Continuous Observation of Crustal Tilt at Usami, the Northern Part of Izu Peninsula

The purpose of the present observations is to clarify the crustal tilt in the northern part of Izu peninsula. Measurement of crustal tilt at the Usami observation site has been carried out by using two sets of TEM-tiltmeters since July 1979. There is a small fault across the observation vault, and the tiltmeters are established on both the sides of the fault. Interesting observational results of tilting motion by rainfall are obtained. The tilting motions are characterized by long-term variations overlapped by short period saw-tooth type variations. It seems that this saw-tooth type tilting motion is very similar to ""stick-slip"" generated by rock fractures and to the displacement pattern of the coseismic crustal deformation