a self consistent model of melting magma migration and buoyancy driven circulation beneath mid ocean ridges numerical modeling and analysis are used to investigate the processes leading to the eruption of mantle derived magma at mid ocean ridges our model includes the following effects melting due to decompression magma migration by percolation and circulation of the mantle driven by both the oceanic plates and the distribution of buoyancy beneath the ridge the distribution of buoyancy is due to both the low density of the liquid and the difference in the density of the residual solids relative to unmelted mantle material the calculation of densities is based on a simple petrological model in which garnet spinel lherzolite melts to form a basaltic liquid and a harzburgite residue we find that the system spontaneously evolves to a state in which a rapid upwelling beneath the ridge axis faster than the plate velocity is confined laterally by stably stratified residual material beneath the newly formed plates this effect is exaggerated if a modest decrease in the shear viscosity of the solid upon melting is included our results provide a simple explanation for the narrowness of the zone of crustal formation at mid ocean ridges the model also predicts a transition from steady state to episodic crustal formation as the spreading velocity is reduced perhaps giving rise to along axis variations in the character of seafloor spreading the narrow rapid upwelling gives rise to substantial porosities at depths that are a large fraction of the depth to the solidus this may allow the liquid at depth to segregate into macroscopic channels which would account for the consensus from experimental petrology that the liquids parental to morb are derived from well below the base of the crust

deep seated gravitational slope deformations related landslides and tectonics abstract deep seated gravitational slope deformations and their relationships with tectonic deformation of rocks is considered to examine the viewpoint of tectonics as a causative factor in slope deformation first a distinction is made between the different types of deep seated gravitational slope deformation then the geomorphological and structural effects of the different macrostructural deformations induced by tectonics on the scale of the whole deforming ridge is briefly discussed finally some case studies that represent either verified or possible cases of gravity deformation in response to tectonic activity are used as illustration

onset and timing of deep seated gravitational slope deformations in the eastern alps italy abstract a previously unrecognised complex of deep seated gravitational slope deformations dsgsd extends 20 km along upper venosta valley in the eastern alps italy mt watles exhibits spectacular features indicative of dsgsds including double ridges trenches and counterscarps the slope deformation occurs along a nappe boundary now corresponding to the schlinig normal fault is also conditioned by recent faults marked by shallow earthquakes and shows glacial paraglacial controls on slope evolution the mt watles dsgsd is a complex deep seated compound slide along a basal shear zone involving the schlinig fault gravitational reactivation of ne trending fractures formed gravitational scarps counterscarps and half grabens in the upper slope whereas the lower part of the slope partially collapsed although our work indicates the importance of the schlinig fault and recent fracturing on slope failure the trigger seems to be postglacial debuttressing of the valley walls radiocarbon dating of peat deposits within one of the major counterscarps indicates that slope deformation started during the lateglacial period and continued during the holocene in several slope sectors

tectonic predesign of mass movements with examples from the chinese himalaya abstract the genesis of landslides has traditionally been ascribed essentially to exogenic nontectonic causes thus it has generally been assumed that progressive erosion oversteepens slopes until they become unstable and collapse by forming slides the specific triggers in each case would be exogenic influences such as for instance an extreme weather period this paper shows that in practically all cases of mass movements endogenic processes are also of fundamental importance in the first place a landscape responds as a complex open system existing in a quasi stationary state at the edge of chaos in which an endogenic input and exogenic outflow of mass and energy occur this quasi stationary state can become unstable resulting in landslides in the second place a direct predesign is present because of endogenic causes viz by a former or the present geotectonic stress field thus some common notable contentions regarding the origin of landslides are shown to be false a better understanding of the mechanisms for landslide genesis is illuminated using examples from the chinese mountain ranges at the east end of the himalayas in these particular cases the orientations of mass movements are directly controlled predesigned by the present day local tectonic stress

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

gravitationally induced caves and other discontinuities detected by 2d electrical resistivity tomography case studies from the polish flysch carpathians abstract widened discontinuities among them crevice type caves are characteristic phenomena of landslides in anisotropic rock massifs forming the flysch carpathians we tested the reliability of 2d electrical resistivity tomography ert in the detection of well mapped cave passages and then tried to explore new subsurface cavities in three sites of crevice type caves in the polish flysch carpathians the jaskinia miecharska jaskinia malinowska and jaskinia diabla dziura caves each comprising a different stage of mass movement development and thus being a representative case study the total of 14 ert profiles was selected while each of them was measured by several electrode arrays dipole dipole wenner and or wenner schlumberger our results show that the selection of an appropriate electrode array and spacing are crucial for the detection of subsurface cavities measurement using the dipole dipole electrode array gave best results in the detection of known structures and its interpretation seems to be most reliable in the extrapolation of non investigated areas the application of ert shows abundant occurrence of air filled voids in gravitationally deformed flysch massifs and in several places its results enable comparison with open spaces detected by speleological exploration ert enables us to identify fractures in deformed slopes before the proper failure of these slopes affected by a landslide as well as in landslides themselves fissure zones connected with trenches less dense segments of colluvial ramparts and some lithological tectonical or gravitationally induced elements of slope structures the reliability of ert detection of potential caves was verified by speleological exploration of a newly discovered cave at the jaskinia miecharska site following the ert campaign

neogene patterns of relative plate motion for africa europe some implications for recent central mediterranean tectonics a detailed relative motion picture for the neogene africa europe plate kinematics is presented the kinematic reconstruction was carried out using the finite difference solution between the rotation parameters determined for anomalies 7 to 2 in the africa north america europe plate motion circuit the analysis shows a motion of africa with respect to europe which is nne directed during late oligocene to burdigalian times becoming nnw trending from the langhian to the early tortonian from upper tortonian times onward the motion changes to a clear north west directed convergence major late neogene tectonic features of the central mediterranean region can to a large extent be explained within the context of the reconstructed major plate motions late tortonian to recent africa europe slip vectors are compatible with a variety of geological phenomenoa such as north west directed subduction beneath calabria south east translation of calabria and extension in the tyrrhenian sea north west trending slip vectors from thrust earthquakes between gibraltar and sicily and dextral strike slip across the north african margin

modeling the stone column behavior in soft ground with special emphasis on lateral deformation abstractamong various ground improvement techniques soft soil reinforcement by stone columns is one of the most common and convenient methods with numerous benefits including increased bearing cap

down slope variation in geotechnical parameters and pore fluid control on a large scale alpine landslide abstract a geotechnical investigation has been carried out on a large volume landslide in the stambach valley on the slopes above the town of bad goisern austria undrained loading has been considered as a means of triggering a large volume debris flow the initiation of this landslide has been linked with the collapse of rock pillars from the rock face of zwerchwand onto the head of the flow the concept of pore tensions resulting from stress relief has been used to account for the time delays of up to 10 months between the loading and the reactivation of the debris flow

mitigation of liquefaction and associated ground deformations by stone columns soil liquefaction and associated ground failures have been a major source of damage during the past earthquakes the risk of liquefaction and associated ground deformation can be reduced by various ground improvement methods including the stone column gravel drain technique this paper presents the current state of the stone column technologies as a liquefaction countermeasure a comprehensive review is provided aiming to a identify key considerations for the general use of stone columns as a liquefaction countermeasure b provide insights for design and construction c compile the latest research developments and d identify sources of useful information case histories of field applications and observed field performance are cited to portray different stone column applications and observed effectiveness the paper identifies areas where more research is needed and includes recommendations for future research and development

crevice type caves as initial forms of rock landslide development in the flysch carpathians crevice type caves formed along joints are very common in the polish flysch carpathians more than 600 have been recorded the caves represent accessible parts of the widened cracks which are basic initial forms of development of deep seated rock landslides structural features of four selected caves situated in different parts of the carpathians were studied in order to determine relations between joint systems and landslide formation the studies prove that the main rock scarps often represent effects of earlier propagation of the cracks cutting surfaces due to loading and unloading shearing stress the cracks are structural forms developed along joints or faults the cutting surfaces represented by cracks caves develop a long time before the main gravitational mass movements whereas the sliding surfaces shearing zones are formed or significantly modified ad hoc during the gravitational transport of rock masses occurrence of the deep initial cracks causes modification of shape of the sliding surfaces which are noncircular the mountain slopes cut by many cracks are permanently developed thus the periodic increase of activity of external factors floods downpours earthquakes etc leads to common formation of the landslides earlier prepared by crack development this model of slope evolution enables us to interpret the occurrence of the landslide phases in the holocene during which increasing of frequency of the landslides is observed

residual mechanisms and kinematics of the relict lemeglio coastal landslide liguria northwestern italy abstract the lemeglio landslide is a deep seated coastal landslide of the liguria region northeastern italy involving heterogeneous rock masses formed by miocene turbidide series whose prevalent lithology varies from sandstones to mudrocks it has been recognized since the end of the nineteenth century and characterized by a relict state of activity besides the general state of slope stability given by the current morpho climatic conditions different from those that determined its original paroxysmal evolution a residual slow kinematics of the accumulation zone still exists posing a threat to buildings and infrastructures located across the landslide foot consequently the lemeglio landslide represents a relevant case of study for advancing knowledge on residual kinematics mechanisms and hazard inherited by a relict slope mass movement phenomenon the study is based on results of several drilling campaigns and geotechnical investigations carried out mainly by the regione liguria in the unstable landslide accumulation zone moreover in this area ground deformations were assessed by inclinometer measurements and adinsar data covering two partially overlapping time spans from june 2009 to july 2011 and from january 2004 to june 2014 respectively by these data joined with field geological and geomorphological surveys an integrated and consistent landslide model was reconstructed which was used for limit equilibrium lem and finite elements modelling fem analyses among principal outcomes is the recognition by field observations stratigraphic and inclinometer data as well as slope stability modelling of a basal sheared and softened band made chiefly of remoulded mudrocks which constrains the current landslide failure surface such basal band can be considered an inherited landslide structure formed during the original paroxysmal stage of the lemeglio landslide which controls the current residual kinematics of the landslide deposits throughout the foot depending also on the coastal marine erosion acting along the landslide toe

