After the submission of the paper, three strong earthquakes with magnitude around 6.0-units occurred on October 17 and October 20, 2005, with epicenters in the Aegean Sea, at a distance {\em only} 100km from MYT station at which the intense signals $M_1$ to $M_4$ -analyzed in the main text- have been recorded. This confirms experimentally the proposed criterion we used for the classification of these signals as Seismic Electric Signals (SES). Moreover, we show that, if we follow the procedure described in [P.A. Varotsos, N. V. Sarlis, H. K. Tanaka and E. S. Skordas {\it Phys. Rev. E} {\bf 72}, 041103 (2005)], the analysis in the natural time of the seismicity after the SES initiation allows the estimation of the time window of the impending earthquakes with very good accuracy.
Electric signals have been recently recorded at the Earth's surface with amplitudes appreciably larger than those hitherto reported. Their entropy in natural time is smaller than that, $S_u$, of a ``uniform'' distribution. The same holds for their entropy upon time-reversal. This behavior, as supported by numerical simulations in fBm time series and in an on-off intermittency model, stems from infinitely ranged long range temporal correlations and hence these signals are probably Seismic Electric Signals (critical dynamics). The entropy fluctuations are found to increase upon approaching burst…
The Huang-Hilbert transform is applied to Seismic Electric Signal (SES) activities in order to decompose them into a number of Intrinsic Mode Functions (IMFs) and study which of these functions better represent the SES. The results are compared to those obtained from the analysis in a new time domain termed natural time after having subtracted the magnetotelluric background from the original signal. It is shown that the instantaneous amplitudes of the IMFs can be used for the distinction of SES from artificial noises when combined with the natural time analysis.
Earthquake hypocenters form the basis for a wide array of seismological analyses. Pick-based earthquake location workflows rely on the accuracy of phase pickers and may be biased when dealing with complex earthquake sequences in heterogeneous media. Time-reversal imaging of passive seismic sources with the cross-correlation imaging condition has potential for earthquake location with high accuracy and high resolution, but carries a large computational cost. Here we present an alternative deep-learning approach for earthquake location by combining the benefits of neural operators for wave propa…
By applying natural time analysis to the time series of earthquakes, we find that the order parameter of seismicity exhibits a unique change approximately at the date(s) at which Seismic Electric Signals (SES) activities have been reported to initiate. In particular, we show that the fluctuations of the order parameter of seismicity in Japan exhibits a clearly detectable minimum approximately at the time of the initiation of the SES activity observed almost two months before the onset of the Volcanic-seismic swarm activity in 2000 in the Izu Island region, Japan. To the best of our knowledge, …
The seismicity, which took place at the Methoni seismogenic area, in the time period of 20/2/2008 - 10/4/2008, is analyzed in terms of its location, time of occurrence and magnitude. Furthermore, it is compared to the tidal (T=14 days, T=1 day) lithospheric oscillation and to the epicentral area suggested by the analysis of the Earth_s electric field registered on 21-22/2/2008 by PYR, ATH and HIO monitoring sites. Moreover, a comparison is made between the actual seismic energy released, during the same time period (20/2/2008 - 10/4/2008) in this specific seismogenic region and the suggested o…
A seismic time reversal experiment based on Time Reversal Mirror (TRM) technique was conducted in the mesoscopically scaled medium at the LSBB Laboratory, France. Two sets of 50 Hz geophones were distributed at one meter intervals in two horizontal and parallel galleries 100 m apart, buried 250 m below the surface. The shot source used was a 4 kg sledgehammer. Analysis shows that elastic seismic energy is refocused in space and time to the shot locations with good accuracy. The refocusing ability of seismic energy to the shot locations is roughly achieved for the direct field, and with excelle…
The normalized raw data of the Earth's electric field, monitored at PYR, ATH, HIO monitoring sites in Greece, are studied as far as it concerns the presence of electric seismic precursors. Electric preseismic pulses, plateau-like anomalous electric field and Very Long Period (VLP) anomalies were detected prior to the occurrence of the July 1st, 2009 large (Ms = 6.3R) EQ in Greece. Further processing of the same data revealed the true form of the generated preseimic potential thus providing an indirect estimation of the time window of the occurrence of the large EQ. Finally, by correlating, at …
