petrology of the mafic rocks of the xigaze ophiolite tibet the xigaze ophiolite yarlung zangbo suture zone southern tibet china shows an unusual crustal sequence characterized by a lack of large masses of cumulate gabbros by dolerites intrusive throughout the whole ophiolite sequence and by the injection of dolerites in already serpentinized peridotites the abyssal tholeiitic nature of all the mafic rocks indicates that they have been generated at an oceanic ridge all the geological arguments and petrological and textural data on the mafic rocks point to very low heat production and large heat losses through widespread intensive sea water circulation for the spreading centre in which they have been formed in good agreement with a slow spreading ridge origin

gis based landslide susceptibility mapping using bivariate statistical analysis in devrek zonguldak turkey devrek town with increasing population is located in a hillslope area where some landslides exist therefore landslide susceptibility map of the area is required the purpose of this study was to generate a landslide susceptibility map using a bivariate statistical index and evaluate and compare the results of the statistical analysis conducted with three different approaches in seed cell concept resulting in different data sets in geographical information systems gis based landslide susceptibility mapping applied to the devrek region the data sets are created from the seed cells of a crowns and flanks b only crowns and c only flanks of the landslides by using ten different causative parameters of the study area to increase the data dependency of the analysis all parameter maps are classified into equal frequency classes based directly on the percentile divisions of each corresponding seed cell data set the resultant maps of the landslide susceptibility analysis indicate that all data sets produce fairly acceptable results in each data set analysis elevation lithology slope aspect and drainage density parameters are found to be the most contributing factors in landslide occurrences the results of the three data sets are compared using seed cell area indexes scai this comparison shows that the crown data set produces the most accurate and successful landslide susceptibility map of the study area

refrigeration of the western cordilleran lithosphere during laramide shallow angle subduction the laramide orogeny has generally been attributed to a shift from normal angle to shallow angle subduction beneath the western margin of the north american plate in addition to important mechanical effects this shift may have had important thermal effects on the lithosphere in the western cordillera before the laramide geothermal gradients in the western cordillera were probably normal to high because of the presence below of a hot asthenospheric wedge with the shift to shallow subduction the wedge was probably expelled and replaced by a cold subducting slab that extended just below the cordilleran lithosphere this would shift the western cordillera into a cold forearc like thermal setting dominated by the refrigeration effects of the subducting slab thermochronologic data from the sierra nevada great basin mojave desert western arizona and perhaps the colorado plateau record latest cretaceous early tertiary cooling that may be evidence of such refrigeration if regional refrigeration occurred it would have several important implications 1 metamorphism in the western cordillera would have waned with the start of the laramide orogeny 2 the crust in the western cordillera would have strengthened and become much more resistant to deformation e g gravitational collapse and extension of thickened crust in the sevier hinterland would have been impeded and 3 latest cretaceous early tertiary isotopic cooling ages may not be valid indicators of a period of major regional uplift and unroofng

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

deep structure of the ocean continent transition in the southern iberia abyssal plain from seismic refraction profiles ocean drilling program legs 149 and 173 transect we present a wide angle seismic refraction study of an 80 40 km region of the southern iberia abyssal plain south of galicia bank an intersecting grid of two e w and four n s wide angle reflection refraction profiles is used to define variations of the basement velocity structure within this unusually wide ocean continent transition oct these structures can be systematically linked to variations in acoustic basement morphology and to results from ocean drilling program odp boreholes lateral changes in the velocity structure of the basement occur abruptly over distances of 20 km where complex variations may be found thinned upper continental crust 2 5 km thick with velocities of 5 0 6 6 km s is limited to a series of n s fault blocks immediately south of galicia bank this crust is underlain by a high velocity layer 7 3 7 9 km s of weakly serpentinized i e 0 25 peridotite which exists throughout the eastern part of the survey area basement within the oct appears to consist dominantly of a broad region of exposed upper mantle that has been serpentinized heterogeneously both vertically and horizontally in the southeast sector of our survey where basement topography deepens and becomes subdued continental fault blocks are absent instead basement contains an upper layer of more pervasively serpentinized i e 25 45 peridotite that is 2 km thick this layer is characterized by low velocity at the top of basement 4 2 km s that increases rapidly with depth and it probably corresponds to a seismically unreflective layer previously identified in reflection profiles to the south of our survey in the western section of our survey beneath a series of elevated basement ridges velocities are reduced within both the upper basement layer 3 5 6 0 km s and lower layer 6 4 7 5 km s these changes suggest that both upper and lower layers have become more highly serpentinized with values of 60 100 in the upper layer and 25 45 in the lower layer probably during the last stages of rifting and immediately before formation of oceanic crust a normal or slow spreading oceanic crustal structure is not found within the survey region thus it appears that the onset of seafloor spreading occurs in the region west of the peridotite ridge sampled at odp site 897 and east of the j magnetic anomaly

application of data driven evidential belief functions to landslide susceptibility mapping in jinbu korea abstract evidential belief function ebf model was applied and validated for analysis of landslide susceptibility in the pyungchang area of korea using geographic information system areas of landslide occurrence in the study area were determined from the interpretation of aerial photographs and subsequent field surveys landslide locations were randomly allocated for landslide susceptibility map generation 70 and validation 30 purposes maps relevant to landslide occurrence topography geology soil and forest cover were assembled in a spatial database from which 17 landslide related factors were extracted the relationships between the observed landslide locations and these factors were identified and quantified using the ebf model three relationships were calculated disbelief dis uncertainty unc and belief bel the quantified relationships between each factor and landslide locations of each factor with known landslides were then used as factor ratings in an overlay analysis to create landslide susceptibility indices and maps the most representative of the resulting susceptibility maps the bel map was validated using the landslide data reserved for validation the landslide susceptibility map demonstrates 85 96 accuracy thus the ebf model was found to be effective in terms of prediction accuracy

andean flat slab subduction through time the analysis of magmatic distribution basin formation tectonic evolution and structural styles of different segments of the andes shows that most of the andes have experienced a stage of flat subduction evidence is presented here for a wide range of regions throughout the andes including the three present flat slab segments pampean peruvian bucaramanga three incipient flat slab segments carnegie guanacos tehuantepec three older and no longer active cenozoic flat slab segments altiplano puna payenia and an inferred palaeozoic flatslab segment early permian san rafael based on the present characteristics of the pampean flat slab combined with the peruvian and bucaramanga segments a pattern of geological processes can be attributed to slab shallowing and steepening this pattern permits recognition of other older cenozoic subhorizontal subduction zones throughout the andes based on crustal thickness two different settings of slab steepening are proposed slab steepening under thick crust leads to delamination basaltic underplating lower crustal melting extension and widespread rhyolitic volcanism as seen in the caldera formation and huge ignimbritic fields of the altiplano and puna segments on the other hand when steepening affects thin crust extension and extensive within plate basaltic flows reach the surface forming large volcanic provinces such as payenia in the southern andes this last case has very limited crustal melt along the axial part of the andean roots which shows incipient delamination based on these cases a palaeozoic flat slab is proposed with its subsequent steepening and widespread rhyolitic volcanism the geological evolution of the andes indicates that shallowing and steepening of the subduction zone are thus frequent processes which can be recognized throughout the entire system

an integrated approach to earthquake induced landslide hazard zoning based on probabilistic seismic scenario for phlegrean islands ischia procida and vivara italy abstract in this study we present an integrated approach to assess earthquake induced landslide hazard at the source area of the slope instability process the method has been applied to the case study of ischia procida and vivara islands that represent an integral part of the campi flegrei a densely populated active volcanic area located at the nw margin of the naples bay italy the proposed method follows a stepwise procedure including 1 probabilistic seismic hazard analysis psha 2 assessment of site and topographic effects 3 input of the psha outputs into a classic sliding rigid block analysis for slope instability newmark s approach 4 construction of landslide frequency magnitude curves for the estimate of the slope failure probability as a function of defined newmark s threshold values under different probabilistic seismic scenarios 5 construction of earthquake induced landslide hazard maps at the source area based on the integration of the probabilistic approach and the geological morphological and geotechnical database available for the study area the probabilistic seismic hazard analysis psha is aimed at the definition of the seismic input with different annual exceedance frequency psha results expressed in terms of peak ground acceleration pga at the bedrock are calculated for 14 return periods t ranging from 10 to 2000 yr pga values have been corrected for the site effect associated with geological and morphologic conditions for each selected return period secondly the corrected pga values have been used as an input for the classic sliding rigid block newmark s approach implemented in a geographic information system gis to assess the relative potential for slope failure landslide susceptibility both in static factor of safety fs and dynamic critical acceleration ac conditions the combination of t dependent site corrected pga with the critical acceleration allowed for the calculation of the expected newmark s displacements dn under different probability of exceeding or return periods probabilistic seismic scenarios as a further step in order to estimate the earthquake induced landslide hazard we defined three dn threshold values that have considered capable to trigger shallow seismic induced landslides in the regional context and mapped the sectors with dn values exceeding such thresholds on this basis we constructed frequency magnitude curves to estimate the probability of slope failures at the source areas as a function of dn by correlating the annual probability of landslide occurrence with the number of terrain cells associated with dn values greater than the selected threshold finally based on the estimated annual landslide frequency of the seismic triggering event for each terrain cell we implemented a 1 5000 scale map of earthquake induced landslide hazard for ischia procida and vivara islands the map reports the zoning and ranking of study area into sub zones on a pixel basis according to the degree of the potential hazard from landslides derived by the frequency of the triggering event

earthquake induced chains of geologic hazards patterns mechanisms and impacts large earthquakes initiate chains of surface processes that last much longer than the brief moments of strong shaking most moderate and large magnitude earthquakes trigger landslides ranging from small failures in the soil cover to massive devastating rock avalanches some landslides dam rivers and impound lakes which can collapse days to centuries later and flood mountain valleys for hundreds of kilometers downstream landslide deposits on slopes can remobilize during heavy rainfall and evolve into debris flows cracks and fractures can form and widen on mountain crests and flanks promoting increased frequency of landslides that lasts for decades more gradual impacts involve the flushing of excess debris downstream by rivers which can generate bank erosion and floodplain accretion as well as channel avulsions that affect flooding frequency settlements ecosystems and infrastructure ultimately earthquake sequences and their geomorphic consequences alter mountain landscapes over both human and geologic time scales two recent events have attracted intense research into earthquake induced landslides and their consequences the magnitude m 7 6 chi chi taiwan earthquake of 1999 and the m 7 9 wenchuan china earthquake of 2008 using data and insights from these and several other earthquakes we analyze how such events initiate processes that change mountain landscapes highlight research gaps and suggest pathways toward a more complete understanding of the seismic effects on the earth s surface

directivity of slope dynamic response to seismic shaking 1 a four year long accelerometric monitoring of a landslide prone slope area in italy provided evidence of amplifications with systematic directional differences in shaking energy by a factor of 2 3 apparently correlated with the directions of local topographic features the examination of regional scale data revealed similar site response directivity phenomena also on some steep rock slopes not affected by amplification the spectral properties of the site responses were investigated using hvsr analysis and a new approach based on the multiplication of spectra from several events the results suggest that such phenomena are caused by a directional redistribution of spectral energy controlled by a combination of interrelated topographic and geologic factors acting in similar directions

regional coseismic landslide hazard assessment without historical landslide inventories a new approach currently regional coseismic landslide hazard analyses require comprehensive historical landslide inventories as well as detailed geotechnical data consequently such analyses have not been possible where these data are not available a new approach is proposed herein to assess coseismic landslide hazard at regional scale for specific earthquake scenarios in areas without historical landslide inventories the proposed model employs fuzzy logic and geographic information systems to establish relationships between causative factors and coseismic slope failures in regions with well documented and substantially complete coseismic landslide inventories these relationships are then utilized to estimate the relative probability of landslide occurrence in regions with neither historical landslide inventories nor detailed geotechnical data statistical analyses of inventories from the 1994 northridge and 2008 wenchuan earthquakes reveal that shaking intensity topography and distance from active faults and streams are the main controls on the spatial distribution of coseismic landslides average fuzzy memberships for each factor are developed and aggregated to model the relative coseismic landslide hazard for both earthquakes the predictive capabilities of the models are assessed and show good to excellent model performance for both events these memberships are then applied to the 1999 chi chi earthquake using only a digital elevation model active fault map and isoseismal data replicating prediction of a future event in a region lacking historic inventories and or geotechnical data this similarly results in excellent model performance demonstrating the model s predictive potential and confirming it can be meaningfully applied in regions where previous methods could not for such regions this method may enable a greater ability to analyze coseismic landslide hazard from specific earthquake scenarios allowing for mitigation measures and emergency response plans to be better informed of earthquake related hazards

forearc hyperextension dismembered the south tibetan ophiolites suprasubduction zone ophiolites are relics of oceanic upper plate forearcs and are typically preserved as discontinuous belts with discrete massifs along suture zones ophiolites usually contain an incomplete condensed section compared to average modern oceanic lithosphere the incompleteness and discontinuity of ophiolites are frequently attributed to dismemberment but tectonic causes remain poorly constrained here we show new paleomagnetic and field geological evidence for the preservation of extensional detachment faults that thinned and dismembered the south tibetan ophiolite belt during the early cretaceous similar to those documented in modern slow and ultraslow spreading ridges these detachments exhumed lithospheric mantle and subophiolitic melange to the seafloor which became unconformably covered by asia derived forearc strata we call this mechanism forearc hyperextension whereby widespread detachment faults accommodate upper plate extension above a subduction zone we propose that hyperextension is the key mechanism responsible for dismemberment of the south tibetan ophiolitic belt shortly after its magmatic accretion

earthquake induced landslides and their effects on alluvial fans abstract earthquakes as small as magnitude 4 0 may dislodge landslides from susceptible slopes and larger earthquakes can generate tens of thousands of landslides throughout areas of hundreds of thousands of square kilometers producing billions of cubic meters of loose surficial sediment these landslides can have significant geomorphic effects that vary depending on the landslide characteristics and materials and on the settings in which the landslides occur a review of data from historical earthquakes indicates that the landslides they generated can be classified into 14 different types these include highly disaggregated and fast moving falls disrupted slides and avalanches more coherent and slower moving slumps block slides and earth slides and lateral spreads and flows that involve partly to completely liquefied material rock falls disrupted rock slides and disrupted slides of earth and debris are the most abundant types of earthquake induced landslides whereas earth flows debris flows and avalanches of rock earth or debris typically transport material the farthest because of their abundance or long distances of transport these landslides generally have the greatest effects on the landscape during and after earthquakes landslide effects on alluvial fans include direct deposition of material on fan surfaces fissuring and displacement of fan materials alterations in drainage basins such as devegetation denudation and changes in channel networks and generation of large amounts of sediment that may be transported to fans by post earthquake water flows or debris flows

statistical approach to earthquake induced landslide susceptibility susceptibility analysis for predicting earthquake induced landslides has most frequently been done using deterministic methods multivariate statistical methods have not previously been applied in this study however we introduce a statistical methodology that uses the intensity of earthquake shaking as a landslide triggering factor this methodology is applied in a study of shallow earthquake induced landslides in central western taiwan the results show that we can accurately interpret landslide distribution in the study area and predict the occurrence of landslides in neighboring regions this susceptibility model is capable of predicting shallow landslides induced during an earthquake scenario with similar range of ground shaking without requiring the use of geotechnical groundwater or failure depth data

major natural hazards in a tropical volcanic island a review for mayotte island comoros archipelago indian ocean abstract mayotte is a french overseas territory of the comoros archipelago since the 1980 mayotte has developed quickly its population has multiplied by four in less than 30 years infrastructure expanded rapidly in lowlands and slums developed in steep areas through deforestation or close to riverbeds this development urgently required steps to ensure the safety of urban areas from 2002 to 2006 a major programme of natural hazards evaluation and zonation was conducted by the french geological survey in the 17 districts of mayotte the programme resulted in the publication of the first single hazard zonation maps for mayotte at 1 25 000 scale in rural areas and at 1 10 000 scale in urban areas hazard maps regarding landslides and rock falls stream floods seismic lithological and topographical amplification potential liquefaction potential and cyclonic marine submersion were produced for mayors and land planners these atlases also included prevention guidelines to minimize risks associated with land use or urbanization within hazard prone areas this article presents the main achievements of the programme whose main problems were the absence of archives of previous studies and the original volcanic geology of the island of mayotte the atlases highlight areas with numerous landslides zones susceptible to flash floods sectors likely to be submerged by storm surges and areas subject to seismic site effects due to thick volcanic weathered formations this programme emphasizes the fundamental role in such tropical volcanic islands of a good knowledge of the weathered formations for the assessment of most natural hazards this initial hazard mapping represented the first step to achieve specific regulatory risk prevention plans for an efficient land use risk mitigation and reduction policy in mayotte

landslide detection and susceptibility mapping in the sagimakri area korea using kompsat 1 and weight of evidence technique the purpose of this study is to detect landslide locations from satellite images and use them for landslide susceptibility mapping in the sagimakri area korea using a geographic information system and a data driven weight of evidence model the landslide location areas were identified from korea multipurpose satellite images by means of change detection technique and further verified by extensive field survey subsequently landslide locations were randomly selected in a 70 30 ratio for training and validation of the model respectively a spatial database was constructed which is composed of topography forest soil and land cover and 14 landslide related factors were extracted from the database the relationships between the detected landslide locations and the factors were identified and quantified by weights of evidence model tests of conditional independence were performed for the selection of factors allowing five different combinations of factors to be analyzed the relationships were used as the contrast values w and w of factor ratings in the overlay analysis to create landslide susceptibility indexes and maps the results of the analysis were validated by comparison with known landslide locations that were not used directly in the analysis

cross application used to validate landslide susceptibility maps using a probabilistic model from korea a study of landslides in youngin janghung and boeun korea using the geographic information system gis validates a spatial probabilistic model for landslide susceptibility analysis locations were identified from aerial photographs satellite images and field surveys topography soil type forest cover and land cover maps were constructed from spatial data sets landslide occurrence is influenced by 13 factors evidence for which was extracted from the database with the frequency ratio of each factor computed landslide susceptibility maps use frequency ratios derived not only from data for each area but also ratios one from the probabilistic model calculated from the other two areas nine maps in all as a cross check of method validity for validation analytical results were compared in each study area with actual landslide locations boeun based on its frequency ratio showed the best accuracy 82 49 whereas janghung based on the boeun frequency ratio showed the worst 69 53

phase relations of peridotites under h2o saturated conditions and ability of subducting plates for transportation of h2o phase relations of peridotites under h2o saturated conditions up to 28 gpa and 2600 c have been clarified based on the high pressure experimental results in the mgo feo sio2 h2o mgo sio2 al2o3 h2o cao mgo al2o3 sio2 h2o and natural systems based on the phase assemblages deduced and the chemical compositions of the phases the maximum h2o contents for two bulk rock compositions lherzolite and harzburgite have been calculated using mass balance then the potential ability of subducting plates for transportation of h2o is discussed by simple models combining the phase relations and the thermal structures of subduction zones as a function of the age of subducting plate a 15 130 ma the subduction velocity u0 2 25 18 cm year and angle 30 and 60 and the mantle potential temperature tp 1300 and 1350 c the results confirm the importance of choke point a cusp around 6 2 gpa and 550 c at which the stability field of major hydrous phases is minimized in terms of temperature although the choke point is exceeded by the mg sursassite bearing assemblage that has the maximum h2o content of 0 4 0 7 wt around 5 7 gpa and 550 700 c if the geotherm of the coldest part across the subducting plate passes below the choke point maximum 4 6 wt h2o can subduct whereas h2o less than 0 4 0 7 wt can subduct above the choke point the critical conditions are clarified as follows if 30 and tp 1300 c a 15 ma with u0 9 cm year or a 30 ma with u0 2 25 cm year is the critical condition if 60 and tp 1300 c or 30 and tp 1350 c the critical conditions slightly shift to an older age or a greater velocity e g a 30 ma with u0 3 5 cm year the slab thermal parameter au0sin is useful to predict roughly the critical condition however within the younger plate the spatial extent of a cold region with major hydrous phases is thinner hence less h2o is subducted even with the same slab thermal parameter this indicates that the age of the plate and the subduction velocity act differently on the h2o transportation ability of subducting plates

deep plate serpentinization triggers skinning of subducting slabs most of the present day ocean floor is continuously being consumed in subduction zones but large fragments of oceanic crust ophiolites have also been recognized on land the process by which oceanic crust is separated from the subducting slab remains enigmatic and several competing hypothesis have been proposed in the past based on numerical experiments we suggest that serpentinized mantle formed in the outer rise regions of subduction zones may provide a mechanically weak horizon within which basal detachment of the oceanic crust is feasible deformation of this serpentinized layer may lead to decoupling and separation of oceanic crust from the downgoing slab fragments of the former oceanic crust can underplate the accretionary wedge or be exposed on continental crust whereas the skinned lithospheric part of the slab subducts into the mantle

earthquake induced rockfall hazard zoning abstract a methodology for quantitative probabilistic hazard zonation for earthquake induced rockfalls is presented and demonstrated in the area of friuli eastern italian alps affected by the 1976 mw 6 5 earthquake four rockfall datasets have been prepared both from historical data analysis and field surveys the methodology relies on a three dimensional hazard vector whose components include the rockfall kinetic energy the fly height and the annual frequency the values of the first two components are calculated for each location along the slope using the 3d rockfall runout simulator hy stone the rockfall annual frequency is assessed by multiplying the annual onset frequency by the simulated transit frequency the annual onset frequency is calculated through a procedure that combines the extent of unstable areas calculated for 10 different seismic hazard scenarios with different annual frequencies of occurrence and the magnitude relative frequency relationship of blocks as derived from the collected field data for each annual frequency of occurrence the unstable area is calculated as a function of morphometric and earthquake characteristics a series of discriminant analysis models using the rockfall datasets and dems of different resolution 1 and 10 m identified the controlling variables and verified the model robustness in contrast with previously published relationships we show that the slope curvature plays a relevant role in the computation of the unstable area

a method for producing digital probabilistic seismic landslide hazard maps abstract the 1994 northridge california earthquake is the first earthquake for which we have all of the data sets needed to conduct a rigorous regional analysis of seismic slope instability these data sets include 1 a comprehensive inventory of triggered landslides 2 about 200 strong motion records of the mainshock 3 1 24 000 scale geologic mapping of the region 4 extensive data on engineering properties of geologic units and 5 high resolution digital elevation models of the topography all of these data sets have been digitized and rasterized at 10 m grid spacing using arc info gis software on a unix computer combining these data sets in a dynamic model based on newmark s permanent deformation sliding block analysis yields estimates of coseismic landslide displacement in each grid cell from the northridge earthquake the modeled displacements are then compared with the digital inventory of landslides triggered by the northridge earthquake to construct a probability curve relating predicted displacement to probability of failure this probability function can be applied to predict and map the spatial variability in failure probability in any ground shaking conditions of interest we anticipate that this mapping procedure will be used to construct seismic landslide hazard maps that will assist in emergency preparedness planning and in making rational decisions regarding development and construction in areas susceptible to seismic slope failure

landslide susceptibility mapping on panaon island philippines using a geographic information system for landslide susceptibility mapping this study applied verified and compared the bayesian probability model the weights of evidence to panaon island philippines using a geographic information system landslide locations were identified in the study area from the interpretation of aerial photographs and field surveys and a spatial database was extracted from srtm shuttle radar topographic mission dem digital elevation model imagery aerial photograph topographic map and geological map the factors that influence landslide occurrence such as slope aspect curvature topographic wetness index and stream power index of topography were calculated from srtm imagery distance from drainage was extracted from topographic database lithology and distance from fault were extracted and calculated from geological database terrain mapping unit was classified from aerial photographs the spatial association between the factors and the landslides was calculated as the contrast values w and w using the weights of evidence model tests of conditional independence were performed for the selection of the factors allowing the large number of combinations of factors to be analyzed for each factor rating the contrast values w and w were overlaid for landslide susceptibility mapping the results of the analysis showed that contrast rating 78 60 for each factor s multiclass had better accuracy of 5 90 than combinations of factor assigned to binary class with w and w 72 70

experimentally based water budgets for dehydrating slabs and consequences for arc magma generation phase diagrams of hydrous mid ocean ridge mor basalts to 330 km depth and of hydrous peridotites to 250 km depth are compiled for conditions characteristic for subduction zones a synthesis of our experimentally determined phase relations of chlorite lawsonite epidote zoisite amphibole paragonite chloritoid talc and phengite in basalts and of phase relations from the literature of serpentine talc chlorite amphibole and phase a in ultramafics permits calculation of h2o contents in hydrous phase assemblages that occur in natural compositions this yields the information necessary to calculate water budgets for descending slabs starting from low grade blueschist conditions 10 20 km depth with h2o contents between 5 and 6 wt for hydrated oceanic crust complete dehydration is achieved between 70 and 300 km depth as a function of individual slab geotherms hydrous phases which decompose at depth below volcanic arcs are lawsonite zoisite chloritoid and talc phengite in mafic compositions and chlorite and serpentine in peridotite approximately 15 35 of the initially subducted h2o are released below volcanic arcs the contribution of amphibole dehydration to the water budget is small 5 20 and occurs at relatively shallow depth 65 90 km in any predicted thermal structure dehydration is a combination of a stepwise and a continuous process through many different reactions which occur simultaneously in the different portions of the descending slab such a dehydration characteristic is incompatible with single phase dehydration models which focus fluid flow through a unique major dehydration event in order to explain volcanic fronts as a consequence of continuously progressing dehydration water ascending from the slab will be generally available to depth of ca 150 200 km the fluid rising from the subducting lithosphere will cause partial melting in the hot portion of the mantle wedge we propose that the volcanic front simply forms above the mantle wedge isotherm where the extent of melting is sufficient to allow for the mechanical extraction of parental arc magmas thermal models show that such an isotherm ca 1300oc locates below volcanic fronts slab surface depths below such an isotherm are compatible with the observed depths of the slab surface below volcanic fronts 1998 elsevier science b v all rights reserved

evaluation of anfis and lr models for seismic rockfalls susceptibility mapping a case study of firooz abad kojour iran earthquake 2004 seismic rockfall is one of the prevalent geohazards that cause huge losses in the earthquake stricken areas in the present research a model is developed to map susceptibility occurrence probability of seismic rockfalls in a regional scale using logistic regression lr and adaptive neuro fuzzy inference system anfis techniques in this research firooz abad kojour earthquake of 2004 was introduced as the benchmark and the model base the susceptible zones predicted by lr and anfis methods were compared with the database distribution map of seismic rockfalls by which the results revealed a good overlapping between the susceptible zones predicted by the anfis and the field observation of rockfalls triggered by this earthquake besides for the statistical evaluation of results obtained by lr and anfis models the verification parameters with high accuracy such as density ratio dr quality sum qs and receiver operating characteristic curve roc were used by analyzing the susceptibility maps and considering the qs index obtained by lr 21 04184 and anfis 26 75592 it could be found that the qs of anfis is higher than that of lr moreover based on the obtained value of the area under the curve auc from lr 0 972 and anfis 0 984 methods anfis provided a higher accuracy in zonation and susceptibility mapping of rockfalls triggered by firooz abad kojour earthquake of 2004 compared to the lr method

a seismic landslide susceptibility rating of geologic units based on analysis of characteristics of landslides triggered by the 17 january 1994 northridge california earthquake abstract one of the most significant effects of the 17 january 1994 northridge california earthquake m 6 7 was the triggering of thousands of landslides over a broad area some of these landslides damaged and destroyed homes and other structures blocked roads disrupted pipelines and caused other serious damage analysis of the distribution and characteristics of these landslides is important in understanding what areas may be susceptible to landsliding in future earthquakes we analyzed the frequency distribution and geometries of triggered landslides in the santa susana 7 5 quadrangle an area of intense seismic landslide activity near the earthquake epicenter landslides occurred primarily in young late miocene through pleistocene uncemented or very weakly cemented sediment that has been repeatedly folded faulted and uplifted in the past 1 5 million years the most common types of landslide triggered by the earthquake were highly disrupted shallow falls and slides of rock and debris far less numerous were deeper more coherent slumps and block slides primarily occurring in more cohesive or competent materials the landslides in the santa susana quadrangle were divided into two samples single landslides 1502 and landslide complexes 60 which involved multiple coalescing failures of surficial material we described landslide morphologies by computing simple morphometric parameters area length width aspect ratio slope angle to quantify and rank the relative susceptibility of each geologic unit to seismic landsliding we calculated two indices 1 the susceptibility index which is the ratio given as a percentage of the area covered by landslide sources within a geologic unit to the total outcrop area of that unit and 2 the frequency index given in landslides per square kilometer ls km2 which is the total number of landslides within each geologic unit divided by the outcrop area of that unit susceptibility categories include very high 2 5 landslide area or 30 ls km2 high 1 0 2 5 landslide area or 10 30 ls km2 moderate 0 5 1 0 landslide area or 3 10 ls km2 and low

osl dating of landslide dammed lake deposits in the north of tehran iran 958 ray taleghan ruyan earthquake abstract one large landslide soleghan in the north of the megacity tehran has been surveyed for dating with osl methods landslide dammed lake deposits of the soleghan landslide was used to obtain the age of the landslide event using the sar protocol for both quartz and feldspar grains the age of the event was 1 09 0 09 ka for quartz and 1 03 0 08 ka and 1 10 0 13 ka for feldspars stimulation at 50 c and 225 c respectively these results suggest that the soleghan mass movement was an earthquake induced landslide triggered by the 23rd february 958 7 7 m ray taleghan ruyan earthquake based on this work thorough review studies of landslides using osl dating methods can be used to determine the age of other mass movements in iran multiple landslides with identical ages which may be attributed to a seismic event could be created by a known earthquake or an unknown earthquake subsequently finding an unknown earthquake will complete the earthquake catalogue resulting in a better hazard assessment

landslides triggered by the 20 april 2013 lushan earthquake sichuan province china abstract the 20 april 2013 lushan earthquake with a magnitude of m s 7 0 induced widespread landsliding along the southern segment of the longmen shan fault zone this paper presents a preliminary analysis of the characteristics of these co seismic landslides triggered in an area of 13 323 km 2 a total of 3810 individual landslide points were identified through an intensive field investigation and from digital aerial photographs taken after the lushan earthquake to facilitate the more detailed analysis on the areal frequency of co seismic landslides as polygons we selected an area of 732 km 2 around the epicenter that had the highest density of co seismic landslides the sizes of the landslides are in general much smaller than those that were triggered by the 2008 wenchuan earthquake the most common types of landslides in the study area were rock falls and shallow disrupted landslides from steep slopes which typically involved the top few meters of weathered bedrock and colluvium in this study the relation between the landslide distribution and five main factors was analyzed fault proximity epicenter proximity peak ground acceleration pga slope angle and lithology our study results show that the landslide concentration tends to decrease with distance from the seismogenic fault and the highest landslide concentration is located within a distance of 5 km regarding the distance to the epicenter the largest landslide density is found at a distance between 5 and 10 km the landslide concentration also increases with increasing slope angle until a maximum for the slope class 45 55 in addition results show that slopes consisting of deeply weathered and fractured sandstones and mudstones were the most susceptible to co seismic landslides in this study we found that the location of the hanging wall and the footwall of the fault did not seem to have an important effect on the landslide distribution this is in contradiction to what has been reported in other earthquake areas such as the wenchuan area

deep structure of the ocean continent transition in the southern iberia abyssal plain from seismic refraction profiles the iam 9 transect at 40 20 n we present a crust and mantle velocity structure for the west iberia passive continental margin derived from a 320 km long wide angle seismic profile acquired in the southern iberia abyssal plain we observe a 170 km wide ocean continent transition zone which includes a pair of overlapping peridotite ridges and is bounded by oceanic crust and landward by fault bounded blocks of continental crust the profile lies 40 km south of the transect sampled by ocean drilling program odp legs 149 and 173 the transition zone structure can be divided into an upper layer 2 4 km thick with velocities of between 4 5 and 7 0 km s 1 and generally a high velocity gradient 1 s 1 and a lower layer up to 4 km thick with a velocity of 7 6 km s 1 and a low velocity gradient a weak moho reflection in this zone was seen only on wide angle profiles at an offset of 30 km the upper layer has a distinctly lower velocity than thinned continental crust adjacent to the continental slope conversely the lower layer has too high a velocity to be magmatically intruded or underplated lower continental crust on the coincident seismic reflection profile fault bounded crustal blocks identified in unequivocal extended continental crust are not observed in the transition zone the upper layer has velocity bounds and gradient similar to oceanic layer 2 observed west of the peridotite ridges but no oceanic layer 3 velocity structure is present while magnetic anomalies have been identified within the transition zone they have not been modeled successfully as seafloor spreading magnetic anomalies nor do they generally form long linear margin parallel features finally odp boreholes 40 km north of our profile and within the interpreted transition zone have recovered up to 140 m thick sections of serpentinite and serpentinized peridotites with little evidence of mafic igneous material we conclude that the transition zone cannot be dominantly composed of either extended continental crust or oceanic crust although current melting models predict a considerably thicker crust of decompression melt products we interpret this region as exposed upper mantle peridotite with little or no synrift extrusive material and limited amounts of synrift material intruded within the serpentinized peridotite

