Abstract
The objective of this contribution is to get new insights into the effects of magnetic field variations of natural and anthropogenic origin on broad-band seismic stations. Regarding natural sources of magnetic perturbations, we have investigated if the Sudden Storm Commencements (SSC) cataloged during the 24th solar cycle (2008–2019) can be systematically identified in broad-band seismic stations distributed worldwide. The results show that the 23 SSC events with a mean amplitude above 30 nT and most of those with lower energy but still clearly identified in the magnetometer detection network can be observed at broad-band stations’ network using a simple low-pass filter. Although the preliminary impulse of those signals is usually stronger at stations located at high latitudes, major SSC are observed at seismic stations distributed worldwide. Regarding anthropogenic sources, we focus on the short period seismic signals recorded in urban environments which are correlated with the activity of the railway transportation system. We have analyzed collocated measurements of electric field and seismic signals within Barcelona, evidencing that significant changes in the electric field following the activity of the transportation systems can be attributed to leakage currents transmitted to the soil by trains. During space weather events, electric currents in the magnetosphere and ionosphere experience large variations inducing telluric currents near the Earth surface, which in turn generate a secondary magnetic field. In the case of underground trains, leakage currents are transmitted to the soil, which in turn can result in local variations in the magnetic field. The observed signals in modern seismometers can be related to the reaction of the suspension springs to these magnetic field variations or to the effect of the magnetic field variations on the force transducers used to keep the mass fixed.
Highlights
This contribution presents examples of electromagnetic signals, both from natural and anthropogenic origins, which are recorded regularly by permanent and temporary broad-band seismometers
Different electromagnetic signals of natural and manmade origin can potentially affect the seismic instruments, including magnetic storms, auroral electrojets, lightening during meteorological storms, magnetic fields produced by local supply currents, perturbations due to the passage of moving magnetic or electrical elements or leakage currents associated to transportation systems
We have shown that broad-band seismometers are widely sensitive to variations in the Earth’s magnetic field, both from natural and anthropogenic origins
Summary
This contribution presents examples of electromagnetic signals, both from natural and anthropogenic origins, which are recorded regularly by permanent and temporary broad-band seismometers. Following the arrival of the magnetic perturbations generated by solar storms, the magnetospheric and ionospheric currents experience large variations, which in turn create secondary magnetic fields, that are systematically recorded by magnetometers. These variations produce the so-called Geomagnetic Induced Currents (GIC) in conductors operating at or near the surface of the Earth (e.g., Ngwira et al 2015; Pulkkinen 2015). All major SSC events in the IAGA catalog can be identified in global-scale seismic networks, with a percentage of observations ranging between 10 and 65% of the locations, with a mean value of 48%.
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