Tremors at Tarawera

Another brief burst of earthquake activity was recorded near Lake Tarawera last night. The mid-evening swarm included a very shallow magnitude 3.3 earthquake that was felt at Rotorua and at several Rotorua lakes.

The activity began at 7:30 p.m. on Thursday the 16th of October 2008 with a shallow magnitude 1.9 earthquake on the southern shore of Lake Tarawera. Two events, the largest of the swarm, then struck 1 minute apart at 7:42 p.m. The larger of the two was a magnitude 3.3 quake, 3 km deep located on the southern shore of Lake Tarawera 20 km north of Reporoa, 20 km south-east of Rotorua. The second quake of the pair was slightly smaller in magnitude, but data for this event is not yet available in GeoNet’s database.

The swarm activity ended at 8:33 p.m. by which time a 6 km-deep magnitude 1.7 quake had been recorded at 8:05 p.m. In all there were 10 distinct events in the swarm, most minor in magnitude.

The largest quake in the swarm was felt in Rotorua and at several of Rotorua’s lakeside communities. By mid-morning Friday, 54 reports describing the quake’s affects had been lodged by the public with GeoNet. Posters on the Trademe website reported feeling the two larger events, but no damage was reported.

The map of the latest 2 months’ of activity shows 24 earthquakes in an area from the southern shore of Laka Tarawera through the Waimangu Block State Forest to Waiotapu. This diagram is updated from GeoNet’s databases and will change as more quakes are added and events age.

The map currently includes the earthquake swarm (details here) which struck the area late on Sunday the 31st of August when another 10 small quakes struck over a period of half an hour.

Earthquake swarms in the Taupo Volcanic Zone, a geologically-defined area which extends from the central North Island volcanoes into the Bay of Plenty, are not uncommon. Residents of Kawerau periodically experience swarms of small quakes and the coastal settlement of Matata continues to feel small earthquakes as part of intermittent swarms which have occurred since 2004. Lake Taupo regularly hosts earthquake swarms, some of which include moderately strong earthquakes.

In 2004, a swarm of earthquakes near Lake Rotoiti which included three events of 5th magnitude, caused landslides, cracked roads and damaged houses and their contents. More than 120 earthquakes were associated with the swarm.

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

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