Earthquakes near but not at White Island

Published: Mon Oct 30 2017 12:00 PM

Late yesterday evening a sequence of small-moderate sized earthquakes occurred about 12-15 km northeast of White Island.

Sunday evening's sequence of small-moderate sized earthquakes occurred about 12-15 km northeast of White Island. As White Island is the nearest geographic location our automated location software naturally reported them as being nearby. White Island is a large volcano with a significant footprint under the sea, being about 6 x 10 km at 300 m depth. However, these earthquakes are beyond the footprint of the volcano, hence we consider them to be caused by regional faulting, rather than related to the volcano.

The locatable earthquakes in the series overnight show they started around 6 pm on Sunday evening with a couple of M2.2 events, two more smaller events followed, then a M3.5 event occurred about 30 minutes before the largest event in the series - a M4.1 event at 11.24 pm and 9 km depth. Since then we have located 13 aftershocks that range in magnitude from M1.8 to 2.9. The depths range 4-5 km deep.

Many active faults are mapped in the offshore Bay of Plenty area; hence it is seismically active and we record numerous earthquakes every year in the area. In the last 12 months, we have located 114 earthquakes in the same area as the earthquakes overnight (see plots below). These have ranged in magnitude from M1.6 to 4.1, while the depths have ranged from around 2-10 km. In the last 5 years there have been 3 earthquakes over M4.0 in the same area.

Location of Sunday's earthquakes near White Island

Location of Sunday's earthquakes near White Island

Locations of earthquakes in last year near White Island

Locations of earthquakes in last year near White Island