tectonic controls on a large landslide complex williams fork mountains near dillon colorado abstract an extensive 25 km2 landslide complex covers a large area on the west side of the williams fork mountains in central colorado the complex is deeply weathered and incised and in most places geomorphic evidence of sliding breakaways hummocky topography transverse ridges and lobate distal zones are no longer visible indicating that the main mass of the slide has long been inactive however localized holocene reactivation of the landslide deposits is common above the timberline at about 3300 m and locally at lower elevations clasts within the complex as long as several tens of meters are entirely of crystalline basement proterozoic gneiss and granitic rocks from the hanging wall of the laramide late cretaceous to early tertiary west directed williams range thrust which forms the western structural boundary of the colorado front range late cretaceous shale and sandstone compose most footwall rocks the crystalline hanging wall rocks are pervasively fractured or shattered and alteration to clay minerals is locally well developed sackung structures trenches or small scale grabens and upslope facing scarps are common near the rounded crest of the range suggesting gravitational spreading of the fractured rocks and oversteepening of the mountain flanks late tertiary and quaternary incision of the blue river valley just west of the williams fork mountains contributed to the oversteepening major landslide movement is suspected during periods of deglaciation when abundant meltwater increased pore water pressure in bedrock fractures a fault flexure model for the development of the widespread fracturing and weakening of the proterozoic basement proposes that the surface of the williams range thrust contains a concave downward flexure the axis of which coincides approximately with the contact in the footwall between proterozoic basement and mostly cretaceous rocks movement of brittle hanging wall rocks through the flexure during laramide deformation pervasively fractured the hanging wall rocks

analysis of massif fracturing during deep seated gravitational slope deformation by physical and numerical modeling abstract both 3 d physical modeling and 2 d numerical modeling were used to analyze the development of deep seated gravitational slope deformations we focused especially on the link between fracturing and morphological features such as sagging sackung physical modeling was performed by using properly scaled analogue materials as well as an original vertical accelerator device this device enables cyclic loading of the model and to advance step by step in the deformation process this technique is thus particularly well suited to analyze rupture initiation and evolution surface deformation is registered with a high resolution digital camera internal model deformation was studied by making cross sections at different experiment stages the failure of one or both mountain sides was observed with a deep seated failure zone that follows an almost circular trajectory it intersects the surface perpendicularly in the upper part other fractures are generated in the moving mass in response to its motion fracture network becomes wider and morphological features such as counterscarps are generated numerical models were performed with a 2 d finite element code named adeli we tried to reproduce physical modeling results by using the same mechanical behaviour and parameters of the analogue material the results reproduced failure initiation well but poorly described moving mass deformation furthermore rupture initiation in the 2 d numerical models occurs more easily e g for a lower acceleration value than in the 3 d physical models confirming the importance of the three dimensional analysis

relations between interrill erosion processes and sediment particle size distribution in a semiarid mediterranean area of se of spain abstract erosion and sediment characteristics were measured using simulated rainfall on two cultivated soils of contrasting lithology quaternary calcareous colluvium and tertiary marls in a semiarid mediterranean area of se spain two rainfall intensities high 56 0 2 4 mm h 1 and medium 31 4 1 4 mm h 1 were used in order to know the mechanisms involved in each selected condition for each simulated event runoff and sediment were sampled at 1 min intervals on a 1 m wide by 2 m long erosion plot the erosion rate was calculated as the total amount of soil lost divided by the time period of the test the duration of the test was that needed to reach steady state runoff an average time of 24 5 min for quaternary calcareous colluvium and 17 7 min for tertiary marls the size distribution of the transported sediment in the field effective size distribution was compared with equivalent measurements of the same samples after chemical and mechanical dispersion ultimate size distribution to investigate the detachment and transport mechanisms involved in sediment mobilisation the results showed that the soil type determined the hydrological response regardless of the rainfall intensity the erosional response was however determined by the rainfall and soil surface characteristics in quaternary calcareous colluvial soils the predominant erosion process depended on the rainfall intensity with a prevailing detachment limited condition in high intensity events and prevailing transport limited conditions in those events of medium intensity these differences in the main erosion processes were reflected in the size of the transported material and in the change in sediment size within the storm thus a time dependent size distribution of the eroded material decreasing coarse fractions and increasing fine fractions with runoff time was observed for high intensity events in medium intensity events on the other hand the time independent size distribution of the eroded material indicated transport limited erosion due to the rapid surface crusting on the tertiary marl soil no differences in the main erosion processes or in the sediment size distribution occurred for the different rainfall intensities tested the erosion of marl soils was determined mainly by the limited quantity of available sediment the effective size of material was a more sensitive parameter than the ultimate size of the sediment to study the way in which the sediment was transported

the acheron dorsum on mars a novel interpretation of its linear depressions and a model for its evolution abstract the acheron dorsum north of olympus mons on mars is a unique 800 km long arcuate ridge apparently unrelated to other adjacent morphologies acheron dorsum is crossed by deep and wide fractures fossae here referred to also as linear depressions or lds commonly interpreted as grabens formed by local lithosphere stress in response to endogenous mantle upwelling we suggest an alternate view that the linear depressions may result from gravitational self adjustment of a loose deposit similar to the deep seated gravitational slope deformations dsgsd or sackung a kind of slow mass movement well documented on earth numerical simulations based on a finite difference numerical model devised for terrestrial dsgsds reproduce the timing and position of lds reasonably well provided that the viscosity of the viscoplastic layer is between 7 10 15 and 10 17 pa s while rock masses typically exhibit much higher values based on comparison with glacial examples we find that these viscosities could be compatible to a rock ice mixture this leads to the hypothesis that the rock underneath acheron dorsum may be highly fragmented and that ice might have been involved in its deformation our hypothesis could shed light on the puzzling stress pattern on acheron dorsum which follows approximately the ridge without requiring the presence of hypothetical small scale endogenous currents

influence of tectonic fractures zones on gravitational rock slope failures new insights from 2 d physical modeling 1 inherited structural discontinuities are known to play a dominant role in rock slope stability the influence of their density and persistence on failure kinematics resulting mobilized volume and slope morphology remains poorly constrained the influence of these parameters is addressed using a 2 d physical modeling technique rather than undertaking a parametric analysis we examine geologically stable model configuration based upon the well documented landslide at randa switzerland the models consisted of a homogeneous material in which several fracture zones were introduced in order to study simplified but realistic configurations of discontinuities results showed that the type of gravitational failure deep seated landslide or sequential failure and resulting slope morphology are very sensitive to the number and geometry of preexisting fracture zones first an increase in the density of fractures led to formation of the gravitational failure and increased the final mobilized volume second fracture persistence exerted a strong control upon the kinematics of slope movements but had little influence on the final volume of the mobilized mass

developments in the analysis of footwall slopes in surface coal mining abstract surface mining of coal particularly in areas of mountainous topography often involves the formation of extensive footwall slopes parallel to the strata dip due to structural deformation steep dips on the limbs of folds may be encountered in association with thrust faults jointing and residual shear strength conditions such an environment necessitates a rigorous assessment of footwall stability in order to ensure safe and economic exploitation of the coal this paper provides a detailed review of the factors influencing footwall slope instability in surface coal mining and the major instability mechanisms which have been recognized within the published literature the analysis of footwalls in the design stage and the back analysis of footwall slope failures has in general been undertaken using predominantly two dimensional limit equilibrium techniques often incorporating a simplistic elastic column analysis the application of numerical modelling techniques to surface coal mine footwalls has received little attention in this paper the authors attempt to illustrate the potential for investigating footwall failure mechanisms and stability using principally the distinct element method

reactivation of basement faults beneath volcanoes a new model of flank collapse in order to explain the presence of voluminous volcanic debris avalanche deposits around a stratovolcano reactivation of vertical faults beneath a volcanic cone has been tested using analogue models reactivation of a single vertical fault beneath a cone generates a normal fault and an upturning of the layers creating a bulge on the flank the upturning induces a flank collapse characterized by a typical horseshoe shaped scar called an avalanche caldera reactivation of two vertical faults beneath a cone also generates a normal fault and a summit bulge this bulge may result from the movement along a reverse fault a large collapse is generated within the angle created by the two vertical faults the angle of the collapse can be up to 140 whereas this angle is typically 120 for a dome intrusion collapse is instantaneous and is favoured by the presence of ductile layers ash and pumice formations in the example considered in a stratovolcano complex the model may be applicable to volcanoes in a state of dormancy or extinction in regions with active regional tectonism we suggest this mechanism of collapse in the case of the cantal stratovolcano massif central france to explain the presence of voluminous volcanic debris avalanche deposits around this volcano

regional scale relief evolution and large landslides insights from geomechanical analyses in the tinee valley southern french alps abstract recurring large rock slope failures of the argentera mercantour massif southern french alps over the past 20 000 years were identified in the field and analyzed using a continuum mechanics approach based on material weakening in a three dimensional finite difference model we compared a mountain slope failure model neglecting the effect of rock strength loss with a model simulating the effect of strength loss and integrating cohesional weakening and frictional strengthening processes the good correspondence between the relative chronology and location of observed and simulated deformations shows that 1 the gradual loss of rock mass strength related to stress release effects following the pleistocene deglaciation can be as long as several thousands of years and 2 the causes and triggering of the present day active landslides are related to this long failure history our study suggests that the episodic nature of massive rock slides can be explained through the gradual development of tensile and shear failure and time dependent strength degradation our numerical model is a good reproduction of large landslides at the regional scale of a mountainous massif

