May 20 2010 - Sleepless in Whakatane

People in Whakatane will have had a sleepless night as 7 earthquakes over magnitude 3 occurred about 10 km north of the town. The largest of them was magnitude 4.3.

Map showing the cluster of earthquakes located north of Whakatane.

Map showing the cluster of earthquakes located north of Whakatane.

Earthquake swarms are not uncommon in the Bay of Plenty. The town of Matata has experienced several episodes of earthquake activity in recent years.

Whakatane lies close to large scale fault structures on the eastern boundary of the Rangitaiki Plains (between Matata and Whakatane). This area is what geologists call a graben. Basically the two masses of land are very gradually pulling apart, although at an extremely slow rate, about 1 cm per year. Faults in the earth's crust have arisen from this east-west spreading across the region. It is movement within these faults that is causing the earthquakes.

We can't predict what will happen with swarms. They may carry on for hours or even days, or the centre of the earthquakes might move around. In the meantime we will be locating the bigger shakes, and please keep the felt reports coming in!