14 July 2004 |
Seismic Activity for June 2004
There was no remarkable activity. to supplementary reports
*On June 11, there was a M5.2 earthquake at a depth of approximately 50km in southern Tokachi subprefecture. 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
There was no remarkable activity. to supplementary reports
*On June 20, there was a M5.1 earthquake under the ocean near Hachijojima.
*The aftershock activity of the earthquake that occurred off-shore southeast of the Boso Peninsula (near the triple junction of the plates) on May 30 (M6.7), has been declining normally. The largest aftershock so far was the M5.6 earthquake on June 9.
*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
*On June 8, there were M4.5 and M4.3 earthquakes at a depth of approximately 10km in the Kii Strait, that accompanied light aftershock activity. Both focal mechanisms showed reverse faults with compression axes in an E-W direction. to supplementary reports
There was no remarkable activity. to supplementary reports
| July 14, 2004 |
| Earthquake Research Committee |
Following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during June 2004.
| M4.0 or greater: 87 (87 events occurred in May.) | |
| M5.0 or greater: 10 (18 events occurred in May.) | |
| M6.0 or greater: 0 |
(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 |
| -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) | |
| -Off-shore southeast of the Boso Peninsula (near the triple junction of the plates) |
M6.7 on May 30, 2004 |
"On June 11, there was a M5.2 earthquake at a depth of approximately 50km in southern Tokachi. 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 was additional activity in Hokkaido region, as follows.
- The seismic activity which started on April 27 near the boundary of Abashiri and Nemuro (Abashiri region, Abashiri subprefecture), has been declining gradually since one of the largest events (M4.8) on May 21. There has been no earthquakes M3.0 or greater since June 11.
- On June 12, there was a M4.6 earthquake at a depth of approximately 55km off-shore of Iwate prefecture.
- On June 27, there was a M4.8 earthquake at a depth of approximately 45km off-shore of Fukushima prefecture.
"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 June 2004 and show no signs of acceleration.
(This evaluation is in agreement with the views presented at the procedural meeting on June 28 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, June 28, 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:
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