Earth Planets Space, Vol. 54 (No. 11), pp. 1049-1053, 2002
Masao Komazawa1 and Masaaki Mishina2
1National Institute of Advanced Industrial Science and Technology, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8567, Japan
2Tohoku University, Aoba-ku, Sendai, Miyagi 980-8578, Japan
(Received January 25, 2002; Revised October 17, 2002; Accepted October 17, 2002)
Abstract: A gravity survey was conducted in and around the Nagamachi-Rifu Fault. The density for both terrain and Bouguer corrections was chosen to be 2,300 kg/m3, because volcanic rocks are dominant over the whole measurement area and the surface layer density is estimated to be low from geological considerations. The Bouguer anomalies are characterized by a low anomaly similar to those of a caldera and the basement structure inferred from two and three-dimensional analysis shows that the depth is often more than 1 km in the caldera region and that there is a circular structure. The gradient of basement is steepest at the southern margin, and it resembles to rim of funnel-shaped caldera.