surface eddy momentum flux and velocity variances in the southern ocean from geosat altimetry abstract satellite altimetry has previously been used to map the magnitude of the surface eddy variability of the global oceans but the direction of the time variable velocities have been more difficult to determine here a technique is presented for resolving both magnitude and direction of residual surface geostrophic velocities at geosat altimeter crossover points providing a two year time series with a temporal resolution of 17 days and horizontal resolution of around 100 km the time series of residual velocity components are then used to determine surface eddy statistics in the southern ocean and to investigate the role of transient eddies in the southern ocean momentum balance the surface eddy statistics from geosat crossover points show a complex spatial distribution in the surface reynolds stresses u 2 v 2 u v in contrast to the assumptions of isotropic variability in previous analyses of altimeter data velocity variance ellipses are found to be distinctly anisotropic in many regions

estimation of quality factors from cmp records estimates of the quality q factor are commonly obtained from vertical seismic data or stacked surface seismic data this paper describes a method that allows q factor to be estimated directly from common midpoint cmp gathers absorption of the wavefield is dependent on three parameters frequency traveltime in the medium and medium q factor assuming that the amplitude spectrum of the seismic source signature may be modeled by that of a ricker wavelet we derive an analytical relation between q factor and seismic data peak frequency variation both along offset and vertical time direction the q factor is estimated from cmp gathers using a layer stripping approach

geophysical geological transect and tectonic evolution of the swiss italian alps a complete alpine cross section integrates numerous seismic reflection and refraction profiles across and along strike with published and new field data the deepest parts of the profile are constrained by geophysical data only while structural features at intermediate levels are largely depicted according to the results of three dimensional models making use of seismic and field geological data the geometry of the highest structural levels is constrained by classical along strike projections of field data parallel to the pronounced easterly axial dip of all tectonic units because the transect is placed close to the western erosional margin of the austroalpine nappes of the eastern alps it contains all the major tectonic units of the alps a model for the tectonic evolution along the transect is proposed in the form of scaled and area balanced profile sketches shortening within the austroalpine nappes is testimony of a separate cretaceous age orogenic event west directed thrusting in these units is related to westward propagation of a thrust wedge resulting from continental collision along the meliata hallstatt ocean further to the east considerable amounts of oceanic and continental crustal material were subducted during tertiary orogeny which involved some 500 km of n s convergence between europe and apulia consequently only a very small percentage of this crustal material is preserved within the nappes depicted in the transect postcollisional shortening is characterized by the simultaneous activity of gently dipping north directed detachments and steeply inclined south directed detachments both detachments nucleating at the interface between lower and upper crust large scale wedging of the adriatic or apulian lower crust into a gap opening between the subduced european lower crust and the pile of thin upper crustal flakes alpine nappes indicates a relatively strong lower crust and detachment between upper and lower crust

inverse q filter for seismic resolution enhancement a principal limitation on seismic resolution is the earth attenuation or q effect including the energy dissipation of high frequency wave components and the velocity dispersion that distorts seismic wavelets an inverse q filtering procedure attempts to remove the q effect to produce high resolution seismic data but some existing methods either reduce the s n ratio which limits spatial resolution or generate an illusory high resolution wavelet that contains no more subsurface information than the original low resolution data in this paper seismic inverse q filtering is implemented in a stabilized manner to produce high quality data in terms of resolution and s n ratio stabilization is applied to only the amplitude compensation operator of a full inverse q filter because its phase operator is unconditionally stable but the scheme neither amplifies nor suppresses high frequencies at late times where the data contain mostly ambient noise the latter property makes the process invertible differ

study on the automatic recognition of oceanic eddies in satellite images by ellipse center detection the iberian coast case ellipse detection has been presented several times in scientific literature as a potential method for finding eddies in satellite images because eddies may be roughly approximated by ellipses in this paper therefore we describe a new eddy detector based on ellipse detection the detector is capable of finding several eddies per satellite image an ability not demonstrated for previously reported eddy detectors based on ellipse detection in the morphology of binary images one important characteristic of this paper is the determination of the method s classification efficiency using a considerable number of eddies such a determination has been rarely performed in the scientific literature on eddy detection the developed detector finds ellipse centers using geometrical properties of ellipses to the best of the author s knowledge the proposed method has never been applied to eddy detection the low value of the maximum temperature gradient of the eddies off the iberian peninsula 0 52degc pixel complicates the application of the detection method because it raises difficulties in outlining the eddies and induces large amounts of noise in the binary images from which the eddies are detected the values of each parameter in the developed system were equal for the images analyzed which suggests that the application of the proposed system to large numbers of images is simple the author did not find any method applicable to the present case in the scientific literature whose classification efficiencies assessed on complete images or a considerable number of eddies were better than those reported here

role of the backstop to cover thickness ratio on vergence partitioning in experimental thrust wedges the ratio between the thickness of the sedimentary sequences offscraped from the subducting plate hc and the average thickness of the backstop hb is expected to significantly influence vergence partitioning in thrust wedges a series of simple sandbox experiments was performed to study the role of the hc hb ratio in model thrust wedges the results obtained show that thrust wedges with hc hb values lower than 1 are essentially pro ward verging with minor retro ward faulting hc hb values greater than 1 imply an increase of vergence partitioning when a threshold value is exceeded fully partitioned doubly vergent thrust wedges develop comparison with natural submarine thrust wedges suggests that these experimental results may provide useful insights on the evolution of structural architecture at convergent margins

analogue modelling of reverse fault reactivation in strike slip and transpressive regimes application to the giudicarie fault system italian eastern alps abstract sandbox analogue models were used to study the reactivation of a reverse fault in strike slip and transpressive regimes for comparison with the evolution of the giudicarie fault system in the central eastern alps the giudicarie system is interpreted as resulting from late miocene sinistral transpressive reactivation of an older late oligocene reverse fault the old reverse fault was reproduced as a pre cut dilatant surface obtained by pulling a stiff metal wire through the model sand layer the position of the pre existing fault with respect to the base plate fault accommodating the strike slip and transpressive faulting phase controlled the extent and geometry of reactivation the clearest reactivation in a pure strike slip regime was achieved in experiments where the basal strike slip fault was immediately below the pre existing fault plane this strong reactivation involved lateral extrusion and lateral stepping of secondary faults from the basal fault to the pre existing reverse fault in the case of transpression the most spectacular reactivation was achieved for a convergence angle of 10 strongly asymmetric structures developed on either side of the pre cut dilatant zone the analogue experiments reproduced very closely the structural features of the giudicarie fault system supporting a model involving a twofold tectonic evolution for the giudicarie fault system with later reactivation in sinistral transpression of an older reverse fault

