Imaging the Crustal Interfaces Along the Ryukyu Arc‐Trough System Using Precursors to Teleseismic sP and pP

Abstract

AbstractThe Ryukyu arc (RA)‐trough system, which is uniquely characterized by the Okinawa trough (OT) experiencing an early stage of continental disintegration, provides an ideal location to study continental rifting processes. However, the crustal structure beneath this region is not well resolved due to limited seismic surveys and station coverage. Here, by taking advantage of the well‐distributed intermediate‐depth earthquakes beneath the RA, we invert for the crustal structures beneath the RA‐trough system from the depth phases pP and sP and their precursors, underside reflected from the Moho and intracrustal interface. Along the RA, the Moho depth varies from 22 to 27 km indicating a thinner continental crust. Beneath the OT, the crustal thickness gradually decreases from 26 km to 15 km toward the south, which correlates with the trough rifting rates. At the south continental shelf, a thick crust with Moho depth of 29 km presents. In the transition region from the middle OT to the continental shelf, we observe multipathed precursors, which can be modeled with a 10 km Moho offset. The offset occurs in a gentle slope with angle of 27° dipping to the northwest, which supports a slow spreading process across the boundary between the middle OT and the continental shelf.