Abstract:
Oceanic transform faults that accommodate strain at mid-ocean ridge offsets represent a
unique environment for studying fault mechanics. Here, I use seismic observations and
models to explore how fault structure affects mechanisms of slip at oceanic transforms.
Using teleseismic data, I find that seismic swarms on East Pacific Rise (EPR) transforms
exhibit characteristics consistent with the rupture propagation velocity of shallow aseismic
creep transients. I also develop new thermal models for the ridge-transform fault
environment to estimate the spatial distribution of earthquakes at transforms. Assuming a
temperature-dependent rheology, thermal models indicated that a significant amount of slip
within the predicted temperature-dependent seismogenic area occurs without producing
large-magnitude earthquakes. Using a set of local seismic observations, I consider how
along-fault variation in the mechanical behavior may be linked to material properties and
fault structure. I use wide-angle refraction data from the Gofar and Quebrada faults on the
equatorial EPR to determine the seismic velocity structure, and image wide low-velocity
zones at both faults. Evidence for fractured fault zone rocks throughout the crust suggests
that unique friction characteristics may influence earthquake behavior. Together, earthquake
observations and fault structure provide new information about the controls on fault slip at
oceanic transform faults.
