Search for hidden fracture zones from dense gravity survey and remote sensing

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(1) On the basis of our new gravity data together with the gravity database of Gravity Research Group of Southwest Japan, "Gravity Anomaly Atlas of the Japanese Islands : South-West and Central Japan" (editors : Yamamoto, A. and Shichi, R.) was published in November 2004.(2) A new gravity anomaly map was drawn from a total of 1328 new gravity measurements in Nagoya City and its environs. The gravity anomaly data combined with bore-hole and surface geology data show that the vertical displacement of pre-Tertiary basements of the Biwajima-Atsuta Fault and the Atsuta-Nisshin Fault is approximately 550m and 350m, respectively.(3) Judging from a dense gravity survey, geological investigation and lineament analysis of the Miya basin area in northern Gifu Prefecture, the Miya basin was formed as a pull-apart basin by right-lateral movements of the Miya-toge and Enako Faults running parallel in NE-SW trend.(4) A detailed fracture mapping and geochemical analysis of granitic rocks in the Atera fault zone reveal that the influence of fracturing of the Atera Fault on the granitic rocks is prominent within 250m from the main fault plane.