effect of partial melting on rock deformation experimental and natural evidences on rocks of granitic compositions abstract deformation tests at constant strain rate 10 5 s 1 at 210 250 mpa confining pressure and at 560 900 c are performed on an aplite with varying water contents the mechanical behaviour is correlated with the microstructure after a stage of plastification depending on the temperature and on the water content the rock strength falls dramatically under such confining pressures before melting and before straining the pores of the wet rocks burst as the thermal expansion of water develops a local high pore pressure which causes cracking and fracturing in our opinion this pore bursting will increase the effects of thermal cracking due to the differential expansion of the minerals the rocks exhibit a uniform crack network with increasing temperature melting occurs in the cataclased rock the crack development and melting depend on the initial water content the loss of cohesion obtained either by cracking or by cracking and melting provokes a dramatic weakening axial shortening induces cracking parallel to 1 and melt transfer into extensional regions deformation is concentrated in dilatant shear bands at the highest temperature 900 c a melt film network is rapidly established and induces a very low flow stress melt effects in naturally deformed gneisses suggest that biotite breakdown furnishes a silicate fluid which induces hydraulic fracture and melt dispersion

tectonic constraints on a deep seated rock slide in weathered crystalline rocks abstract deep seated rock slides dsrss recognised as one of the most important mass wasting processes worldwide involve large areas and cause several consequences in terms of environmental and economic damage they result from a complex of controlling features and processes dsrss are common in calabria southern italy where the complex geo structural setting plays a key role in controlling the geometry of the failure surface and its development this paper describes an integrated multi disciplinary approach to investigate a dsrs in palaeozoic high grade metamorphic rocks of the sila massif it focuses on the definition of the internal structure and the predisposing factors of the serra di buda landslide near the town of acri which is a paradigm for numerous landslides in this area an integrated interdisciplinary study based on geological structural and geomorphological investigations including field observations of weathering grade of rocks minero petrographic characterisations geotechnical investigations and in particular fifteen years of displacement monitoring is presented stereoscopic analysis of aerial photographs and field observations indicate that the serra di buda landslide consists of two distinct compounded bodies i an older and dormant body 7 ha and ii a more recent and active body 13 ha that overlies the previous one the active landslide shows movement linked to a deep seated translational rock slide block slide the velocity scale ranges from slow 1 6 m year during paroxysmal stages to extremely slow

spatial distribution of landslides triggered by the 2008 ms 8 0 wenchuan earthquake china abstract the ms 8 0 wenchuan earthquake of may 12 2008 is one of the most disastrous earthquakes in china the earthquake triggered tens of thousands of landslides over a broad area including shallow disrupted landslides rock falls deep seated landslides and rock avalanches some of which buried large sections of some towns and dammed the rivers the purpose of this study is to investigate correlations between the occurrence of landslides with geologic and geomorphologic conditions and seismic parameters over 56 000 earthquake triggered landslides with a total area of 811 km 2 are interpreted using aerial photographs and remote sensing images taken following the earthquake the spatial distribution of these landslides is analyzed statistically using both landslide point density lpd defined as the number of landslides per square kilometer and landslide area density lad the percentage of the area affected by landslides to determine how the occurrence of landslides correlates with distance from the epicenter distance from the major surface rupture seismic intensity and peak ground acceleration pga slope angle slope aspect elevation and lithology it is found that both lad and lpd have strong positive correlations with slope steepness distance from the major surface rupture and seismic intensity and that pre sinian schist and cambrian sandstone and siltstone intercalated with slate have the most concentrated landslide activities followed by the permian limestone intercalated with shale and devonian limestone statistical analyses also indicate that the major surface rupture has influence on the spatial distribution of landslides because lad and lpd are relatively higher on the hanging wall than on the footwall however the correlation between the occurrence of landslides with distance from the epicenter of the earthquake is complicated rather than a relatively simple negative correlation as found from other reported cases of earthquakes this is possibly due to complicated rupture processes of the earthquake

effects of near fault seismic loadings on run out of large scale landslide a case study this study presents the run out analysis of the daguangbao landslides subjected to near fault multi direction earthquake forces using discontinuous deformation analysis dda the daguangbao landslide is the largest landslide induced by the 2008 wenchuan earthquake in order to investigate the effects of near fault seismic force on landslide run out kinematic behavior of sliding mass is simulated by a dynamic discrete numerical analysis method called dda in this simulation based on the shape of failure surface and the feature of slope geology the whole slope is divided into three parts base block upper sliding mass and lower sliding mass then two sliding masses are divided into the smaller discrete deformable blocks based on pre existing discontinuities size effect of the huge landslide is also considered baseline corrected real horizontal and vertical ground motions are taken as volume force acting to the base block the results show that seismic force has a significant influence on the landslide progression sliding distance and shape of post failure results of the horizontal and vertical situation are in good agreement with those obtained from post earthquake field investigation remote sensing image and description from the survivors

controls on the strength of coupling among climate erosion and deformation in two sided frictional orogenic wedges at steady state 1 many important insights regarding the coupling among climate erosion and tectonics have come from numerical simulations using coupled tectonic and surface process models however analyses to date have left the strength of the coupling between climate and tectonics uncertain and many questions unanswered we present an approximate analytical solution for two sided orogenic wedges obeying a frictional rheology and in a condition of flux steady state that makes explicit the nature and sensitivity of the coupling between climate and deformation we make the simplifying assumption that the wedge grows in a self similar fashion consistent with airy isostasy such that topographic taper is invariant with orogen width tectonic influx rate and climate we illustrate first how and why the form of the erosion rule matters to orogen evolution and then derive a physically based orogen scale erosion rule we show that steady state orogen width crest elevation and crustal thickness are controlled by the ratio of accretionary flux to erosional efficiency to a power dictated by the erosion process remarkably we show that for most combinations of parameters in the erosion law rock uplift rate is more strongly controlled by erosional efficiency than it is by the accretionary flux further assuming frontal accretion with no underplating the spatial distribution of erosional efficiency dictates the relative rock uplift rates on the pro wedge and retro wedge and the time averaged trajectories of rocks through the orogen the restriction to invariant frictional properties is conservative in these respects systems subject to positive feedback between erosion and rheology will exhibit even stronger coupling among climate erosion and deformation than shown here

