On the use of broad-band seismometers to monitor the temporal evolution of magnetic storms; the case of the May 2024 solar storm

During space weather events, electric currents in the magnetosphere and ionosphere induce telluric currents near the Earth’s surface, which in turn generate disturbances of the local magnetic field that perturb the detection systems of broad-band sensors. Seismologist consider this effect as noise masking low frequency seismic waves. However, records of this interference can become an opportunity to study in greater detail the evolution of magnetic events and their effects on Earth.

The May 2024 solar storm, the largest in recent decades, has provided an excellent opportunity to analyze these signals. Thanks to their wide global distribution and their availability through platforms such as EPOS, broad-band seismometers provide extensive coverage of the magnetic signals associated with the solar storm. As an example, more than 310 seismometers have clearly recorded the solar storm in Europe, compared to the few tens of magnetometers available in the Intermagnet network in the same region. This geomagnetic storm has been recorded by broad-band seismometers distributed around the world for a time interval of more than 55 hours. Signals related to magnetic field variations can be identified in seismic data for frequencies below 10 mHz, but are clearer between 1.5 and 5 mHz, the frequency band corresponding to Pc5 magnetic pulsations. In the case of magnetic and seismic signals acquired at close locations, there is an excellent correlation between the seismic records and the time derivative of the magnetic field. The number of seismological stations that detect the signals varies significantly between the various seismic networks analyzed, depending on factors such as the presence of magnetic insulation systems or the bandwidth of the sensor.

Our study shows that the recording of magnetic events in broad-band seismometers can be affected by local effects that modify their amplitude and/or polarity, making a detailed calibration of each seismometer necessary before using seismic data to model the waveforms and amplitudes of the magnetic pulsations. However, broad-band data facilitate the monitoring of the temporal variations of the magnetic field disturbances in a large number of sites around the world, hence providing valuable information to complement data acquired by magnetometers.