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03/21/2021 10:45 AM Weathernews
In the last week, the number of earthquakes observed in Japan has been higher than in the previous week. The earthquakes were conspicuous from Kanto to the Pacific side of Tohoku and Kyushu. There have been seven earthquakes with a seismic intensity of 3 or more. (Added March 15-21 at 10:00)
The earthquake mechanism is analyzed as a type of reverse fault with a pressure axis in the west-northwest-east-southeast direction, and the earthquake is thought to have been caused by the subduction of the Pacific plate.
The Japan Meteorological Agency temporarily issued a tsunami warning for Miyagi Prefecture, but there was no noticeable fluctuation in the tide level and the warning was canceled about 1 hour and 20 minutes after the announcement. Like the earthquake off Fukushima Prefecture (magnitude 7.3) that occurred in February, it is considered one of the activities following the great earthquake that triggered the Great East Japan Earthquake in March 2011.
The government headquarters for the promotion of seismic research will have a 20% probability of an inter-plate earthquake with a magnitude of 7.9 off the coast of Miyagi prefecture in the next 30 years, and an inter-plate earthquake with a magnitude of 7.0 to 7.5, which is close to this scale, will occur. The probability is around 90%. Since the number of earthquakes has increased in Tohoku’s coastal areas this year, please check the earthquake countermeasures again in the wake of this earthquake.
Approximately 30 minutes after the earthquake occurred, an aftershock with a maximum seismic intensity of 3 occurred at 0:59 on the 15th (Monday) and around 11:37, but the activity has calmed down since then.
In Wakayama prefecture, an earthquake with a magnitude of 4.0 and a depth of approximately 4 km occurred on February 15 this year, with an epicenter directly below the city of Wakayama, and a maximum seismic intensity of 4. Given that the epicenter of this time is about 30km to the south, it is considered that there is no direct relationship.
A magnitude 5.5 earthquake occurred in July 2011 near the epicenter, with a maximum seismic intensity of 5 in the upper part of Hirogawa City and a seismic intensity of 3 in a wide range from Kinki to Chugoku and Shikoku. The mechanism of the earthquake is similar and it is the same type of earthquake.
The northern part of Wakayama Prefecture has traditionally been an area of active seismic activity and earthquakes of magnitude 4-5 occur frequently. The epicenter is characterized by a depth of several kilometers, which occurs in a very shallow place, and although it is localized, the rolling of the ground is enlarged and can cause damage.
The epicenter was at the bottom of the sea, and although there were no major earthquakes on the ground, a very small tsunami occurred. We observed tidal level fluctuations of less than 10 cm in the Balearic Islands of Spain and Sardinia in Italy.
Algeria is close to the border between the African plate and the Eurasian plate, and earthquakes of approximately magnitude 6 occur occasionally around the Mediterranean coast. In 2003, a 6.8 magnitude earthquake struck lightly west of the epicenter, causing many buildings to collapse, especially in severely shaken coastal cities, killing more than 2,000 people. Before that, in 1980, there was a magnitude 7.7 earthquake in the interior, which also caused extensive damage.
The big earthquake in this area is a reverse fault type mechanism with a pressure axis in the north-south direction, and the same happened with this earthquake.
At this stage, the eruptive activity is focused on the lava flows and the output range is limited. Due to its remoteness from densely populated areas, it is not expected to have a significant impact immediately.
* Information on the epicenter and seismic intensity in Japan comes from the Japan Meteorological Agency, unless otherwise noted. Information on overseas epicenters comes from the United States Geological Survey (USGS), unless otherwise noted. The epicenter information may differ depending on the issuing organization.
