Further Development of Site Response in NGA Models

Further Development of Site Response in

NGA Models

PEER Lifelines ProgramNGA-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)• 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

Project Management

• Yousef Bozorgnia, PEER, NGA-West2 Project Manager

• Jonathan P. Stewart, UC Los Angeles (Working Group Chair)

• Emel Seyhan, UC Los Angeles (GSR)

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)

• Do we need others?

Working Group Committee (WGC)

• 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

Logistics

Agenda






NGA-West2 Overview and Project Objectives

Yousef Bozorgnia

Background on NEHRP Site Factors

Roger Borcherdt

Results from Previous NGA Site Factor Working Group

Maury Power

Agenda






Outline

• Evaluation of Site Factors– Available approaches– Approaches adopted in NEHRP and NGA

GMPEs– Input parameters

• Comparison of NGA & NEHRP site terms

Evaluation of Site Factors

• Simulation driven: – Computational model,

1D or 3D

Vs

InputRock Att.

G/GMax

D

Output



1D or 3D

Day et al. 2008



1D or 3D– Randomized soil

properties and input motions (1D only)

Walling et al. 2008





– Site factors from simulation results

Walling et al. 2008





– Site factors from simulation results

Day et al. 2008


• Simulation driven: – Not used as “stand alone” factors for active regions– Used to constrain certain aspects of “hybrid” models


• Simulation driven• Empirical (reference

site approach) – Single event– IMsoil/IMref: evaluate

dependence on site condition and PGAref

Borcherdt 2002


• 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


SimulationEmpirical:Ref. Site

Empirical:Non-Ref. Site




NEHRP Factors

Nonlinearity Weak Motion Amplification




NGA: AS, CB

NonlinearityAmplification

level; Vs30-dependence




NGA: BA, CY

Nonlinearity; Amplification

level; Vs30-dependence


• Input parameters:– NEHRP: Vs30, Ss, S1

– AS: VS30, Median PGA1100

– BA: VS30, Median PGA760

– CB: VS30, Median PGA1100

– CY: VS30, Median + i (Sa)1130

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.


• 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)

xxxsxa

xa

xa

Vsa

a

Vsa AFAVFS

S

S

S

S

S,760,exp 30

760

30

760

30

NEHRP E D C B B

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

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

Residuals Analysis

• New data: – Residuals analysis, including Baja earthquake

data, focusing on low Vs30 range.

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).


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)

Working Group Objectives & Scope

Objectives

• Input to NGA-West2 developers• Develop technical basis for, and consensus

behind, revisions to NEHRP site factors– Problems with medians– Different sigmas

Task Order Scope• Database

Further Development of Site Response in NGA Models

Documents

Transcript of Further Development of Site Response in NGA Models