Probabilistic Seismic Hazard Analysis for Ground Shaking

Foreword The purpose of the Delta Risk Management Strategy (DRMS) Initial Technical Framework (ITF) is to guide the analysis of specific technical topics as they relate to assessing potential risks to Delta levees and assets resulting from various potential impacts (e.g., floods, earthquakes, subsidence, and climate change). These ITFs are considered " starting points " for the work that is to proceed on each topic. As the work is developed, improvements or modifications to the methodology presented in this ITF may occur. The effects of earthquakes may be the most significant natural hazard that can impact the Delta levees. In this ITF paper, we describe the approach, methodology, inputs, issues, and project tasks that will be performed to assess the probabilities of the levels and character of earthquake ground-shaking events that will contribute to the risk of levee failure in the Delta. The general approach of performing a probabilistic seismic hazard analysis (PSHA) is standard practice in the engineering seismology/earthquake engineering community (McGuire 2004) and the computations will be state-of-the-art. The PSHA methodology to be used in this study allows for the explicit consideration of epistemic uncertainties and inclusion of the range of possible interpretations of components in the seismic hazard model, including seismic source characterization and ground motion estimation. Uncertainties in models and parameters are incorporated into the hazard analysis through the use of logic trees. A product required of the seismic hazard analysis are the probabilities of occurrence of all plausible earthquake events (defined by their locations, magnitudes, and ground motions). These will be used to develop estimates of risk (defined as the annual probability of seismically induced levee failure) at selected times over the next 200 years The products of the PSHA will include hazard-consistent site-specific acceleration response spectra and time histories at selected levee sites distributed throughout the Delta area and an algorithm that can serve as input to the risk quantification. INTRODUCTION The effects of earthquakes may be the most significant natural hazard that can impact the Delta levees. This is one of several topical area methodology Initial Technical Framework (ITF) papers prepared for the Delta Risk Management Strategy (DRMS) Project that describes an approach to evaluate the risk of failure of the Delta levees under present as well as foreseeable future conditions and to develop a risk management strategy to reduce and manage the risk. In this ITF paper, we describe the approach, methodology, …