7.5 magnitude earthquake strikes Japan's West coast

Authorities in Japan have confirmed that dozens of people were killed when a 7.5 moment magnitude earthquake struck the Noto peninsula on New Year's Day. The island nation is located in one of the most active earthquake zones on earth. So, what happened, and how does Japan cope with such frequent and powerful tremors? Here’s James Jackson, a professor of active tectonics at the University of Cambridge.

James - This earthquake was relatively unusual in Japan in that it was on the West coast of the main island, Honshu, rather than the east coast. So the big earthquake in 2011, the Tohoku earthquake which damaged the nuclear power station at Fukushima, that was on the East coast. And what's happening on the East coast is that the Pacific floor is sliding underneath Japan. And that's happening quite quickly, geologically speaking, at about eight centimetres per year. And that makes very large, big earthquakes under the water and that's why you get big tsunamis. This earthquake was on the West coast of Japan, where that process is not happening. There's nothing sliding back into the earth. The earthquakes are pretty shallow and instead what they represent is Japan being squeezed. It's being crumpled up. So it's not just the escalator sliding underneath Japan, but as that happens, Japan is being squeezed. And occasionally you get faults which pop up along the west coast. And that's what happened this time. And it's happened before the last time there was one this size on that same area of the west coast was in 1964 at Niigata. And that one, the fault was also offshore. So it made a tsunami about five metres high and it killed about 40 people. But this one is about a hundred kilometres down the coast. And as far as we can see, most of the fault which moved was onshore. And that is why there's not really been a significant tsunami.

Will - And you mentioned it then, but it's something that stood out to me that was quite interesting is, as you said, the epicentre of this earthquake was quite shallow. It was only about 10 kilometres. For reference, the 2011 earthquake in Japan was at a depth of 29 kilometres. Does the depth at which the quake takes place have any effect on our experience at the surface?

James - Both of those are relatively shallow. But on the East Coast, the escalator, as it goes down underneath the east coast, goes down as far as 670 kilometres. So you get earthquakes all the way down, because as the escalator, if you like, goes down it also breaks up. And so you get deep earthquakes all the way down there, all those earthquakes. 20 is not going to make much difference frankly, whether you're at 30 kilometres or 15. But it does make a difference if you are 600 kilometres down where you are, even at the surface, so far away nothing really is going to do anything to you.

Will - Japan is no stranger to earthquakes. This is the 14th above magnitude 5.5 in the past 10 years alone. And as you've spoken about the remarkable area in which Japan sits is probably the reason as to why they get so many. But how do the authorities there try to manage the risk for events with such little warning?

James - There are a number of interesting points about this. Firstly, Japan is curiously helped by there being so many earthquakes. Even on the west coast, where they're not that frequent. But between the 1964 one and this one, these are two comparable earthquakes, there were probably half a dozen or a little bit smaller, but enough to shake you up and really scare you. So when you say to people in Japan, 'earthquakes are a problem. You need to do something and make everyone safer and your houses better,' it's not a theoretical discussion. They know this will affect them in their lifetime. This is not something you can say maybe my grandchildren will have to think about. No, it will affect them for sure, but also you and your children. So that means it's really at the forefront of people's consciousness and that's a big help. Japan is indeed very resilient to these things. But that's not chance, that's the result of decades of careful hard work, finding out what the problems are. Lots of conversations between the public, public administrators responsible for public safety, and the scientists, and the engineers. And again and again, earthquakes in Japan show that the architects and engineers can design things which will stay up. And the issue is always, when these buildings are built, do the constructors, the building people, actually follow the instructions precisely. It really matters that you don't cut corners to save time and money because anything you do will weaken that original design. But if you follow it precisely, the buildings are likely to be fine. And that is the message again and again from Japan. These things are sort of a quiet triumph of the integrity of the building industry in Japan, which is much admired and respected around the world because in the rest of the world it really isn't much like that. It probably is getting there in places like Chile and New Zealand. But that is a huge achievement.

Will - And as you say, we are still very much in the process of finding out what's happened, search and rescue, that sort of stage in development. But in the medium to long-term future, do you think there are any lessons that Japan can learn from this earthquake as to perhaps better prepare or change the way they see these sorts of things?

James - I think the Japanese are constantly learning lessons from these events, which is why they get better and better. They're not complacent. I mean these things are a tragedy. This one is a tragedy and a lot of people have died. A lot of destruction. It'll cost a lot of money. Lots of people's lives will be really messed up by all this. But from a perspective of people far away, as I say, Japan is much admired and respected because this size earthquake, anywhere in the big earthquake belt, which goes from the Mediterranean to China, routinely kills tens of thousands of people. And that is not likely to happen in Japan. And that is a tremendous achievement. And sometimes you lose track of that. I mean, it is really an astonishing thing, that huge earthquake in 2011 on the east coast, which was a hundred times bigger than this one. The earthquake itself did very little. It was the tsunami, which is a slightly separate story, coming later which drowned 20,000 people and knocked out the nuclear power station. But the infrastructure was really not that much damaged by the earthquake itself, which is a fantastic achievement.