carbon isotope evidence for changes in antarctic intermediate water circulation and ocean ventilation in the southwest pacific during the last deglaciation 1 deep sea sediment core fr1 97 gc 12 is located 990 mbsl in the northern tasman sea southwest pacific where antarctic intermediate water aaiw presently impinges the continental slope of the southern great barrier reef analysis of carbon 13c and oxygen 18o isotope ratios on a suite of planktonic and benthic foraminifera reveals rapid changes in surface and intermediate water circulation over the last 30 kyr during the last glacial maximum there was a large 13c offset 1 1 between the surface dwelling planktonic foraminifera and benthic species living within the aaiw in contrast during the last deglaciation termination 1 the 13cplanktonic benthic offset reduced to 0 4 prior to an intermediate offset 0 7 during the holocene we suggest that variations in the dominance and direction of aaiw circulation in the tasman sea and increased oceanic ventilation can account for the rapid change in the water column 13cplanktonic benthic offset during the glacial interglacial transition our results support the hypothesis that intermediate water plays an important role in propagating climatic changes from the polar regions to the tropics in this case climatic variations in the southern hemisphere may have led to the rapid ventilation of deep water and aaiw during termination 1 which contributed to the postglacial rise in atmospheric co2

fluid flow during slab unbending and dehydration implications for intermediate depth seismicity slab weakening and deep water recycling 1 subducting oceanic plates carry a considerable amount of water from the surface down to mantle depths and contribute significantly to the global water cycle a part of these volatiles stored in the slab is expelled at intermediate depths 70 300 km where dehydration reactions occur however despite the fact that water considerably affects many physical properties of rocks not much is known about the fluid flow path and the interaction with the rocks through which volatiles flow in the slab interior during its dehydration we performed thermomechanical models coupled with a petrological database and with incompressible aqueous fluid flow of a dynamically subducting and dehydrating oceanic plate results show that during slab dehydration unbending stresses drive part of the released fluids into the cold core of the plate toward a level of strong tectonic under pressure and neutral slab normal pressure gradients fluids progressively accumulate and percolate updip along such a layer forming together with the upper hydrated layer near the top of the slab a double hydrated zone dhz where intermediate depth seismicity could be triggered the location and predicted mechanics of the dhz would be consistent with seismological observations regarding double seismic zones dszs found in most subduction zones and suggests that hydrofracturing could be the trigger mechanism for observed intermediate depth seismicity in the light of our results the lower plane of the dsz is more likely to reflect a layer of upward percolating fluid than a level of mantle dehydration in our models a 20 30 km thick dsz forms in relatively old oceanic plates without requiring an extremely deep slab hydration prior to subduction the redistribution of fluids into the slab interior during slab unbending also has important implications for slab weakening and the deep water cycle we estimate that over the whole of earth s history a volume of water equivalent to around one to two oceans can be stored in nominally anhydrous minerals of the oceanic lithosphere and transported to the transition zone by this mechanism suggesting that mantle regassing could have been efficient even without invoking the formation of high pressure hydrous minerals

evaluation of camel comprehensive areal model of earthquake induced landslides abstract a new comprehensive areal model of earthquake induced landslides camel has been developed to assist in planning decisions related to disaster risk reduction camel provides an integrated framework for modeling all types of earthquake induced landslides using fuzzy logic systems and geographic information systems camel is designed to facilitate quantitative and qualitative representation of terrain conditions and knowledge about these conditions on the likely areal concentration of each landslide type camel has been empirically evaluated with respect to disrupted landslides category i using a case study of the 1989 m 6 9 loma prieta ca earthquake in this case camel performs best in comparison to disrupted slides and falls in soil for disrupted rock fall and slides camel s performance was slightly poorer the model predicted a low occurrence of rock avalanches when none in fact occurred a similar comparison with the loma prieta case study was also conducted using a simplified newmark displacement model the area under the curve method of evaluation was used in order to draw comparisons between both models revealing improved performance with camel camel should not however be viewed as a strict alternative to newmark displacement models camel can be used to integrate newmark displacements with other previously incompatible types of knowledge

statistical analysis of an earthquake induced landslide distribution the 1989 loma prieta california event the 1989 loma prieta california earthquake moment magnitude m 6 9 generated landslides throughout an area of about 15 000 km2 in central california most of these landslides occurred in an area of about 2000 km2 in the mountainous terrain around the epicenter where they were mapped during field investigations immediately following the earthquake the distribution of these landslides is investigated statistically using regression and one way analysis of variance anova techniques to determine how the occurrence of landslides correlates with distance from the earthquake source slope steepness and rock type the landslide concentration defined as the number of landslide sources per unit area has a strong inverse correlation with distance from the earthquake source and a strong positive correlation with slope steepness the landslide concentration differs substantially among the various geologic units in the area the differences correlate to some degree with differences in lithology and degree of induration but this correlation is less clear suggesting a more complex relationship between landslide occurrence and rock properties

