correction to strong ferrimagnetic resonance signal and magnetic susceptibility of the nojima pseudotachylyte in japan and their implication for coseismic electromagnetic changes 1 pseudotachylyte is a glassy fault rock providing certain evidence of ancient seismic fault movement i examine the nojima pseudotachylyte found along the nojima fault which caused the 1995 kobe earthquake m 7 2 in japan using the electron spin resonance technique the nojima pseudotachylyte has a strong ferrimagnetic resonance fmr signal derived from bulky trivalent iron ions in ferrimagnetic iron oxides this fmr signal appears by heating the surrounding fault gouge that is the source material of the nojima pseudotachylyte furthermore the magnetic susceptibilities of the nojima pseudotachylyte are 10 2 10 3 times larger than those of the surrounding fault gouge and are proportional to the fmr signal intensities here i reconstruct the magnetization process of fault gouge during ancient seismic fault slip using the fmr signal the results indicate that the instantaneous magnetization of the nojima fault gouge may have induced instantaneous geomagnetic changes and that the instantaneous geomagnetic changes may have further induced geoelectric changes by electromagnetic induction

the 2004 parkfield earthquake test of the electromagnetic precursor hypothesis 1 a controversy has existed for 30 years concerning the possibility of earthquake prediction using electromagnetic precursors long term electromagnetic monitoring prior to during and after the m6 0 earthquake at parkfield california on 28 september 2004 now provides a definitive test of this hypothesis during the earthquake our instruments recorded clearly documented electrical signals from an earthquake impulsive changes of up to 2 5 mv at an electrode located 250 m from the rupture zone followed by a transient decay lasting at least 3 1 4 hours similar signals 1 5 mv were recorded with the only two m 5 aftershocks but their transient decays lasted for only 17 min these signals are unambiguously a result of the earthquake and can be useful in studies of fluid flow in faults a major current topic in earthquake physics patterns in the distribution of transient voltages differ from static stress changes but are consistent with a small coseismic pressure drop on the fault and fluid flow inward signals at a distance of 1 km from the fault are less than 1 mv and are statistically no different from zero in our analysis transient voltages for the aftershocks have opposite polarity from those recorded with the main shock and are again maximal close to the fault suggesting subsequent outward flow from the fault finally there is no evidence of any precursory signal strongly calling into question previously suggested signals preceding smaller or more distant earthquakes

seismic electric signals ses and earthquakes a review of an updated van method and competing hypotheses for ses generation and earthquake triggering abstract electromagnetic phenomena are sometimes associated with seismic events but earthquake prediction using seismic electric signals ses has not been seriously considered since the early 1990s there are several causes 1 false alarms that have created panics in greece and 2 a strong critique of the varotsos alexopoulos nomicos van method used there an updated van method that includes time series analysis has made successful medium range predictions and short range predictions when coupled with seismic time series analysis four types of potential mechanisms to create precursory ses relying on deformation effects temperature effects ore mineral movement or groundwater variation are reviewed data relevant to each are insufficient to favor a single mechanism records of the number of false positive and missed events for an updated van method have not been well maintained false positives appear to be abundant and render the method unusable co seismic groundwater fluctuations are addressed and two novel hypotheses of earthquake trigger mechanism are also presented ionospherically induced electric and resultant magnetic fields to weaken rock thereby causing failure and volatiles liberated from minerals additionally promoting rock failure recommendations for further study are included

laboratory studies of electrical potential during rock failure we have investigated electrical potential and acoustic emissions signals associated with rock deformation five rock types were studied clashach bentheim and darley dale sandstones all quartz rich and a seljadur basalt and portland limestone both quartz free both air dry and the rocks were tested in distilled water shallow crustal conditions were simulated in a triaxial rock deformation cell with a confining pressure simulating depth of 40 mpa pore pressures ranging 5 35 mpa and strain rates 10 7 10 4 s 1 precursory electric potential signals prior to failure were observed in both saturated and dry samples of the quartz rich sandstones but only observed in the water saturated quartz free rocks co seismic electrical signals were obtained in all tests providing strong evidence that two of the main sources for precursory and co seismic signals are the piezoelectric and electrokinetic phenomena lowering the strain rate resulted in an increase in the number of acoustic emissions the pore volume changes during compaction and dilatancy remained approximately constant for all strain rates streaming potential generated by fluid flow across the sample was also measured at different stages of deformation the potential signals increased with the pore pressure gradient c 2005 elsevier ltd all rights reserved