lateral variations of thermo mechanical properties in the tyrrhenian northern apennine region abstract we present lithospheric strength profiles calculated for a transect running from the island of corsica in the west to the apennine foredeep in the east strength profiles are constructed at locations selected on the basis of the availability of seismic heat flow gravity data and earthquake foci distribution rheological modelling points to the presence of strong lateral variations in the thermo mechanical state of the lithosphere the tyrrhenian tuscany area has a low rigidity in relation with the intense stretching active from the early miocene and with very high heat flow associated with asthenospheric rise on the contrary hinterland corsica and apenninic foreland areas adriatic area show a higher level of lithospheric strength effective elastic thickness estimates confirm this scenario exhibiting a strong reduction from the northern tyrrhenian to the inner apennines and then an abrupt increase in correspondence of the adriatic plate the distribution of earthquake focal depths confirms the presence of a brittle rheology in the first kilometres of the crust in the tuscany area whereas close to the plate boundary much lower thermal gradients partly induced by the westward plunging adriatic plate enable seismic activity to occur at larger depths

mechanics of fold and thrust belts and accretionary wedges cohesive coulomb theory a critically tapered fold and thrust belt or submarine accretionary wedge is one that is on the verge of coulomb failure everywhere including its base where frictional sliding along a decollement is assumed to be occurring cohesion within a wedge can add significantly to the overall strength near the toe the effect of this is to decrease the near toe taper leading to a critical topographic profile that is concave upward if the decollement is planar we obtain an approximate self consistent solution for the state of stress within a thin skinned cohesive critical coulomb wedge and determine the relationship between the wedge taper and its strength and basal friction the theory is then applied to the presently deforming fold and thrust belt of western taiwan fitting of theoretical critical wedge shapes to topographic profiles and measurements of the step up angles of thrust faults from the basal decollement are used to constrain the taiwan wedge strength parameters an attractive assertion fully consistent with all the observations is that the mechanics of fold and thrust belts and accretionary wedges is governed by normal frictional and fracture strengths of rocks measured in the laboratory in particular if byerlee s law b 0 85 is adopted as the coefficient of sliding friction on the base we find a coefficient of internal friction 0 9 1 0 in the wedge and a wedge cohesion so 5 20 mpa other solutions having strengths and ambient stresses up to 4 times lower than this can also however satisfy the data

distribution pattern of earthquake induced landslides triggered by the 12 may 2008 wenchuan earthquake abstract this paper presents the preliminary results of an extensive study of the mapping the distribution of landslides triggered by the wenchuan earthquake in sichuan province china on 12 may 2008 an extensive landslide interpretation was carried out using a large set of optical high resolution satellite images e g aster alos cartosat 1 spot 5 and ikonos as well as air photos for both the pre and post earthquake situation landslide scarps were mapped as points using multi temporal visual image interpretation taking into account shape tone texture pattern elevation and ridge and valley orientation nearly 60 000 individual landslide scarps were mapped the landslide distribution map was compared with the inventory map that was prepared directly after the earthquake which contains about 11 000 individual landslide points through the calculation of normalized landslide isopleths maps remarkable differences were observed as the earlier inventory mapping did not consider the pre earthquake situation and did not consider all individual landslides as part of the landslide inventory landslides were identified that had blocked the drainage and had formed landslide dams the landslide distribution was compared with a number of aspects such as the seismic parameters distance to epicenter distance to fault rupture co seismic fault geometry and co seismic slip distribution and geology the most remarkable correlation found was with the co seismic slip distribution and the fault geometry landslide distribution in the section of the fault that had mainly a thrust component with low angle fault plane was found to be much higher than the sections that had steeper fault angles and a major strike slip component

reaction enhanced ductility the role of solid solid univariant reactions in deformation of the crust and mantle abstract in collision belts and subduction zones penetrative deformation of thrust sheets may be catalyzed by metamorphic reactions if the reactions have a significant effect on the mechanical properties of rocks reaction enhanced ductility may result if a reaction produces a significant decrease in grain size thus allowing the rock to deform superplastically the product grain size of a reaction is a function of the ratio of nucleation and growth rates this ratio varies along any pressure temperature time ptt path and only attains a significant value at a certain distance from an equilibrium boundary a comparison of rates of change of p and t along typical segments of ptt paths for crustal rocks leads to the conclusion that a high nucleation rate a small grain size and resulting superplastic deformation are more likely to be achieved when reaction boundaries are crossed during underthrusting rather than during the thermal readjustments of a perturbed geotherm following crustal thickening or during uplift an example of reaction enhanced ductility occurs in eclogite facies metagranitoids in the sesia lanzo zone western alps where medium grained plagioclase reacted to fine grained jadeite quartz during early alpine underthrusting microstructural evidence from shear zones shows that the jadeite quartz aggregates were highly ductile and it is inferred that the small grain size allowed superplastic deformation further evidence suggests that this process operated during regional deformation of metagranitoids rubie 1982 the reaction of olivine to spinel or the beta phase by metastable overstepping of the two phase stability fields in a subducting plate ringwood 1975 may result in fine grained products and thus may be analogous to the albite jadeite quartz reaction the consequent decrease in effective viscosity is likely to have important consequences for plate dynamics at and below the depths of major phase transitions

