A Discussion on the measurement and interpretation of changes of strain in the Earth - Earthquake fault studies in Japan

Abstract

The paper reviews the current status of earthquake fault studies in Japan, taking the work on the off-Honshu tectonics as an example. Within the Japanese tectonic provinces, the belt along the Pacific coast of central and western Honshu is of special interest from the viewpoints of earthquake prediction as well as of global tectonics. Observations in this field are being made most extensively in the south Kanto district as represented by a complex monitoring system surrounding the Sagami Bay. Complemental use of geophysical instruments with geodetic surveys is successful. The basic mode of strain accumulation thus observed seems consistent with the Sagami trough fault model as proposed by Kanamori and Ando in 1971 to explain the focal processes of the great Kanto earthquake of 1923. Comparison of tiltmeter records at the adjacent stations Aburatsubo and Nokogiriyama suggests crustal strains migrating at an extremely low velocity (20 km/ year, apparently), from east to west (Yamada 1972). Nakamura and Kanamori have shown that correlation of the activities of this fault with those of the Oshima volcano and seismicity in the Kii Peninsula, as seen in old records, provides notable evidence for the mechanism of stress transmission in a tectonic unit.