crustal anisotropy in a subduction zone forearc northern cascadia s wave splitting analyses using low frequency earthquake templates at three component stations across southern vancouver island and northern washington indicate the presence of a heterogeneous distribution of crustal anisotropy in the north american plate for southern vancouver island we investigate contributions to anisotropy from the leech river complex a terrane composed of strongly foliated phyllites and schists with steeply dipping foliations striking east west fast directions across mainland southern vancouver island are subparallel to the dominant leech river complex foliation direction east to west increases in delay times and small scale azimuthal variations in fast directions indicate heterogeneous anisotropy we test azimuthally anisotropic leech river complex models constrained by previous geological and seismic reflection studies through forward modeling using 3 d spectral element method simulations the preferred model of a north northeast shallowly dipping wedge of leech river complex material with varying orientation of anisotropy terminating at midcrustal levels explains the splitting observations at a majority of southern vancouver island stations for stations where anisotropic leech river complex models do not recreate observations fast directions are subparallel to local estimates of maximum compressive horizontal stress suggesting that fluid filled cracks could be a source of anisotropy we assert that the leech river complex is the primary source of crustal anisotropy beneath southern vancouver island not cracks as suggested by prior studies fast directions at stations on northern washington exhibit variations with azimuth and incidence angle suggesting complex anisotropy interpreted as due to a combination of cracks and preferred mineral orientation of metamorphosed slates of the olympic core rocks these slates may also underlay stations on southern vancouver island and represent another source of anisotropy

numerical analysis of initiation and progressive failure in natural rock slopes the 1991 randa rockslide the 1991 randa rockslide in the swiss alps involved several complex mechanisms relating to geological mechanical and hydrological processes for which no clear trigger can be asserted this paper investigates the concept of progressive failure and the numerical modelling of rock mass strength degradation in natural rock slopes using the randa rockslide as a working example results from continuum i e finite element modelling are presented to illustrate a hypothesis suggesting that initiation of a progressive rock mass degradation process ultimately leading to failure began following deglaciation of the valley below discontinuum distinct element modelling is then applied to investigate the underlying mechanisms contributing to the episodic nature of the rockslide finally the use of a hybrid method that combines both continuum and discontinuum techniques to model fracture propagation are discussed in the context of modelling progressive slide surface development linking initiation and degradation to eventual catastrophic failure

seismic structure across the active subduction zone of western canada the vancouver island seismic project was conducted in 1980 to study the structure of the subducting oceanic juan de fuca plate and the overriding continental america plate the principal seismic refraction line line i was a 350 km onshore offshore profile perpendicular to the continental margin an array of 32 receivers was located on the america plate on the mainland and across vancouver island and extended offshore with three ocean bottom seismometers obs s two shots were fired at the eastern end of the line and 17 shots were located along the westernmost 100 km of the profile control for the interpretation of the onshore offshore profile was provided by a reversed refraction profile along the length of vancouver island and by a marine refraction profile recorded on the obs s modeling of the seismic structure of this complex region utilized an iterative inversion method for travel times from explosions in which shots at several locations are recorded on the same set of receivers and utilized an algorithim based on asymptotic ray theory for the calculation of synthetic seismograms through two dimensional media the major features of the refraction structural model are that 1 the oceanic lithosphere dips at 3 or less beneath the continental slope so the bend in the subducting slab occurs landward of the foot of the slope 2 the oceanic lithosphere dips at 14 16 beneath the continental shelf until it passes beneath the continental moho at 37 km depth below western vancouver island 3 an upper mantle reflector may correspond to the base of the subducting lithosphere and 4 a segment of high velocity material above the downgoing crust with velocity 7 7 km s and depth range 20 25 km may represent a remnant of subducted lithosphere perhaps detached when the subduction zone jumped westward to its present position

the loess of north central china geotechnical properties and their relation to slope stability abstract loess is an aeolian deposit consisting of predominantly silt sized quartz particles and containing variable amounts of clay sized minerals loess is generally classified as a water softening material because upon wetting the loess fabric rapidly weakens or collapses the strain hardening of malan loess and the brittle failure of lishi and wucheng loess are in strong contrast to the failure behaviour of these loess deposits in a remoulded state from tests carried out on samples with varying moisture contents using a modified bromhead ring shear apparatus it was found that the effective apparent cohesion gradually increases and the effective internal friction angle decreases with an increase in moisture content when the moisture content reaches a material specific threshold the effective cohesion decreases rapidly and the effective internal friction angle stabilises at a residual value the frequent failure of loess slopes in the western part of the chinese loess plateau is closely related to progressive weathering along zones in these slopes which causes a dramatic decrease in strength from the peak strength condition progressive weathering is common in the loess slopes in the western part of the chinese loess plateau during the process shear strength reduction along potential slip surfaces may be achieved by leaching of readily soluble salts destruction of cementation bonds and redistribution of particles localized collapse of the loess fabric causes internal deformation and consequently peak strength conditions are concentrated on a progressively smaller area of the failure plane therefore the mode of failure of loess slopes is generally determined by brittle failure of the undisturbed and unweathered central parts of the slopes it is important that both the weathered and unweathered strength of the loessmaterials in this area be established in order to analyze the stability of existing loessslopes many of which are steepand lie directly above domestic and industrial urban areas

seismicity of the wrangell and aleutian wadati benioff zones and the north american plate along the trans alaska crustal transect chugach mountains and copper river basin southern alaska the configuration of the aleutian and wrangell wadati benioff zones in southern alaska between longitudes 142 w and 148 w is determined from regionally recorded earthquakes from 1971 to 1986 the earthquakes are located with a simple velocity model calibrated with seismic refraction measurements conducted for the trans alaska crustal transect tact west of the transect meridian approximately 145 20 w and beneath the chugach mountains shocks in the depth range 25 60 km compose the shallow part of the northwest to north dipping aleutian zone this zone can be traced updip and seaward beneath prince william sound east of the transect meridian and north of 61 n latitude the weakly active north northeast dipping wrangell zone extends to a depth of at least 100 km beneath the wrangell volcanoes and along strike for at least 150 km the two zones appear to be continuous at least in the depth range 20 45 km and may define adjacent limbs of a buckle in the subducted oceanic lithosphere north of 61 n focal mechanisms in the shallow aleutian zone are compatible with a uniform stress field characterized by in plane least compressive stress directed toward the steeply dipping deeper part of the aleutian zone north of cook inlet stress orientation in the wrangell zone is unresolved because of the low level of seismicity no focal mechanisms corresponding to slip on a gently northward dipping megathrust have been observed along the transect meridian a change of focal mechanism with depth near the top of the dipping seismic zone is inferred to reflect the interplate boundary beneath the chugach mountains this boundary coincides with a band of strong reflectors imaged by tact vertical seismic profiling the overriding plate appears to be aseismic beneath the northern chugach mountains but minor shallow seismicity occurs beneath the copper river basin first motion patterns for these shallow shocks suggest the most compressive stress within the overriding plate is oriented subhorizontally and approximately north south

reflection mapping across the convergent margin of western canada summary five marine multichannel seismic reflection profiles totalling 520 km were recorded across the western canada convergent margin where the juan de fuca plate is subducting beneath north america the data extend the results of lithoprobe on vancouver island the primary objectives are definition of the offshore accretionary structures and clarification of the convergent interaction between the two plates the main features of this preliminary interpretation are 1 the subduction deformation front is complex with evidence of sediments being accreted and subducted 2 the top of the oceanic crust and the mono are imaged below the deep water sedimentary basin 3 the top of the subducting plate is clearly imaged below the shelf 4 beneath the inner shelf one band of high reflectivity underlain by a zone of lesser reflectivity lies above the plate 5 alternative interpretations place the present zone of decoupling at the base of the reflective band or the top of the plate 6 the san juan and leech river faults that bound small accreted terranes are imaged as thrusts that merge at depth

great earthquakes on canada s west coast a review this article is one of a series of papers published in this special issue on the theme lithoprobe parameters processes and the evolution of a continent geological survey of canada contribution 20090196 the first lithoprobe transect in 1984 across vancouver island had primary objectives to define the structure associated with subduction and constraints on the potential for great thrust earthquakes

soil hydraulic properties in a marly gully catchment draix france abstract runoff is one of the main factors controlling gully development concentrated flow erosion occurs where flow discharge and velocity exceed critical values in southern french alps in black marl gully catchments runoff from hillslopes occurs in the form of hortonian overland flow because rainfall intensities exceed the infiltration capacity of the soil in such a situation spatial variability of infiltration capacities is critical for describing the runoff production this study reports detailed field measurements of near saturation and saturated infiltration properties capillary sorptivity s and hydraulic conductivity k a total of 140 infiltration tests were conducted using tension disc and ponded ring infiltrometers on 6 different regoliths weathering profile encountered in a marly gully catchment the main objectives were to improve our knowledge of the spatial variability of infiltration in black marl areas and to compare different field and data analysis methods hydraulic conductivity values k h at supply pressure heads h ranging from h 100 up to h 0 mm were calculated using steady state flow and wooding s equation wooding r a 1968 steady infiltration from shallow circular pond water resour res 4 6 1259 1273 k h 0 mm was also estimated from the ponded ring infiltrometer data set the estimation of sorptivity was based on transient flow and the solution of haverkamp et al haverkamp r roos p j smettem k r j parlange j y 1994 three dimensional analysis of infiltration from the disc infiltrometer 2 physical based infiltration equation water resour res 30 11 2931 2935 three methods were used to analyse tension disc infiltrometer data multiple radii multiple potential and single test only the multiple radii method was found not suitable in our context due to a large spatial variability in the infiltration properties over small distances the other methods gave similar estimates of the hydraulic conductivity the hydraulic conductivity k h ranged up to two orders of magnitude this result confirms the role played by structural voids when the regolith is at near saturation the dispersion of the estimates of field saturated hydraulic conductivity is larger than unsaturated values the spatial differences found are explained by the topographical position and by the regolith structure observed for the 6 sites an analysis based on the ponding time show that the regolith type plays an important role in the dynamic of the runoff production

controlling factors for deep seated gravitational slope deformation dsgsd in the aosta valley nw alps italy deep seated gravitational slope deformation dsgsd is a common and widespread type of large slope instability in the alps in the aosta valley region in nw italy dsgsds occupy at least 13 5 of the regional territory in this study regional distribution analyses have been coupled with local detailed geological and geomorphological surveys of individual phenom ena to detect the controlling factors deformation processes and evolution stages of dsgsd data and maps from field and remote sensing investigations have been supported by drill data and geo mechanical and hydrogeochemical analyses from project studies for hydroelectric plants and tunnels several phenomena related to dsgsd have been studied thoroughly gravity induced stresses tectonic metamorphic setting morphostructural relations glacial and periglacial mor phodynamics recent tectonic evolution hydrogeological conditions and karst phenomena have been generically indicated as controlling factors in the studied area three of the controlling factors were crucial in differentiating the form and evolution of dsgsds deep dissolution surface tectonics and tectonostructural setting they are presented as possible end members of a classification scheme for dsgsds

