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August 8, 2007 |
| * | On July 16, there was a M6.8 earthquake# at a depth of approximately 10km off-shore of Jo-Chuetsu, Niigata prefecture. This event had maximum seismic intensity 6 Upper in Niigata and Nagano prefectures, and caused damage with 11 persons killed and about 2000 persons injured. # Japan Meteorological Agency named this earthquake the Niigataken Chuetsu-oki Earthquake in 2007. to supplementary reports |
| * | On July 1, there was a M5.8 earthquake at a depth of approximately 130km under northern Nemuro subprefecture. The focal mechanism had a tension axis in the direction of the subducting Pacific plate. This event occurred within the Pacific plate. to supplementary reports | |
| * | There was no remarkable activity. to supplementary reports |
| * | On July 3, there was a M4.5 earthquake at a depth of approximately 50km under the border between Ibaraki and Chiba prefectures [southern Ibaraki prefecture]. The focal mechanism showed a reverse fault with a compression axis in an E-W direction. This event occurred at the boundary between the Pacific and the Philippine Sea plates. |
| * | According to the ocean bottom acoustic survey for the Noto Hanto Earthquake in 2007 on March 25, a previously recognized offshore fault was shown to be an active fault which extends for over 18km long. Associated with the recent event, small movements were seen on parts of the fault. Therefore, the recent earthquake is considered to be related to this active fault. |
| * | (The Niigataken Chuetsu-oki Earthquake in 2007 and its aftershock activity are described in a separate section.) |
| * | There have been no anomalous changes observed in the GPS data for the Tokai region. to supplementary reports |
| * | On July 16, there was a M4.7 earthquake at a depth of approximately 50km under Nara prefecture. The focal mechanism showed a strike-slip fault with a tension axis in a NE-SW direction. This event occurred within the Philippine Sea plate. | |
| * | On July 16, there was a deep M6.7 earthquake at a depth of approximately 370km off-shore of Kyoto prefecture. The focal mechanism had a compression axis in the direction of the subducting plate. This event occurred within the Pacific plate. to supplementary reports | |
| * | There was no remarkable activity. to supplementary reports | |
| * | On August 1, there was a M6.1 earthquake off-shore northwest of the Okinawa Main Island. The focal mechanism showed a strike-slip fault with a tension axis in a NW-SE direction. There also was a M6.3 earthquake at nearly the same location on August 7. | |
| * | On August 2, there was a M6.4 earthquake under the ocean near Sakhalin [near southern Sakhalin]. The focal mechanism showed a reverse fault with a compression axis in an E-W direction. Associated with this event, small tsunamis were observed along the Japan Sea coast in Hokkaido. In this region, there was a M6.9 earthquake on September 6, 1971, which caused tsunamis. | |
[ ] were the regional names of the epicenters used in the Japan Meteorological
Agency announcement.
August 8, 2007
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during July 2007.
| M4.0 or greater: 93 (81 events occurred in June) | |
| M5.0 or greater: 17 (11 events occurred in June) | |
| M6.0 or greater: 3 (There has been a total of 14 events for 2007 by the end of July.) |
(reference)
| M4.0 or greater: 73 / month | (Median number of earthquakes over the past 10 years from 1996 through 2005) | |
| M5.0 or greater: 9 / month | (Median number of earthquakes over the past 30 years from 1976 through 2005) | |
| M6.0 or greater: 1.4 / month, approximately 17 / year | (Average number of earthquakes over the past 80 years from 1926 through 2005) |
The following regions have been noted as having significant seismic activity during the period from July 2006 to the end of June 2007.
| - Off-shore east of the Chishima Islands | M7.9 on November 15, 2006 | |
| - Off-shore east of the Chishima Islands | M8.2 on January 13, 2007 | |
| - Noto Hanto Earthquake | M6.9 on March 25, 2007 (depth approximately 10km) | |
| - Central Mie prefecture | M5.4 on April 15, 2007 (depth approximately 15km) | |
| - Off-shore northwest of Miyakojima | seismic activity with M6.3, M6.7 and M6.1 on April 20, 2007 |
There is no supplementary information for the Hokkaido region.
There is no supplementary information for the Tohoku region.
"There have been no anomalous changes observed in the GPS data for the Tokai region.":
(This evaluation is in agreement with the views presented at the procedural
meeting on July 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, July 30, 2007)
"So far, there have been no changes of activity which are likely to
be associated with the so-called Tokai earthquake.
There was no remarkable seismic activity in general. Under central Shizuoka, the seismicity remains at a level lower than normal within the plate, and higher within the crust. In other regions, seismic activity is generally at a normal level.
There were no notable changes observed in crustal movements in the Tokai region and its neighboring areas."
- On July 20, there was a M4.4 earthquake under the ocean near Izu Oshima Island. The seismic activity was strong at first, however, it has been gradually subsiding. For the recent seismicity under the ocean near Izu Oshima Island, there was similar activity in June 2002, February and July 2004, and June 2006. The seismic activity has been slightly increasing since May 2007.
to the text"On July 16, there was a deep M6.7 earthquake at a depth of approximately 370km off-shore of Kyoto prefecture. The focal mechanism had a compression axis in the direction of the subducting plate. This event occurred within the Pacific plate.":
Since the Pacific plate, which subducts from east to the west, efficiently transmits seismic waves, the areas along the Pacific coast from Hokkaido through the Kanto region had stronger shaking than the area near the main shock. (areas of anomalous seismic intensity).
There is no supplementary information for the Kyushu - Okinawa region.
to the text
- On July 9, there was a M6.2 earthquake off-shore east of the Chishima Islands. This event occurred within the aftershock area of the M7.9 event on November 15, 2006 and the M8.2 event on January 13, 2007.
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Reference 1 Earthquakes that are described in the "Evaluation of Seismic Activity" (Monthly Report of Seismic Activity in Japan) have the following features. 1) Events of M6.0 and greater, or events that have maximum seismic intensity 4 or greater 2) Onshore events of M4.5 and greater that have maximum seismic intensity 3 or greater 3) Events under the ocean areas of M5.0 or greater that have maximum seismic intensity 3 or greater |
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| Reference 2 Information that is described in the "Supplementary Information to the Evaluation" includes: |
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| 1) | Reference information related to seismic activity described in the "Evaluation of Seismic Activity" |
| 2) | Recent earthquake activity over the past year related to the events described in "Major Seismic Activity" in the "Evaluation of Seismic Activity" |
| 3) | Seismic activity that has been evaluated, but not included in the "Evaluation of Seismic Activity" because it is within normal bounds and not prominent |