Provenance analysis is one of the methods used to clarify the formation process of mountains, which is important for safety assessments of geological disposal. In this study, provenance analysis, based on the simultaneous analysis of the chemical composition, mineral species, and abundance ratios of heavy minerals using an electron probe microanalyzer （EPMA）, was applied to samples from the Pleistocene Sarabetsu Formation in Horonobe region, Hokkaido. The concentrations of 16 elements were measured in individual grains to identify the mineral species based on their chemical compositions. This mineral species identification was consistent with thin section microscopic observations. In addition to the gravel composition analysis, the analyses of the heavy minerals suggest that the major provenance rocks of the Sarabetsu Formation were derived from Soya Hill and the Teshio Mountains. Furthermore, Soya Hill rose above sea level by at least 1.5 Ma or later. These results are consistent with the tectonic history of the Horonobe region, as shown by previous studies. In contrast, amphibole is abundant in parts of the Sarabetsu Formation, but is uncommon in both Soya Hill and the Teshio Mountains. This finding suggests that future studies should consider the possibility of a sediment supply from distant areas, such as those transported by the Teshio River.

When considering the mechanism of earthquake occurrence, the stress state in the vicinity of the source fault is essential. In this study, we applied anelastic strain recovery method（ASR method）to a total of 20 rock core samples retrieved from a borehole penetrating the Futagawa fault, one of the source faults of the 2016 Kumamoto earthquakes and succeeded in determining the in-situ stress state using 6 core samples. The results reveal that the normal faulting stress regime dominates in the source area, which says that the vertical stress is the maximum principal stress（σ₁）. This implicates the magnitude of the maximum horizontal stress（S_Hmax）, which is estimated to have been the maximum principal stress（σ₁）before the earthquakes, has dropped significantly due to the strike-slip faulting during the earthquakes. The result that the stress state after the earthquakes is the normal faulting regime is consistent with the results obtained by hydraulic fracturing and focal mechanism conducted in the same area. We also reveal that the direction of the minimum horizontal stress（S_hmin）is almost orthogonal to the strike of the Futagawa fault, which indicates that the horizontal shear stress that causes strike-slip faulting on the fault plane is very small.