Earthquakes in Switzerland and surrounding regions during 2015 and 2016

Abstract

This report summarizes the seismicity in Switzerland and surrounding regions in the years 2017 and 2018. In 2017 and 2018, the Swiss Seismological Service detected and located 1227 and 955 earthquakes in the region under consideration, respectively. The strongest event in the analysed period was the M L 4.6 Urnerboden earthquake, which occurred in the border region of cantons Uri, Glarus and Schwyz on March 6, 2017. The event was the strongest earthquake within Switzerland since the M L 5.0 Vaz earthquake of 1991. Associated ground motions indicating intensity IV were reported in a radius up to about 50 km and locally approached intensity VI in the region close to the epicentre. Derived focal mechanisms and relative hypocentre relocations of the immediate aftershocks image a NNW-SSE striking sinistral strike-slip fault. Together with other past events in this region, the Urnerboden earthquake suggests the existence of a system of sub-parallel strike-slip faults, likely within in the uppermost crystalline basement of the eastern Aar Massif. A vigorous earthquake sequence occurred close to Château-d'Oex in the Préalpes-Romandes region in western Switzerland. With a magnitude of M L 4.3, the strongest earthquake of the sequence occurred on July 1, 2017. Focal mechanism and relative relocations of fore-and aftershocks image a NNE dipping normal fault in about 4 km depth. Two similarly oriented shallow normal-fault events occurred between subalpine Molasse and Préalpes units close to Châtel-St-Denis and St. Silvester in 2017/18. Together, these events indicate a domain of NE-SW oriented extensional to transtensional deformation along the Alpine Front between Lake Geneva in the west and the Fribourg Fault in the east. The structural complexity of the Fribourg Fault is revealed by an M L 2.9 earthquake near Tafers in 2018. The event images a NW-SE striking fault segment within the crystalline basement, which might be related to the Fribourg Fault Zone. Finally, the M L 2.8 Grenchen earthquake of 2017 provides a rare example of shallow thrust faulting along the Jura fold-and-thrust belt, indicating contraction in the northwestern Alpine foreland of Switzerland.

Cockade structures as a paleo-earthquake proxy in upper crustal hydrothermal systems

“…Many smaller cockade examples exist, which would require smaller but more frequent magnitudes. These values are identical to those recently found in active hydrothermal systems of the Valais region 47 . Last but not least, domains of fresh cockades with their grain-supported framework, enhanced porosity and limited cementation by immobile and geopetal cements should sustain a high permeability.…”

A Consistent High‐Resolution Catalog of Induced Seismicity in Basel Based on Matched Filter Detection and Tailored Post‐Processing

“…For the period from mid‐2010 to mid‐2012, no events were previously reported, but our results show that the sequence was indeed still active at a very low level (on average ∼11 events per month). In 2012, however, almost 6 years after the injection, seismicity suddenly increased again with magnitudes up to (Wiemer et al, ; Diehl et al, ) and continued to occur preferentially in episodic sequences until 2018.…”

“…In the same month, a M L 1.2 occurred (Diehl et al, ; Deichmann et al, ). Since then, the SED registered an increase in seismicity, with magnitudes up to M L 1.9 (October 2016; Diehl et al, ). Due to the change in seismic monitoring from 2012 onward, the currently existing catalogs do not cover the life span of the induced sequence consistently in terms of detection sensitivity, magnitudes, and locations.…”

Cenozoic Tectonic Deformation Along the Pontarlier Strike‐Slip Fault Zone (Swiss and French Jura Fold‐and‐Thrust Belt): Insights From Paleostress and Geomorphic Analyses

“…Though most of the deformation in the JFTB is linked to the thin‐skinned development, recent deformation postdating the main stage of the Jura folding and thrusting, possibly since 4 Ma, has been linked to reactivation of inherited basement faults, hence suggesting a thick‐skinned style of deformation (Giamboni et al., 2004; Lacombe & Bellahsen, 2016; Lacombe & Mouthereau, 2002; Madritsch et al., 2008, 2010; Meyer et al., 1994; Mosar, 1999; Ustaszewski & Schmid, 2006). Although the latter is corroborated by seismicity in the basement (Baer, Deichmann, Braunmiller, Husen, et al., 2005; Diehl, Deichmann, et al., 2015), it cannot be excluded that thin‐skinned deformation continues to the present as indicated by the occurrence of significant seismic activity in the detached cover series of the whole alpine foreland (e.g., Abednego et al., 2017; Courboulex et al., 1999; Thouvenot et al., 1998; Vouillamoz, et al., 2016, 2017) and specifically in the JFTB (Diehl, Clinton, et al., 2021).…”