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Natural Local Seismicity

In the historical period of the Earthquake Catalog of Switzerland (250 - 1975), four earthquakes with magnitudes between 3.5 and 4.4 are listed on the northern shore of Lake Geneva, between Versoix and St. Prex. In the Geneva region, about ten earthquakes are listed for the same period. The majority of catalogue entries are based on written testimonies. Therefore, there is a great uncertainty of up to 50 km regarding the exact location of the earthquakes described therein.

The earthquakes in the La Côte region, which have been instrumentally recorded since 1975, are concentrated mainly on the southern shore of Lake Geneva and the Chablais region. To the north of Lake Geneva, earthquakes with magnitudes of 2.5 or greater have occasionally occurred, particularly in the southern part of the Jura. The largest of these earthquakes occurred on 24 May 1995 with a magnitude of 3.6 near Montricher (VD). On August 6, 1995, another earthquake with a magnitude of 3.1 occurred at the same site and was possibly related to the magnitude 3.6 earthquake. Both earthquakes are listed with a source depth between 10 and 12 km. Due to the low station density at the time of the earthquakes, the information is subject to uncertainties. It cannot be ruled out that the earthquakes occurred at shallower depths.

In July 1982, a weak earthquake of magnitude 2.2 occurred near Nyon. On 1 September 2005, a further event of magnitude 2.6 occurred about 5 km west of Nyon, under Lake Geneva. Both earthquakes are listed with source depths of less than 3 km. In the western part of Lake Geneva, a number of other weaker quakes have occurred, which are also assumed to be shallow (depth <= 5km). The uncertainty of the depth determination for all these earthquakes is large, but the character of the seismograms indicates that the earthquakes had shallow sources. Records indicate low natural seismicity in the La Côte region, mainly occurring on near-surface tectonic structures.