progress in birps deep seismic reflection profiling around the british isles abstract the results of 4000 km of new birps profiles are briefly outlined as an introduction to other birps papers in this volume highlights of these profiles include the tracing for 900 km of a reflection pattern in the lower crust associated with the lapetus suture and the observation of more than 20 separate reflections from the mantle while progress in solving the problem of deep water multiples has enabled the joining of the continental and oceanic moho reflections off sw england developments in old interpretational problems are reviewed and the new problem of dating reflections is mentioned

the role of the degree of weathering and groundwater fluctuation in landslide movement in a colluvium of weathered hornblende gabbro abstract shallow translational earth sliding induced by heavy rainfall in slopes made of colluvium of weathered homblende gabbro was investigated in order to elucidate the relationship between weathering soil strength and slope instability the earth slide has a length of 100 m and a maximum width of 40 m and an average depth of about 6 4 m average rate of the initial sliding in early summer of 1976 was estimated to be about 50 mm day and the sliding intermittently continued to the end of 1977 sliding became active due to rising of groundwater table in response to rainfall the average slope angle reduced from 13 9 to 11 3 as a result of the sliding mineralogical investigations indicated that 1 the sliding surface of this earth slide was located in the colluvium of weathered debris from the hornblende gabbro and 2 hornblende in gabbro was altered due to weathering into swelling chlorite geotechnical properties of the colluvium were measured shear tests gave values of c p 0 169 kgf cm2 and p 27 8 for peak strength and c r 0 122 kgf cm2 and r 10 6 for residual strength the infinite slope stability analyses using these values indicated that 1 the soil strength had reduced to the residual strength at the time of initial sliding 2 the analyses using the residual strength well explain the results of the field measurements showing that the earth slide is active when the groundwater table rises to near the slope surface and 3 the slope of 11 3 the post sliding angle is stable even under the most severe condition even when the groundwater rises to the slope surface these results suggest that the sliding surface had been already made before the 1976 1977 event the existing literature shows that chlorite will alter to smectite minerals having a smaller strength r 4 5 as a result of further weathering using this value the ultimate angle of stable slope was estimated to be 8 based on the discussion an idealized diagram illustrating the relationship between weathering strength and slope instability of this hillslope was constructed

local thickening of the cascadia forearc crust and the origin of seismic reflectors in the uppermost mantle seismic reflection profiles from three different surveys of the cascadia forearc are interpreted using p wave velocities and relocated hypocentres which were both derived from the first arrival travel time inversion of wide angle seismic data and local earthquakes the subduction decollement which is characterized beneath the continental shelf by a reflection of 0 5 s duration can be traced landward into a large duplex structure in the lower forearc crust near southern vancouver island beneath vancouver island the roof thrust of the duplex is revealed by a 5 12 km thick zone identified previously as the e reflectors and the floor thrust is defined by a short duration reflection from a b2 km thick interface at the top of the subducting plate we show that another zone of reflectors exists east of vancouver island that is approximately 8 km thick and identified as the d reflectors these overlie the e reflectors together the two zones define the landward part of the duplex the combined zones reach depths as great as 50 km the duplex structure extends for more than 120 km perpendicular to the margin has an along strike extent of 80 km and at depths between 30 km and 50 km the duplex structure correlates with a region of anomalously deep seismicity where velocities are less than 7000 m s 1 we suggest that these relatively low velocities indicate the presence of either crustal rocks from the oceanic plate that have been underplated to the continent or crustal rocks from the forearc that have been transported downward by subduction erosion the absence of seismicity from within the e reflectors implies that they are significantly weaker than the overlying crust and the reflectors may be a zone of active ductile shear in contrast seismicity in parts of the d reflectors can be interpreted to mean that ductile shearing no longer occurs in the landward part of the duplex merging of the d and e reflectors at 42 46 km depth creates reflectivity in the uppermost mantle with a vertical thickness of at least 15 km we suggest that pervasive reflectivity in the upper mantle elsewhere beneath puget sound and the strait of georgia arises from similar shear zones

the moho in subduction zones abstract the moho in subduction zones exists in two distinct forms one associated with the subducting oceanic plate and second with the overriding plate the seismic expression of both forms is linked to the nature of a landward dipping low velocity zone lvz that has been detected in a majority of subduction zones about the globe and that approximately coincides with wadati benioff seismicity we review seismic studies that constrain the properties of the lvz in cascadia where it has been extensively studied for over a quarter century a model in which the lvz is identified with hydrated pillow basalts and sheeted dikes of oceanic crustal layer 2 is consistent with available geological and geophysical data and reconciles previously conflicting interpretations in this model the upper oceanic crust is hydrated through intense circulation at the ridge and becomes overpressured upon subduction as a result of metamorphic dehydration reactions combined with an impermeable plate boundary above and a low porosity gabbroic layer 3 below the resulting seismic velocity contrast approaching 50 for s waves significantly overwhelms that of a weaker underlying oceanic moho at greater depths oceanic crust undergoes eclogitization in a top down sense leading to gradual disappearance of the lvz the large volume change accompanying eclogitization is postulated to rupture the plate boundary allowing fluids to penetrate the cooled forearc mantle wedge pervasive serpentinization and free fluids reduce velocities within the wedge thereby diminishing erasing or even inverting the seismic contrast associated with the moho of the overriding plate this model is tested against observations of lvzs and forearc mantle structure worldwide

the shapes of cold high mountains in sedimentary rocks abstract terzaghi geotechnique 12 1962 251 and young young a 1972 slopes oliver and boyd edinburgh 288 pp described the stable forms of slopes in sedimentary rock masses assuming penetrative discontinuities which are parallel to bedding and joints which are perpendicular to bedding the only movements considered were slides along bedding experience in the canadian rockies indicates that the cohesionless rock masses that exist at or above tree line may also move by toppling buckling and sliding along joints these processes also act to limit the inclinations of stable slopes rock strength is a factor in the critical height of a slope that buckles the processes can be represented as fields on a process diagram a plot of slope inclination against bedding dip using the basic friction angles of the rocks present the process diagram also separates five common mountain peak shapes which form on homoclinal sequences of beds castellate and matterhorn mountains occur in sub horizontal beds cuestas develop in gently to moderately dipping beds hogbacks formed in moderately to steeply dipping beds have similar slope angles on both cataclinal and anaclinal slopes dogtooth mountains occur in steeply dipping sub vertical beds

seismic reflection images of the crust of the northern part of the chugach terrane alaska results of a survey for the trans alaska crustal transect tact deep crustal seismic reflection data show strong reflections from the middle and lower crust of the convergent continental margin near the eastern end of the aleutian trench these data were collected across the border ranges fault system a major suture zone that separates the peninsular and chugach tectonostratigraphic terranes the chugach terrane consists of metamorphosed strongly deformed flysch subduction melange as well as blueschist and greenschist facies rocks even so highly reflective rocks lie at great depth within or beneath this terrane the shallow part of the seismic section 0 5 s reveals only a few reflections which undulate and interweave indicating that some of them originate outside of the plane of the seismic section other undulating events could reveal early cenozoic granitic plutons or antiformal stacks of rock imbricated along thrust faults in contrast to this shallow reflection pattern three reflection bands contain most of the events on the middle part of the seismic section 5 12 s or 12 34 km we interpret divergent reflections within the uppermost band 5 5 5 s as gently north dipping thrust faults and subparallel reflections truncated at the boundaries of the upper and middle bands may image a metamorphic foliation or thrust faults if the truncated reflections represent thrust faults then the reflection geometry suggests that subparallel roof and floor thrust faults bound imbricated rocks forming duplex structures the upper and middle bands are separated by an area on the seismic section that reveals few reflections this area correlates approximately in depth with a high velocity 7 5 km s layer evident in refraction models the poorly reflective high velocity unit might be volcanic rocks like those exposed in the structurally lowest part of the chugach terrane if so then the bottom of the poorly reflective rocks indicates the base of the chugach terrane rocks that cause the upper and middle reflection bands and the intervening poorly reflective volcanic rocks may form a midcrustal shear zone that is about 10 km thick the deepest band of subparallel reflections 30 35 km correlates closely in depth with the top of the wadati benioff zone associated with the underthrusting pacific plate the reflections probably stem from the decollement that separates lithospheric plates within the subduction zone this reflection band increases abruptly in thickness possibly indicating local underplating of subducted sediment no events from the oceanic moho have been recognized neither the border ranges fault system the suture between the chugach and peninsular terranes nor deep crustal layers of the peninsular terrane are evident in these seismic reflection data

numerical modelling of the gravity induced destabilization of a slope the example of the la clapiere landslide southern france abstract a finite difference two dimensional model with hooke mohr coulomb properties and topography derived from the dem are used to reproduce the la clapiere landslide the principal factor defining the gravity driven destabilization of the model is a gradual reduction in the cohesion this reduction simulates a degradation of the material properties with time because of weathering alteration processes the inelastic deformation fracturing and faulting first occur at mountain scale and results in normal fault formation causing crest sagging later the failure process is concentrated in the lower part of the slope and leads to the formation of a localized fault subparallel to the slope surface at a depth of ca 100 m this corresponds to the initiation of the la clapiere landslide and its propagation upslope a slow crest sagging continues during the whole model evolution

lithoprobe southern vancouver island cenozoic subduction complex imaged by deep seismic reflections reply the lithoprobe seismic reflection project on vancouver island was designed to study the large scale structure of several accreted terranes exposed on the island and to determine the geometry and structural characteristics of the subducting juan de fuca plate in this paper we interpret two lithoprobe profiles from southernmost vancouver island that were shot across three important terrane bounding faults leech river san juan and survey mountain to determine their subsurface geometry and relationship to deeper structures associated with modem subduction the structure beneath the island can be divided into an upper crustal region consisting of several accreted terranes and a deeper region that represents a landward extension of the modern offshore subduction complex in the upper region the survey mountain and leech river faults are imaged as northeast dipping thrusts that separate wrangellia a large mesozoic paleozoic terrane from two smaller accreted terranes the leech river schist mesozoic rock

