transition from slab to slabless results from the 1993 mendocino triple junction seismic experiment three seismic refraction reflection profiles part of the mendocino triple junction seismicexperiment allowustocompareandcontrastcrustanduppermantleofthenorth american margin before and after it is modified by passage of the mendocino triple junction upper crustal velocity models reveal an asymmetric great valley basin overlying sierran or ophiolitic rocks at the latitude of fort bragg california and overlying sierran or klamath rocks near redding california in addition the upper crustal velocity structure indicates that franciscan rocks underlie the klamath terrane east of eureka california thefranciscancomplexis onaverage laterallyhomogeneousandisthickestinthe triple junction region north of the triple junction the gorda slab can be traced 150 km inboardfromthecascadiasubductionzone southofthetriplejunction strongprecritical reflections indicate partial melt and or metamorphicfluids at the base of the crust or in theuppermantle breaksinthesereflectionsarecorrelatedwiththemaacamaandbartlett springs faults suggesting that these faults extend at least to the mantle we interpret our datatoindicatetectonicthickeningofthefranciscancomplexinresponsetopassageofthe mendocino triple junction and an associated thinning of these rocks south of the triple junction due to assimilation into melt triggered by upwelling asthenosphere the region of thickenedfranciscancomplexoverliesazoneofincreasedscattering intrinsicattenuation or both resulting from mechanical mixing of lithologies and or partial melt beneath the onshore projection of the mendocino fracture zone our data reveal that we have crossed thesouthernedgeofthegordaslabandthatthisedgeand ortheoverlyingnorthamerican crust may have fragmented because of the change in stress presented by the edge

form facies and depositional history of the north long john rock avalanche owens valley california the prehistoric but geomorphically pristine north long john rock avalanche of the inyo mountains piedmont california formed by the catastrophic collapse and disintegration of a 500 1000 m range front bedrock slab this failure rapidly produced and transferred 25 million cubic metres of new sediment to the piedmont where it was deposited in a trough between two coalesced alluvial fans the avalanche consists of nearly monolithologic aplitic unstratified very angular muddy cobble pebble gravel with boulders concentrated at the top and outer margins the deposits are clast supported except in the lower central zone coarse clasts exhibit crackle breccia fabric and the voluminous equant pebbles are the disaggregated products of these clasts the avalanche deposits are distributed in a u shaped body with paired lateral levees 10 60 m high that extend 1560 m from the range front to a 108 m high distal snout each levee contains three segments that along with the snout overlap and extend progress

landslide hazard assessment in the three gorges area of the yangtze river using aster imagery zigui badong this paper reports a regional assessment of landslide hazard in the three gorges area china based on terra 1 satellite advanced spaceborne thermal emission radiometer aster imagery data including a stereo image derived digital elevation model dem and multi spectral reflective and thermal imagery in combination with limited field investigation the three gorges dam and reservoir project has gained international attention not only for its great potential for hydro electrical power generation and flood control but also for its potentially harmful effects on the environment and socio economy the most significant and widespread natural hazard in the region is slope instability a simple multi variable elimination and characterisation model employing geometric mean and boolean decision rules has been applied to a multi criterion image dataset to categorise the area into a series of potential landslide hazard levels which are presented in map form the results presented here show high levels of hazard in and around all the main inhabited areas along the river limited fieldwork has been conducted to provide reliable ground control and the results of this paper show good correlation with this field evidence

in situ evidence for a low degree of s wave anisotropy in the oceanic upper mantle a seismic refraction survey using ocean bottom seismometers with one vertical and two horizontal component geophones was carried out off western canada this report presents one feature of a comprehensive interpretation of the data set that dealing with shear wave velocity anisotropy in the uppermost mantle amplitude and traveltime corrected sv record sections for two profiles ex2 approximately parallel to the spreading ridge and ex3 approximately parallel to the direction of spreading were compiled from an interpretation based on comparisons with synthetic seismograms the shear wave velocity in the upper mantle is 4 5 km s for ex2 and 4 6 km s for ex3 the corresponding compressional wave velocities are 8 3 km s and 7 5 km s the significant difference in p wave velocities is attributed to azimuthal velocity anisotropy of the type normally found in the pacific basin in contrast the small difference in s wave velocities suggests a very low degree of shear wave anisotropy the combination gives a prominent anisotropy in values of poisson s ratio for the upper mantle the first in situ evidence for this feature these results are consistent with laboratory measurements on ultramafic rock samples from ophiolite complexes

reinterpretation of seismic reflection data over the east pacific rise multichannel seismic reflection data over the axial region of the east pacific rise are depth migrated using detailed velocity information from laboratory measurements of ophiolite samples the data are from the lamont doherty geological observatory s line 17 shot across the rise at 9 sup 0 n the migrated data are interpreted to show the structure of the seafloor and what we believe is the magma chamber roof the polarity and apparent root mean squared velocity of the magma chamber roof are asymmetric with respect to the topographic axis of the ridge the asymmetry is probably real and not an artifact of data collection modeling of the magnetic data gathered along the line shows that spreading has not been proceeding normally a reasonable explanation for the asymmetry is the possibility that the line intersects a transform fault or an abandoned ridge segment near the ridge axis the shape of the roof reflection is convex upward with an approximate slope of 10 sup 0 and a width of 4 km if extrapolated symmetrically to the other side of the ridge axis the magma chamber roof event is consistent with the funnel shaped chamber proposed by pallister and hopson 1981 for the samail ophiolite if the chambermore roof steepens rapidly beyond the extent of the reflection it would be consistent with the mush filled model of sleep 1975 1978 and dewey and kidd 1977 less

large landslides associated with a diapiric fold in canelles reservoir spanish pyrenees detailed geological geomorphological mapping trenching and electrical resistivity imaging abstract detailed geomorphological geological mapping in canelles reservoir the spanish pyrenees reveals the presence of several large landslides overlooked in previous cartographic works one of the slope movements designated as the canelles landslide corresponds to a 40 10 6 m 3 translational landslide reactivated in 2006 by a severe decline in the reservoir water level the geomorphic features mapped in the upper part of the canelles landslide including surface ruptures corroborated by electrical resistivity imaging and trenching indicate multiple displacement episodes previous to the 2006 human induced event consistently the stratigraphic and structural relationships observed in a trench record at least two displacement events older and larger in magnitude than the 2006 reactivation the oldest recorded event occurred in the 6th to 7th centuries and the second in 1262 1679 yr ad this latter episode might be correlative to the 1373 ribagorza earthquake m w 6 2 which caused the reactivation of a landslide and the consequent destruction of a village in the adjacent valley the available data indicate that over more than one millennium the kinematics of the landslide has been characterised by discrete small displacement episodes these data together with the available literature on rapid rockslides do not concur with the acceleration predicted by modelling in a previous investigation which foresees a speed of 16 m s 1 despite the low average dip of the sliding surface 9 10 this case study illustrates that the trenching technique may provide valuable practical information on the past behaviour of landslides covering a much broader time span than instrumental and historical records

