There are several marine terrace surfaces along the western coast of Shimokita Peninsula, northeast Japan. They are classified into H1, H2, M1, M2, A1 and A2 surfaces in descending order around Oma, northwest part of the peninsula. The M1 surface directly covered by Toya tephra (112-115 ka) is correlated with that formed in MIS 5e. A1 and A2 surfaces are Holocene emerged wave-cut benches. The heights of the former shorelines of the Pleistocene marine terrace surfaces around Oma are over 185 m, over 114 m, 60 m and 25 m , respectively. The A1 surface on the Benten-jima Island, to the north of Oma, is 1m higher than that on Oma. Spatially, the H2 and M1 surfaces can be traced for 10 km longshore southward to around Sai. The height of the most continuous M1 former shoreline is in the range of 60 m to less 20 m, indicating distinct southward tilting.
These marine terrace surfaces are planar structural markers that record the actual direction of local tilt. The progressively greater slopes of successively higher marine terrace surfaces clearly record continual crustal tilt in SSW direction around Oma and Sai. The former shorelines of the H2 and M1 surfaces define the planes recording crustal movement. Structural contours on the plane defined by the former shoreline of the M1 surface yield tilting rates of 3.2*10-5/ka. Emerged wave-cut benches are indicative of abrupt relative sea-lebel changes. They are similar to that produced co-seismically associated with major historical earthquakes. In addition, gradual southward tilt is not documented by geodetic data. Thus, the significant tilt in SSW direction suggests that long-term tilt in this area is not continuous, but episodic. These tectonic features have been convincingly owing to the activity of a south-dipping active submarine fault extending over 40 km along the north coast of the west Shimokita peninsula.