The STAK Project: Shear-wave splitting Tomography At Kilauea

Jessica Johnson1*, Richard Herd1, Jade Eyles1, Brian Shiro& Ben McLeod1

1School of Environmental Sciences, University of East Anglia, UK (Jessica.johnson@uea.ac.uk), 2Hawaiian Volcano Observatory, US Geological Survey, USA

Seismic anisotropy is the variation of seismic wave speed with direction and is most frequently observed using shear-wave splitting (SWS). Seismic anisotropy in the crust arises when microcracks in subsurface rocks are aligned, for example when the rock is under differential stress. Therefore, SWS analysis can be used to detect changes in stress and pore-fluid movement during volcanic activity.

Between April and August 2018, Kilauea Volcano produced lava eruptions in its Lower East Rift Zone and collapse events with phreatic explosions at its summit. The rate at which the summit lava lake and shallow magma reservoir drained caused incremental caldera collapse with unprecedented rates of seismicity and measured deformation. This suggests that large amounts of magmatic fluids were mobilised, and the rate of change of crustal stresses were high.

We have deployed an additional four seismic stations to complement the existing USGS network in order to carry out four dimensional SWS tomography at Kilauea using the elevated rates of seismicity. SWS tomography overcomes the problems of heterogeneous anisotropy with migrating seismicity. This has been used to map areas of high stress and subsurface fluid throughout Kilauea, including regions in which the anisotropy has not previously been investigated due to lack of data. The elevated rates of seismicity and additional seismic stations provide enough data to observe temporal variations in anisotropy associated with the volcanic activity, which, when combined with other observations such as ground deformation, can be interpreted in terms of migrating fluids and changing stresses.

 

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