Collaborative Research: Seismic Waves from Volcanoes: Fully Coupled Time-Dependent Models of Fluid Flow Through Elastic Walled Conduits

University Of California-San Diego Scripps Inst Of Oceanography, La Jolla CA

Investigators

Abstract

Mitigating the risks associated with volcanoes requires a detailed understanding of the transport and eruption of magma through cracks and conduits in Earth's crust. Seismic waves excited by magma flow and its coupling to the elastic wall rocks can be used to place valuable constraints on parts of the volcanic system that are otherwise inaccessible. The complexity of observed seismic signals and the difficulty of modeling the coupled fluid-solid system present a formidable challenge. The objective of this collaborative proposal is to develop numerical models describing the high-speed flow of compressible, viscous fluids through narrow channels in elastic bodies, together with the propagation of seismic waves through the solid. The fluid and solid response is fully coupled: elastic deformation changes the cross-sectional area of the conduit through which fluid flows, and changes in fluid pressure push the conduit walls in and out, exciting seismic waves. Specifically, the project group will develop a provably stable and accurate numerical method for time-dependent quasi-one-dimensional fluid flow through conduits in a solid body, together with the elastodynamic response of that solid. The model will include changes in compressibility, sound speed, viscosity, and drag from gas exsolution. The code will be used first to explore the role of conduit wall deformation on steady state eruption dynamics. The group will then assess the stability of steady state eruption solutions. Preliminary analyses indicate that for sufficiently rapid flows, the fluid-solid system is unstable to long wavelength perturbations that appear as conduit wall oscillations of growing amplitude. One first focus will be on seismic waves from basaltic fissure eruptions within the currently implemented two-dimensional plane-strain framework. The group will then extend the model to the axisymmetric geometry appropriate for cylindrical conduits, and study seismic waves from explosive eruptions. Finally, they will calculate far-field body and surface waves and link the time dependence of equivalent single force and moment tensor representations to detailed source processes. This project is supported by the Geophysics and Petrology & Geochemistry Programs.