Mechanics of caldera collapse earthquakes and their seismic representations

Taiyi Wang

Stanford University

Date & Time
Hybrid in-person and online seminar via Microsoft Teams
Kyle Anderson

All instrumented basaltic caldera 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.

In the first part of my talk, I will 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. I 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.

In the second part of my talk, I compare simulation results with 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.

At the end of my talk, I will show ongoing work in deriving rigorous seismic representations of caldera collapse earthquakes from dynamic rupture simulations. The theory is fully general and can be applied to other volcanic processes, enabling parameterization of seismic inverse problems consistent with source physics.

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