What Japan’s “megaquake” warning really tells us
Crucially, this advisory is not a warning that a megaquake is imminent. It means: “be ready for when the big earthquake comes,” says Hubbard. Nobody is mandated to evacuate, but they are asked to know their escape routes. Meanwhile, local news reports that nursing homes and hospitals in the region are tallying emergency supplies while moving immobile patients to higher floors or other locations. The high-speed Shinkansen railway trains are running at a reduced maximum speed, and certain flights are carrying more fuel than usual in case they need to divert.
Earthquake advisories aren’t new. “California has something similar, and has issued advisories before,” says Wendy Bohon, an independent earthquake geologist. In September 2016, for example, a swarm of hundreds of modest quakes caused the U.S. Geological Survey to publicly advise that, for a week, there was a 0.03 to 1% chance of a magnitude-7.0-or-greater quake rocking the Southern San Andreas Fault—an outcome that fortunately didn’t come to pass.
But this megaquake advisory is Japan’s first, and it will have both pros and cons. “There are economic and social consequences to this,” says Bohon. Some confusion about how to respond has been reported, and widespread cancellations of travel to the region will come with a price tag.
But calm reactions to the advisory seem to be the norm, and (ideally) this advisory will result in an increased understanding of the threat of the Nankai Trough. “It really is about raising awareness,” says Adam Pascale, chief scientist at the Seismology Research Centre in Melbourne, Australia. “It’s got everyone talking. And that’s the point.”
Geoscientists are also increasingly optimistic that the August 8 quake isn’t a harbinger of a seismic pandemonium. “This thing is way off to the extreme margin of the actual Nankai rupture zone,” says Tobin—meaning it may not even count as being in the zone of tectonic concern.
A blog post co-authored by Shinji Toda, a seismologist at Tōhoku University in Sendai, Japan, also estimates that any stress transferal to the dangerous parts of the Trough is negligible. There is no clear evidence that the plate boundary is acting weirdly. And with each day that goes by, the odds of the August 8 quake being a foreshock drop even further.
Tech defenses
But if a megaquake did suddenly emerge, Japan has a technological shield that may mitigate a decent portion of the disaster.
Buildings are commonly fitted with dampeners that allow them to withstand dramatic quake-triggered shaking. And like America’s West Coast, the entire archipelago has a sophisticated earthquake early-warning system: seismometers close to the quake’s origins listen to its seismic screams, and software makes a quick estimate of the magnitude and shaking intensity of the rupture, before beaming it to people’s various devices, giving them invaluable seconds to get to cover. Automatic countermeasures also slow trains down, control machinery in factories, hospitals, and office buildings, to minimize damage from the incoming shaking.
