Weekly Earthquake Information 2023.12.3 Large M7.6 earthquake in the Philippines Tsunami of up to 40cm in Japan

At around 11:14 on Friday, December 1st, an earthquake estimated to have a magnitude of 3.9 and a depth of 48 km occurred with its epicenter in southern Ibaraki Prefecture. As a result of this earthquake, a seismic intensity of 2 was observed over a wide area in the northern Kanto region, including Kasama City, Koga City, and Chikusei City in Ibaraki Prefecture, Utsunomiya City, Tochigi City, and Sano City in Tochigi Prefecture, and Kiryu City and Tatebayashi City in Gunma Prefecture.

The area around the epicenter of this earthquake can be called an “earthquake hive” and is an area where earthquakes occur very frequently even in the Kanto region. However, there have been relatively few earthquakes this year, with this being the 11th earthquake of magnitude 2 or higher, and only 3 of magnitude 3 or higher. The number of occurrences of earthquakes with an intensity of 3 or higher is the lowest since 2018.

However, earthquakes with a seismic intensity of 4 or higher occur almost every year, so even though the number of earthquakes this year is low, we cannot let our guard down.

According to an analysis by the U.S. Geological Survey, there have been six earthquakes with a magnitude of 6 or higher. The largest earthquake was a magnitude 7.6 earthquake that occurred near the Philippines.

Late at night on the 2nd (Saturday) Japan time, an earthquake estimated to have a magnitude of 7.6 and a depth of approximately 33km occurred off the coast of Mindanao, Philippines. The mechanism of the earthquake is analyzed to be a reverse fault type, with the pressure axis running in the east-west direction.

Because the earthquake occurred relatively close to land, areas close to the epicenter experienced strong shaking. It is estimated that the shaking was around VIII on the revised Mercalli intensity scale, and although it is not possible to make a strict comparison, it was around 5+ on Japan’s seismic intensity scale.

In addition, after this earthquake, there were a series of earthquakes that appeared to be aftershocks, with four earthquakes exceeding magnitude 6 occurring alone.

In addition, around noon on the 2nd (Saturday) Japan time, an earthquake estimated to have a magnitude of 5.5 and a depth of approximately 39 km occurred with its epicenter in the southern part of Bangladesh. The mechanism of the earthquake is analyzed to be strike-slip type.

Because the epicenter was on land, the shaking was somewhat strong near the epicenter, and the shaking was equivalent to V on the revised Mercalli seismic intensity scale, or 4 on Japan’s seismic intensity scale, although a strict comparison is not possible. Although the epicenter was not far from the capital Dhaka, the area affected by the strong shaking was small and no major damage was reported.

Bangladesh is located near the boundary between the Indian plate and the Eurasian plate. Earthquakes with a magnitude of 6 or more occur from time to time, and the most recent one was a magnitude 6.0 earthquake in 1997. There is a very old record of a magnitude 7.1 event occurring in 1918.