So Randal and I are lying in bed last night at our hotel in Tokyo, watching the news about the earthquake yesterday morning in Niigata-ken. (We didn't have much choice - it was pretty much the only thing playing on any of the channels.) It was a substantial quake, about 6.6 in magnitude. Of course, the earthquake a few months back north of here in Ishikawa-ken was stronger than that (7.1), but it occurred farther off the coast, and Ishikawa-ken is also fairly remote, so a lot less damage occurred. Yesterday's quake killed 9 people and 1 more is missing (as of earlier today, so that may have changed). Dozens of homes and buildings were destroyed. Some of the damage was pretty incredible. And the mystery of this one factory-like building that we kept seeing footage of (the news was all in Japanese, so we could only guess at some of the details), is solved, but slightly troubling: it was a nuclear power plant where some barrels of nuclear waste were damaged (leaked? I'm not sure). That's not very encouraging.
There was also a strong aftershock in Niigata-ken around 3:30 that afternoon that was felt as far away as Tokyo, but we were in Shinjuku at the time and didn't notice a thing. Some neat footage from camera crews who were out in Niigata-ken filming the damage when this aftershock hit.
Anyway, so we're lying there, watching the news, when the bed starts shaking. Yikes! Another earthquake. It was 11:18. This one was quite long, at least a minute in length, and picked up in intensity for about 8 seconds, about 30 seconds in, causing Randal's jacket, where it was hanging from a hook on the wall, to sway somewhat moderately. Of course, the news shows all start reporting on this right away. It seemed it was yet another aftershock, but today, now that I am home, I checked the JMA website, and it seems to be its own separate earthquake, and, additionally, the weirdest one I've ever seen:
OK, even if you're not an earthquake nerd (like me), you can probably figure out what's strange about this picture. The red X marks the epicentre of the quake. Normally, the strength of the quake diminishes the farther you get from the epicentre (with some variation, of course, but this is generally how it works). This earthquake seems to have done the opposite. It occurred in the Japan Sea well north of Kyoto Prefecture, but was felt the strongest in places along the Pacific Ocean coast, like Tokyo (it's listed as a 2-or-stronger in the area of Tokyo where we were staying). And the strongest reading of the earthquake - at 4-or-stronger - was in Hokkaido, which is many hundreds of kilometres away!!! The only explanation that I, as a non-geologist, can offer for this is that perhaps it had something to do with the depth of the quake: It was 370km below the surface, which is really, really deep. Most quakes at that depth wouldn't even be felt, but this one registered 6.6 at the source. Tectonic plates are funny things, so maybe at that depth, it had more time to travel outward before it started to really be felt above-ground - ie., in places much further away.
To compare, here is yesterday morning's quake readings. It was 10km below the surface (quite shallow, which is partly, I think, why it caused the damage it did) and, as I said before, 6.6 at the centre. In Tokyo, where we were, it registered as a 2-or-higher. (They only give exact magnitude readings for the epicentre.)
And in response to Stuart's comment after the Ishikawa quake - yes and no, earthquakes are and are not a semi-regular event in Gifu. Japan is one of the most seismically active zones in the world - it's dangerously sitting on three different tectonic plates. There are probably anywhere from 5-12 quakes somewhere in Japan on any given day. Most of these, however, are barely felt. Some areas are more active than others - Tokyo, for example, gets a small quake probably almost once a week, from what I hear. Upon coming out here, we were told again and again to prepare an earthquake kit with emergency supplies. The Japanese themselves seem quite blasé about earthquakes, but (kind of) prepared - I guess they're like Californians - they know earthquakes will happen. In a way, actually, they're better off than Californians - the Japanese know that the majority of quakes will cause no, or very little, damage.
However, that statement doesn't include the reality for millions of Japanese living in the Tokaido area (which, incidentally, includes Gifu, though it's at the far end) - the area south and southwest of Mt Fuji - this area is about 20 years overdue for a major quake, and the longer the quake takes to come, the worse it will be. Japanese earth scientists are confident they can predict when the quake will strike, with the ability to give anywhere from a few minutes' to a day's warning. I don't know if that makes me feel better or not, if I believe their ability to predict an earthquake at all - a beast which is, by its very nature, quite unpredictable, at least to date. (They were so busy preparing for the Tokaido earthquake 12 years ago that they missed any apparent "warning signs" (if there were any...depends on who you believe) forecasting the devastating 1995 Kobe earthquake.