Pre-Neogene basement rocks beneath the Kanto Plain, central Japan

Abstract

Forty-nine deep borehole data and 31 seismic reflection profiles were used for understanding a distribution of pre-Neogene basement rocks beneath the Kanto Plain, central Japan. Pre-Neogene rocks drilled at each borehole are divided into seven geologic units, namely, Ashio, Tsukuba, Ryoke, Sanbagawa, Chichibu and Shimanto Complexes and Cretaceous sediments. P-wave velocities of pre-Neogene rocks underneath of the Kanto Plain suggest a relationship with each geologic unit. Boundary between pre-Neogene basements and covering sediments are well traced on some seismic reflection profiles, and a boundary between geologic units was suggested by geophysical difference in reflection patterns, such as shapes and intensities. Thus subsurface distribution of pre-Neogene geologic units beneath the Kanto Plain is synthesized based on both geological and geophysical data.