Present‐Day Deformations of the Jura Arc Inferred by GPS Surveying and Earthquake Focal Mechanisms

Abstract

This study presents a compilation of more than 40 years of seismotectonic data, including 54 computed focal mechanisms, combined with 15 years of GPS data coming from a dense network of 35 permanent GPS stations within the Jura arc and its vicinity. These data are compared to previous available geomorphological, geophysical, and structural studies in order to discuss the 3D distribution of the deformation within the Jura arc. GPS data show coherent schemes in terms of velocities and allowed to discriminate between two provinces (NE of the belt and in its front/foreland). They also constrain a low but significant overall strain tensor with a NNW-SSE shortening of 2.16 nanostrain/year associated with an ENE-WSW extension of 0.44 nanostrain/year. The seismotectonic approach is based on a data set of 2,400 events and 54 focal mechanisms. Inversions of the focal mechanisms both globally and in homogeneous sectors highlight a general strike-slip deformation regime, with sigma1 oriented NW-SE and sigma3 oriented NE-SW. We discriminate two different sectors in terms of basement/cover (un)coupling: (1) potentially decoupled deformation between the basement and the sedimentary cover in the NE part; and (2) coupled deformation in the sedimentary cover and its basement in the Jura foreland.

Seismotectonics of southeast France: from the Jura mountains to Corsica

“…N-S normal faults are located, mainly on the external border of the arc and within the Rhine and Bresse grabens and the RBTZ. The Jura massif and the Bresse graben are currently affected by NNW-SSE shortening and strike-slip tectonic regime with the maximum horizontal stressoriented NW-SE [Rabin et al, 2018]. Actually, several studies have highlighted the complexity and variability of the tectonic style in the area according to the present-day coupling/uncoupling between the basement and its sedimentary cover [e.g.…”

“…Actually, several studies have highlighted the complexity and variability of the tectonic style in the area according to the present-day coupling/uncoupling between the basement and its sedimentary cover [e.g. Becker, 2000, Lacombe and Mouthereau, 2002, Madritsch et al, 2008, Rabin et al, 2018.…”

FMHex20: An earthquake focal mechanism database for seismotectonic analyses in metropolitan France and bordering regions

“…• Jura and Upper Rhine Graben: Predominantly strike-slip deformation with a maximum principal stress (s1) oriented NW-SE Rabin et al, 2018).…”

“…As an example of a possible seismotectonic study using complementary datasets such as geodetic data (e.g., Rabin et al, 2018;Walpersdorf et al, 2018), a comparison is shown in Figure 8d with horizontal Global Positioning System (GPS) strain rates. This example corresponds to a strain rate model derived from GPS velocities smoothed over characteristic distances of ca.…”

Seismotectonics in Northeastern France and neighboring regions

“…A total of 216 focal mechanisms (Figure 4) have been used in this study from the new focal mechanism database FMHex20 of RESIF by Mazzotti et al [2021]. For the region under study, the nodal plane parameters have been either determined by Delouis et al [1993], Delacou et al [2004], Vannucci and Gasperini [2004] and Rabin et al [2018], or estimated by the Seismic Observatory of Northeast France at EOST for earthquakes with low magnitude (2.5 to 4.0). The magnitude of these events ranges [Masson et al, 2021].…”