## 3 Results and Discussion
### The Earth's Natural Pulsed Electromagnetic Field  
In Figure 2, a record is shown of the intensity variation of ENPEMF in the VLF band (\(f=7.5\) kHz) obtained with the north-south-oriented antenna of the MGR-02-16 recorder. As happened, at the time of the 4 March 2024, earthquake the antenna was pointing nearly toward its epicenter (see Figure 1). The accumulation time of the ENPEMF pulse signals for each point in the plot equals 5 min; in the figure, these data are presented in normalization to the number of pulses that arrived in one second.  
First, note that during the period between 1 and 20 February 2024, the counting rate of the pulses of the electromagnetic field clearly demonstrates the presence of diurnal oscillation. This is a typical record of the background change in ENPEMF intensity registered by an MGR-02-16 instrument, which the authors [2; 3; 4; 5] explain by the influence of the highly stable daily rhythms of the Earth's crust on mechanoelectrical transformations in rocks.  
The proximity of the earthquake epicenter to the recording equipment of the Geophysical Observatory allowed for the detection of distinct anomalous effects in the ENPEMF intensity during the short-term preparation period of the seismic event. Thus, on 21 February, about 13 days before the earthquake, there occurred a significant suppression of the amplitude of diurnal variation. Next, on 2 March 2024, two days until the main shock, a significant, 4-5 times above the background, growth in the rate of electromagnetic pulses took place, which continued throughout the whole day.  
According to observations, the longer a prognostic signal lasts, the more likely the occurrence of a high-magnitude seismic event [4; 5]. As stated by the authors, detection of decline in ENPEMF intensity is an objective reason to inform the population of possible events.  
Importantly, during the whole observed period, both the meteorological and geomagnetic conditions remained quiet, and there were no thunderstorms or magnetic storms, which could have influenced the electromagnetic field and masked the effects of earthquake preparation. Only on 3 March, one day before the earthquake, was there a minor magnetic storm of a 9 h duration (Figure 3, top). Taking into account possible impact of this magnetic storm, in the two lower panels of Figure 3, a comparison is made between the variation  
Figure 2: The ENPEMF variation in VLF band (\(f=7.5\) kHz) in north–south direction before the 4 March 2024 earthquake. The time of the earthquake is indicated with a solid line (_EQ_); two dashed lines mark the period starting 13 days before the earthquake and lasting 3 days after. The counting rate of electromagnetic signals is expressed as the number of pulses per second (p.p.s).  
of the electromagnetic field and the data on the \(Ap\) index of geomagnetic activity; the latter was borrowed from the website [35]. According to this comparison, the increase in the ENPEMF intensity observed on 2 March can not be related to the magnetic storm that caused the rise of the \(Ap\) index only on 3 March.  
Thus, the anomalous rise of ENPEMF intensity in the VLF band (\(f=7.5\,\mathrm{kHz}\)) 13 days up to the earthquake may be an activation sign of its preparation in the lithosphere. Note that the picture of a short-term earthquake precursor in the ENPEMF variation given in [4; 5], which looks like the vanishing of the characteristic diurnal cycle and the emergence of an intensity burst just near the earthquake, does correspond to our data.  
According to [7; 8; 9], if the ratio between the useful signal and the noise is low, a special data processing technique is required to reveal electromagnetic anomalies among the ENPEMF intensity. However, as our present study has shown, in the case of the close location of measuring equipment to the epicenter of the \(M6.1\) earthquake, the application of any additional special methods for extracting the electromagnetic signal of earthquake preparation is not necessarily needed.