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What mechanism enables intermediate depth earthquakes? - Insights from seismic imaging and modeling

As part of the SWaMMIS-project (Subduction zone Water and Metamorphism: a Modeling and Imaging Study) we want to better understand the mechanisms of intermediate depth earthquakes and their relation to dehydration reactions in subducting slabs. In the project, I am responsible for high-resolution imaging and waveform modeling of subduction zones. The two main candidate mechanisms for intermediate depth earthquakes are dehydration embrittlement and localized thermal runaway, but it is not clear whether one mechanism dominates over the other, whether the two mechanisms can operate concurrently, and whether they may be coupled. To help answer these and related questions regarding the distribution and causes of intermediate-depth seismicity, we are building a catalogue of high-resolution images from migrated receiver functions and relocated earthquakes for a range of subduction zones worldwide and interpret differences. I present an example from the Hellenic Subduction Zone in Greece, where I have conducted local seismic traveltime tomography to relocate earthquakes. I present my first attempts at implementing a modeling framework based on the SEM-FK (Spectral element/frequency-wavenumber) hybrid method to generate full synthetic waveforms for local and teleseismic earthquakes sampling detailed subduction zone structure. These will help us to quantify migrated receiver function images and the location of intermediate depth earthquakes. Furthermore, it gives us the ability to quantify errors of the migrated receiver function method and explore parameter ranges for different subduction zones, which in return should let us specify where the proposed earthquake mechanisms may occur.