Four-Dimensional Rupture Processes of Deep-Focus Earthquakes Near Japan

Abstract:

Deep-focus earthquakes, occurring at depths greater than 300 km, have remained enigmatic since their discovery. Although mechanisms such as transformational faulting, thermal runaway, and dehydration embrittlement have been proposed to explain the occurrence of these earthquakes, discriminating between these different mechanisms using source observations has remained a challenge. In this study, we use a dense network of seismometers in Japan (Hi-net), an improved 3D velocity model of East Asia (EARA2014), and the back-projection method to produce 4D source images of deep-focus earthquakes within the Japan, Kuril, and Izu-Bonin subduction zones. We focus on imaging smaller events (M_w < 7) with higher occurrence rates to understand the relationships between deep-focus earthquakes and the diverse properties of the three subduction zones (e.g., slab age, subduction rates, and obliquity). Additionally, our ability to image deep-focus earthquake ruptures in three spatial dimensions clarifies the locations of these ruptures with respect to the slab and background seismicity, providing valuable constraints on the physical mechanisms controlling these earthquakes. This may not only improve our understanding of deep-focus earthquakes, but also help illuminate slab structure and subduction zone dynamics.