Dynamic rupture simulation of caldera collapse earthquakes: evidence of temporally variable earthquake nucleation sites through the Kīlauea 2018 collapse sequence

Taiyi A. Wang, Eric M. Dunham, Lukas Krenz, Lauren S. Abrahams, & Paul Segall

Published September 10, 2023, SCEC Contribution #12881, 2023 SCEC Annual Meeting Poster #099 (PDF)

All instrumented caldera collapses at basaltic shield volcanoes generate Mw > 5 very long period (VLP) earthquakes. Due to the presence of magma chamber(s) beneath the caldera ring fault, the scaling of co-seismic slip for these earthquakes is distinct from tectonic earthquakes, and their dynamics poorly understood. We present the first dynamic rupture simulation of basaltic caldera collapse using SeisSol (www.seissol.org), capturing the nucleation and propagation of ring fault rupture, the mechanical coupling of the caldera block to the underlying magma (modeled as compressible fluid for basaltic magmas, and a Maxwell viscoelastic material for silicic magmas), and the associated seismic wave field.

We first quantify the effect of wave radiation and magma viscosity on the magnitude of fault slip during collapse, both effects of which are neglected in previous models. Through a numerical parameter study and analytical solutions of elastodynamic anti-plane ring fault slip problem, we show that compressional waves radiated through the magma chamber, in addition to shear waves from the ring fault, can prevent dynamic overshoot and reduce expected co-seismic slip by up to half. Reduced fault slip can also result from high magma viscosity (≥10^6 Pa s) in the chamber underlying the caldera block.

We then use the model to simulate the individual events during the 2018 collapse of Kīlauea volcano and compare with near-field seismic records. Accelerometer-derived seismic waveforms near the ring fault exhibit a phase associated with initial rupture (“double-couple”, in terms of seismic source representation), the location of which is inferred from relocated VLP hypocenters. This rupture phase is distinct from the following phase associated with downward accelerating magma reaching the chamber bottom (“downward single force”) and chamber pressurization (“expansion source”), which is the sole observed phase when the ring fault rupture initiates farther away from the accelerometer. The presented numerical simulation framework can be potentially applied to modeling collapses at silicic calderas and will enhance interpretations of seismic observations in terms of collapse dynamics.

Key Words
Dynamic rupture, caldera collapse, viscoelastic magma, wave radiation

Citation
Wang, T. A., Dunham, E. M., Krenz, L., Abrahams, L. S., & Segall, P. (2023, 09). Dynamic rupture simulation of caldera collapse earthquakes: evidence of temporally variable earthquake nucleation sites through the Kīlauea 2018 collapse sequence. Poster Presentation at 2023 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)