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article: May 11 2007 - Renewed Earthquake Activity Near Matata
Since November of last year, many small earthquakes have been occurring near Matata on the Bay of Plenty coast, west of Whakatane.
Matata swarms: 2005 in blue, 2006-2007 in red.
Almost 700 events have been located, the largest being magnitude 4.2 on May 3 which resulted in more than 100 felt reports to the GeoNet web site. So far in this swarm of earthquakes there have been more than 50 events over magnitude 3 and 5 over magnitude 4. The earthquakes are occurring in two distinct clusters, one about 1 km south of Matata at a depth of about 5 km, and another about 10 km offshore at a depth of about 2 km. The shallow depth of the earthquakes explains why so many quite small events have been felt locally.
The earthquakes are occurring in a slightly different area to a swarm of more than 1000 earthquakes in the Matata area in 2005, but in terms of the duration of the swarm, the number of earthquakes and the total energy release, the two swarms are quite similar.
Based on the current activity’s similarity to the 2005 swarm and to other swarms in the Bay of Plenty, we expect the earthquakes to gradually die away over several months without any significantly larger events. However, the history of the area does include some much larger earthquakes, such as the magnitude 6.1 Edgecumbe earthquake in March 1987, so we cannot rule out the possibility of larger events.
In 2005 GeoNet staff installed three temporary sites to collect additional data on that earthquake swarm. One of those temporary sites has since become a permanent site just to the west of Matata; that and a new permanent site about 15 km west of Matata at Ohinepanea, are now helping to locate the current Matata swarm.
Matata lies close to large scale fault structures on the western boundary of the Rangitaiki Plains (the area between Matata and Whakatane). These faults are moving as a result of east-west extension in the region; it is this movement that is causing the earthquakes.
