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1.
F. Nguyen G. Van Rompaey H. Teerlynck M. Van Camp D. Jongmans T. Camelbeeck 《Journal of Seismology》2004,8(1):41-56
To provide quantitative information on site effects in the northern part of Belgium, forty-seven H/V microtremor measurements were performed with 5 second seismometers over an area of about 15.000 km2. Most of the results show a northward regular increase of the fundamental period in agreement with the augmentation of the Mesozoic and Cainozoic soft sedimentsthickness from a few meters 40 km south of Brussels to 900 m at the Netherlands-Belgium border. The measured resonance frequency values wereconsistent with theoretical computations performed at different sites onthe basis of existing information and shallow seismic experiments. At oneparticular site (Uccle) where borehole data were available, microtremor measurements using an array of four seismological stations with differentapertures allowed to obtain the low frequency part of the Rayleigh wave dispersion curve, extending the range covered by the analysis of surfacewaves artificially generated. The Vs profile derived from the surface waveinversion corroborates the 1 Hz natural frequency of the site. Comparison of these results with the macroseismic information concerning the MS = 5.0 1938 earthquake which occurred 50 km west of Brussels,confirmed the hypothesis that the geological structure of the Brabant massifis likely to control damage distribution during such an earthquake. Comparisonbetween the intensity map of the 1938 earthquake and the resonance period ofsediments obtained by our microtremor study shows a clear relation betweenthe two parameters. During the 1938 earthquake, site effects played a prominent role due to the dimension of the source whose corner frequency wasabout 1 Hz. 相似文献
2.
Image processing of 2D resistivity data for imaging faults 总被引：6，自引：0，他引：6
F. Nguyen S. Garambois D. Jongmans E. Pirard M.H. Loke 《Journal of Applied Geophysics》2005,57(4):260-277
A methodology to locate automatically limits or boundaries between different geological bodies in 2D electrical tomography is proposed, using a crest line extraction process in gradient images. This method is applied on several synthetic models and on field data set acquired on three experimental sites during the European project PALEOSIS where trenches were dug. The results presented in this work are valid for electrical tomographies data collected with a Wenner-alpha array and computed with an l1 norm (blocky inversion) as optimization method. For the synthetic cases, three geometric contexts are modelled: a vertical and a dipping fault juxtaposing two different geological formations and a step-like structure. A superficial layer can cover each geological structure. In these three situations, the method locates the synthetic faults and layer boundaries, and determines fault displacement but with several limitations. The estimated fault positions correlate exactly with the synthetic ones if a conductive (or no superficial) layer overlies the studied structure. When a resistive layer with a thickness of 6 m covers the model, faults are positioned with a maximum error of 1 m. Moreover, when a resistive and/or a thick top layer is present, the resolution significantly decreases for the fault displacement estimation (error up to 150%). The tests with the synthetic models for surveys using the Wenner-alpha array indicate that the proposed methodology is best suited to vertical and horizontal contacts. Application of the methodology to real data sets shows that a lateral resistivity contrast of 1:5–1:10 leads to exact faults location. A fault contact with a resistivity contrast of 1:0.75 and overlaid by a resistive layer with a thickness of 1 m gives an error location ranging from 1 to 3 m. Moreover, no result is obtained for a contact with very low contrasts (1:0.85) overlaid by a resistive soil. The method shows poor results when vertical gradients are greater than horizontal ones. This kind of image processing technique should be systematically used for improving the objectiveness of tomography interpretation when looking for limits between geological objects. 相似文献
3.
