EARTHQUAKESWhat Sets the Recent Japan Earthquake Apart from Others?
On Jan. 1, a magnitude 7.6 earthquake struck the western side of Japan on the Noto Peninsula, killing over 200 people. Japan is prone to earthquakes, including a magnitude 9.1 earthquake in 2011 that triggered a tsunami and killed almost 20,000 people. Geophysicist William Frank discusses how a recent earthquake in Japan relates to an earthquake swarm in the region.
On Jan. 1, a magnitude 7.6 earthquake struck the western side of Japan on the Noto Peninsula, killing over 200 people. Japan is prone to earthquakes, including a magnitude 9.1 earthquake in 2011 that triggered a tsunami and killed almost 20,000 people.
William Frank, the Victor P. Starr Career Development Professor in the Department of Earth, Atmospheric and Planetary Sciences at MIT, has been studying an earthquake swarm in the region where the most recent earthquake occurred. He explains the difference between subduction earthquakes and earthquake swarms, and why the unknown nature of these swarms makes predictions hard.
Q: Why is Japan prone to earthquakes?
A: Japan is prone to earthquakes because it is at the western edge of the Pacific plate and a more complicated junction where two plates are subducting, or plunging, beneath the tectonic plate that Japan is sitting on. It’s at the interface between those plates where you’re going to have a lot of earthquakes, because you’re generating stress as the plates move past one another.
But interestingly, this earthquake was not due to subduction. It’s on the west coast of the island, and the subduction zones are on the east coast. There are still a lot of active tectonics that are not related to subduction. This one place is enigmatic [as to] why there are so many earthquakes, but there’s been this earthquake swarm happening there since 2020. This latest earthquake is the latest big earthquake in the swarm.
Q: What is an earthquake swarm, and how can you tell this earthquake is a part of it?
A: Normally you have the big earthquake, what we call the mainshock, that is followed by a sequence of aftershocks. But in a swarm, there’s no clear mainshock because there’s a lot of earthquakes before and there’s also a lot of earthquakes afterwards. Often there will just be one earthquake that will be bigger than the rest sometime within that swarm duration.
Earthquake swarms are typically around plate boundaries. There’s a lot of them in subduction zones but not only [there] — there are also earthquake swarms, for example, in Southern California. These can last days, months, years. We call it a swarm is because it’s generating many more earthquakes than we expect from that region, in sustained activity, for the past few years.
