Triggers, conditions and nature of the seismic rupture. What do we really know about mantle seismicity?
Thomas Ferrand, Freie Universitat Berlin
Most earthquakes occur within subducting oceanic plates. For geometrical reasons, most of the volume affected by large seismic ruptures consists of peridotite. Relying on the comparison of experimental results and natural features, I have shown that the triggering conditions of a large majority of earthquakes are correlated with the destabilization of mantle minerals. Intermediate-depth seismicity (30-300 km depth) is notably characterized by the double seismic structure. I showed that the lower Wadati-Benioff plane is not a dehydration front but the souvenir of the hydration front, and that this seismicity is due to dehydration-driven stress transfers. The latter fundamentally differs from the concept of “dehydration embrittlement”, i.e. fluid-induced. Destabilizations of minerals of the serpentine and talc groups explain most mantle events between 30 and 200 km depth. Deep-focus earthquakes (≥ 300 km depth) are no exception. I will present recent findings that shed new light on their mechanisms. Additionally, I wonder about the nature of the seismic rupture. I try to understand the transient melting and the conditions of efficient melt lubrication. The sliding and associated dynamic rupture propagation depend on the viscosity of the transient magma. Once the rupture has been triggered, the question is how it stops.
Hosts: Doug Wiens and Walid Ben Mansour
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