Morphology,structure and kinematics of a rainfall controlled slow‐moving Andean landslide,Peru 
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下载免费PDF全文 Swann Zerathe Pascal Lacroix Denis Jongmans Jersy Marino Edu Taipe Marc Wathelet Walter Pari Lionel Fidel Smoll Edmundo Norabuena Bertrand Guillier Lucile Tatard 《地球表面变化过程与地形》2016,41(11):1477-1493
The large slow‐moving landslide of Maca is located in the upper Colca valley (southern Peru), a region characterized by a well pronounced rainy period, and intense and recurrent sustained seismicity. The landslide, developed in deep lacustrine deposits, has recently accelerated, threatening the Maca village. This work aims at understanding the rupture mechanism and the causes of the recent landslide reactivation/acceleration. We present a multidisciplinary characterization of the Maca landslide that includes: (i) geological and morphological mapping in the field; (ii) remote sensing analysis using an historical aerial photograph of 1955 and the Pléiades satellite images (2013); (iii) global positioning system (GPS) including time‐series of surveys over 13 years, and continuous measurements over 14 months; (iv) a geophysical campaign with deep electrical resistivity tomography profiles acquired across the landslide mass. Our study shows that this 60 Mm3 landslide, which can be classified as a clay/silt compound landslide, moved by 15 m between 2001 and 2014 with a large inter‐annual velocity variation (up to a factor of 500) depending on the rainfall intensity. We suggest that these dramatic changes in velocity are the result of the combination of a threshold mechanism and the short intense rainy season in Peru. This study reveals three main driving factors acting at different timescales: (i) over several decades, the river course has significantly changed, causing the Maca landslide reactivation in the 1980s due to the erosion of its toe; (ii) at the year scale, a minimum amount of rainfall is required to trigger the motion and this amount controls the landslide velocity; (iii) transient changes in slide velocity may occur anytime due to earthquakes. This study particularly highlights the non‐linear behaviour of the motion with rainfall. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
4.
Geophysical characterization of the lithological control on the kinematic pattern in a large clayey landslide (Avignonet,French Alps) 总被引：2，自引：1，他引：1
Grégory Bièvre Denis Jongmans David Goutaland Erwan Pathier Vilma Zumbo 《Landslides》2016,13(3):423-436
Lithology variation is known to have a major control on landslide kinematics, but this effect may remain unnoticed due to low spatial coverage during investigation. The large clayey Avignonet landslide (French Alps) has been widely studied for more than 35 years. Displacement measurements at 38 geodetic stations over the landslide showed that the slide surface velocity dramatically increases below an elevation of about 700 m and that the more active zones are located at the bottom and the south of the landslide. Most of the geotechnical investigation was carried out in the southern part of the landslide where housing development occurred on lacustrine clay layers. In this study, new electrical prospecting all across the unstable area revealed the unexpected presence of a thick resistive layer covering the more elevated area and overlying the laminated clays, which is interpreted as the lower part of moraine deposits. The downslope lithological boundary of this layer was found at around 700 m asl. This boundary coincides with the observed changes in slide velocity and in surface roughness values computed from a LiDAR DTM acquired in 2006. This thick permeable upper layer constitutes a water reservoir, which is likely to influence the hydromechanical mechanism of the landslide. The study suggests a major control of vertical lithological variations on the landslide kinematics, which is highlighted by the relation between slide velocity and electrical resistivity. 相似文献
5.
Olivier Le Roux Stéphane Schwartz Jean François Gamond Denis Jongmans Pierre Tricart Michel Sebrier 《International Journal of Earth Sciences》2010,99(2):427-441
In the Belledonne massif, the steep Paleozoic Belledonne Middle Fault (BMF) separates micaschists, displaying numerous landslides,
from amphibolites. The massif is incised by the lower Romanche river valley. When crossing the BMF, the valley widens into
a lozenge-shaped basin recently interpreted as an active pull-apart type structure associated with a major N110 striking Quaternary
fault. Multidisciplinary investigations were carried out in the basin to check if this model has implications on the seismic
and landslide hazard assessment. This study demonstrated the existence of a N80 sinistral strike slip Séchilienne Fault Zone
(SFZ). This fault zone is suspected to offset the BMF by 375 m across the basin. Geophysical experiments revealed that the
bedrock depth increases strongly in the basin, up to 350 m. Our study invalidates the active pull-apart origin of the basin
and suggests it results from Quaternary glacial and fluvial erosion processes, magnified by the intersection of two inherited
structures, the BMF and the SFZ. 相似文献
6.
Geologie en Mijnbouw - 相似文献
7.
