optimizing landslide susceptibility zonation effects of dem spatial resolution and slope unit delineation on logistic regression models abstract we perform landslide susceptibility zonation with slope units using three digital elevation models dems of varying spatial resolution of the ubaye valley south french alps in so doing we applied a recently developed algorithm automating slope unit delineation given a number of parameters in order to optimize simultaneously the partitioning of the terrain and the performance of a logistic regression susceptibility model the method allowed us to obtain optimal slope units for each available dem spatial resolution for each resolution we studied the susceptibility model performance by analyzing in detail the relevance of the conditioning variables the analysis is based on landslide morphology data considering either the whole landslide or only the source area outline as inputs the procedure allowed us to select the most useful information in terms of dem spatial resolution thematic variables and landslide inventory in order to obtain the most reliable slope unit based landslide susceptibility assessment

central zagros fold thrust belt iran new insights from seismic data field observation and sandbox modeling 1 we present five generalized cross sections across the central zagros fold and thrust belt iran these sections show that the fold geometry varies significantly both horizontally and vertically the style is closely related to the changes in the mechanical behavior of the lithostratigraphic horizons and in particular to the presence of intermediate decollements within the sedimentary pile restoration of the sections shows amounts of shortening of the same order from one section to the other however it appears to be unequally distributed suggesting variations in basal decollement shear strength analogue modeling has been performed to systematically investigate the effect of an intermediate decollement level at different depths on the style of folding the models demonstrate that the position of intermediate decollements is an important factor controlling both structural style and fold wavelength models with shallow intermediate decollement show regularly and widely spaced anticlines in these models the fold wavelength depends directly on the thickness of the dominant competent layer and short wavelength superficial structures mask broad anticlines at depth models with deep intermediate decollement are characterized by the rapid propagation of deformation with small rate of shortening along this decollement influencing localization of forthcoming anticlines in the upper levels such propagation favors the development of duplexes and multiwavelength folds on this basis fold kinematics in central zagros is discussed using the variation of structural style along different folds as an indicator of the sequence of deformation detachment folding is the main folding style at least for the initial stages of deformation and thrust faults developed only at later stages some of these faults branched on decollement levels express the progression of folding whereas others are linked to late basement faults cutting through early structures in general the decollement levels are activated sequentially from deeper horizons to shallower ones however in one case gachsaran decollement a shallow decollement is activated during the early stages of folding and then abandoned during the subsequent evolution

limits on the validity of infinite length assumptions for modelling shallow landslides the infinite slope method is widely used as the geotechnical component of geomorphic and landscape evolution models its assumption that shallow landslides are infinitely long in a downslope direction is usually considered valid for natural landslides on the basis that they are generally long relative to their depth however this is rarely justified because the critical length depth l h ratio below which edge effects become important is unknown we establish this critical l h ratio by benchmarking infinite slope stability predictions against finite element predictions for a set of synthetic two dimensional slopes assuming that the difference between the predictions is due to error in the infinite slope method we test the infinite slope method for six different l h ratios to find the critical ratio at which its predictions fall within 5 of those from the finite element method we repeat these tests for 5000 synthetic slopes with a range of failure plane depths pore water pressures friction angles soil cohesions soil unit weights and slope angles characteristic of natural slopes we find that 1 infinite slope stability predictions are consistently too conservative for small l h ratios 2 the predictions always converge to within 5 of the finite element benchmarks by a l h ratio of 25 i e the infinite slope assumption is reasonable for landslides 25 times longer than they are deep but 3 they can converge at much lower ratios depending on slope properties particularly for low cohesion soils the implication for catchment scale stability models is that the infinite length assumption is reasonable if their grid resolution is coarse e g 25 m however it may also be valid even at much finer grid resolutions e g 1 m because spatial organization in the predicted pore water pressure field reduces the probability of short landslides and minimizes the risk that predicted landslides will have l h ratios less than 25

landslide susceptibility revealed by lidar imagery and historical records seattle washington abstract light detection and ranging lidar data were used to visually map landslides headscarps and denuded slopes in seattle washington four times more landslides were mapped than by previous efforts that used aerial photographs the mapped landforms landslides headscarps and denuded slopes were created by many individual landslides the spatial distribution of mapped landforms and 1308 historical landslides show that historical landslide activity has been concentrated on the mapped landforms and that most of the landslide activity that created the landforms was prehistoric thus the spatial densities of historical landslides on the landforms provide approximations of the landforms relative susceptibilities to future landsliding historical landslide characteristics appear to be closely related to landform type so relative susceptibilities were determined for landslides with various characteristics no strong relations were identified between stratigraphy and landslide occurrence however landslide characteristics and slope morphology appear to be related to stratigraphic conditions human activity is responsible for causing about 80 of historical seattle landslides the distribution of mapped landforms and human caused landslides suggests the probable characteristics of future human caused landslides on each of the landforms the distribution of mapped landforms and historical landslides suggests that erosion of slope toes by surface water has been a necessary condition for causing seattle landslides human activity has largely arrested this erosion which implies that landslide activity will decrease with time as hillsides naturally stabilize however evaluation of glacial age analogs of areas of recent slope toe erosion suggests that landslide activity in seattle will continue for the foreseeable future

quantitative risk assessment of landslides triggered by earthquakes and rainfall based on direct costs of urban buildings abstract this paper outlines a framework for risk assessment of landslides triggered by earthquakes and rainfall in urban buildings in the city of medellin colombia applying a model that uses a geographic information system gis we applied a computer model that includes topographic geological geotechnical and hydrological features of the study area to assess landslide hazards using the newmark s pseudo static method together with a probabilistic approach based on the first order and second moment method fosm the physical vulnerability assessment of buildings was conducted using structural fragility indexes as well as the definition of damage level of buildings via decision trees and using medellin s cadastral inventory data the probability of occurrence of a landslide was calculated assuming that an earthquake produces horizontal ground acceleration a h and considering the uncertainty of the geotechnical parameters and the soil saturation conditions of the ground the probability of occurrence was multiplied by the structural fragility index values and by the replacement value of structures the model implemented aims to quantify the risk caused by this kind of disaster in an area of the city of medellin based on different values of a h and an analysis of the damage costs of this disaster to buildings under different scenarios and structural conditions currently 62 of valle de aburra where the study area is located is under very low condition of landslide hazard and 38 is under low condition if all buildings in the study area fulfilled the requirements of the colombian building code the costs of a landslide would be reduced 63 compared with the current condition an earthquake with a return period of 475 years was used in this analysis according to the seismic microzonation study in 2002

slope vulnerability to earthquakes at subregional scale using probabilistic techniques and geographic information systems abstract the susceptibility of slopes to failure during earthquakes is calculated in terms of critical horizontal acceleration on a subregional scale for the upper part of the serchio river basin tuscany italy according to the working scale 1 10 000 and to the availability and accuracy of the input data the infinite slope analysis was judged to be the most appropriate method but particular attention was devoted to the error evaluation due to spatial variability of the geotechnic geometric and hydrologic parameters a geologic geomorphologic and hydrologic survey of the area was therefore performed and the geotechnic parameters were collected at local administrations all the data were stored in a gis used as a tool to build the spatial and attribute data base and to prepare the input data layers for the stability analysis in order to assess the variability of geotechnic parameters a statistical analysis was performed to assign the best fitting probability distribution to cohesion angle of internal friction and unit weight of the soil as hydrogeologic data were not available for the area only surface hydrology information could be used a map of probability of spring occurrences was derived by a bayesian method the weight of evidence modelling and was used as groundwater indicator a monte carlo procedure and a first order second moment method were applied and compared as error estimators in assessing the slope susceptibility to failure the differences between the two methods are discussed and two maps showing respectively the critical horizontal acceleration and the probability of failure associated with each slope are presented together with the curve plotting the reliability index against the probability of failure

landslide susceptibility mapping using lidar and dmc data a case study in the three gorges area china the objective of this study is to map landslide susceptibility in zigui segment of the yangtze three gorges area that is known as one of the most landslide prone areas in china by using data from light detection and ranging lidar and digital mapping camera dmc the likelihood ratio lr and logistic regression model lrm were used in this study the work is divided into three phases the first phase consists of data processing and analysis in this phase lidar and dmc data and geological maps were processed and the landslide controlling factors were derived such as landslide density digital elevation model dem slope angle aspect lithology land use and distance from drainage among these the landslide inventories land use and drainage were constructed with both lidar and dmc data dem slope angle and aspect were constructed with lidar data lithology was taken from the 1 250 000 scale geological maps the second phase is the logistic regression analysis in this phase the lr was applied to find the correlation between the landslide locations and the landslide controlling factors whereas the lrm was used to predict the occurrence of landslides based on six factors to calculate the coefficients of lrm 13 290 553 pixels was used 29 5 of the total pixels the logical regression coefficients of landslide controlling factors were obtained by logical regression analysis with spss 17 0 software the accuracy of the lrm was 88 8 on the whole the third phase is landslide susceptibility mapping and verification the mapping result was verified using the landslide location data and 64 4 landslide pixels distributed in extremely high zone and high zone in addition verification was performed using a success rate curve the verification result show clearly that landslide susceptibility zones were in close agreement with actual landslide areas in the field it is also shown that the factors that were applied in this study are appropriate lithology elevation and distance from drainage are primary factors for the landslide susceptibility mapping in the area while slope angle aspect and land use are secondary

