Fig. 1

The 20 April 2015 eastern offshore earthquake. a The location of the 20 April 2015 Ryukyu subduction zone earthquake. The red star indicates the epicenter of the 0420 event. The aftershocks of the 0420 events are shown by the warm colored circles. The epicenters of the 1994 to 2013 M _L > 6 events are shown by the blue open stars (see also Table 1). The open pink rectangle indicates the surface projection of the fault model, with its shallowest portion indicated with a black dashed line. The gray lines display the depths of the subducting plate in this area (Wu et al., 2009). Detailed source parameters of major earthquakes occurring in offshore eastern Taiwan recorded in the last 10 years are provided in Table 1. b Cross section along the C–C’ profile. Blue thick line and dotted line indicate the plate interface and the bottom of Benioff zone, respectively. The beach balls show the focal mechanisms of the 0420 mainshock and two largest aftershocks. The aftershocks of the 0420 events are shown by the orange circles. The gray dots denote background seismicity (M > 3) recorded from 1990 to 2013, as reported by the CWB