Experimental studies of electromagnetic signals associated with stickslip of quartz free rocks

DOI Web Site
  • Shirai Nobumasa
    AIST, Geological Survey of Japan, Institute of Geology and Geoinformation
  • Tsutsumi Akito
    Division of Earth and Planetary Sciences, Graduate School of Science, Kyoto University

Bibliographic Information

Other Title
  • 封圧下における石英を含まない岩石の摩擦電磁気現象に関する実験的研究
  • 概報 封圧下における石英を含まない岩石の摩擦電磁気現象に関する実験的研究
  • ガイホウ フウ アツカ ニ オケル セキエイ オ フクマナイ ガンセキ ノ マサツデンジキ ゲンショウ ニ カンスル ジッケンテキ ケンキュウ

Search this article

Abstract

    A stick-slip experiment was conducted using dry cylindrical samples saw-cut at an angle of 30° under confining pressures ranging from 30 MPa to 120 MPa. The samples used in the experiment were quartz-free basalt, gabbro, and peridotite. Loading on the rock samples was applied by a manual micro-discharge pump at a controlled rate of ～ 0.003 mm/s. Solenoids aligned circumferentially with the sample were used as sensors for detecting the magnetic field signal, while two pairs of electrodes, each consisting of two copper plates (30×30 mm), were used as sensors for detecting the electric field signal. The electrode pairs were aligned circumferentially with the cylindrical sample, one perpendicular to and the other parallel with the saw-cut surface. Variations in both the electric and magnetic fields were detected at the point of slippage during stick-slip motion in all samples, even in the quartz-free samples. However, no such signals were detected during stable sliding. In almost all of the gabbro samples, the amplitude of the electric field variation measured by the electrode pair aligned parallel to the fault was longer than thet obtained by the electrode pair orientated normal to the fault. This indicates that the gabbro samples are anisotropic. Moreover, the separation of electric charges between the faults and electric discharge is considered to occur simultaneously because the signals detected by the coils and the signals observed on the electrodes occurred almost simultaneously. Furthermore, the amplitude of the electric field variation measured by the electrode pairs was found to increase with the stress drop during stick-slip. Next, signals induced in each of the four copper electrodes were measured individually to confirm the anisotropy of the electric field variation. Results showed that the signals detected by the electrodes positioned parallel sides of the fault of the gabbro sample exhibited opposite polarities in the early stages, confirming anisotropy parallel and normal to the fault. For the basalt samples, although the electric and magnetic fields were too low to measure differences in the two directions for some samples, similar tendencies as those for the gabbro samples were observed.

Journal

Related Projects

See more

Keywords

Details 詳細情報について

Report a problem

Back to top