electrical imaging of sliding geometry and fluids associated with a deep seated landslide la clapiere france this paper deals with the applicability of electrical resistivity tomography ert for the recognition of large landslide structures at depths which have never previously been imaged accurately one of the most studied and instrumented deep landslides in europe is taken as an example the la clapiere landslide the first stage of the study consisted of an accurate geological mapping taking into account a morphological analysis of gravitational deformations this allowed a very fine definition of the landslide structure that could be compared with three provided ert profiles performed within the landslide body very good correlations were obtained for the determination of sub horizontal structures and associated fluid circulations it confirmed the position of the sliding surface that reached a maximum depth of 100 m forward computing was however necessary to determine the influence and then the presence of vertical discontinuities it supports the use of ert as an efficient tool for large scale landslide imaging such as deep seated landslides copyright 2010 john wiley sons ltd

a numerical comparison of 2d resistivity imaging with 10 electrode arrays numerical simulations are used to compare the resolution and efficiency of 2d resistivity imaging surveys for 10 electrode arrays the arrays analysed include polepole pp pole dipole pd half wenner hw wenner wn schlumberger sc dipole dipole dd wenner wb array gm multiple or moving gradient array gd and midpoint potential referred measurement mpr arrays five synthetic geological models simulating a buried channel a narrow conductive dike a narrow resistive dike dipping blocks and covered waste ponds were used to examine the surveying efficiency anomaly effects signal to noise ratios and the imaging capabilities of these arrays the responses to variations in the data density and noise sensitivities of these electrode configurations were also investigated using robust l1 norm inversion and smoothness constrained least squares l2 norm inversion for the five synthetic models the results show the following i gm and wn are less contaminated by noise than the other electrode arrays ii the relative anomaly effects for the different arrays vary with the geological models however the relatively high anomaly effects of pp gm and wb surveys do not always give a high resolution image pd dd and gd can yield better resolution images than gm pp wn and wb although they are more susceptible to noise contamination sc is also a strong candidate but is expected to give more edge effects iii the imaging quality of these arrays is relatively robust with respect to reductions in the data density of a multi electrode layout within the tested ranges iv the robust inversion generally gives better imaging results than the l2 norm inversion especially with noisy data except for the dipping block structure presented here v gd and mpr are well suited to multichannel surveying and gd may produce images that are comparable to those obtained with dd and pd accordingly the gd pd dd and sc arrays are strongly recommended for 2d resistivity imaging where the final choice will be determined by the expected geology the purpose of the survey and logistical considerations

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

a finite element computation of seismic diffraction about the rise axis magma chamber in a previous study models of the crust and magma chamber at 12 50 n on the east pacific rise were derived with a two dimensional ray tracing analysis of rise normal refraction lines the best model featured a 4 km wide axial magma chamber but the data contained diffraction effects that were not modeled by geometric ray theory this raised questions as to whether this model would reproduce the waveform data and whether diffraction might be obscuring a much larger magma chamber we have tested the model with a finite element calculation of synthetic seismograms this method incorporates full wave effects including diffraction the synthetics accurately reproduce the data and exhibit diffraction phenomena similar to those in the data the previous travel time analysis was largely successful and was only slightly compromised by diffraction diffraction in rise normal refraction experiments is therefore not obscuring a large low velocity magma chamber

late holocene episodic displacement on fault scarps related to interstratal dissolution of evaporites teruel neogene graben ne spain abstract the mio pliocene formations of the turolian type section teruel graben spain have sagged due to dissolution of the underlying triassic evaporites generating a 1 7 km long monocline and accompanying synform with 130 m of structural relief the crest of the monocline is affected by a graben that counterbalances the shortening caused by passive bending in the adjacent syncline this graben is controlled by a master synthetic fault and a swarm of antithetic and synthetic faults with a conspicuous geomorphic expression after acquiring ground penetrating radar gpr profiles three trenches were excavated in depressions associated with uphill facing fault scarps to our knowledge these are the first trenches excavated across faults caused by deep seated dissolution of evaporites the geometrical relationships observed in two trenches indicate late holocene episodic displacement as many as 3 events some of the parameters estimated for the investigated faults are clearly different from those expectable for tectonic faults in this intraplate area they include high apparent vertical slip rates 0 6 1 mm yr low average recurrence of faulting events 1 2 2 ka and very high displacement per event values 65 cm for surface ruptures less then 200 m long our findings suggest that considering evaporite collapse faults as creeping structures is not a reliable criterion to differentiate between tectonic faults seismogenic and dissolution induced gravitational faults nonseismogenic

investigation of a large collapse sinkhole affecting a multi storey building by means of geophysics and the trenching technique zaragoza city ne spain an active sinkhole around 100 m long has been investigated in the city of zaragoza ne spain subsidence activity on this depression including the sudden occurrence of a collapse sinkhole 5 m across led to the abandonment of a factory in the 1990s at the present time a building with 100 flats and shallow pad foundations partially built on the sinkhole is affected by rapid differential settlement the development of the sinkhole results from the karstification of the halite and glauberite bearing bedrock and the sagging and collapse of the overlying bedrock and alluvium more than 30 m thick gpr and electrical resistivity profiles have provided information on the distribution and geometry of the subsidence structure the application of the trenching technique and geochronological methods ams and osl dating has allowed us to infer objective and practical data on the sinkhole including 1 limits of the subsidence structure 2 subsidence mechanisms 3 cumulative subsidence 408 cm 4 subsidence rates on specific failure planes 1 8 cm year 5 episodic displacement regime of some fault planes the available information indicates that the progressive deformation recorded in the building will continue and might be punctuated by events of more rapid displacement this work illustrates the practicality of the trenching technique for the study of sinkholes in mantled karst areas

