June 9, 2016
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On May 16, there was a magnitude (M) 5.5 earthquake under the southern Ibaraki prefecture. This event had a maximum seismic intensity 5 Lower observed in Ibaraki prefecture and caused damage with injured persons and so on.
* On May 3, there was a M5.9 earthquake offshore east of Hokkaido. The focal mechanism had a compression axis in an NW-SE direction.
* On May 12, there was a M5.0 earthquake at a depth of approximately 65 km, offshore southeast of Nemuro peninsula. The focal mechanism had a tension axis in the subducting direction of the Pacific plate. This event occurred within the Pacific plate.
* On May 24, there was a M4.4 earthquake at a depth of approximately 50 km, offshore Iwate prefecture. The focal mechanism showed a reverse fault type with a compression axis in a WNW-ESE direction. This event occurred on the boundary between the Pacific and the continental plates.
* On May 16, there was a M5.5 earthquake at a depth of approximately 40 km under the southern Ibaraki prefecture. The focal mechanism of this event showed a reverse fault type with a compression axis in an NW-SE direction. This event occurred on the boundary between the Philippine Sea and the continental plates.
* 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.
* A series of seismic activity of the 2016 Kumamoto earthquakes, in the area extending from Kumamoto region, Kumamoto prefecture to the central Oita prefecture, including a M6.5 earthquake on April 14 and a M7.3 one on April 16, is decaying as a whole. The activity in the Kumamoto region and the Aso region is still rather high: 8 earthquakes with maximum seismic intensity 4 and 43 earthquakes with maximum seismic intensity 3 occurred in May. The activity in the central Oita prefecture has decayed: there were 1 earthquake with maximum seismic intensity 2, and 5 earthquakes with maximum seismic intensity 1, but no earthquake with maximum seismic intensity 3 or over. According to the GNSS observation, crustal deformation after the M7.3 earthquake on April 16 was observed in the area centered on the series of the seismic activity.
* On May 31, there was a M6.2 earthquake at a depth of approximately 240 km, offshore northwest of Ishigakijima. 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 12 at 12:17, there was a M6.5 earthquake near Taiwan, and on the same day at 13:29, there was a M6.4 earthquake at almost the same place. The focal mechanisms of these earthquakes showed a normal fault type with a tension axis in an NNW-SSE direction.
* On May 31, there was a M6.1 earthquake in the northwest Pacific Ocean (offshore east of Simushir island. The focal mechanisms of this earthquake showed a reverse fault type with a compression axis in an NW-SE direction.
Note:GNSS (Global Navigation Satellite System) is a general name of satellite positioning system such as GPS.
June 9, 201
Earthquake Research Committee
The following are the numbers of earthquakes by magnitude that occurred in Japan and the surrounding area during May 2016.
(reference)
The following events for the period from May 2015 to late April 2016 have been listed as "Major Seismic Activities" in monthly "Evaluation of Seismic Activities."
| – Ocean Area near Torishima | M5.9 on May 3, 2015 | |
| – Offshore Miyagi Prefecture | M6.8 on May 13, 2015 (Depth of approximately 45 km) |
|
| – Ocean Area near Amami Oshima | M5.1 on May 22 (Depth of approximately 20 km) |
|
| – Northern Saitama Prefecture | M5.5 on May 25, 2015 (Depth of approximately 55 km) |
|
| – Offshore West of Ogasawara Islands | M8.1 on May 30 (Depth of approximately 680 km) |
|
| – Abashiri Region | M5.0 on June 4, 2015 (At a very shallow depth) |
|
| – Northern Inland of Iwate Prefecture | M5.7 on July 10, 2015 (Depth of approximately 90 km) |
|
| – Southern Oita Prefecture | M5.7 on July 13, 2015 (Depth of approximately 60 km) |
|
| – Tokyo Bay | M5.2 on September 12, 2015 (Depth of approximately 55 km) |
|
| – Central Coast of Chile | Mw8.3 on September 17, 2015 | |
| – Offshore West of the Satsuma Peninsula | M7.1 on November 14, 2015 | |
| – Sanpachi-Kamikita Region, Aomori Prefecture | M4.6 on January 11, 2016 (Depth of approximately 10 km) |
|
| – Offshore Urakawa | M6.7 on January 14, 2016 (Depth of approximately 50 km) |
|
| – Kumamoto Earthquakes | M6.5 on April 14, 2016 and M7.3 on April 16, 2016 (Depth of approximately 10 km) |
There is no supplementary information for Hokkaido region.
There is no supplementary information for Tohoku region.
–"On May 16, there was a M5.5 earthquake at a depth of approximately
40 km under the southern Ibaraki prefecture. (Excerpted).":
After this event, there were some seismic activities such as a M3.9 and
a M4.1 earthquakes occurring on May 17.
–"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 30 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 30, 2016)
"No change of activity which is likely to be associated with the Tokai earthquake has been observed until now. (Excerpted)"
– Non-stationary crustal deformation surrounding the Kii Channel observed from mid-2014 is still continuing. This deformation is thought to be due to a slow slip (slow-slip) at the boundary between the Philippine Sea and the continental plates.
– Non-stationary crustal deformation surrounding the Bungo Channel observed from around December 2015 is still continuing. This deformation is thought to be due to a slow slip (slow-slip) at the boundary between the Philippine Sea and the continental plates.
–"A series of seismic activity of the 2016 Kumamoto earthquakes,
in the area extending from Kumamoto region, Kumamoto prefecture to the
central Oita prefecture, including a M6.5 earthquake on April 14 and a
M7.3 one on April 16, (Excerpted).":
Judging from the present decaying situation of the seismic activity, the possibility of occurrence of a M6 or so aftershock (maximum seismic intensity of order of 6 Lower) in the Kumamoto region, Kumamoto prefecture and Aso region has been lowered.
In cases of the 2014 Mid Niigata prefecture Earthquake (M6.8) and the earthquake in Hamadori, Fukushima prefecture in 2011 (M7.0), aftershocks of M5.0 or so occurred 1 to 2 months after the main shocks. Therefore we should pay attention to an aftershock of M5 or so (maximum seismic intensity of order of 5 Upper) in Kumamoto region, Kumamoto prefecture and Aso region, at least for 1 month or so from now on. In the central Oita prefecture, the present aftershock activity will remain for a while, but the possibility of occurrence of an aftershock of M5 or so (maximum seismic intensity of order of 5 Upper) has been lowered.
In Kyushu region, as is the case for the earthquake in Aso region, Kumamoto prefecture (M6.1) and the earthquake in central Oita prefecture (M6.4), both in 1975, and for the 1997 seismic activity in Satsuma region, Kagoshima prefecture (M6.6 and M6.4), the second earthquake of M of the same order with the first occurred in the neighboring region, 2 or 3 months after the first. Therefore in the region extending from Kumamoto prefecture to Oita prefecture, we should be prepared to the possibility of being shaken with seismic intensity 6 Lower or over, which cannot be denied at least for 1 month or so from now on.
– There was a seismic activity offshore west of Satsuma peninsula beginning on May 6, the maximum earthquake being a M5.5 (maximum seismic intensity 2), and there were 14 earthquakes with maximum seismic intensity 1 or over, until May 24. In the west of this activity area, there was a M7.1 earthquake on November 14, 2015.
There is no supplementary information for other regions.
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: