Characteristics and possible origins of the seismicity in northwestern France

Beucler, É.; Bonnin, Mickaël; Hourcade, Céline; Vliët-Lanoé, Brigitte van; Perrin, C.; Provost, Ludmila; Mocquet, A.; Battaglia, Jean; Geoffroy, Laurent; Steer, Philippe; Gall, Bernard Le; Douchain, Jean-Michel; Fligiel, Damien; Gernigon, Pierrick; Delouis, Bertrand; Perrot, Julie; Mazzotti, S.; Mazet‐Roux, Gilles; Lambotte, Sophie; Grunberg, Marc; Vergne, J.; Clément, C.; Calais, Éric; Déverchère, Jacques; Longuevergne, Laurent; Duperret, Anne; Roques, Clément; Kaci, Tassadit; Authémayou, Christine

doi:10.5802/crgeos.86

Cited by 8 publications

(7 citation statements)

References 85 publications

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“…1). Its Meso-Cenozoic geological history is marked by minor fault reactivations associated with far-field tectonic events (e.g., North Atlantic Ocean opening, Pyrenean orogeny, …), up to the presentday moderate background seismicity indicating small ongoing deformation (Beucler et al, 2021). Overall, the Armorican Massif geology consists primarily of Proterozoic and Paleozoic crystalline basement and metasediment formations, with limited remnants of Meso-Cenozoic sedimentary deposits.…”

Section: Geological and Geomorphological Settingmentioning

confidence: 99%

Late Pleistocene – Holocene denudation, uplift, and morphology evolution of the Armorican Massif (western Europe)

Malcles,

Mazzotti,

Vernant

et al. 2023

Preprint

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Abstract. Elevated Plio-Pleistocene coastal and marine markers in stable continental regions are commonly explained by a combination of eustatic sea-level variations and regional geodynamics (e.g., mantle dynamics, active faults). In this study, we test the role of erosion rates on the Late Pleistocene uplift and landform evolution of the Armorican Massif, western France. Denudation rates are estimated for 19 drainage basins using terrestrial cosmogenic nuclide (10Be) measurements in quartz. They range between 3 and 34 m.Ma-1, with a factor of two difference between the western highland region and the central lowland region (16 ± 8 m.Ma-1 vs. 9 ± 6 m.Ma-1). Assuming a thin elastic plate model, the lithosphere flexural isostatic response to these denudation rates produces an overall uplift of the Armorican Peninsula from 12 – 15 m.Ma-1 in the central lowland region to 4 – 10 m.Ma-1 in the western peninsula and along the coastline. We show that these erosion-driven uplift rates can explain the uplifted Late Pleistocene marine terraces along the Armorican Peninsula coastline as well as the elevated Quaternary marine deposits in the central lowland region, without necessitating additional geodynamic processes such as regional compression or local active faults. Our results suggest that, in stable continental regions, long-term erosion should be taken into account as a driver of uplift and deformation before trying to derive global or regional geodynamic or tectonic conclusions.

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Section: Geological and Geomorphological Settingmentioning

confidence: 99%

Late Pleistocene – Holocene denudation, uplift, and morphology evolution of the Armorican Massif (western Europe)

Malcles,

Mazzotti,

Vernant

et al. 2023

Preprint

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“…The current seismicity is low in Normandy but a little higher offshore, along the faults of the graben system of the English Channel and along the Armorican shear zones, particularly the southern ones. Today, the seismicity never exceeds Mw 6 (Sisfrance BRGM-EDF-IRSN/SisFranc, 2010; SHARE, 2013; see the synthesis in the work of Beucler et al (2021)).…”

Section: Introductionmentioning

confidence: 99%

Neogene and Pleistocene geodynamics: the paleoseismic evolution of Armorica (Western France)

Van Vliet-Lanoë,

Authemayou,

Le Roy

et al. 2024

Front. Earth Sci.

