1/25/2017 - Why are slow earthquakes slow and what does chunky peanut butter have to do with it?

Information:

12:00 PM - 12:50 PM
Geology 1707

Presented By:
An Yin - UCLA

Abstract

Why are slow earthquakes slow and what does chunky peanut butter have to do with it?

Deep (20-45 km) slow earthquakes are commonly referred to as slow-slip events (SSEs). They occur over durations of a few days to a few years with quasi-periodicities of weeks to years. Despite intense studies in the past decade, the physical control on recurring slow-slip events remains poorly understood. In this talk, I will present a new theoretical treatment that invokes a viscoplastic shear zone bounding an elastic overriding plate above and a rigid underthrusting plate below. The new model is inspired by the observation that quartzo-feldspathic mylonites that were formed at similar pressure and temperature conditions are composed of mixtures of cataclastically deformed feldspar and crystal-plastically deformed quartz. The mechanical property of such shear zones is similar to a chucky peanut butter: brittlely fragmented nuts embedded in an oily ductile medium; spreading the peanut butter (i.e., initiating viscous flow) requires the spreading force to exceed the yield strength of the peanut butter. Motion on such a shear zone, with a stepwise increase in yield strength due to shear-zone healing between slow-slip events, reproduces geodetically determined slow-slip histories. Comparing model predictions with observations yields key constraints on the rheological parameters of the subduction zones that host slow earthquakes.

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