Effect of complex fault geometry and slip style on near-fault strong motions and static displacement

Abstract

Although there are many studies that deal with complex slip distribution or rupture propagation on an earthquake fault, they usually regard a fault system as a fault of simple geometry. Actual fault systems have highly heterogeneous slip distribution and very complicated shapes, as is often observed through field surveys of surface breaks. In this study, we synthesize seismograms including static displacement near a fault using the discrete wavenumber method in order to estimate the effects of the above types of fault complexity in a quantitative manner. We introduce a complex slip distribution based on the Nojima Fault associated with the 1995 Hyogo-ken Nanbu earthquake. As a result, we show that strong motions at a frequency of lower than 1.0 Hz are strongly affected by the complexity of the fault geometry, at a scale of not more than several km, rather than the rupture propagation style. Distributions of static displacement fluctuate, depending on the fault geometry characterized by the length of each fault segment. Such small-scale variations in fault geometry (≤1 km) have been mostly ignored prior to this work. Our results also suggest that details of fault segmentation and bending can be determined by dense observations (e.g., GPS or geological surveys) of static displacement near a fault system, indicating the importance of simultaneous studies on static and dynamic near-fault motions.