P. Varotsos

Physical properties of the variations of the electric field of the earth preceding earthquakes, I

Varotsos, P. and Alexopoulos, K., 1984. Physical properties of the variations of the electric field of the earth preceding earthquakes, I. Tecronophysics, 110: 73-98. The electric field variations of the earth that occur before earthquakes have been studied in a network of eighteen stations in Greece. These precursor seismic electric signals (SES) occur 6-115 h before the earthquake (EQ) and have a duration of 1 min to 1 i h. The duration and the lead-time in contrast to other precursors, do not depend on EQ-magnitude (M). These signals appear as a transient change of the potential difference measured between two electrodes (up to a few millivolts for electrodes at a distance of about L = 50 m) depending on M, the epicentral distance r and the local inhomogeneities. The components of electric field are measured in two perpendicular directions (E-W and N-S). The totality of experiments showed that the interesting quantity of each SES is the maximum value AFof the potential change. The SES of an impending EQ appears simultaneously at a number of stations without being accompanied by any significant change in the magnetic field. The following rules have been established: (1) Seismic electric signals recorded on a single line (e.g. E-W) of a given station and emitted from various seismic regions have AI’-values that decrease with the epicentral distance according to a l/r-law (for r > 50 km). (2) For a given line of a given station the SES emitted from a given seismic region (r = const.) have AV-values that increase with the magnitude; to a good approximation log AV versus M gives a straight line with a slope between 0.3 and 0.4. If for the same station and line another seismic region is considered, the straight line is parallel to the previous one but shifted by a constant amount that depends purely on the ratio of the epicentral distances. Therefore, if the quantity log(AV.r) for earthquakes emitted from various seismic regions is plotted versus M, a unique linear relation for each station appears with the same slope. (3) The simultaneous AV-values of a given EQ recorded at various stations do not follow a l/r dependence. The value AV/L of the electric field in each direction, divided by a suitable factor-an empirically determined effective resistivity-gives a quantity characteristic of the variation of the component of the current density in the earth which can be designated as the intensity of the signal in this direction. By combining the values of the two directions the total intensity J of the SES results. This quantity is found to attenuate with the distances of the stations according to a l/r-law so that log( J. r) is an unique linear function of M for all stations and seismic regions. * Mailing address: Knossou Str. 36, Ano Glyfada, 16561 Athens, Greece. 0040-1951/84/

Latest aspects of earthquake prediction in Greece based on seismic electric signals, II☆

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PHYSICAL PROPERTIES OF THE VARIATIONS OF THE ELECTRIC FIELD OF THE EARTH PRECEDING EARTHQUAKES. II. DETERMINATION OF EPICENTER AND MAGNITUDE

Abstract Since 1983, continuous monitoring of the electrotelluric field has been carried out using an array of measuring stations located at various sites in Greece. The basic physical properties of the transient changes—seismic electric signals (SES)—in the electrotelluric field that are forerunners of earthquakes were first described six years ago. Since then a large body of data has been collected resulting in new insight into various aspects of the method. The present paper reviews the latest developments in SES-based earthquake prediction and describes the current procedures used to predict the epicenter and magnitude of an impending earthquake. A detailed list of the predictions officially issued in Greece during the past 3 years (January 1, 1987–November 30, 1989) is also given. Public warnings were issued well before the most destructive seismic activity.

Comparison of models that interconnect point defect parameters in solids with bulk properties

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.

Similarity of fluctuations in correlated systems : The case of seismicity

Two models have been proposed for the interconnection of the defect Gibbs energy gi with bulk properties almost 60 and 30years ago, respectively. The one, proposed by Zener [J. Appl. Phys. 22, 372 (1951)], assumes that gi can account for the work that goes into straining the lattice and hence that it is proportional to the shear modulus of the solid. The other considers that since gi corresponds to an isobaric and isothermal process, it should be proportional to the isothermal bulk modulus and the mean volume per atom. The results of these two models are compared for different processes (defect formation, self-diffusion activation, and heterodiffusion) in a variety of solids including metals (fcc, bcc, and tetragonal) as well as solids that exhibit a superionic behavior. We find that the latter model does better than the former.