buoyancy effects on mantle flow under mid ocean ridges results of a series of two dimensional numerical experiments of mantle flow melting and melt migration under a spreading center are reported the model predicts the distribution of melt in the subridge mantle the width over which most melt is delivered to the crust and the thickness of crust the sources of buoyancy considered are thermal expansion compositional variation caused by melt extraction and the phase change of solid to melt we infer that the steady state average viscosity of the mantle below a ridge cannot be much less than about 1019 pa s for a lower average viscosity thermal convection causes rapid cooling of a large region under a ridge raising the viscosity results imply that transient increases in mantle temperature should lead to larger increases in the oceanic crustal thickness for slow spreading ridges than for fast spreading ridges we assume that the viscosity is proportional to exp 0 where is melt fraction we parameterize the permeability in terms of the reference velocity for percolation of the melt vr where the relative velocity of melt to solid is vr analytic approximations are used to extrapolate the model results to large values of permeability and small values of 0 if vr is less than 1 m yr then more melt would be retained in the subridge mantle than is estimated from analysis of topography and gravity data at fast spreading centers for vr greater than about 100 m yr so little melt would be retained in the mantle that it is difficult to explain the gravity data and the low shear wave velocity structure close to the east pacific rise estimated from seismic surface waves buoyancy effects can lead to a region of mantle upwelling and melting that is as narrow as the observed zone of oceanic crustal accretion for most melt to be added to the crust within a few kilometers of a fast spreading center requires that 0 be less than 0 015 if vr equals 1 m yr and less than 0 003 if vr is 100 m yr

structural constraints on deep seated slope deformation kinematics abstract a significant sackung type deep seated slope gravitational deformation dsgsd was recognised for the first time by the authors in the middle part of valfurva east of bormio rhaetian alps italy the reconstruction of its kinematics age and state of activity is presented through a detailed description of its morphological geomechanical and structural features an integrated multi disciplinary approach was performed to achieve a clear comprehension of the phenomenon field surveys and aero photo interpretation were carried out in order to clarify the structural geological and geomorphological setting in which the dsgsd developed a kinematic conceptual model of the slope deformation was developed through the analysis of morpho structures of their significance and relationships with lithological markers and quaternary deposits after a geomechanical characterisation of the rock mass involved in the slope deformation numerical modelling was performed to verify the hypotheses made on kinematics and driving factors of the phenomenon the sackung affects pre permian metapelites metabasites and marbles belonging to the upper austroalpine basement of the campo nappe as well as late pleistocene and holocene glacial and rock glacier deposits the deformation started after the late wurmian age 15 000 11 000 years b p and continued until few centuries ago not excluding a present day low rate activity deformation consists in a large oblique sagging along a deep confined sliding surface associated with gravitational reactivation of pre existing late alpine and recent tectonic brittle structures leading to the formation of n s and wnw ese trending gravitational morpho structures the evolution of the wnw ese trending system resulting in asymmetric trenches led to progressive failure of the lower part of the slope during the last 10 000 years as testified by large paleo landslide accumulations and it is still in progress numerical modelling indicates post glacial unloading as the main triggering factor of the slope deformation the importance of this deep seated slope deformation is enhanced by the occurrence of the 30 mm 3 active ruinon landslide in the lower part of the slope such landslide is subjected to rapid evolution and threatens the valley floor establishing an important risk factor connected to human lives and socio economic activities

a tectonic model for ridge transform ridge plate boundaries implications for the structure of oceanic lithosphere abstract the first order geologic and morphologic relationships at along and proximal to ridge transform ridge plate boundaries are used to construct an empirical and speculative tectonic model the distinctive but variable morphotectonic fabric and crustal structure of the transform domain are the product of a tectonic continuum that ranges from very slow rates of strain associated with very thick edges of lithosphere slowly slipping ridge transfrom ridge plate boundaries to extremely high rates of strain associated with very thin edges of lithosphere fast slipping ridge transform ridge plate boundaries the geometry of a ridge transform intersection necessitates the juxtaposition of a relatively cold thick edge of lithosphere against the truncated end of an accreting plate boundary the cold face of lithosphere cools the adjacent wedge of asthenosphere rising beneath the axis of accretion and restricts the amount of partial melting thus attenuating the volume of basaltic melt segregated from the asthenosphere per unit time the shallow level manifestation of this cold edge effect is a thinner oceanic crust at depth the evolving lithosphere thickens rapidly as the cold edge is approached creating changes in the properties of the young lithosphere and forming a weld of upper mantle material against the cold edge of truncating lithosphere the ridge transform weld of upper mantle material creates a shear couple in the lithosphere underlying the intersection resulting in the progressive reorientation of the maximum tensile stress from normal to the ridge axis at some distance from the ridge transform intersection to an oblique angle near the boundary the brittle carapace of oceanic crust that overlies the mantle weld will deform accordingly with the development of oblique dip slip faults the model predicts that the geologic expressions of this cold boundary effect will become more dramatic with increasing thickness of the truncating edge at very slow rates of accretion 100 km juxtapose thick 30 50 km edges of lithosphere against the accreting plate boundary all but nullifying the processes that lead to the emplacement of normal oceanic lithosphere in this environment a relatively strong mantle weld will form at the ridge transform intersection and the thick edges of opposing lithosphere along the length of the transform will tend to confine the strike slip tectonism to a relatively narrow and temporally stable principal transform displacement zone in contrast at very fast rates of accretion large offset transforms 100 km place relatively thin edges of lithosphere

passive earth pressures theories and tests the magnitude of the passive earth pressure that resists the movement of a structure is controlled by the amount the structure moves and the direction in which it moves strength and stiffness of the soil that resists its movement friction or adhesion on the interface between the structure and soil and shape of the structure the log spiral theory corrected for 3d effects provides an accurate means of computing ultimate passive pressures a hyperbolic expression together with estimated values of soil modulus and ultimate resistance provides a means of estimating the relationship between structural movement and passive resistance it is essential that the soil strength and stiffness used in making these estimates should be appropriate for the soil and the drainage conditions involved the results of an undrained passive pressure load test in stiff sandy silt and a drained passive pressure load test in well graded gravel are compared with passive pressures computed using the methods discussed reasonable agreement between the calculated and measured values shows that the log spiral theory corrected for 3d effects and the hyperbolic load deflection relationship provide an adequate means of estimating passive resistance for a wide range of conditions

