March 11, 2010
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion

Seismic Activity for February 2010

1 Major Seismic Activity

* On February 7, there was a M6.5 earthquake under the ocean area near Ishigakijima.

* On February 27, there was a M6.9 earthquake (preliminary) under the ocean area near the Okinawa Main Island. This event had maximum seismic intensity 5 Lower in Okinawa prefecture. In addition, small tsunamis were observed in Okinawa prefecture.

* On February 27, there was a Mw8.8 earthquake along the central coast of Chile. This earthquake caused tsunamis observed in a large area of Japan, mostly along the Pacific coast, from Hokkaido through Okinawa.

• Seismic Activity for All of Japan during February 2010 (Magnitude 4.0 and greater)

to supplementary reports

2 Nationwide Seismic Activity by Region

(1) Hokkaido Region

There was no remarkable activity.

• Hokkaido Region

to supplementary reports

(2) Tohoku Region

There was no remarkable activity.

• Tohoku Region

to supplementary reports

(3) Kanto-Chubu Region

* On February 7, there was a M4.0 earthquake at a depth of approximately 10km in the Noto region, Ishikawa prefecture. The focal mechanism showed a strike-slip fault with a compression axis in a NW-SE direction. This event occurred within the crust.

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

• Kanto - Chubu Region
• Earthquake in the Noto Region, Ishikawa Prefecture on February 7
• 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] (February 2009 - February 2010)
• 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 February 21, there was a M4.5 earthquake at a depth of approximately 15km in Iyonada. The focal mechanism showed a strike-slip fault with a compression axis in an ENE-WSW direction. This event occurred within the crust.

• Kinki-Chugoku-Shikoku Region
• Earthquake in Iyonada on February 21

to supplementary reports

(5) Kyushu-Okinawa Region

* On February 7, there was a M6.5 earthquake under the ocean area near Ishigakijima. The focal mechanism showed a strike-slip fault with a tension axis in a N-S direction.

* On February 27, there was a M6.9 earthquake (preliminary) under the ocean area near the Okinawa Main Island. The focal mechanism showed a strike-slip fault with a tension axis in a NW-SE direction. This event caused small tsunamis in Okinawa, one of which was observed to be 0.1m high in Nanjo city, Okinawa prefecture. According to the GPS data, some crustal movements associated with this earthquake were observed in the area centered on the Okinawa Main Island, such as a displacement of approximately 1cm to the northwest at the Yonashiro station.

• Kyushu Region
• Okinawa Region
• Earthquake under the Ocean Area near Ishigakijima on February 7
• Earthquake under the Ocean Area near the Okinawa Main Island on February 27
• Tsunamis Generated by the Earthquake under the Ocean Area near the Okinawa Main Island on February 27
• Crustal Movements Associated with the Earthquake under the Ocean Area near the Okinawa Main Island (February 27, Mw7.0)

to supplementary reports

(6) Other Regions

* On February 6, there was a M6.1 earthquake in the ocean area of the Chishima Islands.

* On February 18, there was a M6.8 earthquake at a depth of approximately 620km near Vladivostok. The focal mechanism had a compression axis in the direction of the subducting Pacific plate. This event occurred within the Pacific plate.

* On February 27, there was a Mw8.8 earthquake along the central coast of Chile. This earthquake caused tsunamis observed in a large area of Japan, mostly along the Pacific coast, from Hokkaido through Okinawa, such as 1.2m high tsunamis seen in Kuji Port, Iwate prefecture and in Susaki Port, Kochi 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 Nazca and South American plates.

• Earthquake in the Ocean Area of the Chishima Islands on February 6
• Earthquake near Vladivostok on February 18
• Earthquake along the Central Coast of Chile on February 27, 2010
• Tsunamis Generated by the Earthquake along the Central Coast of Chile on February 27, 2010 (1)
• Tsunamis Generated by the Earthquake along the Central Coast of Chile (3) – Comparisons to the 1960 Chile Earthquake –

to supplementary reports

Supplement

* On March 1, there was a M4.9 earthquake at a depth of approximately 120km under the southern inland area of Akita prefecture [under the southern inland area of Iwate prefecture]. The focal mechanism had a compression axis in an ENE-WSW direction. This event occurred within the Pacific plate.

* On March 4, there was a M6.4 earthquake in Taiwan.

* On March 6, there was a M5.5 earthquake off-shore east of Hokkaido.

• Earthquake under the Southern Onshore Area of Akita Prefecture on March 1
• Earthquake near Taiwan on March 4
• Earthquake Off-shore East of Hokkaido on March 6

[ ] was the regional name of the epicenter used in the Japan Meteorological Agency announcement.

Supplementary Information to the Evaluation of Seismic Activity for February 2010 by the Earthquake Research Committee

March 11, 2010

1 Major Seismic Activity

The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during February 2010.

• M4.0 or greater: 90 (80 events occurred in January)
• M5.0 or greater: 16 (15 events occurred in January)
• M6.0 or greater: 4 (There has been a total of 4 events by the end of February in 2010.)

(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 February 2009 to the end of January 2010.

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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.

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(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 February 22 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, February 22, 2010)

"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
Within the crust under mid-western Shizuoka prefecture, general seismicity has been slightly strong since mid-2005
There continue to be fewer events within the Philippine Sea plate under the region around Hamana lake
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."

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(4) Kinki-Chugoku-Shikoku Region

  – According to the GPS data, non-stationary crustal movements were observed near Bungo Strait, which are thought to have been caused by slow slip at the boundary between the Philippine Sea and the continental plates. Movements started in the fall of 2009, and there was a displacement of approximately 1cm to the southeast at the Tosashimizu-3 station by early February. In addition, a long-term slow slip was seen in this vicinity during the periods from 1996 through 1997 and from 2003 through 2004.

• Non-stationary Crustal Movements in the Area around Bungo Strait (1)
• Non-stationary Crustal Movements in the Area around Bungo Strait (2)

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(5) Kyushu-Okinawa Region

"On February 7, there was a M6.5 earthquake under the ocean area near Ishigakijima. (excerpted)"
A tsunami advisory was issued associated with this event, although no tsunamis were observed. In this vicinity, there was a M6.7 earthquake and a M6.6 earthquake on August 17, 2009.

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(6) Other Regions

"On February 6, there was a M6.1 earthquake in the ocean area of the Chishima Islands.)"
In this vicinity, there was a M7.9 earthquake on November 15, 2006.

"On February 27, there was a Mw8.8 earthquake along the central coast of Chile. (excerpted)"
In this vicinity, there was a Mw9.5 earthquake in 1960. The generated tsunamis reached Japan and caused damage with 142 dead and injured people (Chile Earthquake Tsunamis).

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