Earthquake rupture processes in circum-Pacific subduction zones

Subduction zone earthquakes release a majority of the world's seismic energy and can produce devastating tsunamis. Understanding the rupture processes of these earthquakes can lead to more accurate seismic and tsunami hazard assessments for the regions in the circum-Pacific. This dissertation examines variations in subduction zone earthquake processes, focusing on 14 subduction zones around the circum-Pacific. Chapter 2 describes observations of depth dependent earthquake source durations for events in these regions and proposes two end member models, depth dependent stress drop or depth dependent rigidity, to explain the observations. Rigidity estimates calculated from the source durations are among the first estimates of this material property on the subduction zone plate interface. The depth dependent rigidity model is explored further in Chapter 3, as I examine the influence of the material property variations on the anomalous tsunami earthquakes. The 1992 Nicaragua tsunami earthquake is modeled successfully using the regionally appropriate depth dependent rigidity model instead of the commonly used constant rigidity model. Chapter 4 describes my attempt to correlate details in the depth dependent earthquake source durations with subduction zone parameters such as convergence rate, plate age, subducted sediment thicknesses, and plate topography. No correlation between the duration variations and the subduction zone parameters is obvious, potentially because of poor data resolution for subduction zone parameters and scatter in my earthquake datasets. In regions where high quality data exist, it is possible to describe earthquake rupture process variations in terms of variations in the subduction zone structure. Chapter 5 presents detailed earthquake source analyses along with recently available bathymetry data and correlates rupture process complexity with distinct features on the subducting Cocos plate off the western coast of Costa Rica. These projects combine in a multi-scale examination of earthquake rupture processes in subduction zones to suggest both depth dependent and lateral variations that can be tied to material properties and structures within the subduction zone system.