2024-05-28
New: list of mass movements now online
Switzerland's highly sensitive seismic network monitors tectonic movements around the clock. Earthquakes though are not the only cause of tremors. Explosions, sonic booms or mass movements such as landslides, rockfalls or mudslides can also be recognised in the seismic recordings once they reach a certain size. Over the past decades, the Swiss Seismological Service (SED) at ETH Zurich has been collecting many such mass movement events and now also publishes this information online in addition to the recorded data on earthquakes and explosions.
It is Sunday, 30 July 2023 in Bisisthal in the canton of Schwyz. Early in the morning, 150,000 cubic metres of rock came loose from the mountain. This was followed by another mass movement in the late afternoon, during which a mass of rock twice as large came crashing down.
Read more...Video recordings document this impressive event, but fortunately, no one was injured. However, the seismic stations also recorded the tremors caused by the landslide, even at distances well over 100 kilometres. In contrast to earthquakes, seismograms of mass movements are comparatively long-lasting and are characterised by a broad distribution of seismic energy. They also lack the clear, impulsive phase arrivals typical of earthquakes. This makes the exact location of a mass movement very uncertain using only the seismic information; it can deviate several kilometres from the true location. However, the origin time of mass movements can be determined to the second.
Only mass movement events that are clearly visible in the seismic data are listed in the newly published SED database. The list of events is therefore incomplete: smaller or slow-moving mass movements or those that occur in areas with poor coverage of the seismic network are not detected. Furthermore, the identification of mass movements is carried out manually, so new events may only be added days after they occur. Some events are externally confirmed and indicated as ‘confirmed’ in the last column of the list. The magnitude is purely indicative and calculated using the scale defined for local Swiss earthquakes. The list of mass movements dates back to 2009 and will continue to be updated.
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