Present-day deformation of the Pyrenees revealed by GPS surveying and earthquake focal mechanisms until 2011

Rigo, Alexis; Vernant, Philippe; Feigl, K. L.; Goula, Xavier; Khazaradze, Giorgi; Talaya, J.; Morel, Laurent; Nicolas, Jean‐Marie; Baize, Stéphane; Chéry, Jean; Sylvander, Matthieu

doi:10.1093/gji/ggv052

Cited by 60 publications

(67 citation statements)

References 57 publications

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“…8) shows no significant strain rates above ∼ 1 × 10 −9 yr −1 , except in the western Pyrenees where north-south to northeast-southwest extension is observed up to ∼ 4 × 10 −9 yr −1 , above the formal uncertainty level. 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).…”

Section: Velocity Solutionsupporting

confidence: 89%

“…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 Solutionsupporting

confidence: 89%

Section: Introductionmentioning

confidence: 99%

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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“…While no significant horizontal strain has been resolved in the eastern Pyrenees, GPS data from continuous network stations lead to estimates for extensional strain across the western Pyrenees in NNW-SSE direction, with rates from~2.5 nanostrain per year (Asensio et al, 2012) to~4 nanostrain per year (Nguyen et al, 2016). The results are similar to estimates from campaign data (~2 nanostrain per year, Rigo et al, 2015). Vertical GPS velocities are not resolved (~0.1 ± 0.2 mm/year, Nguyen et al, 2016), although the small value might solely reflect the net effect due to subsidence from gravitation and uplift from erosional denudation.…”

Section: Present-day Deformation and Potential Energysupporting

confidence: 60%

“…Normal faults are active also in central Iberia (Martín et al, 2015), so, in principle, normal faulting beneath the Pyrenean mountain front could be driven by regional stresses and occur despite of, not because of, postorogenic extension of the chain. On the other hand, a dominant role of local stresses is suggested by the alignment between the strike of the chain, strike of normal faulting mechanisms, and stress tensor in the western Pyrenees (σ 2 at N110°E, Rigo et al, 2015), introducing a~25°rotation of the Pyrenean stress field with respect to central Iberia (De Vicente et al, 2008). Comparing the distribution of Pyrenean seismicity to gravitational potential energy density (Figure 3), we appreciate irregular correlation among them.…”

Section: Discussionmentioning

confidence: 91%

Normal Faulting in the 1923 Berdún Earthquake and Postorogenic Extension in the Pyrenees

Stich

Martín

Batlló

et al. 2018

Geophysical Research Letters

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The 10 July 1923 earthquake near Berdún (Spain) is the largest instrumentally recorded event in the Pyrenees. We recover old analog seismograms and use 20 hand‐digitized waveforms for regional moment tensor inversion. We estimate moment magnitude Mw 5.4, centroid depth of 8 km, and a pure normal faulting source with strike parallel to the mountain chain (N292°E), dip of 66° and rake of −88°. The new mechanism fits into the general predominance of normal faulting in the Pyrenees and extension inferred from Global Positioning System data. The unique location of the 1923 earthquake, near the south Pyrenean thrust front, shows that the extensional regime is not confined to the axial zone where high topography and the crustal root are located. Together with seismicity near the northern mountain front, this indicates that gravitational potential energy in the western Pyrenees is not extracted locally but induces a wide distribution of postorogenic deformation.

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“…The active deformation in the Pyrenees is low and mainly characterized by extension (Chevrot et al 2011;Asensio et al 2012;Rigo et al 2015). Pyrenean seismicity is low to moderate with occasional earthquakes of magnitude up to 5.5 (e.g.…”

Section: Seismicity In the Pyreneesmentioning

confidence: 99%

Absolute earthquake locations using 3-D versus 1-D velocity models below a local seismic network: example from the Pyrenees

Theunissen

Chevrot

Sylvander

et al. 2017

Geophysical Journal International

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S U M M A R YLocal seismic networks are usually designed so that earthquakes are located inside them (primary azimuthal gap <<180• ) and close to the seismic stations (0-100 km). With these local or near-regional networks (0• -5 • ), many seismological observatories still routinely locate earthquakes using 1-D velocity models. Moving towards 3-D location algorithms requires robust 3-D velocity models. This work takes advantage of seismic monitoring spanning more than 30 yr in the Pyrenean region. We investigate the influence of a well-designed 3-D model with station corrections including basins structure and the geometry of the Mohorovicic discontinuity on earthquake locations. In the most favourable cases (GAP < 180• and distance to the first station lower than 15 km), results using 1-D velocity models are very similar to 3-D results. The horizontal accuracy in the 1-D case can be higher than in the 3-D case if lateral variations in the structure are not properly resolved. Depth is systematically better resolved in the 3-D model even on the boundaries of the seismic network (GAP > 180• and distance to the first station higher than 15 km). Errors on velocity models and accuracy of absolute earthquake locations are assessed based on a reference data set made of active seismic, quarry blasts and passive temporary experiments. Solutions and uncertainties are estimated using the probabilistic approach of the NonLinLoc (NLLoc) software based on Equal Differential Time. Some updates have been added to NLLoc to better focus on the final solution (outlier exclusion, multiscale grid search, S-phases weighting). Errors in the probabilistic approach are defined to take into account errors on velocity models and on arrival times. The seismicity in the final 3-D catalogue is located with a horizontal uncertainty of about 2.0 ± 1.9 km and a vertical uncertainty of about 3.0 ± 2.0 km.

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Present-day deformation of the Pyrenees revealed by GPS surveying and earthquake focal mechanisms until 2011

Cited by 60 publications

References 57 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

Normal Faulting in the 1923 Berdún Earthquake and Postorogenic Extension in the Pyrenees

Absolute earthquake locations using 3-D versus 1-D velocity models below a local seismic network: example from the Pyrenees

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