new insights into the 1963 vajont slide using 2d and 3d distinct element method analyses the 1963 vajont rock slide is studied using the distinct element method dem two dimensional 2d and three dimensional 3d dem models were constructed based on information published in the literature in this study a strength reduction approach was used to calculate the slide surface friction angles required for stability the influence of several parameters was investigated in 2d namely the reservoir water level the shear stiffness of the slide surface the rock mass strength the rock mass deformability and rock joint patterns of the parameters which have been investigated the most important parameter was found to be the reservoir water level the rock mass deformability which is neglected by other investigators is also found to be important from the 3d analyses the failure friction angle was found to be sensitive to the assumptions made on the eastern boundary and could affect the failure friction angle by approximately 3 the slope was found to exhibit signs of failure beginning from s

an early pliocene thermal disturbance of the main central thrust central nepal implications for himalayan tectonics since the beginning of the collision between india and asia at about 50 ma the convergence in the himalaya has largely been taken up along major thrust zones in this study samples of the lesser himalaya formations up to 10 km below the main central thrust mct and the greater himalaya sequence up to 12 km above the mct have been analyzed by the 40ar 39ar and u pb methods to investigate the thermal history of the mct the ages can be summarized as follows 1 the youngest ages from muscovites 3 1 ma biotites 3 4 ma and hornblendes 4 1 ma all come from within 1 km of the mct 2 there is a marked asymmetry of ages between the footwall and the hanging wall of the mct the maximum mica age in the hanging wall greater himalaya sequence is 13 ma whereas a muscovite 5 km below the mct in the footwall has an age spectrum with a gradient from 400 to 1400 ma 3 five k feldspars from 6 2 to 11 9 km above the mct all give minimum ages in the range 3 0 6 4 ma and 4 a 206pb 238u age on a brannerite from the greater himalayan sequence is 4 8 ma structural and petrologic observations preclude the possibility that this age distance distribution reflects faulting within the greater himalaya sequence and production of the necessary thermal energy by shear heating requires unrealistically high shear stresses infiltration of hot fluids through the mct zone appears to be the best hypothesis to explain these data simple numerical simulations which account for heat transfer by advection within the fluid flow zone and by conduction outside it indicate that the observed age distribution could have been produced by infiltration of hot fluids through the mct zone at circa 5 to 4 ma within the following range of conditions the fluids heated rocks to temperatures in the range 470 to 510 c for less than 1 million years in a region narrower than the entire mct zone the temperature of the thermal disturbance inferred from the 40ar 39ar data is consistent with petrologic data from albitic alteration assemblages in the greater himalaya sequence and the u pb age of the brannerite is similar to the youngest 40ar 39ar hornblende age this scenario hydrothermal heating culminating at about 4 ma is similar to the model of le fort 1981 for the generation of the high himalayan leucogranites in the late oligocene early miocene by dehydration of the footwall rocks of an active thrust in the younger instance we interpret that fluids derived from the footwall rocks of the main boundary thrust migrated upward through the lesser himalaya formations and were subsequently channeled along the mct producing the thermal disturbance

