Crustal structure and tectonics of the northeast Honshu arc, Japan, revealed from detailed gravity anomalies and late Cenozoic caldera distribution
Fig. 2. Short wavelength components(<125 km) of Bouguer gravity anomalies over the northeast Honshu arc . The topograph ic dens i t y i s assumed to be 2.67 g/cm . The contour interval is 5 mgal. 3 Active faults, Quaternary volcanoes, Seismicity, and GPS strain rate fields... We here report that the distribution of the gravity depressions is, however, strongly corresponding to the distribution of the late Cenozoic large calderas. The caldera structure is a geographical feature with collapsed structure surrounded by a ringfault. They are usually underlaid by plutonic body under cooling that often reaches 10 km or more in the diameter (Yoshida, 2001). Therefore the density structure of these calderas might be a major factor of the gravity undulations of this region. Although the number of the known caldera structures exceeds 80 in the northeast Honshu arc (Yoshida , 1999), Oyagi (2000) was supposed that many calderas still exists under the overlying volcanic rocks of the Quaternary volcanoes. We have examined the detailed map of Bouguer anomaly of the northeast Honshu arc with special attention to caldera structures with related subsurface plutons. The results show that some unexposed calderas may located under the overlying young strata. et al.