Joint modeling and seismic inversions for very-long-period magma resonant modes at Kilauea Volcano from 2008-2018.

Abstract:

Very-long-period (VLP) seismic signals are observed at many volcanoes and often represent oscillatory magma motions that excited resonant modes of the shallow transport network. They thus provide important in situ insight into both magma plumbing system geometry and magma properties. Because changes in VLP properties such as period, decay rate, and displacement patterns often occur over time, these signals provide information useful both for monitoring and understanding the evolution of magma systems.

Many thousands of distinct types of VLP seismic signals have occurred at Kilauea Volcano, USA, from 2008-2018, associated with the Halema'uma'u open vent at the volcano summit. The fundamental mode of the shallow magma system which we term the 'conduit-reservoir mode' is a vertical oscillation of the magma column in the conduit/lake, with restoring forces from gravity and storativity of the shallow magma reservoir (Liang et al., 2020). Shorter period resonant modes, likely deriving from lateral lava lake sloshing, are also present and often occur concurrently. The periods, decay rates, and displacement patterns of these two modes are sensitive to overlapping properties of the shallow magma system, and thus can provide complementary information when considered jointly.

We develop self-consistent models for both the conduit-reservoir and lake sloshing modes that account for variable conduit/lake geometry, viscous boundary layers in the lake and conduit, and stratified magma properties. We use H-C-O-S volatile solubility relations to construct magmastatic depth profiles. We then use these models to conduct joint inversions for events in a new catalog of Kilauea VLP seismicity. This new catalog uses wavelet transforms to robustly detect and categorize VLP signals, including secondary resonant modes, from 2008-2018.

By including additional constraints from other datasets such as lake height, tilt, and SO2 emissions, we are able to constrain changes in magma system properties over timescales from days-years, including precursory trends leading up to intrusions and eruptions. We examine the implications of these changes for the magma outgassing/convective regime and how it changes over time.