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The evolution of the passive Armorican margin (Western France) during the Neogene and Quaternary was analyzed using field data. The morphology of the margin attests to a late Hercynian shaping, further deformation during the Mesozoic mid-Atlantic opening, during the Alpine Orogeny, and ultimately, a Late Cenozoic uplift, mostly related to an onshore isostatic accommodation in response to erosion and limited tectonic activity. A very limited strike–slip dynamic, with very low seismicity, accommodated the Neogene–Pleistocene N170 strains around the rigid Armorican terrane. The South Armorican domain and English Channel floor include shear zones that adjusted the Alpine convergence, facilitating its transpressive slip to the west. The Permo-Triassic N150 faults were reactivated during the inversion phases that began after the Bartonian under the distal control of the Alpine convergence and the decrease in the Atlantic spreading rate after 34 Ma. The Armorican marine platforms were stable after the late Eocene and slightly subsident, experiencing pulsed episodes of transient lithospheric doming during the Neogene and Quaternary. Co-seismic activity onshore without surface rupture was recorded around ∼5.3 Ma, ∼3.7 Ma, ∼2.4–1.2 Ma, and ∼400–250 ka, in tandem with an inland exhumation driven by isostatic adjustment due to an intensification of periglacial erosion at the onset of the early interstadials or by agriculture. Low-magnitude and ubiquitous shallow seismic activities seem to be related today to an isostatic uplifted old brittle–ductile transition due to the accumulation of shearing strain.

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“…Denser seismic station networks and high sensitivity modern instruments improve our understanding of global and local seismicity over the last decade (e.g. Levandowski et al 2018;Beucler et al 2021). As an illustration of the evolution of the seismic data volume, the size of the IRIS DMC (Incorporated Research Institutions for Seismology Data Management Center) archive has grown from 25 terabytes (TB) in 2005 January to 800 TB in 2022 January.…”

mentioning

confidence: 99%

“…In metropolitan France, instrumental seismicity is mostly characterized by low magnitude earthquakes (Cara et al 2015). The deployment of new permanent stations since mid-2018 (Beucler et al 2021;Doubre et al 2021;Larroque et al 2021;Sylvander et al 2021) has conducted to an increase in the number of detected natural and anthropogenic seismic events. However, metropolitan seismicity is now dominated by the detection of anthropogenic events (for instance, see fig.…”

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confidence: 99%

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New CNN-based tool to discriminate anthropogenic from natural low magnitude seismic events

Hourcade

Bonnin

Beucler

2022

Geophysical Journal International

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Summary With the deployment of high quality and dense permanent seismic networks over the last 15 years comes a dramatic increase of data to process. In order to lower the threshold value of magnitudes in a catalogue as much as possible, the issue of discrimination between natural and anthropogenic events is becoming increasingly important. To achieve this discrimination, we propose the use of a convolutional neural network (CNN) trained from spectrograms. We built a database of labeled events detected in metropolitan France between 2020 and 2021 and trained a CNN with three-component 60 s spectrograms ranging frequencies from 1 to 50 Hz. By applying our trained model on independent French data, we reach an accuracy of 98.2 per cent. In order to show the versatility of the approach, this trained model is also applied on different geographical areas, a post-seismic campaign from NW France and data from Utah, and reaches an accuracy of 100.0 per cent and 96.7 per cent respectively. These tests tend to hypothesise that some features due to explosions compared to earthquakes are widely shared in different geographical places. In a first approach, we propose that it can be due to a contrast in the energy balance between natural and anthopogenic events. Earthquake seismic energies seem to be more continuous as a function of frequency (vertical bands features in a spectrogram) and conversely for explosions (horizontal strips).

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Characteristics and possible origins of the seismicity in northwestern France

Cited by 8 publications

References 85 publications

Late Pleistocene – Holocene denudation, uplift, and morphology evolution of the Armorican Massif (western Europe)

Late Pleistocene – Holocene denudation, uplift, and morphology evolution of the Armorican Massif (western Europe)

Neogene and Pleistocene geodynamics: the paleoseismic evolution of Armorica (Western France)

New CNN-based tool to discriminate anthropogenic from natural low magnitude seismic events

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