Significant Earthquake, Canterbury Plains

A moderately strong earthquake struck the Canterbury Plains early this morning, the fourth aftershock of magnitude 5 to strike since February’s devastating earthquake.

Tuesday, 10th May 2011

Aftershock activity across the Canterbury Plains between Darfield and Lyttelton had eased during the early part of May, with an average of just over two events of magnitude 3 or 4 per day. Brief bursts of activity were noted, and a cluster of quakes near Rolleston brought a moderately strong magnitude 5 earthquake in the early hours of this morning.

The area experienced two magnitude 3 events on the 1st and 2nd of May, and only one on Tuesday 3rd. Four magnitude 3 events were recorded on the 4th, with another three and a magnitude 4 event the following day.

Friday 6th was quiet, with only one event of magnitude 3. A magnitude 4 quake was recorded on Saturday and two magnitude 3 events on Sunday.

On Monday, two magnitude 3 earthquakes were recorded as well as a magnitude 4 event, the first of a cluster centred near Rolleston.

At 3:04 this morning, residents were chased from their beds by a magnitude 5.3 earthquake centred near Rolleston, 20 km west of Christchurch, at a depth of 15 km. Damage from this event has been reported from Broadfield, Christchurch, Saint Albans, and Templeton. Slight damage has also been reported from more than 30 locations on the Canterbury Plains. The quake was felt from Wellington to Dunedin.

This event was the third largest aftershock to be reported since the magnitude 6.3 earthquake of February 22nd, equal in strength to the magnitude 5.3 quake centred beneath Diamond Harbour on the 16th of April. Larger aftershocks of magnitude 5.7 and 5.5 had followed within two hours of the main event in February.

Earthquake activity has continued near Rolleston, with a magnitude 3.4 quake at 7:17 this morning, and a magnitude 4.1 quake at 9:09 a.m. The four events which make up the Rolleston cluster have been shallow, at depths between 10 and 15 km.

Once again, this morning’s moderate quake was not entirely unexpected. GeoNet’s forecast had indicated that the likelihood of another magnitude 5 event was small, but that as many as two such events might be expected during the month to May 19th.

[Compiled from data provided by the GeoNet project and its sponsors EQC, GNS Science and FRST.]

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