February 27, 2010

expert reaction to the earthquake in Chile

Chile has been struck by one of the most powerful earthquakes in the country’s history, causing over 700 deaths so far and forcing many others out of their homes.

Dr Brian Baptie, British Geological Survey’s Head of Seismology, said:

“This is largest earthquake to strike central Chile since a magnitude 6.7 earthquake in 2001. The epicenter lies around 200km northeast of the magnitude 9.5 earthquake that struck Chile in 1960. This was the largest earthquake ever recorded and resulted in a destructive tsunami that killed many thousands of people around the Pacific.

“A 1.3m tsunami wave was observed at Valparaiso, 200km north of the epicentre about 20 minutes after the earthquake. Tsunami waves in the deep ocean travel about the same speed as a jet plane and would take about 15 hours to reach Hawaii and about 20 hours to reach the other side of the Pacific.”

Dr Roger Musson, British Geological Survey’s Head of Seismic Hazard, said:

“This earthquake fills in an identified seismic gap – no previous large earthquake had occurred in this area since 1835, when a large earthquake was observed by Charles Darwin. Since then, an estimated 10m of potential displacement has accumulated.”

Dr David Rothery, Dept of Earth & Environmental Sciences at the Open University, said:

“This morning’s (06:34) magnitude 8.8 earthqauke close to the Chilean coast has caused a tsunami that is now radiating away from the epicentre and travelling at several hundred km per hour across the Pacific ocean. The first waves are expected ot Hawaii at 11:19 Hawaii Standard Time but are also travelling along the S America coast and will reach Colombia and Costa Rica after 1300 GMT (see http://www.prh.noaa.gov/ptwc/). Some earthquake damage is to be expected ashore in Chile near the town of Concepcion.

“A magnitude 8 quake is a rare event. On average there is only about one of these per year, globally. This one was caised by the floor of the Pacific ocean being pushed below South America. Because the epicentre was under the sea, the sudden jerking of the sea-floor displaced water and triggered a tsumani. The focus of this quake was at a depth of about 34 km – which is relatively shallow (and hence damaging) though not quite so shallow as the magnitude 9.1 quake in the Sunda Trench that caused the 26 Dec 2004 Indian Ocean Tsunami.”

Prof Colin Taylor, professor of earthquake engineering at the University of Bristol, said:

“A magnitude 8.8 earthquake is a rare and extremely powerful event. Damage away from the epicentre appears to be mainly to masonry buildings, which are notoriously brittle. It would seem that more modern buildings, built from reinforced concrete frames and designed to modern standards, performed quite well.

“It is very important for forensic engineering teams to visit site once the disaster recovery is completed, so that we can improve earthquake design in future. So far, we don’t have a great deal of footage from the epicentral area where we would expect more intensive shaking. From an earthquake engineering point of view, this is a rare opportunity to see how modern buildings, designed with earthquakes in mind, have performed in this ‘full-scale laboratory’.

“Currently, the basic concept is for buildings to be built around frames. These ensure that the columns holding up the building remain intact. The beams between the columns are designed to break up at their ends, forcing the structure to fail in a controlled way. This style is called ‘strong column – weak beam’.

“If shaking is strong enough, the beams will absorb a lot of energy from the earthquake, dampening its power and protecting the building. It is very rare to get modern buildings shaken so much. In Chile, we will see if the methods have worked.”

Dr David Kerridge, Head of Earth Hazards at the British Geological Survey, said:

“The Haiti earthquake ruptured the plate boundary over a distance similar to that between Edinburgh and Glasgow. For the Chile earthquake, the length of the rupture was more than the distance from Edinburgh to London.

“The slip distribution in the Haiti earthquake was concentrated near the capital so it was almost like a ‘direct hit’ on a city of more than 2 million people living in poorly constructed buildings. In the Chilean earthquake the energy was released by slipping distributed over around 300km and caused violent shaking throughout Chile. Photographs from Chile show some buildings now looking like the leaning tower of Pisa, they are leaning but didn’t collapse and kill people. In Haiti many buildings ‘pancaked’ giving very little chance of survival for the people living in them.”

Dr Scott Steedman, a Fellow of the Royal Academy of Engineering, said:

“Chile is a country with recent experience of serious earthquakes and an internationally respected engineering community. There is a high level of preparedness and investment in engineered structures across the country and I would have expected that much of the recent infrastructure had incorporated the lessons from the last major earthquake in 1985.

“It’s very important that we find out why so many structures have failed, particularly the bridges, in case there are lessons to learn for our international design standards for construction.”