Japan, Okinawa: 1966-2018

The Okinawa cluster is named for the island of Okinawa in the Ryukyu Islands. Although there are deeper events in the area, only events with depths less than about 35 km were retained in the cluster. The cluster contains one large event, an Ms 6.5 event on March 2, 1980 to the west of the island that is likely associated with back-arc spreading. All events have depth constraint from arrivals at near- or local-distances, or from teleseismic depth phases in a few cases. Although the setting is broadly oceanic, the Ryukyu Islands are thought to be part of a remannt continental sliver, so it is not so surprising that a crustal model very close to ak135 fits the observed arrival time data well. [...]