This paper discusses problems in predicting the mobility of slow-moving landslides. Three case studies are presented here where research has been carried out by the Utrecht University: The La Valette ...landslide complex in the French Alps, the La Mure landslide in the French pre-Alps near Grenoble and the Hau landslide in Switzerland.
To predict field velocities of these slow-moving landslides the viscosity parameters of the material of these landslides were determined by strain-controlled tests in a ring shear apparatus based on Bishop's design at Utrecht University. The viscosity parameters from the laboratory proved to be 10 to 1000 times lower than viscosities obtained from back analyses on the observed velocities in the field. This discrepancy may be explained by the development of negative pore pressures when the plastic material slides over a rigid, wavy slip surface and/or by convergent flow effects. The associated gain in strength results in a higher apparent viscosity.
A more detailed analysis is made for the movements of the La Valette landslide. Observed velocities at the La Valette landslide are difficult to describe by one parameter set as the response to a change in groundwater level is not the same during a rise or fall in the piezometric level. This deviation may be explained by rapid changes in total stresses and consequently changes in pore pressure under (partly) undrained conditions. The emerging hysteresis with local and temporal variations in pore pressure makes it difficult to predict in detail the moving pattern of landslides.
Terra Nova, 24, 499–504, 2012
The distribution of displacement along faults is a key parameter in various areas of geology such as earthquake studies, three‐dimensional strain restoration, fault ...growth, and reservoir and seal strata relations in hydrocarbon systems. It is essential therefore to understand how local conditions govern displacement distribution. We analyse dip‐parallel displacement profiles of normal faults cutting five alternating limestone and shale layers and we discuss their evolution, from their nucleation to their restriction by lithological interfaces or bed‐parallel faults in clays, or to their further propagation through several layers. Local displacement gradients control the shape of displacement profiles and are highly variable over the course of fault history. Accordingly, the Dmax‐L relation is nonlinear. Bed‐parallel faults prove stronger restrictors than lithological interfaces and the correlation of the local gradient with lithology during restriction and propagation indicates that knowledge of these gradients is required if we are to understand how faults develop in multilayer systems.
A morphometric multivariate and univariate study involving all the three taxa within the Fritillaria tubaeformis complex was carried out. A total of 86 individuals from 8 populations were studied in ...vivo and complemented by the analysis of 116 individuals from herbarium specimens. According to our results, some morphological characters clearly support the separation among F. burnatii, F. tubaeformis and F. moggridgei. Despite this, some morphological overlapping does exist among F. tubaeformis and F. moggridgei, which show contiguous, partially interdigitated, but not overlapping ranges, and we deem more opportune their separation at subspecies level. On the contrary, Fritillaria burnatii is a clearly distinct species, albeit it can occasionally co-occur in the same site with F. tubaeformis subsp. moggridgei. An identification key for both fresh and dry specimens is provided.
In the Western Alps, Oligocene shortening affected a highly heterogeneous European crust with Liassic half‐grabens inherited from the rifting stage and the finite deformation was strongly partitioned ...between the rigid basement and the weak Jurassic sediments. In the Ecrins Massif (Oisans, external crystalline massifs), where the half‐grabens are best exposed and preserved, compressional structures within the basement have to date never been described in details. This massif was shortened under moderate metamorphic conditions (250–350°C and 0.1–0.5 GPa), and the rheological contrast between the basement and the cover is strong. While the sediments are intensely folded, the cover‐basement interface presents apparent open folds underlined by the Lower Triassic layers. The basement itself shows a more localized deformation along several brittle‐ductile shear zones. We here report new evidences of such brittle‐ductile shear zones characterized by anastomosed phyllonitic shear bands rich in phengite and quartz, a low‐strength material where strain has localized. New detailed maps of reverse shear zones, faults, schistosity, and stretching lineations in both the cover and the basement are provided. We show that the Oligocene crustal shortening was mainly E‐W to ENE‐WSW. Local N‐S to NW‐SE shortening occurred and was limited to the eastern border of the Ecrins Massif, around the Penninic Frontal Thrust, which likely was a sinistral transpressive structure in this area. Finally, new balanced cross sections show that these basement shear zones have accommodated more than 50% of the Oligocene crustal shortening.
Key Points
Shortening was mainly accommodated by newly formed brittle‐ductile shear zones
Shortening are mainly E‐W to NE‐SW, NW‐SE shortening is limited around PFT
Amount of shortening is about to 26% ‐ 42 km in the whole external zone
3D field data on mesoscale normal faults were collected to examine the geometries and growth of faults in multilayer systems. Observation and analysis of the fractures include the collection of ...geometric attributes such as fault dips and fault zone thicknesses, detailed mapping in cross-sections and plan views, and the construction of individual and cumulative displacement profiles. Fault zone growth is consistent with a “coherent model” and is strongly influenced by the multilayer system. In the limestone layers, faults grew in several steps, including opening and frictional sliding on 80° dipping segments. Faulting in clay layers was in the form of 40° dipping faults and sub-horizontal faults, the latter being mostly early features developed under the same extensional regime as normal faults and disturbing the fault architecture. The fault zone thickness increases with the limestone thickness and the presence of sub-horizontal faults in clay beds. Numerous connections occur in clay units. The moderate (≈0.08) and low (<0.03) mean displacement gradients in clays and in limestones respectively indicate that the vertical propagation of faults is inhibited in clay layers. Analysis of displacement along fault strike indicates that a 0.08 displacement gradient is associated with the horizontal propagation of fault segments in limestones. According to this value, the fault zones are much longer than expected. It is associated with ‘flat topped’ displacement profiles along some fault segments and connection between segments to form complex fault zones.
► 3D field data on mesoscale faults zones was collected in clay/limestone alternation. ► In multilayer systems, lithology control the fault zone 3D architecture and growth. ► Extensional sub-horizontal faults perturb the fault zone architecture. ► Clay thickness discourage vertical fault propagation.
The early Pleistocene is represented by a succession of glacial–interglacial cycles characterized by a general tendency towards global cooling, with increasing aridity and seasonality. The large deer ...Eucladoceros is found in abundance in Europe during this period of faunal dispersions. The dietary plasticity of Eucladoceros and how it can mirror early Pleistocene climatic variations will be explored here using Dental Microwear Texture Analysis. The wide range of dental microwear textures for Eucladoceros reflects a low selectivity and high plasticity in its diet. It is an appropriate proxy to track vegetal resource availability. Oscillations were identified between a browsing and a grazing signal. This study proposes that a browsing signal is associated with a fossil assemblage deposited during an interglacial event characterized by warmer temperatures and deciduous vegetation. A grazing signal more likely indicates a glacial event with cooler temperatures and a developed herbaceous, bushy layer.
Le Pléistocène inférieur correspond à une succession de cycles glaciaires–interglaciaires caractérisée par une tendance générale au refroidissement global, avec une aridité et une saisonnalité croissantes. Le cervidé de grande taille Eucladoceros est abondant en Europe durant cette période de dispersions fauniques. Grâce à l’analyse de texture de la micro-usure dentaire, nous explorons la plasticité alimentaire d’Eucladoceros et la manière dont celle-ci reflète les variations climatiques du Pléistocène inférieur. La large gamme de textures de micro-usure dentaire d’Eucladoceros reflète sa faible sélectivité et sa forte plasticité alimentaire. De fait, il constitue un outil approprié pour aborder la disponibilité en ressources végétales dans le milieu. Nous identifions des oscillations entre un signal brouteur et un signal paisseur. Nous proposons qu’un signal brouteur soit associé à un assemblage fossile déposé lors d’un évènement interglaciaire caractérisé par des températures plus chaudes et une végétation décidue, tandis qu’un signal paisseur correspondrait plutôt à un évènement glaciaire, avec des températures plus froides et la présence d’une strate herbacée et arbustive développée.
