Magnitude 8.8 earthquake in Chile

The recent earthquake that killed about 250,000 people in Haiti had magnitude of 7.0. It took place in the depth of 15 km, about 50 km from the capital, Port Au Prince, whose population was about 1 million people (well, it's detectably less today).



Concepcion, Chile

Well, sadly, one minute ago, on Saturday, 7:34 a.m. Central European Time, there was a magnitude 8.8 earthquake (see Wikipedia; originally reported as magnitude 8.3) about 60 km below the ground in Chile, 80 km from one metropolitan area of Concepcion with 1.3 million people (300,000 without the suburbs), 100km from two cities with 200,000 people each (Chillan, Talca), and 300 km from the capital, Santiago de Chile, with 5 million people.

The earthquake occurred in the ocean, just 5 km from the land (and only a 100-km arc may have been affected by the tsunami if there was any: see the Google Maps for the location.

The formula for the magnitude says

M_W = 2/3 log₁₀ (M₀) - 10.7

where "M_0" is a kind of mechanical work, more precisely the seismic moment (shear modulus times area times average displacement) in hundreds of nanojoules.




You can see that the additive (Chile vs Haiti) increase of "M_W" by 1.3 or 1.8 means the increase of the base-ten logarithm by 1.95 or 2.7, respectively. If you need to know, 10^{1.95} and 10^{2.7} are close to 89 and 501, respectively. So there was 89-501 times more mechanical work in the Chilean earthquake. The magnitude 8.3 earthquake would become approximately 17th strongest earthquake ever recorded while 8.8 (newer estimate) would be 6th-7th but it will remain well below the 9.3 earthquake that caused the 2004 tsunami and the largest ever seen, magnitude 9.5 earthquake that hit Valdivia, Chile in 1960 (about 500 km from the today's location; the quake 50 years ago had only killed at most 6,000 people).

Let's pray that these are just big numbers that don't have to be translated to other, more human and more sad numbers. The strength was bigger in Haiti but so was the depth and the distance from the big cities. I actually think that the casualties will be limited. They're used to quakes. For example, Santiago only saw some vibrations and blackouts. And yes, a few collapsed buildings, too.