spatially distributed three dimensional slope stability modelling in a raster gis abstract we present a grass gis implementation of a three dimensional slope stability model capable of dealing with shallow and deep seated slope failures r rotstab it exploits a modified version of the revised hovland method and evaluates the slope stability over a large number of randomly selected slip surfaces ellipsoidal or truncated in shape for each raster cell in the modelling domain the factor of safety is taken from the most critical slip surface this results in an overview of potentially unstable regions without showing the individual sliding areas furthermore the model produces a susceptibility index for each cell based on the proportion of slip surfaces with a low factor of safety we test the model in the collazzone area umbria central italy where detailed information on shallow and deep seated landslides morphology and lithology is available the rate of true predictions landslide plus non landslide ranges from 54 7 to 81 2 for shallow landslides and from 58 5 to 87 4 for deep seated landslides depending on the adjustment of the uncertain geotechnical parameters in the same order the rate of true landslide predictions decreases from 80 2 to 19 9 shallow and from 64 3 to 3 6 deep seated so that an increase of the true landslide prediction rate can only be achieved at the cost of a significant increase of the false alarm rate the results for shallow landslides are very similar to those yielded with the infinite slope stability model in terms of the minimum factor of safety but differ substantially in terms of the spatial patterns the evaluation of the landslide susceptibility index yields areas under the roc curves of 0 68 0 70 shallow landslides r rotstab 0 61 0 65 shallow landslides infinite slope stability model and 0 59 0 63 deep seated landslides we conclude that the r rotstab model outperforms the infinite slope stability model

insights from low temperature thermochronometry into transpressional deformation and crustal exhumation along the san andreas fault in the western transverse ranges california 1 the san emigdio mountains are an example of an archetypical transpressional structural system bounded to the south by the san andreas strike slip fault and to the north by the active wheeler ridge thrust apatite u th he and apatite and zircon fission track ages were obtained along transects across the range and from wells in and to the north of the range apatite u th he ages are 4 6 ma adjacent to the san andreas fault and both u th he and fission track ages grow older with distance to the north from the san andreas the young ages north of the san andreas fault contrast with early miocene u th he ages from mount pinos on the south side of the fault restoration of sample paleodepths in the san emigdio mountains using a regional unconformity at the base of the eocene tejon formation indicates that the san emigdio mountains represent a crustal fragment that has been exhumed more than 5 km along the san andreas fault since late miocene time marked differences in the timing and rate of exhumation between the northern and southern sides of the san andreas fault are difficult to reconcile with existing structural models of the western transverse ranges as a thin skinned thrust system instead these results suggest that rheologic heterogeneities may play a role in localizing deformation along the big bend of the san andreas fault as the san emigdio mountains are compressed between the crystalline basement of mount pinos and oceanic crust that underlies the southern san joaquin valley

tectonic control on southern sierra nevada topography california in this study we integrate the apatite u th he thermochronometric technique with geomorphic structural and stratigraphic studies to pursue the origin and evolution of topographic relief related to extensive late cenozoic faulting in the southern sierra nevada the geomorphology of this region reflects a transition from a vast region to the north characterized by nonequilibrium fluvial modification of a relict low relief landscape little affected by internal deformation to a more complex landscape affected by numerous faults regionally the relict landscape surface is readily resolved by age elevation relationships of apatite he ages coupled to geomorphology these relationships can be extended into the study area and used as a structural datum for the resolution of fault offsets and related tilting on the basis of 63 new apatite he ages and stratigraphic data from proximal parts of the san joaquin basin we resolve two sets of normal faults oriented approximately n s and approximately nw quaternary west side up normal faulting along the n s breckenridge kern canyon zone has resulted in a southwest step over from the owens valley system in the controlling structure on the regional west tilt of sierran basement this zone has also served as a transfer structure partitioning neogene quaternary extension resulting from normal displacements on the nw fault set this fault system for the most part nucleated along late cretaceous structures with late cenozoic remobilization representing passive extension by oblate flattening as the region rose and stretched in response to the passage of a slab window and the ensuing delamination of the mantle lithosphere from beneath the region

effects of digital elevation model map scale and data resolution on a topography based watershed model the effects of digital elevation model dem map scale and data resolution on watershed model predictions of hydrologic characteristics were determined for topmodel a topography based watershed model the effects of topography on watershed hydrology are represented in topmodel as the distribution of ln a tan b where ln is the napierian logarithm a is the upslope area per unit contour length and tan b is the gravitational gradient the minimum maximum mean variance and skew values of the ln a tan b distribution were computed from 1 24 000 scale 24k dems at 30 and 90 m resolutions and from 1 250 000 scale 250k dems at 90 m resolution for 71 areas in pennsylvania new york and new jersey an analysis of topmodel showed that model predictions of the depth to the water table the ratio of overland flow to total flow peak flow and variance and skew of predicted streamflow were affected by both the dem map scale and data resolution further topmodel analyses showed that the effects of dem map scale and data resolution on model predictions were due to the sensitivity of the predictions to the mean of the ln a tan b distribution which was affected by both dem map scale and data resolution dem map scale affected the mean of the ln a tan b distribution through its influence on the mean of the ln a distribution which characterizes land surface shape and the mean of ln 1 tan b distribution which characterizes land surface slope dem resolution in contrast affected the mean of the ln a tan b distribution primarily by its influence on the mean of the ln a distribution

dem resolution effects on shallow landslide hazard and soil redistribution modelling in this paper we analyse the effects of digital elevation model dem resolution on the results of a model that simulates spatially explicit relative shallow landslide hazard and soil redistribution patterns and quantities we analyse distributions of slope specific catchment area and relative hazard for shallow landsliding for four different dem resolutions grid sizes of 10 25 50 and 100 m of a 12 km2 study area in northern new zealand the effect of dem resolution is especially pronounced for the boundary conditions determining a valid hazard calculation for coarse resolutions the smoothing effect results in a larger area becoming classified as unconditionally stable or unstable we apply simple empirical soil redistribution algorithms for scenarios in which all sites with a certain landslide hazard fail and generate debris flow the lower initial number of failing cells but also the inclusion of slope limit in those algorithms becomes apparent with coarser resolutions for finer resolutions much larger amounts of soil redistribution are found which is attributed to the more detailed landscape representation looking at spatial patterns of landslide erosion and sedimentation the size of the area affected by these processes also increases with finer resolutions in general landslide erosion occupies larger parts of the area than deposition although the total amounts of soil material eroded and deposited are the same analysis of feedback mechanisms between soil failures over time shows that finer resolutions show higher percentages of the area with an increased or decreased landslide hazard when the extent of sites with lower and higher hazards are compared finer grid sizes and higher landslide hazard threshold scenarios tend to increase the total extent of areas becoming more stable relative to the less stable ones extreme care should be taken when quantifying landslide basin sediment yield by applying simple soil redistribution formulas to dems with different resolutions rather quantities should be interpreted as relative amounts for studying shallow landsliding over a longer timeframe the perfect dem resolution may not exist because no resolution can possibly represent the dimensions of all different slope failures scattered in space and time we assert that the choice of dem resolution possibly restricted by data availability in the first place should always be adapted to the context of a particular type of analysis copyright 2005 john wiley sons ltd

an empirical geomorphology based approach to the spatial prediction of soil thickness at catchment scale 1 catchment modeling in areas dominated by active geomorphologic processes such as soil erosion and landsliding is often hampered by the lack of reliable methods for the spatial estimation of soil depth in a catchment soil thickness h can vary as a function of many different and interplaying factors such as underlying lithology climate gradient hillslope curvature upslope contributing area and vegetation cover making the distributed estimation of h challenging and often unreliable in this work we present an alternative methodology which links soil thickness to gradient horizontal and vertical slope curvature and relative position within the hillslope profile while the relationship with gradient and curvature should reflect the kinematic stability of the regolith cover allowing greater soil thicknesses over planar and concave areas the distance from the hill crest or from the valley bottom accounts for the position within the soil toposequence this last parameter is fundamental points having equal gradient and curvature can have significantly different soil thickness due to their dissimilar position along the hillslope profile the proposed model has been implemented in a geographic information system environment and tested in the terzona creek basin in central italy results are in good agreement with field data mean absolute error is 11 cm with 8 5 cm standard deviation and average errors are lower than those obtained with other topography based methods where mean absolute error ranges from 47 cm for a model based on curvature position and slope gradient to 94 cm for a model based solely on slope gradient as a further test the predicted soil thickness was used to determine derived quantities such as the factor of safety for landsliding potential our model when compared to other empirical methods returns the best results and therefore can improve the prediction of soil losses and sediment production when utilized in conjunction with hydrological and landsliding models

