Temporal variations of repeating low frequency volcanic earthquakes at Ngauruhoe Volcano, New Zealand

초록

A persistent swarm of micro-earthquakes was observed at Ngauruhoe volcano, New Zealand from 2005 to 2010, marking the first unrest episode at the volcano since 1975. Detailed waveform and spectral analysis of the continuous seismic record revealed eight earthquake families (F1-F8) within a sequence of 8561 low-frequency earthquakes. An analysis of stacked waveforms of each family allowed the families to be linked systematically into four super-families that may indicate four different mechanisms, and/or source locations or geometries. The first super-family mostly occurred in 2005 and showed stable waveforms and no significant evolution. The second super-family was dominant over a two-year period starting in mid-2006 and displayed a slow evolution with progressively higher frequency. The third super-family emerged from early 2008 with intermittent occurrence and high seismicity, and progressed to higher peak frequency in 2010. The fourth super-family was mainly observed from late 2008 to mid-2009 and had the highest peak frequency in 2009. The observed evolutionary pattern may be driven by a modest multi-year input of gas and heat from a deeper relict magmatic zone into the shallow volcano hydrothermal system. The interplay of gas from below and seasonal meltwater from above may have modulated the seismic activity and may relate to repeated over pressurization and failure of constricted evolving pathways within a pervasive crack system. (C) 2019 Elsevier B.V. All rights reserved.

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