Laboratory volcano geodesy: Inversion of three-dimensional surface displacements induced by analog magma intrusion in sandbox experiments

Abstract:

Most volcano geodetic models consider a half-space homogeneous medium and assume that the host rock behaves linearly elastically during shallow magma emplacement. However, geological and geophysical observations show that volcanic edifices are not homogeneous but heavily fractured and that non-elastic deformation behavior can dominate, in particular at the magma intrusion propagation front. Deformation processes at that propagation front can only be observed indirectly by using geophysical monitoring techniques. It remains therefore difficult to assess by how much modelled magma intrusion characteristics – volume, geometry, orientation, depth – deviate from reality in circumstances where non-elastic deformation processes and medium heterogeneities are important.

A recently developed application of medical X-ray Computed Tomography (CT) and Digital Volume Correlation allows to image and quantify deformation induced by analogue magma intrusion in granular, non-elastic host media in scaled laboratory experiments (Poppe et al., 2019). We use a tensile Okada dislocation in a homogeneous, linearly elastic half-space (Okada, 1985) to invert the three components of near-surface displacements extracted from laboratory experiments of analogue dyke injection in cohesive mixtures of quartz sand and gypsum powder. The Okada models favored by the inversions are then compared to the three-dimensional characteristics of the analogue magma intrusions observed in the X-ray CT imagery. This test study helps gain insight on the limitations of commonly-used volcano geodesy modeling and inversion methods and provide a novel basis for interpreting geological, geodetic and geophysical data related to volcanic deformation.

Okada (1985). Bulletin of the Seismological Society of America, 75(4), 1135–1154.

Poppe et al. (2019). Frontiers in Earth Science, 7, 62.