Fingerprints of seismic activity in ionospheric electron density variations

In-situ electron density (Ne) observations from Swarm Langmuir Probes can detect ionospheric disturbances originating from lithospheric phenomena like earthquakes or volcano eruptions. Swarm along-track 1D observations provide a large number of very transient inspections of ionosphere located over active places in the lithosphere. The solar and geomagnetic activity, as well as lithosphere-atmosphere-ionosphere coupling (LAIC) can affect Ne signal at different wave periods. The spectral analysis facilitates efficient recognition of ionospheric disturbances at different frequencies. This study applies time-space-frequency analysis by short-term Fourier transform (STFT) to Swarm along-track Ne observations, in the vicinity of tectonic plate boundaries located orthogonally to Swarm orbital footprints. The evolutionary power spectral density (PSD) of residual Ne signals is calculated to find the most sensitive Ne frequencies. The PSD of along-track Ne sampled from selected frequency band is used to create yearly series of Swarm Ne disturbances, which is compared to seismic activity records. The comparisons are made at several selected tectonic junctions. Aside from the seismicity, the solar activity parameters and geomagnetic indices are also reviewed together, and their correlation with Ne is determined. The yearly time spans of Swarm and ancillary observations revealed that PSD of Ne disturbances averaged with several day time window show a significant correlation with seismic activity.