August 6, 2010
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On July 23, there was a M4.9 earthquake under northeastern Chiba prefecture. This event had a maximum seismic intensity 5 Lower in Ibaraki prefecture.
There was no remarkable activity.
* On July 4, there was a M5.2 earthquake at a depth of approximately 5 km in the southern inland area of Iwate prefecture. The focal mechanism showed a reverse fault with a compression axis in an E-W direction. This event occurred within the crust.
* On July 5, there was a M6.4 earthquake at a depth of approximately 35 km, off-shore of Iwate 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 continental plates.
* On July 27, there was a M5.3 earthquake at a depth of approximately 25 km, off-shore of Miyagi prefecture [off-shore of Iwate prefecture]. The focal mechanism showed a reverse fault with a compression axis in an ENE-WSW direction.
* On July 4, there was a M4.5 earthquake at a depth of approximately 90 km, under southern Ibaraki prefecture. This event occurred within the Pacific plate. The focal mechanism had a tension axis in a WNW-ESE direction.
* On July 23, there was a M4.9 earthquake at a depth of approximately 35 km, under northeastern Chiba prefecture. The focal mechanism showed a reverse fault with a compression axis in a NNW-SSE direction. This event occurred at the boundary between the Philippine Sea and the continental plates.
* There have been no anomalous changes observed in the GPS data for the Tokai region
* On July 21, there was a M5.1 earthquake at a depth of approximately 60 km, under Nara prefecture. The focal mechanism had a compression axis in a NW-SE direction. This event occurred within the Philippine Sea plate.
There was no remarkable activity.
* On August 3, there was a M4.6 earthquake at a depth of approximately 80 km, under northern Ibaraki prefecture.
[ ] was the regional name of the epicenter used in the Japan Meteorological
Agency announcement.
August 6, 2010
Earthquake Research Committee
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during July 2010.
(reference)
The following events for the period from July 2009 to the end of June 2010 have been listed as "Major Seismic Activity" in monthly "Evaluation of Seismic Activity"
| – Under Suruga Bay | M6.5 on August 11, 2009 (depth of approximately 25km) | |
| – Off-shore East of Hachijojima | M6.6 on August 13, 2009 | |
| – Under the Ocean Area near Ishigakijima | M6.7, M6.6 on August 17, 2009 | |
| – 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 |
There is no supplementary information for the Hokkaido region.
"On July 4, there was a M5.2 earthquake at a depth of approximately
5 km in the southern inland area of Iwate prefecture. (excerpted)":
This event occurred in the aftershock area of the 2008 Iwate-Miyagi Nairiku Earthquake (M7.2). It is the first time since the M5.3 earthquake on June 16, 2008 (maximum seismic intensity 4) that an earthquake of M5.0 or over occurred in the same aftershock area.
– Near the border between Iwate and Akita prefectures, there has been somewhat strong seismic activity with the largest M3.6 since around July 31.
"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 July 26 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, July 26, 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."
– The somewhat strong seismic activity that occurred in the area off-shore east of Hachijojima (on the east side of the trench axis) since around May 29 has been gradually subsiding.
– On July 23, there was a M4.4 earthquake at a depth of approximately 35 km, under western Kochi prefecture. The focal mechanism showed a strike-slip fault with a compression axis in a S-N direction.
– 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.
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: