Weekly Earthquake Information 2023.11.26 M5.9 earthquake off the eastern coast of Aomori Prefecture, the 4th seismic intensity 4 of the year

At around 6:01 on the 20th (Monday), an earthquake estimated to have a magnitude of 5.9 and a depth of 52 km occurred with its epicenter off the eastern coast of Aomori Prefecture. As a result of this earthquake, a maximum seismic intensity of 4 was observed in Hachinohe City, Noheji Town, and Shichinohe Town in Aomori Prefecture, and a seismic intensity of 3 was observed from Hokkaido to Aomori Prefecture and Iwate Prefecture.

This is the fourth time this year that an earthquake with a magnitude of 4 or higher has been observed off the eastern coast of Aomori Prefecture, since the magnitude 6.2 on August 11th. The mechanism of the earthquake is analyzed to be a reverse fault type with a pressure axis running from west-northwest to east-southeast.

Due to the subduction of the Pacific plate into the land plate off the eastern coast of Aomori prefecture, earthquakes with a magnitude of 6 or more are occurring frequently, and recently in December 2020 there was an earthquake with a magnitude of 6.5 and a maximum seismic intensity of just under 5. came. There are records of earthquakes of magnitude 7 or higher occurring in the past.

At around 0:23 on the 23rd (Thursday), an earthquake estimated to have a magnitude of 3.7 and a depth of 9 km occurred with the epicenter in the Mogami region of Yamagata Prefecture. Due to this earthquake, a maximum seismic intensity of 3 was observed in Shinjo City, Yamagata Prefecture.

This is the first earthquake of magnitude 3 or higher in the Mogami region of Yamagata Prefecture in eight years since 2015, and the mechanism of the earthquake is analyzed to be a reverse fault type with a pressure axis running from west-southwest to east-northeast.

The Shinjo Basin Fault Zone is known in the Mogami region of Yamagata Prefecture, and the epicenter of this earthquake was in an area close to this fault zone. According to the government’s Earthquake Research Promotion Headquarters, the latest activity in the eastern part of the Shinjo Basin fault zone is believed to have occurred approximately 6,200 years ago, and the probability of a magnitude 7.1 earthquake occurring within 30 years is less than 5%.

In recent records, the largest earthquake occurred in 1996 with a magnitude of 5.3 and a maximum seismic intensity of 4, but there is also a risk of stronger earthquakes, so caution is required.

According to an analysis by the U.S. Geological Survey, there have been three earthquakes with a magnitude of 6 or higher. The largest earthquake was a magnitude 6.9 earthquake that occurred near the Mariana Islands.

On the evening of the 24th (Friday) Japan time, an earthquake estimated to have a magnitude of 6.9 and a depth of approximately 16 km occurred with its epicenter near the Mariana Islands. The mechanism of the earthquake is analyzed to be strike-slip type.

Although the earthquake was large and its epicenter was shallow, it was a strike-slip earthquake, so no tsunami was generated. Aftershocks occurred frequently after this earthquake, with 10 earthquakes of magnitude 5 or higher occurring.

The sea near the Mariana Islands is located on the boundary between the Pacific Plate and the Philippine Sea Plate, and is an area where large earthquakes often occur. Earthquakes exceeding magnitude 7 are often deep earthquakes, and examples of shallow earthquakes like this one include the magnitude 7.1 earthquake that occurred in 2001 near the island of Guam, slightly to the south.