Shear wave splitting time variation by stress-induced magma uprising at Mount Etna volcano

Abstract

Shear wave splitting exhibits clear time variations before the July 17th – August 9th, 2001 flanK eruption at Mount Etna. The normalized time delays, Tn, detected through an orthogonal transformation of singular value decomposition, exhibit a clearincrease starting 20 days before the occurrence of the eruption (July 17th); the qS1 polarization direction, obtained using a 3D covariance matrix decomposition, shows a 90°-flip several times during the analyzed period: the last flip 5 days before the occurrence of the eruption. Both splitting parameters also exhibit a relaxation phase shortly before the starting of the eruption. Our observations seem in agreement with Anisotropic Poro Elasticity (APE) modelling, suggesting a tool for the temporal monitoring of the build up of the stress leading to the occurrence of the 2001 eruption at Mt. Etna.