uranium lead isotopic ages of the samail ophiolite oman with applications to tethyan ocean ridge tectonics plagiogranites are a minor but widespread component of the samail ophiolite plutonic member they crystallized from the most fractionated melts generated by magmatic crystallization and differentiation of a steady state magma chamber beneath the tethyan spreading ocean ridge and their ages are thought to mark the time of ocean crust formation isotopic u pb ages of zircons from 13 plagiogranites collected along a 270 km segment of the samail ophiolite subparallel to the regional trend of the sheeted dike complex the former spreading ridge axis direction define a narrow time interval of 93 5 97 9 m y with a pronounced clustering about 95 m y the zircon ages of the plagiogranites agree remarkably well with the early cenomanian to early turonian biostratigraphic ages of sediments that are intercalated within the ophiolite pillow lavas and that lie just above them tippit et al 1981 the agreement of radiometric and biostratigraphic ages provides strong support for the conclusion that the plagiogranite u pb ages closely date the time span of ocean crust formation no step changes in age patterns are observed along the ridge axis sheeted dike direction suggesting that there are no major internal offsets of the ophiolite by transform or other faults along most of the traverse one possible exception occurs at the southeastern end of the sampled interval ibra area where a 3 m y discontinuity might be caused by an unmapped fault assuming that the regional trend of the sheeted dikes n10 25 w marks the direction of the former spreading ridge axis the present array of sample localities spans a distance of 130 to 195 km normal to that axis i e in the spreading direction the data as a whole do not define a clear cut age trend normal to the spreading axis but by eliminating samples that may be aberrant due to faulting the data array suggests a pattern of increasing ages from east to west this would indicate that the samail ophiolite is derived from the western southwestern side of the tethyan spreading system a conclusion reached independently from geological evidence also the gentle age gradient in the spreading direction i e between 130 and 195 km of ocean crust were formed within an age span of no more than 2 m y suggests a very fast spreading rate this conclusion also is supported by independent geologic evidence

dynamical consequences of compositional and thermal density stratification beneath spreading centers extraction of partial melt to form oceanic crust reduces the density of upwelling mantle beneath spreading centers this compositional buoyancy can significantly affect both the rate of upwelling and the pattern of mantle flow the relative importance of buoyant upwelling and upwelling due to plate spreading depends on the mantle viscosity for a low enough mantle viscosity buoyant upwelling can significantly enhance the thickness of the crust relative to that which would be produced by plate spreading alone for a mantle viscosity of 1022 pa s upwelling due to plate spreading is dominant and crustal thickness is predicted to be a strong function of spreading rate however for a mantle viscosity of 1019 pa s buoyancy dominates mantle upwelling and the calculated crustal thickness like the oceanic crust is nearly independent of spreading rate thermal and compositional density variations result in opposing buoyancy forces that can cause time dependent upwelling for a mantle viscosity of 1020 pa s and a low 1 cm yr spreading rate this behavior takes the form of undamped crustal thickness oscillations with a single well defined period for even slightly lower mantle viscosity the frequency increases and crustal thickness oscillations become more complex with two or more frequencies present while numerical experiments have thus far been carried out only for viscosities significantly greater than that likely to characterize the mantle beneath spreading centers we speculate that these crustal thickness oscillations may explain important aspects of seafloor structure

structural control and types of movements of rock mass in anisotropic rocks case studies in the polish flysch carpathians abstract types of gravitational movements in the flysch carpathians are related to tectonic and lithologic anisotropy of rock massifs this article presents the main types of mass movements in the highly anisotropic flysch massifs lateral spreading and rock flow topple translational rotational and compound sliding and complex type of mass movements which are illustrated by chosen forms described using structural analysis joints faults and other structural planes orientation topple is the typical mass movement for double ridges and top trenches e g gaworzyna in the beskid s decki mts translational landslides with flat structural sliding surfaces typical for shallow forms can develop along bedding planes e g duszatyn western bieszczady mts as well as along joints opuszna gorce mts and fault planes rzeki gorce mts currently used classification of the structural landslides is applied only to translational landslides shearing zones of deep seated landslides are composed of structural sections of joints faults bedding planes and shearing elements consequently most of the carpathian landslides have developed as compound type with non circular sliding zones representing complex movements combined with various types of displacement rotation translation and or topple purely rotational movements with circular failure typical for isotropic material have developed in the flysch where thick bedded hard sandstones are underlain by plastic shales e g mt kostrza in the beskid wyspowy mts the influence of anisotropy of these rocks on sliding surface is significantly reduced and plastic type rocks stimulate rock flow development which is usually later transformed into complex landslides with predominant rotational movement e g rotational landslide with topple and flow elements on mt muronka in the beskid l ski mts compound landsliding on mt lubon wielki beskid wyspowy mts represents an antithetic rotational slide with topple and rotational type movements

rapid least squares inversion of apparent resistivity pseudosections by a quasi newton method1 a fast inversion technique for the interpretation of data from resistivity tomography surveys has been developed for operation on a microcomputer this technique is based on the smoothness constrained least squares method and it produces a two dimensional subsurface model from the apparent resistivity pseudosection in the first iteration a homogeneous earth model is used as the starting model for which the apparent resistivity partial derivative values can be calculated analytically for subsequent iterations a quasi newton method is used to estimate the partial derivatives which reduces the computer time and memory space required by about eight and twelve times respectively compared to the conventional least squares method tests with a variety of computer models and data from field surveys show that this technique is insensitive to random noise and converges rapidly this technique takes about one minute to invert a single data set on an 80486dx microcomputer

