GRAVITY IN THE JUNCTION BETWEEN THE JAPANESE AND THE IZU-BONIN ISLANDS

Abstract

Gravity values from the central Honshu to the northern part of the Izu-Bonin (Izu-Ogasawara) Arc have been compiled, and the free air and Bouguer gravity anomaly maps as well as gravity tables have been given. The broad gravity low over the triple junction between the Pacific plate, the Eurasia plate and the Philippine-Sea plate has been explained by considering the possible behavior of the Pacific plate descending from the junction between the Japan and the Izu-Bonin Trenches: It may be that the slab descending at the Japan Trench and the slab descending at the Izu-Bonin Trench geometrically have converging velocity components under the junction area to cause subduction of the Philippine-Sea plate beneath the Eurasia plate, and this subduction gives rise to the negative gravity anomaly. Explanation of some other gravity lows observed over the Japanese Islands has also been made tentatively.