Convection current generated prior to rupture in saturated rocks

Laboratory experiments were performed to study the generation mechanism of electric signals during deformation and rupture of rock, with the focus on the effects of pore water movement. We have developed a triaxial apparatus that is specially designed for this purpose, within the framework of the International Frontier Program on Earthquake Research of the Institute of Physical and Chemical Research (RIKEN). This apparatus can deform a rock specimen that is electrically isolated from the surroundings at a very slow strain rate. Using a cylindrical specimen of intact rock (Inada granite, Makabe granite, Muroto gabbro, and Fujieda sandstone) saturated with distilled water, we carried out triaxial deformation tests under a constant pore pressure at room temperature. During a deformation test we continuously measured the electric current generated in the specimen. In addition, local strains, pore pressure, and pore fluid movement from the intensifier were recorded at a sampling frequency up to 1 kHz. The volume change due to dilatancy was obtained from the average of the local strain measurements at four positions. We found that the convection current flowed before the main fracture, showing good correlation with the dilatancy rate and the water flow rate. The current density of the signal was about 1 mA/m2. This result demonstrated that the electric current is caused by an electrokinetic effect due to the water flow associated with accelerating evolution of dilatancy before the fracture.

[1]  Toshiyasu Nagao,et al.  ANOMALOUS CHANGES IN GEOELECTRIC POTENTIAL PRECEDING FOUR EARTHQUAKES IN JAPAN , 1996 .

[2]  L. Jouniaux,et al.  Laboratory measurements anomalous 0.1–0.5 Hz streaming potential under geochemical changes: Implications for electrotelluric precursors to earthquakes , 1997 .

[3]  M. S. Lazaridou,et al.  Transmission of stress induced electric signals in dielectric media. Part II , 1998 .

[4]  U. Nitsan,et al.  Electromagnetic emission accompanying fracture of quartz-bearing rocks , 1977 .

[5]  J. Byerlee,et al.  Model for episodic flow of high-pressure water in fault zones before earthquakes , 1993 .

[6]  F. D. Morgan,et al.  Streaming potential properties of westerly granite with applications , 1989 .

[7]  Po-zen Wong,et al.  Determination of rock properties by low‐frequency AC electrokinetics , 1999 .

[8]  P. Sammonds,et al.  Electric potential changes prior to shear fracture in dry and saturated rocks , 1998 .

[9]  Panayiotis A. Varotsos,et al.  Physical properties of the variations of the electric field of the earth preceding earthquakes. II. determination of epicenter and magnitude , 1984 .

[10]  J. Avouac,et al.  Streaming potential measurements 2. Relationship between electrical and hydraulic flow patterns from rock samples during deformation , 1999 .

[11]  John W. Pritchett,et al.  Numerical simulation of electrokinetic potentials associated with subsurface fluid flow , 1996 .

[12]  T. Ishido,et al.  Experimental and theoretical basis of electrokinetic phenomena in rock‐water systems and its applications to geophysics , 1981 .

[13]  Laurence Jouniaux,et al.  Streaming potential and permeability of saturated sandstones under triaxial stress: Consequences for electrotelluric anomalies prior to earthquakes , 1995 .

[14]  Frédérique Massenet,et al.  Experimental and theoretical basis of self-potential phenomena in volcanic areas with reference to results obtained on Mount Etna (Sicily) , 1985 .

[15]  Shingo Yoshida,et al.  Electric potential changes associated with slip failure of granite: Preseismic and coseismic signals , 1997 .

[16]  Laurence Jouniaux,et al.  Permeability dependence of streaming potential in rocks for various fluid conductivities , 1995 .

[17]  P. Bernard.  Plausibility of long distance electrotelluric precursors to earthquakes , 1992 .

[18]  W. R. Sill,et al.  Self-potential modeling from primary flows , 1983 .

[19]  H. Hashimoto,et al.  Emission of charged particles from indentation fracture of rocks , 1990, Nature.

[20]  H. Kanamori,et al.  Tomography of the Source Area of the 1995 Kobe Earthquake: Evidence for Fluids at the Hypocenter? , 1996, Science.

[21]  B. T. Brady,et al.  Laboratory investigation of the electrodynamics of rock fracture , 1986, Nature.

[22]  Joel Koplik,et al.  Theory of dynamic permeability and tortuosity in fluid-saturated porous media , 1987, Journal of Fluid Mechanics.

[23]  J. B. Walsh,et al.  Permeability of granite under high pressure , 1968 .

[24]  V. Hadjicontis,et al.  Transient electric signals prior to rock failure under uniaxial compression , 1994 .

[25]  Y. Bernabé,et al.  Effect of the variance of pore size distribution on the transport properties of heterogeneous networks , 1998 .

[26]  C H Scholz,et al.  Earthquake prediction: a physical basis. , 1973, Science.

[27]  M. S. Lazaridou,et al.  Numerical model of the selectivity effect and the ΔV/L criterion , 1999 .

[28]  J. Avouac,et al.  Streaming potential measurements 1. Properties of the electrical double layer from crushed rock samples , 1999 .

[29]  P. Mazur,et al.  Non-equilibrium thermodynamics, , 1963 .

[30]  T. Ishido,et al.  Electrokinetic phenomena associated with earthquakes , 1976 .

[31]  Robert J. S. Brown,et al.  Connection between formation factor for electrical resistivity and fluid‐solid coupling factor in Biot’s equations for acoustic waves in fluid‐filled porous media , 1980 .

[32]  David V. Fitterman,et al.  Electrokinetic and magnetic anomalies associated with dilatant regions in a layered Earth , 1978 .

[33]  Pride,et al.  Governing equations for the coupled electromagnetics and acoustics of porous media. , 1994, Physical review. B, Condensed matter.

[34]  H. Utada.  On the physical background of the VAN earthquake prediction method , 1993 .

[35]  P. Varotsos,et al.  Physical properties of the variations of the electric field of the earth preceding earthquakes, I , 1984 .

[36]  Motoji Ikeya,et al.  Electromagnetic Fault for Earthquake Lightning , 1996 .

[37]  M. Ladd,et al.  Low‐frequency magnetic field measurements near the epicenter of the Ms 7.1 Loma Prieta Earthquake , 1990 .

[38]  J. Byerlee,et al.  Magnetic and electric fields associated with changes in high pore pressure in fault zones : Application to the Loma Prieta ULF emissions , 1995 .