shear wave constraints on a deep crustal reflective zone beneath vancouver island analysis of teleseismic receiver functions recorded in the northern cascadia subduction zone show that large p to s converted phases are generated at the boundaries of a dipping layer of deep crustal reflectors the e zone beneath central vancouver island these data provide the first shear wave constraints on this layer which is clearly observed in seismic reflection sections and is coincident with a region of low electrical resistivity interpreted from a magnetotelluric survey modeling of the amplitudes polarities and arrival times of the p to s converted phases demonstrates that the e zone is a prominent low velocity layer with an s velocity 1 0 0 2 km s lower than the regions above and below the e zone dips 7 5 in the direction n10 e 20 and extends from depths of 36 5 to 41 km at alb b on central vancouver island the estimated s velocity contrast when considered with refraction p velocities yields a poisson s ratio of 0 34 for this zone given the uncertainty in vp and vs this value may range from 0 27 to 0 38 the low p and s velocities and high poisson s ratio combined with electrical resistivity measurements suggest a porosity of 0 1 1 9 and crack aspect ratios of 0 001 0 01 values consistent with a region containing thin fluid saturated cracks and thus supportive of the interpretation of this feature as a major shear zone

basal heave analysis of excavations with consideration of anisotropic undrained strength of clay in this study two cases of excavation to failure were utilized to investigate reasonable analysis methods for basal heave analysis three types of tests were carried out to obtain the undrained sh

evolution of gravity driven rock slope failure and associated fracturing geological analysis and numerical modelling abstract an accurate analysis of fracture and cleavage anisotropies along two landslides in the argentera massif french southern alps was performed in order to relate the fracturing mode to the rock slope failure state the mature la clapiere landslide and the incipient isola landslide were investigated in both cases the gneissic rock schistosity was found sub horizontal in the vicinity of the landslides at shallow depths while it was sub vertical elsewhere at the massif s scale in addition to the well known regional tectonic fracture sets we identified in both cases a new family of vertical valley parallel vp fractures the vp fractures were only observed on the lower part of slopes affected by landslides where schistosity was found sub horizontal the vp fractures are clearly related to the decrease in schistosity dip and correspond to fold extrado like joints the proximity of the schistosity folds and the associated vp joints to the landslides suggests that they are gravity driven the presented 2 d finite difference models of the slope destabilisation in the la clapiere site shade light on possible mechanisms of the indicated gravity induced processes a progressive degradation of the material strength was imposed in these models to simulate the weathering effect which led to inelastic deformation damage at the lower part of slope this was followed by the formation of dense sub vertical deformation bands and then by the initiation of a landslide in the area corresponding to the actual position of the la clapiere landslide it is suggested that the gravity induced damage in the lower part of slope increases the permeability and thereby accelerates the weathering that causes a more rapid strength reduction the latter results in the tilting folding of pre existing fabrics and the related vp fracturing the la clapiere landslide is initiated in the upper part of this zone

new insights into rock weathering from high frequency rock temperature data an antarctic study of weathering by thermal stress a major limitation of many weathering studies has been the acquisition of rock temperature data at insufficiently frequent intervals for the meaningful determination of the rate of change of temperature t t equipment and or logistical constraints frequently facilitate temperature measurement at only hourly intervals or at best every 10 min such data are not adequate for the determination of t t required for the evaluation of the freeze thaw mechanism or thermal stress fatigue recent undertakings at different sites in antarctica and at other cold region locations provide rock temperature measurements at 1 min intervals which indicate that the perception of the weathering regime would be very different from that generally assumed from longer interval geomorphological data these data clearly show that thermal stress fatigue and thermal shock may be more active components of the antarctic weathering regime than have generally been recognised the aridity of the study area limits the role of freeze thaw weathering values of t t of 2 c min 1 that suggest thermal stress fatigue shock is operative were recorded observations of rock flaking are thought to reflect the impact of thermal stress further the data show that contrary to general perceptions the southern aspect can in summer experience higher rock surface temperatures than the north facing exposure an examination of rock fracture patterns found in the field shows great similarity to fracture patterns developed in the laboratory as a direct result of thermal shock the argument is made that greater cognizance should be given to thermal effects

landslide susceptibility assessment by bivariate methods at large scales application to a complex mountainous environment statistical assessment of landslide susceptibility has become a major topic of research in the last decade most progress has been accomplished on producing susceptibility maps at meso scales 1 50 000 1 25 000 at 1 10 000 scale which is the scale of production of most regulatory landslide hazard and risk maps in europe few tests on the performance of these methods have been performed this paper presents a procedure to identify the best variables for landslide susceptibility assessment through a bivariate technique weights of evidence woe and discusses the best way to minimize conditional independence ci between the predictive variables indeed violating ci can severely bias the simulated maps by over or under estimating landslide probabilities the proposed strategy includes four steps i identification of the best response variable rv to represent landslide events ii identification of the best combination of predictive variables pvs and neo predictive variables npvs to increase the performance of the statistical model iii evaluation of the performance of the simulations by appropriate tests and iv evaluation of the statistical model by expert judgment the study site is the north facing hillslope of the barcelonnette basin france affected by several types of landslides and characterized by a complex morphology results indicate that bivariate methods are powerful to assess landslide susceptibility at 1 10 000 scale however the method is limited from a geomorphological viewpoint when rvs and pvs are complex or poorly informative it is demonstrated that expert knowledge has still to be introduced in statistical models to produce reliable landslide susceptibility maps

the electrical conductivity distribution beneath vancouver island a region of active plate subduction magnetotelluric mt and geomagnetic depth sounding gds data were recorded at 25 locations across vancouver island canada over the subducting juan de fuca plate the gds data respond to a number of local conductive features at frequencies above 10 hz while at longer periods the in phase and quadrature induction arrows are colinear and are aligned approximately normal to the continental shelf with a maximum amplitude response near the southwest coast interpretation of the mt data show the presence of a conducting zone at depths greater than 20 km beneath vancouver island and correlating with a strong seismic reflector extensive testing with two dimensional models shows the mt and gds data are consistent with a proposed geoelectrical structure containing a conducting layer extending from the pacific ocean dipping beneath vancouver island and in electrical contact with the mainland conductive region the layer has a horizontal conductance of 200 s that may decrease to 100 s beneath the northeast side of vancouver island related geophysical studies suggest the conductive zone is above the actual thrust surface of the juan de fuca plate the conducting layer is most likely the result of cracks and pores filled with saline fluids which are supplied bymore water subducted with the oceanic crust and by dehydration reactions the presence of fluids has significant implications for thrust earthquakes and for metamorphic reactions that occur in subduction zones the conductance of the upper mantle between 90 and 390 km is best modeled at approximately 1 500 s less

structural constraints on deep seated slope deformation kinematics abstract a significant sackung type deep seated slope gravitational deformation dsgsd was recognised for the first time by the authors in the middle part of valfurva east of bormio rhaetian alps italy the reconstruction of its kinematics age and state of activity is presented through a detailed description of its morphological geomechanical and structural features an integrated multi disciplinary approach was performed to achieve a clear comprehension of the phenomenon field surveys and aero photo interpretation were carried out in order to clarify the structural geological and geomorphological setting in which the dsgsd developed a kinematic conceptual model of the slope deformation was developed through the analysis of morpho structures of their significance and relationships with lithological markers and quaternary deposits after a geomechanical characterisation of the rock mass involved in the slope deformation numerical modelling was performed to verify the hypotheses made on kinematics and driving factors of the phenomenon the sackung affects pre permian metapelites metabasites and marbles belonging to the upper austroalpine basement of the campo nappe as well as late pleistocene and holocene glacial and rock glacier deposits the deformation started after the late wurmian age 15 000 11 000 years b p and continued until few centuries ago not excluding a present day low rate activity deformation consists in a large oblique sagging along a deep confined sliding surface associated with gravitational reactivation of pre existing late alpine and recent tectonic brittle structures leading to the formation of n s and wnw ese trending gravitational morpho structures the evolution of the wnw ese trending system resulting in asymmetric trenches led to progressive failure of the lower part of the slope during the last 10 000 years as testified by large paleo landslide accumulations and it is still in progress numerical modelling indicates post glacial unloading as the main triggering factor of the slope deformation the importance of this deep seated slope deformation is enhanced by the occurrence of the 30 mm 3 active ruinon landslide in the lower part of the slope such landslide is subjected to rapid evolution and threatens the valley floor establishing an important risk factor connected to human lives and socio economic activities

a method for the study of crack propagation in rock structures a method is presented for analysing the stability of rock structures based on the propagation of geological discontinuities discontinuities are modelled as flat cracks and their propagation is analysed using fracture mechanics methods as rock structures are brittle these phenomena can be studied using linear elastic fracture mechanics lefm problems in the application of lefm methods are analysed with regard to the states of compressive stress present in rock a numerical procedure is described which simulates the propagation of natural discontinuities in rock the crack propagation trajectories determined from this analysis are compared with experimental results obtained on mortar specimens the applicability of the method to the study of rock mass stability is shown with reference to the behaviour of rock slopes l article presente une methode permettant d analyser la stabilite de structures rocheuses cette methode est fondeve sur petude de la propagation de discontinuites geologiques ces discon

morphology and sedimentology of a complex debris flow in a clay shale basin coupling morphological sedimentological and rheological studies to numerical simulations is of primary interest in defining debris flow hazard on alluvial fans in particular numerical runout models must be carefully calibrated by morphological observations this is particularly true in clay shale basins where hillslopes can provide a large quantity of poorly sorted solid materials to the torrent and thus change both the mechanics of the debris flow and its runout distance in this context a study has been completed on the faucon stream southeastern french alps with the objectives of 1 defining morphological and sedimentological characteristics of torrential watersheds located in clay shales and 2 evaluating through a case study the scouring potential of debris flows affecting a clay shale basin morphological surveys grain size distributions and petrographic analyses of the debris flow deposits demonstrate the granular character of the flow during the first hectometre and its muddy character from there to its terminus on the debris fan these observations and laboratory tests suggest that the contributing areas along the channel have supplied the bulk of the flow material copyright 2005 john wiley sons ltd