the role of a heterogeneous inclusion during continental collision abstract we study a simple model of the deformation due to collision between two continental plates the model is patterned after the geometry of the india asia collision but it may be applicable to more general situations the collision is modelled by the indentation of a viscoplastic plate asia by a rigid punch india a finite element approach capable of dealing with finite deformation heterogeneity and non linear rheologies is used to study the role of an inclusion of increased rigidity on the viscoplastic flow of the plate the heterogeneous zone was chosen to approximate the shape and position of the tarim basin behind tibet the lateral boundaries of the plate were defined so as to approximate those that are believed to apply for the asian plate i e fixed boundaries to the west and north free boundaries to the west and south several geometries and contrasts of rheology were analyzed to verify the general validity of our results the purpose was to determine the main kinematic features of the flow not to model the particular case of tarim it is found that the heterogeneity affects the flow in a drastic way even for small contrasts of rigidity and for small size heterogeneities the main effect of the heterogeneity is to create two important shear zones or internal boundary layers the most important is in front of the inclusion separating the main flow from the inclusion as the flow proceeds the inclusion rotates and the shear zone progressively bends in qualitative agreement with the bending of the large strike slip faults like the altyn tagh that separates the tarim from tiber our model of continuous deformation does not allow for the formation of faults or fractures but the shear zones may be understood as the initial stages for the generation of fractures or velocity discontinuities another shear zone develops to the left of the inhomogeneity near the fixed boundary and in the wake of the punch the role of these shear zones is to isolate the heterogeneity from the main flow to facilitate its rigid rotation inside the flow of the softer plate a final observation is that in the presence of the heterogeneity the lower left hand corner rotates almost like a rigid block producing a sharp bend on the left hand side of the plate as the inclusion rotates pushed by the punch this rigid block rotates clockwise to open up the space necessary for the homogeneity

stratigraphy and ductile structure of the presidential range new hampshire tectonic implications for the acadian orogeny the presidential range of new hampshire with its unique high relief contains exceptionally well exposed rocks of the acadian orogenic hinterland these rocks are within the central maine terrane a belt of complexly metamorphosed and deformed silurian and devonian metasedimentary rocks the presidential range lies between regions to the south dominated by refolded nappes and synkinematic high grade regional metamorphism and regions to the northeast dominated by overlapping multiple deformation and contact metamorphism produced by late and post acadian plutons to better understand these complex tectonic variations and in particular to clearly and accurately determine the effects of the devonian acadian orogeny in a well exposed region the bedrock geology in the alpine zone of the presidential range was mapped in great detail the results of the stratigraphic and ductile structural analyses are presented here five metasedimentary formations have been recognized and constitute a conformable stratigraphy which from oldest to youngest are the silurian rangeley perry mountain smalls falls and madrid formations and the devonian littleton formation the littleton formation has been subdivided into fifteen different members and three submembers based on variations in bedding style of the schists and quartzites and other lithologic peculiarities the madrid smalls falls and perry mountains formations are extremely thin consistent with their deposition near the silurian tectonic hinge the rangeley formation is interpreted as an olistostromal melange and has been subdivided into three different members and six submembers on the basis of lithologic variations in the gneiss and subordinate units the presidential range preserves three phases of ductile folding f1 f2 and f3 and a single phase of thrust faulting t1 well constrained southeast east or northeast facing directions and consistent asymmetry of f1 nappe limbs suggest that nappe vergence was easterly severe refolding of some nappes resulted during f2 collapse of the nappe pile the west vergent greenough spring thrust fault truncated f1 and f2 structures and juxtaposed nonmigmatized and migmatized rocks f3 east vergent folding dominates the alpine zone and represents the final tightening of acadian structures which occurred after early granitic plutonism and prior to the emplacement of postkinematic granitic sheets the structural and sedimentological evidence supports the existence of a subduction system that was active beginning in the early silurian on the east flank of the bronson hill anticlinorium with a west dipping subducting slab geometry this system persisted throughout the acadian

long term investigation of a deep seated creeping landslide in crystalline rock part i geological and hydromechanical factors controlling the campo vallemaggia landslide slope movements of the deep seated campo vallemaggia landslide in the southern swiss alps have been reported for over 200 years surface and borehole investigations of the unstable mass reveal an u

geodynamics of the tarim basin and the tian shan in central asia the india asia collision has caused crustal thickening in tibet by at least a factor of 2 in the last 20 30 myr of this collision the tian shan mountain range has also been reactivated the tarim basin however shows little internal deformation we describe a series of numerical experiments which constrain the effective lithospheric strength parameters of the tarim basin and the tian shan in the context of a thin viscous sheet model we use a finite element representation of the thin viscous sheet model to approximate the deformation field in the india asia collision and compare model crustal thickness distributions with that inferred from a local isostatic model of topography the experiments show that a strong tarim basin while undergoing little internal deformation transfers strain to the tian shan producing significant crustal thickening in the tian shan region based only on diagnostic parameters such as the maximum thickening in the tian shan and the minimum in the tarim basin the principal features of the topography can be approximately reproduced using models in which either the tarim basin is strong or the tian shan is weak or both for a rheological model in which the stress versus strain rate exponent is n 3 the strength coefficient for the strong tarim basin model vtarim is between about 1 7 and 2 for the weak tian shan model the relative strength coefficient vtian is between about 0 65 and 0 75 if both strong tarim and weak tian shan are included there is a trade off between the required values of vtarim and vtian and the shape of the predicted crustal thickness profiles better matches the observed profiles the steep topographic slope on the southern margin of the tarim basin requires that it is anomalously strong while the rapid decrease of topographic height to the north of the tian shan requires that it is anomalously weak similar conclusions are obtained with a rheological model based on n 10 simplified rheological models of the lithosphere show that the variations in lithospheric strength may be explained by changes to the moho temperature of the order of 10 to 30 c

