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May 9, 2007 |
| * | On April 15, there was a M5.4 earthquake at a depth of approximately 15km in central Mie prefecture. This event had maximum seismic intensity 5 Upper, and caused damage with some injured people. |
| * | On April 20, there was a sequence of seismicity with the largest event a M6.7 earthquake off-shore northwest of Miyakojima. to supplementary reports |
| * | On April 27, there was a M5.2 earthquake at a depth of approximately 60km off-shore of Tokachi. The focal mechanism had a tension axis in a NE-SW direction. It is thought that this event is related to the subduction of the Pacific plate. | |
| * | On April 19, there was a M5.6 earthquake at a depth of approximately 130km under mid-eastern Iburi subprefecture. The focal mechanism had a tension axis in a NNW-SSE direction. This event occurred within the Pacific plate. | |
| * | On April 23, there was a M4.6 earthquake at a depth of approximately 10km in southern Rumoi subprefecture. The focal mechanism showed a reverse fault with a compression axis in an E-W direction. This event occurred within the crust. to supplementary reports | |
| * | On April 10, there was a M4.1 earthquake at a depth of approximately 75km off-shore of Miyagi prefecture [southern coast of Iwate prefecture]. |
| * | On April 5 and 12, there were M4.5 earthquakes at a depth of approximately 10km under Sendai Bay [off-shore of Miyagi prefecture]. The focal mechanisms showed reverse faults with a compression axis in an ENE-WSW direction for one event and in an ESE-WNW direction for the other event. These earthquakes occurred within the crust. to supplementary reports |
| * | On April 14, there was a M5.3 earthquake off-shore east of Hachijojima. | |
| * | On April 15, there was a M5.4 earthquake at a depth of approximately 15km in central Mie prefecture. The seismic activity was a main shock - aftershock sequence. The aftershock activity has been subsiding. The largest aftershock so far was a M4.6 event on April 15. The focal mechanism of the main shock showed a reverse fault with a compression axis in a NE-SW direction. This event occurred within the crust. Located east of the main shock is the eastern part of the Nunobiki-sanchi-toen Fault Zone, which is a reverse fault striking in a NNE-SSW direction and dipping to the west. According to the GPS data, there were no remarkable changes before or after this event. | |
| * | On April 28, there was a M4.6 earthquake at a depth of approximately 10km in mid-western Mino, Gifu prefecture. The focal mechanism showed a reverse fault with a compression axis in an E-W direction. This event occurred within the crust. | |
| * | The aftershock activity of the Noto Hanto earthquake on March 15 (Noto Hanto Earthquake in 2007) has been declining on the whole, although there were M4.7 events on the southwestern side of the aftershock area on April 6, and on the northeastern side on May 2. | |
| * | On April 16, there was a M5.1 earthquake under the ocean near Chichijima. | |
| * | There have been no anomalous changes observed in the GPS data for the Tokai region. to supplementary reports | |
| * | On April 26, there was a M4.0 earthquake at a depth of approximately 5km in northern Wakayama prefecture. | |
| * | On April 26, there was a M5.3 earthquake at a depth of approximately 40km under Touyo, Ehime prefecture. The focal mechanism showed a strike-slip fault with a tension axis in an E-W direction. This event occurred within the Philippine Sea plate. to supplementary reports | |
| * | On April 21, there was a M5.7 earthquake at a depth of approximately 40km near Okinoerabujima [under the ocean near the Okinawa Main Island]. The focal mechanism showed a reverse fault with a compression axis in a WNW-ESE direction. It is thought that this event is related to the subduction of the Philippine Sea plate. |
| * | On April 20, at 10:45 (JST) there was a M6.7 earthquake off-shore northwest of Miyakojima. Although there was strong seismic activity with a M6.3 event at 09:26, and a M6.1 event at 11:23 on the same day, the strong seismic activity subsided by the end of April. The focal mechanism of the largest earthquake (M6.7) showed a normal fault with a tension axis in a NNW-SSE direction. It is thought that this event is related to the extension of the Okinawa Trough. to supplementary reports |
| * | On May 7, there was a M5.1 earthquake at a depth of approximately 50km near Yakushima [under the ocean near Tanegashima]. |
| * | On May 8, there was a M4.5 earthquake at a depth of approximately 45km under southern Ibaraki prefecture. The focal mechanism showed a reverse fault with a compression axis in a NW-SE direction. This event occurred at the boundary between the Philippine Sea and the continental plates. |
[ ] were the regional names of the epicenters used in the Japan Meteorological Agency announcement.
May 9, 2007
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during April 2007.
| M4.0 or greater: 145 (122 events occurred in March) | |
| M5.0 or greater: 35 (16 events occurred in March) | |
| M6.0 or greater: 3 (3 events occurred in March) |
Of the events listed above:
8 earthquakes of M4.0 or greater were associated with the aftershock activity of the Noto Hanto Earthquake in 2007.
