Geological Sciences Theses and Dissertations

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Characterization of Aftershock Sequences from Large Strike-Slip Earthquakes Along Geometrically Complex Faults
(University of Oregon, 2018-09-06) Sexton, Emily; Thomas, Amanda
Large earthquakes often exhibit complex slip distributions and occur along non-planar faults, resulting in variable stress changes throughout the fault region. To better discern the role of stress changes and fluid flow on aftershock sequences, we examine areas of enhanced and reduced mean stress along the structurally complex strike-slip faults that hosted the 1992 Landers, 2010 El-Mayor Cucapah, and 2016 Kumamoto earthquakes. We characterize the behavior of aftershock sequences with the Epidemic Type Aftershock-Sequence Model and use the Maximum Log Likelihood method to determine the optimal set of ETAS parameter values along each fault. This study indicates that extensional areas experience greater secondary aftershock triggering and a higher density of aftershocks directly following the mainshock, which could be attributed to fluid influx. However, our results also highlight some shortcomings of the ETAS model, including high parameter correlation, and influence of catalog size and magnitude cutoff on parameter estimations.