Published: Wed Feb 22 2017 10:34 AM
Updated: Wed Feb 22 2017 10:53 AM
A very common characteristic of the greater Rotorua-Taupo area, known as the Taupo Volcanic Zone is earthquake swarms. Several minor ones occur every year.
Since around 6 pm (Monday 13 February) the GeoNet seismometer network between Taupo and the Tongariro National Park has been recording a swarm of small earthquakes. They locate about 10 kilometres north west of Tokaanu. Since the swarm started we have located over 290 events. The largest been a M3.8 at 9.35 pm Tuesday Feb 21.
Earthquake swarms are defined as a sequence of many earthquakes striking in a relatively short period of time in a localised area. They are differentiated from ‘normal’ earthquakes followed by aftershocks by the fact that no single earthquake in the sequence is obviously the main shock. The larger or largest event can come early in the sequence towards the middle or at the end. The rate that earthquakes occur can also vary through the sequence.
The current swarm west of Tokaanu (Turangi) has comprised three phases. The third phase has included the four largest events (M3.0, 3.4, 3.6 and 3.8) and started Tuesday evening around 5 pm, continuing overnight. We have located about 200 events so far in this phase of the swarm. In total we have located 291 events so far (22 Feb 9.30 am). Their magnitudes have ranged from about M 0.6 to M 3.8, while the depths ranged between 1 and 11 kilometres, with most being 5-7 kilometres deep. As the earthquakes are quite shallow they will feel stronger than the magnitudes indicate.
The Taupo Volcanic Zone is a rifting area, growing wider each year by 6-9 mm. These earthquakes are likely to be related to the long-term ‘tectonic’ stretching of the Zone. Currently, there are no indications that the earthquakes are related to volcanic activity, being located well away from the active volcanoes. As usual, we continue to closely monitor the activity.