Seismic activity by period, after the M6.4 event near Kozushima (2)

There are many hypocenters at a depth of less than 10 km, but those occurring outside of the network of stations are deeper than 10 km.

It appears that the earthquakes are occurring in repeated bursts, and that the hypocenter zones are divided into blocks. The diagonal lines extending from the epicenters represent areas of low activity indicating the borders between blocks. Of these, the third block from Miyakejima is the most clearly defined.

The 1962 seismic activity is also thought to have occurred as divided into blocks. In terms of the blocks seen in the current activity, the 1962 activity seems to have occurred in the second block. However, when the difference in relative positions of the epicenters are considered, the details of the situation remain unclear.

There were about 70 M4 or higher events in the 1962 activity. The current activity has seen nearly three times that number.

Japan Meteorological Agency