the tectonostratigraphy and structure of the eastern nepal himalaya six years of geological research in eastern nepal has resulted in a new geological map of the eastern nepal himalaya which includes the region stretching from the sikkhim border in the east to the kathmandu valley in the west and from the summits of the higher himalaya in the north to the ganges plain in the south this research has permitted the determination of the tectonostratigraphy and structure of one section of the central himalayan arc south of the tibetan plateau the eastern nepal himalaya can be divided into three distinct thrust bound tectonic packages 1 the higher himalayan thrust sheet composed of the higher himalayan crystallines 2 the lesser himalayan thrust sheet composed of the lesser himalayan series and 3 the sub himalayan imbricate zone composed of sedimentary rocks belonging to the siwalik group the higher himalayan thrust sheet of eastern nepal has been thrust over the lesser himalayan metasediments a minimum of 140 km and possibly as much as 175 210 km along the main central thrust mct the lesser himalayan thrust sheet is overlain by the mct and is underlain by the main detachment fault mdf and the main boundary thrust mbt out of sequence thrust faults in the hanging wall of the mbt have breached and offset the presently inactive mct the sub himalayan imbricate zone is an emergent imbricate fan bounded by the mbt to the north and the main frontal thrust mft to the south and is underlain by the mdf which lies at a depth of between 5 km and 7 km a balanced cross section constructed across the higher lesser and sub himalaya of eastern nepal shows that the eastern nepal himalayan orogenic wedge has undergone a minimum of between 210 and 280 km of horizontal north south tectonic shortening since the initiation of the mct the lesser and sub himalaya have absorbed 70 km of north south shortening by thrusting along the basal mdf of which the sub himalayan imbricate zone has accommodated 25 km the sun kosi thrust has accommodated about 10 km and the mbt has accommodated the remaining 35 km of shortening since the initiation of the mct between 15 ma and 25 ma shortening across the eastern nepal himalaya has occurred at an average rate of 8 4 18 6 mm per year the structural geometry of the eastern nepal himalaya suggests an overall piggyback sequence of thrusting with motion transferred from the mct to the underlying mdf and its emergent splay thrust the mbt and with the mbt rotated to its present steep orientation by imbricate thrusting within the sub himalaya

focal depths and fault plane solutions of earthquakes and active tectonics of the himalaya synthetic seismograms were compared with long period body waves for nine earthquakes with epicenters in the himalayan arc to determine depths of foci and to improve fault plane solutions focal depths are shallow 10 20 km inferred slip vectors are locally perpendicular to the mountain range they plunge very gently about 10 deg in the eastern sections of the range and more steeply about 25 deg in western sections assuming india to be a rigid plate the radially oriented slip vectors imply that southern tibet extends at about half the rate of underthrusting in the himalaya and therefore probably at about 5 10 mm yr the shallow depths and gentle dips of the fault planes at least for the events in the eastern half of the range are consistent with coherent underthrusting of the indian plate beneath at least the lesser himalaya the steeper dips of fault planes in the western part of the arc might reflect deformation of the overriding thrust plate or simply a steepening of the main underthrusting zone beneath the greater himalaya

progressive failure of aznalcollar dam using the material point method the material point method which combines features of finite element and particle discretisation methods has been extended to solve coupled flow deformation problems in granular media the method is applied to simulate the construction and failure of the aznalcollar dam the brittle foundation clay is characterised by means of a strain softening mohr coulomb elasto plastic model the rupture process of the foundation is associated with a progressive failure mechanism the model predicts the development of a localised shearing band that initiates at the toe of the dam at some intermediate stage of construction and propagates downstream and upstream the shape and position of the failure surface reproduce actual field observations

aznalcollar dam failure part 1 field observations and material properties the paper describes the failure of aznalcollar dam in southern spain in april 1998 the rockfill dam slid forward and released a flow of acid saturated tailings the geology and geomorphology of the site are described the results of a detailed laboratory testing programme on the tailings material and on the overconsolidated high plasticity foundation clay are given special attention is paid to the identification of cementation of the tailings and to the strength and consolidation properties of the foundation clay failure features are interpreted on the basis of the field evidence taking into account the measured geotechnical properties of the materials involved

constraints on the structure of the himalaya from an analysis of gravity anomalies and a flexural model of the lithosphere the intracontinental subduction of india beneath the himalaya presents several similarities to that occurring at island arcs we study one of those similarities by analyzing gravity anomalies across the himalaya assuming that the topography is supported by the indian elastic plate flexed under the weight of both the overthrust mountains and the sediments in the ganga basin we first examine in detail the effects of each of the following parameters on the configuration of the elastic plate and on the gravity anomalies the flexural rigidity the position of the northern end of the elastic plate the amount of underthrusting of such a plate beneath the range and the density contrasts between the crust and mantle and between the sediments and the crust a plate with a constant flexural rigidity of about 0 7 1025 n m between 0 2 and 2 0 1025 n m allows a good fit to the data from the lesser himalaya and the ganga basin such a plate however cannot underthrust the entire himalaya instead the gravity anomalies show that the moho steepens from only about 3 beneath the lesser himalaya to about 15 beneath the greater himalaya this implies a smaller flexural rigidity beneath the greater himalaya 0 1 to 1 0 1023 n m than beneath the ganga basin and the lesser himalaya even with a thin weak plate beneath the greater himalaya the weight of the mountains depresses the plate too much unless an additional force or moment is applied to the plate the application of a bending moment unit length to the end of the plate of about 0 6 1018 n m is adequate to elevate the indian plate and to bring the calculated gravity anomalies in agreement with those observed both the smaller flexural rigidity and the bending moment can be understood if we assume that part or all of the indian crust has been detached from the lower lithosphere that underthrusts the greater himalaya we study the tectonic implications of these results by means of a series of idealized balanced cross sections from the collision to the present that reproduce several important features of the geology of the himalaya and predict an amount of eroded material comparable to that in the ganga basin and the bay of bengal these cross sections include high grade metamorphic rocks near the main central thrust and a steeper dip of it there than in the lesser himalaya they predict rapid uplift only in the greater himalaya and at the foot of the lesser himalaya

geological interpretation of dekorp 2 s a deep seismic reflection profile across the saxothuringian and possible implications for the late variscan structural evolution of central europe abstract a 250 km long deep seismic section the first of its kind in west germany s dekorp project is interpreted in terms of late variscan collisional tectonics the structural model used is based on the intracontinental thrust tectonics concept of modern collision orogens the crustal profile across the saxothuringian zone seems to indicate north facing ramps antiformal stacks and culminations within the crystalline basement of the internal mid european variscides that have been only partially overprinted by permo mesozoic crustal stretching

seismotectonics of the himalayan collision zone geometry of the underthrusting indian plate beneath the himalaya fault plane solutions and well determined focal depths of medium sized earthquakes topography and landsat imagery in conjunction with seismicity maps cross sections and available geological information are used to investigate the present tectonics of the himalayan continental collision zone most of the accurately located epicenters of events along the himalayan arc 78 e 95 e that occurred between 1961 and 1981 are concentrated in a narrow zone about 50 km wide lying between the northerly dipping main boundary mbt and main central mct thrusts most of these events are located just south of the mct though the epicenters of the events are in general well located their depths as determined by teleseismic travel time data are very unreliable events with accurately determined depths obtained from identification of surface reflected phases define a simple planar zone from about 10 km and 20 km depth with an apparent dip of about 15 this result is all the more remarkable considering that the events used were located along about an 1800 km length of the himalyan arc except for one all available focal mechanisms of events within this zone indicate shallow 30 north dipping thrusts this shallow north dipping zone apparently defines a part of the detachment that separates the underthrusting indian plate from the lesser himalayan crustal block the spatial extent and the geometry of this interplate thrust zone strongly indicate that the mbt and nearby subsidiary surface and blind thrusts rather than the mct are currently the most active structures of the himalayan arc we suggest that the great himalayan earthquakes m 8 occur along the same detachment surface as defined by the thrust type medium sized events events located to the south of the mbt and beneath the ganges foredeep show normal faulting with t axes perpendicular to the himalayan trend the above results suggest that the indian continental plate is underthrusting the himalayan crustal blocks in a relatively coherent and simple geometry and that this geometry is not much different from that observed along oceanic subduction zones the november 19 1980 earthquake that occurred near the mct near 88 5 e shows a predominantly strike slip focal mechanism one of the nodal planes of this mechanism is transverse to the himalayan structural grain and moreover this plane has a trend similar to that of the recently mapped yadong gulu rift in the tethyan himalaya and in southern tibet just northeast of the earthquake we interpret this predominantly left lateral strike slip mechanism to indicate a possible genetic relationship between transverse structural features in the underthrusting indian plate the kishangang basement fault and the upper himalayan blocks and tibet

a procedure for modelling shallow dislocation sources summary expressions for displacements on the surface of a layered half space due to an arbitrary oriented shear dislocation are given in terms of generalized ray expansions useful approximations of these expressions for shallow events as recorded at teleseismic distances for realistic earth models are presented the results of this procedure are used to generate synthetic p sv and sh waveforms for various assumptions of stress drop

reasons for the extremely high ranging planetary boundary layer over the western tibetan plateau in winter abstractthe planetary boundary layer pbl over the tibetan plateau with a mean elevation about 4 km above sea level reaches an unmatched height of 9515 m above sea level the proximity of this height to the tropopause facilitates an exchange between the stratosphere and the boundary layer however the underlying mechanisms responsible for this unique pbl have remained uncertain here the authors explore these mechanisms and their relative importance using measurements of the pbl the associated surface fluxes and single column and regional numerical simulations as well as global reanalysis data results indicate that the dry conditions of both ground soil and atmosphere in late winter cannot explain the special pbl alone rather the results from a single column model demonstrate the key influence of the stability of the free atmosphere upon the growth of extremely deep pbls over the tibetan plateau simulations with the numerical weather prediction model consortium for small scale modelling cosmo

the seismicity of kohistan pakistan source studies of the hamran 1972 9 3 darel 1981 9 12 and patan 1974 12 28 earthquakes abstract long period body waves are examined to show that the hamran 1972 9 3 darel 1981 9 12 and patan 1974 12 28 earthquakes in kohistan had focal depths of about 8 10 km all involved high angle reverse faulting thrusting and had seismic moments of about 2 2 to 2 7 1025 dyne cm these shallow depths contrast with the deeper hypocentres found in the hindu kush and northeast karakoram to the north and in hazara to the south the hamran and patan shocks were assigned depths of 45 km by the isc indicating that even well recorded events in this region may have focal depths in error by 30 km

focal depths and fault plane solutions of earthquakes under the tibetan plateau we compare synthetic and recorded p wave forms to place constraints on the focal depths and fault plane solutions of 16 crustal earthquakes beneath the highest parts 4000 m of the tibetan plateau fault plane solutions for all 16 events show combinations of normal and strike slip faulting with t axes oriented approximately east west none of these solutions show thrust faulting thus the data corroborate previous inferences that the active tectonics are dominated by east west extension focal depths for all 16 events are less than 15 km and appear to be between 5 and 10 km this style of deformation and these depths of faulting are similar to those in the basin and range province of the western united states two intermediate depth events below the crust of southern tibet also show primarily normal faulting with east west t axes the solution for one discussed by chen et al 1981 is unambiguous the solution for the other the event of august 1 1973 27 59 n 89 17 e 85 10 km mb 4 9 is less certain both apparently occurred in the mantle beneath a thick aseismic lower crust and their occurrence suggests that brittle deformation occurs there in response to a stress field similar to that operating at shallow depths beneath tibet

analysis of progressive failure and cracking in old british dams three sections representative of existing old puddle core embankments were analysed using non linear finite element techniques they had shoulders of granular fill puddle clay cores and strong foundations the analyses showed that progressive failure was negligible during drained construction operation and undrained draw down the cores were vulnerable to cracking if they were subjected to full reservoir pressure on their upstream boundary however very slow drained impounding caused mean total stresses to rise so that fracture was not indicated hydraulic fracture was predicted in a deep cut off trench filled with puddle clay cyclic drawdown and impounding increased stresses in the upstream side of the core so increasing the resistance to cracking total stresses increased and decreased with reservoir level as has been observed in the field les auteurs ont utilise des techniques des elements finis non lineaires pour analyser trois sections types de vieux barrages en enrochements a noyau en argi

a laboratory study of post rupture strength stiff intact clays exhibit rapid loss of strength after failure with the formation of slip surfaces and the development of a well defined post rupture strength envelope this paper describes an experimental study of the influence of a number of factors on the post rupture strength of initially intact samples of vallericca clay these include changes in confining pressure after the formation of a slip surface the magnitude of the relative displacement across the surface comparison between the post rupture strength envelopes in triaxial compression and extension and the influence of existing slip surfaces on the formation and strength of subsequent rupture planes formed by rotation of the principal stresses the results show that the post rupture strength envelope is well defined repeatable and not very sensitive to stress history or the rotation of the principal stresses little reduction in shearing resistance takes place for relative displacements up to about 10 mm the results are believed to be