A chemostratigraphic study (δ13C and δ18O) of the Late Cenomanian and Turonian chalk succession from the "Craie 701" Poigny borehole (near Provins in the Paris Basin, France) provides new ...high-resolution stable carbon and oxygen isotope data. Correlation of the bentonite horizons and the isotopic trends from Poigny with its English Chalk equivalent allows the development of a precise stratigraphic framework. δ13C and δ18O variations are synchronous and widespread throughout the European epicontinental seas and Tethyan Ocean. In the Poigny borehole, the Oceanic Anoxic Event 2 (OAE 2) is marked by a large and brief positive excursion of carbon isotopes (a carbon isotope excursions: CIE of 3 ppm amplitude) without any apparent anoxia in the Late Cenomanian Chalk. Comparisons between different key sections on a North-South transect from the Anglo-Paris Basin to the Umbria-Marche Basin (Gubbio Section, Italy) and the Vocontian Basin (South-East France), suggests that the OAE 2 is linked to an increase in marine organic matter production, modulated by a regional effect on the organic carbon burial rate. Thus, the large positive carbon isotope increase spanning the Middle Cenomanian through to the Middle Turonian, including the salient CIE associated with the OAE 2, reflects a global scale increase in marine productivity that would be concomitant with a major long-term sea level rise. The stratigraphic position of the Turonian-Coniacian boundary can also be better defined by this isotopic study. A comparison of δ18O data between the Anglo-Paris Basin and Tethyan Basin shows high-amplitude, long-term synchronous variations reflecting primary paleo-environmental changes which are independent of local facies, sediment thickness and diagenesis. In particular, a negative shift (-1 ppm of amplitude) reflects a warmer climate regime, marking the onset of OAE 2. Two colder phases (+1 ppm amplitude each) occurred in the Early Turonian and the beginning of the Late Turonian.
We present a discontinuous Galerkin method for site effects assessment. The P-SV seismic wave propagation is studied in 2-D space heterogeneous media. The first-order velocity-stress system is ...obtained by assuming that the medium is linear, isotropic and viscoelastic, thus considering intrinsic attenuation. The associated stress-strain relation in the time domain being a convolution, which is numerically intractable, we consider the rheology of a generalized Maxwell body replacing the convolution by a set of differential equations. This results in a velocity-stress system which contains additional equations for the anelastic functions expressing the strain history of the material. Our numerical method, suitable for complex triangular unstructured meshes, is based on centred numerical fluxes and a leap-frog time-discretization. The method is validated through numerical simulations including comparisons with a finite-difference scheme. We study the influence of the geological structures of the Nice basin on the surface ground motion through the comparison of 1-D and 2-D soil response in homogeneous and heterogeneous soil. At last, we compare numerical results with real recording data. The computed multiple-sediment basin response allows to reproduce the shape of the recorded amplification in the basin. This highlights the importance of knowing the lithological structures of a basin, layers properties and interface geometry.
The Aptian–lower Albian succession of the Vocontian Basin (SE France) consists of marine hemipelagic sediments including several black shale horizons. The latter are partly of regional and partly of ...global distribution. This sedimentary succession records the nannoplankton evolution of the Aptian–early Albian interval and thus provides an excellent opportunity to calibrate the calcareous nannofossil record with Tethyan ammonite and planktic foraminiferal biostratigraphy. The calcareous nannofossil biostratigraphy presented in this paper supports previous zonations, but it also provides a much higher resolution and thus improves the correlation of different black shale horizons on a supraregional scale. Up to 23 major (supraregionally significant) and minor (regionally significant) first and last occurrences of calcareous nannofossil taxa are recognized. Nannoconid abundances decrease rapidly in the upper Lower Aptian (nannoconid crisis I, NCI) and in the middle Upper Aptian (nannoconid crisis II, NCII). Both decreases correlate with carbonate–platform drowning events. The upper Lower Aptian interval above the NCI is characterized by high abundances of large specimens of
Assipetra infracretacea and
Rucinolithus terebrodentarius probably of supraregional significance. The uppermost Aptian–Lower Albian is characterized by high abundances of the calcareous nannoplankton taxon
Repagulum parvidentatum, reflecting boreal influence on the Tethyan Realm. This suggests a temporary decrease in surface-water temperatures in the Vocontian Basin.
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