부산대학교 도서관

The discovery of slow earthquakes illuminates the existence of a strange depth dependence of seismogenesis, which contradicts the common understanding of smooth brittle/seismic‐ductile/aseismic transition as going deeper into the earth's surface layers. However, within the transitional layer on plate interfaces, observations have clarified slip velocities of slow earthquakes changing from those slower to faster with increasing depth, as described by the "seismogenic inversion layer." We propose a new mechanical model that can consistently explain the classic brittle‐ductile transition and this inversion phenomenon by considering the heterogeneous fault zone composed of brittle blocks in the ductile matrix. The key mechanism is the interplay between the volumetric fraction of brittle blocks and the viscosity of the surrounding plastically deformed matrix, where the former and the latter decrease with increasing temperature. This model is extended to shallow‐slow earthquakes. Our results open a new pathway to infer the deformation mechanisms underlying slow earthquakes. Plain Language Summary: We have believed that the earth's surface is cold and brittle while the interior is warm and soft, and the brittle layer called the seismogenic layer gradually changes to the soft layer, not generating earthquakes, with increasing depth along plate interfaces. However, recent observations show that this change is not actually gradual. Instead, it involves the layer of the reverse tendency that we call the "Seismogenic Inversion Layer (SIL)" that hosts so‐called deep slow earthquakes. To explain this enigmatic phenomenon, we propose a simple mechanical model based on the fundamental laws of rock physics. We find the key mechanism that generates SIL is the change in rock properties with increasing temperature. Given rocks are composed of relatively brittle parts and soft parts, SIL is explained only if we consider the brittle parts shrink and the soft parts become softer with increasing temperature and depth. Key Points: Depth dependence of slow earthquakes is characterized as the seismogenic inversion layer (SIL); not monotonic brittle‐ductile transitionA simple and general physics‐based model is proposed to describe the depth dependence of slow earthquakes with particular attention to SILThe key mechanism is the reduction of both the fraction of brittle blocks and viscosity of plastically deformed matrix in fault zones [ABSTRACT FROM AUTHOR]