microearthquakes on the east pacific rise at 21 n and the rivera fracture zone during march and april of 1974 three ocean bottom seismometer obs capsules were deployed in arrays on the east pacific rise epr at 21 n for 8 days on the rivera fraction zone rfz for 9 days and at the epr rfz intersection for 12 days seismicity on the epr is characterized by extremely small events none large enough to trigger all of the instruments simultaneously a weak 24 hour periodicity in obs event trigger rate is observed this could be related to earth strain tides or a modulation in the trigger sensitivity due to a varying noise level on the rivera fracture zone an en echelon pattern of earthquakes with a maximum depth of 10 km was observed seismic activity at the junction of the epr and rfz becomes more diffuse and terminates abruptly at the epr the junction array was slightly offset from the active zone of seismicity and the depth of only one event is reliably determined at 5 4 2 km the s wave spectra of microearthquakes at the junction and on the rfz are computed and seismic moments and corner frequencies determined stress drops are between 0 1 and 10 bars and show no systematic difference at the two deployment sites larger earthquakes observed at teleseismic distances do show markedly lower stress drops when they originate near to spreading centers but these differences are not observed at the microearthquake level in this study it is suggested that this is due to a natural tendency for small earthquakes to have small stress drops and a lack of large earthquakes during the rfz deployment

evolution of the ocean crust results from recent seismic experiments we present results from recent analyses of seismic refraction and sea floor microseismicity studies in the pacific and atlantic oceans which lend support to the hypothesis that processes responsible for the construction of ophiolite suites are similar to phenomena extant at midocean ridges seismicity at fast spreading ridges is characterized by very low magnitude 0 1 and shallow 2 3 km microearthquakes and long term oscillations or harmonic tremor a detailed seismic refraction experiment on a fast spreading portion of the east pacific rise supports the hypothesis of the existence of a crustal magma chamber analyses of these data indicate that the chamber is largely unperturbed by the presence of conjugate spreading centres and the inverted deltashaped zone of partial melt is characterized by a half width in excess of 6 km finally a new approach for obtaining upper crustal velocities when applied to data characterized by the presence of shear waves provides several counter examples to the hypothesis that the shallow crust evolves with time

neotectonics and late holocene paleoseismic evidence in the plio quaternary daroca half graben iberian chain ne spain implications for fault source characterization this work has been supported by project cgl2017 85045 p ministerio de economia industria y competitividad gobierno de espana

development of crestal normal faults associated with deepwater fold growth deepwater anticlines during their early stages of development approximately between interlimb angles of 180 and 140 grow and accumulate weak fine grained and poorly lithified sediment on their crests growth of the anticlines induced gravitational instability within the syn kinematic sediments and development of a range of shallow gravity driven failure mechanisms in addition to shallow tens of metres depth to detachment rotational landslides deeper seated normal fault swarms also affect the fold crests and upper fold limbs these faults tend to penetrate to depths between 200 and 800 m are 100s of metres to a few kilometres long planar to weakly curved in cross section and display throws in the order of tens of metres the faults do not sole out into a detachment but die out downwards they can occur as single sets or tiers of faults that have developed at different times in map view the fault patterns range from straight to anastamosing to highly curved with complex cross cutting relationships the number and orientation of faults corresponds to the maximum slope dip and direction and consequently the faults are inferred to be mainly the product of gravity induced deformation although tangential stresses arising from outer arc bending of a fold or crestal collapse in response to a mobile sedimentary unit may contribute to some extent

northern east pacific rise magnetic anomaly and bathymetric framework the oceanic crust in the eastern pacific between 7on and 30on and east of 127ow contains a fairly complete history of the spreading centers associated with the east pacific rise since 25 m y b p late oligocene in this paper we have summarized the seafloor spreading magnetic anomaly data and the bathymetric data that reflect the record of this tectonic history the well defined magnetic lineations north of the clarion fracture zone in the mouth of the gulf of california and on the east flank of the east pacific rise epr are carefully examined and used to provide a guide for interpreting the spreading pattern between the clarion and clipperton fracture zones southward of the rivera fracture zone over the mathematician ridge and over the entire epr east of the mathematician ridge between the rivera and siqueiros fracture zones the bathymetric data provide a trace of the fracture zone pattern in each of the above mentioned areas the fracture zone bathymetry and the seafloor spreading magnetic lineations on the epr south of the rivera fracture zone have a distinctive fanning pattern caused by close poles of rotation and plate boundary reorganizations all these data provide a good record of the plate reorganizations in the middle miocene at magnetic anomaly 5a time 12 5 to 11 m y b p in the late miocene at magnetic anomaly 3 4 time 6 5 m y b p and in the pliocene at magnetic anomaly 2 3 time 3 5 m y b p several abandoned spreading centers including the mathematician ridge were left behind as a result of these reorganizations the mathematician ridge is shown to be a set of ridges and trough whose origin is related to the tectonic activity associated with each of the above mentioned reorganizations since anomaly 5a

criteria for rapid sliding ii thermo hydro mechanical and scale effects in vaiont case abstract thermally induced excess pore pressures have been included into a two wedge evolutive model of vaiont landslide the problem requires the solution of a system of four coupled balance equations for the shear bands and the surrounding rock as well as the joint equation of motion of the entire slide the model predicts the high velocities observed and is consistent with other data slide geometry residual strength and conditions on the sliding surface the interpretation of a sensitivity analysis suggests that there exists a threshold permeability band in the range 10 8 to 10 10 m s which separates potentially fast motions from slow motions this conclusion is maintained if the scale of the landslide is reduced

geology and tsunamigenic potential of submarine landslides in santa barbara channel southern california abstract a large submarine landslide complex and four small landslides developed under the santa barbara channel suggesting a potential hazard from landslide generated tsunamis we integrate offshore stratigraphy and geologic structure multibeam bathymetric information and several kinds of seismic reflection data to understand how and when the submarine landslides formed seismic reflection data show that mass failure along the slope began at least 200 ka ago landslides appear as zones of poor reflectivity having an irregular upper surface and these zones alternate vertically with strong parallel reflections the emplacement ages of two of the three main landslide lobes are well established at 8 and 10 ka the source material for the youngest part of the landslide complex was sediment of probable late pleistocene and holocene age that accumulated in a shelf edge delta directly under this delta growth of faults and anticlines was particularly intense and tended to oversteepen the deltaic deposits these active structures also formed migration pathways and reservoirs for aqueous and hydrocarbon fluids from the deep basin tsunami deposits have been described from a low lying area near santa barbara and numerical modeling of tsunamis generated by hypothetical landslides in santa barbara channel indicates a moderate to severe threat borrero j c dolan j f and synolakis c e 2001 tsunamis within the eastern santa barbara channel geophys res lett 28 4 643 646 involving wave runups of 2 20 m for a range of assumed landslide volumes inundation from these waves however is expected to be highly focused so that only narrow 10 km sections of the shoreline would be affected