nature of the low velocity zone in cascadia from receiver function waveform inversion abstract a dipping low velocity zone lvz is a ubiquitous structural element of subduction zones worldwide in this study we map seismic attributes characterizing the lvz beneath the cascadia subduction zone from northern vancouver island to northern california using receiver function waveform inversion throughout this region the lvz is characterized by high v p v s ratios mean 2 77 strong s velocity contrasts 50 and thicknesses averaging 3 37 km the lvz is immediately underlain by a second weaker layer exhibiting moderate v p v s ratios mean 1 85 with mean thickness of 4 62 km we interpret the combined structure in terms of subducting oceanic crust based on classical structural petrological descriptions and constraints from previous studies of ophiolites and ocean drill cores the lvz is identified with pervasively hydrated high porosity pillow basalts and sheeted dikes of layer 2 with possible contributions from sediments layer 1 fluids released from metamorphic dehydration reactions are maintained near lithosphere fluid pressures through an impermeable plate boundary above and a low porosity gabbroic mafic cumulate dominated layer 3 below

modelling groundwater fluctuations and the frequency of movement of a landslide in the terres noires region of barcellonnette france onn the basis of measurements of hydrological parameters and field monitoring of a landslide in the terres noires in the basin of barcelonnette france a hydrological model was developed describing groundwater fluctuations in relation to precipitation these groundwater fluctuations can be used as input to a stability model in order to assess the temporal frequency of instability of the landslide the calculated groundwater fluctuations which can forecast years with landslide incidents were roughly calibrated against dated movements obtained by dendrochronological research the hydrological system of the landslide can be understood through a three layer sequence a rather permeable colluvial top layer underlain by a less permeable colluvial second layer both overlying the nearly impermeable in situ non weathered black marls terres noires the mean ksat value for the matrix flow in the top layer is 15 7 cm day and in the underlying layer 0 7 cm day however water fluxes in these layers occur by two types of groundwater flow matrix flow obeying darcy s law and more rapid gravitational flow through preferential flow paths increasing the conductivity by a factor of 10 to 100 as cube method ksat measurements revealed the model shows long term yearly fluctuations of the phreatic surface with peaks at the end of winter as well as at the beginning of spring and minimum values during the dry summer period these long term fluctuations are explained by the high drainage capacity of the top colluvial layer and the relatively low vertical water fluxes within the underlying colluvial layer the model shows that maximum critical peak height conditions of the groundwater causing instability occur in wet seasons with at least six consecutive months with high amounts more than 60 mm of precipitation 1997 by john wiley sons ltd

a view on some hydrological triggering systems in landslides abstract in this paper different types of hydrological triggering systems for debris flows shallow and deeper landslides are described the generation of surface run off and high peak discharges in first order alpine catchments is an important triggering mechanism for debris flows failure conditions in shallow landslides can occur when at a critical depth which is determined by the cohesion of the soil and the slope angle the moisture content in the soil becomes close to saturation resulting in a considerable reduction of soil strength deeper landslides 5 20 m depth are in most cases triggered by positive pore pressures on the slip plane induced by a rising ground water level the assessment of meteorological threshold conditions for shallow landslides 1 2 m needs more detailed meteorological information than for deeper landslides in the analyses of the hydrological triggering systems of deeper landslides the presence of a permeable top layer and fissures has to be taken into consideration

influence of structural heterogeneities and of large scale topography on imbricate gravitational rock slope failures new insights from 3 d physical modeling and geomorphological analysis initial topography and inherited structural discontinuities are known to play a dominant role in rock slope stability previous 2 d physical modeling results demonstrated that even if few preexisting fractures are activated propagated during gravitational failure all of those heterogeneities had a great influence on mobilized volume and its kinematics the question we address in the present study is to determine if such a result is also observed in 3 d as in 2 d previous models we examine geologically stable model configuration based upon the well documented landslide at randa switzerland the 3 d models consisted of a homogeneous material in which several fracture zones were introduced in order to study simplified but realistic configurations of discontinuities e g based on natural example rather than a parametric study results showed that the type of gravitational failure deep seated landslide or sequential failure and resulting slope morphology evolution are the result of the interplay of initial topography and inherited preexisting fractures orientation and density the three main results are i the initial topography exerts a strong control on gravitational slope failure indeed in each tested configuration even in the isotropic one without fractures the model is affected by a rock slide ii the number of simulated fracture sets greatly influences the volume mobilized and its kinematics and iii the failure zone involved in the 1991 event is smaller than the results produced by the analog modeling this failure may indicate that the zone mobilized in 1991 is potentially only a part of a larger deep seated landslide and or wider deep seated gravitational slope deformation

seismic reflection imaging of the subducting juan de fuca plate mckenzie and parker s early suggestion1 that the juan de fuca plate is underthrusting north america has since been confirmed by numerous studies evidence for plate convergence along this junction includes a sediment filled trench2 7 intense compressional deformation of the continental slope and shelf sediments2 7 seafloor magnetic anomalies that extend beneath the continental slope2 4 inland andesitic volcanoes8 paired low high heat flow and gravity anomalies9 10 active onshore deformation11 12 onshore crustal earthquakes with compressional axes parallel to the direction of plate convergence13 sinistral strike slip earthquakes along the nootka fault fig 1 14 and a well defined benioff wadati zone6 15 16 here we report the results of a seismic reflection survey that has delineated two slabs of oceanic lithosphere underlying vancouver island one that is currently being subducted and one that is underplated these findings lead us to speculate that successive underplating of oceanic lithosphere may be an important process in the evolution and growth of continents

landslides and climatic conditions in the barcelonnette and vars basins southern french alps france research into the climatic causes behind the triggering and reactivation of landslides has been carried out in two basins in the southern french alps where a great many landslides have occurred over more than a century correlations between landslides and climate are sometimes precise and closely related in time at other times imprecise and more distant the better known the type of landslide and the date of its occurrence the greater the correlation may appear be this as it may climate is never the sole cause this paper deals with the limits of the effects of climate

deep geophysical investigation of the large sechilienne landslide western alps france and calibration with geological data a geophysical imaging campaign including four 950 m electrical profiles and four 470 m long seismic profiles was performed on the large sechilienne landslide with the objective of constraining the depth and the volume of the affected zone compared to the undisturbed ground the moving area exhibits lower velocity and higher resistivity values comparison with existing geodetic geomorphic and geological data investigation gallery and borehole allowed showing that these geophysical parameter variations result from intense fracturing and the progressive development of air filled voids within the moving mass a maximum thickness of 150 m to 200 m was found in the most deconsolidated zones locally near vertical very low resistivity anomalies were evidenced related to cataclasis zones filled with clayey material applying the wyllie s experimental law rock mass porosity images were derived from seismic tomography profiles porosity between 30 and 4 was found from the top to the bottom of the deconsolidated zone explaining the deep water table considering a porosity threshold of 3 7 for the sound bedrock the total volume of the sechilienne landslide was estimated to about 60 10 106 m3 a more precise bracket than the previous estimations 20 106 to 100 106 m3

paraglacial gravitational deformations in the sw alps a review of field investigations 10be cosmogenic dating and physical modelling catastrophic deep seated landslides dsl are generally considered to be the result of large slope deformations also known as deep seated gravitational slope deformation dsgsd this paper aims to build a synthesis of multiple studies made in the tinee valley southern french alps to assess the geometrical kinematical mechanical and chronological relationships between these two gravitational processes at the scale of the valley data issued from geological geomorphological and 10be dating indicate a clear geometrical link between dsgsd and dsl occurring at the base of the slope and suggest that gravitational slope evolution began after the glacial retreat 13 ka bp this is supported by the example of the well documented la clapiere slope a continuous evolution process is characterized geometrically and temporally from geomorphic observations and analogue modelling coupling structural geomorphological physical and chronological studies allowed us to propose a four dimensional 4d deformation model mechanically correlated with progressive failure concept the validity and variability of this reference site are discussed at the valley scale taking isola and le pra slope deformation as examples it allows a rough estimation of the state of slope deformation at the valley scale to be constructed and the slope evolution with time to be considered this 4d model could then be considered as a reference for other deep seated gravitational slope deformations in comparable alpine valleys

10be ages reveal 12 ka of gravitational movement in a major sackung of the western alps france abstract the rognier sackung which extends ne sw for more than 9 km is a major gravitational morpho structure located in the western alps we used the 10 be cosmic ray exposure dating method on 23 samples to unravel its history and better understand its genetic mechanism we found that the average slip rate on sackung faults varies from 0 3 to 3 2 mm yr 1 conjugate sackung faults are contemporaneous in agreement with a model in which the whole mountain ridge is involved in the gravitational deformation 600 m thick multiple samples on single faults suggest that the development of this sackung started before 12 ka and that it is still active we cannot exclude the possibility that the dissolution of the underlying triassic evaporites participated in the sagging of mt rognier however the age of this sackung and the presence of the lauziere sackung on the other side of the arcs valley support glacial erosion and debuttressing following the retreat of the valley glacier as the main causes of these large gravitational structures the long and permanent activity of the rognier sackung contrasts with that of the neighbouring arcs sackung which we previously dated using the same method and showed that it is a result of flexural toppling along with the proximity of the rognier sackung to the belledonne border active fault its long history suggests that earthquake shaking contributed to maintain its activity additionally two ages confirm that in the western alps rock glaciers formed mainly during the younger dryas this study allowed the determination of the best sampling strategy for future cre dating of these types of gravitational structures

