Electric Field Anomalies Research Articles

Characteristics and mechanisms of near-surface negative atmospheric electric field anomalies preceding the 5 September 2022, Ms 6.8 Luding earthquake in China

Abstract. A magnitude 6.8 strike-slip earthquake (EQ) struck Luding, Sichuan Province, China, on 5 September 2022, resulting in significant damage to nearby Ganzi Prefecture and the city of Ya'an. In this research, the near-surface atmospheric electric field (AEF) recorded at four sites 15 d before the Luding EQ was analyzed and differentiated, and multisource auxiliary data including precipitation, cloud base height, and low cloud cover were used at the same time. Nine possible seismic AEF anomalies at four sites were obtained preliminarily. Accordingly, microwave brightness temperature (MBT) data, which are very sensitive to the surface dielectrics and are closely related to the air ionization, together with surface soil moisture, lithology, and a 3D-simulated crustal stress field, were jointly analyzed to confirm the seismic relations of the obtained negative AEF anomalies. The geophysical environment for crustal high-stress concentration, positive charge carrier transfer, and surface accumulation was demonstrated to exist and to meet the conditions necessary to generate local negative AEF anomalies. Furthermore, to deal with the spatial disparities in sites and regions with potential atmospheric ionization, near-surface wind field data were employed to scrutinize the reliability of the AEF anomalies by comprehensively analyzing the spatial relationships among surface charges accumulation areas, wind direction and speed, and the AEF sites. Finally, four negative AEF anomalies were deemed to be closely related to the Luding EQ, and the remaining five possible anomalies were ruled out. A possible mechanism of negative AEF anomalies before the Luding EQ is proposed: positive charge carriers were generated from the underground high-stress concentration areas and then transferred to and accumulated on the ground surface to ionize the surface air, thus disturbing the AEF above the ground. This study presents a method for identifying and analyzing seismic AEF anomalies and is also beneficial for the examination of the pre-earthquake coupling process between the coversphere and the atmosphere.

Study on VLF Electric Field Anomalies Caused by Seismic Activity on the Western Coast of the Pacific Rim

In order to explore the correlation between earthquakes and ionospheric very low-frequency (VLF) electric field disturbances, this article uses VLF data observed by the China Earthquake Electromagnetic Satellite (CSES) to analyze very low-frequency signals before and after earthquakes from January 2019 to March 2023 in terms of the amplitude and signal-to-noise ratio of electric field power spectrum disturbances. Taking 73 earthquakes with a magnitude of 6.0 or higher occurring in the Circum-Pacific seismic belt as an example, comprehensive research on the VLF electric field disturbance phenomenon caused by strong earthquakes is conducted, considering both the earthquake location and source mechanism. The research results indicate the following: (1) there is a strong correlation between earthquakes with a magnitude of 6.0 or above and abnormal disturbances in the VLF electric field, which often occur within 20 days before the earthquake and within 800 km from the epicenter. (2) From the perspective of earthquake-prone areas, the VLF electric field anomalies observed before earthquakes in the Ryukyu Islands of the Taiwan region exhibit small and concentrated field fluctuations, while the Taiwan Philippines region exhibits larger field fluctuations and more dispersed fluctuations. The discovery of this correlation between seismic ionospheric phenomena and seismic activity provides a new and effective approach to earthquake monitoring, which can be used for earthquake prediction, early warning, and disaster prevention and reduction work.

