April 11, 2011
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On March 9, there was a M7.3 earthquake off-shore of Sanriku. This event had a maximum seismic intensity 5 Lower in Miyagi prefecture. This event caused tsunamis on the Pacific coast of a part of the Tohoku, Hokkaido-Kanto regions and Izu Islands.
* On March 11, there was a M9.0 earthquake# off-shore of Sanriku. This
event had a maximum seismic intensity 7 in Miyagi prefecture. This event
caused large tsunamis on the Pacific coast from the Hokkaido, Tohoku and
Kanto regions, with tsunami heights over 8.5 m in Miyako and over 8.0 m
in Ofunato. This event caused huge damage with more than 20,000 dead or
missing people.
# Japan Meteorological Agency named this earthquake "The 2011 off
the Pacific Coast of Tohoku Earthquake"
* On March 12, there was a M6.7 earthquake near the border between Nagano and Niigata prefectures. This event had a maximum seismic intensity 6 Upper in Nagano prefecture, and caused damage with a heavily injured person.
* On March 15, there was a M6.4 earthquake in eastern Shizuoka prefecture. This event had a maximum seismic intensity 6 Upper in Shizuoka prefecture, and caused damage with a heavily injured person.
* On March 19, there was a M6.1 earthquake in northern Ibaraki prefecture. This event had a maximum seismic intensity 5 Upper in Ibaraki prefecture.
* On March 23, there was a M6.0 earthquake in Hamadori, Fukushima prefecture. This event had a maximum seismic intensity 5 Upper in Ibaraki prefecture.
* On March 24, there was a M4.8 earthquake in southern Ibaraki prefecture. This event had a maximum seismic intensity 5 Lower in Ibaraki prefecture.
There was no remarkable activity.
* On March 9, there was a M7.3 earthquake off-shore of Sanriku. The focal mechanism showed a reverse fault with a compression axis in a WNW-ESE direction. This event occurred on the boundary between the Pacific and the continental plates. According to the GPS data, crustal movements associated with this event were observed and there was a movement of approximately 3 cm toward the east-southeast at the Ofunato station (Iwate prefecture)
* Refer to a separate sheet as to the 2011 off the Pacific Coast of Tohoku Earthquake and its aftershock activity.
* On March 11, there was a M5.1 earthquake at a depth of approximately 10 km in Hamadori, Fukushima prefecture.
* On March 11, there was a M5.2 earthquake at a depth of approximately 10 km in southern Miyagi prefecture.
* On March 12, there was a M6.4 earthquake at a depth of approximately 25 km, off-shore of Akita prefecture. The focal mechanism had a compression axis in an ENE-WSW direction.
* On March 23, there was a M6.0 earthquake at a depth of approximately 10 km in Hamadori, Fukushima prefecture. The focal mechanism showed a normal fault with a tension axis in an E-W direction. This is a shallow event that occurred within the crust. According to the GPS data, crustal movements associated with this event were observed, and there was a movement of approximately 6 cm toward the east-southeast at the Iwaki-2 station (Fukushima prefecture).
* On March 12, there was a M4.5 earthquake at a depth of approximately 5 km near the border between Gunma and Tochigi prefectures.
* On March 12 at 03:59 (JST), there was a M6.7 earthquake at a depth of approximately 10 km, near the border between Nagano and Niigata prefectures. The focal mechanism had a compression axis in a NW-SE direction. This event occurred within the crust. Since this event, there has been brisk seismicity such as two shocks with seismic intensity 6 Lower. According to the GPS data, crustal movements associated with this event were observed and there was a movement of approximately 39 cm toward the northeast at the Matsunoyama station (Niigata prefecture).
* On March 15, there was a M4.5 earthquake at a depth of approximately 45 km in northeastern Chiba prefecture. The focal mechanism had a compression axis in a WNW-ESE direction. This event occurred on the boundary between the Pacific and the Philippine Sea plates.
* On March 15 at 22:31 (JST), there was a M6.4 earthquake at a depth of approximately 15 km, in eastern Shizuoka prefecture. The focal mechanism had a compression axis in a N-S direction. There has been brisk seismicity such as a M4.2 earthquake (maximum seismic intensity 4) at 22:40 on the same day. According to the GPS data, crustal movements associated with this event were observed and there was a displacement of approximately 3 cm to the east-northeast at the Susono-1 station (Shizuoka prefecture).
* On March 16, there was a M4.0 earthquake at a depth of approximately 5 km in the Hida region, Gifu prefecture. The focal mechanism showed a strike-slip fault with a compression axis in a WNW-ESE direction. This event occurred within the crust.
* On March 16, there was a M5.4 earthquake at a depth of approximately 50 km in southern Ibaraki prefecture. The focal mechanism showed a reverse fault with a compression axis in a WNW-ESE direction. This event occurred on the boundary between the Pacific and the Philippine Sea plates.