geophysical geotechnical and hydrological investigations of a small landslide in the french alps abstract geophysical geotechnical and hydrological surveys were conducted in the french alps on a small landslide in black marl material to assess the stability the geophysical survey consisting of electromagnetic geo electric and relative differences in water content the data on the basal slip surface together with geotechnical parameters cohesion and angle of internal friction were used to make a stability analysis this analysis revealed that a groundwater level of 4 m below the ground surface is the critical threshold for reactivating the landslide the hydrological investigation which entailed measurements of saturated permeability and pressure heads indicated that instability depended on long term wet conditions with little evapotranspiration

three dimensional physical modeling of deep seated landslides new technique and first results 1 a new technique for physical experimental modeling of landsliding and the first results are presented the technique is based on the use of new elasto brittle plastic analogue materials and an original vertical accelerator device enabling an increase in the gravity acceleration this technique allows slope stability to be addressed in a full three dimensional large strain formulation involving brittle and ductile rupture of the material three sets of experiments on the scale of a mountain 1 km high are presented the first one was designed to define the conditions and the mode of instability deformation in a homogeneous unfractured model instability occurs when the effective compressive strength c of the mountain is as small as 107 pa i e about 1 order of magnitude lower than the typical strength of small rock samples the deformation and rupture involve the whole mountain and correspond to well known deep seated gravitational slope deformation in the second set of experiments we introduced inherited tectonic faults which considerably reduce mountain stability with deformation again developing at the mountain scale the introduction of the local small scale fractures and weak zones in the last set of experiments resulted in smaller scale shallow landslides

seismic imaging of a convergent continental margin and plateau in the central andes andean continental research project 1996 ancorp 96 1 a 400 km long seismic reflection profile andean continental research project 1996 ancorp 96 and integrated geophysical experiments wide angle seismology passive seismology gravity and magnetotelluric depth sounding across the central andes 21 s observed subduction of the nazca plate under the south american continent an east dipping reflector nazca reflector is linked to the down going oceanic crust and shows increasing downdip intensity before gradual breakdown below 80 km we interpret parts of the nazca reflector as a fluid trap located at the front of recent hydration and shearing of the mantle the fluids being supplied by dehydration of the oceanic plate patches of bright quebrada blanca bright spot to more diffuse reflectivity underlie the plateau domain at 15 30 km depth this reflectivity is associated with a low velocity zone p to s wave conversions the upper limits of high conductivity and high vp vs ratios and to the occurrence of neogene volcanic rocks at surface we interpret this feature as evidence of widespread partial melting of the plateau crust causing decoupling of the upper and lower crust during neogene shortening and plateau growth the imaging properties of the continental moho beneath the andes indicate a broad transitional character of the crust mantle boundary owing to active processes like hydration of mantle rocks in the cooler parts of the plate margin system magmatic underplating and intraplating under and into the lowermost crust mechanical instability at moho etc hence all first order features appear to be related to fluid assisted processes in a subduction setting

lateral spreading processes in mountain ranges insights from an analogue modelling experiment abstract the results of a study on gravitational induced lateral spreading phenomena are here reported the lateral spreading processes are widely represented in the italian apennines due to the widespread overlapping of stiff rock masses on more ductile ones the stress strain evolution of these processes was investigated by combining an analogical and a numerical modelling approach the analogue modelling reproduced the evolution of a carbonate ridge thrust over a clayey flysch with reference to the case study of mt roccatagliata mt sant angelo ridge the rock mass juxtaposition was reproduced in a laboratory experiment by overlapping a brittle concrete on a viscous ductile material these materials were selected with rheological properties physically scaled with respect to the natural rock mass prototypes the spreading phenomenon was modelled by opening horizontal panels in sequential stages and monitoring the resulting stresses within the ductile material during the experiment a stress strain modelling was also performed by an fdm numerical solution this modelling replied the laboratory experiment by testing the use of different rheological constitutive laws the resulting stresses and morphological evolutions are comparable with the analogical laboratory experiment only if a time dependent rheological behaviour is assumed for the ductile material the results show that lateral spreading processes can be properly investigated by combining analogue and numerical modelling techniques which take into account the viscous plastic behaviour of the used materials

possible emplacement of crustal rocks into the forearc mantle of the cascadia subduction zone 1 seismic reflection profiles shot across the cascadia forearc show that a 5 15 km thick band of reflections previously interpreted as a lower crustal shear zone above the subducting juan de fuca plate extends into the upper mantle of the north american plate reaching depths of at least 50 km in the extreme western corner of the mantle wedge these reflectors occur in rocks with p wave velocities of 6750 7000 ms 1 elsewhere the forearc mantle which is probably partially serpentinized exhibits velocities of approximately 7500 ms 1 the rocks with velocities of 6750 7000 ms 1 are anomalous with respect to the surrounding mantle and may represent either 1 locally high mantle serpentinization 2 oceanic crust trapped by backstepping of the subduction zone or 3 rocks from the lower continental crust that have been transported into the uppermost mantle by subduction erosion the association of subparallel seismic reflectors with these anomalously low velocities favours the tectonic emplacement of crustal rocks

heat flow variations from bottom simulating reflectors on the cascadia margin abstract a bottom simulating reflector bsr representing the base of the gas hydrate stability field was observed over a closely spaced grid of seismic lines on the continental slope of the northern cascadia margin a simple conductive model was used to calculate heat flow from the depth of the bsr a regional trend was observed in which heat flow decreased landward across the margin from an average of 80 mw m2 at a distance of 15 km from the deformation front to 65 mw m2 at a distance of 40 km this trend reflects the processes of tectonic thickening of accretionary wedge sediments and subduction of the juan de fuca plate and contrasts with the near constant heat flow across the oregon margin where the dip of the subducting plate and thus the rate of sediment thickening are slightly smaller consistent local variations were also observed notably low heat flow values over prominent topographic highs and high heat flow values over the flanks of the topographic highs at some localities over a horizontal distance of 1 2 km heat flow increased by as much as 50 from typical values of 65 to 100 mw m2 much of this variation may be due to focusing and defocusing effects of the topography alone and indicates the importance of carrying out topographic corrections to heat flow in regions of significant relief such as the continental slope however a component of the local heat flow patterns may be due to dynamic effects including the displacement of isotherms by thrust faulting and the upward migration of warm fluids along permeability channels such as faults

experimental study on the progressive collapse mechanism in the braced and tied back retaining systems of deep excavations collapses of braced or tied back excavations have frequently occurred however the influence of the failure of some retaining structure members on the overall safety performance of a retaining sys

experiments on the indentation process during cryptodome intrusions new insights into mount st helens deformation scaled experiments were carried out to study the deformation of a volcanic edifice by forcible intrusion of a cryptodome as the magma analogue is injected vertically into a sand cone asymmetric deformation is caused by the formation of a curved major shear fault which dips inward from one side of the cone to the opposite edge of the intrusion the path of the ascending silicone deviates to follow the trajectory of the fault and a lateral bulge grows slowly from the footwall of the fault the oblique push makes the bulge migrate outward causing extension upslope to form an asymmetric graben in the hanging wall of the major shear fault we suggest that the pattern of internal deformation within mount st helens prior to the may 18 1980 eruption was similar to that observed in our scaled models

seismic reflection imaging of two megathrust shear zones in the northern cascadia subduction zone at convergent continental margins the relative motion between the subducting oceanic plate and the overriding continent is usually accommodated by movement along a single thin interface known as a megathrust1 great thrust earthquakes occur on the shallow part of this interface where the two plates are locked together2 earthquakes of lower magnitude occur within the underlying oceanic plate and have been linked to geochemical dehydration reactions caused by the plate s descent3 4 5 6 7 here i present deep seismic reflection data from the northern cascadia subduction zone that show that the inter plate boundary is up to 16 km thick and comprises two megathrust shear zones that bound a 5 km thick 110 km wide region of imbricated crustal rocks earthquakes within the subducting plate occur predominantly in two geographic bands where the dip of the plate is inferred to increase as it is forced around the edges of the imbricated inter plate boundary zone this implies that seismicity in the subducting slab is controlled primarily by deformation in the upper part of the plate slip on the shallower megathrust shear zone which may occur by aseismic slow slip will transport crustal rocks into the upper mantle above the subducting oceanic plate and may in part provide an explanation for the unusually low seismic wave speeds that are observed there8 9

lithoprobe southern vancouver island seismic reflection sees through wrangellia to the juan de fuca plate multichannel seismic reflection profiles obtained on vancouver island show that above a zone of decoupling between the north american and juan de fuca plates wrangellia is underplated by two accreted terranes of probable oceanic origin both the zone of decoupling and wrangellia are disrupted by easterly dipping faults some of which are thrusts the crustal structure of wrangellia comprises paleozoic and mesozoic volcanic and sedimentary rocks disposed as roof pendants upon and large irregular masses within a ubiquitous jurassic plutonic and metamorphic complex

influence of major inherited faults zones on gravitational slope deformation a two dimensional physical modelling of the la clapiere area southern french alps abstract inherited faults are known to influence rock slope stability and gravitational deformation in spite of that in many studies few faults are identified in field and properly used in models of gravitational slope deformation the aim of this work is to study the influence of inherited faults zone density and geometry on gravitational failure processes at the massif scale using a physical modelling technique which satisfies the similarity criteria models are scaled to the well documented natural example of la clapiere in the southern french alps experiments were conducted using mechanically homogeneous material with variable fault geometry in each of tested configurations the mobilized volume was almost the same results confirmed the hypothesis that the la clapiere landslide is a shallow section of a deep seated gravitational slope deformation furthermore among the various configurations tested only one is enable to reproduce the observed superficial deformation on the la clapiere hillside this result demonstrated that the geometry of the faults at depth plays a major role on the style of gravitational deformation patterns regarding the particular case of la clapiere our results give new insights on the shape of the faults affecting the massif at depth in particular normal listric faults seem to have shallow inflexions compared to a deep seated thrust fault that was either gravitationally formed or pre existing but inactive i e sealed before slope destabilization and then gravitationally reactivated