grustal shortening in the alpine orogen results from deep seismic reflection profiling in the eastern swiss alps line nfp 20 east the deep crustal seismic line nfp 20 east crosses almost the entire swiss alps despite the complex geometry of the well exposed nappe structure and the considerable axial plunge of some of the units the vibroseis survey yielded coherent reflections from several individually identifiable nappe contacts in the northern part of the survey the vibroseis data closely match the internal structure of the helvetic nappes and the underlying autochthonous parautochthonous mesozoic sediments on the northern flank of the aar massif an external basement uplift these mesozoic sediments seem to rise from a depth of approximately 7 8 km below sea level to the surface in a series of steps which is interpreted to represent crustal shortening achieved by a combination of folding and thrusting in the southern part of the survey it was possible to image a number of thin slivers of mesozoic carbonates pinched between slabs of penninic basement nappes as well as nappe contacts between lithologically contrasting units in addition it seems that the insubric fault zone which marks the contact between the penninic zone and the southern alps and which outcrops about 30 km to the south of the survey shows up as steeply north dipping reflections the lower european crust in the northern part of the survey is relatively transparent as opposed to the adriatic lower crust whose reflective nature may stem from shear zones associated with mesozoic crustal stretching the base of both the european and adriatic crust coincides with a 1 s thick band of laterally discontinuous reflections this reflection moho drops to greater depths going from the north toward the center of the alpine chain where it disappears with a steep southerly dip the moho reappears as a reflection band farther south this moho gap is situated above the lithospheric root and may be caused by perturbations related to subduction of lower crustal material the crustal scale structure obtained from the vibroseis data may be interpreted as a continent continent collision with wedge shaped indentation of a piece of adriatic crust into the european crust and vertical escape of the material in the core of the orogen along steeply dipping faults

spatial variations of ductile strain in fold and thrust belts from model to nature abstract fold and thrust belts ftbs accommodate tectonic convergence through folding and faulting of crustal rocks during a collisional event between two continental plates although evidence of distributed deformation is common in ftbs that usually leads to continuous foliations and regionally occurring ductile structures of multiple orders it has rarely been given much attention assuming that zones of localized deformation like shear zones and brittle faults accommodate the entire amount of tectonic convergence this study presents 3d laboratory scale models using viscous thin sheet as crustal layers to understand the evolution of ductile strain in a tectonic wedge we varied the degree of mechanical coupling at the basal decollement i e weak versus strong to investigate this issue at constant convergence velocity in all experiments to avoid the influence of rate dependence on viscous rheology our results reveal that the strength of basal decollement controls the mode of wedge growth and hence the strain pattern particularly towards the hinterland the weak decollement models yield a zone of constriction towards the central part of hinterland explaining the occurrence of isolated patches of l tectonites and cross folds in ftbs while the strong decollement condition allows gravity driven flow to be active in the hinterland leading to orogen parallel recumbent folds in contrast both weak and strong decollement models produce deformation that characterises the commonness of pervasive hinterland dipping ductile fabrics towards the mountain front we correlate our findings to show that spatio temporal variations in basal coupling are responsible for varying occurrence of ductile structures in ftbs

statistical analyses of eddies in the western mediterranean sea based on synthetic aperture radar imagery abstract we analysed 7188 sentinel 1a synthetic aperture radar sar images acquired in a 3 year period between october 2014 and september 2017 in the western mediterranean sea and found imprints of about 14 300 oceanic eddies with diameters ranging from 0 4 km to 160 1 km those eddies manifest on the sar imagery either through the accumulation of surfactants or through wave current interaction and considering the favourable wind speed ranges for both mechanisms we performed statistical analyses to gain insight into the eddies spatio temporal distribution their typical sizes and shapes and into the predominant mechanisms that are responsible for their formation the vast majority of the detected eddies is elliptical with a tendency for only large mesoscale eddies towards a circular shape we found no general influence of the wind on the eddies orientation although mesoscale eddies tend to orient into the main current direction in each subregion submesoscale eddies do not show such tendency submesoscale eddies in the western mediterranean sea are predominantly cyclonic 90 and with increasing eddy diameter there is a transition from cyclonic to anticyclonic sense of rotation in general we found highest densities of submesoscale eddies in autumn when the biological activity is still high and when mean regional winds are already strong but variable in addition instabilities of thermal fronts during summer and autumn and instabilities of the main and secondary currents influence the formation of submesoscale eddies some of our results confirm those previously obtained for other regions

3d geometry of range front blind ramp and its effects on structural segmentation of the southern longmen shan front eastern tibet abstract a 3d fault morphology model has been constructed from seismic profiles covering the piedmont of the southern longmen shan lms eastern margin of the tibetan plateau it reveals a spatial correlation between an 3 5 km high geometrical bump on the range front blind ramp rfbr and the gap between the 2008 m w 7 9 wenchuan and 2013 m w 6 6 lushan earthquakes sandbox modeling is then used to probe the effects of the geometrical irregularity of the rfbr on fault behaviors and the lms range front deformation sand wedges are designed to thrust over artificial blind ramps analogous to the thrusting of the lms orogenic wedge toward the sichuan basin through the rfbr the experiments reproduce the first order deformation features presented in the southern lms range front confirming that along strike geometrical variations of the rfbr have induced the segmentation of both fault motion and the range front deformation their results also suggest that the gap between the wenchuan and lushan earthquakes is located directly within the structural transition zone originating from the geometrical bump on the rfbr additionally there is a duplex structure occurring in the hanging wall of the geometrical bump which localizes significant shear strain with progressive shortening and represents a fracture zone corresponding to the observed geophysical anomaly low seismic velocity underneath the seismic gap it is likely that this fractured body protected the gap from the ruptures of the wenchuan and lushan earthquakes

passive roof thrusting and forelandward fold propagation in scaled brittle ductile physical models of thrust wedges a set of scaled analogue models was performed to investigate the role of a decollement layer in the structural style of fold and thrust belts silicone putty sgm 36 has been employed to represent the ductile decollement while frictional material quartz sand has been used to simulate the brittle behavior of roof and floor sequences situated above and below the decollement respectively in order to explore a wide combination of strength profiles models have been deformed under five distinct rates of compression 0 15 0 3 0 45 0 6 and 1 5 cm h 1 employing four different thicknesses for the silicone layer 0 1 0 2 0 4 and 0 8 cm experimental results indicate that roof sequences exhibit two distinct styles of deformation 1 passive roof duplex prd geometry e g banks and warburton 1986 and 2 outward propagation of folding ofp along the decollement e g davis and engelder 1985 in prd geometry the roof sequence remains relatively stationary being underthrust by a wedge shaped floor duplex while in ofp displacement along the floor thrusts is transferred horizontally along the decollement layer experiments suggest the occurrence of a genetic relationship between shear stresses at the base of the roof sequence b and within the ductile layer d and the development of prd or ofp geometry for a given strain rate the deformation pattern of roof sequences depends upon the b d ratio as well as the absolute b and d values the transition field between ofp and prd styles has been approximated by curvilinear regression of transition style experimental data points with a minimum value of d varying between about 112 and 160 pa to enter the prd field syntectonic sedimentation in the molasse basin is found to inhibit development of folding into the foreland but to promote prd style experiments simulate many of the principal characteristics of fold and thrust belts developed above a basal evaporite decollement as well as the development of passive roof duplexes at mountain fronts shear stress values inferred for many fold and thrust belts correlate well the deformation fields predicted by the present experimental study allowing to propose a simple model describing the mechanical behavior of natural roof sequences underlain by a decollement layer

