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***Wednesday, March 19th***
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Joint Meeting:

Topic: "Basin Effects on Strong Ground Motions, and their Representation in the NGA Models"

Speaker: Paul Somerville, Ph.D., Principal Seismologist, URS Corporation

Location: Stevenís Steak House,
5332 Stevens Place, Commerce, California (Southwest Corner of I-5 & Atlantic Boulevard)
Time: 5:30 p.m.-Social Hour; 6:30 p.m.-Dinner; 7:30 p.m.-Presentation
Cost: $30 per person with reservations, $35 at the door,
Free for students with a valid Student ID
Reservations: RESERVATIONS: J. Adolfo Acosta
By email to
Please make reservations by e-mail prior to: 12 noon, Friday, March 14, 2008

The PEER NGA (next generation attenuation) ground motion models have become available ( Unlike the previous generation of ground motion models, these models have examined basin response in a detailed manner. The NGA models are based on strong motion recordings, many of which come from sedimentary basins, so in that sense they all include basin effects. Some of the NGA models include additional terms that account for the dependence of basin effects on other parameters. These additional terms include the depth to shear wave velocities of 1 km/sec and 2.5 km/sec, and Vs30 - the shear wave velocity in the top 30 meters. Basin depth parameters can be obtained from the SCEC website ( In the talk, I review the representation of basin effects in the NGA models. I also review the application of the NGA models to estimating basin effects at a specific site in downtown Los Angeles.
Speaker Brief Biography:
Dr Paul Somerville was born in Armidale, NSW and received his B.Sc. degree in Geophysics from the University of New England. After teaching at Brandi High School in Wewak, PNG and the PNG University of Technology in Lae, he went on to get his M.Sc. and Ph.D. in Geophysics at the University of British Columbia in Vancouver, Canada. He spent two years as a Visiting Research Fellow at the Earthquake Research Institute, University of Tokyo, and did research on two major damaging earthquakes that occurred during his stay.

Dr Somerville has worked at URS Corporation and its predecessor organization, Woodward-Clyde Consultants, first in San Francisco and then in Pasadena. He has worked in many aspects of seismic hazards and been involved in the development of innovative seismological methods for specifying seismic design ground motions in earthquake engineering practice. He has applied these in the design and analysis of major buildings, bridges, dams and power generation facilities in many countries, including Australia, New Zealand, the United States and Japan. Dr Somerville has extensive research experience in Japan, where he pioneered the development of commonly used procedures for characterizing earthquake sources for the prediction of strong ground motion.