June 8, 2005 |
Seismic Activity for May 2005
| * | There was no remarkable activity. to supplementary reports |
| * | On May 19, there was a M4.8 earthquake at a depth of approximately 60km off-shore of Kushiro. The focal mechanism showed a reverse fault with a compression axis in a WNW-ESE direction. This event occurred at the boundary between the continental and the Pacific plates. to supplementary reports |
| * | On May 21, there was a M5.1 earthquake at a depth of approximately 20km off-shore of Miyagi prefecture. |
| * | On May 27, there was a M4.9 earthquake at a depth of approximately 110km under northern Miyagi prefecture. The focal mechanism had a compression axis in the direction of the subducting Pacific plate. This event occurred within the Pacific plate. to supplementary reports |
| * | On May 8, there was a M4.5 earthquake at a depth of approximately 10km near the border of Tochigi and Gunma prefectures (in southern Tochigi prefecture). There was also a M4.8 earthquake at nearly the same location on May 15. The focal mechanisms showed strike-slip faults with compression axes in a WNW-ESE direction. Both events had relatively strong seismicity immediately following the main shocks, however activity is returning to the level previous to the mainshocks. |
| * | On May 14, there was a M4.4 earthquake at a depth of approximately 55km under northern Ibaraki prefecture. |
| * | On May 19, there was a M5.4 earthquake at a depth of approximately 35km off-shore east of Chiba prefecture. The focal mechanism showed a reverse fault with a compression axis in a NNE-SSW direction. It is thought that this event is related to the subduction of the Pacific plate. |
| * | On May 30, there was a M4.7 earthquake at a depth of approximately 50km under northeastern Chiba prefecture. The focal mechanism showed a reverse fault with a compression axis in an E-W direction. It is thought that this event occurred at the boundary between the Philippine Sea and the Pacific plates. In this vicinity, there was a M4.7 earthquake on May 15. |
| * | On May 7, there was a M4.2 earthquake at a depth of approximately 30km in eastern Tama, Tokyo. |
| * | On May 11, there was a M4.0 earthquake at a depth of approximately 15km in mid-western Yamanashi 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. to supplementary reports |
| * | On May 27, there was a M4.7 earthquake at a depth of approximately 40km under northern Tokushima prefecture. The focal mechanism had a tension axis in an E-W direction. This event occurred within the Philippine Sea plate. to supplementary reports |
| * | The aftershock activity of the earthquake off-shore west of Fukuoka prefecture on March 20 (M7.0) is continuing to decline. The largest aftershock in May was a M5.0 event on May 2 that occurred near the secondary aftershock region associated with the largest aftershock of April 20. |
| * | On May 31, there was a M5.8 earthquake at a depth of approximately 30km in Hyuganada. The focal mechanism showed a reverse fault with a compression axis in a WNW-ESE direction. It is thought that this event occurred at the boundary between the continental and the Philippine Sea plates. The following aftershock activity has been at a low level. to supplementary reports |
| * | On June 1, there was a M4.3 earthquake at a depth of approximately 30km under Tokyo Bay. Including this event, there were three earthquakes equal to or larger than M4.0 and seismic activity increased temporarily, however, seismicity mostly subsided by June 2. |
| * | On June 2, there was a M4.0 earthquake at a depth of approximately 10km onshore in southern Akita prefecture. |
| * | On June 3, there was a M4.8 earthquake at a depth of approximately 10km in the Amakusa Ashikita Region, Kumamoto prefecture. This event had a maximum seismic intensity 5 Lower in Kumamoto prefecture. Seismic activity was a main shock - aftershock sequence, and it is declining. The focal mechanism of the main shock showed a strike-slip fault with a tension axis in a N-S direction. According to the GPS data, there were no remarkable changes before and after this event. In this vicinity, there were six earthquakes equal to or larger than M5.0 since August in 1923. The largest event was a M5.8 earthquake that occurred on December 26, 1931. to supplementary reports |
June 8, 2005
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during May 2005.
| M4.0 or greater: 76 (76 events occurred in April) | |
| M5.0 or greater: 12 (10 events occurred in April) | |
| M6.0 or greater: 0 (There has been a total of 7 events for 2005 by the end of May.) |
(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 2004 to the end of April 2005.
| - Off-shore southeast of the Boso Peninsula (near the triple junction of the plates) | ||
| M6.7 on May 30, 2004 | ||
| - Off-shore of Iwate prefecture | M5.8 on August 10, 2004 (depth approximately 50km) | |
| - Off-shore southeast of the Kii Peninsula (Off-shore of Tokaido) | ||
| M7.4 on September 5, 2004 | ||
| - Chuetsu region, Niigata prefecture (2004 Niigata Chuetsu Earthquake) | ||
| M6.8 on Oct. 23, 2004 (depth approximately 10km) | ||
| - Off-shore of Kushiro | M7.1 on November 29, 2004 (depth approximately 50km) | |
| - Southern Rumoi subprefecture | M6.1 on December 14, 2004 (depth approximately 10km) | |
| - Off-shore southeast of the Boso Peninsula (near the triple junction of the plates) | ||
| M6.8 on January 19, 2005 | ||
| - Southern Ibaraki prefecture | M5.4 on February 16, 2005(depth approximately 45km) | |
| - Off-shore west of Fukuoka prefecture | M7.0 on March 20, 2005(depth approximately 10km) | |
| - Northeastern Chiba prefecture | M6.1 on April 11, 2005(depth approximately 50km) | |
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.":
According to the GPS data, the Pacific side of the Tokai-Chubu region maintained a steady rate with movement to the WNW, consistent with the subduction of the Philippine Sea plate toward the northwest. The results, from observations in the area centered on western Shizuoka prefecture, had been showing a trend of moderate change since about April 2001. Since the earthquakes off-shore, southeast of the Kii Peninsula on September 5, 2004, some changes appeared in the trends. However, the deformation has recently been returning to the trend before the earthquakes.
(This evaluation is in agreement with the views presented at the procedural meeting on May 30 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 30, 2005)
" So far, there have been no changes of activity which are likely to be associated with the so-called Tokai earthquake.to the text
There was no remarkable seismic activity in general. The seismicity continues at a level lower than normal directly under Hamana lake. In other regions, seismic activity is generally at a normal level.
For the crustal movements, since the M7.4 earthquake off-shore of Tokaido (off-shore southeast of the Kii Peninsula) on September 5, 2004, postseismic movements associated with these events were observed. Recently the deformations have been returning to the previous trend, and the long-term crustal movements from the slow slip at the plate boundary is thought to be continuing. "
- On May 25, there was a M4.6 earthquake at a depth of approximately 55km under Bungo Strait.
There is no supplementary information for the Kyushu - Okinawa region.
On June 5, there was a M3.3 earthquake at a depth of approximately 15km in the Chuetsu region, Niigata prefecture, which had a maximum seismic intensity 4. This event was located 10km north of the aftershock region of the 2004 Niigata Chuetsu Earthquake.
| 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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