on the intrinsic shape of oceanic eddies derived from satellite altimetry abstract the fundamental issue of mean eddy shape at the sea surface has been simplified as axially symmetric for a long time this assumption is worth of a reexamination following significant advances in precise tracking of individual eddies thanks to the recent availability of merged altimeter data with a grid resolution of 1 4 1 4 and a time interval of one day based on an orientationally aligned average of the effective boundaries of nearly 2 6 million individual eddies available to date a characteristic shape of a standard eddy has been derived which is found to be a very good approximation to a mathematical ellipsoid with a semimajor axis of a 87 0 km and a semiminor axis of b 54 0 km the oval nature of oceanic eddies appears to be universal in a climatological sense but the best fit ellipse varies with space and time statistically the eddy ellipse has two preferred angles for its major axis a primary angle of 104 284 nearly north south and a secondary angle of 171 351 nearly east west the intrinsic geometric asymmetry in eddy shape and orientation is believed to be one of the fundamental reasons behind the previously observed geophysical anisotropy in eddy properties future integrated analysis in an eddy centric coordinate system with an ellipse geometry may open a new window into nonlinear mesoscale oceanography in terms of eddy kinetics and eddy dynamics

lithospheric scale folding numerical modelling and application to the himalayan syntaxes we describe the eastern and western himalayan syntaxes which are large scale antiforms situated at geodynamically similar locations and the metamorphic evolution of which is coeval in the india asia collisional history to understand the mechanical plausibility of the structural interpretation we present two dimensional finite element modelling of lithospheric folding the models reveal the coeval development of adjacent synformal basins analogous to the peshawar and kashmir basins on both sides of the western syntaxis similarities between geological data and calculated models indicate that lithospheric buckling is a basic response to large scale continental shortening and an efficient mountain building process

lateral extrusion in the eastern alps part 1 boundary conditions and experiments scaled for gravity lateral extrusion encompasses extensional collapse gravitational spreading away from a topographic high in an orogenic belt and tectonic escape plane strain horizontal motion of wedges driven by forces applied to their boundaries in the eastern alps it resulted from 1 an overall northerly compression apulia against eurasia 2 a strong foreland bohemian massif 3 lack of constraint along a lateral boundary carpathian region and 4 a previously thickened gravitationally unstable thermally weakened crust eastern alpine orogenic belt six indentation experiments reproduce lateral extrusion at lithospheric scale the models have two to four lithospheric layers with a mohr coulomb rheology for the upper and a viscous rheology for the lower crust the lithosphere rests upon a low viscosity asthenosphere a broad indenter a narrow deformable area and a weakly constrained eastern margin fullfill as closely as possible conditions in the eastern alps indentation produces both thickening in front of the indenter and escape of triangular wedges lateral variations in crustal thickness become attenuated by gravitational spreading the overall fault pattern includes domains of reverse strike slip oblique normal and pure normal faults strike slip faults in conjugate sets develop serially the narrow width of the deformable area and the strength of the foreland determine the angles between the sets gravitational spreading produces a rhombohedral pattern of oblique and pure normal faults along the unconstrained margin opposite the unconstrained margin the indenter front shows thrusts and folds intersecting with the conjugate strike slip sets a triangular indenter favors spreading high velocity of indentation favors escape high confinement limits lateral motion inhibits spreading and favors thickening lateral extrusion in the eastern alps is best modeled by 1 a weak lateral confinement 2 a broad and straight indenter 3 a narrow width of the deformable area and 4 a rigid foreland crustal thickening lateral escape and gravitational spreading all contribute to the overall deformation

records of the evolution of the himalayan orogen from in situ th pb ion microprobe dating of monazite eastern nepal and western garhwal abstract in situ th pb monazite ages from rocks collected along two transects the dudh kosi everest eastern nepal and the bhagirathi river garhwal himalaya india perpendicular to the main central thrust mct suggest a striking continuity of tectonic events across the himalaya the youngest age reported in this study 5 9 0 2 ma mswd 0 4 from matrix monazite grains collected beneath the mct in the garhwal region is consistent with several age data from rocks at similar structural levels in central nepal providing support for widespread late miocene mct activity the lateral parallelism of orogenic events is further manifested by the 20 7 0 1 ma age of a high himalayan leucogranite from an injection complex that outcrops along the dudh kosi everest transect resembling ages of these bodies reported elsewhere the youngest monazite grain analyzed along the dudh kosi everest transect is 10 3 0 8 ma the absence of 7 3 ma monazite ages in eastern nepal may reflect a different nappe structure which obscures the reactivated ramp equivalent exposed in the garhwal and central nepal garnets from the mct hanging wall greater himalayan crystallines and footwall lesser himalaya display different major element zoning and the patterns are useful for constraining the location of the thrust system that separates the two lithologies pressure temperature paths for two upper lesser himalayan garnets that contain monazite inclusions indicate the utility of an in situ methodology to constrain the metamorphic evolution of the shear zone along the dudh kosi everest transect upper lesser himalayan monazite grains from three rocks record a clear signal at 14 5 0 1 ma mswd 8 4 and the 23 ma age that characterizes the hanging wall is notably absent monazites collected within a large scale greater himalayan crystallines fold yield the 14 ma age consistent with the structure forming due to mct related compression paleo mesoproterozoic 1407 35 ma matrix monazite grains are found within an augen gneiss unit located beneath the mct whereas cambro ordovician 436 8 548 17 ma inclusions are preserved within garnets of the greater himalayan crystallines the presence of 45 2 2 1 ma grains from lower structural levels of the greater himalayan crystallines indicates the unit realized conditions conducive for monazite growth during the eocene

numerical models of tectonic deformation at the baltica avalonia transition zone during the paleocene phase of inversion abstract predictions from dynamic modelling of the lithospheric deformation are presented for northern europe where several basins underwent inversion during the late cretaceous and early cenozoic and contemporary uplift and erosion of sediments occurred in order to analyse the evolution of the continental lithosphere the equations for the deformation of a continuum are solved numerically under thin sheet assumption for the lithosphere the most important stress sources are assumed to be the late cretaceous alpine tectonics localized rheological heterogeneities can also affect local deformation and stress patterns present day observations available in the studied region and coming from seismic structural interpretations and stress measurements have been used to constrain the model our modelling results show that lateral variation in lithospheric strength below the basin systems in central europe strongly controls the regional deformation and the stress regime furthermore we have demonstrated that the geometry of the boundary between baltica and avalonia together with different rheological characteristics of the two plates had a crucial role on local crustal deformation and faulting regime resulting in the baltica avalonia transition zone from the s n alpine convergence

compression versus extension in the exhumation of the dora maira coesite bearing unit western alps italy abstract several recent papers suggest that uplift and exhumation of high pressure low temperature hp lt metamorphic rocks are due to crustal extension coeval with and or post dating the contraction responsible for the metamorphism a detailed survey of the coesite bearing unit of the southern dora maira massif offers an opportunity to discuss the relative importance of extension and compression in the exhumation tectonics of ultra high pressure uhp rocks this uhp unit consists of pre alpine basement rocks which equilibrated at a depth of 100 km probably 120 100 ma ago it is overlain by two units with a similar lithology and eoalpine metamorphic age and high p t gradients which equilibrated at 60 and 50 km respectively this eoalpine basement complex is intercalated between blueschist facies units the whole pile was affected by a mesoalpine greenschist facies mylonitic deformation during which the early contacts were reactivated as low angle shallow dipping shear zones extension is documented only during the mesoalpine collisional period and is referred to the gravity collapse of a thickened orogenic wedge with an exhumation rate of about 1 mm yr the most important part of the exhumation of the uhp rocks occurred earlier at a higher rate close to 4 mm yr a forced return flow or extrusion tectonics of imbricate slices in an on going subduction setting seems appropriate to account for this early stage the fact that the omission of intermediate pressure rocks between juxtaposed units is an unreliable criterion for demonstrating extension is discussed