spatial distribution analysis of landslides triggered by 2008 5 12 wenchuan earthquake china abstract the 2008 5 12 wenchuan earthquake seismic magnitude mw 7 9 according to the usgs triggered a great number of landslides a spatial database of landslides is built by interpreting the remote sensing rs data which covers 11 counties severely damaged by the earthquake with area of about 31 686 12 km2 the geological settings of the study area are detailed mapped including geologic structure and lithology the digital elevation model dem of the study area with resolution of 30 m 30 m is presented to address the topographic characteristics correlations between the occurrence of landslides with geological settings i e active faults the coseismic surface ruptures geological unit slope gradient slope elevation as well as slope aspect are analyzed using spatial modeling in gis with the aids of field investigations it can be concluded that the distance to the causative faults and slope gradient are much more important than other factors landslides are clustered distributed along the causative faults of f2 and f3 and landslides incidence are dramatically decreasing with the increasing of the distance to the causative faults the landslides incidence has an obvious increase near the active faults i e f1 landslide concentration lc landslides km2 has an obvious exponent increase with slope gradient however lc has no obvious relationship with geological unit and slope elevation the difference of lc value in each geological unit each slope elevation category maybe have been the result affected by slope gradient for each geological unit each slope elevation category and distance of each geological unit each slope elevation category to causative fault zone isoseismal map reflects the incidence of landslides in some degree and lc increases dramatically with intensity increasing almost all landslides occurred in the region above vi degree statistics result also indicates that in the near field of causative faults landslides tend to have the initial sliding direction similar to the movement of the causative faults and preliminary study shows that landslides incidence varies in different slopes with different structure and consequent slopes and obsequent slopes have a higher landslides incidence than other layered slopes

thickening the altiplano crust by gravity driven crustal channel flow 1 in the central andes crustal thickness is not well correlated to upper crustal shortening only little shortening is documented in the upper crust of the 60 65 km thick altiplano plateau whose thickening and uplift were delayed with respect to earlier and greater thickening in the adjacent western and eastern cordilleras because crustal thickness variations induce horizontal stress gradients and cause crustal flow a thickness dependent channel flow is modeled here and applied to the central andes in situ thickening is assumed for both cordilleras while the altiplano crustal thickening is generated by lateral flow from these overthickened adjacent domains a 8 1018 pa s viscosity channel is predicted for crustal thicknesses exceeding 45 50 km to match the estimated topographic evolution of the central andes thickening in the cordilleras was sufficient to generate a flow of 6 109 m3 per unit length toward the initially 30 35 km thick altiplano

the importance of earthquake induced landslides to long term slope erosion and slope failure hazards in seismically active regions abstract this paper describes a general method for determining the amount of earthquake induced landsliding that occurs in a seismically active region over time this determination can be used as a quantitative measure of the long term hazard from seismically triggered landslides as well as a measure of the importance of this process to regional slope erosion rates and landscape evolution the method uses data from historical earthquakes to relate total volume of landslide material dislodged by an earthquake to the magnitude m and seismic moment m0 of the earthquake from worldwide data a linear regression relation between landslide volume v and m0 is determined as v m0 1018 9 0 13 where v is measured in m3 and m0 is in dyn cm to determine the amount of earthquake generated landsliding over time this relation is combined with data on seismic moment release for a particular region which may be derived from either earthquake history or fault slip data the form of the m0 v relation allows the rate of production of earthquake induced landslides over time to be determined from total rate of seismic moment release without regard to the distribution of individual events thus simplifying and generalizing the determination application of the method to twelve seismically active regions with areas ranging from 13 275 to 2 308 000 km2 shows that erosion rates from earthquake induced landslides vary significantly from region to region of the regions studied the highest rates were determined for the island of hawaii new zealand western new guinea and the san francisco bay region of california significantly lower rates were determined for iran tibet the sierra nevada great basin region of california and central japan for the time period from 715 ad to the present intermediate rates were determined for peru southern california onshore california turkey and central japan for the time period from 1586 ad to the present to determine the relative long term importance of seismically triggered landslides these erosion rates are compared to erosion rates calculated for other slope processes and to rates calculated from fluvial sediment discharge comparisons with other slope processes indicate that earthquake induced landslides are the predominant agents of slope erosion on the island of hawaii in the san francisco bay region and in western new guinea for hawaii the san francisco bay region and sierra nevada great basin region of california the erosion rates calculated for earthquake induced landslides also exceed the regional erosion rates calculated from fluvial sediment discharge

landslides triggered by the 8 october 2005 kashmir earthquake abstract the 8 october 2005 kashmir earthquake triggered several thousand landslides these were mainly rock falls and debris falls although translational rock and debris slides also occurred in addition a sturzstrom debris avalanche comprising 80 million m3 buried four villages and blocked streams to create two lakes although landsliding occurred throughout the region covering an area of 7500 km2 the failures were highly concentrated associated with six geomorphic geologic anthropogenic settings including natural failures in 1 highly fractured carbonate rocks comprising the lowest beds in the hanging wall of the likely earthquake fault 2 tertiary siliciclastic rocks along antecedent drainages that traverse the hazara kashmir syntaxis 3 steep 50 slopes comprising precambrian and lower paleozoic rocks 4 very steep 50 lower slopes of fluvially undercut quaternary valley fills and 5 ridges and spur crests the sixth setting was associated with road construction extensive fissuring in many of the valley slopes together with the freshly mobilized landslide debris constitutes a potential hazard in the coming snowmelt and monsoon seasons this study supports the view that earthquake triggered landslides are highly concentrated in specific zones associated with the lithology structure geomorphology topography and human presence

gigantic low gradient landslides in the northern periphery of the crimean mountains ukraine abstract large scale low gradient ancient landslides estimated at 5 4 18 9 km 2 in area and 0 2 1 2 km 3 in volume have been studied in the northern hilly periphery of the crimean mountains ukraine they originated on slopes along wide water gaps of rivers belbek kacha alma and biyuk karasu crossing the cuestas of the northern foothills the slopes generally consist of slightly northward tilting miocene mainly sarmatian limestones overlying weak clay rich lower neogene palaeogene substratum with a significant content of smectite although the region is characterised by the least active contemporary morphodynamics within the crimean mountains the landslides which were studied are of the same size or even larger than various types of landslides occupying active geomorphic domains of the highest mountain range in the southernmost part of the peninsula the landslides are generally a spreading type but the sliding mechanics were probably very complex involving toppling rotational slides gravitational folding and translational block slides all the landslides which were studied are located in the vicinity of regional faults and three of them have headscarps aligned along faults a common feature is also a location close within several km to the mesozoic suture zone which is the most important tectonic feature in the northern periphery of the crimean orogene this suture was formerly classified as aseismic however evidence of strong low frequency palaeoearthquakes was collected during the last decade within both the mesozoic suture and the low lying northern part of the crimean peninsula radiocarbon dating of deposits associated with the landslides has revealed at least two phases of increased landslide activity during the late glacial chronozone and holocene epoch the main landslide phase presumably took place at some time between the late glacial and atlantic chronozones minor reactivation of landslide toes occurred during the subatlantic chronozone and some of them have been active up to recent times the first major landslide phase was possibly triggered by an earthquake whereas late holocene activity can be attributed both to seismic and hydroclimatic factors

