August 24 – Tembling In Fear

Today’s factismal: An earthquake is called a temblor by the folks who study them.

The past 24 hours has been very interesting. In that time we’ve seen a Mb 6.8 earthquake in Burma, a Mb 6.2 temblor in Italy, and a Mb 6.0 event in Indonesia.

A comparison of the energy released by the big earthquakes we've had in the past day

A comparison of the energy released by the big earthquakes we’ve had in the past day

Though we still don’t know what the damage from these events will be, most experts expect it to be a few hundred dead in each case because the areas that were affected are mostly un-reinforced masonry buildings. that do not hold up well in an earthquake. Now, the typical lay reader is probably thinking “I should donate to the relief funds” and the typical lay reader would be right. Getting supplies and shelter to those in the disaster areas will definitely help more people survive. But the typical lay reader is probably also thinking “Gosh, three biggies in one day – there has to be something going on” and the typical lay reader would be wrong.

The past week's temblors (Image courtesy USGS)

The past days’s large temblors
(Image courtesy USGS)

The typical lay reader is wrong because there are earthquakes every day. Lots of them. On a typical day, there are about 4,000 earthquakes. Now most of those events are very small; they tend to be Mb 1 or Mb 2. But every year there are 134 or so events with a magnitude between 6 and 7. So on average we would expect to see an earthquake this large about once every three days. And since earthquakes happen at random, the odds of seeing three events in any given 24 hour period are not that bad – about 1 in 27. In other words, we should expect to have a replay of today’s events about once a month or so. Fortunately, most of the Earth is empty ocean so most of those replays take place far, far away from any people.

One year of earthquakes across the world. (Image courtesy the USGS)

One year of earthquakes across the world. (Image courtesy the USGS)

We get earthquakes because the Earth is hot inside. That heat creates motion in the mantle that geology wonks call convection. And the motion of the mantle drives motion of the Earth’s crust, breaking it into large rigid sections called plates. As the plates collide to form mountain ranges or scrape alongside in transform zones, they release energy as earthquakes. For Burma, the plates that are colliding are the India plate and the Eurasian plate and the mountains that are being built are the Himalayas. For Italy, the plates that are colliding are the Nubia plate and the European plate and the mountains that are being built are the Apennines. And for Indonesia, the plates that are colliding are the Australia plate and the India plate and the mountains that are being built are Indonesia. And though the temblors cause a lot of damage and deaths they also give us a chance to learn more about how to make the next one less dangerous.

The different layers of the Earth. Only the outer core is molten; everything else s solid!

The different layers of the Earth. Only the outer core is molten; everything else is solid!

You see, after each earthquake, people who felt it have gone to the Did You Feel It? page and told the USGS what they felt. That helped the geophysicists to determine which parts of the world are most susceptible to earthquake damage which tells  first responders where we need to improve building codes and emergency response.

The results of Did You Feel It? for the past decade (Image courtesy USGS)

The results of Did You Feel It? for the past decade
(Image courtesy USGS)

If you’d like to help, participating is easy. The next time you feel an earthquake, go over to Did You Feel It? and let them know what you felt. Then sit back and enjoy the knowledge that you’ve just helped make us all a little bit safer.

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