Canterbury quakes here for the long run

23:32, Jun 15 2014

A Christchurch earthquake expert says quakes in Canterbury are a fact of life.

University of Canterbury associate professor in tectonics and geomorphology Mark Quigley said there would eventually be more "damaging earthquakes" in the region.

There have been more than 14,000 earthquakes in Canterbury since September 2010, not all able to be felt.

Quigley said there would never be an official announcement or point in time when the earthquakes were considered to be over.

Prior to September 2010, Canterbury averaged a 4.0 magnitude earthquake every two years and a 5.0 magnitude every 20 years. At the moment, the seismic activity in the area was 20 to 30 times higher.

"It will likely take a decade or longer for these rates to return to the ‘background' rate, assuming no more very large earthquakes," Quigley said.


However, if another large shock hit, the return to the background earthquake rate would take longer.

GNS Science is forecasting a 9 per cent chance of an earthquake of 6.0 magnitude or higher in the next year. Quigley said for every magnitude 5.0 quake, there was on average about 10 magnitude 4.0 and 100 magnitude 3.0 quakes.

According to Geonet, there have been more than 50 magnitude 5.0-5.9 earthquakes in the last three years, each setting off its own smaller, well-documented shake sequence.

Quigley said the GNS Science forecast showed the probability of a large earthquake in Canterbury was a higher now than before 2010.

"We must remain aware of this hazard and take steps to reduce our vulnerabilities to it," he said.

Quigley said faults outside Canterbury still posed a "major shaking hazard" for Christchurch, including the Porters Pass, Hope and Alpine Faults.

"For many of us, the likelihood that there is a major earthquake sourced from one of these faults in our lifetimes is quite high," he said.

"So even when the local seismicity rate returns to ‘normal' in this area, we should still be aware that earthquakes are a natural consequence of living astride a tectonic plate boundary."

The Press