12:00 PM - 12:50 PM
James Dolan - USC
On the constancy (or not) of fault slip: Potential controls, implications for seismic hazard and plate boundary mechanics, and the need for systems-level analysis
There is mounting evidence 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 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 that I will discuss in this talk suggest the coordinated waxing and waning of slip on mechanically complementary regional fault systems. Although a thorough understanding of both the causes and generality of such emergent phenomena is of basic importance for fault mechanics and earthquake physics, as well as for more accurate assessment of seismic hazard, our ability to evaluate the importance of these behaviors has been severely data limited, demonstrating the necessity of documenting additional examples of incremental fault behavior. In addition to discussing examples of potentially coordinated fault system behavior from southern California and New Zealand, I will describe several potential mechanisms that have been proposed to explain such behavior, including possible temporal variations in fault strength, which in kinematically complex fault systems may result in the weakest part of any system accommodating faster-than-average rates while mechanically complementary parts of the system move more slowly, and potential variations in local plate boundary rate. These results reinforce the need for system-level analyses of incremental fault slip patterns in efforts to more fully understand the controls on earthquake occurrence, with obvious implications for everything from seismic hazard assessment (including the “P” word) to plate boundary mechanics to the proper interpretation and use of both geologic and geodetic rate data.
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