Why Japan’s New Megaquake Alert Has Everyone on Edge?
There is a Risk of Bigger Quakes Rising
Japan issued its first-ever “megaquake alert” on August 8 following a powerful earthquake that hit Miyazaki prefecture in southern Japan. The earthquake, which had a magnitude of 7.1, caused injuries to at least 16 people and generated minor tsunamis up to 50 centimeters (about 20 inches) high. These waves reached the Japanese coastline about 30 minutes after the quake.
Details of the Earthquake
The earthquake’s epicenter, or hypocenter, was located offshore, about 25 kilometers (15 miles) underground, near a seafloor depression known as the Nankai Trough. This area is known for its large fault zone. Experts are worried that the Miyazaki quake might have changed the stress along this fault, possibly increasing the risk of a larger earthquake in the future.
The Japanese Meteorological Agency (JMA) has warned that there is a higher chance of a major earthquake occurring soon. The megaquake alert will stay in effect for about a week, but the JMA advises people in southern Japan to stay cautious and prepared even after the alert period ends.
Risk of a Larger Earthquake
Seismologist Naoshi Hirata from the University of Tokyo said there is a small chance, about one in several hundred, that a larger earthquake might happen in the next week. He also noted that the probability of a magnitude 8 or 9 earthquake occurring in the Nankai Trough within the next 30 years is 70 to 80 percent.
Morgan Page, a geophysicist with the U.S. Geological Survey, explained that while there is a short-term increase in risk because of the recent earthquake, this risk decreases each day that no new earthquake happens.
Japan’s Earthquake Alert System
Japan is well-known for its earthquake preparedness. The megaquake alert issued on August 8 is the second-highest level under the Nankai Trough Earthquake Extra Information protocol, which was introduced in 2017. This protocol activates when an earthquake of magnitude 6.8 or greater strikes near the Nankai Trough. The highest alert level is for earthquakes of magnitude 8.0 or more.
The Nankai Trough is where the Philippine plate slides under the Eurasian plate, creating a massive fault zone known as the Nankai megathrust. This fault has produced earthquakes of magnitude 8 or greater about every 100 to 150 years. The last major quake in this area occurred in 1946 and was around magnitude 8.1.
Aftershock and Other Earthquakes
On August 9, a magnitude 5.3 earthquake struck about 10 kilometers (6 miles) beneath Kanagawa Prefecture near Tokyo. This quake was outside the area covered by the megaquake alert but shows that aftershocks and additional seismic activity can occur.
It’s not uncommon for a significant earthquake to be followed by a larger quake nearby. The U.S. Geological Survey reports that there is a 5 percent chance that a large earthquake will be followed by an even bigger one within a week. However, predicting earthquakes accurately is very difficult, and it is not possible to know for sure if a major quake will be followed by another.
Last year, researchers found that if a megaquake happens on the Nankai megathrust, the chance of another megaquake occurring nearby within a week could increase significantly.
Earthquake Preparedness
Japan has been a leader in earthquake preparedness. In 2007, it launched the world’s first nationwide earthquake early warning system. This system detects the initial, less damaging waves of an earthquake and issues warnings before the more powerful, destructive waves arrive. For example, the system provided Tokyo residents with a one-minute warning before the strong shaking of the magnitude 9.1 Tohoku earthquake in 2011.
Earthquake Risks in Other Regions
In North America, there is another significant fault known as the Cascadia megathrust, which stretches from Vancouver Island to northern California. This fault is believed to produce megaquakes every 300 to 500 years. The U.S. also has an early warning system called ShakeAlert, which people can sign up for to receive alerts on their phones.
For those living in earthquake-prone areas, being prepared in advance is crucial. The U.S. Geological Survey provides guidelines on emergency supplies, how to prepare for earthquakes, and what to do when an earthquake occurs.
As Japan deals with the aftermath of the recent quake and the megaquake alert, the focus remains on staying prepared and minimizing risks in the face of ongoing seismic activity.
Related News: Massive Earthquake Hits Japan, Triggers Megaquake Warnings
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