[SGL36-P01] The developmental process of the Kazusa basin inferred by high-resolutional seismic reflection data
Keywords:Seismic reflections, the Kazusa Group, tectonics
The survey area is 35°10′N~35°50′N and 140°20′E~141°10′E (the Kujukuri-oki are). We obtained seismic data of ca. 1100 km in total length with a boomer and multi-channel streamer (24 channel with 3.125 m spacing). Seismic data are processed by SPW (Parallel Geoscience Corporation) and provide seismic reflections at 100 m below seafloor.
In the Kujukuri-oki area, we recognize three strata bounded by distinct unconformity and define them as the Kujukuri-oki C Formation, the Kujukuri-oki B Formation and the Kujukuri-oki A Formation in ascending order. Calcareous nannofossils (Nishida et al., 2016) from the Kujukuri-oki B Formation show that this formation correlates to the Kazusa Group. In the Kujukuri-oki B Formation, some anticlines at shelf edge and normal faults dipping eastward off Taitouzaki extend from north to south. Seismic facies of the Kujukuri-oki B Formation is distinct stratification deformed by these anticlines and faults. In addition, the characteristics of normal faults in Kujukuri-oki area are consistent with those of normal faults recognized in the Kazusa Group. Some faults in sea area dip westward and then they compose a graben with normal faults dipping eastward off Kujukuri town.
Our high-resolutional seismic data show that anticlines formed in compressive stress field and normal faults formed in tensile stress field exist closely in the Kujukuri-oki area. The anticlines at shelf edge would work outer ridge and migrate the Kazusa basin toward northwest.