More previously unknown fault lines discovered

5:26 am on 4 June 2011

Investigations have revealed more previously unknown fault lines in Canterbury.

The fault lines are in Pegasus Bay, near Barbadoes Street in central Christchurch, and near the Port Hills.

Researchers from GNS, NIWA and the Universities of Canterbury, Otago and Calgary have been carrying out land-based and offshore surveys for several weeks.

Canterbury has experienced two significant earthquakes in recent times: a magnitude 7.0 quake on 4 September last year, followed by the fatal magnitude 6.3 quake on 22 February.

The researchers estimate the probability of a magnitude 6.0 - 7.0 quake occurring across the entire aftershock area during the next year is 23% and is 6% for the Christchurch city area.

A survey of southern Pegasus Bay has revealed a previously unknown offshore fault about 25km long similar to the Greendale Fault that produced the 4 September quake.

Researchers say it is potentially capable of generating a magnitude 6.0 - 7.0, but there is no strong evidence at present that the aftershocks are migrating in the direction of the Pegasus Bay fault.

Natural Hazards Research platform manager Kelvin Berryman, says the three faults are very slow moving and are likely to rupture at sometime over the next couple of thousand years. However, there is no indication of increased activity at the moment.

He says aftershocks in Canterbury are not moving towards the newly discovered fault lines, so there is no indication they are becoming stressed.