Tomographic low-velocity anomalies in the uppermost mantle around the northeastern edge of Okinawa trough, the backarc of Kyushu

A simultaneous inversion for three-dimensional velocity structure and hypoc entral parameters is used to determine the tomographic images of the backar c of Kyushu, southwestern Japan. The data used in the imaging are the first arrival times of 2736 local earthquakes recorded at 305 stations in a wide region from western Japan to eastern China. Additional data are provided b y including arrival times of 357 teleseismic earthquakes. We got the high r esolution of the uppermost mantle images for P waves at least in the depth range to 150 km, the latitude range of 30 degrees-34 degrees N and the long itude range of 128 degrees-132 degrees E. Results of inversion reveal a maj or zone of strong low velocity under west off Kyushu Island in the depth fr om 40 km to 100 km. This feature may result from partially melting in relat ion to the upwelling of hot mantle around the northeastern edge of the exte nding Okinawa trough.