Tracking Tremor and Drumbeat Locations during the 2022 Unrest Episode of Ruapehu volcano, Aotearoa New Zealand

Ruapehu is one of the most active volcanoes in Aotearoa New Zealand, with over 100 eruptive events over the last 135 years. In 2022, the volcano underwent a significant period of unrest which included a new heating phase in the summit crater lake, increases in gas emissions, and strong levels of seismic tremor, the most intense observed at the volcano for nearly 30 years. The tremor was also notable for featuring a sequence of highly-periodic low frequency “drumbeats”. Both tremor and drumbeats were hypothesised to originate from within a shallow hydrothermal system but a sparse seismic network precluded accurate location information. Here we utilised the network covariance matrix approach to map the location of tremor within the Ruapehu volcanic system before and during the 2022 unrest episode. We find low level tremor is detectable up to three months before the unrest begins, beginning shortly before a small sub-summit earthquake swarm approximately 3 - 4 km below the summit. Tremor during the unrest period is primarily located at shallow depths, within 500 m of the summit vent, suggesting a mechanism within the shallow hydrothermal system. This study was the first to apply the network covariance method for studying tremor at Ruapehu and demonstrates the technique’s value as an effective tool for real-time volcanic tremor monitoring in Aotearoa New Zealand.