Transient electric signals emitted prior to earthquake occurrence are recorded at certain sites in the Earth's crust termed sensitive. These field observations enforce the laboratory investigation of the dielectric response of rocks forming these localities. The dielectric relaxation of granodiorite rock coming from such a sensitive locality (Keratea, Greece) reveals, through complex impedance spectroscopy, that the activation volume for relaxation of this rock is negative which so far has been reported only rarely. This result, however, supports a theoretical model on the pre-seismic electric…
The present paper deals with reliability of a gradient of atmospheric electric field potential as an indicator of seismic activity increase. With this in view, records of atmospheric electric field potential gradients of Caucasus region for 1953-1992 with respect to periods before average and large earthquakes, which took place in the same time interval, were considered. It is worth to pay attention to the fact that the avalanche-like unstable model of fault formation based on theoretical model of self-generated seismo-electromagnetic oscillations of LAI system explains convincingly spectral s…
When monitoring geophysical parameters, data from segments that are contaminated by noise may have to be abandoned. This is the case, for example, in the geoelectrical field measurements at some sites in Japan, where high noise -due mainly to leakage currents from DC driven trains- prevails almost during 70\% of the 24 hour operational time. We show that even in such a case, the identification of seismic electric signals (SES), which are long-range correlated signals, may be possible, if the remaining noise free data are analyzed in natural time along with detrended fluctuation analysis (DFA).
Phase maps, of the earth's electric field monitored at PYR and ATH monitoring sites in Greece, were compiled for two distinct oscillating earth's electric field components long before, during and after the Nafpactos EQs in Greece (January 18th and 22nd of 2010, Ms = 5.7 / 5.6R). The selected periods of the earth's oscillating electric field were the T = 1 day and T = 14 days. The specific components were selected due to the fact that they are highly depended from the corresponding same period tidal waves (M1, K1, P1). It was found that the "strange attractor like" electric seismic precursor pr…
An attempt is made in this work to decompose the "strange attractor like" seismic electric precursor into more simple and elementary components. The basic data files of the orthogonal (NS, EW) components of the Earth's electric field used for the compilation of the corresponding phase maps are decomposed by a joint non-linear inversion scheme into two basic oscillating electric fields. The first one, called "signal", is attributed to a single current source while the second, called "noise", is attributed to the mix-up of some regional and randomly located current sources. The comparison of the…
The electric field of the Earth registered by three monitoring sites (ATH, PYR, HIO) located in Greece, is investigated and analyzed after the occurrence of the Methoni EQ (14th of February, 2008, Ms =6.7R). The period of analysis is performed for 2 days (21st-22nd of February) and 7 days after the occurrence of the main seismic event. The obtained results suggest that the seismogenic area generates electrical signals denoting a specific epicentral area. This area coincides with the already seismically activated area. An estimate for the time of occurrence of this EQ is made by the application…
It is postulated that the preseismic electric signals (SES) are generated by the piezoelectric mechanism applied on small rock grains - blocks during their stress load until fracturing. Specifically, the square electric train pulses are generated by the combination of a stress increase phase which generates a positive piezostimulated polarized current pulse (PSPC) followed, in a short time, by the stress decrease phase at fracturing level which generates a negative piezostimulated depolarized current pulse (PSDC). Moreover, it is shown that the SES signals are closely related to the tidally tr…
During earthquakes preparation periods significant disturbances in the ionospheric plasma density are often observed. These anomalies are caused by lithosphere-atmosphere-ionosphere interaction, particularly by the seismic electric field penetrating from the ground surface into the ionosphere. The seismic electric field produces electromagnetic EB drift changing plasma density over the epicenter region and magnetically conjugated area. The paper is devoted to analysis of regular Global Positioning System observations and revelation of seismo-ionospheric precursors of earthquakes in Total Elect…
