SEISMIC OBSERVATIONS AT THE YAP-ISLANDS AND THE NORTHERN YAP-TRENCH

We conducted two seismic surveys in the Yap region to investigate tect onic activity in this area. One was conducted in the northern Yap Tren ch for ten days using ocean bottom seismometers, the other was conduct ed on the Yap Islands for eight months using a small array. From these observations we,detected many earthquakes beneath the Yap region and found a characteristic pattern of seismicity. Many earthquakes occurre d in the inner trench slope, no seismicity was observed in the axial r egion of the trench, and a few earthquakes occurred in the outer trenc h slope. This pattern is similar to the typical pattern in active subd uction zones. This result indicates that the Yap Trench is still activ ely subducting. We did not detect earthquakes deeper than 40 km during the observations.