Risk of 'megaquake': Japanese PM cancels foreign trip

A magnitude 7.1 earthquake struck southwest Japan on Thursday. The Japan Meteorological Agency (JAM) said the epicenter was about 30 kilometers off the coast of Miyazaki Prefecture on Kyushu Island. Shortly afterward, JAM issued its first-ever emergency advisory for “megaquakes,” warning that the probability of a quake along the Nankai Fault, which stretches from southwestern to central Japan, was “relatively higher than usual.”

Following the warning, Central Japan Railway Co. said the Tokaido Shinkansen line will run slower than usual for about a week while suspending some express trains in the western part of the country.

In January, the government's Earthquake Research Committee predicted that an 8- to 9-magnitude earthquake on the Nankai Fault could occur along the tectonic plate boundary between Suruga Bay in Shizuoka Prefecture and the sea off the coast of Kyushu Island. It warned that this could result in a strong tsunami, which – in a worst-case scenario – would kill more than 230,000 people and destroy about two million buildings. The probability of such a strong earthquake occurring near the Nankai Trench in the next 30 years is 70-80 percent, the Kyodo news agency reported. – The entire Nankai subduction zone (a place where one tectonic plate is pulled under another) is divided into five fault subzones. Historically, they have been hit by large earthquakes, occurring at the contact of tectonic plates, with an average frequency of about 100 years, explained Dr. Hab. Eng. Andrzej Górszczyk from the Geophysical Imaging Department of the Institute of Geophysical Sciences of the Polish Academy of Sciences. The expert noted that the high magnitude of Thursday's quake and its approximate hypocenter at a depth of 30 kilometers indicate that “with great probability” we are dealing with the Philippine tectonic plate sliding under the Eurasian plate.

Prof. Dr. Hab. Eng. Beata Orlecka-Sikora pointed out, however, that “megaquakes”, i.e. earthquakes of magnitude 10 or greater, which the Japanese services warn about, “although theoretically possible, are impossible in practice. – The strength of an earthquake is partly based on the length of the faults, the longer the fault, the greater the earthquake. So far, there are no known faults that could generate “megaquakes” of magnitude 10 or greater – the expert emphasized. – The largest earthquake ever recorded, with a magnitude of 9.5, occurred on May 22, 1960 in Chile as a result of a fault almost 1,500 kilometers long – added Orlecka-Sikora.

The Japan Meteorological Agency on Thursday urged residents of areas where the Nankai Fault earthquake is expected to be the hypocentre to take precautions, including securing furniture from falling during tremors, developing a way to communicate with family members in the event of a disaster and confirming the location of evacuation shelters. It also advised residents and institutions caring for people with mobility problems to consider voluntarily moving to other areas.

Japanese Prime Minister Fumio Kishida on Friday canceled a planned four-day trip to Kazakhstan, Uzbekistan and Mongolia after the weather agency warned there was an increased risk of a potential “megaquake” in a vast swath of the Pacific Ocean stretching from southwestern to central Japan.

– As prime minister, the person with ultimate responsibility for crisis management, I have decided to stay in Japan for at least one week, Kishida told reporters.