Date

2019

Document Type

Dissertation

Degree

Doctor of Philosophy

Department

Earth and Environmental Sciences

First Adviser

Meltzer, Anne

Abstract

Our ability to minimize the risks associated with earthquake hazards is directly linked to our fundamental understanding of the causes, processes and dynamics associated with this type of natural event. This dissertation presents my research work towards a better understanding of earthquake and tectonic processes in two distinct settings: the Mid-Atlantic US passive margin and the Ecuador subduction zone.The first part of my dissertation focused in studying intraplate seismicity and crustal structure in the Mid-Atlantic US. Our understanding of the characteristics of and mechanisms responsible for seismicity in passive margins is limited. To assess a plausible mechanism for intraplate seismicity and deformation in the Mid-Atlantic US, I calculated receiver functions to image the crustal structure, and characterized the spatio-temporal distribution of seismicity. Receiver functions imaged a steep gradient in crustal thickness, in the transition from the Coastal Plain-Piedmont into the Valley and Ridge. The spatial distribution of earthquakes coincides with the observed crustal thickness gradient. This suggests that lateral variations in crustal structure, inherited from past orogenic and rifting processes, play a role in the concentration of stress, and the spatial distribution of seismicity.The second part of my dissertation focused on an active tectonic margin. On April 16, 2016, a Mw7.8 megathrust earthquake ruptured a ~100x40km segment of the Ecuador subduction zone. An automatic catalog of 9,036 events was created to analyze the post-seismic activity associated with this large earthquake. Calibrated multiple-event relocations were calculated for M>4 earthquakes. This seismic sequence is dominated by pronounced spatio-temporal clustering in regions that have remained active during the interseismic period and/or experienced slow slip events, repeaters and swarms. The mainshock appears to have induced stress transfer towards the northern 1958 M7.7 rupture area. Event locations show a sharp downdip limit in seismic activity where the slab reaches a depth of ~30km. This suggests a well-defined transition in frictional properties from the seismogenic zone into the conditionally stable downdip region. A better definition of the updip and downdip limits of the seismogenic zone helps to assess which inland population centers may be more affected by large co-seismic slip in the future.

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