Leader: Paul Somerville
Co-leader: Rob Wesson

2004 Annual Report

SCEC’s major Implementation Interface activity in 2004 was participation in the Next Generation Attenuation (NGA) Project. Ground motion attenuation relationships are the backbone of modern earthquake hazard assessment. These relationships are used in all earthquake hazard assessments ranging from the U.S. National and California seismic hazards maps, to site-specific assessments, both deterministic and probabilistic, used for specific facilities ranging from bridges to dams to power plants. Hazard assessment results are used to establish design strategies and details of the built environment and to predict their performance.

SCEC is a co-sponsor and co-participant with PEER-Lifelines and the USGS in NGA Project. The objective of the current phase of the NGA Project, NGA-E (Empirical), is to update existing ground-motion models for shallow crustal earthquakes in active tectonic regions derived from recorded strong motion data. The NGA-E Project consists of a set of 8 Tasks that are guided by 6 Working Groups, listed in Table III-1, which shows the relationships among them.

SCEC scientists participated in almost all of the tasks and working groups listed in Table III-1. Strong motion simulations by SCEC scientists using validated broadband ground motion simulation techniques were used to constrain features of the NGA-E attenuation models that are poorly constrained by currently available strong motion data, including rupture directivity effects, footwall vs. hanging wall effects for dipping faults, depth of faulting effects (buried vs. surface rupture), static stress drop effects, and depth to basement and basin effects.

Larger imageFigure III-15. Validation of the URS (Graves) broadband simulation procedure against recorded ground motions from five earthquakes. Goodness-of-fit is indicated by lack of trends in residuals against distance, magnitude and the directivity parameter Xcos(Θ).

Larger imageFigure III-16. Magnitude scaling of spectral acceleration for strike-slip earthquakes assuming constant stress drop scaling, normalized at M 7, compared with the Sadigh et al. (1997) empirical model.

Examples of SCEC products for NGA-E are shown in Figures III-15 and III-16. Figure III-15 shows the results of extensive validation of a broadband simulation procedure against the recorded strong ground motions of five large earthquakes. The procedure was tested by examining residuals as a function of distance, magnitude, and directivity parameter for a wide range of periods. Figure III-16 shows the use of three broadband simulation procedures, including two from SCEC (UNR and URS), to model the magnitude scaling of ground motion response spectra for a range of periods.

Implementation of Research Products in Earthquake Engineering. NGA products will fulfill a clearly stated need of the industrial sponsors of PEER-LL (Caltrans, the California Energy Commission, and PG&E) for improved ground-motion prediction models. Potential user organizations include these sponsors and organizations (including ATC, BART, BSSC, CEA, CSSC, CUREE, DOE, DSOD, DWR, EBMUD, FEMA, FERC, LADWP, MAE, MCEER, NRC, NEES, OES, PEER, SCE, SEAOC.) that have an interest in improved earthquake hazard assessment and/or actively use attenuation relations in earthquake engineering practice.