Tokyo’s been a bit shaky this last week. We had three sizeable earthquakes between Sunday night and Thursday morning.
As I reported in my previous post, I was outside at a BBQ when the Sunday evening quake hit, and was surprised to feel the ground moving under my feet. This was the first time that I’ve felt an earthquake naturally, so to speak, without feeling and hearing a creaking, groaning and swaying building around me. It felt like someone had suddenly placed a tumble drier under my feet, and someone had turned it on. Here’s the Japanese Meteorological Agency’s (JMA) seismic report of the earthquake on Sunday evening (8:02pm), showing that Tokyo reached a 3 on the Japanese scale. (A three on the scale is described as “Felt by most people in buildings, felt by some people walking, many people are awoken“).
The earthquake on Tuesday morning was the biggest of the three this week. It got me out of bed with a jolt at just after 5am, with the building groaning and creaking. The first thing I do after an earthquake is turn on the TV to learn where the epicentre was, and how big it was. Reports come out very quickly, and if big enough news announces will break into normal programming to provide information. This one was big enough. The news was instantly awash with reports of the earthquake, centred off the coast of Shizuoka, and there was even a tidal wave warning issued for a while. Here’s the map of Tuesday morning (5:07am), with Tokyo registering a 4 on the Japanese scale. (A four on the scale is described as “Most people are startled, felt by most people walking, most people are awoken.”)
The third was again early in the morning, just before 8am on Thursday morning. It was the most minor of the three with a more gentle swaying feeling, but again big enough at the epicentre off Hachijojima south of Tokyo. This is the map of Thursday morning (7:49am). I was about to leave for work, but managed to get a live Tweet out whilst everything was still shaking. This one was only a 2 on the scale, which is “Felt by many people keeping quiet in buildings, some people may be awoken.”
There was largely no damage in Tokyo from any of these, except for some very very minor damage at my apartment building on Tuesday morning. When I stepped out my front door a few hours afterwards, I found a metal strip had fallen and was lying on the walkway, but I couldn’t even tell where it had fallen from! As you can see, the building is not going to fall down as a result of this. However, the lift was still shut off, which I imagine is an automatic cut-off.
If you’re not already familiar with the Japanese earthquake scale, you will have gleaned from above that it’s different to the Richter scale.
The Richter scale measures the intensity of the epicentre of an earthquake. The Japanese seismic intensity scalemeasures how strong an earthquake is at any given location, based on how it feels. I guess this is a little similar to how the Beaufort wind scale describes wind conditions.
The Japanese scale ranges from 0 to 7, with 0 being almost imperceptible to people, and 7 being enough movement for a major calamity. I think that the Japanese scale is more meaningful to people than reporting the magnitude of the earthquake generally, as people can immediately understand how an earthquake felt in various places. It’s certainly more often quoted in Japan than the Richter scale.
Here’s a summary of how the scale works:
- 0. Imperceptible to humans
- 1. Felt slightly by some people in buildings
- 2. Felt by many people in buildings, lamps and curtains sway
- 3. Felt by most people, waking up many. Electricity wires outside sway
- 4. Startles most people. Things in cupboards rattle. Electric wires outside swing significantly.
- 5 minor (5-). Many people frightened enough to hold onto something, many items rattle violently. Windows may break.
- 5 major (5+). People have trouble walking. Unsecured items may fall or topple. Weakly constructed items may crack or crumble.
- 6 minor (6-). Difficult to remain standing. Furniture will move and doors wedge shut. Unreinforced concrete may topple.
- 6 upper (6+) and 7. Impossible to stand up, people may be thrown in the air. Unsecured furniture likely to move or topple. Even reinforced concrete buildings may collapse
I was in Kyoto when the Great Hanshin Earthquake struck in 1995. In Kyoto it was a 5, and I remember windows cracking and items in the bathroom rattling around violently. It was a 7 in Kobe that morning, which explains all the terrible damage and loss of life.
There is a useful description of the Japanese seismic scale in a table at the JMA website. And it wouldn’t be Japan without a description in cute pictures (PDF), also at the JMA website.