ridge forces absolute plate motions and the intraplate stress field torque poles are calculated for a variety of possible forces acting on the plates including ridge push slab pull and collisional resistance these torque poles are then compared to the directions of absolute plate motions there is a strong correlation between ridge torque poles and the azimuth of absolute plate motions for the north american south american pacific cocos and eurasian plates simple slab pull torques correlate well with absolute motion azimuths for the pacific nazca and cocos plates and moderately well with the absolute motion azimuth of the indoaustralian plate collisional resistance torque poles correlate with the absolute motion azimuth of the eurasian plate only the correlations are presented as further evidence that the absolute reference frame for plate motion is determined by the surface plates themselves torque poles for various forces are also compared with several long wavelength features of the global intraplate stress field that also tend to be aligned with absolute motion directions in general ridge torque directions agree well with the orientations of maximum horizontal stresses for stable north america western europe and south america and provide an alternative explanation for the alignment in terms of ridge push forces rather than basal drag collisional resistance forces can also explain the alignment of stresses in western europe for the indoaustralian plate the torque pole for collisional resistance forces is consistent with the general pattern of stresses in at least the western half of the plate but is not a good predictor of the entire data set for the plate other processes in addition to collisional resistance must be important for the indo australian plate ridge push forces may account for a significant portion of the long wavelength features of the intraplate stress field especially away from continental collisions such a conclusion is consistent with negative buoyancy of the slab being an important component of the driving mechanism as previously suggested slab forces may be largely balanced within the subducted slab itself and thus have limited effect on deformation of the surface plates

evidence from the oman ophiolite for active mantle upwelling beneath a fast spreading ridge it is commonly accepted that as oceanic lithosphere cools it slides away from the spreading centre under its own weight1 it has been suggested2 5 that even at the spreading axis this process controls the dynamics causing asthenospheric mantle material to rise passively before being dragged away from the ridge by the overlying lithosphere alternatively the upwelling of the asthenosphere at the ridge might be active caused by the buoyancy of partial melt6 10 or of the less dense peridotite left behind by such melting11 12 at slow spreading ridges bull s eye gravity anomalies13 14 have been interpreted as suggesting focused accre tion and hence active mantle diapirs at fast spreading ridges however these anomalies are weaker and less clearly three dimensional15 which may reflect passive mantle upwelling16 here we show that structural data from the oman ophiolite which is thought to have been created at a fast spreading ridge17 18 are consistent with active mantle upwelling beneath the ridge and not with models of passive flow the absence of well marked bull s eye anomalies at fast spreading ridges may be explained by their relatively constant crustal thickness and near isostatic equilibrium

high resolution seismic refraction method using surface and borehole data for site characterization of rocks abstract the authors have developed a new method for the analysis of seismic refraction data which can handle both surface and borehole data simultaneously the main features of the method we developed are as follows 1 the algorithm of analysis is based on the tomographic reconstruction technique and refraction data can be analyzed almost automatically after traveltime picking 2 the method is applicable to both layered velocity structures and those showing a velocity gradient with depth 3 in order to apply the seismic refraction technique to a site that has a more complex structure the method can use the data obtained from sources and receivers on the surface as well as those within boreholes simultaneously numerical and actual field examples have shown that the method can greatly improve the accuracy and the reliability of the seismic velocity models obtained by the seismic refraction method as compared to the conventional analysis methods it can also shorten the data processing time drastically and reduce the survey cost

stratigraphy and tectonics of an internal unit of the southern apennines implications for the geodynamic evolution of the peri tyrrhenian mountain belt the parasicilide succession is a key element of the southern apennine orogen being originally located in the distal portion of the apulian palaeomargin at the neotethys ocean continent transition the succession presently included in the upper nappe complex of the thrust belt has been described elsewhere as a broken formation however detailed investigations carried out in the sele valley point out that there the parasicilide unit is characterized by a coherent stratigraphy therefore in the study area these rocks form a coherent sheet of distal continental margin oceanic sedimentary cover material included within the peri tyrrhenian mountain belt stratigraphic and structural constraints obtained from both pre and synorogenic deposits the latter including both foredeep and thrust top basin sediments suggest that the pre orogenic part of the parasicilide succession subsided into the apennine foredeep in the first part of the burdigalian the studied rocks were then involved in thrusting prior to late burdigalian early langhian times

