Earthquake swarm near Tarawera, New Zealand may be caused by a dike intrusion

Abstract:

Earthquake swarms are a common feature of volcanic settings, and provide a window into the behaviour of these systems, and the underlying tectonic and magmatic processes. We analyzed an earthquake swarm centered 12 km NE of Mt. Tarawera, which last erupted in 1886, and lies within the Okataina caldera, formed between 45,000-55,000 years ago in New Zealand's Taupō Volcanic Zone . This study used a non-linear algorithm to locate earthquakes occurring from 12-15 March, 2019. The earthquakes were then relocated with relative location methods to highlight structures in the swarm. Focal mechanisms for a selection of the largest events in the swarm were also calculated. The events delineate a 2 km long planar structure, striking 72 degrees from North and dipping vertically, between Kawerau geothermal field and Tarawera at a depth of 8-12 km. The earthquakes were also observed to migrate along the structure. The leading edge of the swarm propagated East to West along the strike of the structure with a velocity of 0.44±0.08 ms^-1. This structure is interpreted to be a magmatic dike intruding from the lower crust. Magmatic dike intrusions have occurred in the region before, and have the potential to drive eruptions such as the 1886 Tarawera eruption, New Zealand's deadliest eruption in written history.