EAPS

Special Seminar: William Frank (EAPS)
Date Time Location
May 16th, 2017 1:00pm-2:00pm 54-209
"A Multidisciplinary Investigation of the (slow) Grind of Tectonic Release"

A combination of earthquake seismology and geodesy has led to the recent discovery of slow transient deformation in subduction zones and other plate boundaries. Geodetic data have been able to directly constrain the largest of these slow slip events, suggesting a slow rupture that is smooth in both time and space. On the other hand, seismology provides indirect observations of slow slip that highlight a rough and intermittent evolution of slip on the plate interface. I will show here how to reconcile these contradictory observations by exploiting the time history of slow seismicity (tectonic tremor and low-frequency earthquakes) to uncover new geodetic constraints that force us to reconsider the consensus model of slow deformation dynamics.

First, I will show how GPS records between previously identified slow slip events do not represent continuous convergent motion. In fact, this convergence can be decomposed into two distinct regimes of tectonic loading and release. This intermittent release demonstrates that the plate boundary where slow slip occurs can be as strongly coupled as the seismogenic zone and undergoes a cyclic build-up and release of stress over a wide range of time scales. I will then describe the short-period dynamics at the plate interface during a large slow slip event. I show that while the long-period surface displacements suggest a six month duration, motion in the direction of tectonic release only sporadically occurs over <60 days, and its surface signature is attenuated by rapid relocking of the plate interface. These results demonstrate that our current conceptual model of slow and continuous rupture is outdated and is an artifact of low-resolution geodetic observations of a superposition of small, clustered slip events.

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