a late holocene deep seated landslide in the northern french pyrenees abstract a very large deep seated landslide dsl in the northern pyrenees with over 1 4 10 9 m 3 was mapped and dated based on sedimentation rates and 10 be terrestrial cosmogenic radionuclide surface exposure cre dating our analysis on the landslide reveals the role of inherited structures in the landslide process and highlighted typical gravitational morpho structures and a small lake trapped at the toe of the landslide head scarp the rate of lake sedimentation 0 86 0 57 mm yr 1 also provided us with the approximate age of the landslide 1106 540 yr the cre dating result highlights two main slope destabilization phases then we discussed the history of dsl activity and its controlling factors information related to historic markers and the absence of particular climate markers and changes during the medieval dark ages point to a single event in ad 1380 due to a major seismic event lavedan earthquake

characteristics mechanism and development tendency of deformation of maoping landslide after commission of geheyan reservoir on the qingjiang river hubei province china abstract based on field investigation of the constituent structure and geological formation of the maoping landslide the authors made an in depth study of the deformation characteristics and triggering mechanism of the reservoir induced slide through comprehensive analysis of the about 13 years observation data the maoping landslide the largest ancient landslide in geheyan reservoir with a volume of 23 5 million m3 is located on the left bank of the qingjiang river 66 km upstream of geheyan dam in april 1993 reservoir inundation reactivated the landslide which resulted in relocation of a village of 290 people since then the landslide body has been experiencing persistent deformation with an observed maximum displacement of 2841 4 mm up to october 2005 therefore further development of deformation of the landslide becomes a great concern for the safety of the reservoir and dam the analysis results show that the maoping landslide is an ancient landslide that is an accumulation of several consequent slides along the bank slope and experienced several secondary slumps in its front in later stages the ongoing deformation of the reactivated landslide is controlled by mechanical properties of materials and hydraulic effects induced by reservoir the slip process is of creep deformation as a whole and appears to be attenuating in later stage which indicates very low possibility of the high speed slip and integral failure of the slide

reply to the discussion by pinyol et al 2016 on gutierrez et al 2015 large landslides associated with a diapiric fold in canelles reservoir spanish pyrenees detailed geological geomorphological mapping trenching and electrical resistivity imaging

integrated geophysics and soil gas profiles as a tool to characterize active faults the amer fault example pyrenees ne spain the combined use of geophysical and soil gas composition exploration methods allows to rapidly obtain at relative low cost information that might be related to seismic activity conditions in this study we carried out geochemical soil gas sampling 222rn 220rn and co2 electrical resistivity tomography and seismic refraction profiles in two selected zones near the town of amer in the spanish pyrenees where the presence of recent fractures is evident in the field data analysis clearly reveals anomalous values for each gas at specific positions along the electrical imaging transects geomorphologic and hydrogeologic data and the integration of geophysical data and soil gas measurements indicate that 1 endogene gases radon 222rn and carbon dioxide co2 are released from the meta sedimentary basement rocks across the main fractured zones with higher permeability values while lower cenozoic detrital sedimentary formations act as an impervious boundary 2 sites with highest radon concentrations 52 kbq m 3 coincide with the zones in the amer fault showing more recent geomorphic evidence of activity and more specifically with those areas covered by thinner surficial formations 3 the lowest 222rn values 0 2 0 4 kbq m 3 were recorded just on the master active fault plane this pattern could be explained by a dilution effect resulting from high rates of soil co2 efflux 267 g m 2 day 1 4 soil thoron 220rn activity is maximum 143 kbq m 3 in areas with high surficial fracturing 5 groundwater pumping may cause important distortions in the natural flow dynamics and in the measured concentrations of gases the agreement between the different data geochemical geophysical and hydrogeological and field observations geology and geomorphology leads us to propose a preliminary tectonic gravitational model for the study area

spatial prediction of landslide susceptibility using an adaptive neuro fuzzy inference system combined with frequency ratio generalized additive model and support vector machine techniques abstract the spatial prediction of landslide susceptibility is an important prerequisite for the analysis of landslide hazards and risks in any area this research uses three data mining techniques such as an adaptive neuro fuzzy inference system combined with frequency ratio anfis fr a generalized additive model gam and a support vector machine svm for landslide susceptibility mapping in hanyuan county china in the first step in accordance with a review of the previous literature twelve conditioning factors including slope aspect altitude slope angle topographic wetness index twi plan curvature profile curvature distance to rivers distance to faults distance to roads land use normalized difference vegetation index ndvi and lithology were selected in the second step a collinearity test and correlation analysis between the conditioning factors and landslides were applied in the third step we used three advanced methods namely anfis fr gam and svm for landslide susceptibility modeling subsequently the results of their accuracy were validated using a receiver operating characteristic curve the results showed that all three models have good prediction capabilities while the svm model has the highest prediction rate of 0 875 followed by the anfis fr and gam models with prediction rates of 0 851 and 0 846 respectively thus the landslide susceptibility maps produced in the study area can be applied for management of hazards and risks in landslide prone hanyuan county

reconstructing the internal structure and long term evolution of hazardous sinkholes combining trenching electrical resistivity imaging eri and ground penetrating radar gpr abstract the approaches aimed at characterising specific damaging sinkholes have received limited attention compared with other ground instability phenomena e g landslides moreover the practicality of the trenching technique in combination with numerical dating and retro deformation analysis for sinkhole site investigations has been barely explored this work illustrates the advantages of combining geomorphic mapping electrical resistivity imaging eri ground penetrating radar gpr and trenching for sinkhole characterisation and shows how the trenching technique contributes to fill significant gaps that neither geomorphic nor geophysical methods can address two large sinkholes 200 m long related to the interstratal karstification of evaporites and generated by contrasting subsidence mechanisms sagging collapse were investigated in the fluvia valley ne spain although gpr data may provide high resolution information on subsidence related stratigraphic and structural features at shallow depth the profiles acquired in the investigated sites with 100 mhz shielded and 40 mhz unshielded antennae provided limited insight into the internal geometry of the sinkholes due to reduced signal penetration related to the presence of conductive clayey material the eri sections satisfactorily imaged the general geometry of the sagging and collapse subsidence structures up to depths higher than 100 m and clearly captured the basal contact of the low resistivity sinkhole fill in the sections with adequate layout and resolution the trenches despite their limited depth ca 5 m allowed us to obtain valuable objective information on several key aspects of the subsidence phenomenon 1 mechanisms deformation style and kinematics progressive versus episodic 2 limits of ground deformation 3 temporal evolution expansion versus contraction 4 chronology and timing of most recent deformation phase 5 rates of subsidence and sedimentation and 6 the role played by subsidence in the development of lacustrine environments and the associated sedimentation patterns