Identification and Analysis of Multi-Station Atmospheric Electric Field Anomalies before the Yangbi Ms 6.4 Earthquake on 21 May 2021

This study reports the atmospheric electric field (AEF) anomalies associated with seismic-geological activity recorded by the monitoring network in the Sichuan–Yunnan region of China during the 15–30 days prior to the Yangbi earthquake in Yunnan Province, China, on 21 May 2021. Based on the real-time AEF data from continuous observation, this study summarized the characteristics of the anomalous interference of different meteorological factors on the AEF, compared the simultaneous meteorological data of the AEF anomalies, and ruled out the influence of precipitation, wind, fog, and other weather factors on the AEF anomalies in Yangbi County prior to the Yangbi Ms 6.4 earthquake. The AEF anomalies were identified and extracted from the two-month data from 1 April to 1 June, which were from multiple days, stations, and rupture zones near the 100 km radius from the epicenter of the Yangbi Ms 6.4 main earthquake. Using time series and wavelet transform analysis methods, the obvious common features of the anomalies were summarized, and the homology of the anomalies was verified. The main outcome of the investigation in this study will be used to distinguish and characterize the AEF anomalies associated with pre-seismic geologic activity of non-meteorological elements in the near future.

Analysis of Ionospheric Perturbations Possibly Related to Yangbi Ms6.4 and Maduo Ms7.4 Earthquakes on 21 May 2021 in China Using GPS TEC and GIM TEC Data

On 21 May 2021 (UT), Yangbi Ms6.4 and Maduo Ms7.4 earthquakes occurred in mainland China. This paper analyzed the ionospheric perturbations possibly related to the earthquake, based on global positioning system (GPS) total electron content (TEC) and global ionosphere map (GIM) TEC data. We identified GPS TEC anomalies by the sliding quartile, based on statistical analysis. After eliminating the days with high solar activity levels and strong geomagnetic disturbances, the time series analysis of GPS TEC data showed that there were significant TEC anomalies from 5 to 10 May. TEC anomalies were mainly positive anomalies. We obtained the spatial and temporal distributions of TEC anomalies using natural neighbor interpolation (NNI). The results showed that the TEC anomalies were distributed in the seismogenic zone and surrounded the epicenters of the Maduo and Yangbi earthquakes, indicating that they may be related to the earthquakes. From the GIM TEC difference map, we found the TEC enhancement in the seismogenic zone and its magnetic conjugate area of the Maduo and Yangbi earthquakes at 10:00–12:00 (UT) on the 5 and 6 May. We discussed our results according to the lithosphere-atmosphere-ionosphere coupling mechanism. Finally, based our results, we suggested that the Yangbi and Maduo earthquakes may affect the ionosphere through seismogenic electric field and thermal anomalies generated during the process of lithosphere-atmosphere-ionosphere coupling.

On the Spatio-Temporal Dependence of Anomalies in the Atmospheric Electric Field Just around the Time of Earthquakes

In this study, we report atmospheric electric field (AEF) anomalies observed around the time of earthquakes (EQs) in Japan. Using a newly developed AEF observation network with three spatially separated stations in Japan (Chofu, Kakioka, and Iwaki), we conducted a study for two EQs that occurred within a few 100 km from the EQ epicenter under relatively good local weather conditions as shown by a local all-sky camera and weather information. Time series and wavelet analyses of the AEF indicate that fluctuation anomalies in the AEF with periods of 10–60 min and larger than 70 min were observed from a few hours before up to a few hours after the occurrence of the EQs. The lag in the onset time increased with increasing distance from the EQ epicenter to the field site. The above-mentioned characteristics of these AEF fluctuation anomalies were similar among the three stations, and therefore the observed AEF anomalies were considered to be an imminent precursor of EQs. The observed AEF anomalies were likely to be caused by internal gravity waves (IGWs) generated around the EQ epicenter a few hours before the EQ, passing over the field site while changing the AEF by changing the space charge density in the surface layer of the atmosphere.