can slab melting be caused by flat subduction slab melting has been suggested as a likely source of adakitic arc magmas i e andesitic and dacitic magmas strongly depleted in y and heavy rare earth elements existing numerical and petrologic models however restrict partial melting to very young 5 ma oceanic crust typically at 60 80 km depth paradoxically most of the known pliocene quaternary adakite occurrences are related to subduction of 10 45 ma lithosphere which should not be able to melt under normal subduction zone thermal gradients we propose an unusual mode of subduction known as flat subduction occurring in 10 of the world s convergent margins that can produce the temperature and pressure conditions necessary for fusion of moderately old oceanic crust of the 10 known flat subduction regions worldwide eight are linked to present or recent 6 ma occurrences of adakitic magmas observations from chile ecuador and costa rica suggest a three stage evolution 1 steep subduction produces a narrow calc alkaline arc typically 300 km from the trench above the asthenospheric wedge 2 once flat subduction begins the lower plate travels several hundred kilometers at nearly the same depth thus remaining in a pressure temperature window allowing slab melting over this broad distance and 3 once flat subduction continues for several million years the asthenospheric wedge disappears and a volcanic gap results as in modern day central chile or peru the proposed hypothesis which reconciles thermal models with geochemical observations has broad implications for the study of arc magmatism and for the thermal evolution of convergent margins

cretaceous tertiary shortening basin development and volcanism in central tibet the geologic map pattern of the qiangtang terrane in central tibet defines a 600 km long and up to 270 km wide east plunging structural culmination it is characterized by early mesozoic blueschist bearing melange and upper paleozoic strata in the core and mainly triassic jurassic strata along the limbs in the western qiangtang terrane 84 e the culmination is unconformably overlain by weakly deformed mid cretaceous volcanic flows and tuffs along the bangong suture to the south 32 n 84 e mid cretaceous nonmarine red beds and volcanic rocks lie unconformably on jurassic suture zone rocks these relationships demonstrate that west central tibet was above sea level during the mid cretaceous and experienced significant denudation prior to mid cretaceous time growth of the qiangtang culmination is inferred to have initiated during southward emplacement of a thrust sheet of early mesozoic melange and upper paleozoic strata during the early cretaceous lhasa qiangtang collision the north south width of the inferred thrust sheet provides a minimum slip estimate of 150 km at 84 e decreasing eastward to 70 km at 87 e paleogene deformation in the qiangtang terrane is characterized by widely distributed mainly north dipping thrust faults that cut eocene oligocene red beds and volcanic rocks in their footwall along the bangong suture the north dipping shiquanhe gaize amdo thrust system cuts 64 and 43 m y old volcanic tuffs in its footwall and accommodated 40 km of post mid cretaceous shortening the tertiary south dipping gaize siling co backthrust bounds the southern margin of the bangong suture and marks the northernmost limit of mid cretaceous marine strata in central tibet cretaceous deformation and denudation in central tibet is attributed to northward underthrusting of the lhasa terrane beneath the qiangtang terrane along the bangong suture this model implies that 1 cretaceous strata along the bangong suture and in the northern lhasa terrane were deposited in a flexural foreland basin system and derived at least in part from the qiangtang terrane and 2 the central tibetan crust was thickened substantially prior to the indo asian collision although its magnitude is poorly known tertiary shortening in the qiangtang terrane is more prevalent than in the lhasa terrane this difference may be attributed to the presence of underthrust melange in the deeper central tibetan crust which would have made it weaker than the lhasa terrane during the indo asian collision

earthquake induced landslides in central america central america is a region of high seismic activity and the impact of destructive earthquakes is often aggravated by the triggering of landslides data are presented for earthquake triggered landslides in the region and their characteristics are compared with global relationships between the area of landsliding and earthquake magnitude we find that the areas affected by landslides are similar to other parts of the world but in certain parts of central america the numbers of slides are disproportionate for the size of the earthquakes we also find that there are important differences between the characteristics of landslides in different parts of the central american isthmus soil falls and slides in steep slopes in volcanic soils predominate in guatemala and el salvador whereas extensive translational slides in lateritic soils on large slopes are the principal hazard in costa rica and panama methods for assessing landslide hazards considering both rainfall and earthquakes as triggering mechanisms developed in costa rica appear not to be suitable for direct application in the northern countries of the isthmus for which modified approaches are required

numerical model of the effect of serpentinites on the exhumation of eclogitic rocks insights from the monviso ophiolitic massif western alps abstract the intimate association of serpentinite melange with eclogites worldwide suggests that serpentinites may have played an important role in the exhumation of eclogites serpentinites may have formed by fluid percolation in the mantle wedge or by underplating of oceanic serpentinites we have tested numerically the role of serpentinites in the exhumation of eclogites using physical parameters obtained in the monviso massif of the western alps our calculation shows that the buoyancy of serpentinized peridotites in dense anhydrous peridotites may contribute to the exhumation of eclogitic blocks small eclogitic blocks 3 may be exhumed in completely hydrated mantle wedge but it is not common considering the absence of totally serpentinized peridotites in mantle wedges the exhumation of large eclogitic blocks 50 km 3 requires a viscosity of the serpentinite wedge to be between 10 20 and 10 21 pa and a density difference between the serpentinite wedge and the surrounding mantle on the order of 100 400 kg m 3 this condition is satisfied by only partially hydrated peridotites containing 10 50 serpentinites such serpentinized peridotites are expected to form at a depth ranging from 20 to 60 km in subduction zones by dehydration of subducting plates our conclusion is supported by the common occurrences of partially hydrated peridotites in close association with high pressure to ultra high pressure metamorphic rocks