Large earthquakes occur every year, devastating communities around the world. In the past ten years, earthquakes in India, Turkey, Taiwan, Japan, and the United States have caused billions of dollars of damage and thousands of casualties. Producing appropriate earthquake ground motion time histories, a necessary step for designing earthquake resistant structures, requires an understanding of the earthquake source in addition to an understanding of the wave propagation, crustal geology, and the soil conditions at the site. As a result, earthquake engineering is an interdisciplinary field combining expertise in structural engineering, geotechnical engineering, seismology, and geology.
The proposed collaborative work bridges the gap between engineering and seismology in the numerical modeling of moderate magnitude earthquakes. The intellectual merit of the proposed work is to take moderate-sized earthquakes in the magnitude (M) range from 4 to 5 to understand regional wave propagation, earthquake sources, and local site effects with the long term goal of extrapolating these results to large earthquakes and strong ground motions for that region. By carefully accounting for and validating the source, path, and site effects in a moderate earthquake, we hypothesize that we can .qualitatively. predict the characteristics of ground response for large earthquakes. Our second hypothesis is that including detailed soil conditions in a crustal model will result in more accurate simulated ground motions (accurate to a higher frequency) than is currently common. Our research plan consists of four specific tasks: 1) Determine the source mechanisms of three recent moderate earthquakes each in the San Francisco Bay and in the Osaka Bay regions. 2) Develop and validate a crustal model for wave propagation for each study region: San Francisco Bay and Osaka Bay. 3) Evaluate effect of the soil layer by assessing predicted waveforms at Vertical Arrays. 4) Validate method for large earthquakes. The research team is multidisciplinary and consists of experts in seismology and geology/geotechnical earthquake engineering. Baise is a geology/geotechnical earthquake engineer, with experience studying wave propagation and site effects. Baise will lead the project to ensure that the result is of engineering use and importance. Dreger and Abercrombie are earthquake seismologists and will provide guidance as well as active participation in the areas of source characterization (Abercrombie and Dreger) and wave propagation techniques (Dreger).
The broader impact of this study is three-fold. First, the proposed method can be used in areas of low seismicity to predict regional earthquake effects for large earthquakes. The proposed research will therefore improve ground motion simulations and reduce seismic losses. Secondly, the effort will broadly impact the educational environment at all three universities involved when seismologists and engineers are brought together in research and in a classroom. Finally, through continuing efforts of the PI both graduate and undergraduate students from underrepresented groups will be recruited to participate in this research.
