Fault topography and fault outcrop around the southern end of the Uwandaira fault group in the Kitakami lowland western marginal fault zone, northeast Japan

Abstract

This paper aims to clarity the relationship between fault segments and fault geometry at the southern end of the Uwandaira fault group convexing along the western margin of the Kitakami lowlands, based on fault parameters and fault history. Neogene strata thrust over the terrace deposits along the high-angle fault plane dipping more than 48 degrees. Several angular unconformities in the fault outcrop and the displacement of the post-last glacial L2 terrace yield at least four paleoseismic events since the last glacial stage. The average vertical slip rate is calculated to be ca. 0.3±0.1 m/ky based on the displacements and ages of terrace deposits. The net displacement per event was estimated to be 2.4-3.4 m based on the plunge of slickenlines. The values of the average vertical slip rate and the net event displacement are equivalent to those of the central part of the Uwandaira fault group. These results imply that a geometric form of active fault trace does not always correspond to a fault segment.