October 12, 2010
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* There was no remarkable activity.
* On September 4, there was a M5.1 earthquake at a depth of approximately 60km, off-shore of Kushiro. The focal mechanism showed a reverse fault with a compression axis in a NNE-SSW direction.
* On September 28, there was a M5.3 earthquake at a depth of approximately 100km near Kunashir Island. The focal mechanism showed a strike-slip fault with a compression axis in a WNW-ESE direction. This event occurred within the Pacific plate.
* On September 1, there was a M5.0 earthquake at a depth of approximately 45km, off-shore of Miyagi 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.
* On September 13, there was a M5.8 earthquake at a depth of approximately 65km, off-shore east of Aomori 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.
* On September 29 at 16:59 (JST), there was a M5.7 earthquake at a depth of approximately 5km in Nakadoori, Fukushima prefecture. The focal mechanism had a compression axis in an E-W direction. This event occurred within the crust. In addition, there has been brisk activity of earthquakes such as M4.8 at 12:01 on 29th and M4.6 at 01:23 on 30th. Since then, the activity has gradually been decaying and continuing. According to the data of continuous GPS monitoring and Synthetic Aperture Radar (SAR) from the advanced land observing satellite, "Daichi", crustal movements were observed near the epicenter.
* On September 22, there was a M4.5 earthquake at a depth of approximately 35km, under northeastern Chiba prefecture. This event occurred near the boundary between the Philippine Sea and the continental plates. The focal mechanism showed a normal fault with a tension axis in a NE-SW direction.
* On September 27, there was a M4.5 earthquake at a depth of approximately 70km, under northwestern Chiba prefecture. The focal mechanism had a compression axis in a WNW-ESE direction. This event occurred at the boundary between the Pacific and the Philippine Sea plates.
* There have been no anomalous changes observed in the GPS data for the Tokai region.
There was no remarkable activity.
There was no remarkable activity.
* On October 3, there was a M4.7 earthquake at a depth of approximately 20km in the Joetsu region, Niigata prefecture. The focal mechanism showed a reverse fault with a compression axis in a WNW-ESE direction. This event occurred within the crust.
* On October 4, there was a M6.4 earthquake under the ocean area near Miyakojima. The focal mechanism had a compression axis in a NE-SW direction.
* On October 6, there was a M4.5 earthquake in Tosa Bay.
October 12, 2010
Earthquake Research Committee
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during September 2010.
(reference)
The following events for the period from September 2009 to the end of August 2010 have been listed as "Major Seismic Activity" in monthly "Evaluation of Seismic Activity".
| – Off-shore East of the Izu Peninsula | Seismic activity with M5.0 on December 17, M5.1 on December 18, 2009 |
|
| |
–Under the Ocean Area near Ishigakijima | M6.5 on February 7, 2010 |
| – Under the Ocean Area near the Okinawa Main Island | M7.2 on February 27, 2010 | |
| – Along the Central Coast of Chile | Mw8.8 on February 27, 2010 | |
| |
– Off-shore of Fukushima Prefecture | M6.7 on March 14, 2010 |
| |
– Off-shore of Fukushima Prefecture | M6.2 on June 13, 2010 |
| |
– Northeastern Chiba Prefecture | M4.9 on July 23, 2010 |
There is no supplementary information for the Hokkaido region.
–There is no supplementary information for the Hokkaido region.
"On September 22, there was a M4.5 earthquake at a depth of approximately
35km, under northeastern Chiba prefecture. (Excerpted)":
At almost the same place as the recent event, there was a M5.0 earthquake
on July 23, 2010 (maximum seismic intensity 5 Lower), and its focal mechanism
showed a reverse fault with a compression axis in a NNW-SSE direction.
This mechanism is different from that of the recent event.
"There have been no anomalous changes observed in the GPS data for the Tokai region.":
(This evaluation is in agreement with the views (reference below) presented
at the procedural meeting on September 27 of the Assessment Committee for
Areas under Intensified Measures against Earthquake Disaster.)
(Reference) Recent seismic and crustal activity in the Tokai region and its vicinity (Seismological and Volcanological Department, Japan Meteorological Agency, September 27, 2010)
"So far, there have been no changes of activity which are likely to be associated with the Tokai earthquake.
1. Status of seismicity
General seismicity has been slightly strong since mid-2005 within the crust under mid-western Shizuoka prefecture.
There continue to be fewer events within the Philippine Sea plate under the region around Hamanako. In other regions, seismic activity is generally at a normal level.
2. Status of crustal movements
There have been no remarkable changes observed over the entire region.
According to the GPS data and leveling results, the trend of long-term subsidence at Omaezaki has been continuing as before."
– Non-stationary crustal movements are still observed near Bungo Strait, which have been seen since around autumn 2009. It is thought that they have been caused by slow slip at the boundary between the Philippine Sea and the continental plates.
There is no supplementary information for the Kyushu-Okinawa region.
"On October 4, there was a M6.4 earthquake under the ocean area near Miyakojima. (Excerpted)"
The tsunami warning associated with this earthquake was issued, but no
tsunami was observed. In the vicinity of the recent event, there was a
M6.5 earthquake on August 5, 2009.
The magnitude of the earthquake that occurred under the northeastern Chiba prefecture on July 23, 2010 was 4.9 in the "Evaluation of Seismic Activity for July 2010". It is now 5.0 as a result of detailed inspection.
Reference 1
Earthquakes that are described in the "Evaluation of Seismic Activity" (Monthly Report of Seismic Activity in Japan) have the following features.
Reference 2
Information that is described in the "Supplementary Information to the Evaluation" includes: