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SCEC UGMS Committee Meeting

Conveners: C.B. Crouse and Tom Jordan
Dates: May 12, 2014 (10:00 - 17:30)
Location: SCEC Boardroom, USC, Los Angeles

SUMMARY: The SCEC Committee for Utilization of Ground Motion Simulations (or "UGMS Committee") is tasked to develop long-period response spectral acceleration maps for Los Angeles region for inclusion in NEHRP and ASCE 7 Seismic Provisions and in Los Angeles City Building Code. The maps would be based on 3-D numerical ground-motion simulations, and ground motions computed using latest empirical ground-motion prediction equations from the PEER NGA project. This project is coordinated with (1) the SCEC Ground Motion Simulation Validation Technical Activity Group (GMSV-TAG), (2) other SCEC projects, such as CyberShake and UCERF, and (3) the USGS national seismic hazard mapping project.

Presentation slides may be downloaded by clicking the links following the title. PLEASE NOTE: Files are the author’s property. They may contain unpublished or preliminary information and should only be used while viewing the talk.

Monday, May 12, 2014

10:00 - 10:10 Welcome, Attendee Introductions, and Agenda Review C.B. Crouse
10:10 - 10:30 SCEC UGMS Committee overview (PPT, 2.5MB) C.B. Crouse
10:30 - 11:30 Overview of CyberShake and the SCEC ground motion simulation program (PDF, 22.9 MB) Tom Jordan
11:30 - 12:00 Group Discussion  
12:00 - 13:00 Lunch  
13:00 - 13:30 Development of the SCEC Community Velocity Models (PDF, 22.9 MB) Tom Jordan
13:30 - 14:00 Comparisons among CyberShake models and with NGA models (PDF, 22.9 MB) Tom Jordan
14:00 - 14:30 Group Discussion  
14:30 - 15:00 Break  
15:00 - 15:30 Plans for future CyberShake development (PDF, 22.9 MB) Tom Jordan
15:30 - 17:30 SCEC UGMS Committee Executive Session
17:30 Adjourn


UGMS Members Attending:
*Norm Abrahamson (PG&E)
Bob Bachman (R.E. Bachman)
Jacobo Bielak (CMU)
C.B. Crouse (AECOM)
*Art Frankel (USGS)
*Rob Graves (USGS)
*Ron Hamburger (Gumpertz & Heger)
*Curt Haselton (CSUC)

John Hooper (MKA)
Marty Hudson (SEAOSC AMEC)
Tom Jordan (USC)
Charles Kircher (Kircher & Associates)
Marshall Lew (MACTEC)
Nico Luco (USGS)
*Farzad Naeim (Farzad Naeim, Inc.)


UGMS Members Absent:
John Anderson (UNR)
Jack Baker (Stanford)
Paul Somerville (AECOM)
Brad Aagaard (USGS)
Nenad Bijelic (Stanford)
Scott Callaghan (USC)
Gregory Deierlein (Stanford)
Ting Lin (Marquette)
Kevin Milner (USC)
Fabio Silva (USC)
Andreas Skarlatoudis (AECOM)
Ricardo Taborda (Memphis)
En-Jui Lee (USC)

*Remote Participants


Marshall Lew and Marty Hudson, geotechnical engineers in AMEC’s Los Angeles office, were added as new members and both attended the meeting.


Crouse presented an overview of the pilot project, with the ultimate objective of producing long period response spectral acceleration maps of the Los Angeles Metropolitan region. The plan is to develop the maps in coordination with (1) the SCEC Ground Motion Simulation Validation Technical Activity Group (GMSV-TAG), (2) other SCEC projects, such as Cybershake and UCERF, and (3) the USGS national seismic hazard project. The maps would be submitted to the NEHRP Provisions Update Committee next code cycle. The tentative schedule was attached to the minutes of the 1st UGMS committee meeting in April 2013.


Much of the meeting was devoted to a discussion of the CyberShake platform for generating ground-motion simulations throughout Southern California. T. Jordan first presented an overview of CyberShake and the SCEC ground motion simulation program. Jordan followed with presentations on the SCEC community velocity models, and comparisons of ground-motion predictions from CyberShake and the empirical NGA equations. Jordan also showed that Cybershake was able to reproduce long period ground motions from recent local earthquakes. Jordan’s final presentation was plans for future CyberShake development, which included extending the frequency band to 1.3 Hz to better define 1-sec period motions.