evaluation of trenching ground penetrating radar gpr and electrical resistivity tomography ert for sinkhole characterization this paper explores the suitability and advantages of combining the trenching technique with geophysical surveys ground penetrating radar gpr and electrical resistivity tomography ert for sinkhole characterization in a mantled karst area the approach is applied to two active sinkholes concealed by anthropogenic deposits and formed by contrasting subsidence mechanisms collapse and sagging the ert section acquired across the collapse sinkhole images the clayey fill of the depression as an obvious low resistivity area showing the approximate location of the sinkhole edges spatially dense gpr surveys provide information on the position of the boundaries of the concealed subsidence structures and their three dimensional 3d internal geometry revealing the dominant subsidence mechanism we illustrate the impact of several factors on the quality of the gpr data such as sinkhole size nominal frequency of the antennas antenna shielding and the presence of backfilled excavations and above surface objects trenches provided detailed information on the subsurface structure of the sinkhole subsidence magnitude partitioning of the strain and the position of the sinkhole edges especially when they are deep enough and excavated across the central sector and perpendicular to the boundaries the stratigraphic and structural relationships observed in the trench were then used to infer the spatial evolution of the sinkholes e g enlargement their kinematic behavior episodic versus progressive and to differentiate discrete subsidence events and their associated magnitude numerical dates were used to estimate average subsidence rates and the recurrence of subsidence events such integrated data sets may be used as an objective basis to forecast the future behavior of potentially damaging sinkholes and to assess the associated hazard and risk copyright 2013 john wiley sons ltd

on long term thickening of the oceanic crust a number of studies of seismic refraction data have resulted in suggestions that the oceanic crust thickens with age perhaps over a long time span it is difficult to reconcile notions of crustal thickening with many of our ideas about crustal structure and formation in this study we have re evaluated data compiled from a number of sources to obtain crustal thickness and age parameters for 105 different refraction profiles in the pacific an attempt was made to exclude data which might have poorly determined values of crustal thickness the crust does appear to thicken with age to 30 or 40 m y but the effect is very subtle once probable biases are removed from the data crustal thickening is not significant to a 95 confidence limit if ten m y samples are used however if one takes sample intervals of 0 30 m y and 30 100 m y there appears to be some difference in the average crustal thickness even in the latter case the amount of thickening is far less than previous studies have suggested only 45 km thus evidence for the long term addition of mass to the crust remains tenuous

axial intrusion zone beneath the median valley of the mid atlantic ridge at 37 n detected by explosion seismology summary four seismic refraction lines three of which had shots every 250 m were shot across along and parallel to the median valley of the mid atlantic ridge at 37 n a method has been developed for calculating the effect on the travel times of the rough sea floor relief beneath the profiles and has been used to correct all the travel times for this effect most arrivals were from a main refractor of apparent velocity 5 4 to 6 3 km s 1 only beyond 35 km were faster arrivals observed from an 8 09 36 km s 1 refractor the main refractor corresponds in depth at least approximately to the top of layer 3 of the ocean basins but its velocity is significantly less than normal for layer 3 perhaps due to dip a study of time residuals along two profiles across the median valley indicates the presence of a 2 to 3 km wide low velocity zone about 3 2 km s 1 beneath the median valley floor this zone extends over the upper 2 5 km of the crust and is believed to represent a zone of intrusion through which magma passes on its way to the sea floor

mass rock creep and landsliding on the huangtupo slope in the reservoir area of the three gorges project yangtze river china the huangtupo slope is one of the most noted large scale slopes with geologic hazards that cause problems related to the residential safety of immigrants in the reservoir area of the three gorges project yangtze river china the gravitational process blended with tectonic deformation large scale covering of loose debris and long term surficial mass movement complicates the huangtupo slope and gives rise to a lack of consensus on the slope nature and stability characterization of the structural geometry of the slope deformation and reconstruction of its development history are believed to be pivotal in understanding what has happened and what will happen to the slope based on a thorough field investigation combined with an electrical resistivity survey a three stage model involving mass rock creep primary landsliding partial reactivation is proposed the first stage follows the incision of the yangtze river along the axes of the guandukou syncline when huangtupo experienced long term gravitational deformation referred to as mass rock creep mass rock creep in the huangtupo slope can be classified as two basic processes toppling and deep seated creep toppling mainly occurs on the exterior part of the slope and is characterized by inclination sliding and segmentation of brittle deformation of cleavage rocks deep seated creep occurs predominantly in the interior part of the slope and brittle ductile flow folding accompanying low angle shearing is its representative deformation a primary large scale landslide occurred in the second stage as a subsequence of previous mass rock creep the landslide was ca 4 107 m3 in volume with elevations of 640 m a s l at the head and of 80 m a s l at the foot significant evidence for the landslide is the variation of attitudes of structural foliation and lineation among outcrops in the slope the last stage began subsequent to the original sliding surficial and partial reactivation on the huangtupo landslide plays a leading role in this stage two sliding events in this area in 1995 were ascribed to the partial reactivation mainly due to rainfall water level fluctuation of the yangtze river as well as human activity it was suggested that analogous failures in 1995 would continue on the huangtupo landslide and become even more frequent under the combined effect of human activity and reservoir filling

geomorphic and stratigraphic evidence of quaternary diapiric activity enhanced by fluvial incision navarres salt wall and graben system se spain abstract the structural and stratigraphic geological features associated with salt structures have received extensive attention from geologists however there is limited work on the geomorphic and quaternary record of diapiric activity despite its practical implications e g salt and hydrocarbon extraction geostorage activities this work analyses the quaternary geomorphic and stratigraphic evidence of diapiric activity in the navarres salt wall se spain developed along the axis of a neogene graben this salt system is located in a region characterized by a peculiar network of orthogonal grabens that control the configuration and evolution of the drainage network the protruding salt walls are spatially associated with the erosionally unloaded and deeply entrenched graben sections situated close to the regional base level evidence of recent current activity in the navarres salt wall include 1 internally drained areas in a marginal withdrawal basin with long sustained aggradation 2 distorted drainage network defeated and deflected streams wind gaps knickpoints changes in fluvial style which changed from an initial axial longitudinal pattern to a longitudinal marginal distribution at the flanks of the salt wall 3 development of diapiric fault scarps at the edge of the salt wall 4 tilted fluvial terraces dipping away from the salt wall and with localized sediment thickening the available data indicate along strike variability in deformation style and long term vertical deformation rates these range from 0 09 mm yr to significantly higher values 0 2 0 4 mm yr in the section where the salt wall displays a more prominent relief and is affected by deep fluvial entrenchment the regional analysis and the characterization of the navarres salt wall suggest that quaternary diapirism in the region is enhanced by erosional unloading related to fluvial entrenchment which expands from the regional base level through the upstream propagation of an incision wave

