Analysis of global positioning system data shows that the rate of crustal deformations in the Tokai region of Japan, a seismic gap area, changed over the past 18 months. Kalman filtering analysis shows aseismic slip on the plate boundary in the western Tokai region centered on Lake Hamana, adjacent to the anticipated Tokai earthquake source area. The cumulative moment magnitude reaches 6.7 in June 2002 with a relative slip increase northeast of Lake Haman from January 2002. An existence of aseismic slip in the western Tokai supports the hypothesis of a silent event as the cause of uplifting several days before the 1944 Tonankai earthquake.

Analysis of Global Positioning System (GPS) data shows transient crustal deformation in the Boso peninsula, central Japan, for about fifty days from October 2002. The southeastward horizontal displacements detected suggest the occurrence of interplate aseismic slip between the Philippine Sea plate and the North American plate, six years after a similar event in 1996. We estimate an area of aseismic slip with moment magnitude (Mw) 6.6 centered off the Boso peninsula, adjacent to associated seismic activity. Slip evolution of the 2002 aeismic slip started on October 4 and migrated from north to south for about ten days, followed by gradual subsidence and restarting of slip which lasted until ∼December 2, propagating more southward. Similarities in focal area and slip process between the 1996 and the 2002 events suggest the Boso aseismic slips as characteristic silent earthquakes, together with the repetitive occurrence of seismic swarm in a similar region every six to seven years. A more tightly coupled southern area that did not release enough energy in the 1996 event may have caused the differences in magnitude, central slip area, and duration between the 1996 and the 2002 events, if the hypothesized recurrence interval for strain accumulation is true, based on swarm seismicity.

Abstract.Intense crustal activity including earthquake In this study, we show the crustal deformation observed at the permanent GPS sites and construct a model based on the observed displacements. The dates and times in this article are based on Universal time(UT).

The permanent Global Positioning System (GPS) array in Japan detected coseismic and postseimic deformation of the 2003 Tokachi-oki earthquake (M w 8). We estimate the time evolution of its postseismic slip, together with its coseismic slip distribution. The result shows that the postseismic slip has been occurring mainly in an area adjacent to the coseismic slips, propagating to the northeast and southwest. This suggests that, as of March 6, 2004, the postseismic slip of the strongly coupled area neighboring the coseismic rupture partly released seismic moment, equivalent to an earthquake of M w 7.8.

Analysis of Global Positioning System (GPS) data has shown transient crustal deformation in the Bungo channel, in southwestern Japan, since late August 2003, six years after a similar event in 1996–1997. Considering the southeastward motion at many of the GPS sites and the similarity between the 1996–1997 and 2003 events, it is highly likely that the transients were caused by aseismic interplate slip between the Philippine Sea plate and the Amurian plate. The 2003 aseismic slip is estimated beneath the Bungo channel and the relative slip increased with time on the west side, with a moment magnitude (Mw) amounting to 7.0. In contrast to the gradual subsidence of low‐frequency earthquakes which began and ended in coincidence with the 2003 event, the 2003 transient crustal deformation proceeded at a roughly constant rate until the end of November 2003. The Bungo channel area may release energy accumulated from the subduction of the Philippine Sea plate by aseismic slip.