mechanical model for subduction collision tectonics of alpine type compressional orogens alpine type orogens are characterized by three distinct convergent tectonic phases subduction with deformation that has primarily single vergence a transition from subduction to collision and continental collision with double vergence although the cenozoic history of the european alps has additional complexities a mechanical explanation for these three phases would provide the necessary crustal scale framework in which to develop an understanding of the smaller scale processes we present results from a simple numerical model which explain the mechanics of these three phases as a consequence of the changing buoyancy of the lithosphere subducted beneath the orogen the development and exhumation of a subduction complex suture zone and basement nappe stack piemont suture penninic nappes the presence of a crustal scale back fold and thrust insubric line and uplift of basement on the pro european side of the orogen external basement massifs may be explained as a simple consequence of changing dynamics during the transition from subduction to collision

coherent mesoscale eddies in the north atlantic subtropical gyre 3 d structure and transport with application to the salinity maximum the mean vertical structure and transport properties of mesoscale eddies are investigated in the north atlantic subtropical gyre by combining historical records of argo temperature salinity profiles and satellite sea level anomaly data in the framework of the eddy tracking technique the study area is characterized by a low eddy kinetic energy and sea surface salinity maximum although eddies have a relatively weak signal at surface amplitudes around 3 7 cm the eddy composites reveal a clear deep signal that penetrates down to at least 1200 m depth the analysis also reveals that the vertical structure of the eddy composites is strongly affected by the background stratification the horizontal patterns of temperature salinity anomalies can be reconstructed by a linear combination of a monopole related to the elevation depression of the isopycnals in the eddy core and a dipole associated with the horizontal advection of the background gradient by the eddy rotation a common feature of all the eddy composites reconstructed is the phase coherence between the eddy temperature salinity and velocity anomalies in the upper 300 m layer resulting in the transient eddy transports of heat and salt as an application a box model of the near surface layer is used to estimate the role of mesoscale eddies in maintaining a quasi steady state distribution of salinity in the north atlantic subtropical salinity maximum the results show that mesoscale eddies are able to provide between 4 and 21 of the salt flux out of the area required to compensate for the local excess of evaporation over precipitation

eoalpine and mesoalpine tectonics in the southern alps according to structural and stratigraphic data eoalpine and mesoalpine tectonics can be clearly recognized in the southern alps and distinguished from the better known neoalpine deformation

exhumation during crustal folding in the namche barwa syntaxis geological observation in the eastern end of the himalaya shows that the asia india suture is folded metamorphic rocks derived from india occur structurally below the suture in the core of a regional antiform isotopic and fission track dating establish cooling exhumation of rocks from c 30 km depth within the last 4 myr we argue that exhumation is caused by 10 mm yr 1 erosion coeval with crustal scale folding

overturned marble layers evidence for upward extrusion of the backbone range of taiwan abstract the backbone range is part of the taiwan mountain belt which was formed due to the oblique collision between the luzon arc and the eurasian passive continental margin from plio pleistocene to the present stable isotope compositional profiles of thin marble layers from this mountain range show that marble layers from rock sections with an inverted metamorphic zonation were all overturned after the peak metamorphism and that marble layers from rock sections with a normal metamorphic zonation were not overturned exhumation folding seems to be the responsible process an upward extrusion exhumation model is therefore postulated as the probable mechanism for the mountain building process this model can well explain the fanning orientation of rock cleavage s dipping in a regional scale as well as the metamorphic characteristics across the mountain range the model also shows that the recorded stretching lineation is secondary in nature meaning the exact direction of rock movement during the initial exhumation stage in response to the oblique collision cannot be deduced

the influence of nonlinear mesoscale eddies on near surface oceanic chlorophyll oceanic rossby waves have been widely invoked as a mechanism for large scale variability of chlorophyll chl observed from satellites high resolution satellite altimeter measurements have recently revealed that sea surface height ssh features previously interpreted as linear rossby waves are nonlinear mesoscale coherent structures referred to here as eddies we analyze 10 years of measurements of these ssh fields and concurrent satellite measurements of upper ocean chl to show that these eddies exert a strong influence on the chl field thus requiring reassessment of the mechanism for the observed covariability of ssh and chl on time scales longer than 2 to 3 weeks the dominant mechanism is shown to be eddy induced horizontal advection of chl by the rotational velocities of the eddies

robust prestack q determination using surface seismic data part 1 method and synthetic examples the accurate determination of seismic attenuation or 1 q is useful for signal enhancement and reservoir characterization to arrive at the necessary accuracy however a number of issues must be addressed in the measurement technique specifically spectral interference from closely spaced reflections is a major concern in addition to the assumptions and errors associated with the raypath geometries of the reference and measured reflections we have developed a robust method for measuring attenuation from prestack surface seismic gathers that helps minimize these issues in our prestack q inversion technique the presence of spectral interference was first reduced by making use of a variable window time frequency transform to minimize the effects of the remaining interference we then made use of an inversion scheme operating simultaneously in the frequency and traveltime difference coordinates a by product of this inversion was a collection of the frequency independent amplitude changes which in the

geographical variability of the first baroclinic rossby radius of deformation global 1 83 18 climatologies of the first baroclinic gravity wave phase speed c1 and the rossby radius of deformation l1 are computed from climatological average temperature and salinity profiles these new atlases are compared with previously published 5 83 58 coarse resolution maps of l1 for the northern hemisphere and the south atlantic and with a 1 83 18 fine resolution map of c1 for the tropical pacific it is concluded that the methods used in these earlier estimates yield values that are biased systematically low by 5 15 owing to seemingly minor computational errors geographical variations in the new high resolution maps of c1 and l1 are discussed in terms of a wkb approximation that elucidates the effects of earth rotation stratification and water depth on these quantities it is shown that the effects of temporal variations of the stratification can be neglected in the estimation of c1 and l1 at any particular location in the world ocean this is rationalized from consideration of the wkb approximation

tectonic versus glacial isostatic deformation in europe 1 tectonic deformation induced by the alpine collision and glacial isostatic adjustment gia in europe are modelled by means of a finite element scheme and viscoelastic normal modes techniques in order to compare the resulting deformation patterns with the itrf2000 international terrestrial reference frame geodetic dataset due to the alpine collision and to the flow from the equatorial mantle to the deglaciated regions in the northern hemisphere both tectonics and gia contribute to the observed widespread shortening with tectonics playing a major role in the southern part of the modelled domain from potsdam to the alpine front and gia affecting the shortening in proximity of the region subject to post glacial rebound since the stiff baltic shield causes a counterclockwise rotation of the collision velocity away from the shield itself and the gia induced velocities are directed outward from the deglaciated region both tectonics and gia contribute to the observed east west baseline extension of 0 8 1 1 mm yr at the latitude of onsa

