Records of magnetic declination variations on July 30-31, 2025 in Kamchatka

The issue of earthquake effects, including precursors, in the Earth’s magnetic field has been the subject of active investigations by the global scientific community for more than one decade. Nevertheless, there is still no reliable and convincing answer.

Regular monitoring of the Earth’s magnetic field is carried out at Paratunka Complex Geophysical Observatory of IKIR FEB RAS located at Paratunka, Kamchatskiy kray. Magnetic declination variations recorded on July 30-31, 2025 is illustrated in Fig. 1.

Of course, it is easy to attribute the large declination variations with the range of almost 3000 nTl to the strongest over the latest decades earthquake in Kamchatka, which occurred on July 30, 2025 at 11:25 LT and had the magnitude of more than 8. There are similar oscillations of lower amplitude on the graph. They are associated with aftershocks. Here it is, the seismic effect that is the aim of the investigation of many scientists. However, it is not just the way it looks like at first sight.

The obtained record was commented on by the Leading Researcher of IKIR FEB RAS, Cand. Sci. (Phys.-Math.) Khomutov Sergey Yurevich: «Several magnetometers are used at Paratunka Complex Geophysical Observatory. They are operating on different physical principles and implemented in varying hardware configurations. In some of them, the magnetic sensor blocks are fixed on a gimbal unit, i.e. are hung loos, to compensate slow inclination of the magnetometers and their bases. Such a construction makes the magnetometer look like a seismograph. During mechanical oscillations, including those during seismic wave passage, the sensor block begins to swing generating the signals, which on the record are similar to magnetic variations.

In reality, these are just noise with no relation to the natural magnetic field, the aim of our monitoring. There is a dilemma for a magnetologist if he/she should remove this noise, making gaps in measurements, or keep it, making a false signal. Unfortunately, both solutions are bad.

Fig. 2 show a fragment of the end of the record illustrated above. Noise from the earthquakes is removed from it. Data losses are huge. Almost all the record after the main shock should be deleted. Of course, such cases are not frequent. However, other processes, including artificial ones, for example, bursts, heavy machinery passage, strokes near the buildings etc., can cause the effect similar to an earthquake. Moreover, we can see manifestations from strong earthquakes in Japan, Indonesia, Philippines in Paratunka.

Thus, the researchers using «raw» magnetic data should consider critically the effects illustrated above».