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

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 Fukuoka City and other areas. 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 about the mean recurrence interval, and the possibility of future earthquake occurrence in the Nishiyama fault zone remains unclear.

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, at midnight on the 14th (Tuesday) Japan time, an earthquake with an epicenter in the southwestern part of Romania with a magnitude of 5.6 and an estimated depth of about 10 km occurred. 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, a short 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.

*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.