At locations with more seismic noise, the marine microseismics are increasingly masked by brief interference (e.g. station SGT01, which is very close to St. Gallen), which are usually due to human activity and follow a typical daily pattern. However, strong winds and storms can cause similar interference, too. Man-made interference can be very substantial over very brief periods, e.g. when an aircraft flies past the station, but in most cases it is limited to the local area and only shows up in the recording made by the single, closest station.
With a little luck, seismograms can pick up signals of earthquakes or explosions. Recordings of these events are characterised by a brief increase in amplitude that shows up on seismograms recorded by several stations within a few seconds. Earthquakes and quarry explosions in Switzerland its neighbours can be picked up by these stations and be seen on seismograms, as can more distant earthquakes (so-called 'teleseismic events'). However, filtering tends to prevent most teleseismic events from showing up on seismograms.
Do you think you've spotted an earthquake or explosion on the seismogram? Find out if you were right by checking your suspicion against the list of local earthquakes and global events.