Possible ELF/VLF Electric Field Disturbances Detected by Satellite CSES before Major Earthquakes

The electric field data of ELF/VLF frequency bands recorded by space Electric Field Detector (EFD) on satellite CSES were utilized to analyze the abnormal electromagnetic (EM) emission associated with seismic activities. Two adjacent earthquakes (EQ), which are the Mw6.9 EQ on 7 July and the Mw7.2 EQ on 14 July 2019 in Indonesia, were selected as examples. The disturbance of the electric field in the ELF/VLF band was extracted by using observational and comparative analysis methods. The results of this study indicate the following. (1) The significant electric field anomalies in the ELF/VLF band (mainly from about 49 to 366 Hz) were detected near the epicenter, exactly in the northeast, of two strong low-latitude earthquakes by the electric field detector of CSES. (2) The electric field disturbances were mainly detected by satellite CSES over the epicenters at night, i.e., along the ascending orbits. (3) These abnormal enhancements will gradually diminish as the frequency increases. (4) The electric field anomalies started to appear in the northeast of the epicenters before the mainshocks and gradually moved closer to the sources after them. At the same time, a clear magnetically conjugated feature also gradually appeared before the first earthquake, but then faded away when approaching the next one.

Preliminary Study on the Generating Mechanism of the Atmospheric Vertical Electric Field before Earthquakes

Precursor signals for earthquakes, such as radon anomalies, thermal anomalies, and water level changes, have been studied in earthquake prediction over several centuries. The atmospheric vertical electric field anomaly has been observed in recent years as a new and valuable signal for short-term earthquake prediction. In this paper, a physical mechanism of the atmospheric vertical electric field anomaly before the earthquake was proposed, based on which the Wenchuan earthquake verified the correctness of the model. Using Monte Carlo simulations, the variation of the radon concentration with height before the earthquake was used to simulate and calculate the ionization rates of radioactive radon decay products at different heights. We derived the atmospheric vertical electric field from −593 to −285 V/m from the surface to 10 m before the earthquake by solving the system of convection-diffusion partial equations for positive and negative particles. Moreover, negative atmospheric electric field anomalies were observed in both Wenjiang and Pixian before the Wenchuan earthquake on 12 May, with peaks of −600 V/m in Pixian and −200 V/m in Wenjiang. The atmospheric electric field data obtained from the simulation were shown to be in excellent concordance with the observed data of the Wenchuan earthquake. The physical mechanism can provide theoretical support for the atmospheric electric field anomaly as an earthquake precursor.

An Assessment on Earthquake Precursory Signals for Applications of Monitoring and Mitigation Strategies

Forecasting earthquakes entails the existence of time-dependent processes that are dependent on changing conditions deep inside the Earth's crust prior to the occurrence of major seismic activity. Mechanical variables, such as precursory ground deformation and earlier seismic events, have long been the focus of seismology research. The purpose of this review is to acknowledge that there have been numerous reports of a variety of precursory phenomena, including the emission of electromagnetic waves ranging from ultralow frequency (ULF) to visible (VIS) and near-infrared (NIR) light, the emission of radon gas, various electric and magnetic field anomalies, and unusual animal behaviour. Earthquake prediction research has been going on for almost a century with no obvious success.

Frequency and temperature dependent electric polarization, relaxation, and transport properties of Mo and W doped BaTiO3

In this article, we report the structural, dielectric, electronic, and transport properties of Mo and W doped BaTiO3 ceramic. The BaTiO3 (BTO), BaTi0.85Mo0.15O3 (BTMO), and BaTi0.85W0.15O3 (BTWO) samples were prepared by double sintering ceramic technique. The X-ray diffraction patterns confirmed the tetragonal phase of the perovskite structure with the P4mm space group including some extra phases in BTMO and BTWO. A relaxation peak in the real part of electric modulus M'' is observed for BTO and BTMO at 3kHz. The dielectric constants, (εr' , εr'') and loss tangent (tanδ) for all samples were measured from 300 K to 450 K under the application of 100kHz electric field and temperature dependent dielectric anomalies ensure a ferroelectric (tetragonal) to paraelectric (cubic) phase transition in all samples. BTO and BTMO crystals display between normal ferroelectric and ideal relaxor behavior while BTWO crystal approaches to ideal relaxor ferroelectric behavior identified as canonical relaxor. Moreover, solid–liquid state anisotropy during the phase transition in all samples has been illustrated in terms of Fröhlich entropy. Apart from this, in BTO and BTWO samples, the conduction mechanism is highly dominated by the frequency of applied field compared to BTMO sample. Moreover, all studied samples exhibit semiconducting behavior with positive temperature coefficient of resistance (PTCR) effect in between 300 K and 450 K. The BTMO sample with maximum PTCR peak (2.9%/K at 415K) may find suitability for temperature controlled device application.