Transmission of stress induced electric signals in dielectric media

We report a similarity of fluctuations in equilibrium critical phenomena and nonequilibrium systems, which is based on the concept of natural time. The worldwide seismicity as well as that of the San Andreas fault system and Japan are analyzed. An order parameter is chosen and its fluctuations relative to the standard deviation of the distribution are studied. We find that the scaled distributions fall on the same curve, which interestingly exhibits, over four orders of magnitude, features similar to those in several equilibrium critical phenomena (e.g., two-dimensional Ising model) as well as in nonequilibrium systems (e.g., three-dimensional turbulent flow).

Investigation of seismicity after the initiation of a Seismic Electric Signal activity until the main shock

The conditions under which pressure (stress) variations on solids, containing charged defects, can lead to the emission of transient electric signals, are discussed. The resulting electric field E varies as 1/d3 (where d denotes the distance from the emitting source), in the simple case when the surrounding medium is homogeneous and isotropic. We show that this behavior changes to 1/d when studying the electric field within a cylindrical channel of radius R and infinite length having conductivity appreciably larger than that of the host medium; this holds up to a certain (reduced) distance d/R, which increases versus the conductivity ratio. We also investigate the variation of the electric field, versus the distance, inside a layer of width w and infinite extent having conductivity appreciably larger than that of the host medium; we then find that the electric field decreases as 1/d2, in a wide range of distances up to a certain value of d/w, which is controlled by the conductivity ratio. In both conducti...

Natural Time Analysis: The New View of Time

The behavior of seismicity in the area candidate to suffer a main shock is investigated after the observation of the Seismic Electric Signal activity until the impending main shock. This is based on the view that the occurrence of earthquakes is a critical phenomenon to which statistical dynamics may be applied. In the present work, analysing the time series of small earthquakes, the concept of natural time chi was used and the results revealed that the approach to criticality itself can be manifested by the probability density function (PDF) of kappa(1) calculated over an appropriate statistical ensemble. Here, kappa(1) is the variance kappa(1)(=-(2)) resulting from the power spectrum of a function defined as Phi(omega)= summation operator(k=1)(N) p(k) exp(iomegachi(k)), where p(k) is the normalized energy of the k-th small earthquake and omega the natural frequency. This PDF exhibits a maximum at kappa(1) asymptotically equal to 0.070 a few days before the main shock. Examples are presented, referring to the magnitude 6 approximately 7 class earthquakes that occurred in Greece.

Natural time analysis of critical phenomena

Part I Seismic Electric Signals.- 1. Introduction to Seismic Electric Signals-V.- Part II.- 2. Natural Time. Background-F.- 3. Entropy in Natural Time-E.- Part III Natural Time Applications.- 4. Natural Time Analysis of Seismic Electric Signals-AS.- 5. Natural Time Investigation of the Effect of Significant Data Loss on Indentifying Seismic Electric Signals-ASL.- 6. Natural Time Analysis of Seismicity-AEQ.- 7. Indentifying the Occurence Time of an Impending Mainshock-AIM.- 8. Natural Time Analysis of Dynamical Models-AD.- 9. Natural Time Analysis of Electrocardiograms-AEL.- References.

Fluctuations, under time reversal, of the natural time and the entropy distinguish similar looking electric signals of different dynamics

A quantity exists by which one can identify the approach of a dynamical system to the state of criticality, which is hard to identify otherwise. This quantity is the variance of natural time χ, where and pk is the normalized energy released during the kth event of which the natural time is defined as χk = k/N and N stands for the total number of events. Then we show that κ1 becomes equal to 0.070 at the critical state for a variety of dynamical systems. This holds for criticality models such as 2D Ising and the Bak–Tang–Wiesenfeld sandpile, which is the standard example of self-organized criticality. This condition of κ1 = 0.070 holds for experimental results of critical phenomena such as growth of rice piles, seismic electric signals, and the subsequent seismicity before the associated main shock.