Systematics of the Fault-Zone Seismogenic Width of Strike-Slip Plate Boundaries

Strike-slip plate boundaries commonly exhibit elevated seismicity that tapers with distance from the area of high strain about the plate boundary faults. Although this typical seismicity pattern is well documented for the entire seismogenic depth, the variation of the fault-zone seismogenic width (FZSW) with depth is unclear. Here, we examine earthquake catalogs along twenty-three segments of four major strike-slip plate boundaries: the San Andreas, the Dead Sea, the North Anatolian, and the East Anatolian faults. For each segment catalog, we calculate the seismicity densities normal to the faults and stack events on one side of the fault. We define the FZSW as the distance of 30% of the peak density from the fault. First, we calculate the FZSW represented by the entire catalog. Then, to examine the influence of distinct events, we compare the density pattern of declustered catalogs with clustered events. This analysis reveals that the declustered catalog presents a systematic density decay pattern, which can be diluted by large events that trigger aftershocks at nearby faults. We exclude all aftershocks and measure the FZSW at two depth intervals with respect to the median depths of each fault segment. Our analysis reveals a general decrease of the seismogenic width with depth from 5 to 13.5 km in the shallow sections to a systematic width of 3 to 5 km. Segments with a width > 5 km at both depth intervals indicate fault segmentation or activity on concealed faults. This study provides an independent measurement of the seismogenic damage zone around strike-slip faults and is useful for fault and seismic hazard modeling.