Seismogenic Disturbances of the Ionosphere During High Geomagnetic Activity

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.

How Effective and Prerequisite Are Electromagnetic Extremely Low Frequency (ELF) Recordings in the Schumann Resonances Band to Function as Seismic Activity Precursors

ELF recordings, especially in the 0–50 Hz range (Schumann Resonances), have gained great interest during the last twenty years because of their possible relation to many geophysical, climatological, solar, and even biological phenomena, which several well-known scientists have reported. A very important question that still has not been answered is whether some particular variations in the Schumann Resonances (SR) band operate as precursors of forthcoming seismic activity. Greece and the wider Mediterranean area are a very seismic territory where medium size earthquakes (4–6.5 Richter) occur very often, contributing to a high percentage of the natural hazards of the area. In our effort to make evident how effective and prerequisite SR recordings are in the detection of forthcoming earthquakes, we analyze data collected for almost five years by two SR stations located in the north and the south edge of the Greek territory, respectively. We have come to the conclusion that particular SR modulations are very useful in the predictability of forthcoming seismic activity, but they need to be completed with additional observations of adjoining effects which can contribute to the final decision.

Research on Pre-Seismic Feature Recognition of Spatial Electric Field Data Recorded by CSES

In order to study the abnormal disturbance of the space ionosphere caused by strong earthquakes, the methods of SGF + WTA and EMD + ER are proposed and compared. The methods are applied to the 7.7 magnitude earthquake that occurred on the southern coast of Cuba on 29 January 2020 based on the electric field ultra-low frequency waveform data recorded by the ZH-1 electromagnetic satellite. Analyzing the electric field waveform data of the six orbits in and around the epicenter within five days before the earthquake and revisiting the orbit within two months, the significant information about the changes in the ionospheric electric field before the earthquake is obtained. The results demonstrate that: (1) in terms of time, large anomalies appeared before the earthquake on 16 January, and some orbital perturbations lasted until 2 February; (2) in terms of location, the disturbance changes are mainly concentrated over the central earthquake zone, and there are few conjugate zones; (3) in terms of amplitude, during the five days before the impending earthquake, most of the orbital disturbances exceeded the threshold of the background value while some of the orbital disturbances were less than the threshold; (4) in terms of morphology, the fluctuation that did not exceed the threshold appeared in the south of the earthquake area while a few appeared in the north. At the same time, the analysis method proposed in this paper is able to effectively extract the characteristics of electric field signal, clearly describe the abnormal signal change information before the earthquake, and provide a new method reference for the study of spatial electric field waveform data.

Correlations between Earthquake Properties and Characteristics of Possible ULF Geomagnetic Precursor over Multiple Earthquakes

In this study, we improved and adapted existing signal processing methods on vast geomagnetic field data to investigate the correlations between various earthquake properties and characteristics of possible geomagnetic precursors. The data from 10 magnetometer stations were utilized to detect precursory ultra-low frequency emission and estimate the source direction for 34 earthquakes occurring between the year 2007–2016 in Southeast Asia, East Asia, and South America regions. As a result, possible precursors of 20 earthquakes were identified (58.82% detection rate). Weak correlations were obtained when all precursors were considered. However, statistically significant and strong linear correlations (r ≥ 0.60, p < 0.05) were found when the precursors from two closely located stations in Japan (Onagawa (ONW) and Tohno (TNO)) were exclusively investigated. For these stations, it was found that the lead time of the precursor is strongly (or very strongly) correlated with the earthquake magnitude, the local seismicity index, and the hypocentral depth. In addition, the error percentage of the estimated direction showed a strong correlation with the hypocentral depth. It is concluded that, when the study area is restricted to a specific location, the earthquake properties are more likely to have correlations with several characteristics of the possible precursors.