Weekly Earthquake Information 2023.2.19 M4.3 off the northwest coast of Fukuoka Prefecture Epicenter different from 2005 activity – Weather News

2023/02/19 10:11 Weather news

The number of felt-earthquakes observed in Japan over the past week is at a lower level than the previous week.

There are no areas where earthquakes are particularly concentrated, and they occur sporadically from Hokkaido to Kyushu and Okinawa. There were two earthquakes with a seismic intensity of 3 or higher. (Tally from February 13th to February 19th at 10:00)

Japan: The seismic intensity 3 with the epicenter off the northwest coast of Fukuoka Prefecture was the first in regarding 3 years

Earthquake off the northwest coast of Fukuoka Prefecture

At around 19:38 on the 17th (Friday), an earthquake estimated to have a magnitude of 4.3 and a depth of 16 km occurred off the northwest coast of Fukuoka Prefecture. This earthquake recorded a maximum seismic intensity of 3 in Munakata City, Fukuoka Prefecture, and a seismic intensity of 2 in Fukuoka, Nagasaki, and Yamaguchi Prefectures.

This is the first earthquake with a seismic intensity of 3 or more with an epicenter off the northwest coast of Fukuoka Prefecture since March 2020, and the mechanism of the earthquake is analyzed as a reverse fault type with a pressure axis in the east-west direction.

In 2005, an earthquake with a magnitude of 7.0 and a maximum seismic intensity of lower 6 occurred due to the activity of the Kego fault zone off the northwest coast of Fukuoka Prefecture, causing damage to a wide area, including Fukuoka City. Most of the subsequent earthquakes with a seismic intensity of 3 or higher occurred in the 2005 activity area. However, the epicenter of this quake occurred further northeast than in 2005.

The Nishiyama fault zone is distributed near the epicenter of this earthquake. The location of the known fault and the epicenter are slightly apart, so it cannot be said at this point that it is activity in the fault zone.

The Nishiyama fault zone can be roughly divided into three sections: the “Oshima offshore section”, the “Nishiyama section”, and the “Kamatoge section”. According to the government’s Headquarters for Earthquake Research Promotion, it is estimated that an earthquake of magnitude 7.3 to 7.6 would occur if each of them were active, and an earthquake of magnitude 7.9 to 8.2 would be possible if all of them acted at the same time.

There are many unclear points regarding the mean recurrence interval, and the possibility of future earthquake occurrence in the Nishiyama fault zone remains unclear.

Epicenters where anomalous seismic regions are likely to appear

Abnormal seismic regions often appear in deep earthquakes off the southeast coast of Mie prefecture. In many earthquakes, areas with strong shaking are distributed concentrically from the epicenter. On the other hand, in deep earthquakes, strong tremors are transmitted along the subducting plate, and a phenomenon in which tremors become stronger far from the epicenter can be seen, and this is called an “abnormal seismic zone.”

Other than the southeastern offshore of Mie Prefecture, similar deep earthquakes often occur in the Sea of ​​Okhotsk, the Sea of ​​Japan, the southern offshore of Tokaido, and the sea near Torishima, and once every few years, an earthquake with a magnitude of 6 or more also occurs.

Even if the tremors were small near the epicenter, strong tremors were transmitted far away. Mie Prefecture, which is close to the epicenter, did not have any locations where felt earthquakes were observed, and the maximum seismic intensity of 4 was observed in Ibaraki and Fukushima prefectures. A large-scale earthquake may cause tremors exceeding seismic intensity 5 lower, so caution is required.

Japan: Deep earthquake abnormal seismic area seen off the west coast of the Ogasawara Islands

At around 13:50 on the 16th (Monday), an earthquake estimated to have a magnitude of 5.9 and a depth of 422 km occurred off the west coast of the Ogasawara Islands. In this earthquake, a maximum seismic intensity of 3 was observed in Ogasawara Village, and a seismic intensity of 1 was observed from the Kanto region to the southern Tohoku region.

Because it was a deep earthquake with a depth of 400 km, the epicenter distribution was in an abnormal seismic area. In many earthquakes, strong tremors are distributed concentrically from the epicenter, but in deep earthquakes, strong tremors are transmitted along the subducted plate, and a phenomenon in which the tremors become stronger in the distance near the plate boundary is observed. This is called an “abnormal seismic area”.

In this earthquake, it is thought that the shaking propagated to the Pacific coast of northern Japan and eastern Japan along the Pacific plate where seismic waves easily propagate.

Japan: A strong earthquake in January this year with a seismic intensity of 4 in Hyuga Nada

At around 3:06 on the 18th (Sunday), an earthquake estimated to have a magnitude of 5.4 and a depth of regarding 30 km occurred with an epicenter in Hyuga-nada. In this earthquake, a maximum seismic intensity of 4 was observed in Miyazaki City and Nichinan City, and a seismic intensity of 3 was observed in Miyakonojo City and Kobayashi City in Miyazaki Prefecture, Kirishima City and Kanoya City in Kagoshima Prefecture, and Kumamoto City in Kumamoto Prefecture.

This is the first earthquake with a seismic intensity of 4 or higher with its epicenter in Hyuga-nada since January 22, 2018. The mechanism of the earthquake was analyzed as a normal fault type with a tension axis in the east-west direction.

The epicenter is further south than the magnitude 6.6 earthquake that occurred in January, and the area is close to the magnitude 7.0 earthquake that occurred in 1961.

World: Strong tremor near M5.6 epicenter in Romania

Earthquakes of M4.5 or higher around the world (quoted from USGS website/processed by Weathernews)

There have been three earthquakes with a magnitude of 6 or higher according to US Geological Survey analysis. All three quakes occurred at the boundary of the Pacific plate and had a magnitude of 6.1.

In addition, an earthquake estimated to have a magnitude of 5.6 and a depth of regarding 10 km occurred at midnight on the 14th (Tuesday), Japan time, with an epicenter in the southwestern part of Romania. The earthquake mechanism is analyzed as a normal fault type with a tension axis in the north-south direction. It is believed that there was a strong tremor of VII on the revised Mercalli seismic intensity scale near the epicenter, but it does not appear to have caused major damage.

Romania is located on the Eurasian plate and is some distance from the plate boundary. Although earthquakes exceeding magnitude 5 sometimes occur, most of them are rather deep earthquakes with a depth of around 100 km. There are also records of earthquakes with a magnitude of 7 or higher, with the most recent being a magnitude 7.0 earthquake in May 1990 and a magnitude 7.5 earthquake in 1977, which caused extensive damage in the capital city of Bucharest.

Turkey is a seismic country on multiple plate boundaries

Most of Turkey is located on a small plate called the “Anatolian Plate”. It is surrounded by multiple plate boundaries, with the African plate to the south, the Arabian plate to the southeast, and the Eurasian plate to the north.

The first magnitude 7.8 earthquake is believed to be the activity of the “East Anatolian Fault” formed on the boundary between the Anatolian Plate and the Arabian Plate.

The 7.6 magnitude earthquake in 1999 is one of the most damaging earthquakes in Turkey in recent years. The earthquake, also known as the Izmit Earthquake, was different from this one in that it was caused by the activity of the North Anatolian Fault, and caused extensive damage in the northwestern part of Turkey, including the large city of Istanbul.

Reference materials, etc.

*Information on earthquake sources and seismic intensity in Japan is from the Japan Meteorological Agency unless otherwise specified. Overseas epicenter information is from the United States Geological Survey (USGS) unless otherwise specified. There may be differences in hypocenter information depending on the publishing organization.