Location map of the sites described in this study. Latitude and longitude are from Ogawa (1987a). The area outlined in pink shows the Northern Tohoku Conducting Belt (NTCB), following Ogawa (1987a). A gray rectangle indicates the Sengan geothermal area. A thick blue line shows the Ou backbone range. Thin horizontal lines (L0 to L5) indicate the locations of cross-sectional profiles shown in later figures. Dashed lines denote prefectural boundaries. Red triangles indicate the locations of major quaternary volcanoes; triangles with three-letter codes denote active volcanoes, as identified by the Japan Meteorological Agency (JMA). OSR, Mt. Osore; IWK, Mt. Iwaki; HKD, Mt. Hakkoda; TWD, Mt. Towada; YKY, Mt. Yakeyama; HCM, Mt. Hachimantai; IWT, Mt. Iwate; KNG, Mt. Komagatake; CHK, Mt. Chokai; KKM, Mt. Kurikoma; NRG, Mt. Narugo; HJO, Mt. Hijiori.