near lithostatic pore pressure at seismogenic depths a thermoporoelastic model summary a model is presented for pore pressure migration through a transition layer separating a meteoric aquifer at hydrostatic pressure from a deeper reservoir at lithostatic pressure this configuration is thought to be pertinent to the south iceland seismic zone sisz and to other tectonically active regions of recent volcanism where volatiles are continuously released by ascending magma below the brittle ductile transition poroelastic parameters are computed for basaltic rock the model is 1 d the fluid viscosity is temperature dependent and rock permeability is assumed to be pressure dependent according to a dislocation model of a fractured medium environment conditions are considered pertinent to basalt saturated with water at shallow depth case i and at mid crustal depth case ii if the intrinsic permeability of the rock is high no significant effects are observed in the pressure field but advective heat transfer shifts the brittle ductile transition to shallower depths if the intrinsic permeability is low the pressure dependent permeability can propagate near lithostatic pore pressures throughout most of the transition layer while the temperature is practically unaffected by advective contributions so that the rock in the transition layer remains in brittle condition geometrical parameters characterizing the fracture distribution are important in determining the effective permeability in particular if an interconnected system of fractures develops within the transition layer the effective permeability may increase by several orders of magnitude and near lithostatic pore pressure propagates upwards these modelling results have important bearings on our understanding of seismogenic processes in geothermal areas and are consistent with several geophysical observations in the sisz in connection with the two 2000 june m 6 5 earthquakes including i fluid pressure pulses in deep wells ii low resistivity at the base of the seismogenic layer iii low vp vs ratio and time dependent seismic tomography iv heterogeneity of focal mechanisms v shear wave splitting vi high b value of deep foreshocks vii triggered seismicity and viii radon anomalies

physical properties of the variations of the electric field of the earth preceding earthquakes ii determination of epicenter and magnitude abstract as reported in the preceding paper a transient change of the electric field of the earth seismic electric signal hereafter called ses appears many hours before an earthquake eq by measuring this change in a given direction and dividing it with a suitable relative effective resistivity one obtains a quantity that reflects the current density in this direction measurements in two directions e w and n s give the relative signal intensity jrel at the station under consideration by measuring jrel at a number of stations and considering that it attenuates according to a 1 r law the epicenter can be determined with an accuracy usually around 100 km once the epicenter has been determined the product jrel r can be evaluated so that the magnitude m can be estimated by resorting to an empirical log jrel r versus m plot the uncertainty of m is around 0 5 units following sobolev 1975 and for the statistics to be beyond any doubt predictions were officially documented before the eq occurrence for 23 earthquakes with a magnitude equal or greater than ms 5 0 two events were missed the present method is compared to other electrical methods used in china japan and soviet union a number of problems concerning the origin of the effect its directivity and the attenuation with distance remain open for further studies

geology and petrology of ejecta from the 1999 eruption of shishaldin volcano alaska shishaldin volcano erupted repeatedly during april and may 1999 with major eruptive events on 19 april and 23 april tephra deposits 20 cm thick were distributed across the southern flanks and hyperconcentrated debris flows ran down the northern slope all analyzed clasts were basaltic in composition with abundant 29 vol phenocrysts of plagioclase olivine and magnetite glass inclusion analyses indicate low volatile contents 900 to 58 ppm respectively comparisons of sulfur contents in glass inclusions and groundmass glasses suggest significant degassing occurred even prior to eruption trace element studies suggest that the magma reservoir below shishaldin may not be a closed long lived chamber and u th ra isotopic analyses indicate short crustal residence times on the order of at most a few thousand years for the 1999 products comparison of the deposits from this eruption with other similarly sized eruptions suggests the 19 april explosive event should be classified as a sub plinian basaltic eruption such eruptions are rare the 19 april explosive event was the largest at shishaldin during the last 175 years however the petrology chemistry and deposit thickness and distribution resemble those of at least 11 scoria deposits in the last 9 000 years suggesting that this type of eruption is common for shishaldin

electric potential changes prior to shear fracture in dry and saturated rocks electric potential changes before shear rupture were measured using darley dale sandstone quartz rich and icelandic basalt quartz free on both dry specimens and in the presence of pore fluid we find that electric potential changed markedly just prior to dynamic rupture in dry and saturated sandstones and saturated basalt but we did not detect precursory signals in dry basalt the absence of signals in dry basalt provides strong evidence that the piezoelectric effect and electrokinetic effect are dominant sources for precursory signals moreover we find that the amplitude of the precursory signals due to electrokinetic effect in saturated sandstone were as large as the coseismic signals we propose that this signal is caused by accelerating evolution of dilatancy as cracks grow in the rock before rupture resulting in water flow into the dilatant region with an electric current produced concurrently

