On 22/3/2020 at 05:24:02 UTC, an earthquake with magnitude M 5.4 (EMSC-CSEM data) occurred in Zagreb (Croatia). The seismic signal produced by this earthquake was distinctly detected by the stations of the Cornegliano Stoccaggio seismic network, which is located approximately 500 km from the epicentre. Below, we show as an example the seismograms (daily traces in helicorder form) recorded at the OL02 station, displayed with two different filters, to emphasize high frequencies (above 1 Hz) and low frequencies (below 1 Hz). For strong events that take place at great distances, such as the one in Zagreb, low-frequency energy dominates the seismograms. In the graphs, in addition to the main event, the next event is recognized (also called an aftershock) with M 5.0 at 06:01:20 UTC.

Daily tracks (vertical component) recorded on 22/3/2020 at the OL02 station, filtered with a high-pass filter at a minimum frequency of 1 Hz. This is also the representation adopted for the display of seismograms in real time.

Daily tracks (vertical component) recorded on 22/3/2020 at the OL02 station, filtered with a low-pass filter at a maximum frequency of 1 Hz.