2022/07/03 11:09 Weathernews
Earthquakes on the Pacific coast of Kyushu and around Kumamoto were conspicuous. There have been two earthquakes with a seismic intensity of 3 or higher. (Aggregation from June 27th to July 3rd at 10:00)
Domestic: M5.9 at a depth of 320km in the Soya Strait
The mechanism of the earthquake seems to be a reverse fault type with a pressure axis in the west-southwest-east-northeast direction.
While this earthquake did not observe shaking in the Kamikawa and Abashiri regions of Hokkaido, which are relatively close to the epicenter, it shook over a wide area on the Pacific side of the Tohoku region, and is a common “abnormal earthquake” during deep-focus earthquakes. It is a distribution called “region”. Hashikami Town, Aomori Prefecture, where seismic intensity 3 was observed, is about 600 km away from the epicenter.
Seismic intensity distribution peculiar to deep-focus earthquakes
It is probable that the quake propagated along the Pacific coast of northern Japan along the Pacific plate where seismic waves are easily transmitted in this earthquake.
The possibility of a tsunami is small for deep-focus earthquakes, and it is generally considered that there is almost no concern about tsunami for earthquakes with epicenters deeper than 100 km.
Similar deep-focus earthquakes often occur in the Sea of Okhotsk, the Sea of Japan, off the southeastern coast of Mie Prefecture, off the southern coast of the Tokaido, and in the waters near Torishima, and earthquakes with a magnitude of 6 or more occur once every few years. On the other hand, it is also characterized by the fact that there are almost no aftershocks in a single earthquake.
A large deep-focus earthquake with a magnitude of 6.7 occurred in December 2020 just north of the epicenter.
Domestic: Seismic intensity 3 in the Ariake Sea
In the vicinity of this epicenter, the number of earthquakes has increased since the activity of the 2016 Kumamoto earthquake, and magnitude 4 class earthquakes occasionally occur.
It is believed that part of the Futagawa fault zone, which is related to the activity of the Kumamoto earthquake, extends to the sea area. Since the epicenter of this time is located a little north of the fault zone, it is not clear whether it is a direct fault activity.
However, on Sunday, the 26th of last month, an earthquake with a maximum seismic intensity of less than 5 just occurred in the active area of the Kumamoto earthquake. There is no particular increase in activity, but some caution is required.
In the past, there was a M6.0 earthquake
Most of the earthquakes are concentrated around 10km in depth even in the east-west cross section. There are few occurrences deeper than 20km, but slightly more deeper than 100km. Earthquakes that occur near the boundary between the Pacific plate and the Eurasian plate or inside the Pacific plate.
Most deep-focus earthquakes have a magnitude of around 4, but in May 2014, a large-scale earthquake with a magnitude of 6.0 occurred. In this earthquake, a maximum seismic intensity of 5 lower was observed in Chiyoda-ku, Tokyo, and shaking with a seismic intensity of 3 to 4 was observed in a wide area of the Kanto region, causing damage such as injuries.
World: A series of M6 class earthquakes in southern Iran
On the morning of Saturday, July 2, Japan time, there were two magnitude 6.0 earthquakes with epicenters in southern Iran. Both are shallow at a depth of about 10 km and about 16 km, and the mechanism is analyzed as a reverse fault type with a pressure axis in the north-south direction.
According to the latest analysis near the epicenter, it seems that the revised Mercalli Intensity Class VII shook, and although it is not possible to make a strict comparison, it is equivalent to a seismic intensity of 4 to 5 lower when converted to the Japan Meteorological Agency seismic intensity class. In areas where the shaking was strong, damage such as collapse of buildings occurred.
Iran is located on the border between the Arabian plate and the Eurasian plate, and the epicenter this time is slightly south of the plate border. Although there are not many earthquakes with a magnitude of 7 or more in this area, there are many 6-class earthquakes, and an earthquake with a magnitude of 6.4 occurred in November last year.
M5.5 near the Strait of Gibraltar
The Strait of Gibraltar is the strait that separates Europe and Africa, and is also the boundary between the Eurasian plate and the African plate. Since it is not a subduction zone, there are many strike-slip earthquakes, and the magnitude 6.3 and 2004 magnitude 6.4 earthquakes that occurred in 2016 have the same mechanism.
Since there are many shallow earthquakes, if it occurs near the land or in the land area, it will cause strong shaking near the epicenter.
Reference materials, etc.
* Information on the epicenter and seismic intensity in Japan is from the Japan Meteorological Agency unless otherwise stated. Information on overseas epicenters is from the United States Geological Survey (USGS) unless otherwise stated. The epicenter information may differ depending on the issuing organization.