LP or VT signals? How intrinsic attenuation influences volcano seismic signatures constrained by Whakaari volcano parameters
James Clarke, Ludmila Adam, Kasper van Wijk
Abstract
Long Period (LP) seismicity is considered a key indicator of fluid migration in the volcanic edifice, with a source mechanism typically ascribed to fluid resonance in the volcano conduit and fractures. Our viscoelastic numerical wave propagation models at laboratory and field scales are based on quantitative estimates of wave speeds and intrinsic attenuation from Whakaari rocks saturated with a range of fluid types. Such models display path effects in homogeneous and layered media that influence the frequency content and duration of the seismic waveforms. We find that volcano-tectonic (VT) earthquakes can resemble short-duration LP events when propagating through fully or partially gas-saturated ash tuff deposits. Meanwhile, in a shallow volcanic subsurface comprising low-velocity, attenuative ash tuff and high-velocity, low-attenuation lava layers, VT signals may be distorted to resemble long-duration LP events. Such geological models are built based on interpretations of the shallow hydrothermal system at Whakaari volcano, and discussed in the context of other volcanoes around the world.