estimation of interval anisotropic attenuation from reflection data knowledge of interval attenuation can be highly beneficial in reservoir characterization and lithology discrimination we combine the spectral ratio method with velocity independent layer stripping to develop a technique for the estimation of the interval attenuation coefficient from reflection seismic data the layer stripping procedure is based on identifying the reflections from the top and bottom of the target layer that share the same ray segments in the overburden the algorithm is designed for heterogeneous arbitrarily anisotropic target layers but the overburden is assumed to be laterally homogeneous with a horizontal symmetry plane although no velocity information about the overburden is needed interpretation of the computed anisotropic attenuation coefficient involves the phase angle in the target layer tests on synthetic p wave data from layered transversely isotropic and orthorhombic media confirm the high accuracy of 2d and 3d versions of the algorithm we also demonstrate that the interval attenuation estimates are independent of the inhomogeneity angle of the incident and reflected waves

river transport effects on compressional belts first results from an integrated analogue numerical model 1 erosion deposition and tectonic processes interact to define the style of deformation in compressional belts this paper introduces a method of integrating a numerical model for surface transport with analogue sandbox models of compressional belts to further improve our understanding of this interplay the analogue model provides the numerical model with the rising topography whereas the numerical model calculates the river network and the resulting amount of erosion and sediment transport compared to previous analogue models with uniform two dimensional erosion this method provides a tool to incorporate process based rates of erosion and deposition with spatial distributions that depend on the river network developed on the evolving topography rivers running parallel to the evolving mountain belt induce along strike changes in erosion and deposition that in turn result in asymmetric tectonic deformation the additional load of sediments controls the propagation of thrust as well as the direction of vergence of the main thrust high erosion rates do not always lead to fewer thrusts within the compressional belts but generally steepen and lengthen the lifetime of the affected faults

eddy momentum flux and its contribution to the southern ocean momentum balance a large amount of momentum is transferred to the southern ocean by strong westerly winds analytical and numerical models have suggested that transient eddies may be important in transporting this momentum away from the region of wind forcing either horizontally1or vertically downwards where it is balanced by bottom topographic drag2 5 there are however few long term in situ observations of horizontal eddy momentum flux6 8 and no large scale measurements of vertical eddy fluxes to test these models as a result the momentum balance of the antarctic circumpolar current acc remains uncertain and the role of eddies controversial here we use geosat satellite altimeter data to resolve directional eddy kinetic energy and horizontal eddy momentum flux in the acc on fine spatial and temporal scales the complex spatial distribution of surface eddy momentum flux is strongly influenced by bottom topography the horizontal eddy momentum flux tends generally to concentrate the mean flow although some regions of divergence are observed our results show that the zonally averaged horizontal eddy momentum flux from transient eddies is an order of magnitude too small and in the wrong direction to directly balance the eastward momentum input from wind1

analogue modelling of thrust systems passive vs active hanging wall strain accommodation and sharp vs smooth fault ramp geometries we present new analogue modelling results of crustal thrust systems in which a deformable brittle hanging wall is assumed to endure passive internal deformation during thrusting i e exclusively as a consequence of having to adapt its shape to the variable geometry of a rigid footwall building on previous experimental contributions we specifically investigate the role of two so far overlooked critical variables a concave convex cc vs flat ramp flat frf thrust ramp geometry and b presence vs absence of a basal velocity discontinuity vd regarding the first variable we compare new results for considered cc smoother ramp types against classical experiments in which frf sharp ramp geometries are always prescribed our results show that the considered sharp vs smooth variation in the thrust ramp geometry produces important differences in the distribution of the local stress field in the deformable hanging wall above both lower and upper fault bends with corresponding styles of strain accommodation being expressed by marked differences in measured morpho structural parameters regarding the second variable we for the first time report analogue modelling results of this type of experiments in which basal vds are experimentally prescribed to be absent our results critically show that true passive hanging wall deformation is only possible to simulate in the absence of any basal vd since active shortening accommodation always necessarily occurs in the hanging wall above such a discontinuity i e above the lower fault bend in addition we show that the morpho structural configuration of model thrust wedges formed for prescribed vd absence conditions complies well with natural examples of major overthrusts wherein conditions must occur that approximate a frictionless state along the main basal thrust plane

satellite observations of chlorophyll phytoplankton biomass and ekman pumping in nonlinear mesoscale eddies nonlinear mesoscale eddies can influence biogeochemical cycles in the upper ocean through vertical and horizontal advection of nutrients and marine organisms the relative importance of these two processes depends on the polarity of an eddy cyclones versus anticyclones and the initial biological conditions of the fluid trapped in the core of the eddy at the time of formation eddies originating in the eastern south indian ocean are unique in that anticyclones typically associated with downwelling contain elevated levels of chlorophyll a enhanced primary production and phytoplankton communities generally associated with nutrient replete environments from analysis of 9 years of concurrent satellite measurements of sea surface height chlorophyll phytoplankton carbon and surface stress we present observations that suggest eddy induced ekman upwelling as a mechanism that is at least partly responsible for sustaining positive phytoplankton anomalies in anticyclones of the south indian ocean the biological response to this eddyinduced ekman upwelling is evident only during the austral winter during the austral summer the biological response to eddy induced ekman pumping occurs deep in the euphotic zone beyond the reach of satellite observations of ocean color

the building of the central swiss alps an experimental approach abstract a kinematic model explaining the building of the central swiss alps is proposed from a review of various kind of data including structural geophysical petrological and geochronological data the eo alpine event is taken into account in order to determine the thermo mechanical evolution from the cretaceous to the late tertiary the stacking process of crustal wedges which took place during cretaceous time has led to the formation of a thickened crust with a very low geothermal gradient high pressure low temperature metamorphism this period was followed by a lull in tectonic activity during which thermal relaxation took place the major tertiary deformation is thought to result from horizontal compression of a thickened crust having a geothermal gradient higher than the average horizontal surface forces are due to the adriatic sub plate acting as a rigid indenter the model explaining the present day structure of the swiss alps emphasizes vertical extrusion and horizontal intrusion of the deepest highly ductile basement units several scale model experiments have been carried out in order to test this basic kinematic idea they display quite similar structures to those identified for the swiss alps striking features of the swiss alps such as their metamorphic and uplift history are discussed and compared with the timing of the tectonic evolution we conclude that the general process of vertical extrusion and horizontal intrusion can possibly explain the overall structure of the central swiss alps external crystalline massifs and the penninic zone

seismic attenuation tomography using the frequency shift method we present a method for estimating seismic attenuation based on frequency shift data in most natural materials seismic attenuation increases with frequency the high frequency components of the seismic signal are attenuated more rapidly than the low frequency components as waves propagate as a result the centroid of the signal s spectrum experiences a downshift during propagation under the assumption of a frequency independent q model this downshift is proportional to a path integral through the attenuation distribution and can be used as observed data to reconstruct the attenuation distribution tomographically the frequency shift method is applicable in any seismic survey geometry where the signal bandwidth is broad enough and the attenuation is high enough to cause noticeable losses of high frequencies during propagation in comparison to some other methods of estimating attenuation our frequency shift method is relatively insensitive to geometric spreading reflection and transmission effects source and receiver coupling and radiation patterns and instrument responses tests of crosswell attenuation tomography on 1 d and 2 d geological structures are presented

