A Possible Origin of Volcanic Tremor

Monday, 15 December 2014
Ataru Sakuraba, University of Tokyo, Bunkyo-ku, Japan
Sakuraba and Yamauchi (2014) found in their linear stability analysis that a laminar flow through an infinitely extended sheetlike conduit embedded in an infinite elastic medium is destabilized with a much slower critical speed than previously thought, and proposed that this instability might be an origin of volcanic tremor. In their results, the viscous drag due to the main fluid flow amplifies the surface (Rayleigh) wave that involves flexural deformation of the conduit. The oscillation period of the surface wave, essentially determined by wavelength, naturally falls into a narrow range of about 0.1-1 s if their result is applied to a typical volcanic setting, firstly because there is an upper bound in the conduit (dike) length and secondly because there is an upper bound in the magma flow speed. The above flow-induced oscillation can explain why most of volcanic tremors produce similar oscillation periods despite the variety of volcanos, but there still remain some uncertainties in the model. Most importantly, the model assumes an infinitely extended dike and cannot explain emergence of multiple spectral peaks that is one of the most remarkable characteristics of volcanic tremor. In this presentation, I am going to report some results of a laboratory experiment. In order to understand the nature of a finitely extended sheetlike conduit as a wave generator, I am planning to observe oscillations of a gel in which a thin slit is made and a viscous fluid such as syrup is force to flow through it. The project is currently ongoing, but I expect that an oscillation can be excited due to a similar mechanism to that predicted in the linear study.