Fig. 1
![Fig. 1](http://media.springernature.com/full/springer-static/image/art%3A10.1186%2Fs40623-019-1081-z/MediaObjects/40623_2019_1081_Fig1_HTML.png)
Tectonic maps in and around Hokkaido, Japan. a Tectonic map in and around Japan. Our study area of Hokkaido, the northernmost island in Japan, is colored in pink. HCZ: the Hidaka Collision Zone. b Geological units forming Central Hokkaido (Kimura 1994; Ueda 2016) and seismic reflection and refraction/wide-angle reflection lines of the 1998–2000 Hokkaido Transect (Iwasaki et al. 2001, 2004; RGES 2002a, b). Other reflection lines in the southern part of Central Hokkaido (e.g., Arita et al. 1998; Tsumura et al. 1999; Ito 2000, 2002) are also shown. A yellow circle indicates the epicenter of the Hokkaido Eastern Iburi earthquake (M = 6.7) on Sep. 6, 2018 by Japan JMA (2018a). OB: Oshima Belt; SYB: Sorachi-Yezo Belt; HB: Hidaka Belt; TB: Tokoro Belt; Iz: Idon’nappu zone: Hmz: Main zone of the HB; Ynz: Yubetsu-Nakanogawa zone of the HB; Kz: Kamuikotan zone; Hmr: Hidaka metamorphic rocks; HMT: Hidaka Main Thrust