a lithospheric cross section through the swiss alps ii constraints on the mechanical structure of a continent continent collision zone summary the calculation of strength profiles along the european geotraverse egt through the swiss alps yields constraints on the large scale vertical and lateral mechanical structure through the alpine continent continent collision zone strength profiles are evaluated for different assumptions on petrological stratification and strain rate and are based on temperature depth profiles derived from transient thermo kinematic modelling of the neoalpine orogeny the main contribution to the total strength results from the mantle lithosphere which is strongly controlled by temperature in contrast the crustal contribution is mainly determined by variations in petrological stratification a direct correlation between surface heat flow and the total strength of the crust the mantle lithosphere and the entire lithosphere crust and mantle lithosphere is not observed our results demonstrate that in tectonically active areas a transient thermal model along with detailed knowledge of the deep structure and petrology is necessary to evaluate lithospheric strength envelopes inside the collision zone strain rate has a strong control on the bottom of the mechanically strong crust whereas outside the collision zone the effect is less significant the cut off depth of seismicity along the profile which correlates largely with the bottom of the mechanically strong crust deviates from the 300 400 c isotherm the inferred effective elastic thickness for the molasse basin north of the alps is in agreement with flexural modelling results whereas for the southern alps the predictions deviate

evaluating the role of syn thrusting sedimentation and interaction with frictional detachment in the structural evolution of the sw tarim basin nw china insights from analogue modeling abstract the structural evolution of the fold and thrust belt in sw tarim basin nw china is poorly understood as the region is covered by thick pliocene quaternary conglomerate which significantly decreases the quality of seismic images we here improve the understanding of the thrust belt evolution with an investigation using analogue modeling on the deformation mechanism based on a case of real geological section in which we focus on the impact of syn thrusting sedimentation on the structural style and evolution the results show that syn thrusting sedimentation significantly increases the distance and rate of foreland propagation resulting in a much broader fold and thrust belt the modeling results also suggest that the fold and thrust belt exhibits different structural patterns under different syn thrusting sedimentary conditions in the case of thick syn thrusting sediments a frictional detachment layer of mudstone acts as decollement and the fold and thrust belt develops a duplex pattern in the hinterland in the case of thin syn thrusting deposits the belt develops a pop up structure with backthrusts in the foreland region which cut through the detachment layer the striking similarity between the model with thick syn thrusting sediments and the real geologic section implies that the overlying thick pliocene quaternary sediments play a major role in shaping the structure pattern in the fold and thrust belt of sw tarim basin

lithospheric scale structures from the perspective of analogue continental collision abstract analogue models were employed to investigate continental collision addressing the roles of 1 a suture zone separating different crustal blocks 2 mid crustal weak layers and 3 mantle strengths these models confirmed that low amplitude lithospheric and crustal buckling is the primary response to shortening with a wavelength mainly controlled by the strong upper crust and or lithospheric mantle with increasing shortening bivergent thrusts formed across the brittle layers equivalent to upper crust at inflection points of the buckles while ductile layers lower crust and mantle continued being folded the resulting geometries displayed pop ups and pop downs above the boundaries sutures between blocks further shortening led to wider thrust bounded deformation zones belts in front of the stronger blocks identified as effective indenters during shortening upward extrusion into belts allowed exhumation of deep material weak layers enhanced strain localisation these modelling results have similarity in large scale structures of modern orogens and are relevant to the understanding of natural collisional processes

episodic accretion and strain partitioning in a model sand wedge we model led thrust wedge accretion and deformation partitioning in a passively layered sand detached and shortened above a smooth rigid decollement the thrust wedge accretes in piggyback style during forward advance of a rear wall the passively layered sand accommodates the shortening penetratively by kinking ramp folding and by imbrication in single layers the style of compression changes with time and or stratigraphic position within the sand prism initial penetrative layer shortening above a slipped zone of decollement is succeeded by formation of monoclinal or conjugate shear bands at temporary terminations of decollement the shear bands subsequently narrow down and lock as thrust ramps the model sand wedge accrets episodically rather than steadily episodicity is controlled by the stick slip mode of decollement propagation and by volume loss and compaction of the wedge material in response to convergence this results in formation of a wedge with a convex upwards cross sectional topography

some aspects of vortex structure related to tropical cyclone motion abstract some effect of tropical cyclone structure on the vortex motion are examined in a nondivergent barotropic numerical model with no basic current as suggested earlier by demaria the initial maximum wind speed has little effect on the track vortex translation associated with the beta effect depends sensitively on the strength of the flow between 300 and 1000 km from the center if the flow in this annulus is made more cyclonic the track will turn cyclonically and move more toward the west in the northern hemisphere the dynamics of this beta drift is studied via a decomposition into symmetric and asymmetric circulations the symmetric flow experiences a slight weakening of the maximum wind speed and an anticyclonic circulation is induced beyond 600 km the asymmetric circulation is dominated by an azimuthal wavenumber one circulation with an anticyclonic gyre east of the center a cyclonic gyre to the west and a nearly uniform broad scale ventilation flow between the gyres the vortex translati

styles of crustal deformation in compressional orogens caused by subduction of the underlying lithosphere abstract crustal scale deformation is calculated for models in which the driving mechanism corresponds to the asymmetric detachment and underthrusting of the underlying mantle lithosphere the plane strain finite element model results provide indications of the styles of deformation to be expected in small compressional orogens in particular these styles occur where shortening of the mantle lithosphere is achieved by the nearly rigid convergence between lithospheric mantles and the subduction of one mantle beneath the other the crust is modelled using coulomb plastic frictional and thermally activated power law viscous rheologies and the effects of compositional layering and variable geothermal gradients are included results are presented for a range of models in which the strength of the coupling between the model crust and its basal boundary surface denudation partial and total subduction of the crust and compositional layering are examined the results show the development of inclined step up shear zones which are a consequence of conjugate thrusting in regions of coulomb controlled rheology these zones link to sub horizontal shear zones which occur where composition and temperature render the crust viscously weak the model strain fields are interpreted in terms of deformation on discrete planes and the seismic reflectivity fabric that may be associated with this discrete deformation finally we ask whether similar seismic reflectivity fabric can be recognized in observations from small compressional orogens

final stages of the variscan orogeny at the southern iberian massif lateral extrusion and rotation of continental blocks 1 the southern part of the iberian massif contains one of the sutures of the european variscan belt several systems of faults and dikes appear as a result of a period of brittle deformation during the late stages of the variscan tectonic evolution of this zone a detailed analysis of these structures has been carried out in this work four successive deformation phases have been identified a first strike slip normal faulting stage a transcurrent stage a second strike slip normal faulting stage and finally a thrusting stage the age of these phases vary between around 310 ma and less than 270 ma the computed trajectories of the deformation axes show a progressive anticlockwise rotation of around 90 these data together with the results of previous geological and geophysical studies of this zone and of the variscan belt as a whole lead us to propose a model of tectonic evolution for the last stages of the variscan collision comparison with modern examples of collisional belts and with the results of analog experiments suggests that a promontory of the continental lithosphere of the downgoing plate indented against the active continental margin of the upper plate the indenter suffered an intense deformation in accordance with the predictions of some recent analog models simulating the indentation of a four layer continental lithosphere the variscan and late variscan brittle deformation episodes represent the waning stages of the variscan collision and not an independent tectonic event

