Fault-Rupture Hazard Characterization: Applications of Paleoseismic Trenching for Detailed Mitigation Design

Ground rupture caused by an earthquake is a major consideration for the siting of engineered structures and mitigation of existing lifelines that cross active faults. Ready availability of new digital data sources, including digitized mapped fault traces and high-resolution topographic datasets, allows for rapid incorporation of existing information towards evaluation of fault rupture hazard. However, available digital and non-digital fault data generally are not detailed enough for site-specific evaluation and design. Precise information from targeted fault (paleoseismic) trenching provides additional information required for siting and mitigation of critical facilities and lifelines. In addition to defining the locations of active fault strands that can be used to develop set backs for building footprints and mitigation plans for existing structures, paleoseismic trenching can provide vital information on the style, amount, and probability of surface faulting. Trenching of `secondary' faults that are structurally related to underlying, larger faults can provide indirect evidence for the determination of timing and probable fault offset on deeper, often inaccessible (`blind') faults. This paper provides several current applications of paleoseismic trenching performed to address unique project-specific surface-rupture issues and obtain seismic parameters for engineering design.