* On March 19, there was a M6.1 earthquake at a depth of approximately 5 km in northern Ibaraki prefecture. The focal mechanism showed a normal fault with a tension axis in a NE-SW direction. This event occurred within the crust. According to the GPS data, crustal movements associated with this event were observed and there was a movement of approximately 2 cm toward the west-southwest at the Satomi station (Ibaraki prefecture). According to the data of Synthetic Aperture Radar (SAR) from the advanced land observing satellite, "Daichi", crustal movements were observed in the vicinity of the epicenter.
* On March 21, there was a M4.8 earthquake at a depth of approximately 5 km in the Hida region, Gifu prefecture. The focal mechanism showed a reverse fault with a compression axis in a NW-SE direction. This event occurred within the crust.
* On March 22, there was a M4.8 earthquake at a depth of approximately 45 km in northeastern Chiba prefecture.
* On March 24, there was a M4.8 earthquake at a depth of approximately 50 km in southern Ibaraki prefecture. The focal mechanism showed a reverse fault with a compression axis in a NNW-SSE direction. This event occurred on the boundary between the Philippine Sea and the continental plates.
* There have been no changes of activity which are likely to be associated with the Tokai earthquake in the GPS data for the Tokai region.
There was no remarkable activity.
* On March 7 at 19:13 (JST), there was a M5.1 earthquake under the ocean near Tokara Islands. The focal mechanism showed a normal fault with a tension axis in a NNE-SSW direction. There was brisk seismicity such as a M4.5 earthquake at 18:49 on the same day.
* On April 1, there was a M5.0 earthquake at a depth of approximately 10 km in the northern inland, Akita prefecture. The focal mechanism had a compression axis in an E-W direction. This event occurred within the crust.
* On April 2, there was a M5.0 earthquake at a depth of approximately 55 km in southern Ibaraki prefecture. The focal mechanism showed a reverse fault with a compression axis in a NW-SE direction. This event occurred on the boundary between the Philippine Sea and the continental plates.
April 11, 2011
Earthquake Research Committee
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during March 2011.
(reference)
The following events for the period from March 2010 to the end of February 2011 have been listed as "Major Seismic Activity" in monthly "Evaluation of Seismic Activity"
| – Off-shore of Fukushima Prefecture | M6.7 on March 14, 2010 (Depth of approximately 40km) |
|
| – Off-shore of Fukushima Prefecture | M6.2 on June 13, 2010 (Depth of approximately 40km) |
|
| – Northeastern Chiba Prefecture | M5.0 on July 23, 2010 (Depth of approximately 35km) |
|
| |
– Joetsu Region, Niigata Prefecture | M4.7 on October 3, 2010 (Depth of approximately 20km) |
| – Under the Ocean near Miyakojima | M6.4 on October 4, 2010 | |
| |
– Under the Ocean near Chichijima | M7.4 on December 22, 2010 |
There is no supplementary information for the Hokkaido region.
"On March 9, there was a M7.3 earthquake off-shore of Sanriku.(The rest is omitted.)"
In the vicinity of the recent event, there was brisk seismicity such as
four earthquakes of M5.0 or over in the last month.
"On March 23, there was a M6.0 earthquake at a depth of approximately 10 km in Hamadori, Fukushima prefecture. (The rest is omitted.)"
Since this event, there was brisk seismicity such as three earthquakes
of M5.0 or over..
"There have been no changes of activity which are likely to be associated
with the Tokai earthquake in the GPS data for the Tokai region":
(This evaluation is in agreement with the views presented at the regular
meeting on March 28 of the Assessment Committee for Areas under Intensified
Measures against Earthquake Disaster (reference below).)
(Reference) Recent seismic and crustal activity in the Tokai region and its vicinity (Seismological and Volcanological Department, Japan Meteorological Agency, March 28, 2011)
"So far, there have been no changes of activity which are likely to be associated with the Tokai earthquake.
1. Status of seismicity
In the Tokai area, there have been no remarkable changes of the seismicity associated with the 2011 off the Pacific Coast of Tohoku Earthquake. On March 15, there was a M6.4 earthquake in eastern Shizuoka prefecture, and its aftershock activity has been declining.
General seismicity has been slightly brisk 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.
Step changes associated with the 2011 off the Pacific Coast of Tohoku Earthquake were observed in the data of strain meters and GPS. Adding to this, the similar changes associated with the earthquake in eastern Shizuoka prefecture on March 15 were observed. These changes have recovered to a normal state.
According to the GPS data and leveling results, the trend of long-term subsidence at Omaezaki has been continuing. In view of the observation data of tilt, strain meters and others as a whole, the data showing remarkable changes associated with coupling state of the Philippine Sea and the continental plates in the expected focal region of the Tokai earthquake and its surrounding area have not been obtained."
– Since the 2011 off the Pacific Coast of Tohoku Earthquake, seismic activities have been brisk in inland from Tohoku through Kanto-Chubu regions. Such brisk activities have been seen in the southern inland of Akita prefecture, Aizu region of Fukushima prefecture, central Nagano prefecture, western Kanagawa prefecture, Izu region of Shizuoka prefecture, and the ocean near Niijima-Kozushima, except for the regions which are evaluated in Nationwide Seismic Activity by Region.
There is no supplementary information for the Kinki-Chugoku-Shikoku region.
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: