deformation history of tectonic melange and its relationship to the underplating process and relative plate motion an example from the deeply buried shimanto belt sw japan map to microscopic scale structural analysis of the hanazono assemblage of the shimanto belt in sw japan an excellent example of a deeply buried accretionary complex indicates a detailed process from underthrusting to underplating the earliest underthursting process is recorded in fabric of melange which has deformed by shear along the decollement characterized by thinning strain due to extensional breakage of blocks of sandstone and exotic materials such as basalt and pelagic sediments of oceanic affinities the deformation mechanism for melange formation for domain i is plastic flow concordant with metamorphic grade which is higher than that of domain ii the deformation mechanism for domain ii is predominantly pressure solution partly with grain scale brittle breakage for the less metamorphosed part of the hanazono assemblage the posterior underplating process recorded is contraction and thickening due to thrust stacking and folding locations of the folds developed beneath thrusts are emphasized because they are a line of evidence of thickening the main deformation mechanism of the second stage is plastic flow for domain i and cataclasis for domain ii the cataclasis in domain ii may be a result of change in strain rate and seems to be related to seismicity at the time of underplating kinematics deduced from fabric analysis of the earliest deformed melange indicates a good consistency with a relative plate motion between the eurasian and oceanic plates that is estimated from a hot spot reference plate circuit model by engebretson et al 1985 while that of the subsequent thrusting is not this fact suggests that strain partitioning in association with oblique subduction of oceanic plate was minimum during subduction another possibility for strain partitioning is the requirement of coupling between plates that are recorded by the deformation mechanisms

geology and tectonics of japanese islands a review the key to understanding the geology of asia abstract the age of the major geological units in japan ranges from cambrian to quaternary precambrian basement is however expected as the provenance of by detrital clasts of conglomerate detrital zircons of metamorphic and sedimentary rocks and as metamorphic rocks intruded by 500 ma granites although rocks of paleozoic age are not widely distributed rocks and formations of late mesozoic to cenozoic can be found easily throughout japan rocks of jurassic age occur mainly in the jurassic accretionary complexes which comprise the backbone of the japanese archipelago the western part of japan is composed mainly of cretaceous to paleogene felsic volcanic and plutonic rocks and accretionary complexes the eastern part of the country is covered extensively by neogene sedimentary and volcanic rocks during the quaternary volcanoes erupted in various parts of japan and alluvial plains were formed along the coastlines of the japanese islands these geological units are divided by age and origin i e paleozoic continental margin paleozoic island arc paleozoic accretionary complexes mesozoic to paleogene accretionary complexes and cenozoic island arcs these are further subdivided into the following tectonic units e g hida oki unazuki hida gaien higo hitachi kurosegawa south kitakami nagato renge nedamo akiyoshi ultra tamba suo maizuru mino tamba chichibu chizu ryoke sanbagawa and shimanto belts the geological history of japan commenced with the breakup of the rodinia super continent at about 750 ma at about 500 ma the paleo pacific oceanic plate began to be subducted beneath the continental margin of the south china block since then proto japan has been located on the convergent margin of east asia for about 500 ma in this tectonic setting the most significant tectonic events recorded in the geology of japan are subduction accretion paired metamorphism arc volcanism back arc spreading and arc arc collision the major accretionary complexes in the japanese islands are of permian jurassic and cretaceous paleogene age these accretionary complexes became altered locally to low temperature and high pressure metamorphic or high temperature and low pressure metamorphic rocks medium pressure metamorphic rocks are limited to the unazuki and higo belts major plutonism occurred in paleozoic mesozoic and cenozoic time early paleozoic cambrian igneous activity is recorded as granites in the south kitakami belt late paleozoic igneous activity is recognized in the hida belt during cretaceous to paleogene time extensive igneous activity occurred in japan the youngest granite in japan is the takidani granite intruded at about 1 2 ma during cenozoic time the most important geologic events are back arc opening and arc arc collision the major back arc basins are the sea of japan and the shikoku and chishima basins arc arc collision occurred between the honshu and izu bonin arcs and the honshu and chishima arcs

buckling deformations at the 2017 xinmo landslide site and nearby slopes maoxian sichuan china abstract a large catastrophic rock avalanche with a total volume of 18 0 106 m3 occurred at 5 38 am 24th june 2017 at xinmo village maoxian sichuan china resulting in 102 casualties 10 deaths 3 injuries and 89 missing we have been conducting a geological and geomorphological investigation in and around the xinmo landslide site since 2015 and we present our results here including data obtained before and after the landslide event the landslide which had an initial volume of 4 46 106 m3 of its source area was induced by rainfall on a previous landslide scar near the ridge top this initial landslide then struck and remobilized older landslide deposits in the middle and lower parts of the slope which subsequently buried xinmo village at the landslide toe the landslide occurred on a dip slope of triassic calcareous psammitic and pelitic schists the bedding plane which dips downslope to the south with an orientation of n80 w 48 s and high angle ne sw striking joints bounded the landslide source area at its base and sides respectively satellite image analysis and field observations of the slope of the landslide scar before and after the landslide strongly suggest that the beds in the source area had already begun gravitationally deforming e g buckling prior to the 2017 landslide moreover pits on the slip surface were likely the result of the dissolution of calcareous material dissolution probably reduced the rock strength along the bedding plane a rainfall event from the 16th to 24th of june 2017 probably dominated the groundwater drainage and finally triggered the catastrophic rock avalanche in addition to the 2017 landslide the hillslope just to the east of the xinmo landslide exhibits pronounced gravitational slope deformation including a tent like structures and warps induced by buckling this suggests that this slope could also fail like the xinmo rock avalanche during a future rainfall or earthquake event

long term gravitational deformation of rocks by mass rock creep abstract subsurface rocks beneath slopes are deformed to various degrees in various ways by mass rock creep mrc when they are subjected to a gravitationally unstable state for a long period mrc forms folds faults and numerous kinds of fractures such deformation is one of the main factors for deteriorating rock masses on slopes and also precursors of many landslides mrc deformations which have often been ascribed to tectonic origins can be distinguished from tectonic ones by their deformational features landforms and relationships between slope morphology and subsurface structures mrc folds are flexural slip folds that have the following mesoscopic to microscopic characteristics their axial surfaces are not smooth but are jagged and many visible openings or open fractures develop in association with the folds the jagged axial surfaces become smoother at depth and openings decrease in width with increasing overburden at the deformation site macroscopic types of mrc folds change according to the relationship between foliations and slopes buckling folds form in consequent slopes drag folds form in a deeper part of obsequent slopes and bending folds form in slopes with steep dipping foliations consequent or obsequent by downslope bowing of foliations shear fractures and tension fractures are the main deformational structures formed by mrc in massive rocks among shear fractures those of listric origin are remarkable tension fractures in general occur either in networks dividing rocks into fragments that slip and rotate irregularly in relation to each other or in parallel arrays of steeply dipping fractures an mrc fault has a shear zone consisting of a pulverized zone with gouge and a phyllitic or brecciated zone in a densely foliated rock the phyllitic zone is formed by microscopic slip along foliations in a sparsely foliated rock the brecciated zone is formed by random crushing except for the faults made through the shear fractures in massive rocks landforms due to mrc are gentle slopes bounded by horseshoe knicklines upslope convex slopes ridge top depressions multiple ridges uphill facing scarps and ridge crossing depressions

formation of inner gorges abstract under certain conditions a distinctive type of landform the inner gorge evolves in drainage basins undergoing persistent base level lowering inner gorges are typical of basins in north coastal california u s a and one such basin was selected for detailed study based on analysis of along channel distribution of rock types streamside land sliding and stored sediment as well as computation of stream power the following set of conditions appears to accompany the formation of an inner gorge 1 inner gorge parent materials are relatively competent homogenous rock types 2 in inner gorge reaches there is an absence of any base level control that would prevent downcutting 3 continued downcutting occurs due to continued base level fall and this fall is most likely induced by tectonic uplift 4 mass slope failures that form steep straight slopes debris slides are the main denudational hillslope process in the inner gorge 5 sufficient stream power is available to transport landslide derived material out of the inner gorge reach such that alluvial sediment does accumulate in the reach over time and 6 the initial condition of the landscape is a low relief erosionally mature land surface into which the inner gorge is cut this initial condition implies that inner gorges develop in tectonically rejuvenated landscapes the processes of denudation on inner gorge slopes acting over a time scale of 105 years result in a style of landform evolution that approximates parallel slope retreat this type of slope retreat maintains the distinct inner gorge morphology during sustained downcutting though the analysis is confined to one basin in northern california so as to provide a detailed framework to understand inner gorge landform inner gorges appear to be commonplace in areas of moderate to high uplift where lithologic and tectonic conditions are appropriate for their formation a global search for this landform yet to be undertaken is needed to confirm whether it indeed occurs where the above conditions are met

large deep seated landslides controlled by geologic structures prehistoric and modern examples in a jurassic subduction accretion complex on the kii peninsula central japan abstract the relationship between large deep seated landslides and geologic structures characteristic of accretionary complexes were examined in the chichibu belt on the eastern part of the kii peninsula central japan in the chichibu belt bedrock consists of jurassic accretionary complexes composed of basalt limestone chert permian triassic boundary siliceous shale ptbs mudstone sandstone and melanges with sheared shale matrices the landslides treated in this paper include prehistoric examples involving volumes greater than one million cubic meters located in the karako sono kasagi and aso areas and the modern kasugadani landslide that was triggered by the typhoon meari on 29 30 september 2004 the age of the landslide in the sono area was estimated at 20 440 70 bp and 20 820 70 bp based on ams 14c ages of wood fragments embedded in the dammed lake sediments while ages of the other prehistoric slides are not known all of the landslides occurred on dip slopes the bedding foliation and fault planes of the rocks in the area generally trend e w and dip to the north although those in the kasugadani area dip to the south as a result of local folding the landslides selectively slid along the planes of 1 ptbs horizons that were less strong than those of underlying chert 2 lithologic boundaries with physical contrasts or 3 boundary faults between melange units these geologic structures including the north dipping bedding cleavage fault planes were formed during jurassic subduction accretion and later uplift processes the movement directions estimated for the 269 landslides and unstable slopes in this region are also n nne and their slip planes are subparallel to the general bedding cleavage planes in this area thus future slides are also likely to occur on north facing slopes

a review of methods used to estimate initial landslide failure surface depths and volumes abstract this paper presents an overview of existing methods developed to characterize initial landslide failure surfaces and compute volumes based on surface information when it is buried this paper reviews the simplest models such as volume estimation based on ellipsoids and the information that can be obtained from surface displacement and morphology a simple method to define the volume of a rockslide using the identified discontinuities is also outlined the sloping local base level slbl which is able to automatically obtain a possible failure surface on the basis of a digital elevation model dem is described the balanced cross section methods applied to landslides are illustrated and can give the depth of the failure surface using predefined assumptions such as vector displacement parallel to the failure surface we can obtain an approximation of the failure surface either along translational or circular slides and this method can be improved by adding a mass balance equation recent work has also shown that using an inverse model a mass balance equation and assumptions about the rheology enables estimation of the failure surface these methods are illustrated with examples and they are applied to case studies and compared when the data available makes it possible the advantages and disadvantages of the methods are discussed this paper shows that the use high resolution topography and interpretation of the morphology is underexploited to extract information about failure surfaces geometry

fluvial incision history that controlled the distribution of landslides in the central range of taiwan abstract hillslope processes which are affected by long term river incision give rise to the risk of landsliding in active orogens we studied the river incision history and the subsequent response of rock slopes in the upstream dahan river catchment north taiwan by analyzing river long profiles hillslopes and landslide scars the results were combined with chronological data from several landform surfaces to reconstruct the history of landscape evolution at the study area the landscape comprises three levels of knickpoints and corresponding slope breaks these knickpoints propagated upstream along trunk and tributary rivers undercutting and destabilizing nearby slopes of which the oldest is a paleosurface dated to ca 150 kyr by cosmogenic nuclide dating consequently three levels of v shaped inner gorges up to 600 m deep are incised into the paleosurface the inner slopes of the three levels of gorges have mean inclinations of 35 6 37 7 and 39 8 and steepen from the higher to the lower inner gorges these three series of knickpoints and corresponding slope breaks suggest the occurrence of three phases of river incision based on analyses of the steepness indices of the river long profiles cosmogenic nuclide dating and the regional tectonic and climatic history the two earlier phases of incision are inferred to have been caused by prevailing tectonic uplifts during the middle to late pleistocene and the most recent phase by climate change in addition to uplift the long term history of river incision has controlled the distribution of deep seated gravitational slope deformation and landslides many areas of deep seated gravitational slope deformation and deep seated rockslide avalanches are aligned along the higher and middle slope breaks and debris slide avalanches are concentrated along the middle and lower slope breaks

the palliser rockslide canadian rocky mountains characterization and modeling of a stepped failure surface abstract this paper presents the results of an investigation of the prehistoric palliser rockslide rocky mountains canada conventional aerial photograph interpretation and field mapping are complemented by terrestrial digital photogrammetry these techniques allow quantification of the rockslide debris volume and reconstruction of the pre slide topography it has been estimated that the volume of rock involved in the most recent large rockslide is 8 mm 3 terrestrial digital photogrammetry is used in the characterization of the failure surface morphology which is subdivided into four types of step path geometry comprising both pre existing discontinuities and intact rock fractures incorporation of these data into various rock slope stability numerical modeling methods highlights a complex failure mechanism which includes sliding along a large scale curved failure surface intact rock bridge fracturing and lateral confinement a preliminary quantification of the contribution of intact rock bridges to the shear strength of the failure surface is presented in terms of the apparent cohesion apparent tensile strength and cumulative length of the intact rock segments

a large rockslide debris avalanche in cohesive soil at pink mountain northeastern british columbia canada abstract in early july 2002 a large rockslide debris avalanche occurred on the west slope of the pink mountain anticline in northeastern british columbia 57 04 n 122 52 w the slopes have been subjected to previous deformation and landsliding pre and post slide digital elevation models dems were created from aerial photography approximately 1 04 m m 3 of sandstone and shale travelled nearly 2 km from an elevation of 1460 m to 1010 m the landslide has a fahrboschung of 11 6 and covered 43 ha the rock debris entrained a certain amount of fine textured till and colluvium increasing its volume by 15 this entrainment caused partial liquefaction of the underlying soil thereby enhancing the mobility of the landslide we used a bingham rheological model to dynamically model the landslide with excellent correspondence between the analysis of the actual observed behaviour of the landslide

the mechanisms and characteristics of a complex rock debris avalanche at the nigeria cameroon border west africa abstract we describe a rock debris avalanche which occurred on steep symmetrical ridges resulting from fracture controlled erosion in the valley the fractures were partially filled with clayey materials probably derived from the weathering of feldspar major fault lines trending n s were located less than 7 km from the landslide location exposed sections revealed that the basal rock units were migmatites and gneisses while the upper section consisted of porphyritic granites a failure of the residual clay rich soil composed of visible crystals of feldspar and mica is thought to have triggered a long chain of events that led to the development of a rock debris avalanche which diverted the course of the rivers in the valley the area was characterised by a shallow water table in the dry season 2 to 3 m and this might have facilitated the formation of a slip surface at the regolith rock interface field observations and laboratory analysis showed that the regolith probably failed first because of high pore pressure build up and rapid reduction in shear resistance this then triggered the failure of the fractured rock units the slope movement was perpendicular to the foliation of the gneissic rocks which probably contributed to landslide mobility of interest was that changing saturation level at constant relative density of about 32 resulted in either complete or limited liquefaction indicating that the mechanism of failure depended on the moisture content of the regolith

deep seated gravitational deformation of mountain slopes caused by river incision in the central range taiwan spatial distribution and geological characteristics abstract fluvial undercutting can cause the large scale destabilization of mountain slopes and induce deep seated gravitational slope deformation dgsd that eventually leads to catastrophic failures this study analyses these processes in the catchment of the dahan river northern taiwan the area has experienced phases of river incision of up to 600 m since the middle to late pleistocene and middle pleistocene paleosurfaces at higher elevations were incised to form v shaped valleys a dgsd inventory was compiled by visual interpretation of high resolution images and field surveys were conducted to clarify the geological structures associated with dgsds and major rockslide avalanches the observed relationships between dgsds and the topography modified by long term river incision show that about 53 of all dgsds occurred on slopes along the rims of paleosurfaces which is approximately 2 and 2 5 times as many as in the incised valleys and on the paleosurfaces respectively a comparison of the power law scaling exponents of cumulative frequency area distributions shows that the frequency of dgsds along the rims of the paleosurfaces decreases less rapidly with dgsd area than for dgsds on other slopes geological investigations suggest that there are two dominant types of dgsd one is flexural toppling of slate and argillite with high angle cleavage and the other is buckling of alternating beds of sandstone and mudstone on parallel or underdip cataclinal slopes catastrophic landslides observed along or below the rims of paleosurfaces were preceded by buckling of alternating beds of sandstone and shale these beds dipped at 50 to 58 and each bed was 10 1 10 0 m thick this study suggests that the peripheral zones of the paleosurfaces may be most susceptible to future catastrophic landslides particularly on parallel or underdip cataclinal slopes comprising alternating beds of sandstone and mudstone dipping at 50 to 60 thus an understanding of the geological characteristics spatial distribution of dgsd occurrence and landscape evolution within a particular area can provide important information for landslide hazard level zoning

middle triassic evaporite sedimentation in the catalan basin implications for the paleogeographic evolution in the ne iberian platform abstract the eastern sector of the epicontinental iberian platform underwent restriction after the sedimentation of the lower muschelkalk carbonates middle triassic under extensional regime this resulted in the accumulation of the marine evaporites and the alluvial siliciclastics of the middle muschelkalk facies in the triassic catalan basin which varied between 100 and 120 m in thickness this facies consists of three lithostratigraphic units sedimented at basin scale lower middle and upper each of which includes a distinct evaporite unit in the lower unit the evaporitic sedimentation started as a transgressive sulfate lagoon pauls gypsum unit during the middle unit time a regressive evaporitic mudflat made up of a mosaic of shallow gypsum salinas surrounded by anhydrite sabkhas arboli gypsum unit developed in the northeastern half of the basin an alluvial plain was formed by siliciclastics guanta sandstone unit of a west and northwest provenance lleida high during the upper unit time a new transgressive sulfate lagoon occupied the southern half of the basin camposines gypsum whereas an evaporitic mudflat of red to variegated mudstones marls and lacustrine carbonates developed in the northern half cyclic sedimentation was mainly recorded in the evaporitic mudflat alluvial plain complex of the middle unit the sulfur isotopic values of gypsum in the three evaporite units show a decrease in 34s with time and also a clear distinction from the values of the keuper facies in the basin a division of the lithostratigraphic succession into two third order depositional sequences is proposed the middle muschelkalk succession in the catalan basin is compared with the equivalent one in the subsurface of the adjacent triassic maestrat basin which was filled with 600 m of marine evaporites

geological and geomorphological precursors of the chiu fen erh shan landslide triggered by the chi chi earthquake in central taiwan abstract special features were correlated to the geological causes of the chiu fen erh shan landslide a gigantic rockslide on a dip slope induced by the chi chi earthquake ml 7 3 in central taiwan in 1999 an aerial photo interpretation and the succeeding geological mapping of the failure were employed in this study a linear depression a steep step and a low drainage density in the landslide area were detected from the aerial photos taken in 1998 the gravitational creep was believed to result in the features of the linear depression and the low drainage density the steep step represented a buckling feature found in the field the landslide area is composed of stratified sandstone and shale with dip angles ranging 20 36 the slip surface developed along a pre existing bedding fault that resulted from flexural slip folding before the chi chi earthquake the rock on the upslope side buckled and was retained by a thick bedded sandstone downslope the earthquake shock seriously damaged the sandstone support and led to the catastrophic landslide this type of landslide is likely to occur on the moderately dipping slope of stratified rocks that were previously deformed by flexural slip folding

the role of tectonic deformation on rock avalanche occurrence in the pampeanas ranges argentina abstract both tectonic and long term gravitational slope deformation in several mountain settings have been shown to be key drivers of large scale slope instability the roles of both mechanisms are investigated in this study of the potrero de leyes rock avalanche one of the largest and better preserved slope failures in the pampeanas ranges in argentina this rock avalanche involved 0 25 km3 of highly fractured granitic rocks cropping out on an uplifted planation surface the rock avalanche left a lobate deposit up to 4 km run out into the piedmont a field survey 3d terrestrial lidar photogrammetry and gigapixel panoramic photos allowed us to map the structures on the headscarp and on the planation surface we observed a dense network of fractures with joints sets striking nne ssw ene wsw and nw se respectively representing foliation riedel and anti riedel structures that developed during the paleozoic as suggested by previous studies the decrease of rock mass strength caused by tectonic fracturing the exposure of those highly fractured rocks along a tectonically active mountain front and potential deep seated gravitational deformation occurring along nne ssw foliation planes along the mountain front suggest that tectonic and gravitational processes were key causal factors leading to the occurrence of the potrero de leyes rock avalanche

the mechanics of deep seated landslides results are presented of a sequence of laboratory tests undertaken to elucidate the behaviour of deep seated landslides in deep seated failures deformation has been reported at depths of up to 250 m in the movement zone owing to the weight of the overburden and the surrounding stress environment conventional soil mechanics cannot be used to explain effectively associations between the landslip activity and the deformation mechanisms operating within the moving mass a series of experiments has been undertaken on london clay using a high pressure servohydraulically controlled triaxial deformation system to replicate the stresses acting at the base of a large deep seated landslide a number of tests were undertaken the most significant focusing on the transition between ductile and brittle behaviour although sediments usually behave in a brittle manner at low effective stresses common to many geomorphological studies and in a ductile manner at high effective stresses the results presented here identify for the first time in mudrocks a transitional phase of behaviour in which creep like movement will manifest itself at the base of a deep seated landslide as the growth of microcracks the microcracks may eventually coalesce to form a shear surface a consequence of which is likely to be sudden failure the results thus have important implications in the understanding of movement mechanisms in large deep seated failures rates of displacement and how they may change through time 1997 by john wiley sons ltd

forecasting hazard scenarios and implications for the evaluation of countermeasure efficiency for large debris avalanches abstract the key objective of a slope failure study is to reduce deaths injuries and property damage predictions of slope failures are mandatory to reduce hazard and vulnerability of elements at risk with appropriate warning policy and properly designed countermeasures numerical modelling has been recently used as an approach to back analyse real events but few attempts have been carried out to forecast potential failure scenarios recently a debris avalanche involving about 1 2 million m 3 of debris and a nearby debris slide flow with failure volume of 0 1 million m 3 occurred in the italian prealps from the accumulation of a paleo landslide field surveys and monitoring revealed that the upper part of the slope above the largest recent landslide is unstable with a possible failure volume between 1 and 1 5 million m 3 we conducted comprehensive fieldwork and analyses including geological and geomorphological surveys compilation of a landslide inventory map collection of rainfall records study of triggering mechanisms and geotechnical properties of the failed materials slope stability analyses and back analyses of the runout phase of the landslide events through a series of slope stability analyses the possible failure volume sliding surface and topography are estimated consistent with field monitoring data furthermore with the help of calibration through back analyses of the past landslide events we assign a given degree of danger to slope elements with analogous conditions we then numerically predict the runout patterns and mobility of the potential instabilities the effectiveness of the planned passive countermeasures for potential zoning management is evaluated

seismic recordings of landslides caused by typhoon talas 2011 japan 1 large deep seated landslides occurred in nara wakayama and mie prefectures of western japan when typhoon talas passed through the region on september 3 4 2011 signals of large landslides have been recorded by seismic networks around the world and overall force estimates have been previously determined for large landslides using long period waves this study focuses on the high frequency waveforms and presents signals of 18 landslides caused by typhoon talas 2011 the location of the landslides can be determined by a seismological back projection technique and these locations correlate with the observed surface features we have found that the volumes of the landslide correlated with an energy parameter derived from the seismic records

deep seated rockslide avalanches preceded by mass rock creep of sedimentary rocks in the akaishi mountains central japan abstract seven large rockslide avalanches of sedimentary rocks are known in japan almost all of these major landslides were preceded by gravitational deformation of rocks mass rock creep mrc as inferred from geologic and geomorphic investigations of five rockslide avalanches in the akaishi mountains the mrc that preceded the rockslide avalanches in the akaishi mountains was characterized by a slow but steady downslope bowing of steeply dipping foliations which accompanied intensive deformation and fragmentation of the rock mass by shearing along foliations this deformation and fragmentation of the rock mass provides a basic cause for the occurrence of rockslide avalanches which occur when a creeping rock mass has lost its support from the lower part of a slope by stream erosion this type of mrc continues for a long time after a part of the creeping area has slid and results in longterm generation of debris by the landslide sear of the rockslide avalanche

precedent long term gravitational deformation of large scale landslides in the three gorges reservoir area china abstract large scale landslides are common in the three gorges reservoir region due to steep slopes and complex geological conditions fluctuations of reservoir level etc many phenomena and formation mechanisms related to these landslides are not well understood and need more research in this study large scale landslide evolution and formation mechanisms are thoroughly investigated in terms of precedent long term gravitational deformation pltgd three large scale landslides in the three gorges reservoir region huangtupo landslide htpl huanglashi landslide hlsl and baotaping landslide btpl are taken for example to discuss their phenomena and features of pltgd and to investigate the correlation between the pltgds and landslide many features associated with landslides are caused by slow downslope gravitational processes before landslide failure and three criteria for recognition of the pltgd features are summarized the investigation results reveal that the pltgds play an important role in landslide evolution and formation mechanism overall this paper presents evidences for pltgds of large scale landslides and their correlation with landslide evolution which is helpful to understand the formation mechanism of large scale landslides in the three gorges reservoir region

underplating process from melange formation to duplexing example from the cretaceous shimanto belt kii peninsula southwest japan accretionary complexes are considered to form through off scraping and underplating which results in the lateral and vertical growth of an accretionary prism accretion of the upper part of the oceanic crust and the formation of melange are important components of the accretionary process although the origin of melange is considered controversial in order to better understand the origin of melange and its role in accretion in particular during underplating we have studied the relationship between the formation of melange and duplexing in the miyama assemblage here the melange is composed dominantly of shale basalt chert and sandstone this study stresses the following features 1 the structure of the miyama assemblage appears to be a composite suite of landward and seaward dipping duplexes 2 the melange fabric displays a systematic asymmetry which may have resulted through shearing along the decollement and 3 facing of horses within duplexes changes from north to south coinciding with a change in the sense of shear inferred from the melange fabric which suggests that it formed prior to duplexing

landslides induced by the 2008 wenchuan earthquake sichuan china the 2008 wenchuan earthquake with a magnitude of mw 7 9 induced numerous slope movements on the hanging walls of fault surface ruptures and on steep inner valleys along the minjiang river landslide moving directions showed preferred orientations normal to the fault ruptures indicating the effect of the directivity of the seismic wave the most common landslides were of carbonate rocks which are easily dissolved and decrease the contact surfaces the largest non volcanic landslide in history was induced in bedded dolomite by the earthquake and was preceded by gravitational deformation with ridge top depressions valley fill materials were mobilized at 36 locations probably by pore water pressure build up

temporal behavior of deep seated gravitational slope deformations a review abstract deep seated gravitational slope deformations dsgsds are slow moving hillslope scale mass movements featuring characteristic landforms such as double crested ridges and upslope facing scarps that occur in diverse landscapes throughout the world although these deformations have been studied since the 1960s significant insights to the rates of dsgsds have only been gained within the last two decades owing to progress in geochronology remote sensing and instrumental monitoring absolute age and monitoring data indicate that dsgsd movements are observable over long term 102 years and short term future research directions include constraining the lifespan of dsgsds with absolute age dating and precise high resolution monitoring of spatio temporal displacement across dsgsd bodies it is of great importance to include absolute time scales in the numerical models of dsgsds furthermore combining remote sensing techniques such as synthetic aperture radar interferometry with high resolution lidar scanning and near surface geophysics offers a promising toolkit for collecting very detailed and accurate data on the short term deformation rates of dsgsds

topographic precursors and geological structures of deep seated catastrophic landslides caused by typhoon talas abstract typhoon talas crossed the japanese islands between 2 and 5 september 2011 causing more than 70 deep seated catastrophic landslides in a jurassic to paleogene lower miocene accretion complex detailed examination of the topographic features of 10 large landslides before the event recorded on 1 m dems based on airborne laser scanner surveys showed that all landslides had small scarps near their future crowns prior to the slide and one landslide had linear depressions along its future crown as precursor topographic features these scarps and linear depressions were caused by gravitational slope deformation that preceded the catastrophic failure although the scarps may have been enlarged by degradation their sizes relative to the whole slopes suggest that minimal slope deformation had occurred in the period immediately before the catastrophic failure the scarp ratio defined as the ratio of length of a scarp to that of the whole slope both measured along the slope line ranged from 5 to 21 careful examination of aerial photographs from another four large landslides for which no high resolution dems were available suggested that they also developed scarps at their heads beforehand twelve of the 14 landslides we surveyed in the field had sliding surfaces with wedge shaped discontinuities that consisted of faults and bedding suggesting that the buildup of pore pressure occurs readily on wedge shaped discontinuities in a gravitationally deformed rock body most of the faults were undulatory and were probably thrust faults that formed during accretion other types of gravitational deformation were also active e g flexural toppling and buckling were observed to have preceded one landslide

buckling of high natural slopes the case of lavini di marco trento italy abstract layered limestones with marly clayey interbeds are widespread in mountain regions where tectonics has not changed the original structure they frequently form homocline slopes that since the last deglaciation have evolved through planar block slides along bedding joints a typical dip slope showing this evolution is represented by the left flank of the adige river valley south of rovereto north eastern italy even though layers never daylight at the slope toe the exceptional persistence and weakness of bedding joints allows buckling of layers which occasionally collapse causing rock avalanches before monitoring started deformations were believed to be no longer active this conviction being strengthened by the high safety factors provided by limit equilibrium analyses sar satellite interferometry performed between 1990 and 2002 and probe inclinometer measures indicate that the slabs located uphill from the buckle folds are slowly sliding since some doubts have been raised about rock mass behaviour slope geometry and hydraulic conditions assumed in the analyses buckling was back analysed using the distinct element method dem and the discontinuous deformation analysis dda these treat the rock mass as a discontinuum and account for deformation and failure of the rock material to perform numerical analyses rock mass structure strength and stiffness were determined through extensive in situ and laboratory investigations for this purpose field surveys borehole core logging and geophysical surveys were performed and laboratory geotechnical tests on the rock material clayey interbeds and bedding joints were conducted discontinuous analyses confirmed that buckling deformations are definitely possible if some conditions are present high water pressure minor flexures modelling also indicate that buckling deformations may evolve into failures and should therefore be taken into account in evaluating long term stability of the slope

catastrophic landslide induced by typhoon morakot shiaolin taiwan abstract typhoon morakot induced the catastrophic and deadly shiaolin landslide in southern taiwan on 9 august 2009 resulting in more than 400 casualties we undertook a geological and geomorphological investigation with the aim of reconstructing the events leading up to this landslide and to clarify factors that contributed to its development cumulative rainfall reached up to 1676 5 mm in about three days under the influence of the typhoon and the shiaolin landslide with a volume of 25 106 m3 occurred one day after the peak in rainfall intensity the landslide occurred on a dip slope overlying late miocene to early pliocene sedimentary rocks consisting of silty shale massive mudstone and sandstone it started as a rockslide in the upper third of the landslide area and transformed into a rock avalanche that crossed a series of terraces and displaced or buried the village below it buried the riverbed of the chishan river and ran up the opposite slope creating a landslide dam 60 m high which was breached about 1 h and 24 min later flooding the village the velocity of the landslide is estimated to have been 20 4 to 33 7 m s 1 and its apparent friction angle was 14 which indicates its high mobility the detachments in the source area consist of combinations of bedding planes and joints or faults the landslide was preceded by gravitational deformation which appeared as hummocky landforms before the landslide and as buckle folds exposed after the event the landslide deposits consist of fragments of mudstone shale and sandstone as well as clayey material at its base this clayey material consisting of illite chlorite quartz feldspar and calcite is assumed to have strongly influenced the long rapid runout