the possible role of brittle rock fracture in the 1963 vajont slide italy abstract we use a state of the art numerical simulation approach to investigate the vajont slope failure a large catastrophic landslide that resulted in the loss of 1910 lives this study represents the first three dimensional 3d brittle fracture simulation of the vajont slide that includes the effect of groundwater on the failure process a realistic representation of the vajont slope geometry failure surface and discontinuities in a 3d lattice spring code allowed us to study the kinematics of the landslide using a lattice spring block model approach the relations among the number of blocks slope damage and stability are investigated the influence of an elevated groundwater table on displacements and cracking within the model is evaluated the results show a good agreement with the reported microseismic events prior to the failure two new techniques damage intensity d 32 and the ellipsoid of damage are introduced and used to quantify brittle damage within the numerical simulations

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

crustal channel flows 1 numerical models with applications to the tectonics of the himalayan tibetan orogen 1 plane strain thermal mechanical numerical models are used to examine the development of midcrustal channel flows in large hot orogens in the models radioactive self heating reduces the viscosity of tectonically thickened crust and increases its susceptibility to large scale horizontal flow channels can be exhumed and exposed by denudation focused on the high relief transition between plateau and foreland we interpret the himalaya to have evolved in this manner channel flows are poorly developed if the channel has a ductile rheology based on wet quartz flow laws and well developed if there is an additional reduction in viscosity to 1019 pa s this reduction occurs from 700 c to 750 c in the models and is attributed to a small percentage of in situ partial melt melt weakening model ht1 provides an internally consistent explanation for the tectonic evolution of many features of the himalayan tibetan orogenic system erosional exhumation exposes the migmatitic channel equivalent to the greater himalayan sequence ghs between coeval normal and thrust sense ductile shear zones corresponding to the south tibetan detachment and the main central thrust systems outward flow of unstable upper crust rotates these shears to low dip angles in the model both the ghs and the lesser himalayan sequence are derived from indian crust with the latter from much farther south similar models exhibit a range of tectonic styles including the formation of domes resembling north himalayan gneiss domes model results are relatively insensitive to channel heterogeneities and to variations in the behavior of the mantle lithosphere beneath the model plateau

numerical models of crustal scale convection and partial melting beneath the altiplano puna plateau we employ 2 d thermo mechanical modelling to study possible mechanisms for generating large scale crustal magmas in the altiplano puna region of the central andes the peak of ignimbrite activity in the late miocene and pliocene is associated in space and time with tectonic shortening and plateau uplift a seismic low velocity zone and other geophysical observations indicate that partial melting in the mid crust is still present under the ignimbrite province today we show that neither radiogenic heat production in a thickening crust nor shear heating due to tectonic shortening nor heat brought by intrusions of arc magmas into the mid crust can heat the mid crust to the degree and within the time frame suggested by the geologic petrologic and geophysical observations a viable mechanism to achieve high temperatures within the time constraints is convective heat and mass transfer by partially molten lower crust which itself was heated by enhanced mantle heat flow possibly associated with delamination of the mantle lithosphere during tectonic shortening and intensified magmatic arc activity the thermo mechanical models explain the mid crustal low velocity zone and the high and strongly variable surface heat flow observed in the altiplano convection by bulk flow of the crust appears when the middle and lower crust are mechanically weak quartz dominated rheology the basal heat flow from the mantle is high s 60 mw m 2 and tectonic shortening is active we argue that these conditions are satisfied in the central andes orogen 6 2002 elsevier science b v all rights reserved

silicon diffusion in a natural quartz aggregate constraints on solution transfer diffusion creep abstract silicon bulk diffusion rates were determined in a fine grained 1 2 m diameter natural quartz aggregate novaculite from hot springs ar the diffusion experiments were done at 600 800 c and 150 mpa confining pressure hydrothermal and at 800 1100 c and 1 atm in a stream of dry n2 the technique employed an isotopic tracer 30si and standard step scan analysis using an ion microprobe sims the temperature dependence of silicon bulk diffusion in the novaculite is described by the arrhenius parameters d0 bulk 3 7 10 10 m2 s and q 137 18 kj mol and d0 bulk 6 2 10 9 m2 s and q 178 38 kj mol for the hydrothermal and dry experiments respectively at 800 c the silicon bulk diffusion rate at 150 mpa hydrothermal is about a factor of 10 greater than at 1 atm dry for an assumed effective grain boundary width of 2 nm the silicon grain boundary diffusion rates in novaculite are a factor of two to three less than oxygen diffusion rates for similar hydrothermal conditions and more than 12 orders of magnitude greater than anhydrous silicon volume diffusion rates extrapolated to the temperature of these experiments the results of this study provide valuable constraints on the role of diffusion accommodated deformation in quartz rich rocks

geological and morphological study of the daguangbao landslide triggered by the ms 8 0 wenchuan earthquake china abstract landslides are one of the most significant geomorphic processes in mountainous regions recently a gigantic landslide daguangbao dgb landslide with a volume of 1 2 109 m3 was triggered by the ms 8 0 wenchuan earthquake china and has attracted widespread attention this landslide 28 38 16 93 e 104 06 02 35 n is located 85 km north northeast nne of the epicenter and on the hanging wall side 4 km away from the surface rupture zone of the earthquake our long term 2008 present study which includes topographic interpretation and geological and geomorphological investigations allows us to define the geological model of the dgb landslide and estimate the initiation and traveling mechanisms the topography was studied by using high resolution digital elevation models arial images and abundant photos at different scales are used to performed geomorphological analysis the geology in the landslide area was studied by exploratory trenches a tunnel and terrestrial laser scanning tls the results show that the mass movement destabilized a folded slope along a deep seated average depth of 400 m bedding fault developed in the dolomite of the sinian formation the morphology of the landslide main scarp is characterized by steep 55 75 and high up to 730 m release surfaces resulting from the linkage of three joint sets an excess pore water pressure dependent loss of shear strength at the basal layer during the earthquake is assumed to have favored landslide initiation an internal shear running subparallel to the stratification surface is confirmed to have dominated the longitudinal mobility of the landslide and driven landslide mass thrusting to a height of 500 m on the slopes on the other side of the valley the dgb landslide as a transient destabilization and morphogenesis event has largely contributed to erosion in the study area

metamorphism transient mid crustal rheology strain localization and the exhumation of high grade metamorphic rocks 1 we present a series of three dimensional numerical models investigating the effects of metamorphic strengthening and weakening on the geodynamic evolution of convergent orogens that are constrained by observations from an exposed mid crustal section in the new england appalachians the natural mid crustal section records evidence for spatially and temporally variable mid crustal strength as a function of metamorphic grade during prograde polymetamorphism our models address changes in strain rate partitioning and topographic uplift as a function of strengthening weakening in the middle crust as well as the resultant changes in deformation kinematics and potential exhumation patterns of high grade metamorphic rock results suggest that strengthening leads to strain rate partitioning around the zone and suppressed topographic uplift rates whereas weakening leads to strain rate partitioning into the zone and enhanced topographic uplift rates deformation kinematics recorded in the orogen are also affected by strengthening weakening with complete reversals in shear sense occurring as a function of strengthening weakening without changes in plate boundary kinematics

exhumation of the main central thrust from lower crustal depths eastern bhutan himalaya geothermometry and mineral assemblages show an increase of temperature structurally upwards across the main central thrust mct however peak metamorphic pressures are similar across the boundary and correspond to depths of 35 45 km garnet bearing samples from the uppermost lesser himalayan sequence lhs yield metamorphic conditions of 650 675 c and 9 13 kbar staurolite kyanite schists about 30 m above the mct yield p t conditions near 650 c 8 10 kbar kyanite bearing migmatites from the greater himalayan sequence ghs yield pressures of 10 14 kbar at 750 800 c top to the south shearing is synchronous with and postdates peak metamorphic mineral growth metamorphic monazite from a deformed and metamorphosed proterozoic gneiss within the upper lhs yield u pb ages of 20 18 ma staurolite kyanite schists within the ghs a few metres above the mct yield monazite ages of c 22 1 ma we interpret these ages to reflect that prograde meta morphism and deformation within the main central thrust zone mctz was underway by c 23 ma u pb crystallization ages of monazite and xenotime in a deformed kyanite bearing leucogranite and kyanite garnet migmatites about 2 km above the mct suggest crystallization of partial melts at 18 16 ma higher in the hanging wall south verging shear bands filled with leucogranite and pegmatite yield u pb crystallization ages for monazite and xenotime of 14 15 ma and a 1 2 km thick leuco granite sill is 13 4 0 2 ma thus metamorphism plutonism and deformation within the ghs con tinued until at least 13 ma p t conditions at this time are estimated to be 500 600 c and near 5 kbar from these data we infer that the exhumation of the mct zone from 35 to 45 km to around 18 km occurred from 18 to 16 to c 13 ma yielding an average exhumation rate of 3 9 mm year 1 this process of exhumation may reflect the ductile extrusion by channel flow of the mctz from between the overlying tibetan plateau and the underthrusting indian plate coupled with rapid erosion

earthquake triggering of landslides in highly jointed rock masses reconstruction of the 1783 scilla rock avalanche italy abstract the scilla rock avalanche occurred on 6 february 1783 along the coast of the calabria region southern italy close to the messina strait it was triggered by a mainshock of the terremoto delle calabrie seismic sequence and it induced a tsunami wave responsible for more than 1500 casualties along the neighbouring marina grande beach based on subaerial and submarine surveys a 5 106 m3 subaerial landslide was identified together with a 3 106 m3 submarine scar area whereas block deposits are present in both the subaerial and submerged regions a detailed geological reconstruction of the slope was obtained and a geomechanical characterisation of the metamorphic rocks involved in the landslide was performed based on this reconstruction intense jointing conditions of the rock mass can be related to main fault zones parallel and normally oriented to the actual coastline an engineering geology model of the landslide was devised according to an equivalent continuum approach to evaluate both stiffness and strength of the rock mass within the slope a finite difference stress strain numerical modelling of the scilla landslide was performed under dynamic conditions to back analyse the landslide trigger as well as local seismic amplifications this modelling gave new insights into the physical interactions between seismic inputs and slopes as it demonstrated the fundamental role played by i the interaction between the seismic input and geological setting of unsheared rock slopes i e without preexisting landslide masses ii cumulated strain effects due to seismic sequences and iii jointing conditions of the involved rock masses responsible for the seismic amplification of the landslide prone volume driving it toward failure conditions

surface erosion control on the evolution of the deep lithosphere russell n pysklywec geology v 34 no 4 pp 225 228 april 2006 1 figure 1 has been corrected and replaced by the author the corrected figure 1 is below figure 2 1 lookup doi 10 1130 g21963 1 2 pending yes

conodont zonation across the permian triassic boundary at the xiakou section yichang city hubei province and its correlation with the global stratotype section and point of the ptb xiakou section is situated north of the central yangtze platform with successive late permian to early triassic strata thicker than the global stratotype section and point gssp of the permian triassic boundary ptb we recognized three conodont zones across the ptb in this section by high precision biostratigraphy they are the hindeodus latidentatus clarkina meishanensis zone hindeodus parvus zone and isarcicella isarcica zone in ascending order which correspond well with the gssp the present biostratigraphic work on xiakou section certainly confirmed the conodont zonation through the ptb at the gssp and also testified to the correctness of the ptb demarcation in xiakou section based on this precise demarcation of the ptb the appearance of a clay layer bed zsji266 just beneath the ptb should be an important advantage over the gssp because this clay layer approaches to the ptb much in contrast with those two clay layers bed 26 and bed 28 in the gssp therefore the radiometric isotopic da

diffusion creep and partial melting in high temperature mylonitic gneisses hope valley shear zone new england appalachians usa field petrographic microstructural and isotopic studies of mylonitic gneisses and associated pegmatites along the hope valley shear zone in southern rhode island indicate that late palaeozoic deformation c 275 ma in this zone occurred at very high temperatures 650 c high energy cuspate lobate phase boundary microstructures a predominance of equant to sub equant grains with low internal lattice strain and mixed phase distributions indicate that diffusion creep was an important and possibly predominant deformation mechanism field and petrographic evidence are consistent with the presence of an intergranular melt phase during deformation some of which collected into syntectonic pegmatites rb sr isotopic analyses of tightly sampled pegmatites and wall rocks confirm that the pegmatites were derived as partial melts of the immediately adjacent isotopically heterogeneous mylonitic gneisses the presence of syntectonic interstitial melts is inferred to have permitted a switch from dislocation creep to melt enhanced diffusion creep as the dominant mechanism in these relatively coarse grained mylonitic gneisses 200 500 lm syn deformational grain size a switch to diffusion creep would lead to significant weakening and may explain why the hope valley shear zone evolved into a major regional tectonic boundary this work identifies conditions under which diffusion creep operates in naturally deformed granitic rocks and illuminates the deformation processes involved in the development of a tectonic boundary between two distinct late proterozoic avalonian basement terranes

geotechnical characteristics of large rapid rock slides based on the analysis of 51 case studies of large rapid rock slides for a landslide to travel rapidly after failure there has to be a significant loss of strength on the basal surface of rupture lateral margins and or internally within the slide mass or the factor of safety has to be maintained below 1 0 after failure by high groundwater pressures internally sheared compound slides and translational slides may all travel rapidly depending on their detailed geotechnical and geometric characteristics the characteristics of these landslides that suggest an increased likelihood of rapid failure have been identified all the rapid rock slides examined in this study involved relatively high strength rock masses most cases were considered to be first time landslides largely involving brittleness on the basal rupture surface however there were some cases considered to be reactivated or active landslides on pre sheared rupture surfaces for this latter group the loss of strength leading to rapid lands

on the relationship between the formation of shear zones and the form of the flow law for rocks undergoing dynamic recrystallization abstract the formation and maintenance of shear zones in rocks at high temperatures when viscous flow takes place at constant volume requires strain weakening several processes can lead to a strain weakening characteristic in the flow of such rocks to high strains but conventional experimental rock mechanics techniques cannot normally provide high quality mechanical data to high strains recent experimental data for calcite marble have demonstrated strain weakening accompanied by dynamic recrystallization a power law with strain exponent r can be used to describe the dependence of the flow stress on strain together with the conventional description of the dependence of strain rate on stress described by a stress exponent n the stable localization of strain into shear zones is favoured by more negative values of r e g r 0 8 and more positive values of n e g n 5 to 7 a further important factor is the critical strain e0 for the onset of recrystallization and hence strain weakening shear zone formation is favoured by smaller values for e0 shear zone formation weakens the crustal section in which they occur but the amount of weakening may not be great perhaps no more than 50 of the previous steady state flow stress certain rock types such as mafic igneous rocks may through their mechanical properties be more susceptible to shear zone formation than others such as mica schists it is emphasized that the analysis presented is based upon a strain dependent flow law that describes single phase dynamic recrystallization by grain boundary migration that leads to enhanced recovery without any change in deformation mechanism no consideration is given to possibly important effects arising from the activation of grain size sensitive flow or to potential weakening effects arising from syntectonic metamorphic reactions

crustal channel flows 2 numerical models with implications for metamorphism in the himalayan tibetan orogen 1 results from a thermal mechanical model ht1 that includes midcrustal channel flow are compatible with many features of the himalayan tibetan system radioactive self heating and rheological weakening of thickened model orogenic crust lead to the formation of a hot low viscosity midcrustal channel and a broad plateau channel material corresponding to the greater himalayan sequence ghs flows outward from beneath the plateau in response to topographically induced differential pressure at the plateau flank it is exhumed by focused surface denudation and juxtaposed with cooler newly accreted material corresponding to the lesser himalayan sequence lhs the model channel is bounded by coeval thrust and normal sense ductile shear zones interpreted to represent the main central thrust mct zone and south tibetan detachment system respectively inverted metamorphism associated with the model mct zone results from distributed ductile shear along the mct and extrusion of the hot channel a variety of model p t t path styles resembling those observed in the ghs and lhs are produced for points traveling through contrasting tectonic regimes that coexist in different parts of the model predicted times of peak metamorphism cooling and erosion of metamorphic facies are generally compatible with observations although model ghs cooling ages are too young the times of m1 and m2 metamorphic events observed in the ghs correspond to model times of maximum burial and maximum heating respectively the results highlight the need to integrate tectonics and metamorphism in continental collision models and demonstrate the importance of lateral transport of both heat and material in large hot orogens

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

some comments on the rheologically critical melt percentage abstract the concept of rheologically critical melt percentage rcmp originally proposed by arzi tectonophysics 44 1978 173 184 for partially molten granitic rocks is re examined it is shown that there is no experimental support to show the presence of rcmp the published experimental data suggest that the effective viscosity of partially molten granitic rocks is reduced rapidly and continuously with increasing melt fraction it is also shown that the experimental data may be modeled by means of the upper bound behavior the voigt bound of two phase material by assuming a melt localization which implies that there is no partitioning of strain between the solid and the melt

