Evaluating Ground Motion Predictions of Usgs 3d Seismic Model of the San Francisco Bay Area with Broadband Seismograms

Evaluating Ground Motion Predictions of Usgs 3d Seismic Model of the San Francisco Bay Area with Broadband Seismograms (left) Snapshot of vertical component dis- placement for an earthquake near Glen Ellen with BDSN and USArray broadband stations (green triangles). (right) Comparison of observed (blue) and computed (red) three-component seismograms at stations BKS (Berkeley, top) and JRSC (Stanford, bottom).
The USGS (Menlo Park) developed a three-dimensional (3D) geologic and seismic model of the greater San Francisco Bay Area for the purposes of computing earthquake ground motions. This model was used to compute scenario ground motions for the 1906 San Francisco [Aagaard et al., 2008b], 1989 Loma Prieta [Aagaard et al., 2008a] and a suite of Hayward Fault earthquakes [Aagaard et al., in press]. While scenario ground motion calculations are important for investigating the amplitude, duration and variability of motions from large damaging earthquakes, the accuracy of such predictions depends on the accuracy of the 3D model. We evaluated the USGS 3D model of the Bay Area by computing predictions of broadband waveforms for 12 moderate (Mw 4-5) earthquakes and comparing them to the observed waveforms [Rodgers et al., 2008]. Calculations were performed using WPP (an elastic finite difference code developed at LLNL) on massively parallel computers. Data were obtained from IRIS for Berkeley Digital Seismic Network (BDSN) and USArray broadband stations. The figure below shows a snapshot of the vertical component displacements for an earthquake near Glen Ellen (Sonoma County). Also shown is the comparison of the observed (blue) and computed (red) three-component seismograms at two stations: BKS (Berkeley) and JRSC (Stanford). Note that the motions at BKS are more complex and longer duration due to basin propagation effects from the San Pablo Bay, however the 3D model predicts this energy quite well. The motions at JRSC are simpler and the 3D model predicts the weaker late arriving energy on the transverse (T) component. This analysis found that the USGS 3D model could predict the amplitude, duration and wave-form shapes of moderate earthquake ground motions quite well however we did find that phase delays reveal that shear velocities in the model were too fast. This information was used to revise the model for subsequent ground motion modeling.
</p><p>Aagaard, B., T. Brocher, D. Dreger, A. Frankel, R. Graves, S. Harmsen, S. Larsen, K. McCandless, S. Nilsson, N. A. Petersson, A. Rodgers, B. Sjogreen and M. L. Zoback, (2008b). Ground motion modeling of the 1906 San Francisco earthquake II: Ground motion estimates for the 1906 earthquake and scenario events, Bull. Seismol. Soc. Amer., 98, 1012-1046
</p><p>Rodgers, A., A. Petersson, S. Nilsson, B. Sjogreen and K. McCandless (2008). Broadband Waveform Modeling of Moderate Earthquakes in the San Francisco Bay Area To Evaluate the USGS 3D Seismic Velocity Model, Bull. Seismol. Soc. Amer., 98, 969-988
</p><p>Acknowledgements: This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore Nation</p>


No comments yet.



Welcome to the IRIS Image Gallery – a diverse collection of photographs and visuals that encompass the range and breadth of seismology and the seismological community.

Please browse through our albums. These low and medium-resolution images can be freely used for personal and educational/academic purposes, but we request you recognize the image contributor by including in your product or presentation the credit displayed with each image.

More information is available in the Image Use Agreement.

If you have any comments, questions, or suggestions related to the IRIS Image Gallery, you can send them to gallery@iris.edu.

Photo info

Popular tags