reconstructing the geochronological evolution of large landslides by means of the trenching technique in the yesa reservoir spanish pyrenees abstract detailed geomorphological mapping has revealed that the slopes upstream of the yesa dam are affected by several flysch landslides the largest landslides correspond to la refaya rotational slide 11 million m3 situated just upstream of the spillway and el vertedero translational slide 6 million m3 located 1 5 km upstream of the dam a portion of el vertedero landslide 3 million m3 was reactivated in 2006 due to overloading caused by an earth heap a higher earth dam will be built on the downstream side of the existing gravity concrete dam to raise the maximum water level of the reservoir by 23 m the retrodeformation analysis of the deposits exposed in two trenches excavated in the upper part of these landslides together with the obtained absolute ages c14 and osl have provided information on the kinematics and evolution of these slope movements the main findings derived from the 45 m long trench dug in the closed depression developed at the foot of the head scarp of la refaya landslide include 1 the landslide is older than 12 ka and has undergone a cumulative rotation higher than 17 yielding a mean rotation rate of about 1 4 millennium 2 most of the rotation 14 occurred before 5 8 ka and according to the trench stratigraphy the kinematics of the landslide has been dominated by progressive displacement no evidence of catastrophic reactivation has been found the 45 m long trench excavated across the scarp and bench situated at the head of the non reactivated portion of el vertedero translational slide reveals that 1 the landslide is older than 38 ka 2 the trenched portion has undergone at least one reactivation subsequent to 20 ka and has remained inactive for a long time as suggested by the highly degraded bedrock scarp with a slope of 18 compared to the 60 dip of the underlying failure plane based on this study corrective measures with an estimated cost of 11 5 million euros have been designed for this slope the investigation illustrates the usefulness and cost effectiveness of the trenching technique allied with geochronological methods to obtain information on the precise limits age failure mechanism kinematics progressive vs episodic displacement movement rate and chronological evolution of landslides

localization and characterization of an active fault in an urbanized area in central guatemala by means of geoelectrical imaging article i nfo article history the polochic and motagua faults define the active plate boundary between the north american and caribbean plates in central guatemala a splay of the polochic fault traverses the rapidly growing city of san miguel uspantan that is periodically affected by destructive earthquakes this fault splay was located using a 2d electrical resistivity tomography ert survey that also characterized the fault damage zone and evaluated the thickness and nature of recent deposits upon which most of the city is built ert images show the fault as a 50 m wide near vertical low resistivity anomaly bounded within a few meters by high resistivity anomalies forward modeling reproduces the key aspects of the observed electrical resistivity data with remarkable fidelity thus defining the overall location geometry and internal structure of the fault zone as well as the affected lithologies our results indicate that the city is constructed on a 20 m thick surficial layer consisting of poorly consolidated highly porous water logged pumice this soft layer is likely to amplify seismic waves and to liquefy upon moderate to strong ground shaking the electrical conductivity as well as the major element chemistry of the groundwater provides evidence to suggest that the local aquifer might at least in part be fed by water rising along the fault therefore the potential threat posed by this fault splay may not be limited to its seismic activity per se but could be compounded its potential propensity to enhance seismic site effects by injecting water into the soft surficial sediments the results of this study provide the basis for a rigorous analysis of seismic hazard and sustainable development of san miguel uspantan and illustrate the potential of ert surveying for paleoseismic studies

electrical resistivity tomography technique for landslide investigation a review abstract in the context of in situ geophysical methods the electrical resistivity tomography ert is widely used for the near surface exploration of landslide areas characterized by a complex geological setting over the last decade the technological improvements in field data acquisition systems and the development of novel algorithms for tomographic inversion have made this technique more suitable for studying landslide areas with a particular attention to the rotational translational and earth flow slides this paper aims to present a review of the main results obtained by applying ert for the investigation of a wide spectrum of landslide phenomena which affected various geological formations and occurred in different geographic areas in particular significant and representative results obtained by applying 2d and 3d ert are analyzed highlighting the advantages and drawbacks of this geophysical technique finally recent applications of the time lapse ert tl ert for landslide investigation and the future scientific challenges to be faced are presented and discussed

differentiating between gravitational and tectonic faults by means of geomorphological mapping trenching and geophysical surveys the case of the zenzano fault iberian chain n spain abstract the zenzano fault scarp has been developed on the top of a 475 m high erosional escarpment underlain by an upper brittle sequence and a lower halite bearing evaporitic formation the 1850 m long fault with a maximum displacement of 45 m and parallel to the escarpment has offset the back of a dip slope generating an antislope scarp with prominent triangular facets up to 38 m high and obstructing consequent transverse drainages defeated streams both gravitational and tectonic interpretations were previously proposed for this active surface rupture the fault scarp has been investigated by detailed geological and geomorphological mapping geophysical surveys gpr and ert and two trenches excavated across the fault in disrupted drainages the geophysical profiles clearly imaged the fault helping to site the trenches and roughly estimate the thickness of the deposits accumulated in the downthrown block although the maximum displacement to length ratio dmax l of the fault fall within the range of tectonic faults of similar length according to the world database the geological and geomorphological context together with several parameters reveal that this structure corresponds to a gravitational failure 1 anomalously high vertical displacement per event 1 4 m 2 high apparent vertical slip rate 0 6 mm year and 3 short recurrence interval of faulting events the negligible horizontal displacement component on the dip slip fault as well as the presence of very large caprock collapse sinkholes and saline springs strongly suggest that interstratal karstification of the halite bearing evaporites has played a primary role in the development of the gravitational failure the formation of this morphostructure has been favoured by pre existing tectonic faults erosional unloading related to the removal of an overburden ca 800 m thick and enhanced groundwater recharge due to the blockage of the drainage this work illustrates that the proposed multidisciplinary approach allows the identification of features and calculation of parameters that may help to elucidate whether an active failure has a gravitational or a tectonic origin

