(This post is dedicated to my friend, Fernando)
One thing you get used to, when living abroad in an area plagued by earthquakes, is explaining to despairing parents why when they see on TV:
“MAG (very high) EARTHQUAKE IN (some place), TSUNAMI WARNING WAS ISSUED!”
They should not immediately announce to their friends the world is ending, and call their son urgently to return home.
Let’s start with the Tsunami warning. In principle, EVERY earthquake where it’s center is in the ocean issues a Tsunami Warning. The earthquakes are not observed directly, and it is just good practice to be aware of the possibility until it is confirmed. Of course you must take precautions. In my experience, though, most of these warnings are soon removed.
Now let’s talk about the Magnitude. A Magnitude of say, 7, is very scary, and indeed indicates a very strong quake. But it hardly tells the whole story. Location, Location, Location. Remember that as energy spreads, its energy is reduced, at an exponential rate. Not only that, Different rock compositions can help or hinder the spread of the seismic wave, to the point of in certain cases forming an “echo” bowl where the waves go back and forth until they die out (in Japan known as “long-period earthquakes”. So in the end, the Magnitude at the epicenter says very little about how the actual effects of the quake in areas farther away.
A better guide to report earthquake on inhabited areas would be a network of sensors that measure local shaking, such as the one provided by the earthquake in Japan. For example, the following image was taken from weather.yahoo.co.jp:
The X marks the place of the actual quake (a Magnitude 5.6 one) the different circles show how strong the quake was felt, according to the Japanese Quake Scale (about which I spoke a while ago). Notice that the white and light blue circles were barely felt, and the dark blue circles were on a “wow, a quake, haha!” level.
Why is this important? Peer and Family pressure are powerful tools. During the big Fukushima Earthquake this year, many foreigners in Japan who were in places not affected by the quake at all (such as Kansai) were urged, and eventually forced to leave Japan unnecessarily due to their preoccupied families. These relatives were bombarded every day by irresponsible media that, due to either laziness or malice (or both) gave an incomplete and exaggerated picture of the already very serious catastrophe. This has shown that, when it comes to natural disasters, we usually have to do our own homework in order to properly access risks and take decisions.
