[S-CG43] スラブ内地震とその発生メカニズム

[SCG43-P03] A systematic detection of intermediate-depth earthquakes within the Bucaramanga earthquake nest, Columbia

*土山 絢子¹、Frank William¹、Prieto Germán² (1.Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology、2.Departamento de Geosciencias, Universidad Nacional de Colombia, Colombia)

キーワード：subduction zone、intermediate-depth earthquakes

Intermediate-depth earthquakes (70-300 km depth) are generated in a deeper portion of subduction slabs where the extremely high pressures and temperatures make frictional slip unlikely. Seismicity in the deep Earth can provide essential information on the physical processes that control fluid distribution within the mantle, yet the mechanism of intermediate-depth earthquakes is still enigmatic. Under extreme conditions with high pressure and temperature in the subduction zones, three plausible models might explain the rupture process of intermediate-depth earthquakes; (1) dehydration of minerals in the subducting slab along pre-existing faults where dehydrated fluids can easily concentrate (2) dehydration-driven stress transfer where fluid overpressures are unlikely, (3) thermal shear instabilities that account for high-stress drops and repeating earthquakes. Both models essentially depend on the local fluid distribution likely sourced from the subducting slab that controls the kinematic properties and rupture process of the fault and seismicity. The Bucaramanga earthquake nest in Colombia, where intermediate-depth earthquakes are significantly concentrated in both time and space (with a magnitude up to 6). A high-resolution catalog of Bucaramanga seismicity will likely yield key information on the rupture process of intermediate-depth earthquakes.

Here we systematically explore the Bucaramanga seismicity with matched-filtering to construct a high-resolution earthquake catalog. We use continuous-waveform data from 2015 to 2020 recorded on more than 20 seismic stations operated by the Servicio Geológico Colombiano (SGC). In our method, we choose a template waveform in the original event catalog determined by SGC, then detect earthquakes through each template by matched-filter detection. Using all catalog events as templates, we will significantly update the total number of events including smaller earthquakes. Our dense, detailed catalog will provide precise intermediate-depth source information such as magnitude, clustering of events into families, and correlation coefficients, that will allow us to estimate earthquake relocations, earthquake source properties via spectral analysis, and seismic tomography to understand the particular conditions of the intermediate-depth source region.