Ground Motion Prediction Using Virtual Earthquakes

Stanford University, Stanford CA

Investigators

Abstract

This research is motivated by the fact that there exist few quantitative measurements of the strength of shaking close to the epicenters of large earthquakes. Information on how strong the ground will shake is critically important because structural engineers use this information to design earthquake-resilient structures. We will further develop and apply a new approach for predicting the strength of shaking in future earthquakes that doesn?t rely on recording earthquakes directly, but uses the ambient seismic field for that purpose. The ambient field consists of seismic waves in the solid Earth that are generated by wave action in the ocean. We can use these to develop ?virtual earthquakes? using ground motion sensors deployed at a location on the Earth where we expect future earthquake rupture to occur. Virtual earthquakes quantify the shaking that will occur when such an earthquake happens. Specifically, our research will advance this method by improving the calibration of the strength of shaking, applying it to areas of particular concern where we expect the shaking to be strong and potential problematic for buildings, and by extending the technique to shorter periods, which are important for earthquake-resistant design. Ground motion prediction is an area of key importance for earthquake seismology as it is where the multi-disciplinary endeavor of understanding earthquake behavior meets the societal concern of mitigating earthquake losses. We propose to improve and apply a new method for predicting spatial variations in ground motion using the ambient seismic field to construct virtual earthquakes. The virtual earthquake approach is possible because the waves that comprise the ambient field, and the waves in large earthquakes, propagate through the same complex geologic structure and are affected by it in the same way. While this approach does not account for nonlinear effects, and does not address earthquake source characterization, it does provide a genuinely new way to predict the complex linear wave propagation effects that strongly influence the intensity of earthquake shaking. The proposed research seeks to improve the accuracy and applicability of the virtual earthquake approach by: (1) improving the reliability of measured amplitudes, (2) exploring complex basin effects that have not been incorporated into ground motion prediction equations, and (3) pushing the technique to shorter periods that better overlap the period range of primary earthquake engineering concern. Continued development of the virtual earthquake approach for ground motion prediction is essential for it to realize its full potential. We will continue our collaboration with scientists at
the Earthquake Research Institute at the University of Tokyo and at ISTerre, Grenoble. We will also work to develop an emerging collaboration with scientists and engineers at Universidad Nacional Autonoma de Mexico, in Mexico City.