Investigation of Scale-Dependent Groundwater/Surface-water Exchange in Rivers by Gradient Self-Potential Logging: Numerical Modeling and Field Experiments

Exchanges of groundwater and surface-water are fundamental to a wide range of water-supply and water-quality management issues but challenging to map beyond the reach scale. Waterborne gradient self-potential (SP) measurements are directly sensitive to water flow through riverbed sediments and can be used to infer exchange locations, direction (gain versus loss), scale, and relative changes, but to date applications to river corridor hydrology are limited. Numerical modeling and field experiments were therefore performed herein, each emphasizing waterborne gradient SP logging for identifying and locating focused vertical groundwater discharge (surface-water gain) and recharge (surface-water loss) in a river. Two and three-dimensional numerical models were constructed to simulate the polarities, appearances, and peak amplitudes of streaming-potential and electric-field anomalies on a riverbed and in the surface-water that were attributable to steady-state vertical fluxes of groundwater through high-permeability conduits in the riverbed. Effects of varied hydraulic length-scale of exchange and surface-water depth were tested through numerical modeling. Modeling results aided in data acquisition and interpretation for three repeated field experiments performed along a 1.5–2.0 km reach of the Quashnet River in Cape Cod, Massachusetts, where focused, meter-scale groundwater discharges occur at discrete locations within otherwise ubiquitous and more diffuse groundwater upwelling conditions. Strong gradient SP anomalies were repeatedly measured in the Quashnet River at previously confirmed locations of focused groundwater discharge, showing the efficacy of waterborne gradient SP logging in identifying and characterizing groundwater/surface water exchange dynamics at multiple river network scales.

Earthquake precursors in the light of peroxy defects theory: Critical review of systematic observations

Forecasting earthquakes implies that there are time-varying processes, which depend on the changing conditions deep in the Earth's crust prior to major seismic activity. These processes may be linearly or non-linearly correlated. In seismology, the research has traditionally focused on mechanical variables, including precursory ground deformation (revealing the build-up of stress deep below) and on prior seismic events (past earthquakes may be related to or even trigger future earthquakes). Since the results have been less than convincing, there is a general consensus in the seismology community that earthquake forecasting on time scales comparable to meteorological forecasts is still quite far in the future, if ever attainable. The starting point of the present review is to acknowledge that there are innumerable reports of other types of precursory phenomena observable on the ground or in near-Earth space ranging from the emission of electromagnetic waves from ultralow frequency (ULF) to near-infrared (NIR) and visible (VIS) light, electric field and magnetic field anomalies of various kinds (see below), all the way to widely reported but never fully understood unusual animal behavior. These precursory signals are intermittent and seem not to occur systematically before every major earthquake. As a result they are not widely accepted, because no one could fully explain their origins. In addition, the diversity of these signals makes them look unrelatable, hampering any progress. In the first part, we review evidence for a solid-state mechanism based on decades of research bridging semi-conductor physics, solid state chemistry and rock physics, that is capable of providing explanations for the diversity of reported pre-earthquake phenomena. In fact, it appears that all pre-earthquake phenomena might be traceable to a single fundamental process on the atomic scale: the rupture of peroxy bonds via activation of electronic charges, electrons and positive holes, in rocks subjected to tectonic stresses prior to seismic activity. The positive holes are defect electrons in the O2- sublattice. They are unusual inasmuch as they are able to flow out of the stressed rock volume, into and through the surrounding unstressed or less stressed rocks. They form electric currents that travel fast and far, causing along the way a wide range of physical and chemical follow-on processes: electrical ground potentials, stimulated infrared emission, massive air ionization, radon emanation, increased levels of ozone, toxic levels of carbon monoxide (CO) and more. In the second part, we critically examine satellite and ground station data, recorded before a selection of past large earthquakes. Some of the phenomena can be directly related to the peroxy defect theory, namely, radon gas emanations, corona discharges, thermal infrared emissions, air ionization, ion and electron content in the ionosphere, and electro-magnetic anomalies. Of course there is a need for further systematic investigations, continuing statistical examination of the relevance and confidence levels of the observable precursors. Only then will the scientific community be able to assess and eventually improve the performance of earthquake forecasts.