evaluating quaternary activity versus inactivity on faults and folds using geomorphological mapping and trenching seismic hazard implications abstract the incorporation of active faults in seismic hazard analyses may have a significant impact on the feasibility design and cost of major engineering projects e g nuclear facilities dams especially when located in the site vicinity the regulatory definition of active versus inactive fault is generally based on whether the fault has ruptured or not after a specific chronological bound i e fault recency this work presents a methodology mainly based on geomorphological mapping and trenching for determining whether specific faults can be considered as active or inactive the approach is illustrated through the analysis of several faults located in the spanish pyrenees loiti leyre la trinidad ruesta faults the 29 km long loiti thrust was included in the neotectonic map of spain as a probable neotectonic structure previous works based on geomorphological investigations incorporated the 28 km long leyre thrust as a significant seismic source in a probabilistic seismic hazard analysis which challenged the seismic design of nearby large dams the production of detailed geomorphological strip maps along the faults allowed the recognition of specific sites where the faults are covered by quaternary deposits the establishment of chronosequences pediments terrace sequences and the available geochronological data helped identifying the most adequate morpho stratigraphic units for satisfactorily evaluating fault activity vs inactivity the excavation of trenches at the selected sites provided unambiguous information on the presence or lack of deformation in the quaternary cover overlying the fault and the origin of scarps tectonic versus erosional trenches were also useful for collecting samples and reliably measuring the relative height of terraces overlain by thick colluvium the evidence gathered by these methods were complemented with the numerical dating of non deformed slope deposits covering a fault the analysis of the longitudinal profiles of old pediment surfaces located in the proximity of a fault the examination of a cave situated next to a fault searching for speleoseismological evidence and regional geodetic and seismotectonic data gps measurements earthquake focal mechanisms the integration of all the data and especially the trenches dug in non deformed old terrace deposits 100 ka truncating the faults indicates that the analysed faults can be considered inactive and that previous neotectonic postulations were based on non valid geomorphological interpretations

microearthquakes in the black smoker hydrothermal field east pacific rise at 21 n in july and august 1980 an array of five ocean bottom seismographs was deployed within 3 km of the 350 c hydrothermal vents at the rivera submersible experiment rise site at 21 n on the east pacific rise two of these instruments were placed within 600 m of the vents using a transponder navigation network the array detected four basic types of events the first type consisted of local very small microearthquakes locations obtained for 11 of these events place three within 1 km of the vents with the others elsewhere along the rise crest they appear to originate either from movement on the faults in the area or from the hydrothermal system beneath this area a study of the s p times of this type indicates a maximum hypocentral depth of 2 3 km implying a similar limit to the depth of hydrothermal circulation and brittle fracturing in the vicinity of the vents the second type of event found consisted of emergent earthquakes that have many of the characteristics of volcanic harmonic tremor the frequency of these events falls in the 1 5 hz range and are similar in appearance to those seen at mount st helens prior to and during its may 1980 eruption they may be either hydrothermal or volcanic in origin the third type of event produced a very monochromatic high frequency seismogram with the energy concentrated at 20 hz these events also appear to have a local origin the particle motion of these earthquakes shows almost pure stonely wave propagation and they appear to originate from a regularly oscillating dilatational source the nature of the source of event types two and three is clearly not the usual sort of motion on a fault and is still not understood the fourth type of earthquake recordings were regional events apparently from the nearby rivera and tamayo fracture zones the low frequency acoustic noise in the water was 16 64 times higher within 300 m of the vents than it was 2 km away this implies that the black smoker vents may be generating a large acoustical disturbance as the 350 c water pours into the ocean the observations are among the first of seismicity on moderate to fast spreading ridges and many of the events appear to be related to the hydrothermal activity found there

landslides triggered by the 1949 khait earthquake tajikistan and associated loss of life abstract earthquake triggered landslides are a major geological hazard in central asia in july 1949 the m7 4 khait earthquake triggered many hundreds of landslides in a mountainous region near the southern limit of the tien shan mountains central tajikistan these landslides involved widespread rock slope failure as well as large numbers of flowslides in loess that mantles the steep slopes of the region in the yasman valley hundreds of loess landslides coalesced to form a massive loess flow est vol 245 mm 3 that travelled up to 20 km on a slope of only 2 in an adjacent valley the khait landslide involved transformation of an earthquake triggered rockslide into a very rapid flow by the entrainment of saturated loess into its movement it travelled 7 41 km over a vertical distance of 1421 m with an estimated average velocity of 30 m s we estimate its volume as 75 mm 3 an order of magnitude less that previously published estimates the khait landslide was simulated using dan the number of casualties due to earthquake triggered landslides in the epicentral region was considerable approximately 4000 people were killed in the yasman valley loess flow as 20 villages kishlaks were overwhelmed in the khait landslide alone we estimate ca 800 people lost their lives when the villages of khait and khisorak were overrun by rapidly moving debris our data indicates that a total of approximately 7200 people were killed by earthquake triggered landslides in the epicentral region of the khait earthquake and that in terms of loss of life the 1949 yasman valley loess flow was one of the most destructive landslides in recent history

sinkholes collapse structures and large landslides in an active salt dome submerged by a reservoir the unique case of the ambal ridge in the karun river zagros mountains iran abstract ambal ridge covering 4 km2 is a salt pillow of gachsaran formation with significant salt exposures in direct contact with the karun river zagros mountains the highly cavernous salt dome is currently being flooded by the gotvand reservoir second largest in iran geomorphic evidence including the sharp deflection of the karun river and defeated streams indicate that ambal is an active halokinetic structure probably driven by erosional unloading around 30 of the salt dome is affected by large landslides up to ca 50 106 m3 in volume slope oversteepening related to fluvial erosion and halokinetic rise seems to be the main controlling factor a total of 693 sinkholes have been inventoried 170 sinkholes km2 for which a scaling relationship has been produced the depressions occur preferentially along a belt with a high degree of clustering this spatial distribution is controlled by the proximity to the river slope gradient and halite content in the bedrock a large compound depression whose bottom lies below the normal maximum level of the reservoir will likely be flooded by water table rise forming a lake the impoundment of the reservoir has induced peculiar collapse structures 220 280 m across expressed by systems of arcuate fissures and scarps rapid subsurface salt dissolution is expected to generate and reactivate a large number of sinkholes and may reactivate landslides with a significant vertical component due to lack of basal support

a microearthquake survey at the junction of the east pacific rise and the wilkes 9 s fracture zone summary an ocean bottom seismograph survey of the junction of the east pacific rise and the wilkes fracture zone detected only three microearthquakes beneath the rise crest during seven days of recording in contrast during the same period 41 events were detected on the fracture zone all at distances greater than 10 km from the junction these results suggest that near the rise crest the thin crust can support sufficient stress only to generate infrequent small earthquakes and that most faulting may take place by aseismic slip at 10 km from the rise axis part of the crest has become competent enough to support stress resulting in earthquakes probably at depths of up to 5 km below the sea bed gear 5 waves on the seismometer records indicate that a magma chamber if it exists near the junction is less than 10 km across

oceanic ridge crest processes oceanic ridge crest processes constitute a vigorous frontier of multidisciplinary research with global ramifications in the earth atmospheric and biologic sciences this deep ocean frontier is gradually opening in response to investigations which are elucidating the role of these processes in the lithosphere hydrosphere atmosphere and biosphere and the application of advanced instrumental and interpretive techniques which are increasing the quality and quantity of data these techniques include crustal drilling with borehole logging deep sea drilling project reports high resolution bathymetry sea beam etc side scan sonar seamarc i and ii gloria etc imagery with video and photography multichannel seismics determination of water column properties ctd with rosette sampler etc and submersible applications

