August 10, 2009
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion

Seismic Activity for July 2009

1 Major Seismic Activity

There was no remarkable activity.

• Seismic Activity for All of Japan during July 2009 (Magnitude 4.0 and greater)

to supplementary reports

2 Nationwide Seismic Activity by Region

(1) Hokkaido Region

* On July 28, there was a M4.0 earthquake at a depth of approximately 10km, off-shore of Matsumae [off-shore southwest of Hokkaido]. The focal mechanism had a compression axis in a NW-SE direction. This event occurred within the crust.

• Hokkaido Region
• Earthquake Off-shore of Matsumae [Off-shore Southwest of Hokkaido] on July 28

to supplementary reports

(2) Tohoku Region

There was no remarkable activity.

• Tohoku Region

to supplementary reports

(3) Kanto-Chubu Region

*There have been no anomalous changes observed in the GPS data for the Tokai region.

• Kanto-Chubu Region
• Continuous GPS Monitoring in the Area from Kakegawa to Omaezaki
• Recent Crustal Movements in the Tokai Region (Horizontal Movements) [Ogata is the fixed reference point] (July 2008 – July 2009)
• Crustal Movements in the Tokai Region, Time series, Ogata is the fixed reference point (Postseismic movements have been removed)

to supplementary reports

(4) Kinki-Chugoku-Shikoku Region

* On July 22, there was a M4.6 earthquake off-shore of Cape Muroto [off-shore of Shikoku].

• Kinki-Chugoku-Shikoku Region
• Earthquake Off-shore of Cape Muroto [Off-shore of Shikoku] on July 22

to supplementary reports

(5) Kyushu-Okinawa Region

*On July 14, there was a M6.5 earthquake near Taiwan. The focal mechanism showed a reverse fault with a compression axis in a N-S direction.

• Kyushu Region
• Okinawa Region
• Earthquake near Taiwan on July 14

to supplementary reports

Supplement

* On August 3, there was a M4.7 earthquake at a depth of approximately 10km in the Amakusa Ashikita region, Kumamoto prefecture. The focal mechanism showed a strike-slip fault with a tension axis in a NNW-SSE direction. This event occurred within the crust.

* On August 5, there was a M6.5 earthquake under the ocean area near Miyakojima. The focal mechanism showed a reverse fault with a compression axis in a NW-SE direction. It is thought that this event occurred at the boundary between the Philippine Sea and the continental plates.

* On August 5, there was a M5.0 earthquake at a depth of approximately 35km under Hyuganada. The focal mechanism had a tension axis in a ENE-WSW direction. This event occurred within the Philippine Sea plate.

• Earthquake in the Amakusa Ashikita Region, Kumamoto Prefecture on August 3
• Earthquake under the Ocean Area near Miyakojima on August 5
• Earthquake under Hyuganada on August 5

to supplementary reports

[  ] were the regional names of the epicenters used in the Japan Meteorological Agency announcement.

Supplementary Information to the Evaluation of Seismic Activity for July 2009 by the Earthquake Research Committee

August 10, 2009

1 Major Seismic Activity

The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during July 2009.

• M4.0 or greater: 72 (90 events occurred in June)
• M5.0 or greater: 11 (15 events occurred in June)
• M6.0 or greater: 1 (There has been a total of 5 events by the end of July in 2009.)

(reference)

• M4.0 or greater: 73 / month (Median number of earthquakes over the past 10 years from 1998 through 2007)
• M5.0 or greater: 9 / month (Median number of earthquakes over the past 35 years from 1973 through 2007)
• M6.0 or greater: 1.4 / month, approximately 17 / year (Average number of earthquakes over the past 84 years from 1924 through 2007)

The following regions have been noted as having major seismic activity during the period from July 2008 to the end of June 2009.

to the text

2 Nationwide Seismic Activity by Region

(1) Hokkaido Region

There is no supplementary information for the Hokkaido region.

to the text

(2) Tohoku Region

There is no supplementary information for the Tohoku region.

to the text

(3) Kanto-Chubu 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 27 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" (Seismological and Volcanological Department, Japan Meteorological Agency, July 27, 2009)

"So far, there have been no changes of activity which are likely to be associated with the so-called Tokai earthquake.
1. Status of seismicity
There was no remarkable seismic activity in general.
There are continued less frequent occurrences of events equal to or larger than M3.5 within the Philippine Sea plate under mid-western Shizuoka prefecture. Also, there continue to be fewer events within the Philippine Sea plate under the region around Hamana lake. On the other hand, seismicity has been continuing to be slightly strong within the crust in mid-western Shizuoka prefecture. In other regions, seismic activity is generally at a normal level.

2. Status of crustal movements
There were no notable changes observed in general.
According to the GPS data and leveling results, the trend of long-term subsidence at Omaezaki has been continuing as before."

to the text

(4) Kinki-Chugoku-Shikoku Region

"On July 22, there was a M4.6 earthquake off-shore of Cape Muroto [off-shore of Shikoku]."
This earthquake occurred within the expected focal region of the Nankai Earthquake. The impact of this event on the Nankai Earthquake remains to be seen at this point.

to the text

(5) Kyushu-Okinawa Region

There is no supplementary information for the Kyushu-Okinawa region.

to the text

Supplement

- On August 2, there were M4.9 and a 4.8 earthquakes off-shore of Kaetsu, Niigata prefecture.

• Earthquakes Off-shore of Kaetsu, Niigata Prefecture on August 2

to the text

[  ] were the regional names of the epicenters used in the Japan Meteorological Agency announcement.