Ground surface displacements and stress localization driven by dual magma chamber dynamics: analytical and numerical model estimates

Abstract

In volcanic belts, magma influx into magma chambers generates excess pressure, amplifying the initial stress field to cause crustal deformation with significant ground displacements, which manifests in topographic relief. Quantifying such volcano-driven ground surface displacements is a fundamental requirement to embark on a criticality analysis of volcanotectonic events and associated hazard monitoring strategies. This study theoretically examines the underlying dynamics of surface displacements in a volcanic plumbing system comprising multiple magma chambers. The classical Mogi equation is extended to derive a set of analytical solutions to evaluate surface displacements as a function of separations between two off-axis chambers, measured along both horizontal and vertical directions. The resulting surface displacement plots, from the analytical solutions are compared with those calculated from a set of finite element (FE) model simulations run with the same parameters considered for the analytical formulations. Both the analytical and FE results suggest that horizontal (S_h) and vertical (S_v) separations of magma chambers largely control the vertical (U_z) and lateral (U_r) ground-displacement components. Spatially varying U_z attains its peak value at a specific location above the chambers, but increasing horizontal separation (S_h ~ 10 km) transforms the single-peak U_z pattern to a weakly developed double-peak U_z pattern, which eventually give way to two prominent high-amplitude peaks above the chambers when S_h ~ 25 km. Similarly, a large vertical separation (S_v ~ 6 km) yields double peaks in the U_z profile, which merge to form a single peak for small S_v (~ 1.5 km). The FE model results are used to map the stress fields around the two magma chambers to show that inter-chamber mechanical interaction can influence the deformation behaviour around the chambers, depending on S_h and S_v magnitudes. Finally, the model estimates are evaluated using available reports on the naturally occurring volcanoes: Teide volcano (Tenerife, Spain) and Long Valley Caldera (USA).

Graphical abstract