Search

Your search keyword '"Steer, Philippe"' showing total 176 results
Start Over Author "Steer, Philippe"
176 results on '"Steer, Philippe"'

1. Characteristics and possible origins of the seismicity in northwestern France

Author

Beucler, Éric, Bonnin, Mickaël, Hourcade, Céline, Van Vliet-Lanoë, Brigitte, Perrin, Clément, Provost, Ludmila, Mocquet, Antoine, Battaglia, Jean, Geoffroy, Laurent, Steer, Philippe, Le Gall, Bernard, Douchain, Jean-Michel, Fligiel, Damien, Gernigon, Pierrick, Delouis, Bertrand, Perrot, Julie, Mazzotti, Stéphane, Mazet-Roux, Gilles, Lambotte, Sophie, Grunberg, Marc, Vergne, Jérôme, Clément, Christophe, Calais, Éric, Deverchère, Jacques, Longuevergne, Laurent, Duperret, Anne, Roques, Clément, Kaci, Tassadit, and Authemayou, Christine

Subjects
Résif-Epos, Brittany, Auvergne, SCR, Magnitude, Detection, Earthquake, Geophysics. Cosmic physics, QC801-809, Chemistry, QD1-999, Geology, QE1-996.5
Abstract

The macroseismic and instrumental observations accumulated by the Bureau Central Sismologique Français and other national agencies over the last 100 years show that the northwestern part of metropolitan France is affected by an apparently diffuse and moderate intraplate seismicity. Far from any plate boundary, well-documented inherited structures, such as the Armorican shear zone network, the Sillon Houiller, and the normal faults related to the Atlantic ocean margin, likely exert significant control on the regional seismicity pattern. However, in the absence of a clearly measurable strain field, processes other than far-field tectonic stress loading such as erosion, gravitational potential energy, and/or hydraulic loadings can co-exist, but their respective influence on the current seismicity is debated and remains to be fully addressed. Reliable detection/location of low-to-moderate magnitude events is one of the most important challenges in the near future to better understand the processes that control this intraplate seismicity. As shown here for a limited region, this issue can be achieved positively, thanks to the new Résif-Epos network, in conjunction with sophisticated algorithms for both earthquakes’ detection and discrimination.

Published
2021
Full Text
View/download PDF

9. Interactions Between Tectonic Deformation and Erosion During the Seismic Cycle in Mountain Ranges

Author

Steer, Philippe, Géosciences Rennes (GR), Université de Rennes (UR)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Rennes (OSUR), Université de Rennes (UR)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 2 (UR2)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 2 (UR2)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Centre National de la Recherche Scientifique (CNRS), and Frédérique Rolandone

Subjects
[SDU.STU.GM]Sciences of the Universe [physics]/Earth Sciences/Geomorphology
Abstract

International audience; The foundations of modern quantitative geomorphology have thus been built around this paradigm of steady-state landscapes responding to progressive changes in climatic or tectonic condition. In ice-free landscapes, the evolution of continental landforms over large time scales is generally described by a competition between tectonic uplift and erosion of rivers and hillslopes. The initiation of co-seismic landslides is generally attributed to the passage of seismic waves, and in particular to the peak ground acceleration associated with volume waves. The volume of landslides is then generally obtained using empirical scaling laws with their area. Co-seismic landslides have a geomorphological impact that goes beyond the co-seismic phase. The principle of a landscape at a steady state, with a balance between the rates of erosion and uplift, needs to be reconsidered due to the amplitude and variability of tectonic and geomorphological processes during the seismic cycle

Published
2022
Full Text
View/download PDF

29. Characteristics and possible origins of the seismicity in northwestern France

Author

Beucler, Éric, primary, Bonnin, Mickaël, additional, Hourcade, Céline, additional, Van Vliet-Lanoë, Brigitte, additional, Perrin, Clément, additional, Provost, Ludmila, additional, Mocquet, Antoine, additional, Battaglia, Jean, additional, Geoffroy, Laurent, additional, Steer, Philippe, additional, Le Gall, Bernard, additional, Douchain, Jean-Michel, additional, Fligiel, Damien, additional, Gernigon, Pierrick, additional, Delouis, Bertrand, additional, Perrot, Julie, additional, Mazzotti, Stéphane, additional, Mazet-Roux, Gilles, additional, Lambotte, Sophie, additional, Grunberg, Marc, additional, Vergne, Jérôme, additional, Clément, Christophe, additional, Calais, Éric, additional, Deverchère, Jacques, additional, Longuevergne, Laurent, additional, Duperret, Anne, additional, Roques, Clément, additional, Kaci, Tassadit, additional, and Authemayou, Christine, additional

Published
2022
Full Text
View/download PDF

37. Modelling the effects of ice transport and sediment sources on the form of detrital thermochronological age probability distributions from glacial settings

Author

Bernard, Maxime, Steer, Philippe, Gallagher, Kerry, Lundbek Egholm, David, Géosciences Rennes (GR), Centre National de la Recherche Scientifique (CNRS)-Observatoire des Sciences de l'Univers de Rennes (OSUR)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES), Aarhus University [Aarhus], Université de Rennes (UR)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Rennes (OSUR), and Université de Rennes (UR)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 2 (UR2)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 2 (UR2)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Centre National de la Recherche Scientifique (CNRS)

Subjects
lcsh:Dynamic and structural geology, lcsh:QE500-639.5, [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry
Abstract

The impact of glaciers on the Quaternary evolution of mountainous landscapes remains controversial. Although in situ or bedrock low-temperature thermochronology offers insights on past rock exhumation and landscape erosion, the method also suffers from potential biases due to the difficulty of sampling bedrock buried under glaciers. Detrital thermochronology attempts to overcome this issue by sampling sediments at e.g. the catchment outlet, a component of which may originate from beneath the ice. However, detrital age distributions not only reflect the catchment exhumation, but also spatially variable patterns and rates of surface erosion and sediment transport. In this study, we use a new version of a glacial landscape evolution model, iSOSIA, to address the effect of erosion and sediment transport by ice on the form of synthetic detrital age distributions. Sediments are tracked as Lagrangian particles formed by bedrock erosion, and their transport is restricted to ice or hillslope processes, neglecting subglacial hydrology, until they are deposited. We base our model on the Tiedemann Glacier (British Columbia, Canada), which has simple morphological characteristics, such as a linear form and no connectivity to large tributary glaciers. Synthetic detrital age distributions are generated by specifying an erosion history, then sampling sediment particles at the frontal moraine of the modelled glacier. Results show that sediment sources, reflecting different processes such as glacier and hillslope erosion, can have distinct bedrock age distribution signatures, and estimating such distributions should help to identify predominant sources in the sampling site. However, discrepancies between the detrital and bedrock age distributions occur due to (i) the selective storage of a large proportion of sediments in small tributary glaciers and in lateral moraines, (ii) the large range of particle transport times due to varying transport lengths and strong variability of glacier ice velocity, (iii) the heterogeneous pattern of erosion, and (iv) the advective nature of glacier sediment transport along ice streamlines. This last factor leads to a poor lateral mixing of particle detrital signatures inside the frontal moraine, and then local sampling of the frontal moraine is likely to reflect local sources upstream. Therefore, sampling randomly across the moraine is preferred for a more representative view of the catchment age distribution. Finally, systematic comparisons between synthetic (U-Th)/He and fission track detrital ages, with different bedrock age-elevation profiles and different relative age uncertainties, show that the nature of the age-elevation relationship and age uncertainties largely control the ability to track sediment sources in the detrital record. However, depending on the erosion pattern spatially, qualitative first-order information may still be extracted from a thermochronological system with high uncertainties (>30 %). Overall, our results demonstrate that detrital age distributions in glaciated catchments are strongly impacted not only by erosion and exhumation but also by sediment transport processes and their spatial variability. However, when combined with bedrock age distributions, detrital thermochronology offers a novel means to constrain the transport pattern and time of sediment particles.

Published
2020
Full Text
View/download PDF

38. Quantifying active deformation within the Southwestern Foothills of Taiwan, from incised fluvial terraces and sedimentary data

