Ng: Spared

Thursday, February 9, 2012

WHEN the earthquake struck early this week, I started to check in the office that everything and everybody was all right as well as the building. I then climbed the highest point of the building and viewed things around. The city was okay. The shake was not that hard (at least the way I felt it) and it looked like the damage was minimal.

I started checking on the Internet. There were a lot of comments, particularly in Twitter, but this is good because when people posts, you can get wind of the response.

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I started to do some research and found the earthquake was 6.9. It didn’t feel that strong. Here are some of the things I learned, some of which I sent to my colleagues, which calmed them down in the afternoon.

The extent of damage to earthquake is due to two things;

a) How long the earthquake is. Common sense says that an earthquake lasting a minute will do much more damage as that lasting only a few seconds. Luckily, most estimates say that ours was only 15 to 20 seconds. In contrast, the earthquake in Japan last March 2011 lasted over 6 minutes and the Indian Ocean earthquake that caused the tsunami in Indonesia, Thailand and other countries lasted eight to nine minutes.

b) Intensity of the earthquake. The earthquake epicenter was in Negros and it was 6.9.

By most accounts Cebu is far and is probably about 5.0. We were not as badly hit.

Moreover, earthquakes are measured by a Richter scale which is logarithmic. A logarithmic scale means that every increase in one is a factor of 10 in terms of tremor intensity and a factor of 32 in terms of energy released. So a 6.0 earthquake is 10 times the tremor of a 5.0 and releases 32 times more energy than a 5.0. A 7.0 earthquake is 100 times the tremor of a 5.0 and releases 1000 times (32.x multiply by 32.x) more energy.

If we got a 5.0 then the epicenter in Negros being a 6.9, the tremor in Guihulngan was close to a hundred times what was felt in Cebu and released closed to a thousand times more energy.

The Japan earthquake in 2011 was intensity 8.9 and the one in the Indian Ocean was a 9.1. By most accounts, they not only lasted 20 to 30 times longer but their intensity was easily (compared to 5.0) a thousand times ours, with energy unleashed probably close to a million times. Thus the comparison of the damage to properties and to life was also huge.

As for the tsunami, most experts say that a tremor of 6.9 would probably generate a tsunami one meter high. The tsunami in Japan and the Indian Ocean, generated as it is by minutes-long shakes with about 9.0 intensity at the bottom of the sea, went up to 30 or 40 meters. Moreover, the Philippines , most especially Cebu, is shielded by many islands so it is unlikely any earthquake outside the country will have a tsunami that will reach Cebu. We would be at risk only with a very strong earthquake whose epicenter would be in the sea between Bohol and Cebu.

Once again, just like typhoon Sendong two months ago, and the earthquake today, Cebu has been spared. Let us thank God for it and let us be a little bit generous to help our brothers in Negros.

(www.twitter.com/wilsonng)