There have been few examples in which the slip vector of lateral active faults distributed in the mountains was calculated and the slip rate was examined. In the western Chugoku region, it has recently been found that many lateral strike-slip faults are distributed. But, no detailed study on the slip vector and the slip rate has been conducted. We performed a detailed landform analysis that uses the digital elevation model (DEM) based on light detection and ranging (LiDAR), and aerial photographs, and conducted a field survey, on the Tsutsuga fault that extends from northwestern Hiroshima prefecture to northeastern Yamaguchi prefecture in the northeast-southwest direction. We also calculated or examined the slip vector and rate of the fault. As a result, the following was newly found.

　 We found many features associated with recent faulting, such as systematic right-lateral offset streams and cumulative displacement of the Late Pleistocene terrace, and fault outcrops displacing the sandy gravel layers since the late Pleistocene along the Tsutsuga fault. Activity of the Tsutsuga fault is presumed to be a continuous right-lateral movements with a component of northwest uplift. The slip vector of the Tsutsuga fault calculated from the lateral displacement and vertical displacement of the terrace is dominated by lateral displacement, where vertical displacement is approximately 6-29% of the lateral displacement. The slip rate of the Tsutsuga fault is estimated to be 0.5-0.9 mm/yr, because the YsⅤ terrace surfaces likely formed during 25-30 ka from the study of wide-spread tephra deposition and terrace formation process, and the net slip of the YsV terrace surfaces due to the Tsutsuga fault is 14.4-22.4 m

　 We conducted S-wave shallow seismic reflection profiling to reveal subsurface structure and strata deformed by the faulting on the northern section of the East Matsumoto Basin fault (N-EMBF) along the Itoigawa–Shizuoka tectonic line active fault system. The Itoigawa–Shizuoka tectonic line divides into the NE and SW Japan arcs, and it is one of the most major tectonic lines in Japan. The N-S trending and east dipping N-EMBF extends along the eastern margin of the Matsumoto Basin, and it is one of the reverse faults that compose the northern segment of the ISTL active fault system. The seismic profiling consisted of E-W trending survey lines EW-1, 2, and 3 and N-S trending lines NS-1, 2, and 3 whose lengths range 130-500 m. A S-wave portable vibrator (OYO-CAG) was used as seismic source. Both the standard shot intervals and receiver intervals were 2 m. After careful processing for the acquired common mid-point seismic reflection data, we obtained depth converted seismic sections showing subsurface structures above the maximum depth of about 50 m. The sections EW-1 and 3 revealed the east dipping fault with 20 degrees. The section EW-2 exhibits a flexure zone which is located along an active fault trace reported by the past tectonic geomorphic surveys. Considering the vertical component of coseismic displacement and the ages of seismic events estimated by the previous paleoseismic investigation and subsurface structure of the active reverse fault detected in this study, we have calculated that the coseismic displacement and the Holocene slip rate at the survey site are about 5.3 m and 1.5-2.1 mm/yr respectively.

　 Afterslip, mostly aseismic creep on and on the margins of the seismic source fault, occurs not only after a large subduction megathrust earthquake but also rarely on an onshore surface rupture such as the 1966 and 2004 Parkfield, California, earthquakes on the San Andreas fault. Here we present evidence for afterslip as post-seismic continuous creep along the part of the coseismic surface rupture of the 16 April 2016 Kumamoto earthquake of M_w 7.0 (M_JMA 7.3). We describe evident surface afterslip on five sites along the northermost Hinagu fault that experienced 30-65 cm coseismic right-lateral slip. Even though the post-seismic tape measurements are not highly accurate and contains approximately±1-3 cm uncertainty depending on site condition, maximum right-lateral displacement have reached ~20 cm during the first one year after the mainshock. Additionally, up to 5-cm cumulative right-lateral slip of a wall newly built in February 2017 across the coseismic rupture proves that the post-seismic creep has been lasting for at least one year, probably longer than three years. Together with the field survey, we also mapped one-year postseismic ground displacement from analysis of interferometric synthetic aperture radar (InSAR) images. About 2.5 cm contraction across the Hinagu fault from InSAR is a little short but mostly consistent with ~3.5 cm contraction estimated from ~20 cm right-lateral post-seismic slip on the N10°E trending rupture zone. Furthermore, our field observation is also in agreement with the timeseries of horizontal movement of a GNSS station ~2 km southeast of the fault zone. To examine the contribution of local aftershocks to the afterslip, we examined the cumulative moment release of all the aftershocks that reached ~5.1 x 10²⁴ dyne-cm. Assuming a 10 km by 10 km fault plane, one could expect ~16 cm slip that is roughly equivalent to the amount of measured surface afterslip. However, the numerous aftershocks are located probably off the subsurface Hinagu fault so that shallow aseismic creeping would play an essential role for surface afterslip. Although our field measurements, InSAR and aftershock analysis cannot simply judge that the afterslip has been continuously loading to the unruptured sections of the Hinagu fault zone, significant aftershock activity has been still occurring beyond the southern edge of the afterslip zone. The Hinagu afterslip gives us clues not only to understand the postseismic fault behavior but also how to prevent from postseismic damage of fault-crossing structures and better assess the timing of restoration.