| 9 June 2004 |
| Headquarters for Earthquake Research Promotion |
| Earthquake Research Committee |
Seismic Activity for May 2004
On May 30, there was a M6.7 earthquake off-shore southeast of the Boso
Peninsula (near the triple junction of the plates). It caused
tsunamis with heights of less than 10cm at Miyakejima, Oshima and Hachijojima
of the Izu Islands. to supplementary reports
*On May 21, there was a M4.8 earthquake near the boundary of Abashiri and Nemuro (Abashiri region, Abashiri subprefecture).
*On May 6, there was a M5.7 earthquake at a depth of approximately 45km off-shore of Kushiro.
The focal mechanism showed a reverse fault with a compression axis in a NW-SE direction.
It is thought that this event is an aftershock of the 2003 Off-shore Tokachi Earthquake.
to supplementary reports
*On May 29, there was a M5.9 earthquake at a depth of approximately 40km
off-shore of Fukushima prefecture. The focal mechanism showed a reverse
fault with a compression axis in a WNW-ESE direction. This event occurred
at the boundary between the Pacific and the continental plates. to supplementary reports
*On May 30, there was a M6.7 earthquake off-shore southeast of the Boso Peninsula (near the triple junction of the plates). It caused tsunamis with heights of less than 10cm at Miyakejima, Oshima and Hachijojima of the Izu Islands. The focal mechanism showed a reverse fault with a compression axis in an E-W direction. Aftershock activity is declining with the largest event of M5.3 on June 1.
*The long-term changes that have been observed since 2001 in the continuous GPS data in the Tokai region, still appear to be continuing. to supplementary reports
There was no remarkable activity. to supplementary reports
*On May 20, there was a M5.1 earthquake at a depth of approximately 45km under the ocean near the Okinawa Main Island. to supplementary reports
*On May 19, there was a M6.1 earthquake near Taiwan.
*On May 6, there was a M5.7 earthquake at a depth of approximately 40km off-shore of Kushiro.
| June 9, 2004 |
| Earthquake Research Committee |
Following are the numbers of the earthquakes by magnitude that occurred in Japan and the surrounding area during May 2004.
| M4.0 or greater: 87 (82 events occurred in April.) | |
| M5.0 or greater: 18 (8 events occurred in April.) | |
| M6.0 or greater: 2 (2 events in total by the end of May in 2004) |
(reference) Average numbers of earthquake occurrences over the past thirty years (1971 - 2000)
| M4.0 or greater: 46 / month | |
| M5.0 or greater: 8 / month | |
| M6.0 or greater: 1.3 / month, 16 / year |
The following regions have been noted as having significant seismic activity during the period from May 2003 to the end of April 2004.
| -Off-shore of Miyagi prefecture | M7.1 on May. 26, 2003 (depth of approximately 70km) | |
| -Northern Miyagi prefecture | M6.4 on July 26, 2003 (depth of approximately 10km) | |
| -Off-shore of Tokachi (2003 Off-shore Tokachi Earthquake) | M8.0 on Sep. 26, 2003 (depth of approximately 40km) | |
| -Off-shore of Fukushima prefecture | M6.8 on Oct. 31, 2003 (depth of approximately 30km) |
"On May 21, there was a M4.8 earthquake near the boundary of Abashiri
and Nemuro (Abashiri region, Abashiri subprefecture).":
There has been light seismic activity since April 27 in this vicinity.
The recent event is the largest earthquake so far.
"On May 6, there was a M5.7 earthquake at a depth of approximately
45km off-shore of Kushiro. The focal mechanism showed a reverse fault with
a compression axis in a NW-SE direction. It is thought that this event
is an aftershock of the 2003 Off-shore Tokachi Earthquake.":
The aftershock activity of the 2003 Off-shore Tokachi Earthquake is continuing to decline. According to the GPS data, postseismic movements that were seen following the main shock have been continuing at a low level.
There is no supplementary information for the Tohoku region.
"The long-term changes that have been observed since 2001 in the continuous
GPS data in the Tokai region, still appear to be continuing.":
The Pacific side of the Tokai-Chubu region maintains a steady rate with movement to the WNW, consistent with the subduction of the Philippine Sea plate toward the northwest. The results from GPS observations in the area centered on western Shizuoka prefecture, have been showing a trend of moderate change since about April 2001. The trends have continued through May 2004 and show no signs of acceleration.
(This evaluation is in agreement with the views presented at the procedural
meeting on May 31 of the Assessment Committee for Areas under Intensified
Measures against Earthquake Disaster. (see reference below))
(reference) "Recent seismic and crustal activity in the Tokai region
and its vicinity" (Japan Meteorological Agency, Department of Seismology
and Volcanology, May 31, 2004)
"So far, there have been no changes of activity which are likely to be associated with the so-called Tokai earthquake.
There is no remarkable seismic activity in general. The seismicity continues at a level lower than normal directly under Hamana lake. In the other regions, seismic activity is generally at a normal level.
The long-term changes in crustal movements in the Tokai region and its vicinity caused by the slow slip on the plate boundary, have been continuing."
There is no supplementary information for the Kinki-Chugoku-Shikoku region.
There is no supplementary information for the Kyushu-Okinawa region.
| Reference 1 Earthquakes that are described in the "Evaluation of Seismic Activity"(Monthly Report of Seismic Activity in Japan) are events of M6.0 and greater, or events of M4.0 and greater (M5.0 or greater off-shore) that have maximum intensity of 3 or greater. Reference 2 Information that is described in the "Supplementary Information to the Evaluation" includes:
|