Relation between continental strike‐slip earthquake segmentation and thickness of the crust

Abstract

High‐resolution maps of large continental strike‐slip earthquake surface ruptures show that they are formed of fault segments. These segments are bounded by fault bends, step overs, or combinations of the two. The lowest limit in size for such segments may not be relevant in the understanding of earthquake mechanics, as it pertains to the granular properties of fault zones. The maximum limit in segment length, however, is important as it is directly relates to the maximum extent of seismic rupture. To measure the length of the segments, a new quantitative method based on piecewise linear fitting is developed and is used to automatically retrieve segments from earthquake rupture maps. Next, this approach is tested against a set of ten continental strike‐slip earthquake ruptures derived from similar, high quality maps. The test suggests that segments have a maximum length of ∼18 km, independent of regional tectonic setting. Slip‐inversions for earthquakes, based on seismological and/or geodetic data, most often are not unique and can show some variability even for one particular event. Some basic characteristics, however, such as total moment release or general source geometry, seem to persist that are relevant to earthquake mechanics. Measurements of the maximum horizontal extent of individual slip‐patches derived from seismic source inversion for strike‐slip ruptures show that their strike dimension does not increase infinitely with magnitude, but instead reaches a maximum value of ∼25 km. These two independent lines of observations, complemented by earlier data and analog experiments, suggest that it is the thickness of the seismogenic crust that controls the structural scaling of the length of seismic segments, and that it is independent of the ultimate size of individual earthquakes.