The Japan Meteorological Agency (JMA) is concerned about the possible arrival of a strong earthquake of magnitude 8.0 or higher (journalistically called “megaearthquake”) and a violent tsunami next week in the Nankai Trench area, with an earthquake warning between the Kanto and Kyushu regions and a tsunami warning between the Kanto and Okinawa regions. The warning, which will last for 7 dayscomes in the aftermath of the 7.1 magnitude earthquake that struck the island of Kyushu yesterday, August 8, and left 13 injured. In response to the alert, the Prime Minister Smoke Kishida he decided to cancel a business trip to Central Asia.
After the earthquake, JMA geologists organized an extraordinary meeting to assess the situation, since the area affected by the 7.1 earthquake is connected to the Nankai Trencha subduction region off the east coast of Japan about 900 km south of the island of Honshu. The fault beneath this trench has historically produced several megaearthquakes.
The Japan Meteorological Agency analyzed statistical data of earthquakes in the area between 1904 and 2014. In this sample, 6 earthquakes of magnitude 8.0 or higher occurred within 7 days after an earthquake of magnitude 7.0 or higher in the same area. In the same period, 1,437 earthquakes of magnitude 7.0 or greater were recorded. For example, the magnitude 9.0 earthquake that caused the Fukushima disaster on March 11, 2011 was preceded by an earthquake of magnitude 7.0 2 days earlier.
At least looking at the statistical data, therefore, it seems that there is the possibility that the earthquake of magnitude 7.1 of August 8 could be followed within a week by a more powerful earthquake of magnitude 8.0, capable of generating a violent tsunami. However, it must be reiterated that This is in no way a prediction (earthquakes cannot be predicted): the fact that it has happened a certain number of times in the past does not necessarily mean that it will happen this time. The JMA considers the probability to be higher than 1%although it cannot quantify this number more precisely. So no, we are not even remotely talking about a probability of 70-80% as reported by some newspapers.
