ON THE CONSTANCY (OR NOT) OF FAULT SLIP: POTENTIAL CONTROLS, IMPLICATIONS FOR SEISMIC HAZARD AND PLATE BOUNDARY MECHANICS, AND THE NEED FOR SYSTEM-LEVEL ANALYSIS

Mounting evidence suggests that the occurrence of large earthquakes on both single faults and fault systems is not a random process. Earthquakes often cluster in both space and time, leading to episodic increases or decreases in slip that can span multiple earthquake cycles and tens of meters of fault slip. Comparisons between geodetic and longer-term geologic rates demonstrate that such clusters and lulls may in some instances coincide with transiently elevated or decreased periods of elastic strain accumulation. Moreover, recent observations from several plate boundaries suggest the coordinated waxing and waning of slip on mechanically complementary regional fault systems. In addition to describing examples of potentially coordinated fault system behavior, I will discuss several potential mechanisms that have been proposed to explain such behavior, including possible temporal variations in fault strength, complex kinematic interactions amongst mechanically complementary faults, and potential variations in local plate boundary rate. These results reinforce the need for system-level analysis of incremental fault slip patterns in efforts to more fully understand the controls on earthquake occurrence and patterns of fault displacement through time and space, with obvious implications for everything from seismic hazard assessment to plate boundary mechanics to the proper interpretation and use of both geologic and geodetic rate data.