Monday, July 13, 2020
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Tokyo Likely to Get a Big Earthquake

At the risk of sounding like I’m sensationalizing things… Tokyo is at risk. This is a metropolis that houses around 35 million people (even more than the entire population of Canada, the 2nd biggest country in the world) and I do seriously fear for the safety of people in the area. The Great Eastern Japan Earthquake of March 11 was damaging not because it was perhaps the biggest earthquake in Japan’s history (it at least the biggest since Japan started recording earthquake data), but because it triggered the tsunami that killed tens of thousands. In truth, the earthquake probably only killed hundreds, and many of those were in Tokyo. Now, scientists are saying that Tokyo is at risk for a massive earthquake right under its feet. That has got me worried.

Location, Location, Location

The silver lining about the March 11 earthquake location is that Tohoku isn’t as populated as Tokyo, because otherwise the death toll would have been that much more like Haiti’s 2010 earthquake. If a tsunami of that size came to Tokyo, we would have seen hundreds of thousands of deaths, guaranteed, if not millions. But I’m not concerned about a tsunami reaching Tokyo, because scientists have not informed us of any threat like that. What I’m concerned about is a huge earthquake striking the Tokyo area.

In case you didn’t know, the instance of one earthquake is not necessarily independent from others. For example, one earthquake (usually the bigger ones) can cause others, which is why Japan has been getting hundreds if not thousands of them over the past 6 months. Consider this excerpt from the BBC:

“The massive [M9.1] Sumatra quake in 2004 was followed by many others above Magnitude 7.0, including two above Magnitude 8.0 in 2005 and 2007. Some generated tsunamis that claimed more than 100 lives; and it is thought they occurred because the original earthquake, on 26 December, increased stresses along the tectonic plate boundary that lies to the west of Sumatra and Java.”

The University of Tokyo’s Earthquake Research Institute (ERI) has been monitoring the tectonic plates beneath Tokyo, and has found an increase in frequency of innocuous earthquakes around Magnitude 3 after March 11. On average, they usually occurred around twice a week. Since the massive quake, they have been occurring practically every day. And by innocuous, I mean that people can’t feel them – so we can’t even physically sense that the chances of a big quake are increasing.

Researchers have said that a huge earthquake – we’re talking levels up to Magnitude 7.3 – could be amplified by seismic activity in multiple focal areas under Tokyo.  Compared to a Magnitude 9.0, this seems a lot safer… but we’re comparing a relatively country-side region of Japan (Tohoku) to a place with one of the highest skylines in the world. The taller the buildings, the more damage they can do if they collapse.

And it would sure be a shame to lose a skyline like this

Tokyo is like a mine-field compared to Tohoku, because its buildings are just so big. Signs fall, glass breaks, and buildings collapse – all of which happened on March 11th, despite the hundreds of kilometers that separated Tokyo from the epicenter. In fact, it was probably the fact that Tokyo was so far away which could account for the comparatively low number of people killed in Tokyo.

The Volatile State of Japan

Around 2007, calculations suggested there was a 30% chance of a massive earthquake (M7 or higher) in the Tokyo area, according to the US Geological Survey (USGS), which is a joint U.S. and Japanese collaboration. After the earthquake, they said that “the [threat of such an earthquake in Tokyo] is either unchanged or higher than it was beforehand.”

At least compared to places like Sumatra or Haiti, both of which had strong earthquakes last year, the area around Japan has been well-studied, and a lot of data has been collected. However, despite Japan being the most well-educated nation in terms of earthquake science, the earthquake off the East coast of Japan changed the way a lot of scientists thought about the science of plate tectonics.

Japan’s the one that shares four freaking plates, in the top left of the map here

Chris Goldfinger, a researcher at Oregon State University who collaborates with Japanese scientists, said that the size of the Tohoku quake just proved that the understanding of subduction zones is incomplete. Subduction zones are the points at which one tectonic plate (a section of the planet’s hard shell, as seen in the picture above) slides under another, sinking into the mantle of the Earth’s. Tsunamis are usually caused by earthquakes that occur within subduction zones. Goldfinger said this about the Tohoku zone:

“It was well known to put out quakes at M 8.3-8.4 quakes, but on the seismic hazard maps it was lightly treated – all the hazard was thought to be on the Nankai Trough [on the boundary of the Eurasian and Philippine plates]. […] [It] had been written off as a really great seismic source, […] but it surprised everyone; and that’s why I no longer write off faults unless they’re proven dead.”

So despite the fact that Tokyo was relatively safe on March 11 because of the well-planned engineering and architecture that kept buildings from toppling (something that was never done in Haiti), we still don’t know enough about earthquakes to protect people from potentially disastrous results in the big city. But luckily, since Japan has such an impressive network of seismographic sensors and earthquake-measuring technology set up in Japan, the quake is not being wasted; it’s quickly becoming the most studied one we’ve ever recorded.

What scientists are saying

Research based off the March 11 earthquake led researchers to raise the risk of another big earthquake in or around Tokyo from 30% to over twice that amount. A study – conducted by the USGS, the Woods Hole Oceanographic Institute in the U.S., and Kyoto University – led the head researcher to increase the reported risk to over 70%. This projection is for a 30-year time-frame, but it still means that we will almost certainly be hit with a quake. If we do, I guarantee (you might even say I’d “stake my life on it”) that we will see a lot of deaths.

The 1923 Great Kanto Quake (M7.9) killed over 140,000 people. Yes, this was before the buildings were reinforced with the latest earthquake-proofing technology; but whereas Tokyo and Yokohama had a combined population of less than 8 million in 1920, the figure is now over 35 million.

The government’s Central Disaster Management Council has stated that an earthquake of magnitude-8 or greater will not occur in the near future in Kanto, but the ERI says this may be false. As the Daily Yomiuri reports, “the Great East Japan Earthquake has largely changed conventional thinking about the region’s seismology.” One researcher at the ERI – who is also on the government’s Earthquake Research Committee – remarks “If there is drastic plate movement, there is no guarantee that the scale of the quake will be in line with the government’s prediction of up to magnitude 7.3.”


Hopefully we don’t have to experience the reality of a devastating earthquake in Tokyo within the next few decades, but it seems that the chances are good. [Update: 78% of Japanese people polled, over 1500 in total, said that they too worried about another big earthquake in Tokyo.] I still don’t feel deterred enough to keep away from Tokyo, but the next time I move, I might prioritize living and working somewhere in Tokyo that’s not surrounded by skyscrapers.

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