vs30, Ax)=Fx(Vs30, Ax)-Fx(760, Ax)

  30. D C B B NEHRP E

  31. Suggestions on NEHRP-NGA comparisons • Average Sa across all NGA periods in the ranges for Fa and Fv. Use average of logs + limits. Exact middle of the range too (e.g. 0.3 sec for Fa, 1.2 sec for Fv) • Average across velocities in site class: use wt average based on histograms of Vs30. • Ask Brian how he plotted F vs PGA • Check coding using full models. • Check NGA errata for AS

  32. Residuals Analysis • WS: run NGA for 760 with NEHRP factors and look at residuals. • All sites and estimates Vs only • Use GMRotI50 • New data: • Use June 2010 version of NGA flat file • Alan Yong, USGS: he has funding to perform site investigations. His site list has been approved, previous efforts to provide input on sites to investigate have been resisted

  33. Residuals Analysis • New data: • Residuals analysis, including Baja earthquake data, focusing on low Vs30 range.

  34. Other recommendations • USGS maps for all Vs30s, with interpolation (next generation of mapping) • When we have the new factors, compare hybrid predictions with them & old factors with full psha for various sites in Nor Cal and So Cal. • Check sites without Vs using Virtual Geotechnical Data Center (TS will send url and password). • Google earth file with CA stations, see where E stations are (look at other categories too).

  35. NGA-NEHRP Comparisons Differences: • NEHRP Fv high • Esp for C to E • NEHRP nonlinearity stronger for C to D • NEHRP Fa and Fv high for rock (Class B)

  36. Working Group Objectives & Scope

  37. Objectives • Input to NGA-West2 developers • Develop technical basis for, and consensus behind, revisions to NEHRP site factors • Problems with medians • Different sigmas

  38. Task Order Scope • Database

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