Seismogenic potential of the High Durance Fault constrained by 20 yr of GNSS measurements in the Western European Alps

Mathey, Marguerite; Walpersdorf, Andréa; Sue, Christian; Baize, Stéphane; Déprez, Aline

doi:10.1093/gji/ggaa292

Cited by 15 publications

(17 citation statements)

References 40 publications

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“…Their inversion shows a majority of strike-slip mechanisms, with a pattern of extension localized in the inner part of the chain in the southern Valais area, east of the CPF trace (seismicity cluster and corresponding complex faulting style already described in previous studies; see, e.g. Maurer et al, 1997;Eva et al, 1998;Diehl et al, , 2021. A small extensional zone appears at 10 km depth under the northern Valais seismic zone, encompassed in a major transcurrent signal.…”

Section: Probabilistic Reconstruction Of Tectonic Regimes Throughout the Western Alpssupporting

confidence: 53%

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Present-day geodynamics of the Western Alps: new insights from earthquake mechanisms

et al. 2021

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Abstract. Due to the low to moderate seismicity of the European Western Alps, few focal mechanisms are available in this region to this day, and the corresponding current seismic stress and strain fields remain partly elusive. The development of dense seismic networks in past decades now provides a substantial number of seismic records in the 0–5 magnitude range. The corresponding data, while challenging to handle due to their amount and relative noise, represent a new opportunity to increase the spatial resolution of seismic deformation fields. The aim of this paper is to quantitatively assess the current seismic stress and strain fields within the Western Alps, from a probabilistic standpoint, using new seismotectonic data. The dataset comprises more than 30 000 earthquakes recorded by dense seismic networks between 1989 and 2013 and more than 2200 newly computed focal mechanisms in a consistent manner. The global distribution of P and T axis plunges confirms a majority of transcurrent focal mechanisms in the entire western Alpine realm, combined with pure extension localized in the core of the belt. We inverted this new set of focal mechanisms through several strategies, including a seismotectonic zoning scheme and grid procedure, revealing extensional axes oriented obliquely to the strike of the belt. The Bayesian inversion of this new dataset of focal mechanisms provides a probabilistic continuous map of the style of seismic deformation in the Western Alps. Extension is found to be clustered, instead of continuous, along the backbone of the belt. Robust indications for compression are only observed at the boundary between the Adriatic and Eurasian plates. Short-wavelength spatial variations of the seismic deformation are consistent with surface horizontal Global Navigation Satellite System (GNSS) measurements, as well as with deep lithospheric structures, thereby providing new elements with which to understand the current 3D dynamics of the belt. We interpret the ongoing seismotectonic and kinematic regimes as being controlled by the joint effects of far-field forces – imposed by the anticlockwise rotation of Adria with respect to Europe – and buoyancy forces in the core of the belt, which together explain the short-wavelength patches of extension and marginal compression overprinted on an overall transcurrent tectonic regime.

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Section: Probabilistic Reconstruction Of Tectonic Regimes Throughout the Western Alpssupporting

confidence: 53%

“…From the end of the 1990s onward, seismotectonic studies brought increasing constraints on the current strain and stress states of the Western Alpine realm as a whole (e.g. Maurer et al, 1997;Kastrup et al, 2004;Eva et al, 2020). The progressive development of dense permanent and temporary seismic networks in the Western Alps (e.g.…”

Section: Introductionmentioning

confidence: 99%

Present-day geodynamics of the Western Alps: new insights from earthquake mechanisms

et al. 2021

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“…The horizontal geodetic deformation in the Alps is well correlated with the seismotectonic one in terms of deformation 615 style and of orientations (Figure 11; Walpersdorf et al (2018)). In particular, the extensional tectonics observed in the core of the belt are now generally identified by recent GNSS studies (Masson et al, 2019;Mathey et al, 2020;Sánchez et al, 2018;Walpersdorf et al, 2015).…”

Section: Implications On Alpine Geodynamicsmentioning

confidence: 73%

“…At a larger scale, 260 a majority of the events are indeed located within the Briançonnais or Piémontais seismic arcs, which are characterized by complex parallel fault networks. Within these arcs, some surface fault traces are mapped from field works and could be associated with focal mechanisms at the local scale (for instance the High Durance and East-Briançonnais Faults (Mathey et al, 2020;Sue and Tricart, 2003)). However, due to the large spatial scale of the present study, we did not 265 perform any detailed analysis of focal mechanisms distribution with regard to individual faults.…”

Section: Focal Mechanism Distributionmentioning

confidence: 99%

Present-day geodynamics of the Western Alps: new insights from earthquake mechanisms

