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Dynamic rupture simulations of caldera collapse earthquakes: Effects of wave radiation, magma viscosity, and evidence of complex nucleation at Kīlauea 2018
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  • Taiyi Wang,
  • Eric M Dunham,
  • Lukas Krenz,
  • Lauren S Abrahams,
  • Paul Segall
Taiyi Wang
Stanford University

Corresponding Author:[email protected]

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Eric M Dunham
Stanford University
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Lukas Krenz
Department of Informatics, Technical University of Munich
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Lauren S Abrahams
Stanford University
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Paul Segall
Stanford University
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Abstract

All instrumented basaltic collapses generate Mw > 5 very long period earthquakes. However, previous studies of source dynamics have been limited to lumped models treating the caldera block as rigid, leaving open questions related to how ruptures initiate and propagate around the ring fault, and the seismic expressions of those rupture dynamics. We present the first 3D numerical model capturing the nucleation and propagation of ring fault rupture, the mechanical coupling to the underlying viscoelastic magma, and the associated seismic wavefield. We demonstrate that seismic radiation, neglected in previous models, acts as a damping mechanism reducing coseismic slip by up to half, with effects most pronounced for large magma chamber volume, high magma compressibility, or large caldera block radius. Viscosity of basaltic magma has negligible effect on collapse dynamics. In contrast, viscosity of silicic magma significantly reduces ring fault slip. We use the model to simulate the 2018 Kīlauea caldera collapse. Three stages of collapse, characterized by ring fault rupture initiation and propagation, deceleration of the downward-moving caldera block and magma column, and post-collapse resonant oscillations, in addition to chamber pressurization, are identified in simulated and observed (unfiltered) near-field seismograms. A detailed comparison of simulated and observed displacement waveforms corresponding to collapse earthquakes with hypocenters at various azimuths of the ring fault reveals a complex nucleation phase for earthquakes initiated on the northwest. Our numerical simulation framework will enhance future efforts to reconcile seismic and geodetic observations of caldera collapse with conceptual models of ring fault and magma chamber dynamics.
17 Nov 2023Submitted to ESS Open Archive
22 Nov 2023Published in ESS Open Archive