[S-SS28] Active faults and paleoseismology

[SSS28-P07] Offshore active survey "Kamogawa lowland fault zone" -Result of high-resolution stratigraphic survey-

*Izumi SAKAMOTO¹, Masatoshi YAGI¹, Yoshiyuki TAKINO¹, Kaharu MATSUSHITA¹, Takuya ARAKAWA¹, Mikio FUJIMAKI², Shintarou ABE³ (1.School of Marine Science and Technology, Tokai Univ., 2.COR, 3.AIST)

Keywords:active fault, Kamogawa lowland fault zone

Kamogawa lowland fault zone is EW-trending, it is located the south part of Boso peninsula. This fault zone consists of North Kamogawa graben fault and South Kamogawa graben fault. The recurrence period and slip-rate of Kamogawa lowland fault zone has not been clarified until now.
We performed high-resolution stratigraphic survey to confirm a formation, distribution, and displacement of coastal area of the Kamogawa lowland fault zone. Survey area divided into two sub-area 1) Hota area (North-West side extension of the fault zone). 2) Kamogawa area (South-East side extension of the fault zone). We describe results for each sub-area as follow:
< Hota area >
We have carried out the seismic survey with NS direction survey line. Acoustic transparent layer with poor internal reflection was covered in this survey area. And acoustic basement exposed to the seafloor in spots.

We have carried out the seismic survey with NE-SW or NS direction survey line. Acoustic basement exposed to the seafloor in North part and South part of this area. We recognized the steep escarpment of trending EW and continuing about 3km long. And also tilting structure with NE direction in dip is observed around the coastal side. These two structures distribute to the echelon arrangement.
As described above, we have captured distribute of fault by tectonic relief. But we have not able to gain the proof of recent activity.