HR: 16:15h
AN: G24A-02 INVITED     [Abstracts]
TI: Gravity Signals Associated With Seismic and Volcanic Activities
AU: * Imanishi, Y
EM: imanishi@ori.u-tokyo.ac.jp
AF: Ocean Research Institute, The University of Tokyo, 1-15-1, Minamidai, Nakano, Tokyo, 164-8639 Japan
AU: Nawa, K
EM: k.nawa@aist.go.jp
AF: Geological Survey of Japan, AIST, Tsukuba Central 7, 1-1-1, Higashi, Tsukuba, Ibaraki, 305-8567 Japan
AU: Kazama, T
EM: takujin@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, The University of Tokyo, 1-1-1, Yayoi, Bunkyo, Tokyo, 113-0032 Japan
AU: Okubo, S
EM: okubo@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, The University of Tokyo, 1-1-1, Yayoi, Bunkyo, Tokyo, 113-0032 Japan
AB: Earthquakes cause permanent changes in Earth's mass distribution, and therefore in the gravity potential field of Earth. Although such coseismic effects are generally small, gravity steps associated with faulting have been detected on some events (Barnes, 1966; Tanaka et al., 2001). The 2003 Tokachi-oki Earthquake (Mw 8.0) provided the first instance of detection of coseismic gravity changes from continuous observations with a modern high-resolution gravimeter network (Imanishi et al., 2004). This was immediately followed by another report (Nawa et al., 2005) on the 2004 Off Kii Peninsula Earthquake (Mw 7.4). These results show that gravimetry can be applied to studies of earthquake source mechanism. In addition to earthquakes, volcanic eruptions are another source of geodynamically generated gravity changes to be investigated with gravimetry (Furuya et al., 2003). In the case of the latest eruption of Mt. Asama, Japan in 2004 (Kazama et al., 2005), absolute gravity measurements detected clear signals associated with volcanic activities, proving that gravity can provide a useful tool for directly monitoring the movement of magmatic fluid. It may be stressed that in these experiments correction for environmental effects on gravity is essential for extracting useful signals from raw observations. In particular, underground water often poses a difficult problem in the interpretation of observed gravity changes. In this paper, we will summarize recent results on earthquakes and volcanoes in Japan obtained from absolute and relative gravimetry. We will also discuss a possibility of establishing a network of absolute and superconducting gravimeters densely distributed throughout Japan, which would be extremely useful for investigation of any local-to-regional scale phenomena involving relative mass movements, including earthquakes, volcanic eruptions, crustal deformations, atmospheric and oceanic loading, and groundwater movements.
DE: 1217 Time variable gravity (7223, 7230)
DE: 1244 Standards and absolute measurements
DE: 8419 Volcano monitoring (7280)
SC: Geodesy [G]
MN: Fall Meeting 2005