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2003年12月,在冲绳海槽西南部布设了15台海底地震仪。在10天的被动地震实验中,记录定位到了超过3000次的微震。地震活动的特点表现为在所有仪器的附近始终不断地有小地震发生。除了一群地震位于西南冲绳海槽的南部外(群2),所有的地震活动基本上限制在西南冲绳海槽的中部。地震活动带在梨山断层北东-南西向的延伸带上突然中断。大多数地震沿东-西向正断层排列,显示了冲绳海槽当今活动正断层发生的位置以及它是如何解释冲绳海槽南北向扩张的。根据位于弧后火山痕迹区下方的深地震估计出的纵波速度谱,3～10Hz带宽内低频地震的出现证实了下地壳/上地幔岩浆房的存在。
In December 2003, 15 seabed seismographs were deployed in the southwestern part of the Okinawa Trough. In the 10-day passive earthquake experiment, the records locate more than 3000 microseisms. Seismic activity is characterized by the constant occurrence of small earthquakes near all instruments. Except for a group of earthquakes located in the south of the Southwest Okinawa Trough (Group 2), all seismic activity is basically confined to the middle of the Southwest Okinawa Trough. Seismic activity belt abruptly interrupted on North-East-Southward extension of Lisheng Fault. Most of the earthquakes are aligned along the east-west normal fault, revealing the location of today’s active normal faults in the Okinawa Trough and how it explains the north-south expansion of the Okinawa Trough. According to the P-wave velocity profile estimated from the deep earthquakes beneath the back-arc volcanic trace area, the presence of low crustal / upper mantle magma chambers is confirmed by the occurrence of low-frequency earthquakes within the bandwidth of 3 ~ 10Hz.