Author

Steer, Philippe, lefils, valentine, Simoes, Martine, Shyu, J. Bruce H., Siame, Lionel, Géosciences Rennes (GR), Université de Rennes (UR)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire des Sciences de l'Univers de Rennes (OSUR), Université de Rennes (UR)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 2 (UR2)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 2 (UR2)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Centre National de la Recherche Scientifique (CNRS), Institut de Physique du Globe de Paris (IPGP (UMR_7154)), Institut national des sciences de l'Univers (INSU - CNRS)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), National Taiwan University [Taiwan] (NTU), Centre européen de recherche et d'enseignement des géosciences de l'environnement (CEREGE), Institut de Recherche pour le Développement (IRD)-Aix Marseille Université (AMU)-Collège de France (CdF (institution))-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Centre National de la Recherche Scientifique (CNRS)-Observatoire des Sciences de l'Univers de Rennes (OSUR)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Rennes 1 (UR1), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES), Institut de Physique du Globe de Paris (IPGP), and Institut national des sciences de l'Univers (INSU - CNRS)-IPG PARIS-Université de La Réunion (UR)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)

Subjects
[SDU.STU.GM]Sciences of the Universe [physics]/Earth Sciences/Geomorphology
Abstract

International audience; The Taiwan mountain range stands as one of the most active regions on Earth. With an overall shortening rate of ~40 mm/yr and an average erosion rate of ~4 mm/yr, this mountain range appears ideal to better understand the interactions between tectonics and surface processes, and how these shape active landscapes. Here we explore the geomorphic and sedimentary record of active deformation within the Southwestern Foothills of Taiwan, and we quantify from there the kinematics of active faults. In particular, we investigate the downstream portion of the meandering Tsengwen river - one of the largest rivers of this region - where we identify and correlate remnants of 7 terrace levels, progressively abandoned over the last ~5 kyr. The incision of these terraces is interpreted as being controlled to the first-order by folding and uplift related to underlying active faults. The evolution of the river is reconstructed from correlated terrace remnants, and our results indicate that the overall river sinuosity and gradient did not vary significantly during the past ~5 kyr in response to tectonics. Incremental tectonic uplift is retrieved from terrace incision corrected for sedimentation at the mountain front, and is used to derive the incremental shortening since terrace abandonment. Downstream, within the Coastal Plain, the Tsengwen river reaches its base level and aggrades. Sedimentary facies within boreholes of the Coastal Plain record vertical displacements relative to sea level, spatially consistent with potential blind active faults. When corrected for eustatic variations, these data allow for quantifying tectonic uplift rates within the Coastal Plain over the last ~20 kyr. Taken altogether, our quantitative analysis of the Tsengwen river record, from terrace incision to dowsntream aggradation, reveals that the most frontal active faults absorb a shortening rate of at least ~35 mm/yr, that is most of - if not all - the shortening rate to the absorbed across the whole mountain range.

Published
2020

42. Size, shape and orientation matter: fast and automatic measurement of grain geometries from 3D point clouds.

Author

Steer, Philippe, Guerit, Laure, Lague, Dimitri, Crave, Alain, and Gourdon, Aurélie

Subjects
SEDIMENTS, AQUATIC ecology, GEOMORPHOLOGY, WATERSHEDS, GRAIN size
Abstract

The grain-scale morphology of sediments and their size distribution inform on their transport history, are important factors controlling the efficiency of erosion and transport and control the quality of aquatic ecosystems. In turn, constraining the spatial evolution of the size and shape of grains can offer deep insights on the dynamics of erosion and sediment transport in coastal, hillslope and fluvial environments. However, the size distribution of sediments is generally assessed using insufficiently representative field measurements and determining the grain-scale shape of sediments remains a real challenge in geomorphology. Here we determine the size distribution and grain-scale shape of sediments located in coastal and river environments with a new methodological approach based on the segmentation and geomorphological fitting of 3D point clouds. Point cloud segmentation into individual grains is performed using a watershed algorithm applied here to 3D point clouds. Once the grains are individualized into several sub-clouds, each grain-scale morphology is determined by fitting a 3D geometrical model applied to each sub-cloud. If different geometrical models can be conceived and tested, including cuboids and ellipsoids, this study focuses mostly on ellipsoids. A phase of results checking is then performed to remove grains showing a best-fitting model with a low level of confidence. The main benefits of this automatic and non-destructive method are that it provides access to 1) an un-biased estimate of surface grain-size distribution on a large range of scales, from centimeters to meters; 2) a very large number of data, only limited by the number of grains in the point-cloud dataset; 3) the 3D morphology of grains, in turn allowing to develop new metrics characterizing the size and shape of grains; and 4) the in-situ orientation and organization of grains and grain clusters. The main limit of this method is that it is only able to detect grains with a characteristic size greater than the resolution of the point cloud. [ABSTRACT FROM AUTHOR]

Published
2022
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results