Regional and Teleseismic Constraints on Intermediate-Depth and Deep focus Earthquake Mechanisms

Abstract:

The systematic behavior of earthquake rupture as a function of earthquake magnitude and/or tectonic setting is key in our understanding of the physical mechanisms involved during earthquake rupture. Following the dip of an idealized subducting plate, we observe a great diversity of earthquake rupture behavior, slow tsunamigenic near the trench, high frequency radiation in the seismogenic zone, tectonic tremor and finally intermediate-depth and deep focus earthquakes. Although all these events have a common source mechanism, predominantly they all represent shear slip along a fault, both static and dynamic source parameters may vary as a function of depth. We will show here a thorough analysis of global and regional records of intermediate-depth and deep earthquakes to try and better understand the mechanisms that may help explain the differences between these deep earthquakes and shallow seismicity in a subduction setting. We present results for earthquake location, source duration/corner frequencies, stress drops and radiated energies for earthquakes at the global scale, intermediate-depth earthquakes in Alaska and South America, and an intraplate earthquake in North America. Some differences between different subduction zones are evident, although there is no clear correlation with plate age. Some of the differences can be explained by local control of the geometry of the slab. Several contrasting behavior is also observed between intermediate-depth earthquakes in Alaska and Southamerica, and also when comparing non-subduction related earthquakes. We discuss how some of the proposed mechanism for deep earthquakes, agree or not with the observed source parameters.