D. Jongmans D. Demanet C. Horrent M. Campillo F.J. Sanchez-Sesma 《Soil Dynamics and Earthquake Engineering》1996,15(8):549-559
Seismic experiments were conducted in Mexico City in order to determine the dynamic characteristics of the soft clay layer present at the surface in the lake bed zone. In-situ measurements of Vp, Vs, Qp and Qs were performed in the Texcoco lake area. Qs values ranging from 8 to 60 have been found from the surface down to 30 m depth, while Vs values are between 30 and 115 m/s for the same depths. These relatively low Q values support the idea that surface waves generated at the edges of the Mexico basin cannot propagate very far in the structure. During this study, the elastic characteristics of the surficial basalt layers outcropping in the hill zone have also been investigated. Very low P-wave velocity values (500–800 m/s) have been found in the basalt. In the hill zone where basalts are interbedded with soil, numerical modeling has shown that such low values can only be partially explained by the relation between wavelength and basalt thickness and that other mechanisms, like fracturation, must be involved. 相似文献
8.
Initiation of earthquake-induced slope failure: influence of topographical and other site specific amplification effects 总被引：2，自引：0，他引：2
Increased structural damage caused byearthquakes on hilltops and along ridgeshas often been related to amplification ofground motion due to the presence oftopography. However, comparison betweenobservations and numerical modeling hasshown that amplification is only partlydependent on the prominent surfacemorphology. Strong effects are also inducedby soft layers, such as weathered rockmaterial or colluvium, covering thetopographies.Numerous seismically triggered landslidesare reported to occur in the same materialsthat are likely to amplify ground motions.Therefore, it can be suspected that groundmotion dynamics significantly contribute tothe observed slopes failures. Thispotential relationship is the subject ofthe present case study, the Ananevorockslide in the northeastern Tien Shanmountains. The survey included geophysicalprospecting, earthquake recordings andstructural analyses of the rock fabric. Onthe basis of the field data, observedamplification effects could be related tothe local geological conditions andparticularly to the surface morphology andto the presence of low-velocity layers –deeply weathered rocks – on the top of thebedrock. Surface layer- andtopography-dependent amplification has alsobeen studied numerically by 2D and 3Dfinite element modeling of ground motiondynamics. The present paper focuses onadditional effects that may be induced bythe presence of a fault zone and of thelandslide scarp. Further, observed andcomputed ground motion dynamics areconnected with slope failuresusceptibility: 2D numerical simulationsreveal that strain localization is closelyrelated to wave amplification in surficiallow-velocity layers, particularly belowconvex surface morphologies. 相似文献
9.
H.-B. Havevith D. Jongmans K. Abdrakhmatov P. Trefois D. Delvaux I.A. Torgoev 《Surveys in Geophysics》2000,21(4):351-370
In summer 1998, a geophysical survey including seismic profilesand electrical tomography has been carried out in the Suusamyr valley, Kyrgyzstan. The scope wasto investigate surface effects induced by the Ms = 7.3 Suusamyr earthquake, the 19th of August, 1992. Inthis paper, special attention is paid to the case study of a debris slide triggered by the earthquake.Seismic data are analysed by P-wave refraction technique and by surface wave inversion. Electrical tomographicprofiles are processed by 2D-inversion.Using geotechnical and geological information, P-velocity modelsand resistivity sections are interpreted in terms of geological materials, in order to build a geological3D model. On the basis of the latter, we carried out static finite element computations as well as staticand pseudo-static calculations with Janbus method. Newmark displacement was computed, considering or notthe influence of the shallow soft deposits. The results are compared to the real displacementobserved in the field and conclusions are drawn about the mechanism of the landslide. 相似文献
10.
Fiolleau Sylvain Jongmans Denis Bièvre Gregory Chambon Guillaume Lacroix Pascal Helmstetter Agnès Wathelet Marc Demierre Michel 《Landslides》2021,18(6):1981-2000
Landslides - The mass transfer mechanisms in landslides are complex to monitor because of their suddenness and spatial coverage. The active clayey Harmalière landslide, located 30 km south of... 相似文献