Figure 1
Distribution of low-frequency earthquakes. (a), Map of the locations of the analysed low-frequency earthquakes (circles) and the Hi-net stations (triangles). The events are coloured as follows: blue, yellow, green and magenta circles indicate low-frequency earthquakes extracted from the time-periods corresponding to the largest tectonic tremor sequence of each analysed year and occurring during this tremor sequence; grey circles correspond to all other events. Inset, top: The geographic location of the western Shikoku area and the main tectonic features, such as the geometry of the plate interface (grey contours) and the main tectonic plates (Philippine Sea: PS and Pacific: PA), for Japan. Inset, bottom: Depth cross-section of the analysed events projected along the strike of N 40° E (A-A’). (b), Space–time plot of the events. Coloured rectangles mark the time-periods of largest tremor sequences, corresponding to event coloured as in (a).
