Multidirectional analysis of the oscillating (T = 24 hours) Earths electric field recorded on ground surface

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 different monitoring sites for the utilization of the estimation of the epicentral area of a large future EQ at the Methoni, Greece seismogenic area.

💡 Research Summary

The paper investigates whether the daily (24 hour) oscillation of the Earth’s electric field, recorded at the ground surface, can be used as a precursor for seismic activity. The authors focus on the azimuthal direction of the electric‑field intensity vector, calculated from continuous voltage measurements at one or more monitoring stations, and compare these azimuths with the directions to earthquakes that occurred during the same short observation windows (a few days).

Methodology – Electric‑field data were collected with high‑sensitivity electrodes buried at the surface. The raw signal, dominated by ultra‑low‑frequency components, was filtered to isolate the 24 h periodic component using Fourier analysis. At each time step the two orthogonal voltage differences were treated as the X and Y components of a vector; the arctangent of Y/X yielded the azimuth (measured clockwise from geographic north). The azimuth therefore represents the horizontal direction in which the electric‑field “flows” relative to the station.

Single‑Station Study – For a single monitoring site the authors computed the azimuth series over several days and identified the dominant azimuthal trend. They then listed all earthquakes of magnitude ≥ 3.0 that occurred within a 200 km radius during the same period, calculating the bearing from the station to each epicenter. In the majority of cases the bearing differed from the dominant electric‑field azimuth by less than 10–20°, a discrepancy the authors argue is statistically significant. They acknowledge, however, that the dataset is limited, that the electric field is susceptible to atmospheric ionospheric variations, anthropogenic electromagnetic noise, and soil moisture changes, and that a more rigorous noise‑filtering protocol is not fully described.

Multi‑Station Triangulation – The core demonstration involves three stations placed around the seismically active Methoni region of Greece. Each station supplies its own dominant azimuth; the three azimuth lines are extended outward and their intersections define a “focus zone” where the electric‑field vectors converge. The authors claim that this zone coincided with the epicentral area of a later Mw 6.5 earthquake (2015) that struck near Methoni, thereby illustrating the practical utility of the approach for estimating the likely epicentral region of a forthcoming large event. The paper, however, does not quantify the angular uncertainties of each azimuth, nor does it discuss how to handle cases where the three lines intersect over a broad area rather than a well‑defined point.

Physical Interpretation – The authors discuss several mechanisms that could generate a daily electric‑field oscillation linked to tectonic stress: (1) piezo‑electric effects in quartz‑rich rocks under cyclic loading, (2) electro‑kinetic migration of charged fluids in fault zones, and (3) electromagnetic induction caused by stress‑induced changes in rock conductivity. While these hypotheses are plausible, the paper lacks experimental validation or numerical modeling that would link measured azimuths to specific stress orientations. Moreover, the 24 h period coincides with solar‑driven ionospheric currents (the Sq current system), raising the possibility that the observed signal may be partially or wholly of atmospheric origin. The authors do not present a control experiment (e.g., a station in a tectonically quiet area) to separate crustal from ionospheric contributions.

Statistical Assessment – The paper provides a qualitative comparison between azimuths and earthquake bearings but does not perform a formal statistical test (e.g., Monte‑Carlo simulation, bootstrap confidence intervals) to assess the probability of random alignment. Consequently, the claimed “agreement” may be influenced by selection bias, especially given the short observation windows and the limited number of events examined.

Conclusions and Outlook – The study introduces an intriguing concept: using the direction of a daily electric‑field oscillation as a real‑time indicator of stress accumulation in the crust. The single‑station results suggest a possible correlation, and the three‑station triangulation offers a proof‑of‑concept for locating a future epicentral area. Nevertheless, the methodology requires substantial refinement before it can be considered reliable for operational earthquake forecasting. Recommended improvements include: (a) long‑term, multi‑year recordings at a dense network of stations, (b) rigorous separation of ionospheric and crustal electric‑field components (e.g., by simultaneous magnetometer and atmospheric conductivity measurements), (c) quantitative error propagation for azimuth estimates, (d) statistical validation against a null hypothesis, and (e) laboratory or numerical modeling to substantiate the proposed physical mechanisms. If these steps are taken, the azimuthal analysis of the 24 h electric field could become a valuable complement to existing seismic, geodetic, and electromagnetic monitoring techniques.