June 9, 2015
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On May 3, there was a magnitude (M) 5.9 earthquake under the ocean area near Torishima. In addition to tsunami with height of 0.6 m observed at Yayene, Hachijojima, slight tsunami was observed along the Pacific coasts from Chiba to Okinawa prefectures.
* On May 13, there was a M6.8 earthquake offshore Miyagi prefecture. The maximum seismic intensity 5 Upper was observed and damage of partially collapsed houses was caused in Iwate prefecture.
* On May 22, there was a M5.1 earthquake under the ocean near Amami Oshima. The maximum seismic intensity 5 Lower was observed at Amami city, Kagoshima prefecture.
* On May 25, there was a M5.5 earthquake under the northern Saitama prefecture. The maximum seismic intensity 5 Lower was observed and damage of seriously injured persons was caused in Ibaraki prefecture.
* On May 30, there was a M8.1 deep earthquake offshore west of Ogasawara Islands. The maximum seismic intensity 5 Upper was observed in Tokyo (Ogasawara village) and Kanagawa prefectures and damage of injured persons was caused.
There was no remarkable activity.
* On May 3, there was a M5.0 earthquake at a depth of approximately 45 km, offshore Fukushima prefecture. The focal mechanism of this event showed a reverse fault type with a compression axis in a WNW-ESE direction. This event occurred at the boundary between the Pacific and the continental plates.
* On May 13, there was a M6.8 earthquake at a depth of approximately 45 km, offshore Miyagi prefecture. The focal mechanism of this event showed a reverse fault type with a compression axis in an E-W direction. This event occurred at the boundary between the Pacific and the continental plates. Small crustal deformation accompanying this event was observed in GNSS observations.
* On May 15, there was a M5.0 earthquake at a depth of approximately 50 km, offshore Fukushima prefecture. The focal mechanism of this event showed a reverse fault type with a compression axis in a WNW-ESE direction. This event occurred at the boundary between the Pacific and the continental plates.
* On May 3, there was a M 5.9 earthquake under the ocean area near Torishima. In addition to tsunami with height of 0.6 m observed at Yayene, Hachijojima, slight tsunami was observed along the Pacific coasts from Chiba to Okinawa prefectures.
* On May 11, there was a M6.3 earthquake under the ocean area near Torishima. The focal mechanism of this event showed a reverse fault type with a compression axis in an E-W direction.
* On May 25, there was a M5.5 earthquake at a depth of approximately 55 km under the northern Saitama prefecture. The focal mechanism of this event had a tension axis in an ENE-WSW direction. This event occurred within the Philippine Sea plate.
* On May 30, there was a M4.8 earthquake at a depth of approximately 55 km under the southern Ibaraki prefecture. The focal mechanism of this event had a compression axis in an N-S direction.
* On May 30, there was a M8.1 deep earthquake at a depth of approximately 680 km, offshore west of Ogasawara Islands. The focal mechanism of this event had a tension axis in an E-W direction. This event occurred within the Pacific plate.
* On May 31, there was a M6.6 earthquake under the ocean area near Torishima. The focal mechanism of this event showed a normal fault type with a tension axis in an ENE-WSW direction. This event occurred within the Pacific plate near the ridge axis.
* In the GNSS data for the Tokai region, there has been no change of activity which is likely to be associated with the Tokai earthquake.
There was no remarkable activity.
* On May 22, there was a M5.1 earthquake at a depth of approximately 20 km, under the ocean area near Amami Oshima. The focal mechanism had a tension axis in an NE-SW direction. This event occurred within the crust of the continental plate.
* On May 22, there was a M5.1 earthquake at a depth of approximately 20 km, under the ocean area near Amami Oshima. The focal mechanism had a tension axis in an NE-SW direction. This event occurred within the crust of the continental plate.
Note: [ ] was the regional name of the epicenter used in the Japan Meteorological Agency announcement.
GNSS (Global Navigation Satellite System) is a general name of satellite
positioning system such as GPS.
June 9, 2015
Earthquake Research Committee
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during May 2015.
(reference)
The following events for the period from May 2014 to late April, 2015 have been listed as "Major Seismic Activities" in monthly "Evaluation of Seismic Activities".