Deterministic/stochastic methods were mentioned as possible approaches to expand CyberShake’s ability to model higher frequency ground motions. This was not viewed as a necessary development for the successful production of the long period maps, because the maps at higher frequencies would continue to be developed using the traditional empirical ground- motion prediction equations. Jordan asked the committee whether long period maps for the vertical component would be useful to structural engineers, since CyberShake automatically generates this component in addition to the two orthogonal horizontal components. There was general agreement that it would be informative to see vertical ground motions as a check with provisions for the vertical component that were added to the 2009 NEHRP Seismic Provisions.

Nico Luco said (and Jordan confirmed) that unlike the USGS seismic source model, the CyberShake so far has only computed ground motions from ruptures on known active faults, whereas, the USGS also includes random earthquakes in its seismic hazard analysis. The question to be addressed is whether the random earthquakes increase the ground motion hazard at long periods by an insignificant amount. The USGS can quickly answer this question by examining the source deaggregations in its PSHA.

Another discussion topic was the performance measures that should be used in validating the simulations from CyberShake. Simulated ground motions will be compared to ground motions from the empirical NGA equations, as a benchmark, but that exercise does not necessarily represent a validation. Art Frankel questioned whether the absolute values from CyberShake could be trusted because of the uncertainties in the fault slip function. Art is using 3-D simulations to compute long period basin amplification factors for the Puget Sound region. The uncertainty in the source slip function needs to be considered. Rob Graves was not present to offer his views on the subject, but the topic will need to be addressed in the future.


The UGMS continued to affirm that the long period mapping project will proceed on two parallel tracks, in which PSHA/DSHA will be conducted from the 3-D numerical simulations using CyberShake and from the traditional empirical approach using the NGA-West equations. It was agreed that the results from the 3-D simulations could be used to refine the equations ultimately used in the empirical approach. The topic of how to use the results from the two approaches to construct the long period maps was discussed will be deferred until the results are generated.

Sensitivity studies will be conducted to evaluate the effect of the near surface velocity structure on the long period ground motions. Varying the mesh size in the near surface would address the issue, and depending on the results, some refinements the the near surface velocity structure may be made.


T. Jordan will present results of the 3-D Cybershake model at selected sites in Southern California. The results will consist of 5% damped, horizontal component response spectra, generated according to the requirements of Chapter 21 in the ASCE 7 standard. The approach will be the same as used by the USGS in creating the national risk-targeted Maximum Considered Earthquake (MCER) maps at 0.2-sec and 1.0-sec periods. The probabilistic and deterministic MCER response spectra would be computed for periods in the 2.0 to 10 sec range, and compared with similar results generated using the NGA West2 equations.


Crouse will select sites for the CyberShake calculation of the MCER response spectra, and N. Luco will provide the Matlab routine to do calculate the probabilistic MCER from the hazard curves. Crouse will provide details on the calculation of the maximum direction shaking component.


The next UGMS committee meeting is tentatively scheduled for one day in the fall of this year in the time window, November 3 to November 21. A Doodle poll will be sent to members to arrange a date. 

Map of CyberShake sites. Purple sites are along a 10 km x 10 km mesh, orange sites are near SCSN broadband stations, and yellow sites are locations of interest.
Site Name NGA-1
3 second curve
5 second curve
3 second curve
5 second curve
LADT LADT 3 sec LADT 5 sec LADT 3 sec LADT 5 sec
CCP CCP 3 sec CCP 5 sec CCP 3 sec CCP 5 sec
P22 P22 3 sec P22 5 sec P22 3 sec P22 5 sec
s429 s429 3 sec s429 5 sec s429 3 sec s429 5 sec
STG STG 3 sec STG 5 sec STG 3 sec STG 5 sec
s684 s684 3 sec s684 5 sec s684 3 sec s684 5 sec
s688 s688 3 sec s688 5 sec s688 3 sec s688 5 sec
PAS PAS 3 sec PAS 5 sec PAS 3 sec PAS 5 sec
s758 s758 3 sec s758 5 sec s758 3 sec s758 5 sec
SBSM SBSM 3 sec SBSM 5 sec SBSM 3 sec SBSM 5 sec
STNI STNI 3 sec STNI 5 sec STNI 3 sec STNI 5 sec
WNGC WNGC 3 sec WNGC 5 sec WNGC 3 sec WNGC 5 sec
s355 s355 3 sec s355 5 sec s355 3 sec s355 5 sec


Hypocenter distribution for source 244, rupture 5 (M6.55, Puente Hills) Slips for a single realization of source 244, rupture 5 (M6.55, Puente Hills)
Hypocenter distribution for source 128, rupture 1296 (M8.15, Southern San Andreas) Slips for a single realization of source 128, rupture 1296 (M8.15, Southern San Andreas)