Low velocity structure within the lower crust below the ocean−floor in the south−east to the Ogasawara Plateau

Abstract

Analysis of multi−channel seismic reflection survey and seismic refraction survey data acquired on four nearly parallel survey lines in the Northwest Pacific Basin reveals that there exists low-velocity structure within lower crust. Average P-wave velocity in the low−velocity structure, below top of the lower crust with a P-wave velocity of 6.9–7.0km/s, can be estimated as 6.2–6.7±0.2–0.3km/s. However, a low-velocity structure cannot be observed below a survey line, which crosses to the four lines. I consider several models which would explain the difference of the velocity structures of the lower crust between the survey lines.