Earthquakes are measured using well defined seismic parameters such as seismic moment (Mo), moment magnitude (Mw), and released elastic energy(E). How this tremendous amount of energy is accumulated silently deep inside the earth's crust? The most obvious question in seismic research remains unanswered. We found an inherent and intriguing connection between the released energy in an earthquake and electrochemical potential induced in an ultra-thin metal oxide electrode immersed in an aqueous pH solution, which leads us to understand the origin of the energy accumulation process in an earthquak…
Seismologists often need to gather information about the subsurface structure of a location to determine if it is fit to be drilled for oil. However, there may be electrical noise in seismic data which is often removed by disregarding certain portions of the data with the use of a notch filter. Instead, we use a convolutional encoder decoder network to remove such noise by training the network to take the noisy shot record as input and remove the noise from the shot record as output. In this way, we retain important information about the data collected while still removing coherent noise in se…
On Feb. 5 2016 (UTC), an earthquake with moment magnitude 6.4 occurred in southern Taiwan, known as the 2016 (Southern) Taiwan earthquake. In this study, evidences of seismic earthquake precursors for this earthquake event are investigated. Results show that ionospheric anomalies in Total Electric Content (TEC) can be observed before the earthquake. These anomalies were obtained by processing TEC data, where such TEC data are calculated from phase delays of signals observed at densely arranged ground-based stations in Taiwan for Global Navigation Satellite Systems. This shows that such anomali…
The Andravida EQ, Greece (8/6/2008, Ms=7.0R) seismic parameters: location, time of occurrence and magnitude were determined "a posteriori" in an attempt to verify the predictability of the large EQs. The Earth's electric field, after its processing by de-noising techniques, was used, in conjunction with appropriate physical models, for the determination of the epicenter by triangulation. The time of occurrence was determined in very short-term mode by the use of the tidal waves (M1, K1) and the "strange attractor like" seismic electric precursor, while its magnitude was calculated by the appli…
We introduce the first fully self-consistent model combining the seismic micro-ruptures occurring within a generalized Burridge-Knopoff spring-block model with the nucleation and propagation of electric charge pulses within a coupled mechano-electrokinetic system. This model provides a general theoretical framework for modeling and analyzing geoelectric precursors to earthquakes. In particular, it can reproduce the unipolar pulses that have often been reported before large seismic events, as well as various observed anomalies in the statistical moments of the ambient electric fields and the po…
The recent large EQ that occurred in Greece (April 1st, 2011, Ms = 6.7R) is investigated as far as it concerns regional geophysical features of the Greek territory. In particular, the EQ location is compared to the deep lithospheric fracture zones and faults, derived from the analysis of the corresponding earth's gravity field; to the current seismic potential map determined from the study of the past seismicity, while its time of occurrence is compared to the peaks of the M1 and diurnal tidal waves. The detailed investigation of the earth's electric field that was recorded by the ATH monitori…
The Earth's preseismic oscillating (T = 24h) electric field recorded for a short-time period of some days is analyzed in terms of its intensity vector azimuthal direction calculated at one monitoring site. The calculated azimuthal directions are compared to the concurrent seismicity observed for the same period of time. Examples are presented for proving the agreement between the electric field intensity vectors calculated azimuths and the corresponding ones referring to the EQs - monitoring site location. Finally, an example is presented on account of the use of this methodology upon three di…
A characteristic change of seismicity has been recently uncovered when the precursory Seismic Electric Signals activities initiate before an earthquake occurrence. In particular, the fluctuations of the order parameter of seismicity exhibit a simultaneous distinct minimum upon analyzing the seismic catalogue in a new time domain termed natural time and employing a sliding natural time window comprising a number of events that would occur in a few months. Here, we focus on the minima preceding all earthquakes of magnitude 8 (and 9) class that occurred in Japanese area from 1 January 1984 to 11 …