erosion and sediment transport on steep marly hillslopes draix haute provence france an experimental field study abstract despite a thin regolith layer measured sediment yields indicate denudation rates of more than 10 to 20 mm yr 1 on strongly denuded slopes in black marl terres noires near draix alpes de haute provence overland flow and rainfall simulation experiments were conducted on three slopes in the draix erosional research basin to determine the nature and intensity of hillslope erosion processes the experiments showed that during a single storm sediment transport includes water solid mixtures with a wide range of concentrations from highly charged rill flow up to 400 g l 1 to hyperconcentrated flow up to 800 g l 1 to debris flows up to 1400 g l 1 miniature debris flows mdfs strongly controlled sediment transport as long as the sediment store was not depleted slope surfaces were completely reworked in the winter and the regolith layer was rebuilt temperature records from nine recent winter periods indicate that conditions are favourable for soil frost processes

landslide inventories for climate impacts research in the european alps landslides present a geomorphological hazard in alpine regions threatening life infrastructure and property here we present the development of a new regional landslide inventory ri for the european alps this database provides a substantial temporal and spatial picture of landsliding in the alps with particular focus on the swiss and french alps we use segmented models to evaluate recording bias in the temporal record we use scaling relationships to calculate landslide area based on a given volume for similar types of landslide with the result of this being that 9 5 of the landslides recorded in the ri now have area data recorded these landslide area data are then used to examine the log linear trend which exists between landslide area and frequency in inventories we show that this relationship is present for this historical dataset however none of the individual databases nor a unification of these contain a complete record with the small and larger landslides being recorded more consistently the use of segmented models on the temporal distribution of landslides in the ri shows that the post 1970 portion of the database is more reliable highlighted through an improved power law relationship although the frequency of medium sized landslides is still underestimated we show that creating a unified database ri can increase the reliability of datasets and consistency in recording for the use by researchers for attribution and detection studies

improved compound support system for coal mine tunnels in densely faulted zones a case study of china s huainan coal field abstract when tunnelling in densely faulted zones of coal mines serious deformation often occurs due to adverse geological conditions such as extremely broken and weak rock mass high tectonic stress fissure water to investigate a more efficient support strategy for tunnels passing through densely faulted zones a tunnel in china s huainan mining area is taken as an experimental site to study an improved support method some key factors associated with the stability of tunnels in the densely faulted zone are analysed based on the analysis of failure characteristics of a previously excavated tunnel a detailed procedure for the improved support method is proposed in which a long pipe pre grouting method together with a new kind of grouting cable are applied finally the improved support strategy is implemented in the experimental tunnel the monitoring results suggest that serious deformation is avoided and the improved compound support method is feasible for tunnels in densely faulted zones

a magnetotelluric sounding across vancouver island detects the subducting juan de fuca plate magnetotelluric1 mt and geomagnetic2 depth sounding measurements have been made at 18 sites 7 with remote reference3 across vancouver island fig 1 beneath which the juan de fuca plate is underthrusting4 5 vancouver island is part of the old accretionary wrangellia terrane6 and is located in the central portion of a 350 km forearc region that extends from the sediment filled trench7 to the garibaldi volcanic belt8 gravity9 and seismic refraction studies10 suggest that the descending plate has a shallow northeasterly dip of 8 16 with perhaps higher dips beneath northeastern vancouver island a high resolution seismic reflection survey11 along lines 1 and 3 fig 1 located a zone of strong acoustic reflections the e horizon11 near the top of the subducting juan de fuca plate at depths of 23 34 km our model of the broad band mt data defines a sloping highly conducting zone also near the top of the subducting plate at the same depths as the seismic e horizon the high electrical conductivity in this zone the e conductor is the result of saline fluid within the pore spaces of sedimentary and mafic materials of the upper oceanic crust that have been subducted to those depths beneath vancouver island these are the first data which clearly define a dipping conductive layer associated with the boundary region between converging plates they have significant implications for thrust earthquakes and metamorphic reactions that occur in subduction zones

juan de fuca slab geometry and its relation to wadati benioff zone seismicity 1 a new model of the subducted juan de fuca plate beneath western north america allows first order correlations between the occurrence of wadati benioff zone earthquakes and slab geometry temperature and hydration state the geo referenced 3d model constructed from weighted control points integrates depth information from earthquake locations and regional seismic velocity studies we use the model to separate earthquakes that occur in the cascadia forearc from those that occur within the underlying juan de fuca plate and thereby reveal previously obscured details regarding the spatial distribution of earthquakes seismicity within the slab is most prevalent where the slab is warped beneath northwestern california and western washington suggesting that slab flexure in addition to expected metamorphic dehydration processes promotes earthquake occurrence within the subducted oceanic plate earthquake patterns beneath western vancouver island are consistent with slab dehydration processes conversely the lack of slab earthquakes beneath western oregon is consistent with an anhydrous slab double differenced relocated seismicity resolves a double seismic zone within the slab beneath northwestern california that strongly constrains the location of the plate interface and delineates a cluster of seismicity 10 km above the surface that includes the 1992 m7 1 mendocino earthquake we infer that this earthquake ruptured a surface within the cascadia accretionary margin above the juan de fuca plate we further speculate that this earthquake is associated with a detached fragment of former farallon plate other subsurface tectonic elements within the forearc may have the potential to generate similar damaging earthquakes

influence of large scale topography on gravitational rock mass movements new insights from physical modeling 1 gravitational slope failures and associated rock mass movements can be observed at various scales in the same area it seems obvious that the different movement scales should be interrelated but their relationships are poorly understood we address this problem using 3 d physical modeling experiments were conducted with mechanically homogeneous models with two scale topographic features a large scale corresponds to the whole mountain several kilometers and a smaller one to a part of a mountain slope one kilometer results show that large scale relief induces large scale large volume gravitational movements introduction of small scale topographic features results not only in the generation of smaller scale landslides but also in considerable changes in the deformation pattern the various scale processes occur simultaneously and affect each other to predict the evolution of a landslide it is therefore necessary to take into account the topography and deformation pattern at various scales

a kinematic model for the formation of the siletz crescent forearc terrane by capture of coherent fragments of the farallon and resurrection plates 1 the volcanic basement of the oregon and washington coast ranges has been proposed to represent a pair of tracks of the yellowstone hotspot formed at a mid ocean ridge during the early cenozoic this interpretation has been questioned on many grounds especially that the range of ages does not match the offshore spreading rates and that the presence of continental coarse clastic sediments is difficult to reconcile with fast convergence rates between the oceanic plates and north america updates to basement geochronology and plate motion history reveal that these objections are much less serious than when they were first raised forward plate kinematic modeling reveals that predicted basement ages can be consistent with the observed range of about 55 49 ma and that the entire basement terrane can form within about 300 km of continental sources for clastic sediments this kinematic model indicates that there is no firm reason to reject the near ridge hotspot hypothesis on the basis of plate motions a novel element of the model is the resurrection plate previously proposed to exist between the farallon and kula plates by including the defunct resurrection plate in our reconstruction we are able to model the farallon hotspot track as docking against the oregon subduction margin starting about 53 ma followed by docking of the resurrection track to the north starting about 48 ma accretion of the farallon plate fragment and partial subduction of the resurrection fragment complicates the three dimensional structure of the modern cascadia forearc we interpret the so called e layer beneath vancouver island to be part of the resurrection fragment our new kinematic model of mobile terranes within the paleogene north american plate boundary allows reinterpretation of the three dimensional structure of the cascadia forearc and its relationship to ongoing seismotectonic processes

tectonic vs gravitational morphostructures in the central eastern alps italy constraints on the recent evolution of the mountain range abstract deep seated gravitational slope deformations dsgsds influence landscape development in tectonically active mountain ranges nevertheless the relationships among tectonics dsgsds and topography are poorly known in this paper the distribution of dsgsds and their relationships with tectonic structures and active processes surface processes and topography were investigated at different scales over 100 dsgsds were mapped in a 5000 km2 sector of the central eastern alps between the valtellina engadine and venosta valleys detailed lineament mapping was carried out by photo interpretation in a smaller area about 750 km2 including the upper valtellina and val venosta fault populations were also analysed in the field and their mechanisms unravelled allowing to identify different structural stages the youngest being consistent with the regional pattern of the ongoing crustal deformation finally four dsgsd examples have been investigated in detail by geological and 2d geomechanical modelling dsgsds affect more than 10 of the study area and mainly cluster in areas where anisotropic fractured rock mass and high local relief occur their onset and development is subjected to a strong passive control by mesoscopic and major tectonic features including regional nappe boundaries as well as nw se n s and ne sw trending recent brittle structures the kinematic consistency between these structures and the pattern of seismicity suggests that active tectonics may force dsgsds although field evidence and numerical models indicate slope debuttressing related to deglaciation as a primary triggering mechanism

new records of oligocene diffuse hydrocarbon seeps northern cascadia margin abstract fossil methane seeps are preserved in late eocene through pliocene marine sedimentary units of the cascadia margin of the northeastern pacific all cascadia fossil seeps are situated in the uplifted accretionary wedge that overlies extensive middle eocene coal bearing units and the paleocene early eocene siletzia large igneous province this study describes eight previously unrecorded oligocene seeps all of which are identified by small scattered carbonates with or without accompanying characteristic seep macrofauna from both inner and outer shelf depths we interpret these deposits as reflecting spatially and temporally diffuse seepage of hydrocarbon enriched fluids sourced from various carbon sources within the actively deforming accretionary prism and term them diffuse seeps 13c and 18o values from foraminiferal carbonate from the studied stratigraphic units have broad variability authigenic carbonates occurring as nodules blebs burrow fill and fracture fill indicated microbial and thermogenic methane and multiple fluid flow pathways from within the actively deforming accretionary wedge it is apparent that the complex fluid flow regime observed in modern seeps of the cascadia margin is a continuation of one established in the late eocene

runout of dry granular avalanches laboratory experiments on granular avalanching of dry sands and gravels reveal a consistent pattern of runout distance varying with fall height fall slope and volume of material for volumes rangi

