ELECTRIC-POTENTIAL CHANGES ASSOCIATED WITH SLIP FAILURE OF GRANITE - PRESEISMIC AND COSEISMIC SIGNALS

Citation
S. Yoshida et al., ELECTRIC-POTENTIAL CHANGES ASSOCIATED WITH SLIP FAILURE OF GRANITE - PRESEISMIC AND COSEISMIC SIGNALS, J GEO R-SOL, 102(B7), 1997, pp. 14883-14897
Citations number
23
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Geochemitry & Geophysics
Journal title
JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH
ISSN journal
2169-9313 → ACNP
Volume
102
Issue
B7
Year of publication
1997
Pages
14883 - 14897
Database
ISI
SICI code
2169-9313(1997)102:B7<14883:ECAWSF>2.0.ZU;2-3
Abstract
Electric potential changes were measured for stick-slip events in gran ite samples with a three-block direct shear arrangement at 8 MPa norma l stress. Two electrodes were mounted on the left- and right-hand bloc ks, and the electric potential difference between each electrode and t he ground was measured with a high input impedance recording system of frequency range from DC to 100 Hz. As well as coseismic electric sign als of about 1.5 V which appeared the moment of the dynamic slip event , preseismic signals were detected just before the slip event. The cos eismic signal rises stepwise with opposite polarities at the two elect rodes and exponentially decays with a time constant of epsilon/s, wher e epsilon is the permittivity and s is the conductivity of the rock sa mple. We conducted a simple test of rapid stress drop without slipping and observed almost the same electric signal as the coseismic signal. This suggests that the electric signal is generated by the piezoelect ric effect. We proposed a generation model based on the piezoelectric effect and the resultant relaxation process and obtained a theoretical frequency response, which is in agreement with experimental data. The preseismic signal appears about 2-3 s before the dynamic event with a n amplitude of about 50 mV. The local strains along two sliding surfac es were also measured to monitor the growth of the rupture nucleation zone. When the growth of the rupture nucleation zone occurred on the l eft sliding surface, a clear preseismic signal was detected at the ele ctrode mounted on the left granite block. When the growth occurred on the right-hand surface, a signal was detected at the electrode on the right block. This shows that the preseismic electric signal is caused by stress change in the rupture nucleation zone. These preseismic and coseismic signals were also detected with an antenna, which was placed away from the sample surface.