Electric field emission and anomalies of electrical conductivity above room temperature in heterogeneous NiO-SnO2 nano-ceramic composites

Microstructural NiO–SnO2 nano-ceramic matrix was synthesized via a solgel auto-combustion technique with a perspective to investigate its noteworthy electric field emission and temperature-induced conduction anomaly. Exceptional field emission performance of nickel-tin oxide composites was discovered with a low turn-on field of 3.9 V/μm and a threshold field of 5.30 V/μm with a good field emission current density of 110.44 μA/cm2 and current stability. Density functional theory was employed to estimate its local work function (Φ) 3.365 eV, and the field enhancement factor (β) was obtained as 1570 by Fowler–Nordheim plot. The anomalies in conductivity spectra at 523 K were detected by a number of physical properties measurement including impedance, conductivity, dielectric, and differential scanning calorimetry with thermal expansion. These phenomena can be rationalized in terms strain-dependent thermal hysteresis effects and localized/delocalized eg electron with a transition from inferior conductive linkage [Ni2+–O2−–Ni2+] and [Sn2+/Sn4+–O2−–Sn2+/Sn4+] to higher conductive linkage [Ni2+–Ni3+] and [Sn2+–Sn4+] of coupled NiO–SnO2 matrix. The temperature dependence frequency exponent (n), ln τ, Rg, Rgb, Cg, and Cgb support additionally the conduction anomaly behavior, and the variation of dielectric constant (ɛr) and loss (tan δ) with temperature around 523 K has been explained in terms of the reduction of space charge layers due to reversal movement of delocalized eg electrons from the grain boundary limit. The frequency dispersing impedance, conductivity, and dielectric spectra with elevated temperature were also demonstrated to comprehend its conduction mechanism with theoretical correlation.

Earthquake-related Electric Field Changes Observed in the Ionosphere and Ground

The changes of the ionospheric electric field before and after four huge earthquakes, which include the Ms 8.7 earthquake of 2004 and the Ms 8.5 earthquake of 2005 in Sumatra of Indonesia, the Ms 8.0 Wenchuan earthquake of 2008 in China, the Ms 8.8 earthquake of 2010 in Chile, and their strong aftershocks are studied in this paper. The significant results revealed that the power spectral density of low-frequency electric field below 20 Hz in the ionosphere, a kind of electromagnetic radiation phenomena, increased abnormally before and after the earthquakes and partially corresponded to the increased power spectral density of the low-frequency geoelectric field in time. This research preliminarily indicates that the low-frequency electromagnetic radiation during the imminent stages before such earthquakes could be detected by the observation of the ionospheric electric field. However, the spatial, temporal, and intensive complexities of the electric field anomalies in the ionosphere before earthquakes have come in sight also.

Ground-based and satellite DC-ULF electric field anomalies around Wenchuan M8.0 earthquake

The ground-based and satellite DC-ULF electric field data were analyzed around Wenchuan M8.0 earthquake on May 12, 2008 in China. The results show that ground electric field anomalies occurred at 3 stations located to the north and south of the epicenter with the amplitude of 3–100mV/km. The change shapes and their amplitude of ground electric field anomalies are different largely due to their individual underground layer conductivity, water level and so on. The analysis of long time series illustrates that the abnormal geoelectric field started since March 2008. Onboard the DEMETER satellite, the ULF waveforms of electric field were collected and processed by wavelet transform method. The disturbances in the ionosphere were about 3–5mV/m at a frequency band lower than 0.5Hz. When the ground and space electric field anomalies were compared, their occurrence time and spatial distribution points are consistent with each other, including the long time anomalies from March 2008 and the short term ones 1–2 days before the Wenchuan earthquake. Finally, the coupling mechanism was discussed.