structural evolution of a subducted continental sliver the northern dora maira massif italian alps continental crust of the dora maira massif was subducted in part to pressures of 30 kbar during early stages of the alpine orogeny a new investigation in a transect across the north of the massif has shown that much of the dominant foliation in the upper dora maira pellice unit was formed at high pressures of the order of 11 kbar but at lower pressure than the locally preserved relicts of eclogite facies metamorphism this dominant deformation phase produced large recumbent isoclinal folds with intensely flattened limbs in the pellice unit basement and the overlying permian mesozoic cover now white augen gneisses and calcschists the rocks were thus part of the upper crust prior to their subduction unless an unrealistically large thickness of mesozoic rocks now removed is hypothesized the pellice unit was later emplaced over the chisone unit in greenschist facies conditions all shear sense indicators are top to west implying a simple but prolonged history in which high pressure units were emplaced westwards over lower pressure ones whilst being exhumed the intense horizontal stretching recorded in the basement gneisses may have helped bring them closer to the surface by thinning indirect arguments suggest that such tectonic thinning is not on its own sufficient to explain the present setting of the eclogite units one or more sheets of eclogite material may have been extruded from the eoalpine subduction zone in addition such slabs would be bounded below by west directed and above by east directed shears as the dora maira massif forms the structurally lowest eoalpine eclogite unit in the alps the observed history is not incompatible with this model east or southeast directed structures in the alps are commonly identified as backthrusts but an origin for some as the extensional shears predicted by this model should not be excluded

forces driving continental collision reconciling indentation and mantle subduction tectonics two end member classes of models indentation and mantle subduction that have been proposed to explain patterns of crustal deformation during continental collision may be reconciled using a model that includes a combination of indentation from the side and basal forcing from underlying subducting layers measurement of the width of deformation across strike can be used to indicate the predominant forcing mechanism and shows that the combined case is controlled by mantle subduction if the crust is well coupled to the underlying mantle lithosphere or by indentation if the crust and mantle lithosphere are decoupled an increase in the width of deformation with convergence as a result of the effect of gravity on crustal thickening can cause a change in the primary control of an orogenic system from mantle subduction to indentation this transfer may be enhanced by diffusional or convective heating at the base of the thickened crust the india eurasia collision is an example where the deformation width may initially have depended on mantle subduction but is now controlled by the indenter limit

the evolution and propagation of quasigeostrophic ocean eddies abstractthe long term evolution of initially gaussian eddies is studied in a reduced gravity shallow water model using both linear and nonlinear quasigeostrophic theory in an attempt to understand westward propagating mesoscale eddies observed and tracked by satellite altimetry by examining both isolated eddies and a large basin seeded with eddies with statistical characteristics consistent with those of observed eddies it is shown that long term eddy coherence and the zonal wavenumber frequency power spectral density are best matched by the nonlinear model individual characteristics of the eddies including amplitude decay horizontal length scale decay and zonal and meridional propagation speed of a previously unrecognized quasi stable state are examined the results show that the meridional deflections from purely westward flow poleward for cyclones and equatorward for anticyclones are consistent with satellite observations examination of the fluid transport properties of the eddies shows that an

the influence of backstop dip and convergence velocity in the growth of viscous doubly vergent orogenic wedges insights from thermomechanical laboratory experiments abstract we investigate the effects of convergence velocity and backstop geometry on the evolution of experimental viscous doubly vergent orogenic wedges experiments are performed in a thermomechanical shortening box using the newtonian properties of 52 54 en type paraffin as analogue to the natural strength distribution in the continental crust a velocity discontinuity is imposed at the subduction slot where the base plate is pulled below a rigid backstop the mobile base plate dips 5 two different backstop dips 60 and 30 are used in combination with constant convergence velocities of 2 and 10 cm h 1 results point out that backstop geometry exerts a first order control on the evolution of doubly vergent experimental wedges steeply dipping backstops cause the stationary uplift of the wedge axial region above the subduction slot whereas shallow dipping backstops allow its retroward translation in concomitance with a more pronounced deformation in the retrowedge convergence velocity controls the uplift in the wedge axial region and the amount of the outward migration of the deformation front in both the prowedge and retrowedge regions for fast convergence velocity and shallow dipping backstop deformation in the retrowedge is favoured an increase in the backstop dip and or a decrease in the convergence velocity favour deformation in the prowedge both prowedge and retrowedge tend to grow in self similar conditions with an aspect ratio depending upon the backstop dip and convergence velocity these results may have important consequences for the evolution and deformation style of ductile dominated orogenic wedges suggesting that location of the axial region and deformation progression in natural orogens can be strongly controlled by boundary and kinematic conditions

estimation of q from surface seismic reflection data reliable estimates of the anelastic attenuation factor q are desirable for improved resolution through inverse q deconvolution and to facilitate amplitude analysis q is a useful petrophysical parameter itself yet q is rarely measured estimates must currently be made from borehole seismology this paper presents a simple technique for determining q from conventional surface seismic common midpoint cmp gathers it is essentially the classic spectral ratio method applied on a trace by trace basis to a designatured and nmo stretch corrected cmp gather the variation of apparent q versus offset qvo is extrapolated to give a zero offset q estimate studies on synthetics suggest that for reasonable data quality s n ratios better than 3 1 shallow 5 dips and stacking velocity accuracy 5 source to reflector average q is recoverable to within some 3 and q for a specific interval depending on its two way time thickness and depth is recoverable to 15 20 three case studies are reported first

analogue model of gravitational collapse and surface extension during continental convergence most mountain belts occur where continents collide so it is not surprising that the dominant form of surface deformation is shortening but there is also abundant geological evidence for extension in the central parts of many mountain belts at the same time as shortening occurs elsewhere previous models for extension require temporal changes in the thermal structure of the lithosphere1 2 the rate of convergence2 3 the strength of the crust3 or the geometry of accretion4 here we present a simple model in which no such changes are required for surface extension during the convergent thickening of a viscous crusta layer convergence is driven by the motion of two plates at the base of the layer in the area where one plate subducts under the other the surface begins to extend soon after the start of convergence eventually stretching by more than 60 per cent extension occurs because gravity drives horizontal flow faster at the free surface than in the centre of a viscous layer that is fixed at its base in real mountain belts mid crustal weaknesses may allow the depth dependent motion required for surface extension

