Latest earthquake information revealed

Christchurch is likely to experience more magnitude five or six earthquakes during the coming months but larger earthquakes are likely to be further away from the city causing less damage, experts say.

The latest earthquakes which have been occurring off the coast in Pegasus Bay are also unlikely to produce a large earthquake of magnitude seven, resulting in a life threatening tsunami.

GNS Science and Tonkin and Taylor experts today briefed the city’s elected members, local Members of Parliament and media about the latest seismic information at a meeting in the Christchurch Events Village in North Hagley Park. Mayor Bob Parker called the meeting following the latest aftershocks which began on 23 December 2011.

GNS Science Earthquake Scientist Kelvin Berryman said, “Our expectation is that the current sequence of earthquakes will start to decrease over the coming months and certainly we believe that a lot of the stress has already been released on the fault lines closer to the city. We believe we are progressing into a period similar to after the February and June 2011 earthquakes. They will go on for some time but they will become undetectable over time.”

He also said that the risk of tsunami had not changed as a result of the recent earthquakes.

“From the information we have, a local source tsunami from an earthquake fault in Pegasus Bay is thought to be unlikely.”

Other key points made at today’s briefing include:

• The magnitude six earthquake that occurred on 23 December was only slightly above what scientists had predicted. Scientists have previously said that there was a 50% chance of a magnitude 5-5.9 earthquake occurring in the coming year.

• The probability of a magnitude seven earthquake is low.

• The peak ground acceleration (a measurement of how hard the ground shakes) is decreasing. The peak ground acceleration during the 23 December aftershocks was less than the 13 June aftershocks and significantly lower than that experienced during the 22 February earthquake, which caused significant building and ground damage.

• It is difficult to predict how long the region will continue to experience earthquakes but it could last for up to several decades. However, they will become undetectable except on sensitive instruments over time.

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