influence of man made cuts on the stability of pyroclastic covers campania southern italy a numerical modelling approach intense rainfall in may 1998 and december 1999 caused disastrous landslides in the sarno quindici and cervinara areas campania southern italy the landslides began with slips of the local pyroclastic covers mantling the carbonate relief and then evolved into debris flows avalanches the study discussed in this paper used a numerical modelling approach to assess the influence of man made cuts on the stability conditions of pyroclastic covers the model that was developed took into account initial failure conditions in order to better simulate the impact of man made cuts along the slopes with or without water seepage into the permeable pumiceous layers of the pyroclastic multilayer numerical analysis of stress strain field clearly showed that tracks or geomorphological discontinuities had a negative impact on the multilayer stability conditions consequently preservation of this vulnerable environment requires correct forest management practices

extension during continental convergence with application to the tibetan plateau the tibetan plateau is the product of crustal thickening caused by the collision between india and asia and is the largest active example of extensional tectonics in a zone of continental collision throughout most of the tertiary the tectonics of the plateau were dominated by north south shortening a significant proportion of which took place on east west striking thrust faults for the last 5 m y or so the plateau has been thinning by the mechanism of extension on north south trending normal faults previous investigations of the collision have been able to account for the large scale features of the tertiary deformation but have failed to explain the transition in the late tertiary to quaternary strain rate field of the plateau from north south compression to east west extension the transition could in principle be effected by a reduction in the rate of convergence between india and asia or by a uniform reduction in strength of the whole continental lithosphere of asia it could not however be effected by a reduction in strength of the elevated region alone this produces increased compressional strain rates in the weakened zone an alternative explanation for the transition to extension comes from considering the thermal evolution of thickened continental lithosphere the lower part of the lithosphere consists of a thermal boundary layer which when thickened by horizontal shortening is colder and denser than its surroundings convective instability of the thickened thermal boundary layer and its replacement by hot asthenosphere would rapidly raise the surface elevation and gravitational potential energy of the overlying part of the lithosphere the convective instability would happen in a time brief compared with the collision time scale 50 m y in the case of india and asia but would only occur after there had already been substantial thickening of the lithosphere numerical experiments show that for a range of lithospheric parameters the increase in surface height as much as 2 km and of potential energy 5 to 10 1012 n m 1 resulting from convective instability of the lower lithosphere are sufficient for east west extension to replace north south compression as the dominant feature of the stress field of the tibetan plateau

a study of critical state on an unsaturated silty soil critical state models for unsaturated soils have been proposed in recent years however the proposed models have been based on limited experimental data compacted specimens have generally been used for research and the complications of soil fabric resulting from the compaction procedures have brought difficulties into the interpretation of fundamental soil behavior there is a need to undertake further laboratory research studies on unsaturated soils particularly to obtain a fundamental understanding of the shear strength and critical state of unsaturated soils by testing soil specimens with simple soil structures suction controlled triaxial drained shear tests on an unsaturated silt were carried out as part of this research program specimens were prepared by gradually consolidating the initially slurried soil the resulting specimens had a relatively simple soil fabric and stress history the results showed that applying suction to an initially saturated specimen has a similar influence on the stre

qualifying mass failures on loess gully sidewalls using laboratory experimentation abstract the morphology of the failure scar has been a long debated issue concerning the loess plateau of china and the lack of normative data has hampered vital research in this area in this study a series of laboratory experiments were conducted to observe failure geometries and volumes under rainfall simulations the following six failure scar types occurred the sequence of the types described here may be same to that of the following text namely tf cd cu ia ps and co the number of failure masses in the experiment for scar types tf cd cu ia ps and co amounted to 45 26 23 3 2 and 1 of the total and the corresponding volumes were 58 16 20 2 3 and 1 of the total respectively this implies that tf cd and cu were the three major types of failure scars during the process of gravity erosion on a steep loess slope and the scar tf was the most significant the sensitivity coefficient the degree of variation in the target value caused by a change in a crucial factor when other conditions remain unchanged of the slope gradient and rainfall intensity for the total volume of the tf scar were 4 5 and 3 7 respectively in other words a relatively dangerous failure scar tf might appear if the slope became steeper or if the rainfall became more intensive in addition the sensitivity coefficients of the rainfall duration for the total volume of the cu scar was significant being 12 4 this shows that a long duration storm could easily induce a large volume failure with a cu scar the experimental results obtained here provide a morphogenic insight into the gravity erosion control on a loess gully sidewall

three dimensional geological structures and sliding factors and modes of loess landslides loess environments such as the chinese loess plateau are geologically fragile because of their great thickness loose structure crisscrossing ravines and gullies broken terrain dry climate severe erosion and unevenly distributed rainfall as a consequence loess areas are highly prone to environmental problems and geological hazards the geological structure of the loess is one of the main factors that controls occurrence of these geohazards this study investigated the mechanism of loess landslides and their sliding control mode from the perspective of their geological structure using this mechanism a three dimensional geological model of loess landslides was established the study shows that the structural planes in loess divide a complete slope into separate blocks which enables the fast and deep infiltration of surface water via seepage channels and reduces the shear strength of the soil mass inducing landslides the development and formation of loess landslides are primarily controlled by structural planes and influenced by infiltrated water softening the structural plains various types of structural planes may combine and form structural bodies of different types and scales which control the type depth and scale of loess landslides

the effects of slope length and slope gradient on the size distributions of loess slides field observations and simulations abstract in this study we characterize and consider the effects of slope length and slope gradient on the size distributions of loess slides to carry out this study we employ data on 275 loess slides within zhidan county central loess plateau china these data were collected in the field and supplemented by the interpretation of remote sensing images both the field observations and slope stability analysis show that loess slide size increases with the slope length slide sizes is significantly correlated with slope length showing a power law relationship in both cases however the simulation results show that slope gradient is not associated with loess slide size the main part of the link between slope gradient and slide size seen in the observations is only apparent as indicated by the strong connection between slope gradient and length statistical analysis of the field observations reveals that slope gradient decreases with increasing slope length and this correlation interferes with the potential relationship between landslide sizes and slope gradient seen in the field observations in addition the probability densities of the areas of loess slides occurring on slopes of different slope lengths are determined using kernel density estimation this analysis shows that slope length controls the rollover of the frequency size distribution of loess slides the scaling exponent increases with slope length

research on loess flow slides induced by rainfall in july 2013 in yan an nw china the yan an area located on the loess plateau in northern shaanxi province china experienced heavy and prolonged rainfall in july 2013 which induced 8 135 slope failures loess landslides and loess flow slides destroying approximately 10 000 cave dwellings and killing 45 people field investigations have indicated that the occurrence of loess flow slides is closely related to infiltration depth slope angle slope morphology rainfall intensity and loess strength the results from this study showed that a most of the loess flow slides in yan an were small scale ranging in volume from tens of cubic meters to hundreds of cubic meters b the loess flow slides only occurred at a depth of 2 m and can effectively prevent loess flow slides

three dimensional stability evaluation of a preexisting landslide with multiple sliding directions by the strength reduction technique landslide 1 is located on the right bank of the downstream side of the dam for hongjiadu hydropower station in guizhou province china in view of its close proximity to important workings the stability of the slide is of great concern ground investigation showed that the slide is potentially unstable and has two sliding directions reinforcement mainly by piles was proposed as the stabilization measure but two key questions were raised during the design of the piles 1 how could the stability of the slope be evaluated as there are two major sliding directions 2 how could the shear strength parameters of the slip band be determined as it contains a significant proportion of coarse particles in this paper we demonstrate how these issues can be addressed by the strength reduction technique first the strength parameters of the slip band are back analyzed by assuming a factor of safety of unity second the major sliding directions are determined by carrying out finite difference analyses third

failure mechanism of a slope with a thin soft band triggered by intensive rainfall rainfall is considered as one of the paramount factors for slope failures in many regions around the world particularly in tropical and subtropical regions to study the effect of rainfall storm and its duration on the stability of slopes with a thin soft band layer a 2d seepage numerical analysis and experimental investigation were implemented on an unsaturated model consisting of clayey sand soils with a thin soft layer inclined to the horizontal level by 30 at a slope angle of 50 it was subjected to intensive rainfall 20 mm h for 8 h positive pore water pressures and horizontal earth pressures were monitored during the rainstorm using sensors distributed inside the experimental model both the experimental and numerical simulation results showed that the stability of the slope decreased during the time of the rainfall storm infiltration of rainwater resulted in reduction of soil shear strength due to the loss occurring in soil suction after 1 h of rainstorm the tension cracks appeared at the top of the slope and a certain displacement was observed in the sliding blocks during the time of rainstorm the infiltrated water flowed out from the slope through the weak interlayer near to the toe causing piping and local failure so the formed cracks at the top of slope grew and expanded due to sliding of the failed soil blocks moreover the ground water table rose and the positive pore water pressures increased resulting in a reduction of effective stress which is considered as a main factor in soil shear strength a surface runoff was also present following the full saturation of the slope leading to dragging the fine particles with water flow causing erosion the combination of piping and erosion effects led to a quick local failure at the toe as well as sliding of the failed blocks and spreading of the cracks

interaction between landsliding materials and the underlying erodible bed in a loess flowslide abstract loess landslides exhibit strong interactions with the terrace sediments of the jing river on the south jingyang platform jingyang xi an china analysis of past landslide events revealed that the sand layer of this terrace was thrust up to the surface accompanied by other terrace sediments of carrying this led to the formation of a thrust nappe structure over a long distance we performed ring shear tests to examine the shear behavior of this sand layer with the finding that saturated sand was highly susceptible to liquefaction induced failure the groundwater level of the study area is high resulting in near saturation of the sand layer therefore topographic interferences contributed additional variables and increased interaction complexities simulations indicated that the liquefied sand layer was compressed and forced due to the absence of constraints the sand layer near the bottom of the slope was sheared out over a relatively short distance on the other hand particle interia and constraints of the stable layer resulted in the sand layer near the distal part of the deposits being sheared upward to the ground finally an initiation movement model of loess flowslides is proposed it describes static liquefaction of the loess layer of the slope resulted in occurrence of flowslides collisions between the deposits from the platform edge slope and terrace sediments resulted in the shear liquefaction of sands the landslide experienced four stages as they moved scraping collisions floating scrapes folded thrusts and nappe accumulation

failure mechanisms in loess and the effects of moisture content changes on remoulded strength abstract investigations into the failure mechanisms of loess slopes in the loess region of north central china have shown that a majority of mass movements are associated with shallow slab slides predominantly moving under tension the effects of soil moisture content are of paramount importance when dry vertical slopes in loess may exceed 15 m in height but under conditions close to saturation the structural strength of loess rapidly decreases causing failure of the slopes mass failure of loess occurs as collapse due to hydroconsolidation and disintegration of the loess fabric as a result of liquefaction or fluidization and can be associated with progressive failure processes local destruction of the openwork fabric of the loess can lead to small plastic movements within the loess deposits this is as close as loess can come to creep

the relationship between calc alkaline volcanism and within plate continental rift volcanism evidence from scottish palaeozoic lavas lower carboniferous lavas from the midland valley and adjacent regions of scotland are mildly alkaline and intraplate in nature the sequence is dominated by basalt and hawaiite although mugearite benmoreite trachyte and rhyolite are also present basic volcanic rocks display the lil element and lree enrichment typical of intraplate alkali basalt terrains low initial87sr 86sr 0 7029 0 7046 high end 0 4 to 5 6 and moderately radiogenic206pb 204pb 17 77 18 89 ratios are also comparable with alkali basalts from other continental rifts and oceanic islands when the carboniferous lavas are compared with subduction related lavas of old red sandstone age erupted in and around the midland valley ca 50 ma earlier at 410 ma remarkable similarities are apparent significant overlap occurs in nd and pb isotopic compositions sr isotopic compositions are however more radiogenic in the older subduction related lavas this combined with high k and rb concentrations in ors lavas may be explained by the incorporation of a sediment component derived from the subducted slab which by lower carboniferous times had been lost from the mantle source region by convection a pronounced negative nb anomaly in the ors subduction related lavas may be explained by the retention of a nb bearing phase in the mantle during hydrous melting of the mantle wedge above the subduction zone allowing for the effects of the added component from the subducted slab there appears to be no necessity to invoke separate mantle source regions for the two suites of lavas both may have been derived from chemically similar portions of mantle if volcanic arc lavas are derived from the mantle wedge the implication is that such a source lies at relatively shallow depth within the upper mantle the same may therefore apply to the carboniferous continental rift basalts this evidence combined with the fact that there is no evident hot spot trail across the midland valley despite a long period of within plate volcanism and rapid plate movements during the carboniferous suggests that the alkali basalt magmatism is not the product of a deep seated mantle plume rather the volcanism appears to owe more to passive rifting and to diapiric upwelling from a source region within the uppermost mantle

topographic controls on evolution of shallow landslides in pastoral wairarapa new zealand 1979 2003 abstract this study aims to identify topographic influence on shallow landslides and their evolution during 1979 2003 in the pastoral lower north island new zealand landslide affected sites were mapped from aerial photographs and an aster satellite image the two landslide maps were overlaid in a geographic information system arcgis to detect the changes that have taken place in landslide affected areas the change map and the landslide distribution maps were overlaid with three topographic layers of slope gradient slope position and slope aspect that had been derived from a digital elevation model in arcgis the overlay analysis revealed that landslides affected area increased from 23 75 ha in 1979 to 110 97 ha in 2003 the distribution of landslide affected sites is inversely correlated with slope gradient but positively with slope position northern aspects are the most vulnerable to landsliding containing about 78 of the total affected sites moderate slope gradients suffered the most severe landsliding in the lower to middle slopes the overall magnitude and frequency of landsliding is also related to northern and eastern octants on the moderate slope gradients in the low to moderate slope positions although the same topographic setting is conducive to landsliding in both 1979 and 2003 the rate of landsliding varies with topographic setting hence topography is critical not only to landsliding but also to the evolution of sites already affected by landslides such an understanding over large spatial scales is possible only with the use of multitemporal remote sensing data and gis that are able to speed up data collection and analysis

size distribution of loess slides in relation to local slope height within different slope morphologies abstract loess slides are widespread and dangerous gravity induced surface processes on the loess plateau of north central china the local slope height and slope morphology have been considered as important conditioning factors for landslide susceptibility mapping however the quantitative relationship between landslide size and local slope height within different slope morphologies is not very clear in this study an inventory of 155 loess slides was developed based on detailed field investigation and remote sensing image interpretation statistical analysis and gis were applied to find the quantitative relationships between the size of these loess slides and local slope height in different types of slope morphologies the analysis shows that the relationship between the loess slides volume and area exhibits a similar trend within different types of slope morphologies in addition the analysis demonstrated that loess slides are more frequent on local slope height from 40 to 100 m stepped slopes with higher pore water pressure are prone to sliding and approximate 34 19 of total loess slides occur in these stepped slopes moreover the analysis shows that the mean loess slide area and volume rapidly increase with increasing local slope height furthermore the result underlines the fact that both the local slope height and the slope morphology are two fundamental factors that control the occurrence as well as size distribution of loess slides the loess slide size remarkably increases with increasing local slope height within every type of slope morphologies these findings indicate that local slope height can limit the loess slide size and their spatial extent moreover we quantified the correlation between the loess slide size and local slope height using power law form and the scaling exponents of the correlations are different within different slope morphologies

structural and engineering geology of the east gate landslide purcell mountains british columbia canada the east gate landslide is a prehistoric landslide that was reactivated in january 1997 the slope failure took place in the lower greenschist metasedimentary units of the precambrian horsethief creek group the grizzly creek thrust is a regional overturned fault that coincides with the location of the headscarp of the east gate landslide four discontinuity sets were recognised from detailed engineering geological mapping of the headscarp and surrounding area the main scarp of the section reactivated in 1997 was sub divided into three structural domains based on its position within the landslide lithology and orientation of the discontinuity sets limit equilibrium techniques finite difference flac and distinct element udec codes were used to investigate the failure mechanism of the 1997 event the results of the field observations and numerical models suggest that the 1997 failure involved a complex mechanism incorporating components of rock slumping bi planar and pseudo circular failure that was controlled by both the orientation of the discontinuity sets and reduced rock mass quality due to tectonic deformation

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

formation mechanism analysis of irrigation induced retrogressive loess landslides abstract the loess plateau covers about 6 6 of the total land area of china landslides are serious concerns in loess plateau of china and the south jingyang tableland on the loess plateau of china has received significant attention because of frequent occurrence of gradual retrogressive loess landslides grll there however the characteristics and mechanism of grll are largely unknown in this study three typical landslide groups namely miaodian zaitou landslide group jiangliu landslide group and dabuzi landslide group are chosen as examples to analyze the characteristics of grll by performing a field survey and undrained triaxial shear tests loess fissures are found to play a key role in controlling the evolution of landslides on the one hand the mechanical properties of loess surrounding fissures rapidly weaken due to water infiltration into loess fissures on the other hand the self weight of the overlying loess increases since water infiltrates into fissures the undrained triaxial shear tests results indicate that loess specimen shows either strain hardening or strain softening behavior depending on its initial moisture content furthermore reduction in the shear strength of loess samples is observed as moisture content increases three factors associated with the characteristics and mechanism of grll group including strata lithology slope shape irrigation and rainfall are discussed finally the formation mechanism and evolution of grll are summarized into three stages namely a creep tensional stage a localized liquefaction stage and a sliding stage this study provides important insights on gradual retrogressive characteristics of loess landslides and facilitates appropriate safeguards to reduce the risk of such landslide hazards

a framework for unsaturated soil behaviour a framework is put forward which explains the shear behaviour of an unsaturated soil in terms of the total stresses and suctions acting within the soil it is based on the critical state model for

collapsibility and deformation characteristics of deep seated loess in china abstract lin z g and wang s j 1988 collapsibility and deformation characteristics of deep seated loess in china eng geol 25 271 282 as part of a comprehensive research program laboratory tests were conducted on samples of deep seated loess from different locations of the loessial regions of northern china including shaanxi gansu shanxi and honan provinces the information thus acquired on some aspects of the engineering properties of the samples such as the unit collapse pressure relationships the initial collapse pressure versus the preconsolidation pressure and deformation pressure characteristics is interesting and may prove useful to geotechnical engineers who work on projects on water poor plateaux or high river terraces in loessial regions throughout the world

erosion rates in the southern oregon coast range evidence for an equilibrium between hillslope erosion and sediment yield the relationship of hillslope erosion rates and sediment yield is often poorly defined because of short periods of measurement and inherent spatial and temporal variability in erosion processes in landscapes containing hillslopes crenulated by alternating topographic noses and hollows estimates of local hillslope erosion rates averaged over long time periods can be obtained by analysing colluvial deposits in the hollows hollows act as local traps for a portion of the colluvium transported down hillslopes and erosion rates can be calculated using the age and size of the deposits and the size of the contributing source area analysis of colluvial deposits in nine oregon coast range hollows has yielded average colluvial transport rates into the hollows of about 35 cm3cm 1yr 1 and average bedrock lowering rates of about 007 mm yr for the last 4000 to 15000 yr these rates are consistent with maximum bedrock exfoliation rates of about 0 09 mm yr calculated from six of the hollows supporting the interpretation that exfoliation rates limit erosion rates on these slopes sediment yield measurements from nine coast range streams provide similar basin wide denudation rates of between 0 05 and 0 08 mm yr 1 suggesting an approximate steady state between sediment production on hillslopes and sediment yield in addition modern sediment yields are similar in basins varying in size from 1 to 1500 km2 suggesting that erosion rates are spatially uniform and providing additional evidence for an approximate equilibrium in the landscape

neogene clay and its relation to landslides in the southwestern loess plateau china loess occurs widely in northwestern china covering neogene clay and other sedimentary units that overlie the bedrock the neogene clays of the baoji region of shaanxi province north china including the eolian hipparion and paleo sanmen lake fluvial deposits are typical clays of the southern chinese loess plateau these clays are also sensitive key strata controlling the development of large scale landslides along the slope of the loess tableland surrounding the guanzhong basin to investigate the neogene clay types and landslides in the region soil samples were tested and the macro and micro structures of the clay strata were analyzed comprehensive analysis methods including the pipette method and fine x ray diffraction were applied to quantitatively analyze the sample composition and determine the clay mineral types the neogene clays are mainly composed of illite and montmorillonite mixed layer minerals on the williams discrimination diagram of swelling potential both types of clay are medium to strongly expansive soil two case studies illustrate that rainfall reduces the shear strength of the neogene clay and raises the groundwater level rainfall has gradually destroyed the structure of the neogene clay transforming it to sliding belt soil the sliding belt lies mainly within the neogene clay layers significantly affecting the occurrence and characteristics of landslides in baoji the rise in groundwater level and weakening of the shear strength of the neogene clay are important factors in the occurrence of landslides the long term strength is a key factor affecting the development of loess landslides along the loess tableland in baoji

isotopic evidence for lithospheric thinning during extension southeastern great basin mafic rocks erupted during late cenozoic extension near las vegas nevada show temporal patterns of variation in nd and sr isotope ratios and in bulk chemistry the patterns indicate that depths of magma generation were varying through time and that lithospheric mantle was partially replaced with asthenospheric mantle as extension proceeded in alkalic rocks epsilon sub nd changed through time from minus 9 1 typical of lithospheric mantle in this area before the onset of major 16 ma extension to 6 4 typical of asthenospheric mantle after extension 4 6 ma near the end of the period of major extension 10 6 ma tholeiitic rocks erupted the epsilon sub nd of which ranged from minus 10 1 to minus 7 9 this indicates that the lithosphere had not thinned sufficiently by that time to bring asthenospheric mantle into the depth range of tholeiitic magma generation 33 50 km the lithosphere in the las vegas area appears to have thinned by about 50 less than would be predicted by the magnitude of upper crustal extension a factor of 3 or 4 and indicative of a nonuniform lithospheric response to extension

the mechanical behaviour of an unsaturated compacted silty clay a comprehensive experimental study has been carried out to investigate the volumetric and shear strength behaviour of a compacted silty clay which exhibited collapse on wetting behaviour the experiments consisted mainly of suction monitored triaxial tests carried out in a new apparatus the test results are interpreted on the basis of an elasto plastic framework using the conventional stress variable approach net stress and suction as well as an approach that takes into account the degree of saturation within two modified stress variables the evidence for critical states was examined based on the stress dilatancy relationships it was found that a critical state was observed experimentally in cases where the samples contracted over much of their stress paths but was not truly established in other cases relationships between the shear strength and specific volume at the ultimate state were established for samples over a wide range of degrees of saturation from fully saturated to the air dried state

analysis of retrogressive loess flowslides in heifangtai china abstract the heifangtai terrace is located in the arid loess area in northwestern china where a large number of landslides was induced by agricultural irrigation on the terrace resulted in slope retreat at the terrace edge at an estimated rate of 0 024 km 2 yr 1 on the basis of field investigation and monitoring remote sensing and aerial images and laboratory tests we analyzed the characteristics of slope retreat and the failure mechanism of the loess flowslides the retreat of slope is caused by the retrogressive behavior of the loess flowslide of which new failure develops at the backwall of the preceding one the groundwater level variation governs the failure process and mechanism of the flowslides the observed loess flowslides were accompanied by rapid slope deformation high velocity and long runout distance exhibiting liquefaction and fluidization during the movement in the event of a loess flowslide a small scale drained slope failure produces a concave recession first intensifies localized groundwater flow on the slope surface while the flow is being impeded by the deposit which produces an undrained condition with increasing localized pore water pressure and in turn facilitates the subsequent flowslide results of the isotropically consolidated undrained triaxial tests icu and constant shear stress drained triaxial tests csd revealed the strain softening behavior in the saturated reconstituted loess and they showed that the excess pore water pressure is associated with a small axial displacement and possibly facilitated by some alternations in the loess structure at the micro scale

new paleomagnetic results from northern china collision and suturing with siberia and kazakhstan abstract we report new results from our paleomagnetic studies of the inner mongolia autonomous region in northeastern china and the xinjiang autonomous region in northwestern china primary magnetizations are isolated in tertiary cretaceous late jurassic and late permian rocks and secondary components of magnetization of late jurassic and recent ages are seen in strata of inner mongolia western junggar basin and part of the tarim block suffered widespread complete tectono thermal remagnetization at about 280 ma permian the paleomagnetic evidence suggests that the sampled areas in inner mongolia have been part of the north china block at least since late permian time and the junggar block collided with the tarim block by late permian time our own paleomagnetic results together with available data from other parts of eastern eurasia suggest a tectonic model in which kazakhstan europe and siberia collided with each other and formed the europe siberia kazakhstan plate eur sib kaz in late permian time to the east mongolia outer mongolia inner mongolia and the north china block were also wedged together forming the mongolia north china plate mon nc by this time these two composite continental plates were not a stable unit in the late permian the geometrical relationship of the paleomagnetic poles for these two plates suggests that collision initially occurred in the late permian near the western end 50 n 75 e of the southern siberian fold belt and progressed eastward as the mon nc plate rotated and clockwise about 117 relative to the eur sib kaz plate during the early mesozoic suturing and rotation were probably complete by the late jurassic significant relative motion between the tarim and siberia blocks continued from early triassic to late jurassic as tarim moved northeastward 1400 km relative to siberia

modeling bed changes in meandering rivers using triangular finite elements a two dimensional depth averaged model was used for the simulation of scour and deposition in sand bed meandering channels with fixed banks the model employs unstructured meshes based on triangular elements and incorporates the effects of curvature induced helical flow and transverse bed slope in the direction of bed load sediment transport the model was tested using experimental data from a well known laboratory curved channel and a full scale meandering river the numerical results agreed well with observed data demonstrating that the model can reproduce the main features of bed profiles along meandering rivers such as the formation of point bars and pools

spatial variation of saturated hydraulic conductivity of a loess slope in the south jingyang plateau china abstract water infiltration in loess soils is an important trigger causing landslides in which the hydraulic conductivity of the loess plays an important role by analyzing a soil trench and soil samples from the south jingyang plateau northwest china a loess slope was investigated a horizontal adit in a lishi loess layer was also analyzed using variable head permeability tests the saturated horizontal hydraulic conductivity k h and saturated vertical hydraulic conductivity k v of the loess samples were measured results showed that the majority of the k h values are larger than the k v values indicating that the loess exhibits permeability anisotropy lilliefors test was used to determine the normality of the k h and k v results test results indicate that k h and k v measurements of the loess samples collected in the trench and adit all show log normal distribution while a number of the k h and k v values also reflect a normal distribution geo statistical analysis shows that the spherical model and the gaussian model provide the best fit variograms of k h and k v values along the trench analysis along the adit indicated the opposite results the variogram range values suggest that the spatial correlation of loess k v is greater in the vertical direction in a horizontal plane while the spatial correlation of k h in the adit is greater than that in the vertical direction loess structure rather than randomness decides the spatial variation of k h and k v measurements except for k h variation along the adit which depends on both structural factor and randomness k h and k v values of loess tend to decrease with depth results which can be described by an exponential decay model

late mesozoic calc alkaline volcanism of post orogenic extension in the northern da hinggan mountains northeastern china abstract late mesozoic calc alkaline volcanism in the northern da hinggan mountains ndhm ne china exhibits geochemical and sr nd isotopic characteristics similar to those of cenozoic calc alkaline volcanism in the basin and range province usa whole rock k ar dating results show that these volcanic sequences were erupted during 138 116 ma composed of basaltic andesites trachyandesites group 1 hornblende andesites trachytes group 2 and rhyolite lavas group 3 they are characterized by low mgo contents 4 20 lile lree enrichment and significant nb ta depletion as well as a little depleted to slightly enriched nd and weakly enriched sr isotopic ratios group 1 initial 87sr 86sr 0 70502 0 70572 nd t 0 78 to 0 91 group 2 initial 87sr 86sr 0 70497 0 70518 nd t 0 86 to 1 26 group 3 initial 87sr 86sr 0 70510 0 70635 nd t 0 41 to 0 25 the systematic variations in major and trace elements homogeneous sr nd isotope data and temporal consistency among three volcanic groups indicate that they were derived from a similar mantle source metasomatized by fluids related to the closure of the paleo asian and or mongolia okhotsk oceans and were produced through different degrees of fractional crystallization of the primary melts group 1 basaltic rocks were formed through removal of olivine and pyroxene of the primary melts while group 2 trachytes which contain the lowest lree contents e g la 24 28 ppm and relatively less enriched sr and higher nd isotope ratios were generated after removal of a few percent of lree rich minerals such as hornblende clinopyroxene and apatite of melts like group 1 group 3 rhyolite lavas exhibiting the highest abundances of strongly incompatible elements such as rb and k moderate lree contents e g la 28 53 ppm as well as apparently negative eu and sr anomalies represent the final crystallized products following a plagioclase predominant fractionation of melts like group 2 the low mgo contents and evolved affinities of the volcanic rocks imply that beneath the ndhm there existed many crustal magma reservoirs throughout the eruption episodes in which mantle derived primary melts had experienced intense differentiation these facts in combination with the contemporaneous basin and range tectonic regime suggest that the extensive calc alkaline volcanism in the ndhm was attributed to post orogenic diffuse extension rather than either an upwelling mantle plume or mesozoic oceanic plate subduction

a stochastic hydro geomorphological model for shallow landsliding due to rainstorm abstract a prediction model of shallow landsliding is proposed it considers not only the deterministic aspects containing slope stability saturated throughflow and a soil regolith depth development but also the stochastic aspects of intensity and duration of rainfall it turns out that the probability of saturated throughflow which is the direct trigger mechanism to shallow landsliding can be expressed by a log normal distribution the short term probability of landsliding is defined as the excess probability that the depth of saturated throughflow surpasses the critical value the average recurrence interval t av of landsliding can be calculated as the expected value this model was applied to a test field where a lot of shallow landsliding occurred at a heavy rainstorm in 1988 then a dem of 5 m grid interval was utilized to calculate t av at every grid point consequently it was found that the percentage of the landslide grid number to the total grid number for every t av rank increases when t av decreases therefore it is confirmed that t av is an index of the susceptibility to shallow landsliding and the distribution map of t av can be regarded as a kind of hazard map the spatial distribution of t av reveals its significant dependence on the topography

formation and development of the structure of collapsing loess in china abstract gao g 1988 formation and development of the structure of collapsing loess in china eng geol 25 235 245 it is well known that in china the regional variations in microstructure of loess are in phase with the overall tendency for collapsibility gradually decreasing from the northwest to the southeast these differences are consistent with variations in climatic conditions this indicates that the structure of collapsing loess is closely related to the climatic condition and geological environment based on the microstructure analyses it can be assumed that the formation and development of the structure of collapsing loess in china has undergone five stages the loessization stage the formation stage the development stage the degeneration stage and the clayization stage the five stages of loess regularly exist in different regions of the loess plateau this also shows that under the modern climatic condition the collapsing loess in the northwest of the loess plateau in china is still developing however the feature of collapsing loess is gradually disappearing in the southeast of the loess plateau

occurrence of landsliding on slopes where flowsliding had previously occurred an investigation in a loess platform north west china abstract loess slides in south jingyang platform shaanxi province usually occur on slopes where loess flowslides had previously occurred numerical modeling shows that flowslide occurrence causes conditions that increase shear stress and water content in the subsequent slopes both of these factors move the soil stress states towards its theoretical failure line under these conditions only small increases in water content can cause soil collapse this leads to the backscarps of former flowslides being much more prone to landsliding wetting test results show that the loess can collapse suddenly as the water content gradually increases therefore the wetting process induced by continued irrigation may result in the subsequent slides during constant water content tests of the loess material soil shear strength increases with the development of specimen deformation therefore slide mobilization which may be a relatively slow process is dependent on whether the wetting conditions exist finally a slope evolution model for loess platforms is proposed in this study

the geodynamic evolution of the eastern eurasian margin in mesozoic times abstract the cenozoic features of eurasia such as marginal seas and intracontinental deformation are unraveled using available paleomagnetic and field data the late cretaceous shape of eurasia is then reconstructed from the examples of sw japan and south russian far east the major features of the mesozoic eurasian margin suture zones marked by ophiolites or high pressure metamorphic rocks olistostromes characterized by the lithology of the olistoliths calc alkaline magmatism and strike slip faults are outlined correlations of the ophiolitic belts and the olistostromes along the eastern eurasian margin from borneo to siberia allow the definition of four microcontinents the west philippines south japan and the anuy and okhotsk sea microblocks from south to north the mesozoic structure of the eurasian margin is due to three processes 1 1 oceanic subduction and the accretion of subduction complexes 2 2 the collision of these microcontinents with eurasia between the late jurassic and the late cretaceous and 3 3 the reactivation of the ophiolitic sutures by left lateral wrench faulting

irrigation induced loess flow failure in heifangtai platform north west china because the construction of dams and hydro electric power stations of liujiaxia and yanguoxia across the yellow river in west gansu province north west china inhabitants in the reservoir areas were resettled in heifangtai loess platform irrigation thus started in 1968 perched water table was significantly raised and resulted in many loess flow failures in the past 30 years this type of landslide was often featured by long runout distance high speed and recurrence laboratory tests along icu and csd stress paths were performed it is shown that the loess has a strong strain softening behavior and instability can occur in drained condition before undrained liquefaction the failure mechanism of loess flow can be interpreted as the following process with increasing perched water table collapse in loess was first triggered in drained condition and led to undrained loading to adjacent soil in the lower saturated part of the loess platform under gravity loading applied by upper dry loess undrained flow failure mobilized eventually

analysis of the distributions of stress in natural ridge forms implications for the deformation mechanisms of rock slopes and the formation of sackung abstract stress distributions in general asymmetric ridge forms derived from 13 ridges in british columbia and colorado are modelled in two dimensions with a finite difference method in each of the 13 ridges sackung scarps tension cracks trenches can be found spatial correlations between stress concentrations and these sackungen landforms are investigated for the mean ridge forms rock mass properties for the modelled ridges are developed using the hoek brown criterion and the geological strength index gsi gravity loading and combined gravity tectonic loading on the ridge forms are considered the importance of representing in situ rock masses with an elastoplastic as opposed to elastic constitutive criterion is discussed the resulting stress distributions for the three general ridge classes indicate that different processes are responsible for the formation of sackungen landforms and slope deformations in each type of ridge

laboratory characterization of rainfall induced loess slope failure loess slopes are widely distributed throughout the northwestern region of china and are prone to slope failure in response to heavy rainfall we undertook three groups of flume experiments in the laboratory to study loess slope dynamics under artificial rainfall conditions additionally a laser scanner was used to observe loess landslide deformation characteristics and failure development a numerical analysis of unsaturated seepage in loess slopes because of rainfall infiltration was performed moisture content pore water pressure and slope deformation were monitored to quantify the relationship between rainfall infiltration and loess slope stability movement of the wetting front near the slope surface was triggered by rainfall and related to rainfall intensity and duration which is consistent with the numerical solution rainfall infiltration increased pore water pressure producing gravity driven landslides we observed that landslide development began with local failure in the toe slope that gradually retreated toward the crown forming a multi sliding displacement and eventually resulting in total slope failure