[S-CG46] スラブ内地震とその発生メカニズム

[SCG46-P04] Rheological segmentation of the Cocos slab and its relation with the 2017 M8.2 Tehuantepec earthquake

*Marina Manea^1,2、Vlad Constantin Manea^1,2、Shoichi Yoshioka^2,3、Erika Jessenia Moreno²、Nobuaki Suenaga² (1.Computational Geodynamics Laboratory, Centro de Geociencias, Universidad Nacional Autónoma de México, Campus Juriquilla, Querétaro, 76230, México、2.Research Center for Urban Safety and Security, Kobe University, Kobe 657-8501, Japan、3.Department of Planetology, Graduate School of Science, Kobe University, Kobe 657-8501, Japan)

キーワード：Subduction, 2017 Mw8.2 Tehuantepec earthquake, numerical modeling, slab segmentation

Tectonic plates bend and deform when approaching a subduction zone, creating intense faulting and highly variable stress and strain fields across short distances inside the slab. In September 2017 a large M_w8.2 intraslab normal fault earthquake occurred in southern Mexico, with an epicentral area located within a seismic gap where no megathrust earthquakes occurred in more than a century. Despite the relatively young and hot Cocos plate, this seismic event ruptured almost the entire slab below the brittle-ductile transition zone that normally limits the depth extent of such events. Here we present an updated high-resolution thermomechanical model of spontaneous subduction for this area where bending-induced brittle and ductile deformation and grain plate damage are considered. Modeling results show that the 2017 M_w8.2 Tehuantepec normal fault earthquake occurred in a hydrated region (chlorine stability field) located in the lithospheric mantle at the transition limit between the brittle and ductile regimes. Moreover, the earthquake rupture orientation is consistent with a region where a clear localized shear band of reduced effective viscosity is obtained. We propose that this intraslab event originated from dehydration embrittlement and propagated in the ductile portion of the slab by a thermal runaway mechanism.