prediction of the occurrence of slope instability phenomenal through gis based hazard zonation slope instability hazard assessment is based on the analysis of the terrain conditions at sites where slope failures occurred in the past for the analysis of the causative factors the application of geographic information systems gis is an essential tool in the data analysis and subsequent hazard assessment three scale levels of hazard mapping are defined a direct experience driven mapping at reconnaissance level a statistical approach to determine the causative factors in a quantitative susceptibility mapping and a methodology at large scale making using of deterministic models

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

application of the topographic position index to heterogeneous landscapes topographic position index tpi is an algorithm increasingly used to measure topographic slope positions and to automate landform classifications we applied tpi to a geoarchaeological research project in northwestern belgium but its use led to erroneous landform classifications in this heterogeneous landscape we asked whether deviation from mean elevation dev was a better method for landform classification than tpi we found that it enabled more accurate geomorphological assessment when using northwestern belgium as a case study

verification of landslide susceptibility mapping a case study a methodology is proposed for mapping susceptibility to landsliding and validating the results heavy rains in late 1996 and early 1997 led to a large number of landslids in the rute sector cordoba southern spain where landslide susceptibility mapping had previously been carried out using a matrix method developed with a geographical information system gis analysis of the distribution of the new landslides or reactivated earlier ones enabled the methodology to be validated by calculating association coefficients and determining the closeness of the match between subsequent field evidence and the previously defined susceptibility levels from the data obtained it can be concluded that the susceptibility mapping effectively explained the spatial distribution of landslides thus providing valuable information on stability conditions over a widespread area copyright 1999 john wiley sons ltd

the effect of dem resolution on the computation of the factor of safety using an infinite slope model abstract the quality of digital elevation models dems is essential for reliable landslide susceptibility assessments in this paper two dems derived from aster aster gdem v 2 with 30 m horizontal resolution and terrasar x geoelevation10 with 10 m horizontal resolution data are compared to study the effects of resolution on the derived slope and wetness index parameters in the application of the infinite slope model for the computation of the factor of safety several slope stability scenarios representing different wetness conditions with 5 10 and 100 mm d 1 of steady state recharge were calculated for the eastern flank of mount rinjani volcano on lombok island indonesia each scenario was conducted by computing the static factor of safety with mean values of the bulk density angle of internal friction cohesion and failure depth parameters as well as for their normally distributed values by monte carlo simulation all scenarios were applied to both dems the scenarios were evaluated by calculating the success prediction rate using the respective area under the curve auc and an existing landslide inventory additionally uncertainties in the estimated positions of landslides were taken into account depending on the particular scenario the success rate of the geoelevation10 model shows differences up to 3 compared to the aster gdem model this apparent improvement is mainly caused by the higher ground resolution in geoelevation10 however the success rate increases for the 10 mm d 1 and decreases for the 100 mm d 1 steady state recharge conditions consequently the more detailed flow direction in the geoelevation10 dem has the highest impact under conditions with lower water saturation the slight improvement in the total model quality shows that the higher resolution of the dem has a small impact on poorly parameterized models in which the material properties are described by roughly estimated parameters therefore the application of a high resolution dem to areas with a lack of data on the soil s physical properties is inefficient due to its low cost benefit ratio for quick analysis the aster gdem is of a suitable quality to fully benefit from the high resolution of the dems other parameters should be available in appropriate detail

deep below north america plate tectonics is the dominant process behind the creation and decomposition of the crust and the uppermost part of earth s mantle the lithosphere did plate tectonic processes also operate on the early earth in her perspective van der lee 1 reviews the evidence from laurentia the predecessor of the north american continent 1 http www sciencemag org cgi content full 294 5545 1297

the prediction of hillslope flow paths for distributed hydrological modelling using digital terrain models the accuracy of the predictions of distributed hydrological models must depend in part on the proper specification of flow pathways this paper examines some of the problems of deriving flow pathways from raster digital terrain data in the context of hydrological predictions using topmodel distributed moisture status is predicted in topmodel on the basis of spatial indices that depend on flow path definition the sensitivity of this index to flow path algorithm and grid size is examined for the case where the surface topography is a good indicator of local hydraulic gradients a strategy for the case where downslope subsurface flow pathways may deviate from those indicated by the surface topography is described with an example application