I might not even have heard about it if I hadn't been watching television. The regular news was interrupted with a flash, and colleagues in the office in Tokyo where I work gathered around the screen. There were phone interviews with people in the affected area, and a curious and hastily- put-together map. It looked like a weather chart, but instead of temperatures, the number alongside each place name indicated the intensity of the quake on the Japanese scale: five in Hokuryu, four in Rumoi and Fukagawa. It was different from a weather map in another respect. Despite billions of yen spent on research in monitoring and research, nobody has successfully predicted an earthquake.
I have been in Japan for two months now, after a year's absence, and - even in a city as protean as Tokyo - this is undoubtedly the biggest change. In a part of their minds, Tokyoites have been tensed for disaster for years, but since the Kobe catastrophe in January this sense of anticipation has become acute. In subtle and frequently mundane ways, everyone is thinking about earthquakes.
A couple of times a week, you used to find yourself on an expressway or in an underground shopping centre and think: what if the Big One struck now? Now these thoughts occur three or four times a day, and even the most trivial activities become a cause for quake anxiety. Finding an apartment, as I have recently done, brings many of these fears into focus. Question One: is this flat convenient, well-appointed and reasonably priced? Question Two: will it fall on top of me when the ground starts to shake?
The other day a group of us sat down and tried to work out where would be the very worst place to be in a big earthquake. A friend suggested the Tokyo monorail, a slender ribbon of steel and concrete on which trains from the airport glide high over the chemical and petroleum tanks in the south of the city. I reckoned it would be in a lift - they are programmed to shut down automatically at the first sign of a tremor. Then someone indicated the restaurant in which we were sitting. It was a dark, narrow snuggery on the eighth floor of a 10-storey building. Behind the counter, the chef was gleefully pouring oil and sake on to a pan which flared with a foot-tall plume of flame. The walls, doors and mats on which we were sitting were made of wood, paper and rushes.
Later that evening, on my way home, I experienced a further revelation. I was on a flimsy pedestrian bridge straddling a six-lane road. Below me cars were speeding past at 40 miles an hour. Above me were two more overhead expressways, with trucks and buses travelling at 70 miles an hour. I was in an earthquake sandwich. On top of this, like most of the thousands of Friday-night revellers around me, I'd had a few. I crept home, keeping close to the buildings, virtually on my hands and knees.
I'm not the only one worrying about all this. In elections for the governorships of Japan's cities earlier this year, the one thing that all the candidates agreed on was the need for "earthquake defence measures". But, short of dismantling Tokyo and rebuilding all its old houses, ageing offices, and multi-storey roads, there is very little that can practically be done.
In Kobe, 5,500 people died, almost a reassuring figure given the population of the affected area; even the most darkly apocalyptic predictions for Tokyo's next Big One project 60,000 dead, just half a per cent of a population of 12 million. But one's safety depends entirely on location and activity. No variety of disaster is so impervious to precaution and common sense, or so completely a matter of chance.