A large earthquake has hit central Chile, with a tsunami alert issued but later lifted.
Prof. David Rothery, Professor of Planetary Geosciences at The Open University, said:
“Last night’s earthquake off the coast of Chile was a result of the floor of the Pacific ocean being thrust down below South America, which is happening at an average rate of about 7.5 centimetres per year. This event was Richter magnitude 8.3, and represents a jerk of more than a metre along a 200 km length of the subduction zone fault. The rupture initiated at a depth of about 25 km. Given the large magnitude of the earthquake this was shallow enough to violently displace the sea-bed and sea off a series of tsunami waves in the ocean.
“The small number of deaths reported from Chile appear to result from the earthquake itself rather than the tsunami. The promptness of the evacuation from low-lying coastal areas in this case perhaps shows lessons learned in Chile in 2010 (27 Feb) when a tsunami triggered by a slightly larger offshore earthquake further south claimed hundreds of lives. This resulted in the sacking of the head of the Chilean oceanographic institute because no official tsunami warning was issued when the earthquake was felt, although fortunately some harbourmasters sounded alarms on their own initiative.
“In the first 14 hours after the initial quake there have been 38 aftershocks stronger than magnitude 4.5 (the largest was 7.0). These will continue, generally becoming smaller, for several days, posing the risk of collapse in already-damaged buildings.
“The tsunami threat cross the Pacific has now passed, although coasts as far away as New Zealand were rightly put on alert.”