split from slip and schist crustal anisotropy beneath northern cascadia from non volcanic tremor 1 polarization and splitting analyses of minute long windows of non volcanic tremor at 3 component stations in the vicinity of southern vancouver island provide new evidence for the presence of anisotropy within the crustal portion of the north american plate beneath cascadia as reported previously tremor particle motions are predominantly horizontal and inferred to manifest an upgoing wavefield composed primarily of s waves under this assumption estimates of incidence angle and back azimuth can be deduced from orientation of the smallest principle direction of motion when subjected to standard s wave splitting analysis most stations yield systematic and reproducible fast polarization directions estimates of original polarization direction are more scattered and splitting times often exhibit multimodal distributions numerical simulations wherein band limited synthetic seismograms comprising contributions from multiple sources are analyzed for splitting neatly reproduce these characteristics and thereby provide a framework for interpretation a number of stations in our study sit astride the san juan fault which based on reflection studies dips approximately 60 to 70 to the north underlying these stations is the leech river complex consisting of strongly foliated greenschist facies phyllites with steeply dipping foliations striking parallel to fast polarization directions of split s waves detailed laboratory velocity measurements at elevated pressures show that as little as 2 to 3 km of vertically dipping leech river phyllite are required to produce the observed splitting these phyllites have some of the highest s wave anisotropies measured to date and are part of a once continuous belt of anisotropic crust extending over 2000 km along the western north american coast from southern vancouver island to southwest alaska

geological and geotechnical properties of the terres noires in southeastern france weathering erosion solid transport and instability abstract the geological formation known as the terres noires covers large areas of southeastern france between the rhone valley and the pre alpine hills this formation consists mainly of dark marls of the basal upper jurassic these marls are very susceptibility to weathering and are particularly prone to erosion resulting in high solid transport this paper attempts to quantify this transport in experimental catchment areas and shows that a forest cover can play a major role in preventing this type of phenomenon weathering of this formation may also lead to gravity instabilities in fresh marl although this is rare and much more frequently in the surficial weathered material

deterministic and reliability assessment of basal heave stability for braced excavations with jet grout base slab abstract for braced excavations in deep deposits of soft clays it is common to construct a jet grout slab jgp beneath the excavation in order to restrain the wall deformation reduce the forces acting on the struts and to increase the basal heave factor of safety in this paper finite element analyses were carried out to assess the basal heave factor of safety for excavations in soft clays supported by jgp the finite element analyses indicate that the interface friction between the jet grout slab and the wall is a key component contributing to the resistance of the excavation system to basal heave failure comparison of the factor of safety from the finite element analyses with limit equilibrium predictions based on the slip circle method and the modified terzaghi method was then performed since the conventional factor of safety approach does not explicitly reflect the uncertainties of the soil and jgp properties and the excavation geometry on the excavation system performance a series of reliability analyses were also carried out to assess the basal heave factor of safety for excavations supported by jgp the provided spreadsheet template can be used to estimate the probability of basal heave failure for deep excavations supported by jet grout slabs

dipping seismic reflectors electrically conductive zones and trapped water in the crust over a subducting plate the lithoprobe program across the northern cascadia subduction zone at vancouver island has obtained geophysical data that suggest a dipping zone of trapped free pore water in the overlying continental crust land and marine multichannel seismic reflection profiles show several bands of reflectors the primary one at a depth of about 30 km is about 5 km thick dips inland and appears to coincide with an electrically conductive layer defined by magnetotelluric data the downgoing oceanic crust is imaged as a thin reflector dipping at about 15 and 10 km deeper than the primary reflector a location that is consistent with seismicity and seismic refraction data both the reflectors and the conductor have been modeled by near horizontal lamellae with 1 4 saline water porosity detailed geothermal measurements defining heat flow that decreases inland indicate that the dipping bands are nearly isothermal at a temperature of 400 500 c it is suggested that free water generated by dehydration of the downgoing oceanic plate migrates upward until reduced temperature results in hydration reactions and mineral precipitation that forms an impermeable barrier low vertical permeability is required to keep the water from separating to the top of the layer this can be reconciled with the low electrical resistivity if pore interconnection is through thin grain boundary tubes as predicted by theoretical equilibrium pore geometry although very small effective grain size is necessary an abrupt transition from high permeability to very low permeability is predicted at a several percent porosity in agreement with the modeled porosity such pore geometry with low permeability may be restricted to temperatures above about 400 c i e in greenschist to amphibolite facies conditions where grains will deform to equilibrium geometry and cracks are annealed the region above the reflective and conductive band is estimated to be within blueschist conditions consistent with the inferred high seismic velocity from refraction data and high density from gravity data

instability conditions of marly hillslopes towards landsliding or gullying the case of the barcelonnette basin south east france abstract black marl hillslopes in the french alps are strongly affected either by mass movements or by gully erosion due to their susceptibility to weathering processes this paper presents experimental data geomorphological geotechnical geomechanical and hydrological on the parameters of the material of three well known earthflows and of the two stratigraphic parts of the callovo oxfordian black marl the main objectives are to define the geomechanical behaviour of the various formations using different characterisations grain size distribution mineralogy retention capacity consolidation test direct shear test and triaxial test and to demonstrate how such soils can affect the stability of natural slopes particular care must be taken when interpreting the geomechanical tests on this evolving and very heterogeneous clay rich material there are strong relationships between the parent rock and the landslide materials this paper presents a conceptual model of the development of strength over a period of time and investigates the parameters of the material for use in slope stability analysis and risk assessment

lithospheric structure north of scothland i p wave modelling deep reflection profiles and gravity the w reflector and the flannan reflector are two enigmatic planar structures in the lithospheric mantle north of scotland mapped in three dimensions using deep reflection profiling the flannan reflector dips eastwards from the moho to a depth of 80 km at an angle of 30 whilst the w reflector is subhorizontal lying 10 20 km beneath the moho and terminating westwards against the flannan both reflectors have a strong impedance contrast and are laterally coherent over tens of kilometres wide angle seismic reflection and refraction data are used here to constrain the p wave velocity structure of the lithosphere in this region and to investigate the physical properties and geometry of these reflective structures we report the results from an integrated seismic survey in which a series of explosive shots fired at sea were recorded by ocean bottom seismographs land stations and a streamer towed by a second ship in an expanding spread configuration a well resolved p wave velocity structure for the lithosphere above the mantle reflectors is derived by inverting the seismic traveltimes to optimize the fit of the model to the data and by generating synthetic seismograms from the model to match the relative amplitudes of the observed seismic phases a high amplitude post critical reflection indicates the existence of a discrete reflecting interface dipping gently westwards between 40 and 50 km depth in the lithospheric mantle the p wave velocity model is converted to two way reflection time and correlated with normal incidence reflection data the moho structure agrees well and the reflecting interface defined by the wide angle data is coincident with the subhorizontal w reflector less distinct later arrivals observed in the data are consistent with modelled reflections from the flannan reflector in the mantle and from the extrapolated position of the outer isles fault in the lower crust modelling of the relative amplitudes and critical distances of the wide angle mantle reflection shows that the reflecting layer must be at least 3 km thick and that it has considerably higher velocity 8 5 km s 1 and density 3 5 g cm 3 than normal mantle further modelling tests the vertical structure within the layer and constrains the sharpness of the upper interface and whether the reflection amplitude could have been enhanced by internal layering gravity data measured over the region are consistent with the velocity model and with the high density layer in the mantle which is constrained by the gravity modelling to be less than 10 km thick published laboratory measurements of the physical properties of mantle rocks indicate that mafic eclogite with high velocity and density satisfies all the observations from the mantle layer our preferred hypothesis for the origin for such a layer is that it is a fragment of oceanic crust that has been subducted and metamorphosed to eclogite facies

forensic study on the collapse of a high rise building in shanghai 3d centrifuge and numerical modelling this paper reports a forensic investigation on the unexpected collapse of a 13 storey high rise residential building in shanghai soft clay prior to the building collapse a shallow excavation was

estimation of large scale mechanical properties of a large landslide on the basis of seismic results abstract knowledge of large scale mechanical properties is essential for estimating the stability of rock slopes being deformed by deep creep and especially for predicting a transition to rapid sliding standard geomechanical testing procedures may not result in significant values as the volume of the mass movements under consideration exceeds the volume of even the largest in situ tests by several orders of magnitude seismic measurements may help to estimate some of the relevant mechanical properties by direct correlation with the seismic velocities however not all parameters necessary for a stability analysis correlate closely with seismic velocities an alternative approach could be the geomechanical modelling of the structures and properties of the creeping or sliding mass as determined from seismic exploration in this paper we present an application of this approach to the giant landslide of koefels the development of the creeping rock mass which represents the initial phase of the mass movement has been successfully modelled by assuming a transition of the originally compact rock mass to soft rock controlled by a mohr coulomb and no tension yield criterion geomechanical parameters are determined by fitting the geomechanical model to the seismic results an apparent angle of internal friction has been determined in the range 20 24 these low values are compatible with the fact that a transition to rapid sliding took place in the past

seismic velocity increase and deep sea gas hydrate concentration above a bottom simulating reflector on the northern cascadia continental slope the amount of gas hydrates in the accretionary wedge sediments of the northern cascadia subduction zone off vancouver island has been estimated from multichannel seismic mcs and ocean drilling program odp data derailed semblance velocity analyses and full waveform inversion of mcs data combined with previously published odp sites 889 890 sonic log and vertical seismic profile vsp data show that sediment velocities increase downward more rapidly than the no hydrate no gas reference profile from about 1500 m s near the seafloor to a maximum of 1900 m s just above the bottom simulating reflector bsr at a subbottom depth of 224 m immediately below the bsr the mcs velocities drop to 1700 m s a low velocity of 1500 m s from the vsp data probably represents a thin layer 20 m containing free gas the difference between the reference and observed velocities is used to estimate hydrate concentration which reaches a maximum of 20 30 of the pore space above the bsr a simple interpretation of the drill core chlorinity dilution data at the odp site yields a similar hydrate concentration of 35 the estimated hydrate concentration with subbottom depth represents about 7 m 3 of hydrate per square meter of seafloor the total methane gas at stp including hydrate above the bsr and the small amount of free gas below is about 800 m 3 per square meter of seafloor or 200 tcf trillion cubic feet on the vancouver island continental slope application of the same method in the blake bahama region of the eastern u s margin indicates that the velocity enhancement and inferred hydrate concentration are very similar