Fig. 1

Distribution of slow and fast earthquakes in the Japan Trench and Nankai Trough. Green and blue symbols semi-schematically show the distribution of slow earthquakes (tectonic tremors, short-term slow slip events, and long-term slow slip events). Red symbols indicate the distribution of fast, regular earthquakes. For an explanation of the other symbols, refer to the legend in the figure. The distribution of slow and fast earthquakes in the Nankai Trough is adapted from Obara and Kato (2016) and Obara (2020). Depth contours of the upper surface of the Pacific and Philippine Sea plates are based on Baba et al. (2002), Nakajima and Hasegawa (2006), Nakajima and Hasegawa (2007), Hirose et al. (2008), Nakajima et al. (2009), and Kita et al. (2010). The slip distributions of the March 11, 2011, Tohoku-Oki earthquake (10 m or larger) and other megathrust earthquakes are from Yagi et al. (1998), Yagi et al. (1999), Nagai et al. (2001), Tanioka and Seno (2001), Murotani et al. (2003), Yamanaka and Kikuchi (2004), Earthquake Research Center (2005), Mochizuki et al. (2008), Research Center for Seismology, Volcanology, and Disaster Mitigation (2008), Iinuma et al. (2012), Ohta et al. (2012), Kubo et al. (2013), and Kubo and Nishikawa (2020). The distribution of small repeating earthquakes is from Uchida and Matsuzawa (2013) and Igarashi (2020). The distribution of tectonic tremors is based on Idehara et al. (2014), Yamashita et al. (2015), Araki et al. (2017), Nishikawa et al. (2019), Yabe et al. (2019), and Yamashita et al. (2021). The distribution of short-term slow slip events is based on Ito et al. (2013), Nishimura et al. (2013), Nishimura (2014), and Nishimura (2021). The source area of the 1992 Sanriku-Oki ultraslow earthquake is from Kawasaki et al. (2001). The locations of subducting ridges and seamounts are based on Kodaira et al. (2000), Park et al. (2004), Mochizuki et al. (2008), and Yamamoto et al. (2013). The northeastern limit of the Philippine Sea Plate is from Uchida et al. (2009a). Seafloor topography is from Smith and Sandwell (1997). The plate motion is based on Bird (2003)