a two and three dimensional analysis of gravity anomalies associated with the east pacific rise at 9 n and 13 n we have used a unique data set collected during the 1985 east pacific rise multichannel seismic experiment to reevaluate the constraints that gravity data can place on the crustal structure of the east pacific rise epr the close spacing of track lines within the two main survey areas 8 45 n 9 55 n and 12 20 13 30 n allowed us to perform three dimensional analyses of high quality gravity data 1 mgal uncertainity obtained with the bell aerospace bgm 3 gravity meter our gravity modeling was enhanced by the availability of high resolution sea beam bathymetric data and by independent structural constraints provided by seismic reflection and refraction data to model the crustal and upper mantle density structure at the ridge axis we first calculated the gravity anomalies due to the density contrasts at the water crust and crust mantle boundaries and the changes in density caused by the cooling of the lithosphere with age and subtracted these predictable signals from the observed free air anomaly the residual anomalies were then used to place constraints on the magnitude and distribution of anomalous mass at the epr our results show that over 90 of the power in the observed free air anomaly can be modeled by these predictable components of the gravity signal the amplitude and wavelength of the small residual anomaly can be modeled by a broad region 20 km wide centered on the rise axis of slightly lower than normal crustal and or upper mantle densities 0 03 mg m 3 this region of anomalous mass and density variations in the underlying mantle provide the principle isostatic support for the axial topographic high the anomalies are consistent with but do not require the presence of a low density crustal magma chamber at the rise axis if a largely molten magma chamber exists then the gravity data require that it be a narrow volumetrieally small body there are first order differences in the distribution of anomalous mass between the two survey areas with the 9 n region generally being characterized by lower densities in the axial region along axis variations in anomalous mass within each of the survey areas correlate with first order changes in the depth and cross sectional shape of the epr axial high we attribute these differences in axial morphology and the amplitude of the associated gravity anomalies to along strike changes in the size of the crustal magma chamber the width of the surrounding zone of cooling crustal rocks and densities in the uppermost mantle beneath the rise axis

evidence from the oman ophiolite for sudden stress changes during melt injection at oceanic spreading centres the system of dikes in the uppermost mantle below oceanic spreading centres bears witness to the processes involved in the supply of melt to the ridge such systems cannot be studied on currently active ridges but can be seen in ophiolites in particular the oman ophiolite allows us to examine segments of a fast spreading ridge1 here we present a statistical analysis of the orientation of intrusions in the uppermost mantle section of the oman ophiolite spreading centres which points to the existence of two systems dikes whose azimuth is parallel to the sheeted dikes which we thus consider as related to the extensional lithospheric stress field and sills roughly parallel to the moho2 branching contemporaneous dikes and sills are frequently observed we suggest that these relations can be explained by repeated sudden changes of the dominant stress field from lithospheric to asthenospheric such changes could result from the episodic relaxation of lithospheric stress in response to tension fracturing of the lithospheric lid related to sudden melt surges this episodic behaviour is recorded in the sheeted dike complex with each dike each about one metre wide representing one of these fractures

gravity anomalies isostasy and mantle flow at the east pacific rise crest bathymetry and gravity data obtained during a detailed hydrosweep survey of the southern east pacific rise from 7 s to 9 s are used to investigate isostasy at the axis of a fast spreading mid ocean ridge in particular we examine the manner in which the bathymetric crestal high is supported and how this support varies along the axis within the 160 km long 7 12 s 8 38 s ridge segment the crestal high stands about 400 m above the adjacent ridge flanks and has a nearly constant minimum axial depth for a distance of 140 km the summit is broad and flat and an axial summit caldera is present for the entire length of the ridge segment however the width and cross sectional shape of the crestal high vary systematically along the axis it is broad with gentle slopes in the center of the segment but becomes progressively narrower and steeper toward the ends of the ridge segment the ridge crest is marked by a free air gravity anomaly high about 15 20 km wide with an amplitude of 10 15 mgal relative to the ridge flanks mantle bouguer anomalies vary systematically along the axis with minimum values found near the center of the segment the axial mantle bouguer anomalies thus do not reflect the axial depth but are correlated with changes in the cross sectional area of the crestal bathymetric high the effects of cooling and subsidence away from the axis were removed from the bathymetry and free air anomalies to isolate residual topographic and gravity anomalies associated with the ridge crest the residual crestal bathymetric high was modeled as a flexural feature resulting from the upward buoyant load of a region of low density material centered beneath the axis the lithosphere was treated as a broken plate either with a constant flexural rigidity or an effective elastic thickness te which grows at a rate proportional to the square root of distance from the axis the best fitting values of te for the constant rigidity case are in the range of 0 3 0 6 km for the growing plate model te increases at a rate of 0 2 0 3 km the gravity constrains the mass deficiency to extend to a depth of 20 30 km for both lithospheric models we interpret this low density material as a region of partial melt feeding magma to the ridge axis the best fitting density anomalies imply that a 4 9 melt fraction is present beneath the crestal high upwelling of melt to the axis is thus confined to a narrow zone within about 10 km of the axis the mass deficiency and thus the upwelling partial melt are not distributed evenly along the ridge axis but rather are concentrated in the central portion of the ridge segment it thus appears that differences between the along axis gravity and depth patterns observed at slow spreading and at fast spreading ridges are not the result of a change from three dimensional focused upwelling at slow spreading ridges to two dimensional sheetlike upwelling at fast spreading ridges rather the differences in axial gravity and depth between fast and slow spreading ridges reflect differences in the efficiency of the shallow along axis magma distribution

