Weekly Earthquake Information 2022.1.23 22nd (Sat) Hyuga-nada M6.6 Earthquake Strong shaking with a seismic intensity of 5 or higher before dawn –Weathernews

2022/01/23 10:09 Weathernews

The number of earthquakes observed in Japan in the past week is higher than the previous week.

The large earthquakes that occurred in Hyuga-nada and their followingshock activity account for the majority. There were 6 earthquakes with a seismic intensity of 3 or higher during this period, all of which originated in Hyuga-nada. (Aggregation from January 17th to January 23rd at 10:00)

Domestic: Observed seismic intensity 5 upper in Oita City and Nobeoka City

Hyuga Nada Earthquake

Around 1:08 on Saturday, 22nd, there was an earthquake with a magnitude of 6.6 and an estimated depth of 45km with the epicenter of Hyuga-nada. Due to this earthquake, a seismic intensity of 5 upper was observed in Oita City, Saiki City, Taketa City, Miyazaki Prefecture, Nobuoka City, and Takachiho Town, and a seismic intensity of 5 lower was observed in Sukumo City, Kochi Prefecture, Aso City, Kumamoto Prefecture, and Usuki City, Oita Prefecture. It has been hit by shaking with a seismic intensity of 3 or higher over a wide area from various parts of Kyushu to parts of Chugoku and Shikoku.

This is the first earthquake with a magnitude of 6.5 or more that originated in Hyuga-nada in regarding 25 years since the earthquake with a magnitude of 6.7 and a maximum seismic intensity of less than 5 on December 3, 1996. The mechanism of the earthquake is analyzed as a type with a tension axis in the west-northwest-east-southeast direction.

Is it an earthquake that occurred inside the plate?

Hyuga-nada seismic activity

In Hyuga-nada, the Philippine Sea plate subducts under the Eurasian plate, causing frequent large earthquakes, including plate-boundary earthquakes. Looking only following 1960, there were three magnitude 7.1 in 1984, 7.5 in 1968, 7.0 in 1961 and 7 magnitude classes, and these earthquakes also caused tsunamis.

The epicenter this time occurred a little deeper than the plate boundary. It is believed that the earthquake was caused by the pulling of the subducting Philippine Sea Plate.

Within the next 30 years, the government’s Headquarters for Earthquake Research Promotion will reduce the probability of an earthquake between Hyuga-nada plates, which is expected to be around 7.6, to be around 10%, and the probability of an earthquake, which is expected to be a little smaller, to be around 7.1. It is set to ~ 80%. It is an area where it is safe to have a larger earthquake than this time, so it would be good to check the countermeasures once more with this earthquake as a trigger.

Stay alert to the tendency for activities to subside

Seismic activity in the waters near the Tokara Islands became active around noon on the 4th (Sat). The number of felt earthquakes with a seismic intensity of 1 or higher has reached 277 by 24:00 on the 10th (Friday).

Looking at the number of earthquakes by day, the number of earthquakes on the 5th (Sun) is the highest at 87. On the 9th (Thursday), when an earthquake with a seismic intensity of 5 or higher occurred, there were 36 times, which was a little high, but on the 10th (Friday), it was only 5 times, and the activity as a whole tends to be settled.

However, during the activity in October 2000, when the same tremor with a seismic intensity of 5 or higher occurred, an earthquake with a seismic intensity of 4 occurred regarding 3 weeks following the active state settled down. You need to be careful regarding strong shaking for a while.

Domestic: Earthquake swarm from Saturday, 4th in the Tokara Islands

Earthquakes have occurred frequently in the sea near the Tokara Islands in the Amami region of Kagoshima prefecture from around noon on the 4th (Sat). The first felt earthquake had a magnitude of 2.9 and a maximum seismic intensity of 1 at around 12:32 on Saturday, 4th, and an earthquake of magnitude 4.0 and a maximum seismic intensity of 3 occurred at 19:48. After that, the earthquakes continued, and as of 10 o’clock on the 5th (Sun), there were 87 felt earthquakes, of which 6 were earthquakes with a seismic intensity of 3.

These earthquake swarms often occur in the waters near the Tokara Islands. Recently, earthquakes have occurred frequently since April 9th ​​this year, and on April 10th, more than 100 felt earthquakes occurred in one day. During the three days from the 10th to the 12th, when the activity was at its peak, we observed 229 felt earthquakes, 15 seismic intensity 3 and 5 seismic intensity 4.

In many cases, the active situation from past activities lasts for several days, and the maximum seismic intensity may reach a little over 4-5. It is necessary to be careful regarding strong shaking for a while.

World: M5.3 strong tremors near the epicenter in Afghanistan

World M4.5 and above earthquakes (USGS homepage quote / Weathernews processing)

Three earthquakes with a magnitude of 6 or greater have occurred, as analyzed by the United States Geological Survey. The largest earthquake was magnitude 6.3 (magnitude 6.6 analyzed by the Japan Meteorological Agency) that occurred in Hyuga-nada.

The notable earthquake is the Afghanistan earthquake that occurred on the night of January 17th (Monday), Japan time. The magnitude of the earthquake is estimated to be 5.3 and the depth is estimated to be regarding 19km.

According to the United Nations Office for the Coordination of Humanitarian Affairs, more than 20 people died due to the collapse of houses, etc.

In Afghanistan, earthquakes often occur in the eastern part near the plate boundary, and there are not many earthquakes in the western part like this time. There are no records of earthquakes with a magnitude of 5 or more near the epicenter since 1960, and it is possible that the buildings were vulnerable to shaking, leading to great damage for their scale.

M6.0 earthquake in Crete, Greece

On the followingnoon of the 27th (Monday) of Japan time, there was an earthquake with a magnitude of 6.0 and a depth of regarding 9km, which had its epicenter near Crete, Greece. The mechanism of the earthquake is analyzed as a normal fault type with a tension axis in the northwest-southeast direction.

Since the epicenter was shallow, less than 10 km, and it was an earthquake in the land area, it seems that there was a tremor of regarding VII of the revised Mercalli seismic intensity class around the epicenter. Although it is not possible to make a strict comparison, it is a tremor equivalent to a seismic intensity of less than 5 when converted to the Japan Meteorological Agency seismic intensity class. A building collapsed near the epicenter, and some people died according to local authorities.

The area around Greece is sandwiched between the Eurasian plate and the African plate, and it is said that there is a microplate called the Anatolian plate between them. The movement of these plates has caused many major earthquakes.

Earthquakes with a magnitude greater than 6 occasionally occur around Crete Island, with a magnitude 6.1 earthquake on the northern coast of Crete Island in 1994 and a magnitude 6.1 earthquake with an epicenter on the island’s land as in 1959. happened.

Reference materials, etc.

* Information on the epicenter and seismic intensity in Japan is from the Japan Meteorological Agency unless otherwise stated. Information on overseas epicenters is from the United States Geological Survey (USGS) unless otherwise stated. The epicenter information may differ depending on the issuing organization.