Crustal movements around the Beppu Bay area, East-Central Kyushu, Japan, observed by GPS 1996–1998

In order to detect the crustal movement in the Beppu Bay area, where the highest intra-plate strain rates in Japan is expected, precise GPS measurements have been repeatedly conducted since 1994 at one-year intervals. The result shows N-S or NNE-SSE extension taking place at a rate of more than 10 mm/yr around Beppu Bay. This is essentially consistent with the result obtained by the geodetic survey conducted over the last 100 years, and it suggests a constant rate of crustal motion over the period. The result gives a strong constraint for future modeling of the stress field recovery in the area. However, we failed to identify whether the movement occurred at any specific fault. A denser array of GPS points is needed in the area, and especially near the major faults, in order to investigate possible fault-related motion.