role of pore fluids in the generation of seismic precursors to shear fracture a systematic study of temporal changes in seismic b values defined as the log linear slope of the earthquake frequency magnitude distribution has shown that large earthquakes are often preceded by an intermediate term increase in b followed by a decrease in the months to weeks before the earthquake1 the onset of the b value increase can precede earthquake occurrence by as much as 7 years a recently proposed fracture mechanics model of the earthquake source2 explains these temporal fluctuations in b in terms of the underlying physical processes of time varying applied stress and crack growth the model predicts two minima in b separated by a short lived maximum here we report the results of controlled laboratory deformation experiments done in simulated upper crustal conditions on both air dried and water saturated rock specimens as found in previous experiments3 5 shear fracture in dry specimens is characterized by a decline in b during anelastic deformation to a single minimum reached just before failure but in water saturated specimens when pore fluid volume is kept constant by servo control we also observe a second intermediate term b value minimum so reproducing the double b value anomaly predicted by the model2

short time electrical effects during volcanic eruption experiments and field measurements laboratory experiments on the fragmentation and expansion of magmatic melt have been performed using remelted volcanic rock at magmatic temperatures as magma simulant a specially designed dc amplifier in combination with high speed data recording was used to detect short time electrostatic field effects related to the fragmentation and expansion history of the experimental system as documented by simultaneous force and pressure recording as well as by high speed cinematography it was found that 1 the voltage time ratio of electrostatic field gradients 100 to 104 v s reflects different physical mechanisms of fragmentation and expansion and 2 the maximum voltage measured in 1 m distance 0 1 to 180 v can be correlated with the intensity of the respective processes based on these experimental results a field method was developed and tested at stromboli volcano in italy a 0 8 m rod antenna was used to detect the dc voltage against local ground i e the electrostatic field gradient at a distance of 60 to 260 m from the respective vent upwind position of the detection site was chosen to prevent interference caused by contact of charged ash particles with the antenna a standard 8 hz geophone was used to detect the accompanying seismicity three types of volcanic activity occurred during the surveillance operation two of these could be clearly related to specific electrical and seismical signals a typical delay time was found between the electrical and the seismical signal corresponding to the seismic velocity within the crater deposits using a simple first order electrostatic model the field measurements were recalibrated to the laboratory scale comparison of field and laboratory data at first approximation revealed striking similarities thus encouraging the further development of this technique for real time surveillance operation at active volcanoes

electric potential changes associated with slip failure of granite preseismic and coseismic signals electric potential changes were measured for stick slip events in granite samples with a three block direct shear arrangement at 8 mpa normal stress two electrodes were mounted on the left and right hand blocks and the electric potential difference between each electrode and the ground was measured with a high input impedance recording system of frequency range from dc to 100 hz as well as coseismic electric signals of about 1 5 v which appeared the moment of the dynamic slip event preseismic signals were detected just before the slip event the coseismic signal rises stepwise with opposite polarities at the two electrodes and exponentially decays with a time constant of e s where e is the permittivity and s is the conductivity of the rock sample 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 piezoelectric 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 an amplitude of about 50 mv the local strains along two sliding surfaces were also measured to monitor the growth of the rupture nucleation zone when the growth of the rupture nucleation zone occurred on the left sliding surface a clear preseismic signal was detected at the electrode 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

self potential observations during hydraulic fracturing 1 the self potential sp response during hydraulic fracturing of intact sierra granite was investigated in the laboratory excellent correlation of pressure drop and sp suggests that the sp response is created primarily by electrokinetic coupling for low pressures the variation of sp with pressure drop is linear indicating a constant coupling coefficient cc of 200 mv mpa however for pressure drops 2 mpa the magnitude of the cc increases by 80 in an exponential trend this increasing cc is related to increasing permeability at high pore pressures caused by dilatancy of microcracks and is explained by a decrease in the hydraulic tortuosity resistivity measurements reveal a decrease of 2 prior to hydraulic fracturing and a decrease of similar to 35 after fracturing an asymmetric spatial sp response created by injectate diffusion into dilatant zones is observed prior to hydraulic fracturing and in most cases this sp variation revealed the impending crack geometry seconds before failure at rupture injectate rushes into the new fracture area where the zeta potential is different than in the rock porosity and an anomalous sp spike is observed after fracturing the spatial sp distribution reveals the direction of fracture propagation finally during tensile cracking in a point load device with no water flow a sp spike is observed that is caused by contact electrification however the time constant of this event is much less than that for transients observed during hydraulic fracturing suggesting that sp created solely from material fracture does not contribute to the sp response during hydraulic fracturing