slope stability analyses in stiff fissured clays results of torsional ring shear direct shear and triaxial compression tests on cohesive soils reveal that the fully softened shear strength is stress dependent and related to the type of clay mineral and quantity of clay size particles an empirical relationship for the fully softened friction angle is presented that is a function of liquid limit clay size fraction and effective normal stress studies of first time slides i e slopes that have not undergone previous sliding in stiff fissured clay with a liquid limit between 41 and 130 suggest that the mobilized shear strength along the failure surface can be lower than the fully softened shear strength recommendations are presented for estimating the mobilized shear strength in first time slides based on soil plasticity soils with a liquid limit greater than 30 exhibit a large difference between the fully softened and residual friction angles in these soils the presence or absence of a pre existing shear surface should be clarified

finite element analysis of progressive failure of carsington embankment progressive failure occurs when brittle soils are loaded non uniformly the average shear stress at collapse is less than peak strength the effect cannot be examined by conventional limit equilibrium stability analysis the carsington embankment slipped in 1984 just before it reached full height the slide was 30 m deep and 500 m long and instrumentation had been installed and read up to the moment of collapse the strengths of the soils involved were carefully established as was the exact geometry of the slip limit equilibrium analysis showed that at collapse the average shear stress mobilized was less than peak strength with a safety factor based on peak strength of 1 2 since the soils involved were brittle progressive failure was a probable cause of the discrepancy finite element analyses were performed in which strain softening soil properties were assumed some of these analyses are reported here the pre failure displacements the collapse height and collapse mechanism were recovered by t

aznalcollar dam failure part 2 stability conditions and failure mechanism an analysis of the conditions that led to the failure of the aznalcollar dam is made in the paper pore water pressures prevailing in the foundation clay at the time of the failure have been established on the basis of piezometric observations made after the failure a simplified consolidation analysis is first presented to interpret pore water pressure generation and dissipation and to evaluate the evolution of shear stresses along the potential failure plane both limit equilibrium and finite element analysis are used to back analyse the failure and to derive representative strength parameters along the failure surface three dimensional effects introduced by the layered nature of the foundation clay are then described they provide an explanation for the location of the slide which affected only the south eastern portion of the embankment the failure is examined in the final part of the paper from the perspective offered by the current knowledge of the strength behaviour of brittle clays the signifi

aznalcollar dam failure part 3 dynamics of the motion the motion of the aznalcollar dam slide after the initiation of the failure is examined in the paper the moving mass remained essentially rigid and newton s second law provides the basic equation to determine the resulting dam displacement velocity and acceleration resisting forces have been derived from a previous analysis of the conditions leading to failure pore water pressures induced by the forward motion of the dam are approximated as an undrained loading of the clay driving forces and their evolution in time derive from the liquefaction of tailings and the condition of constant volume of liquefied tailings pushing the moving dam forward the stable cliff left by the motion inside the tailings lagoon supports this hypothesis the model is able to reproduce closely the distance travelled by the dam it shows a low sensitivity with respect to reasonable changes of the main parameters the model computes that the slide motion lasted about 15 s and that the maximum acceleration experienced by

delayed collapse of cut slopes in stiff clay delayed failure of railway cutting slopes in stiff clays excavated in the nineteenth and early twentieth centuries has been studied for some forty years known failures have generally been deep seated more recently failures have been a problem in the slopes of motorway cuttings and embankments although generally these have been shallow the average operational strength at failure in these slides has been significantly less than the peak strength and progressive failure has been postulated as the probable cause of this progressive failure can now be analysed using advanced numerical techniques a series of coupled finite element analyses have been conducted assuming strain softening soil with properties based on the brown london clay and the results are reported they show that progressive failure is considerable and fully explain the observed field behaviour the delays experienced in the field are also recovered by the analyses progressive failure is generated primarily by the high lateral stresse