Displaying the Structure and Rheological Properties of a Fault Zone in the Characteristics of Background Seismicity

Spatial heterogeneity of structural and rheological properties of a fault is one of the key factors determining the dynamics of its deformation. The paper analyzes spatial and temporal patterns of seismic localization in several segments of the San Andreas fault zone. Groups of background and clustered events are distinguished. It is shown that background events exhibit structural features of the fault. Asperities in the fault plane appear as dense clusters of background events. Foci of strong earthquakes with magnitudes exceeding the maximum magnitude of background events 1.5–2 times completely rupture at least one contact spots. The fault area located between the asperities controls the slow postseismic slip and, consequently, postseismic aftershock activity. The number of aftershocks is maximal at the boundary of the earthquake's focal area and decreases monotonously with distance from the hypocenter. In the area between the asperities, the speed of aftershock migration is 0.01–10 km/day.