study on electrical potential inversion imaging of abnormal stress in mining coal seam during the mining activities coal rock dynamic disasters have caused grievous casualties and massive property losses it is the severe problem for regional monitoring of abnormal stress electrical potential ep can be produced on coal rock under loading and its response is related closely with the loading stress and damage evolution meanwhile electric field inversion has the advantage to realize regionalization monitoring in the space to identify the abnormal stress localization characteristics in mining coal seam after theoretical derivation the strategy of ep inversion imaging on is studied under bilateral model further simulation experiment of coal rock under loading is conducted the abnormal probability zones of sample can be identified with ep inversion imaging while it corresponds with severe damage zones with significant crack propagation it can be utilized to reveal the localized characteristics of damage and failure of coal rock spatially finally the results of ep inversion in the mining coal seam indicate that the abnormal probability zones can be considered as stress concentration and dynamic hazard areas its effectiveness is verified by microseismic monitoring and rock burst hazard assessment the study provides a new idea to monitor abnormal stress zone regionally and forecast dynamic disasters in the field

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

error propagation in electromagnetic transfer functions what role for the magnetotelluric method in detecting earthquake precursors summary whether electromagnetic precursors exist is a contentious issue that should be considered in the context of the focal depth and epicentral distance at which earthquakes nucleate and with due regard to externally driven changes in the electromagnetic fields recorded at the earth s surface if high frequency electromagnetic signals are generated by earthquakes then these signals may not be detectable because of attenuation occurring between the focal depth of the earthquake and the earth s surface this is particularly true in seismotectonic regions e g subduction zones where saline fluids including seawater raised heat flow and partial melts often lead to enhanced conductivities a technique for examining temporal variations in magnetotelluric mt spectra is presented which i considers both non inductive and inductive parts of the mt transfer function ii allows electromagnetic skin depths and adjustment distances to be calculated iii takes account of error propagation in the transfer functions and and iv acknowledges possible nonearthquake sources of observed variations in transfer functions and their errors data processing tends to eliminate non stationary electromagnetic disturbances of the source field hence the method is more suited to detecting hypothesized changes in subsurface conductivity than short lived electromagnetic bursts the technique is applied to mt data from seismotectonic regions in new zealand mt ruapehu the andes western cordillera and the mediterranean montecristo island and to a culturally quiet control site situated on a stable craton in central australia we demonstrate that the mt method can resolve apparent conductivity changes of the order of a few percent over 48 hr time intervals and give thresholds for other interval lengths comparison of the results obtained from seismotectonic regions with those from central australia and consideration of external source field effects highlight how temporal variations of electromagnetic fields might be speciously interpreted as earthquake precursors

physical properties of the variations of the electric field of the earth preceding earthquakes i abstract in an earlier paper we described the physical properties of the preseismic transient variations in the electrotelluric field the present letter clarifies a few points that were not properly emphasized in our previous publications furthermore recent results like that of the destructive kalamata earthquake on september 13 1986 indicate that the duration of a preseismic electric signal may reach considerably high values lasting up to several hours

fluid flow near reservoir lakes inferred from the spatial and temporal analysis of the electric potential electric self potential sp variations have been monitored continuously from 1995 to 1998 at 14 points on a ridge separating the roselend and la gittaz reservoir lakes in the french alps the lakes have level variations of at least 50 m over yearly cycles seasonal variations of sp associated with lake level variations are observed on five points of the array for three points located on the banks of the lakes a positive correlation to the lake level variations is observed with a maximal amplitude of about 180 mv corresponding to an average response of 2 4 mv per meter of water for two points located on the bottom of each lake the correlation is negative with a maximal magnitude of about 50 mv corresponding to an average response of 1 1 mv per meter of water two independent temporary electrical arrays located on the banks of each lake confirm these measurements and allow a better spatial characterization of the sources associated with the observed sp variations in particular near the roselend lake the electrical response to lake level variations is increasing for decreasing altitude the measured sp variations are proposed to result from the electrokinetic coupling associated with a vertical groundwater flow connecting a constant pore pressure source to the bottom of the lakes numerical modeling indicates that the spatial variation of the response and the nonlinear response observed at one point can be explained by leakage currents in the conductive lake water the values of the streaming potential coefficient spc measured in the laboratory with crushed rock samples from the site range from 14 to 50 mv 0 1 mpa for an electrolyte resistivity of 40 m and are compatible to first order with the magnitude of the observed seasonal sp variations a detailed quantitative electrokinetic modeling is currently limited mainly by the poor knowledge on the contribution of electrical leakage currents and the local variability of the spc this experiment indicates that spatial and temporal variations of the electric potential are promising tools to characterize and monitor shallow groundwater flow and provide practical data for the investigation of groundwater flow associated with volcanic or tectonic activity

