Coherence between geodetic and seismic deformation in a context of slow tectonic activity (SW Alps, France)

Walpersdorf, Andréa; Sue, Christian; Baize, Stéphane; Cotte, Nathalie; Bascou, P.; Beauval, Céline; Collard, Philippe; Daniel, Guillaume; Dyer, H.; Grasso, J. R.; Hautecoeur, O.; Helmstetter, Agnès; Hok, Sébastien; Langlais, Mickaël; Ménard, Gilles; Mousavi, Zahra; Ponton, Fleur; Rizza, Magali; Rolland, Lucie; Souami, D.; Thirard, Louise; Vaudey, P.; Voisin, Christophe; Martinod, Joseph

doi:10.1016/j.jog.2015.02.001

Cited by 29 publications

(29 citation statements)

References 40 publications

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“…This strain rate pattern is consistent with that derived from shorter time series of the Spanish continuous sites (Asensio et al, 2012) and campaign GPS data in the Pyrenees, where Rigo et al (2015) estimate a north-south extension of ∼ 2 × 10 −9 yr −1 in the western region but no significant strain in the central and eastern regions. In contrast, our estimation of non-significant strain rates (< 1 × 10 −9 yr −1 ) in the Western Alps does not agree with campaign GPS results in the Briançon region where east-west extension rates of (16 ± 11) × 10 −9 yr −1 are estimated (Walpersdorf et al, 2015). This disagreement may be due to the high spatial wavelength of our solution (∼ 100 km or more), whereas campaign data from Walpersdorf et al (2015) sample a much smaller area (∼ 30 km), and to the fact that we have less sites in Italy in our solution.…”

Section: Velocity Solutioncontrasting

confidence: 99%

“…In contrast, our estimation of non-significant strain rates (< 1 × 10 −9 yr −1 ) in the Western Alps does not agree with campaign GPS results in the Briançon region where east-west extension rates of (16 ± 11) × 10 −9 yr −1 are estimated (Walpersdorf et al, 2015). This disagreement may be due to the high spatial wavelength of our solution (∼ 100 km or more), whereas campaign data from Walpersdorf et al (2015) sample a much smaller area (∼ 30 km), and to the fact that we have less sites in Italy in our solution.…”

Section: Velocity Solutioncontrasting

confidence: 99%

“…Global Positioning System (GPS) data show that central Europe east of the Rhine Graben and north of the Alps behaves rigidly at ∼ 0.4 mm yr −1 and defines a stable European reference frame (e.g., Altamimi et al, 2011;Nocquet and Calais, 2003). To first order, horizontal deformation across the Alps and the Pyrenees is unresolvable at the level of GPS uncertainty, ∼ 0.5 mm yr −1 (Nocquet, 2012;Rigo et al, 2015;Vigny et al, 2002), although recent studies suggest small possible extension in the French Alps (Walpersdorf et al, 2015) and the western Pyrenees (Asensio et al, 2012;Rigo et al, 2015). In contrast, studies of vertical velocities from GPS data indicate significant uplift rates in the Western and Central Alps (up to ∼ 2 mm yr −1 ), decreasing toward the Eastern Alps (Serpelloni et al, 2013).…”

Section: Introductionmentioning

confidence: 99%

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3-D GPS velocity field and its implications on the present-day post-orogenic deformation of the Western Alps and Pyrenees

Nguyen¹,

Vernant²,

Mazzotti³

et al. 2016

Solid Earth

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Abstract. We present a new 3-D GPS velocity solution for 182 sites for the region encompassing the Western Alps, Pyrenees, and southern France. The velocity field is based on a Precise Point Positioning (PPP) solution, to which we apply a common-mode filter, defined by the 26 longest time series, in order to correct for network-wide biases (reference frame, unmodeled large-scale processes, etc.). We show that processing parameters, such as troposphere delay modeling, can lead to systematic velocity variations of 0.1-0.5 mm yr −1 affecting both accuracy and precision, especially for short (< 5 years) time series. A velocity convergence analysis shows that minimum time-series lengths of ∼ 3 and ∼ 5.5 years are required to reach a velocity stability of 0.5 mm yr −1 in the horizontal and vertical components, respectively. On average, horizontal residual velocities show a stability of ∼ 0.2 mm yr −1 in the Western Alps, Pyrenees, and southern France. The only significant horizontal strain rate signal is in the western Pyrenees with up to 4 × 10 −9 yr −1 NNE-SSW extension, whereas no significant strain rates are detected in the Western Alps (< 1 × 10 −9 yr −1 ). In contrast, we identify significant uplift rates up to 2 mm yr −1 in the Western Alps but not in the Pyrenees (0.1 ± 0.2 mm yr −1 ). A correlation between site elevations and fast uplift rates in the northern part of the Western Alps, in the region of the Würmian ice cap, suggests that part of this uplift is induced by postglacial rebound. The very slow uplift rates in the southern Western Alps and in the Pyrenees could be accounted for by erosion-induced rebound.

