US west coast at risk of “mega-quake”

The west coast of North America, the Lesser Antilles, Chile, Sumatra and Japan are all at risk from subduction zone “mega-quakes” in the near future according to Professor Bill McGuire of the Aon Benfield UCL Hazard Research Centre.

Adding to the report the centre released this morning, Professor McGuire said that a "mega-quake" in California is ranked in his top 10 most likely natural disasters at present and could hit "any day."

He explained that major quakes in the Cascadia region (on the west coast) cluster into series of up to five events and we look to be in the middle of one of these series. He said that subsidence has been reported since 1992 and supsidence has been reported as a precursor to "mega-quakes" in the past.

He added that as the quake is likely to occur off the coast shaking will not be extreme but there will be a tsunami risk and shaking could last as long as 3 or 4 minutes and this kind of shaking can be destructive, especially to high-rise buildings.

Professor McGuire also highlighted the risk of "mega-quakes" in Japan. He added that whilst Tokyo is not in the region most effected but a smaller event directly beneath Tokyo is expected. He said there is around a 30% probability of a M+7.3 event under Tokyo in the next 30 years which the Japanese government has estimated could lead to economic losses of up to $1trn.

Subduction zone earthquakes are produced at the interface where an oceanic plate, known as the upper plate, and the down-going plate descends into the interior of the Earth as a subducted slab. This type of earthquake includes almost all mega-earthquakes to affect the Earth. This term "mega-earthquake" refers to events of moment magnitude greater than 8.

Professor McGuire also listed volcanic eruption in his list of top 10 most likely natural disasters. He said there is a "strong possibility" of an eruption of the Katla volcano in Iceland over the next few months. He added that this would not necessarily be a large event as the volcano erupts relatively frequently.

However, Professor McGuire warned that there is the potential for a significant eruption in an urban centre in the developed world with 52 European volcanoes with many classed as active. He added that the Bay of Naples in Italy is at risk with the potential for a moderate explosive event with as short as a couple of weeks notice with extensive property damage and the need to evacuate around 600,000 people.