Ionospheric quasi-static electric field anomalies during seismic activity in August–September 1981

Abstract. The paper proposes new results, analyses and information for the plate tectonic situation in the processing of INTERCOSMOS-BULGARIA-1300 satellite data about anomalies of the quasi-static electric field in the upper ionosphere over activated earthquake source regions at different latitudes. The earthquake catalogue is made on the basis of information from the United State Geological Survey (USGS) website. The disturbances in ionospheric quasi-static electric fields are recorded by IESP-1 instrument aboard the INTERCOSMOS-BULGARIA-1300 satellite and they are compared with significant seismic events from the period 14 August–20 September 1981 in magnetically very quiet, quiet and medium quiet days. The main tectonic characteristics of the seismically activated territories are also taken in account. The main goal of the above research work is to enlarge the research of possible connections between anomalous vertical electric field penetrations into the ionosphere and the earthquake manifestations, also to propose tectonic arguments for the observed phenomena. The studies are represented in four main blocks: (i) previous studies of similar problems, (ii) selection of satellite, seismic and plate tectonic data, (iii) data processing with new specialized software and observations of the quasi-static electric field and (iiii) summary, comparison of new with previous results in our studies and conclusion. We establish the high informativity of the vertical component Ez of the quasi-static electric field in the upper ionosphere according observations by INTERCOSMOS-BULGARIA-1300 that are placed above considerably activated earthquake sources. This component shows an increase of about 2–10 mV/m above sources, situated on mobile structures of the plates. The paper discusses the observed effects. It is represented also a statistical study of ionospheric effects 5–15 days before and 5–15 days after the earthquakes with magnitude M 4.8–7.9.

Methods and results of monitoring of the natural telluric field in the Baikal rift zone

Variations in horizontal and vertical components of the telluric field are studied within the range of periods from a few tens of seconds to diurnal and longer variations. Variations caused by an external ionospheric source are used for studying the geoelectric heterogeneity of the medium. For this purpose, an electric tipper is introduced by analogy with the geomagnetic field and its frequency response is examined. The magnetotelluric impedance is studied using data of remote geomagnetic observatories. According to the data of monitoring of the electric tipper and magnetotelluric impedance, anomalous effects are revealed that can be related to earthquakes with K ≥ 12. A method is developed for the extraction of electric field anomalies produced by intraterrestrial electric sources.

A multiple fracture model of pre-seismic electromagnetic phenomena

Among three main stages of the process of earthquake nucleation long-, middle- and short-term the final stage is characterized by abrupt activation of the process of stress-strain state variation. The strain rates increase by orders of magnitude throughout the whole region of preparation, which increases the signal-to-noise ratio, and therefore the fracture, is easier to detect through monitoring geophysical parameters. The near-critical stresses existing in the Earth's crust and near the surface make it necessary to take into account the real rheology of the rocks, which, as is well known, is characterized by clearly pronounced plastic properties. The condition is favorable for developing creep processes in general and in its avalanche phase immediately before the fracture. The process is completely nonlinear but not chaotic. Based on the assumption that the attenuation of the stress-strain field is proportional to r − 3 , a possible scenario of the final stage of earthquake nucleation process is proposed on the basis of the slip weakening mechanism in the source and the associated mosaic pattern of precursors on the Earth's surface. The formulas for estimating the ultimate distance of precursor detection and the duration of precursor events depending of normalized epicentral distance at the final stage of inelastic deformation preceding brittle failure of rocks are proposed. The data of electromagnetic precursors are interpreted in terms of a multiple fracture model. The results of in situ observations of electric field anomalies in the atmosphere are analyzed in relation to seismic activity. The possibility of constructing a physical model for the generation of a quasi-stable field and electromagnetic emission on the basis of the deformation process prior to an earthquake is discussed. Numerical estimates are obtained for polarization density and life time of an ensemble of electric dipoles generated in surface layers of the crust due to opening of microcracks and other dislocation mechanisms. The origin of quasi-constant electric field along a deformation region on a scale of the preparation zone is advantageous for the propagation of seismic anomalous atmospheric electric fields from the Earth's surface into the ionosphere. The field can be regarded as a physical agent of lithosphere–ionosphere connection.