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

emplacement of the longmen shan thrust nappe belt along the eastern margin of the tibetan plateau abstract the topographic descent from the eastern margin of the tibetan plateau to the sichuan basin passes through the longmen shan thrust nappe belt which is sub divided by six nw dipping major listric thrusts with accompanying duplexes and imbricate fans into five large scale nappes each nappe has its own stratigraphic and deformational features in the inner longmen shan longmen mountains allochthonous nappe units have incorporated both mesoproterozoic basement and sinian neoproterozoic to triassic cover sequences as thick skinned horses whereas in the frontal longmen shan sinian cretaceous cover sediments have been stripped from the basement as thin skinned fold and thrust sheets including the extensively distributed klippen structures pre thrusting extension during devonian to middle late triassic times resulted in syn depositional normal faults structural inversion of these faults initiated the peng xian guan xian basement complex jiuding shan and tangwangzhai nappes during the early episode of the indosinian orogeny norian to rhaetian this was followed by episodic thrusting during latest triassic to early cretaceous times to develop the guan xian an xian and southeastern marginal nappes that have incorporated sediments from the neighbouring foreland basin into the frontal part of the thrust nappe belt during a late miocene reactivation of the pre existing thrusts differential thrusting occurred across the thrust nappe belt

gigantic paleolandslide associated with active faulting along the bogd fault gobi altay mongolia on the basis of analyses of satellite imagery aerial photographs and field observations we describe the occurrence of one of the largest paleolandslides 50 km3 ever recognized in an intracontinental domain the slide occurred along the active bogd fault in the gobi altay mountain range in mongolia morphological and structural analyses of the relationships between the landslide and the area affected by active tectonics suggest that this gigantic mass movement was associated with surface faulting during a strong earthquake

critical wedges in three dimensions analytical expressions from mohr coulomb constrained perturbation analysis we present simple analytical expressions for evaluating three dimensional stress fields in critical wedges coulomb failure throughout that are deforming within an oblique convergent zone we assume that the load and geometry variations in the lateral direction and the topographic slope are relatively small the stress state of a two dimensional critical wedge is perturbed by admitting a small lateral shear which is accommodated to maintain criticality by a reduction in the dominant normal compressive stress cohesionless cases are further simplified with taylor series expansions in the topographic slope the analytical expressions distinguish the behavior of strong base wedges associated with steep slopes from weak base wedges with more modest slopes and are reliable for lateral shear values as large as half the lithostatic load in the weak base case where the vertical shear is small the orientations of the principal stresses are very sensitive to the perturbation as the lateral shear increases through relatively small values the roles of the lateral and vertical coordinate axes are interchanged with a resultant transition from predominantly thrust failure to strike slip failure transition to strike slip in the strong base case is more gradual the particular value of horizontal shear for which transition occurs also depends on the difference of the minor normal stresses we produce an analytical expression predicting displacement patterns compatible with those observed in natural and analog orogens displacement partitioning is predicted for weak base wedges due to minor changes in lateral boundary conditions associated with variable orogen geometry

the gigantic seymareh saidmarreh rock avalanche zagros fold thrust belt iran the seymareh rock avalanche first described by j v harrison and n l falcon in the 1930s is the largest known subaerial non volcanic landslide on earth the volume of its debris 44 gm 3 is approximately equal to that of the largest known subaerial landslide of any kind the 100 ka collapse of mount shasta volcano 45 gm 3 and approaches those of gigantic landslides on mars using satellite imagery srtm 3 data and detailed field investigations we gain a new understanding of the gigantic rock avalanche the initial failure 38 gm 3 involving a dip slope consisting of a relatively weak interbedded limestone mudrock sequence capped by resistant asmari limestone had an average thickness of 410 m along a 15 5 km width of the kabir kuh anticline the rockslide transformed into a rock avalanche that travelled 19 0 km with a fahrboschung the angle between the highest point of the pre landslide source area topography and the distal limit of the debris of only 3 6 initial failure involved complex planar sliding dictated by four structural elements 1 bedding parallel shears and 2 across bedding break throughs combined to produce a low angle 11 overall sliding surface that 3 broke out through the asmari carapace at the toe of the failed slope while 4 tectonically weakened bedding normal joints provided lateral release surfaces nine discrete bedding parallel basal sliding surfaces divided the detached mass into nine stacked plates the upper plate 23 gm 3 included 20 7 gm 3 of asmari limestone analysis of accelerator mass spectrometry radiocarbon dates from this study and by others indicates that the rock avalanche occurred between c 8710 and 9800 14 c years bp supplementary material a summary of the tectonics stratigraphy and physiography of the zagros fold thrust belt together with a description of surficial gravity collapse structures in the region harrison falcon 1934 1936 is available at www geolsoc org uk sup18612

the eaux bonnes landslide western pyrenees france overview of possible triggering factors with emphasis on the role of groundwater the purpose of this study is to achieve an understanding of the failure mechanisms which caused the eaux bonnes landslide the geological investigations carried out on the slope of the landslide showed that the sliding mass was cut by numerous faults the factors controlling the landslide failure were complex and it is known that neither earthquakes nor heavy precipitation could have triggered the disruption the groundwater within the solid rock mass has been surveyed because significant precipitation events during the 2 years preceding the beginning of the paroxysmal phase of the landslide could have led to an increase in pore water pressure along these fractures thereby triggering the landslide in order to achieve a full understanding of the failure mechanism and to identify the origin of the groundwater a hydrogeochemical survey was carried out over a period of 1 year the results reveal the existence of high sulphate concentrations in the groundwater originating in springs located at the bottom of the landslide the sulphate concentrations are correlated with high calcium concentrations and clearly indicate the presence of gypsum in the vicinity of the lower reaches of the landslide the presence of gypsum in this area of the pyrenees suggests that deep groundwater played a role in triggering the landslide