| – Ocean Area near the Izu Oshima | M6.0 on May 5, 2014 (Depth of approximately 160 km) |
|
| – Rat Islands, Aleutian Islands | Mw7.9 on June 24, 2014 | |
| – Offshore Iwate Prefecture | M5.9 on July 5, 2014 (Depth of approximately 50 km) |
|
| – Middle Eastern Iburi Region | M5.6 on July 8, 2014 (Depth of approximately 5 km) |
|
| – Offshore Fukushima Prefecture | M7.0 on July 12, 2014 | |
| – Offshore East of Aomori Prefecture | M6.1 on August 10, 2014 (Depth of approximately 50 km) |
|
| – Northern Tochigi Prefecture | M5.1 on September 3, 2014 (Depth of approximately 5 km) |
|
| – Southern Ibaraki Prefecture | M5.6 on September 16, 2014 (Depth of approximately 45 km) |
|
| – Northern Nagano Prefecture | M6.7 on November 22, 2014 (Depth of approximately 5 km) |
|
| – Southern Tokushima Prefecture | M5.1 on February 6, 2015 (Depth of approximately 10 km) |
|
| – Offshore Sanriku | M6.9 on February 17, 2015 | |
| – Offshore Iwate Prefecture | M5.7 on February 17, 2015 (Depth of approximately 50 km) |
|
| – Ocean Area near Yonagunijima | M6.8 on April 20 |
There is no supplementary information for Hokkaido region.
There is no supplementary information for Tohoku region.
– Within the aftershock area of the Tohoku-Oki Earthquake, the number
of earthquakes of M4.0 or over, during one year from March 2012 (March
2012 - February 2013) became less than one fifth, during one year from March
2013 (March 2013 - February 2014) became less than one tenth, and during
one year from March 2014 (March 2014 - February 2015) became less than one
fifteenth, of the number during about one year just after the Tohoku-Oki
Earthquake, and thus the aftershock activity has been decaying.
According to the GNSS data, crustal deformation which is thought to be postseismic deformation has still been observed in a wide area from the Tohoku through the Kanto-Chubu regions. During about one month just after the Tohoku-Oki Earthquake, at the maximum value, the horizontal movement was 30 cm, and the vertical subsidence and upheaval were 6 cm and 5 cm, respectively. Although both the horizontal and the vertical deformations were almost less than 1cm during the recent one month, the deformation has not yet returned to the state before the Tohoku-Oki Earthquake.
In case of the earthquake (Mw 9.1) offshore west of the northern Sumatra Island in 2004, there were Mw8.6 after four months, Mw8.5 after about two and a half years, Mw7.5 after about five and a half years, and Mw8.6 after about seven and a half years in the region of outer rise. Thus, there have been large earthquakes for long period within the source area and its surroundings.
Although the aftershock activity is gradually decaying as a whole, the activity is still in higher state than the one before the Tohoku-Oki Earthquake. In addition, there are overseas examples for gigantic earthquakes. Synthetically judging from these facts, within the aftershock area and its surroundings, there is fear that large earthquakes will occur from now on, and there is a possibility of strong shaking and high tsunami. It is necessary to pay attention continuously for it.
–"On May 3, there was a M 5.9 earthquake under the ocean area
near Torishima. (Excerpted)":
In the vicinity of this event, there were a M5.9 earthquake on June 13,
1984, a M6.2 one on September 5, 1996, and a M5.9 one on January 1, 2006,
which all caused tsunami observed, as well as in this case, in spite of
their rather small magnitude of 6.0 or so. Tsunami Advisory was announced
for this event.
–"On May 30, there was a M8.1 deep earthquake at a depth of
approximately 680 km, offshore west of Ogasawara Islands. (Excerpted)":
At this event, seismic intensity 1 or over is observed at every district
in Japan. Especially in the area ranging from Ogasawara Islands to the
eastern Japan, strong motion with the maximum seismic intensity 5 Upper
was observed, due to the intensive seismic waves propagated within the
subducting Pacific plate (seismic anomaly). The aftershock activity is
low. The maximum aftershock is a M5.6 earthquake which occurred on June
3. In the vicinity of the epicenter of this event, at the depth of 500
km or so, a stationary seismic activity is observed. But no seismic activity
is observed in the vicinity of the hypocenter of this event. Deep earthquakes
at a depth exceeding 600 km of M8 or so, are rare in the world.
–"In the GNSS data for the Tokai region, there has been no change of activity which is likely to be associated with the Tokai earthquake":
((This evaluation is in agreement with the views presented at the regular
meeting on May 18 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, May 18, 2015)
"No change of activity which is likely to be associated with the Tokai earthquake has been observed until now. (Excerpted)"
– In Mt. Hakone, there have been clusters of small magnitude earthquakes from April 26 (the maximum is M3.0 as of May 31). Tilt-meters and volumetric-strain-meters around Mt. Hakone and GNSS observations show a slight crustal deformation at the same period.
There is no supplementary information for Kinki-Chugoku-Shikoku region.
There is no supplementary information for Kyushui-Okinawa region.
–"On June 4, there was a M5.0 earthquake at a very shallow depth
in Abashiri region [Middle southern Kushiro region].(Excerpted)":
In the area near the epicenter, there were 9 earthquakes with the maximum
seismic intensity 1 or over until June 7.
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: