Controls on Earthquake Rupture and Triggering Mechanisms in Subduction Zones

Andrea Llenos, Ph.D., 2010
Jeffrey McGuire, Advisor

This thesis investigates earthquake rupture and triggering in subduction zones using earthquake observations, statistical and physical modeling.   Comparison of rupture characteristics of M≥7.5 earthquakes with fore-arc structure suggests that frictional heterogeneities (asperities) primarily control the extent of large earthquakes.  To identify stress accumulation on the megathrust that could cause an asperity to rupture, this thesis develops a new method to detect space-time variations in stressing rate from earthquake catalogs, based on observations that strain transients due to aseismic processes such as fluid flow or slow slip trigger seismicity, often as swarms.  These swarms are modeled with two approaches for investigating driving mechanisms in catalogs: the stochastic Epidemic-Type Aftershock Sequence model [Ogata, 1988] and the rate-state friction model [Dieterich, 1994].  These approaches are combined into a model accounting for seismicity rate variations due to both aftershocks and aseismic processes, which is implemented in a data assimilation algorithm to detect transients in earthquake catalogs.  The technique is evaluated with a synthetic test and applied to the Salton Trough in southern California and the Hokkaido corner in northeastern Japan.  The algorithm successfully identifies aseismic transients in these multi-decade catalogs and may ultimately be useful for mapping spatial variations in frictional conditions on the megathrust.