A BASIC INTRODUCTION TO QUANTITATIVE SEISMIC HAZARD ASSESSMENT

Abstract

We provide an overview of some of the issues that need to be considered in the context of quantitative seismic hazard assessment. To begin with, one needs to inventory and characterize the major faults that could produce earthquakes that would impact the region of interest. Next, one needs a seismographic network that continually records ground motion throughout the region. Data from this network may be used to assess and locate seismicity, calibrate ground motion simulations, and to conduct seismic early-warning experiments. To assess the response of engineered structures to strong ground motion, seismographs should also be installed at various locations within such engineered structures, e.g., on bridges, overpasses, dams and in tall buildings. The ultimate goal would be to perform 'end-to-end' simulations, starting with the rupture on an earthquake fault, followed by the propagation of the resulting seismic waves from the fault to an engineered structure of interest, and concluding with an assessment of the response of this structure to the imposed ground motion. To facilitate accurate ground motion and end-to-end simulations, one needs to construct a detailed three-dimensional (3D) seismic model of the region of interest. In particular, one needs to assess the slowest shear-wave speeds within the sediments underlying the metropolitan area. Geological information, and, in particular, seismic reaction and refraction surveys are critical in this regard. In the context of end-to-end simulations, detailed numerical models of engineered structures of interest need to be constructed as well. Data recorded by the seismographic network and in engineered structures after small to moderate earthquakes may be used to assess and calibrate the seismic and engineering models based upon numerical simulations. Once the seismic and engineering models produce synthetic ground motion that match the observed ground motion reasonably well, one can perform simulations of hypothetical large earthquakes to assess anticipated strong ground motion and potential damage. Throughout this article we will use the Los Angeles and Taipei metropolitan areas as examples of how to approach quantitative seismic hazard assessment.