potential of airborne lidar data analysis to detect subtle landforms of slope failure portaine central pyrenees abstract slope failures have been traditionally detected by field inspection and aerial photo interpretation these approaches are generally insufficient to identify subtle landforms especially those generated during the early stages of failures and particularly where the site is located in forested and remote terrains we present the identification and characterization of several large and medium size slope failures previously undetected within the orri massif central pyrenees around 130 scarps were interpreted as being part of rock slope failures rsfs while other smaller and more superficial failures were interpreted as complex movements combining colluvium slow flow slope creep and rsfs except for one of them these slope failures had not been previously detected albeit they extend across a 15 of the studied region the failures were identified through the analysis of a high resolution 1 m lidar derived bare earth digital elevation model dem most of the scarps are undetectable either by fieldwork photo interpretation or 5 m resolution topography analysis owing to their small heights 0 5 to 2 m and their location within forest areas in many cases these landforms are not evident in the field due to the presence of other minor irregularities in the slope and the lack of open views due to the forest 2d and 3d visualization of hillshade maps with different sun azimuths provided an overall picture of the scarp assemblage and permitted a more complete analysis of the geometry of the scarps with respect to the slope and the structural fabric the sharpness of some of the landforms suggests ongoing activity which should be explored in future detailed studies in order to assess potential hazards affecting the portaine ski resort our results reveal that close analysis of the 1 m lidar derived dem can significantly help to detect early stage slope deformations in high mountain regions and that expert judgment of the dem is essential when dealing with subtle landforms the incorporation of this approach in regional mapping represents a great advance in completing the catalogue of slope failures and will eventually contribute to a better understanding of the spatial factors controlling them

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

actively growing anticlines beneath catania from the distal motion of mount etna s decollement measured by sar interferometry and gps we used sar interferometry and gps to measure the rise of an anticline beneath the urban area of catania italy which originates from outward thrusting above the basal decollement of etna volcano the anticline grows at a rate of over 0 015 m a 1 of se thrusting and about 0 007 m a 1 of relative uplift by relating this growth to the simultaneous extension measured at the summit of the volcano we demonstrate the occurrence of active volcanic spreading this process may exert a control on eruptions earthquakes sector collapses and landslides

overlapping spreading centres new accretion geometry on the east pacific rise in a detailed seabeam investigation of the east pacific rise epr from 8 n to 18 n a new kind of volcano tectonic geometry associated with fast spreading centres has been discovered figs 1 2 at several locations along the rise axis the neovolcanic zone is discontinuous and is laterally offset a short distance 1 15 km in contrast to a classic ridge transform ridge plate boundary however the offset ridge terminations overlap each other by a distance approximately equal to or greater than the offset they curve sharply towards each other and often merge into one another along strike separating the overlapping spreading centres oscs is a closed contour depression up to several hundred metres deep which is sub parallel to the trend of the oscs the region between the oscs is a complex zone of both shear and rotational deformation with no obvious transform parallel structures based on wax model studies of spreading centres we suggest here that transform faults fail to develop at fast spreading centres where the lateral offsets are small 15 km because the lithosphere is too thin and weak to maintain a classic rigid plate spreading centre transform fault pattern the osc geometry is unstable and evolves rapidly one of the two oscs prevails while the other is abandoned a significant area of sea floor created at fast spreading rates may bear the imprint of this newly observed process

can flexural slip faults related to evaporite dissolution generate hazardous earthquakes the case of the grand hogback monocline of west central colorado a paleoseismological investigation of flexural slip faults related to interstratal evaporite dissolution suggests that such gravitational structures might have the potential to generate earthquakes with damaging magnitude the carbondale collapse center in the southern rocky mountains of colorado is a morpho structural depression of 1200 km 2 where miocene volcanic rocks are downdropped as much as 1200 m due to interstratal dissolution of halite bearing evaporites on the western margin of the collapse center the debuttressing effect related to active evaporite dissolution drives unfolding of the steeply dipping late laramide grand hogback monocline accompanied by displacement on bedding parallel faults these flexural slip faults rupture unconformable miocene basalts and quaternary mantled pediments generating conspicuous half graben depressions bounded by antislope fault scarps parallel to the underlying strata of the monocline two trenches dug across flexural slip fault scarps developed in each stratigraphic marker basalt cap mantled pediment revealed unexpected evidence of multiple late quaternary faulting events e g faulted colluvial wedge sharp unconformities with displacement per event values of 1 m three faulting events were inferred from the trench dug in the pediment w around 6

comparison of gpr 2d resistivity and traditional techniques for the subsurface exploration of the oschingen landslide swabian alb germany abstract numerous rotational and translational slides of different sizes cause considerable economic damage in the swabian alb sw germany and are a challenge for risk assessment the oschingen landslide is a typical example for landslides occurring along the escarpment lithology consists of jurassic sedimentary rocks involving clays overlain by marls and limestones a combination of traditional methods drilling mapping inclinometers and geophysical techniques 2d resistivity ert ground penetrating radar gpr was applied to gain knowledge about the thickness and internal structure of the landslide the drillings and penetration tests provided point information on landslide extent structure and material involved in general all inclinometers showed very little movement if at all the gpr results were affected by strong signal attenuation and by overhead reflections from the nearby woods despite these general obstacles for the application of gpr on landslides near surface sediment structures were detected in the 2d resistivity sections higher resistive limestone blocks reaching 10 15 m in thickness could be clearly distinguished from the underlying bedrock the detailed two dimensional data of the electrical resistivity tomography ert along with the rather high survey speed turned out to be the best choice to gain detailed spatial information on thickness and extent of the slope movement the measured profiles coincide with the gpr data and correspond to borehole data surprisingly all results from the applied methods clearly detected the absence of large landslide blocks in the north west of the study area this finding could not be concluded from local geomorphology of this area regarding the current landslide displacement derived from the inclinometer measurements the large landslide blocks seem to be dormant during the measured period

zonation of the landslide hazards in the forereservoir region of the three gorges project on the yangtze river on the basis of the investigation and statistic analysis of the landslide hazards in the forereservoir region of the three gorges project on the yangtze river the major factors that are found to have affected the slope stabilities are outlined and a zonation of landslide hazards of the region is made using an integrated information model it is divided into destructive disastrous slightly disastrous likely disastrous and essentially non disastrous areas the first two cover an area of less than 5 of the total region and are at a distance of more than 20 km from the three gorges dam and so a landslide over there will impose no direct impact to the tgp but may effect to some degree the navigation of the yangtze river and nearby highway transportation reservoir slopes and building of cities and towns