June quakes' magnitude upgraded

A car is swamped by flooding caused by liquefaction in the suburb of New Brighton after a series of earthquakes that struck Christchurch. Photo / Simon Baker

The aftershocks from last Friday's large earthquakes are dropping in strength and frequency, but larger jolts are still a possibility.

This morning, a magnitude 3.6 struck at 1.25am, 10km east of Christchurch at a depth of 9km, and a magnitude 3.9 hit at 5.32am, also 10km east of the city at a depth of 9km.

GeoNet project director Ken Gledhill said the aftershocks following last week's magnitude 6 and 5.8 earthquakes are not going to continue like they did after the February 22 event.

"It looks like a repeat of the June sequence as far as the energy dropping off and the aftershocks becoming less frequent. But we could certainly have another larger aftershock."

Mr Gledhill expects to the see the bulk of the aftershocks in the future in a similar location to the December 23 jolts, which were centred near the coast of New Brighton.

"I think a lot of the aftershocks will be clustered around the east coast, either off or just on shore.

"But there will still be the occasional earthquake right across the earthquake field, right out to Darfield."

Meanwhile the magnitude of the two largest June 13 quakes have been increased by Geonet. The 1.01pm jolt has gone from being a 5.7 to a magnitude 5.9, while the magnitude 6.3 event at 2.20pm is now classed as a 6.4.

"We do the best we can with the data we have on the day they first happen. Over time we get more data and the magnitude may change," Mr Gledhill said.

However the changes are relatively insignificant, as the measurements are accurate to about 0.1.

Mr Gledhill said last Friday's quakes are likely to be adjusted again over time, although not by much.