Hawke’s Bay Earthquake Swarm

A swarm of off-shore earthquakes struck near the Hawke’s Bay town of Wairoa overnight.

Saturday 23rd February 2013

A swarm of light undersea earthquakes struck Hawke’s Bay overnight. The activity began just after 5:30 last evening with a magnitude 3.1 quake at 5:36 p.m. A magnitude 3.5 event followed at 5:43, a magnitude 4.1 quake struck at 5:46 and a magnitude 3.4 event at 5:51. The four earthquakes were centred 30 to 35 km south or south-east of Wairoa at depths between 15 and 18 km.

A couple of magnitude 2 events were recorded after 6 p.m. and activity eased. Activity recommenced at 9:45 p.m. with a magnitude 3.3 earthquake centred 30 km south of Wairoa at a depth of 15 km.

Magnitude 2 events followed, with bursts of activity around 10 o’clock, and around 1 a.m. Activity then ceased until 7:22 this morning when a magnitude 4.8 earthquake struck 40 km south-east of Wairoa at a depth of 67 km. This event was felt from southern Hawke’s Bay to the Gisborne district.

A magnitude 3.4 quake followed at 7:34 this morning. This event was shallower at 17km and close to Wairoa, being centred 30 km south of the town.

For the moment, activity seems to have eased following a magnitude 2.9 event at 8:17 a.m.

GeoNet has issued an article summarising the activity and describing earthquake swarms. From past experience in this area, Kevin Fenaughty of GeoNet suggests that the Hawke’s Bay earthquake swarm could run its course in a matter of days.

Earthquake swarms have occurred at several different locations in New Zealand in recent times. The swarms off the coast near Tolaga Bay, near Masterton, beneath Lake Taupo and off the Horowhenua and Wellington coasts had different characteristics. Swarms of earthquakes centred near Matata in the Bay of Plenty in recent years sometimes ran their course in days, while others lasted weeks or months.

During the latter part of March 1976, Wairoa experienced a swarm of earthquakes that included four earthquakes of 5th magnitude. This swarm was centred in the same bay area, about 30 km south of Wairoa.

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

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