out of sequence thrusts out of sequence thrusts oost are those thrusts which do not obey the foreland propagating or in sequence deformation style they include both isolated thrusts which develop hindward of the thrust front and sequences of break back thrusts which propagate from the foreland to the hinterland two end members of a series of oost types are recognized 1 older in sequence thrusts which are reactivated along their entire length and 2 completely new thrusts which propagate through already deformed thrust sheets between the two end members are thrusts composed partially of reactivated in sequence thrust sequences and partially of new entirely out of sequence segments oosts can be initiated for a variety of reasons including 1 keeping the orogenic wedge at critical taper 2 break back sequences from the suture zone in the overriding plate 3 ramping to overcome a sticking point which inhibits in sequence thrust propagation and 4 during simultaneous displacement along two stacked thrusts culminations which bow up segment of the upper thrust may be chopped through to permit continued displacement on the upper thrust many different types of thrust behavior including gravity sliding plucking and derivation of isolated horses from ramps may mimic some of the characteristics of oosts consequently it may be difficult to conclusively prove an oost origin for a complex thrust geometry

an overview of recent large catastrophic landslides in northern british columbia canada at least thirty eight large catastrophic landslides each either larger than 0 5 m m 3 or longer than 1 km have occurred in northern british columbia in the last three decades the landslides include low gradient flowslides in cohesive sediments long runout rock slides rock avalanches and complex rock slide flows the flowslides have occurred in a variety of sediments including glaciolacustrine silt clay rich till and clay rich colluvium the rock failures have happened in weak shale overlain by sandstone and volcanic rocks the frequency of large landslides in northern british columbia appears to be increasing suggesting a link to climate change d 2005 elsevier b v all rights reserved

large scale brittle and ductile toppling of rock slopes slow ductile toppling of rock masses commonly creates large scale mountain slope deformations in some cases rock toppling can initiate an extremely rapid catastrophic landslide this theoretical and field based study was aimed at distinguishing the two alternative modes of toppling the idea that certain key parameters of the undeformed rock mass may influence failure behaviour in a quantifiable way was examined through a parametric study of a large rock slope using the universal distinct element code udec the slope was modelled using variations of rock mass strength discontinuity orientation and persistence and toe over steepening the results indicated two distinct types of failure behaviour i ductile self stabilizing flexural toppling in weak rock with a single dominant joint set and ii brittle catastrophic block toppling in strong rock containing persistent down slope oriented or horizontal cross joints which act as surfaces of separation at the base of the toppling blocks the two m

distribution of gravitational slope deformation and deep seated landslides controlled by thrust faults in the shimanto accretionary complex abstract the cretaceous shimanto accretionary complex is a typical accretionary complex uplifted without significant deformation after accretion and in which many rain induced deep seated landslides dls have occurred we undertook a thorough geological and geomorphological investigation of the middle kii peninsula where many rain induced dls occurred in 1889 and 2011 during intense and prolonged rainfall associated with typhoons geomorphological investigations using 1 m digital terrain models dtms obtained from airborne light detection and ranging lidar before and after the 2011 typhoon allowed us to examine the microtopography e g small scarps and linear depressions and to locate deep seated gravitational slope deformations dgsds and dls low angle thrust faults with 1 m thick incohesive fault rocks were found to be aligned subparallel to each other with spacings of a few kilometers and control the distribution of dls and dgsds when a thrust fault forms a cataclinal slope river incision removes the overburden and undercuts and destabilizes the slope this process causes gravitational deformation which forms downhill facing scarps and linear depressions at higher elevations on the slope tephrochronology applied to the deposits in the dgsd induced depressions revealed that such deformation began at least 30 000 50 000 years ago and is ongoing when a high angle fault strikes along the line of maximum slope it separates a volume of the rock mass from the juxtaposing slope and facilitates gravitational slope deformation and ultimately catastrophic failure a rock mass on a thrust fault that forms a downslope plunging syncline can also be gravitationally deformed and fail a crush zone of a large scale thrust fault is a continuous weak layer that also forms a barrier to groundwater flow thus leading to a rapid increase in pore pressure during rainstorms potentially triggering catastrophic slope failure accretionary complexes which typically contain thrust faults with incohesive fault rocks thus provide a location for dgsds and dls

september 2005 rain induced catastrophic rockslides on slopes affected by deep seated gravitational deformations kyushu southern japan river rejuvenation forms convex slope breaks that can destabilize nearby slopes leading to gravitational deformation and in some cases catastrophic sliding of the slopes during heavy rainstorms such landslides were induced by typhoon 0514 which passed to the west of kyushu island japan on 6 september 2005 five large catastrophic rockslides occurred aligning along convex slope breaks 150 to 300 m above the present river bed of the mimi river the slope breaks are inferred to have been formed by rejuvenation of the river geological and geomorphological investigation revealed that these slides occurred in sandstone and mudstone of the cretaceous shimanto group and were preceded by slope deformation which generated gravitational folds and faults that appeared as scarplets at the tops of the deformed areas the slopes seem to have been in critical condition just before catastrophic failure which was triggered by the rainstorm