The Tokamachi Fault Zone (TFZ) and the Nagano Basin Western Margin Fault Zone (NBWMFZ) are active fault zones located in the middle part of Honshu Island. These two fault zones are distributed subparallel, and the southeastern end of the TFZ and the northwestern end of the NBWMFZ are separated by about 20 km. To discuss the continuity of these two fault zones, we mapped short active faults distributed in the gap between the TFZ and the NBWMFZ, measured the vertical offsets, and estimated the vertical slip rates. These active faults consist of WNW-ESE trending short (less than several kilometers) faults distributed subparallel to each other, and they are interpreted as normal faults, considering their linear fault traces. These faults consist of the Busuno-toge Fault Group, the Nonomi-toge Fault Group, the Hirataki Fault, and the Akasawa Fault Group. The Akasawa Fault Group has displaced the Maibara Terrace by <9 m, and vertical slip rates were estimated to be <0.04 mm/yr. These slip rates are two orders of magnitude smaller than these of the TFZ and the NBWMFZ. Based on distribution pattern, deformation style, and slip rates of faults, we interpreted that these short active faults have been formed indirectly by activities of blind right-lateral slip fault located between the TFZ and the NBWMFZ. This interpretation indicates that the TFZ and the NBWMFZ may have a continuous structure, or that the southwestern end of the TFZ may extend to near the western end of the Busuno-toge Faults.
