EAPS Department Lecture Series - Marine Denolle, Harvard University

Marine Denolle, Assistant Professor of Geophysics, Harvard University
Wednesday, February 17, 2016 - 4:00pm to 5:00pm

"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.

About the Speaker

My research focuses on earthquakes and the hazards they pose to population. My PhD research focused on characterizing seismic hazard using the ambient seismic field to construct the Earth's response to impulse forces. I build large virtual earthquakes with the ambient noise Green's functions and local surface-wave excitation, and this allowed me to investigate long period seismic amplification in urban areas such as Los Angeles and Tokyo, and developed a new approach to ground motion prediction. Currently, I have strong research interest in investigating earthquake source processes. The physics of dynamics controls the earthquake energy partitioning, which I investigate from the numerical and the observational side.

About the Series

Weekly talks given by leading thinkers in the areas of geology, geophysics, geobiology, geochemistry, atmospheric science, oceanography, climatology, and planetary science.