Mathey¹,

Sue²,

Pagani³

et al. 2020

Preprint

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Abstract. Due to the low to moderate seismicity of the European Western Alps, few focal mechanisms are available to this day in this region, and the corresponding current seismic stress and strain fields remain partly elusive. The development of dense seismic networks in the past decades now provides a substantial amount of seismic records down to low magnitudes. The corresponding data, while challenging to handle due to their amount and relative noise, represent a new opportunity to increase the spatial resolution of seismic deformation fields. The aim of this paper is to quantitatively assess the current seismic stress and strain fields within the Western Alps, from a probabilistic standpoint, using new seismotectonic data. The dataset comprises more than 30,000 earthquakes recorded by dense seismic networks since 1989 and more than 2200 focal mechanisms newly computed in a consistent manner. The global distribution of P and T axes plunges confirms a majority of transcurrent focal mechanisms in the overall alpine realm, combined with pure extension localized in the core of the belt. We inverted this new set of focal mechanisms through several strategies, including a seismotectonic zoning scheme and grid procedure, revealing extensional axes oriented obliquely to the strike of the belt. The Bayesian inversion of this new dataset of focal mechanisms provides a probabilistic continuous map of the style of seismic deformation in the Western Alps. Extension is found clustered, instead of continuous along the backbone of the belt. Compression is robustly retrieved only in the Po plain, which lays at the limit between the Adriatic and Eurasian plates. High frequency spatial variations of the seismic deformation are consistent with surface horizontal GNSS measurements as well as with deep lithospheric structures, thereby providing new elements to understand the current 3D dynamics of the belt. We interpret the ongoing seismotectonic and kinematic regimes as being controlled by the joint effects of far-field forces –imposed by the counterclockwise rotation of Adria with respect to Europe- and of buoyancy forces in the core of the belt, which together explain the high frequency patches of extension and of marginal compression overprinted on an overall transcurrent tectonic regime.

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“…In the Western Alps, the Penninic frontal thrust, or PFT, represents a major thrust structure at lithospheric scale (e.g. Tardy et al, 1990;Mugnier et al, 1993;Zhao et al, 2015) that accommodated the main collisional phase during the Palaeogene-Neogene (e.g.…”

Section: Introductionmentioning

confidence: 99%

Extensional reactivation of the Penninic frontal thrust 3 Myr ago as evidenced by U–Pb dating on calcite in fault zone cataclasite

et al. 2021

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Abstract. In the Western Alps, the Penninic frontal thrust (PFT) is the main crustal-scale tectonic structure of the belt. This thrust transported the high-pressure metamorphosed internal units over the non-metamorphosed European margin during the Oligocene (34–29 Ma). Following the propagation of the compression toward the European foreland, the PFT was later reactivated as an extensional detachment associated with the development of the High Durance extensional fault system (HDFS). This inversion of tectonic displacement along a major tectonic structure has been widely emphasized as an example of extensional collapse of a thickened collisional orogen. However, the inception age of the extensional inversion remains unconstrained. Here, for the first time, we provide chronological constraints on the extensional motion of an exhumed zone of the PFT by applying U–Pb dating on secondary calcites from a fault zone cataclasite. The calcite cement and veins of the cataclasite formed after the main fault slip event, at 3.6 ± 0.4–3.4 ± 0.6 Ma. Cross-cutting calcite veins featuring the last fault activity are dated at 2.6 ± 0.3–2.3 ± 0.3 Ma. δ13C and δ18O fluid signatures derived from these secondary calcites suggest fluid percolation from deep-seated reservoir at the scale of the Western Alps. Our data provide evidence that the PFT extensional reactivation initiated at least ∼ 3.5 Myr ago with a reactivation phase at ∼ 2.5 Ma. This reactivation may result from the westward propagation of the compressional deformation toward the external Alps, combined with the exhumation of external crystalline massifs. In this context, the exhumation of the dated normal faults is linked to the eastward translation of the HDFS seismogenic zone, in agreement with the present-day seismic activity.

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Seismogenic potential of the High Durance Fault constrained by 20 yr of GNSS measurements in the Western European Alps

Cited by 15 publications

References 40 publications

Present-day geodynamics of the Western Alps: new insights from earthquake mechanisms

Present-day geodynamics of the Western Alps: new insights from earthquake mechanisms

Present-day geodynamics of the Western Alps: new insights from earthquake mechanisms

Extensional reactivation of the Penninic frontal thrust 3 Myr ago as evidenced by U–Pb dating on calcite in fault zone cataclasite

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