Weekly Earthquake Information 2022.12.18 Seismic intensity 3 near Kuromatsunai lowland fault zone in Shiribeshi region, Hokkaido – Weather News

2022/12/18 10:36 Weather news

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

There is no particular concentration of earthquakes, and they occur all over Hokkaido, Kyushu, and the Nansei Islands. There were four earthquakes with a seismic intensity of 3 or higher. (Tally from December 12th to December 18th at 10:00)

Domestic: Multiple felt earthquakes in the Shiribeshi region of Hokkaido

Shiribeshi region earthquake

At around 13:30 on the 15th (Thursday), an earthquake estimated to have a magnitude of 4.3 and a depth of 13 km occurred with an epicenter in the western Shiribeshi region of Hokkaido. In this earthquake, a maximum seismic intensity of 3 was observed in Kuromatsunai Town, Niseko Town, Suttsu Town, Toyoura Town, etc., and a seismic intensity of 2 was observed in Date City, Kutchan Town, etc.

At around 13:50 and 15:58, earthquakes with a maximum seismic intensity of 2 occurred at almost the same epicenter. The mechanism of the earthquake is presumed to be a reverse fault type with a pressure axis in the WNW-ESE direction.

There are not many earthquakes with epicenters in the western Shiribeshi region, since 1919 when detailed records of the Japan Meteorological Agency remain, and only on November 24th last month and this time there was a seismic intensity of 3 or more.

However, the epicenter of this quake is located in the area where the Kuromatsunai low-lying fault zone is distributed. The government’s Headquarters for Earthquake Research Promotion states that the probability of an earthquake of magnitude 7.3 or higher occurring within 30 years is 2-5% or less. Among the major active fault zones in Japan, it belongs to a group with a high probability of occurrence, so it is necessary to pay attention to the occurrence of future earthquakes.

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 the tremors become larger far from the epicenter can be seen, and this is called an “abnormal earthquake 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: Magnitude 6 or higher for the first time in 16 years near Amami Oshima

Earthquake near Amami Oshima

At around 23:25 on the 13th (Tuesday), an earthquake estimated to have a magnitude of 6.0 and a depth of 37 km occurred near Amami Oshima. In this earthquake, a maximum seismic intensity of 4 was observed in Setouchi Town, Kagoshima Prefecture, and a seismic intensity of 3 was observed in Amami City and Isen Town.

The sea near Amami Oshima is the area where the Philippine Sea plate is subducting. M6-class earthquakes occur occasionally at depths of around 30 km. It was the first time in 16 years since the M6.0 earthquake in November 2006 that the sea near Amami Oshima had an epicenter. In 1995, there was also a large earthquake with a magnitude of 6.9 and a maximum seismic intensity of 5 (the seismic intensity scale at that time), so we cannot let our guard down.

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

Hyuganada earthquake

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: M5.4 occurred last month in Texas, USA

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

There has been one earthquake with a magnitude of 6 or higher according to US Geological Survey analysis. The largest earthquake was a magnitude 6.3 that occurred off the coast of the Aleutian Islands.

On the morning of the 17th (Saturday) Japan time, an earthquake estimated to have a magnitude of 5.4 and a depth of regarding 8 km occurred in Texas, USA. The earthquake mechanism is analyzed as a normal fault type with a tension axis in the north-northwest-southeast direction. Because the earthquake occurred in a shallow place, it is believed that there was a quake of VI on the revised Mercalli seismic intensity scale near the epicenter.

Although there is no known active fault near the epicenter, seismic activity has increased in recent years. According to the U.S. Geological Survey, since 2018, there have been regarding 120 earthquakes with a magnitude of 2.5 or greater within 50km of this epicenter. Also, on the 16th of last month, an earthquake with a magnitude of 5.4 occurred regarding 200km to the west.

A study linked earthquakes in the area to human activity, and concluded that the 2020 earthquake was caused by a significant increase in wastewater injection. Many of the other earthquakes that are increasing in the central and eastern United States are thought to be related to human activities such as mining.

M6.1 in northwestern Turkey, area with past major earthquakes

On the morning of the 23rd (Wednesday) Japan time, an earthquake estimated to have a magnitude of 6.1 and a depth of regarding 10km occurred in northwestern Turkey. The earthquake mechanism is analyzed as strike-slip type. In the vicinity of the epicenter, it is believed that there was a maximum tremor of regarding VIII on the revised Mercalli seismic intensity scale.

Turkey is located on a huge bedrock called the Eurasian Plate. It is an area where distortion energy tends to accumulate in the bedrock, such as the boundary between the African plate and the Arabian plate. For this reason, there are many faults in Japan, and the earthquake that occurred on the 23rd is believed to have occurred near the North Anatolian fault.

Turkey, which is located on a plate boundary and is seismically active like Japan, has had more than 100 fatal earthquakes since 1900, and similar to this time, the earthquake occurred near the North Anatolian Fault. In 1999, a large earthquake with a magnitude of 7.6 called the “Izmit Earthquake” killed more than 10,000 people.

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.