4 Discussion
Our results show that: (1) the foreshocks of the 2017 M5.3 Kagoshima Bay
earthquake sequence occurred on a single plane with a steep dip to the
east, whereas aftershocks occurred on several more complex planar
structures, (2) the foreshock hypocenters formed a seismic gap, and (3)
the foreshock and aftershock hypocenters exhibit clear migration
behaviors. In this section, we integrated these observations and propose
a simple model that can explain the occurrence of the
foreshockâmainshockâaftershock sequence of the 2017 M5.3 Kagoshima Bay
earthquake based on the upward fluid movement, which is similar to the
fault-valve model proposed by Sibson (1992).