In order to study active tectonics and related matters, it is very important to know the actual distribution and nature of active faults. The western boundary faults of the northern part of the Kitakami lowland are composed of MBF (Main Boundary Fault), FAF (Frontal Active Fault), and SAF (Secondary Antithetic Fault). The former two are west-dipping reverse faults. SAF is east-dipping antithetic reverse fault located between MBF and FAF. There was a disagreement about the existence of another west-dipping active reverse fault to the east of FAF. We surveyed fluvial terrace surfaces and observed a new outcrop. In addition, we examined geomorphic features based on 5 m-mesh DEM. The results are summarized as follows: (1) The average vertical slip-rate of FAF, located in the east of MBF, is ca. 0.3 mm/yr. (2) Geologic structures to the east of FAF do not coincide with west-dipping reverse fault. Fluvial terrace surfaces do not display any tectono-geomorphic feature indicative of active faulting there. Therefore, we deny a possibility of active fault to the east of FAF.
