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Seismic Noise as a Window into Volcanic Unrest: Observations from Ruapehu, New Zealand in 2022

Mustafa Almassri ^1^; Oliver D. Lamb2; Stuart Mead1; Georg F. Zellmer1

  • Affiliations: ^1^ School of Agriculture and Environment, Massey University, Palmerston North, New Zealand. 2 Te Pu Ao | GNS Science, Wairakei Research Centre, Taupo, New Zealand.

  • Presentation type: Poster

  • Presentation time: Thursday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 135

  • Programme No: 2.1.45

  • Theme 2 > Session 1

Abstract

We applied Moving Window Cross-Spectral Analysis (MWCS) of ambient noise at Ruapehu volcano to monitor subtle temporal variations in the elastic properties during the March-June 2022 unrest episode. This unrest episode was significant, with temperature of the volcanic crater lake reaching 41°C, the strongest volcanic tremor since the 1995-1996 eruptive sequence, and SO2 emissions peaking at 390 tonnes per day. Our analysis revealed a ~0.5% decrease in relative seismic velocity at the beginning of 2022, coinciding with earthquake swarms. This correlation suggests that the process triggering the swarms may also be responsible for the observed velocity drop. A similar ~0.5% relative seismic velocity reduction was observed during the volcanic unrest in the East-North of the volcanic edifice. This seismic velocity drop appears to be a reversible process, likely driven by magmatic or fluid movement. Possible causes include the opening of fractures within the magmatic reservoir, fluid fluxes, magmatic anomalies/intrusion, or environmental factors (e.g. rainfall or atmospheric pressure changes) that could contribute to the formation of low-velocity zones. By mid-May, volcanic tremor and crater lake temperature began to decline, most likely due to a reduction in fluid circulation, possibly due to sealing processes. However, the reduction seismic velocity persisted, indicating potential ongoing subsurface alteration. This study highlights the importance of using ambient noise monitoring to detect seismic velocity changes during volcanic unrest. By providing a potential insights into subsurface processes, this method can complement current monitoring techniques and improving eruption forecasting and hazard assessment at Ruapehu.