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Section: Velocity Solutioncontrasting

confidence: 99%

Section: Velocity Solutioncontrasting

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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3-D GPS velocity field and its implications on the present-day post-orogenic deformation of the Western Alps and Pyrenees

Nguyen¹,

Vernant²,

Mazzotti³

et al. 2016

Solid Earth

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“…It also excludes the hypothesis of crustal- or lithospheric-scale collapse of the mountain range29 which would imply crustal thinning and surface lowering, rather than the observed surface uplift. The crustal state of stress within the western Alps is characterized by widespread extension radial to the belt as indicated by normal faults, extensional focal mechanisms, local geodetic studies3031, and extension seen in our GPS solution (Fig. 1b).…”

mentioning

confidence: 74%

Present-day uplift of the western Alps

Nocquet

Sue

Walpersdorf

et al. 2016

Sci Rep

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102

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Collisional mountain belts grow as a consequence of continental plate convergence and eventually disappear under the combined effects of gravitational collapse and erosion. Using a decade of GPS data, we show that the western Alps are currently characterized by zero horizontal velocity boundary conditions, offering the opportunity to investigate orogen evolution at the time of cessation of plate convergence. We find no significant horizontal motion within the belt, but GPS and levelling measurements independently show a regional pattern of uplift reaching ~2.5 mm/yr in the northwestern Alps. Unless a low viscosity crustal root under the northwestern Alps locally enhances the vertical response to surface unloading, the summed effects of isostatic responses to erosion and glaciation explain at most 60% of the observed uplift rates. Rock-uplift rates corrected from transient glacial isostatic adjustment contributions likely exceed erosion rates in the northwestern Alps. In the absence of active convergence, the observed surface uplift must result from deep-seated processes.

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“…The concentration of earthquakes with EW oriented extensional focal mechanisms in the southwestern Alps (suggesting a possible accumulation of present‐day deformation in this zone) motivated the geodetic study of Sue et al (). Remeasurement of the dense local campaign network by Walpersdorf et al () showed EW extension (16 nanostrain/year or 0.5 mm/year across the 30‐km‐wide network) over a measurement interval of 15 years. Thanks to the long observation span, the GPS velocities converged, reaching values below 1 mm/year, indicating geodetic deformation of the same style and amplitude as the seismic deformation recorded over 37 years (Sue, Delacou, Champagnac, Allanic, Burkhard, ).…”

Section: Previous Workmentioning

confidence: 99%

Does Long‐Term GPS in the Western Alps Finally Confirm Earthquake Mechanisms?

et al. 2018

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The availability of GPS survey data spanning 22 years, along with several independent velocity solutions including up to 16 years of permanent GPS data, presents a unique opportunity to search for persistent (and thus reliable) deformation patterns in the Western Alps, which in turn allow a reinterpretation of the active tectonics of this region. While GPS velocities are still too uncertain to be interpreted on an individual basis, the analysis of range-perpendicular GPS velocity profiles clearly highlights zones of extension in the center of the belt (15.3 to 3.1 nanostrain/year from north to south), with shortening in the forelands. The contrasting geodetic deformation pattern is coherent with earthquake focal mechanisms and related strain/stress patterns over the entire Western Alps. The GPS results finally provide a reliable and robust quantification of the regional strain rates. The observed vertical motions of 2.0 to 0.5 mm/year of uplift from north to south in the core of the Western Alps is interpreted to result from buoyancy forces related to postglacial rebound, erosional unloading, and/or viscosity anomalies in the crustal and lithospheric root. Spatial decorrelation between vertical and horizontal (seismicity related) deformation calls for a combination of processes to explain the complex present-day dynamics of the Western Alps.

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Coherence between geodetic and seismic deformation in a context of slow tectonic activity (SW Alps, France)

Cited by 29 publications

References 40 publications

3-D GPS velocity field and its implications on the present-day post-orogenic deformation of the Western Alps and Pyrenees

3-D GPS velocity field and its implications on the present-day post-orogenic deformation of the Western Alps and Pyrenees

Present-day uplift of the western Alps

Does Long‐Term GPS in the Western Alps Finally Confirm Earthquake Mechanisms?

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