I am finally back, repairing some of the damages in our labs. The situation in Chile is not good. The deaths are raising slowly, but continoulsy, over 800 people now. Also, some data regarding thousands of missing people is also of great concern.
Regarding to science, several laboratories have reported serious damages, including lost of data, expensive equipment (you must consider that, due to the location of Chile, far from the manufacturers, equipments and reagents cost three or four times more expensive than in USA or Europe).
The observations and predictions (at a glance)
It is surprising that researchers had predicted the earthquake almost two years ago . Teachers always say to students “nature is unpredictable; you can’t know where an earthquake will occur”. But technology advances, and together with mathematical modeling and observation, just like Darwin did in his travel to Chile almost 170 years ago, describing the earthquake of 1835 , researchers can formulate hypotheses about when, and how strong an earthquake will occur.
Ruegg and coworkers published a paper in “Physics of the Earth and Planetary Interiors” (Ruegg JC, 175:78–85, 2009). The team made observations in a range from 1996 to 2002, focusing in the area from Constitución to Concepción, since no major earthquakes occurred in that space since 1835 (described by Darwin). They measured the displacement of the plate (more exactly, the velocity of the movement). The results (at a big glance, since I am not a geologist) showed that coastal regions had a higher velocity compared with regions in the Andes area. Assuming that no major earthquakes released the accumulated force since 1835, a deficit of horizontal displacement of 10 m will have accumulated.
To Ruegg and coworkers, this could mean, in a worst case scenario, “that the southern part of the Concepción–Constitución
gap has accumulated a slip deficit that is large enough to produce a very large earthquake of about Mw = 8.0–8.5”.
What happened in Chile?
This February 27, at 3:34 am (Chile’s time), an earthquake with a magnitude of 8.8 in Ritcher scale occurred in a site very close to Cobquecura, located between Concepción and Constitución (see map below). The plates moved 8 m, and since Ruegg and coworkers calculated a 10 m of slip deficit, either the calculations are overestimated or the earthquake should have been even worse.
Figure 1. Earthquake and areas affected. Notice the location of the epicenter, just as predicted by Ruegg and coworkers.
Nonetheless, the prediction of Ruegg and his team is shocking. They were right about the epicenter and magnitude. The final phrase of the abstract is: “… in a worst case scenario, the area already has a potential for an earthquake of magnitude
as large as 8–8.5, should it happen in the near future”.
Earthquakes in Chile show a striking regularity: every almost 17 years, a major earthquake (above 8 in Richter scale) occurr. Even more, the majority of the most destructive earthquakes ocurred in the chilean summer:
Figure 2: Major earthquakes in Chile since 1906. The box around 1939 and 1943 shows that the average (1941) was considered to calculate the years between the events (between 1922 and 1941, and between 1941 and 1960). 50% of the events occurred in summer or beginning autumn.
An obvious conclusion for our country, Chile, is the following: scientific observations can assist to make predictions about the most probable sites of a future earthquake, including information about the magnitude. Ideally, a global network across the identified seismic gaps in Chile (one at the north, one near to Valparaiso, one located between Concepción-Constitución and one near to Valdivia, epicenter of the greatest earthquake in the last 200 years) and some other regions , could help to be better prepared for a new earthquake. I don’t know of such an approach is being used in other seismic regions on Earth.
1. Ruegg, J., Rudloff, A., Vigny, C., Madariaga, R., de Chabalier, J., Campos, J., Kausel, E., Barrientos, S., & Dimitrov, D. (2009). Interseismic strain accumulation measured by GPS in the seismic gap between Constitución and Concepción in Chile Physics of the Earth and Planetary Interiors, 175 (1-2), 78-85 DOI: 10.1016/j.pepi.2008.02.015
2. Richard A. Kerr (2010). Did Darwin Help Predict Chilean Quake? Science Now