Abstract
Seismic survey using "Bubble Pulser" was carried out in Miho Bay off eastern Shinji lowland, Southwest Japan. Based on the seismic profiles, geologic history since the Late Pleistocene was reconstructed.
Three distinctive reflectors, formed before the Jomon transgression were recognized in seismic profiles. The lowest reflector was formed before the last interglacial stage. The distinctive reflector in Sakaiminato area was recognized along old scour hole. The uppermost reflector was formed during the last glacial maximum. The geologic history since the late Pleistocene in the eastern Shinji lowland can be divided into following five stages. Stage 1 (MIS 6) was the regression period before the last interglacial. At stage 2 (MIS 5), the sea level was the same as of now, and also the old Yumigahama Peninsula was formed at the position where it is at the present. The erosional scour hole at the northern end of Yumigahama Peninsula was formed at this stage by the tidal current erosion. Topographical features similar to the present basin was formed. At stage 3 (MIS 4-3), scour hole was buried by clastic materials at the northern end of Yumigahama Peninsula. At stage 4 (MIS 2), valley system was formed during the late Pleistocene at eastern Shinji Lowland. At stage 5 (Holocene), present geographical features are formed after the Jomon transgression.