Marine self potential exploration*

Recent marine self potential (SP) measurements south of Eyre Peninsula, South Australia and Rose Canyon, San Diego, California have been made. In both cases, a series of horizontal electrode dipoles were towed close to the seafloor in water depths of up to 100 m to measure the electric potential gradients generated by mineralisation beneath the seafloor. A proton-precession magnetometer was also towed at the surface in the Eyre Peninsula experiment. Marine SP measurements show significantly lower noise levels than land measurements, due to the uniform marine environment and low contact resistance of the electrodes, so that anomalies of less than a few tens of microvolts per metre can be detected. The major source of noise is from ocean swell and waves, which may be minimised by coherent stacking of signals, and by bandpass filtering. South of Eyre Peninsula SP electric field anomalies of 100 μV/m and width 2 km were observed in a number of traverses perpendicular to the trend of an onshore mylonite zone. Little correlation exists between the SP and magnetic data, suggesting that the SP sources are probably due to non-ferrous minerals such as graphite, and/or from the electrokinetic effect of groundwater flow through the fracture zone.

A kind of information on short-term and imminent earthquake precursors—research on atmospheric electric field anomalies before earthquakes

The long-time practice of observational research on earthquake prediction has shown that the information on short-term and imminent earthquake precursors can hardly be detected, but it is very important for practical and effective earthquake prediction. The result of analysis and study in this paper has shown that the anomaly of quasi-static atmospheric electric field may be a kind of reliable information on short-term and imminent earthquake precursors. On such a basis, the 20 years’ continuous and reliable data of atmospheric electric field observed at the Baijiatuan seismic station are used to study the correlation between the anomalies in seismic activity and relative quiet periods bear on the occurrence of near earthquakes within 200 km range around Beijing after the Tangshan earthquake. The observational results recently reported before hand in written form and earthquakes that actually occurred in near field in corresponding time periods are compared and analyzed. The efficacy of these written prediction opinions about near earthquakes in the recent 10 years is tested. From the test results, the brilliant prospect that the anomaly of quasi-static atmospheric electric field may really become a reliable mark for making short-term and imminent earthquake predictions is discussed. Besides, as a preliminary step, some judgment indexes for predicting earthquakes by use of the observational data of atmospheric electric field before earthquakes are put forward. In the last part, it is pointed out that it would be possible to obtain more believable judgment indexes for determining the three elements of near earthquakes before greater earthquakes (M S≥5) only if a relatively reasonable station network (2–4 stations every 10 000 km2) is deployed and further investigation is made.

Ultra low frequency electromagnetic wave anomaly and its spectrum characteristics before earthquakes

Many observations and researches show that abundant and intense ultra low frequency (ULF) electromagnetic anomalies appeare before local earthquakes. In order to understand this phenomenon systematically, the transmission property and the formation of the seismic-electric dipole are discussed in this paper. The results show that the vertical component of the ULF electric anomaly before earthquake has the properties of better penetration, less disturbance and high signal-to-noise ratio. The signal can be easily extracted and received. The anomaly should be an important way to seek for reliable short-term and imminent earthquake precursors. After the spectrum analysis of the (ULF) electric field anomalies, we found that the periods of the anomaly related to local earthquakes are from a few minutes to a dozens minutes. There is a relation between the spectrum of the anomaly and the epicentral distance. The ULF electric field anomalies strongly rely on the orientation of the seismogenic zone. The percolation electric field anomaly and its spectrum amplitude do not have obvious relation with the size of local earthquakes.