Events

Wednesday, February 17, 2016 -
4:00pm to 5:00pm
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MIT, 54-915, 21 Ames St., Cambridge

MIT EAPS Departmental Lecture Series

Marine Denolle, Assistant Professor of Geophysics, Harvard University, will discuss "From Small to Large Earthquake Ruptures: A Self-Similar Process?" Understanding of earthquake source processes across multiple scales is fundamental to accurately assessing seismic hazard of great earthquakes. Can we distinguish physical processes of large ruptures from those of the more frequent smaller earthquakes? Earthquakes are self-similar if their fault geometry, source duration, and slip follow known scaling relations that preserve the shape of the source time (or slip-rate) function and its amplitude spectrum. Self-similar earthquakes have constant static stress drop and ratio of radiated energy ER to moment M0 (scaled energy). The most common source time function, or spectral shape, only captures a single time scale, the duration of the earthquake. We find instead that two time scales better explain the source-time function of the large earthquakes. We analyze the spectral shape from over 1000 shallow thrust earthquakes of magnitude 5.5 and above recorded on the Global Seismic Network. The scaling of earthquake duration with earthquake size varies between small and large earthquakes in a way that is well explained by variable fault geometry. We investigate the possible mechanism for the second and shorter time scale that strongly alters the spectral shape, and by doing so violates the principle of self similarity. Over all, both scaled energy and stress drop remain constant with earthquake size, but the mechanisms preserving them are not self similar.

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