| 11 October 2000 |
| Headquarters for Earthquake Research Promotion |
| Earthquake Research Committee |
Seismic activity near the island of Akusekijima (the sea near Amami Oshima)
*Akusekijima is situated within a volcanic range that includes active volcanoes, and it has been characteristic for seismic activity in this type of volcanic region for a number of events of similar magnitude to the maximum magnitude event to occur in series. However, when the incidence of M3.0 and greater events in the current activity is examined, it can be seen that the total incidence of such events in the three days from October 2nd was just over thirty, while there have only been 2 to 3 such events per day from day four onward, indicating that the activity is decreasing over time. At present, the indications are that this activity takes the form of aftershocks to the main shock that occurred at 4:44 p.m. on October 2nd.
*The focal mechanism of this event was a normal fault type with a northwest-southeast tension axis. From the submarine topography, it appears that the stress field in this area is a northwest-southeast tension field, which matches the focal mechanism of this event.
*In this region, there was an M5.9 event on August 3rd 1991. Also, for about two weeks beginning on December 15th 1995, there was seismic activity including a maximum 5.4 event, in which time the first week showed high activity levels. The active zone for the current activity borders the active zone of the 1995 activity immediately to the north.
*From the above, it is believed that the chances of an event with greater than M5.0 (with seismic intensity 5 lower at the source) occurring are decreasing.