streaming potential and permeability of saturated sandstones under triaxial stress consequences for electrotelluric anomalies prior to earthquakes the streaming potential due to fluid circulation in rock was measured on saturated sediments fontainebleau sandstones the electrokinetic coupling coefficient which is the ratio of the streaming potential and the excess pore pressure is proportional to the fluid resistivity additionally for a fluid conductivity of 10 3 s m the electrokinetic coupling coefficient varies from 10 to 6642 mv 0 1 mpa for sample permeability in the range of permeabilities from 0 15 10 15 to 1220 10 15 m2 the different values of the electrokinetic coupling coefficient have been explained by the effect of increasing surface conductivity which becomes nonnegligible compared to fluid conductivity for low permeability when the sample is deformed under triaxial stress up to failure the vertical permeability along the principal stress drops by about 0 20 0 1 mpa when failure occurs the typical variation of the electrokinetic coupling coefficient is a large increase beginning with the onset of the localization of the shear band at about 75 of the yield stress and stopping at the failure this increase of the electrokinetic coupling coefficient is due to an increase of potential in the shear zone when new surfaces are created and connected possible consequences of our results are given concerning the electrical fields which could appear during the preparation of an earthquake it is shown that in some cases self potential anomalies reported in the deformed zone preceding an earthquake occurrence could be due to an increase of the electrokinetic coupling coefficient from 75 of the yield stress to rupture in the vicinity of one of the electrodes any variation of fluid resistivity or permeability in the vicinity of one electrode could change the electrokinetic coupling coefficient inducing a surface electrokinetic potential anomaly in regard to the interpretation of the electrokinetic effect which occurs at large distance from the epicenter a larger electrokinetic potential anomaly could be measured between electrodes situated along a vertical fluid flow for instance in a shallow borehole an electrokinetic potential anomaly up to 30 mv for a fluid conductivity of 0 01 s m and a rock permeability of 10 12 m2 could be observed with a change of the underground water table level as slight as 50 cm 50 mbar moreover if the permeability between the electrodes is increased by a factor of 8 103 the electrokinetic coupling coefficient could be enhanced by a factor up to 650

earthquake prediction research and the earthquakes of 2000 in the south iceland seismic zone abstract the purpose of this paper is to describe and to model long and short term processes that preceded two large earthquakes that occurred in 2000 in the south iceland seismic zone sisz the results are based on some key findings from multinational earthquake prediction research projects in the sisz since 1988 it involves a fusion of significant old and new results the paper presents a new hypothesis for earthquake build up processes in the region followed by a discussion on how interseismic and preseismic observations can be explained by this model and a discussion about a plausible earthquake cycle in light of the new hypothesis the research described here started in 1988 with the south iceland lowland sil project a significant outcome was the development of a seismic acquisition and evaluation system the sil system retrieving source information from earthquakes down to magnitude zero the research continued with the use of more multidisciplinary and multinational projects revealing new information about crustal processes related to large earthquakes in the area the validity of the work was tested in 2000 when two magnitude 6 6 m s earthquakes occurred in the central part of the sisz the earthquakes had a long term assessment of place a short term warning within short about the location and size of a probable impending earthquake was issued 25 hours before the second earthquake

permeability dependence of streaming potential in rocks for various fluid conductivities streaming potentials have been measured on sandstone and limestone samples in a large range of permeabilities the electrokinetic coupling coefficient increases with permeability and we explain this effect by the related variation of surface conductivity a model is proposed to study this effect for various fluid conductivities and it is shown that the dependence of the electrokinetic coupling coefficient on permeability is stronger for high fluid resistivity and is weaker for lower fluid resistivity when fluid resistivity is below 1 m permeability and streaming potential are no more related