15 earthquakes of M4.0 or greater, 8 earthquakes of M5.0 or greater, and 3 earthquakes of M6.0 or greater were associated with the seismic activity of the earthquake off-shore northwest of Miyakojima.
27 earthquakes of M4.0 or greater and 6 earthquakes of M5.0 or greater were associated with the seismic activity of the earthquake off-shore southeast of Etorofu Island.
(reference)
| M4.0 or greater: 73 / month | (Median number of earthquakes over the past 10 years from 1996 through 2005) | |
| M5.0 or greater: 9 / month | (Median number of earthquakes over the past 30 years from 1976 through 2005) | |
| M6.0 or greater: 1.4 / month, approximately 17 / year | (Average number of earthquakes over the past 80 years from 1926 through 2005) |
The following regions have been noted as having significant seismic activity during the period from April 2006 to the end of March 2007.
| - Off-shore east of the Izu Peninsula | seismic activity with M5.8 on April 21 and M4.5 on April 30, 2006 | |
| - Central Oita prefecture | M6.2 on June 12, 2006 (depth approximately 150km) | |
| - Off-shore east of the Chishima Islands | M7.9 on November 15, 2006 | |
| - Off-shore east of the Chishima Islands | M8.2 on January 13, 2007 | |
| - Noto Hanto Earthquake | M6.9 on March 25, 2007 (depth approximately 10km) |
"On April 23, there was a M4.6 earthquake at a depth of approximately 10km in southern Rumoi subprefecture. The focal mechanism showed a reverse fault with a compression axis in an E-W direction. This event occurred within the crust."
This event occurred within the aftershock area of the M6.1 earthquake on December 14, 2004 (maximum seismic intensity 5 Upper).
- From late March through early April, light seismic activity was observed off-shore southeast of Etorofu Island, with the largest earthquake a M5.5 event (on April 2).
"On April 10, there was a M4.1 earthquake at a depth of approximately 75km off-shore of Miyagi prefecture [southern coast of Iwate prefecture]."
This event occurred within the aftershock area of the M7.1 earthquake on May 26, 2003 (maximum seismic intensity 6 Lower).
"On April 5 and 12, there were M4.5 earthquakes at a depth of approximately 10km under Sendai Bay [off-shore of Miyagi prefecture]. The focal mechanisms showed reverse faults with a compression axis in an ENE-WSW direction for one event and in an ESE-WNW direction for the other event. These earthquakes occurred within the crust."
In the vicinity of this event, there is a fault that shows signs of having
had activity in the Quaternary.
"The aftershock activity of the Noto Hanto earthquake on March 15 (Noto
Hanto Earthquake in 2007) has been declining on the whole, although there were M4.7 events on the southwestern side of the aftershock area on April 6, and on the northeastern side on May 2."
Crustal movements associated with the fault plane of the Noto Hanto Earthquake were observed using the data from Synthetic Aperture Radar (SAR) from the advanced land observing satellite, "Daichi".
"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 April 23 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" (Japan Meteorological Agency, Department of Seismology and Volcanology, April 23, 2007)
"So far, there have been no changes of activity which are likely to be associated with the so-called Tokai earthquake.
There was no remarkable seismic activity in general. The seismicity remains at a level lower than normal directly under the area from eastern Hamana Lake through central Shizuoka prefecture. In other regions, seismic activity is generally at a normal level.
There were no notable changes observed in crustal movements in the Tokai region and its neighboring areas."
to the text
There is no supplementary information for the Kinki - Chugoku - Shikoku region.
"On April 20, at 10:45 (JST) there was a M6.7 earthquake off-shore northwest of Miyakojima. Although there was strong seismic activity with a M6.3 event at 09:26, and a M6.1 event at 11:23 on the same day, the strong seismic activity subsided by the end of April. The focal mechanism of the largest earthquake (M6.7) showed a normal fault with a tension axis in a NNW-SSE direction."
Associated with this event, a tsunami forecast (tsunami advisory) was issued, but no tsunami was observed. to the text
Reference 1Earthquakes that are described in the "Evaluation of Seismic Activity"(Monthly Report of Seismic Activity in Japan) are events of M6.0 and greater, or events of M4.0 and greater (M5.0 or greater off-shore) that have maximum intensity of 3 or greater. |
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| Reference 2 Information that is described in the "Supplementary Information to the Evaluation" includes: |
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| 1) | Reference information related to seismic activity described in the "Evaluation of Seismic Activity" |
| 2) | Recent earthquake activity over the past year related to the events described in "Major Seismic Activity" in the "Evaluation of Seismic Activity" |
| 3) | Seismic activity that has been evaluated, but not included in the "Evaluation of Seismic Activity" because it is within normal bounds and not prominent. |