天然地震形成的一种机制:地壳结构不稳定性

Abstract

Regional crustal structure instabilities are potentially a significant cause of earthquakes, although current research focuses on other causes such as interactions between tectonic plates and the existence of fluids or faults. The Jiashi area, located at the junction of the Tarim block, the Tianshan orogenic belt, the West Kunlun orogenic belt, and the Pamir syntax, is subject to frequent earthquakes. Wide-angle reflections and refractions and near-vertical seismic reflection profiling data show that the crustal structure of the Jiashi area bears a special instability. The velocity distribution at subsurface depths above ~75 km suggests that the crust is structurally complex and hosts a number of high-and low-velocity blocks. Near-vertical seismic reflection profiles show detailed structural characteristics at a depth of 20 s two-way travel time. Sedimentary cover has well-layered reflections, and there is a stable zone highlighted by Reflectors C and D below the unstable zone of Reflectors A, B and E. A model of the crustal structure instability of the Jiashi area has been established, in which an unstable belt is formed by stacking a combination of high-and low-rigidity blocks that are correspondingly represented by high-and low-velocity blocks. They are hosted in the crust, within the stability belt of Reflectors C and D. The structural instability is aided by regional compression and deep crustal faults that intensify regional seismicity. Crustal structural instabilities also exist in the Japanese archipelago and Erdos Basin.