kinematics and geological constraints of the slow moving pisciotta rock slide southern italy abstract the pisciotta landslide is a slow moving deep seated rock slide in the campania region of southern italy which has damaged a provincial road several times in the last decades and currently poses a hazard to the national railway that intersects the toe of the landslide the landslide involves an oligocene turbidite series which is composed of intercalated calcarenites marls and mudrocks the principal objectives of this study were to investigate the morphological evolution of the unstable slope quantitatively analyse ground deformations and construct an engineering geological model that is consistent with the spatial features of the landslide the long term evolution of the unstable slope was assessed through the examination of available aerial photos from 1943 to 2006 kinematic analyses of the ground deformations were conducted based on observed progressive displacement of the road as evident from the topographic maps and orthophotos 1955 2006 and the bi weekly displacement survey of 50 targets distributed across the landslide area september 2006 march 2009 the engineering geological model of the landslide was reconstructed from the stratigraphic data obtained from the study of borehole data and monitoring of inclinometers as well as from geological structural and geophysical surveys the analysis of the aerial photographs revealed an early stage of deformation in 1943 which has been gradually widening since then in addition to the main scarp and the landslide flanks other significant landslide structures such as the longitudinal and transverse cracks as well as the positive or negative morphologies were monitored and mapped in the subsequent years these studies indicated a progressive erosion of the upper part of the slope and a bulging of the foot long term kinematic analysis based on the progressive displacements of the road allowed the measurement of the ground deformations from 1955 to 2009 which revealed a cumulative horizontal displacement of up to 53 m and an average velocity of 0 98 m year 1 which has increased in the recent decades in addition the recent monitoring of the ground deformations demonstrated a continuous activity with an approximately constant rate of displacement and a composite kinematic history of the landslide body through differential displacements and associated velocities the engineering geological model of the landslide was found to be controlled by specific stratigraphic and structural constraints the landslide involves a stratigraphic interval of the saraceno formation nord calabrese tectonic unit with a largely marly argillaceous composition whose structural setting displays complex folding at the mesoscale and faulting with an approximately monocline attitude of bedding and a downslope dip direction at the macroscale the left flank of the landslide rests on a normal fault

evidence from gravity data for focused magmatic accretion along the mid atlantic ridge gravity data from the mid atlantic ridge between latitudes 27 50 n and 30 40 n show that the accretion of magma at the ridge is focused at discrete centres along the spreading axis large positive gravity anomalies equivalent to reductions of almost 50 in crustal thickness are observed over non transform discontinuities bounding spreading segments

the pressure distribution along stone columns in soft clay under consolidation and foundation loading the mechanism whereby foundation loading is transmitted through the column has received little attention from researchers this paper reports on some interesting findings obtained from a laboratory based model study in respect of this issue the model tests were carried out on samples of soft clay 300 mm in diameter and 400 mm high the samples were reinforced with fully penetrating stone columns of three different diameters made of crushed basalt four pressure cells were located along each stone column the 60 mm diameter footing used in the model was supported on a clay bed reinforced with a stone column and subjected to foundation loading under drained conditions the results show that the dissipation of excess pore water pressure developed during the initial application of total stresses when the foundation was subjected to no loading generated considerable stresses within the column and that this was directly attributable to the development of negative skin friction the pressure distributions

application of geophysical methods for the investigation of the large gravitational mass movement of sechilienne france several geophysical techniques electromagnetic profiling electrical tomography seismic refraction tomogra phy and spontaneous potential and seismic noise measurement were applied in the investigation of the large gravita tional mass movement of sechilienne france the aim of this study was to test the ability of these methods to characterize and delineate the rock mass affected by this complex movement in mica schists whose lateral and vertical limits are still uncertain a major observation of this study is that all the zones strongly deformed previously and at present by the movement are characterized by high electrical resistivity values 3 k m in contrast to the undis turbed mass which exhibits resistivity values between a few hundred and 1 k m as shown by the surface observa tions and the seismic results this resistivity increase is due to a high degree of fracturing associated with the creation of air filled voids inside the mass other geophysical techniques were tested along a horizontal transect through the movement and an outstanding coherency appeared between the geophysical anomalies and the displacement rate curve these preliminary results illustrate the benefits of combined geophysical techniques for characterizing the rock mass in volved in the movement results also suggest that monitoring the evolution of the rock mass movement with time lapse geophysical surveys could be beneficial resume plusieurs techniques geophysiques profil electromagnetique tomographie electrique tomographie sismique et potentiel spontane et bruit de fond sismique ont ete appliquees pour la reconnaissance du grand mouvement de ter rain de sechilienne france situe dans des micaschistes l objectif de cette etude etait de tester ces methodes geophy siques afin de caracteriser et de delimiter la masse de roche affectee par ce mouvement complexe dont la limite laterale reste incertaine l etude a montre que toutes les zones tres deformees encore actuellement et dans le passe par le mouvement sont caracterisees par de fortes valeurs de resistivite electrique superieur ea3k m tandis que dans la zone non perturbee les valeurs de resistivite sont de quelques centaines de m a1k m comme le montrent les observations de surface et les profils de tomographie sismique cette augmentation de resistivite est due a une frac turation importante associee a la creation de vides remplis d air au sein du massif les techniques electromagnetiques ps et de mesure de bruit ont ete testees le long d un profil transversal recoupant le mouvement une correlation remar quable est obtenue entre les anomalies geophysiques et le taux de deplacement ces resultats preliminaires soulignent l interet de combiner les methodes geophysiques pour caracteriser la masse de roche impliquee dans le mouvement et pour determiner l evolution du mouvement par un suivi temporel des parametres geophysiques mots cles mouvement gravitaire methodes geophysiques sechilienne meric et al 1115

