|
September 10, 2007 |
| * | On August 2, there was a M6.4 earthquake off-shore west of Sakhalin [near southern Sakhalin]. | |
| * | Since August 13, there has been seismic activity near the coastal area of Kujukurihama [off-shore east of Chiba prefecture] with the largest earthquake a M5.3 event on August 16. In addition, a M4.8 event on August 18 had a maximum seismic intensity 5 Lower. | |
| * | On August 16, there was a M8.0 earthquake along the coast of Peru. Related to this event, small tsunamis were observed along all of the Pacific coast of Japan. to supplementary reports |
| * | On August 26, there was a M5.4 earthquake at a depth of approximately 50km off-shore east of Hokkaido. The focal mechanism had a compression axis in a NW-SE direction. This event occurred within the Pacific plate. | |
| * | On August 22, there was a M5.4 earthquake at a depth of approximately 120km under eastern Oshima subprefecture. The focal mechanism had a compression axis in a nearly N-S direction. This event occurred within the Pacific plate. to supplementary reports | |
| * | There was no remarkable activity. to supplementary reports |
| * | Since August 13, there was seismic activity near the coastal area of Kujukurihama [off-shore east of Chiba prefecture] with the largest earthquake a M5.3 event on August 16. A M4.8 event on August 18 had a maximum seismic intensity 5 Lower. The focal mechanisms of those events showed reverse faults with compression axes in a nearly NNW-SSE direction. It is thought that those events occurred near the boundary between the Philippine Sea and the continental plates. Around the same time as this seismic activity, crustal movements were observed on the Boso Peninsula. In this region, slightly strong seismic activity has coincided with slow slip events, as recently seen in 1996 and 2002. For this activity, slow slip is also thought to have occurred around the same time as the seismicity. It is estimated that the slow slip was equivalent to approximately a Mw6.4 event. |
| * | The aftershock activity of the Niigataken Chuetsu-oki Earthquake in 2007 on July 16 has been declining. According to the GPS data, postseismic movements were observed in the area near the focal region. |
| * | There have been no anomalous changes observed in the GPS data for the Tokai region. to supplementary reports |
| * | There was no remarkable activity. to supplementary reports | |
| * | Off-shore northwest of the Okinawa Main Island, there was a M6.1 earthquake on August 1 and a M6.3 earthquake on August 7. Focal mechanisms of both events showed strike-slip faults with tension axes in a NW-SE direction. | |
| * | On August 9, there was a M5.1 earthquake at a depth of approximately 45km near Okinoerabujima [under the ocean area near the Okinawa Main Island]. The focal mechanism showed a reverse fault with a compression axis in a WNW-ESE direction. It is thought that this event is related to the subducting Philippine Sea plate. to supplementary reports | |
| * | On August 2, there was a M6.4 earthquake off-shore west of Sakhalin [near southern Sakhalin]. The focal mechanism showed a reverse fault with a compression axis in an E-W direction. | |
| * | On August 16, there was a M8.0 earthquake along the coast of Peru. Related to this event, small tsunamis were observed along all of the Pacific coast of Japan. There was also a M8.2 earthquake on June 24, 2001 along the coast of Peru, which caused similar size tsunamis observed in Japan. to supplementary reports | |
| * | On September 4, there was a M6.3 earthquake at a depth of approximately 130km under the Chishima Islands. | |
| * | On September 7, there was a M6.5 earthquake near Taiwan. | |
[ ] were the regional names of the epicenters used in the Japan Meteorological Agency announcement.
September 10, 2007
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during August 2007.
| M4.0 or greater: 125 (93 events occurred in July) | |
| M5.0 or greater: 21 (17 events occurred in July) | |
| M6.0 or greater: 3 (There has been a total of 17 events for 2007 by the end of August.) |
(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 August 2006 to the end of July 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 | |
| - Niigataken Chuetsu-oki Earthquake in 2007 | M6.8 on July 16, 2007 (depth approximately 10km) |
"On August 26, there was a M5.4 earthquake at a depth of approximately 50km off-shore east of Hokkaido.
The focal mechanism had a compression axis in a NW-SE direction. This event occurred within the Pacific plate.":
This event occurred within the aftershock area of the 1994 Off-shore East Hokkaido Earthquake.
There is no supplementary information for the Tohoku region.
"The aftershock activity of the Niigataken Chuetsu-oki Earthquake
in 2007 on July 16 has been declining.":
According to an aftershock study from rapid survey observations, several
complicated fault structures were seen in a shallow area of the focal 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 September 1 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, September 1, 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."
There is no supplementary information for the Kyushu-Okinawa region.
There is no supplementary information for the Kyushu-Okinawa region.
to the text
"On August 2, there was a M6.4 earthquake off-shore west of Sakhalin
[near southern Sakhalin]. The focal mechanism showed a reverse fault with
a compression axis in an E-W direction.":
According to the National Oceanic and Atmospheric Administration, small tsunamis were observed on southern Sakhalin associated with this event. Tidal level changes were observed on the coasts of the Japan Sea and Okhotsk Sea in Hokkaido. These were confirmed to be before the arrival time of the tsunami for this earthquake, and showed large peak values. At that time, a tsunami forecast (tsunami advisory) was issued, based on the observation data. However, judging from the observed data of air pressure variations, the main cause of the signals is thought to be meteorological disturbances.
|
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 |
|
| Reference 2 Information that is described in the "Supplementary Information to the Evaluation" includes: |
|
| 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 |