The Saint-Ursanne earthquakes of 2000 revisited: evidence for active shallow thrust-faulting in the Jura fold-and-thrust belt

Abstract The interpretation of seismotectonic processes within the uppermost few kilometers Earth’s crust has proven challenging due to often significant uncertainties in hypocenter locations and focal mechanisms shallow seismicity. Here, we revisit seismic sequence Saint-Ursanne March April 2000 apply advanced seismological analyses reduce these uncertainties. sequence, consisting five earthquakes which largest one reached a local magnitude (M L ) 3.2, occurred vicinity two critical sites, Mont Terri rock laboratory Haute-Sorne, is currently evaluated as possible site for development deep geothermal project. Template matching analysis period 2000–2021, including data from mini arrays installed region since 2014, suggests that source not been persistently active ever since. Forward modelling synthetic waveforms points very source, between 0 1 km depth, mechanism indicates low-angle, NNW-dipping, thrust mechanism. These results combined with geological suggest likely related backthrust fault located sedimentary cover shed new light on hosting lithology kinematics sequence. Together other more recent faulting near Grenchen Neuchâtel north-central portion Jura fold-and-thrust belt (FTB), findings provide insights into present-day FTB northern Switzerland still undergoing seismically contraction at rates < 0.5 mm/yr. depths indications this low-rate NE least partly accommodated possibly decoupled basement.