Electrokinetic and magnetic fields generated by flow through a fractured zone: A Sensitivity study for La Fournaise Volcano

Abstract : A number of electric and magnetic signals have been observed on La Fournaise volcano, attributed to electrokinetic effects. A simple model is proposed here to check this hypothesis. The volcano is idealized as a 2d heterogeneous structure composed of a fractured zone located between two porous zones through which meteoritic waters flow downwards; flow occurs predominantly in the fractured zone and induces electromagnetic fields. Correct orders of magnitude are obtained for the measured surface fields. The importance of the heterogeneous character of the underground medium is demonstrated; local measurements of various quantities are recommended. magnetic field in the vicinity of a vertical fault (cf also the recent review by Johnston, 1997). The major purpose of the pre•ent note is to provide a sensitivity analysis of the electrokinetic effect for La Fournaise volcano. This paper is organized as follows. An idealized model of the system is proposed and the governing equations are presented as well as the method of resolution and the range of parameters. The last section is devoted to a presentation and discussion of the results.