eddy induced particle dispersion in the near surface north atlantic abstractthis study investigates the anisotropic properties of the eddy induced material transport in the near surface north atlantic from two independent datasets one simulated from the sea surface height altimetry and one derived from real ocean surface drifters and systematically examines the interactions between the mean and eddy induced material transport in the region the lagrangian particle dispersion which is widely used to characterize the eddy induced tracer fluxes is quantified by constructing the spreading ellipses the analysis consistently demonstrates that this dispersion is spatially inhomogeneous and strongly anisotropic the spreading is larger and more anisotropic in the subtropical than in the subpolar gyre and the largest ellipses occur in the gulf stream vicinity even at times longer than half a year the spreading exhibits significant nondiffusive behavior in some parts of the domain the eddies in this study are defined as deviations from the long term time mean the contr

the determination of the seismic quality factor q from vsp data a comparison of different computational methods1 ten methods for the computation of attenuation have been investigated namely amplitude decay analytical signal wavelet modelling phase modelling frequency modelling rise time pulse amplitude matching technique spectral modelling and spectral ratio in particular we have studied the reliability of each of these methods in estimating correct values of q using three synthetic vsp seismograms for plane p waves with different noise contents the investigations proved that no single method is generally superior rather some methods are more suitable than others in specific situations depending on recording noise or geology the analytical signal method has been demonstrated to be superior if true amplitude recordings are available otherwise spectral modelling or in the noise free case the spectral ratio method is optimal finally two field vsps in sediments are investigated only in the case of the highest quality vsp can significant information be deduced from the computed attenuation

dynamics of orogenic wedges and the uplift of high pressure metamorphic rocks subduction accretion complexes can be approximated as wedge shaped continua with a rigid buttress behind and a subducting litho spheric slab beneath thick wedges undergoing prograde metamorphism have a negligible long term yield strength and are likely to exhibit a complex nonlinear viscous rheology such a wedge will tend to deform internally until it reaches a stable configuration in which the gravitational forces generated by the wedge geometry balance the traction exerted on its underside by the subducting slab accretion of material at the wedge front will lengthen the wedge and cause it to shorten internally to regain the stable geometry this shortening will be expressed as late out of sequence thrusting backthrusting and folding conversely underplating of sediment or crustal slices will thicken the wedge which may need to extend internally to regain stability extension will cause listric normal faults that may merge downward into zones of ductile extension continued underplating at depth and compensating extension above provides a mechanism for bringing high p low t metamorphic rocks to upper levels in the rear of the wedge where they are commonly observed many major tectonic boundaries in convergent orogens such as the coast range thrust in the franciscan complex major nappe contacts in the alps and the contact between the nevado filabride and higher betic nappe complexes in the betic cordillera show abrupt increases in metamorphic grade downward across them this is consistent with their origin or reactivation as uplift related extensional structures

the role of lateral strength contrasts in orogenesis a 2d numerical study in this paper we present a series of thermo mechanical experiments on continent continent collision zones to investigate the role of lateral strength contrasts in terms of collision dynamics and orogen geometries our results show that differences in crustal rheology may lead to a variety of different patterns of deformation and crustal geometries upper plate indentation forms a sequence of foreland propagating thrust units made of brittle upper crust on the lower plate the strong deformation of the lower plate stands in stark contrast to the undeformed upper plate in contrast subduction of strong lithosphere beneath a weak upper plate forms a complex pattern of deformation deformation initiates on the lower plate and forms an antiformal stack made of brittle upper crust before it indents the upper plate hence deformation is present on both the lower and upper plate despite differences in initial strength the outcome of this study has direct implications to natural collision zones where differences in strength between the upper and lower plate exist for example along strike variability of upper vs lower plate shortening in the alps are likely to be controlled by contrasts in crustal strength furthermore we suggest that the antiformal stack in the axial zone of the pyrenees might indicate a strong lower plate at the onset of collision our results may therefore provide important constraints for the rheological state of continents during collision

measurements of attenuation from vertical seismic profiles values of attenuation have been extracted from five detailed velocity surveys significant amounts of attenuation are observed in all five wells measured values of attenuation vary by a factor of 10 ranging from less than 0 1 to 0 9 db wavelength correlation of attenuation with lithology is good considering the resolution limits of the surveys one of the surveys was performed in west texas and the other four were carried out in the gulf coast area the total number of recording depths in each survey varied from 31 to 208 with downhole recordings taken every 10 or 20 ft over key stratigraphic zones in all five surveys a monitor geophone was placed near the well to check for source consistency our procedure for measuring attenuation involved constructing the spectral ratio between each downhole pulse and one particular reference pulse a value of cumulative attenuation ca was then extracted from each spectral ratio and plotted as a function of geophone depth this method allowed us to use many m

deformation style and controlling geodynamic processes at the eastern guadalquivir foreland basin southern spain the tectonic structure of the guadalquivir foreland basin becomes complex eastwards evolving from a single depocenter to a compartmented basin the deformation pattern within the eastern guadalquivir foreland basin has been characterized by combining seismic reflection profiles boreholes and structural field data to output a 3d model high dipping nne ssw to ne sw trending normal and reverse fault arrays deform the variscan basement of the basin these faults generally affect tortonian sediments which show syntectonic features sealed by the latest miocene units curved and s shaped fault traces are abundant and caused by the linkage of nearby fault segments during lateral fault propagation preexisting faults were reactivated either as normal or reverse faults depending on their position within the foreland at tortonian time reverse faults deformed the basin forebulge while normal faults predominated within the backbulge along strike variation of the betic foreland basin geometry is supported by an increasing mechanical coupling of the two plates alboran domain and variscan basement towards the eastern part of the cordillera thus subduction would have progressed in the western betics while it would have failed in the eastern one there the initially subducted iberian paleomargin nevado filabride complex was incorporated into the upper plate promoting the transmission of collision related compressional stresses into the foreland since the middle miocene nowadays compression is still active and produces low magnitude earthquakes likely linked to nne ssw to ne sw pre exiting faults reactivated with reverse oblique slip kinematics seismicity is mostly concentrated around fault tips that are frequently curved in overstepping zones

indenter growth in analogue models of alpine type deformation a series of analogue experiments were carried out to simulate continental convergence as seen in a profile through the central alps a rigid indenter representing the adriatic plate was driven laterally into a sand pack representing the brittle upper crust of europe detached and thickening above its subducting ductile lower crust the rigid indenter advanced at the same steady rate in each experiment but the dip of its front face was steepened in 15 increments from 15 to 90 where the rigid indenter face dipped at 45 or less a sand wedge rose and was bound by a series of forekinks that nucleated at the toe of the indenter where the face of the rigid indenter dipped 60 or more the wedge was defined by a single forekink and one or more backkinks that nucleated from a point advancing in front of the indenter toe we interpret these results as indicating that slices of the sand pack and rising wedge are transferred across kink bands to build an effective indenter with a frontal dip closer to that dictated by the changing shear strength of the sand pile which thickens vertically as it shortens laterally one of our models with a rigid indenter dipping 75 simulates most of the major structures shown in recent syntheses of surface geology and deep seismic data in the central alps without the isostatic lithospheric depression this model accounts for the late collisional stage oligocene to present complex strain and metamorphic histories in the core of the orogenic wedge the rapid rise and extrusion of small pips of alpine eclogites and the current passivity of the insubric line it also emphasizes that lateral extension along gently dipping thrusts orogen normal horizontal escape is confined to the extruded portion of the rising wedge