Physics-based model reconciles caldera collapse induced static and
dynamic ground motion: application to Kīlauea 2018
Abstract
Inflationary deformation and very long period (VLP) earthquakes
frequently accompany basaltic caldera collapses, yet current
interpretations do not reflect physically consistent mechanisms. We
present a lumped parameter model accounting for caldera block/magma
momentum change, magma chamber pressurization, and ring fault shear
stress drop. The effect of pressurizing a spheroidal chamber is
represented as a tri-axial expansion source, and the combined caldera
block/magma momentum change as a vertical single force. The model is
applied to Kīlauea 2018 caldera collapse events, accurately predicting
near field static/dynamic ground motions. In addition to the tri-axial
expansion source, the single force contributes significantly to the VLP
waveforms. For an average collapse event with fully developed ring
fault, Bayesian inversion constrains ring fault stress drop to
~0.4 MPa and the pressure increase to
~1.7 MPa. That the predictions fit both geodetic and
seismic observations confirms that the model captures the dominant
caldera collapse mechanisms.