assessing the coefficient of the earth pressure at rest from shear wave velocity and electrical resistivity measurements abstract determination of earth pressure coefficient k 0 in natural soil deposits is a significantly important issue in geotechnical engineering this paper evaluates the feasibility of predicting k 0 values from measurements of vertical and horizontal shear wave velocities v s vh v s hh and v s hv and vertical and horizontal electrical resistivities s v s h a series of seismic piezocone tests scptu improved crosshole ch tests and soil resistivity tests using a modified laboratory apparatus were carried out at two research sites in jiangsu province of china and results were used to develop two existing k 0 shear wave velocity correlations for prediction of k 0 the seismic and electrical resistivity test results showed that both the shear wave velocity ratios v s hh v s hv or v s hv v s vh and the horizontal to vertical electrical resistivity ratio s h s v may provide a good indicator of the inherent soil anisotropy at these sites the existing v s k 0 prediction framework largely requires determining c s hv c s hh ratio and a simple procedure for evaluating this ratio based on the measured horizontal and vertical electrical resistivities the k 0 values predicted by shear wave velocity at both sites are also compared with values determined by jaky s formula and mayne kulhwy s formula in normally consolidated nc soils the k 0 values predicted from these methods showed good agreement however for over consolidated oc soils at shallow depths certain variations between different methods are noted further investigations of the effects of overconsolidation ratio on k 0 predictions will lead to the correction factors for better prediction of k 0 for oc soils this paper has confirmed that reasonable predictions of k 0 for natural soil deposits can be made using the proposed methodology

evolution stages of large deep seated landslides at the front of a subalpine meridional chain maritime alps france abstract studying long term evolution of gravitational slope evolution is a key to understanding deep seated landslide processes this paper deals with three large deep seated landslides dsls at a front of a subalpine meridional chain on the la marbriere slope near the town of grasse alpes maritimes france the geological framework controlling the stability and morphology of the dsls is associated with thick and tamped triassic layers of mudstone with gypsum overlain by highly faulted jurassic limestone gravitational deformation affects the entire slope involving a movement of about 1 1 10 8 m 3 of rock material it creates large disturbances in landscape morphology such as scarps counter slope scarps trenches and other typical gravitational morpho structures geomorphological mapping coupled with deep electrical resistivity tomography ert reveals a strong correlation between these morpho structures and inherited brittle tectonic features this observation relies on spatial and geometrical relations on the surface and at the depth of more than 150 m checked by ert between the most persistent fault and the gravitational morpho structures the specific distribution of the morpho structures on the basis of their morphological typologies and variations in the stage of evolution of three dsls provides an interpretation of their kinematics during the last 400 ka it appears that soft substratums combined with inherited persistent anisotropies are key factors in the development of the dsls indeed outflow of mudstone due to the lithostatic pressure imposed by individual limestone compartments has led to general slope subsidence then a progressive toppling of a rock mass may have led to the catastrophic rock collapse along bedding planes the evolution of the dsls can be divided into three distinct stages represented by three zones a young collapse stage zone 1 a pre collapse stage zone 2 and an old mature stage 400 ka zone 3 as the dsls occur on the same slope and in the same geological context this area offers interesting perspectives for understanding factors controlling the long term gravitational evolution of slopes

consolidation theory for a composite foundation considering radial and vertical flows within the column and the variation of soil permeability within the disturbed soil zone to remedy the contradiction between the equal strain assumption and the flow continuity assumption at a soil column interface the traditional flow continuity assumption was abandoned and the radial and vertical flows within a stone column were incorporated to consider the column consolidation and deformation in a coupled fashion moreover two possible variation patterns of the horizontal permeability coefficient of soil within the disturbed soil zone were included to reflect the detrimental influence on the surrounding soil due to column construction in addition a linearly changed total vertical stress along the column depth was assumed to achieve a more realistic stress distribution in practice by considering the above mentioned characteristics the governing equations for this type of consolidation problem were developed the solutions for the governing equations were subsequently derived by using a new initial condition obtained from the equilibrium condition and equal strain assumption on the

spreading rate dependence of three dimensional structure in oceanic spreading centres segmentation by transform faults and other types of along axis discontinuity1 is a well described but poorly explained characteristic of oceanic spreading centres here we use numerical experiments to explore the dynamics of mantle flow and melting beneath a mid ocean ridge buoyant upwelling driven by compositional density variations resulting from the extraction of the melt that forms the ocean crust exhibits a spreading rate dependent transition between two dimensional and three dimensional upwelling structures for low spreading rates and mantle viscosities an initial two dimensional structure transforms into a three dimensional one at high spreading rates an initially two dimensional structure remains two dimensional these results suggest that the origin of spreading centre segmentation may be different at fast and slow spreading rates

mantle flow at oceanic spreading centers models derived from ophiolites abstract the internal structures of eleven ophiolite complexes have been structurally investigated the attitude of the foliation and the lineation in the peridotites is related to asthenospheric flow in the uppermost mantle at an oceanic spreading center from the orientation of these structures with respect to the paleohorizontal plane two oceanic situations are distinguished the horizontally spreading asthenosphere illustrated by the table mountain massif newfoundland is characterized by 1 a homogeneous regular and sub horizontal plastic flow pattern over large distances 2 b flat paleo mono and absence of large scale folding 3 c rare economical chromite deposits and depleted mantle the diapirically spreading asthenosphere illustrated by the acoje type philippines displays 1 a inhomogeneous and sub vertical plastic flow pattern 2 b deformed paleo moho and large scale folds 3 c important economical chromite deposits and less depleted mantle presumably due to secondary magmatic impregnation this leads to vogt s model of asthenospheric flow beneath an oceanic ridge the direction of which being equated with the dike swarm in this model the horizontally spreading asthenosphere is derived from the diapirically spreading one in the following way the vertical mantle flow at the diapir center diverges horizontally in every direction including that parallel to the ridge at about 50 km from the diapir center the mantle flow becomes progressively perpendicular to the ridge due to the damming effect of transform faults an important economical consequence of this model is that large chromite deposits are expected preferentially in the diapiric type of ophiolite because chromite is preferentially precipitated at the diapir center from pristine magma