unsaturated hydraulic conductivity in limestone dolines influence of vegetation and rock fragments abstract vegetation and rock fragments have a profound impact on runoff generation in the dolines of the sierra de gador southeastern spain this study investigated the effect of vegetation and rock fragments on unsaturated hydraulic conductivity k h in three limestone dolines and examined whether variation in k h was consistent with differences in runoff from simulated rainfall tension infiltrometers were used to measure unsaturated hydraulic conductivity at three pressure heads h of 30 60 and 120 mm at 70 locations within the three dolines generally the trends of the k h were consistent with the simulated rainfall data and accounted for difference in runoff for the vegetated surfaces vegetation resulted in high infiltration with unsaturated hydraulic conductivities at 30 and 60 mm are significantly greater for the vegetated surface than for the rock fragment covered surface and bare soil surface rock fragments had no obvious effect on soil hydraulic conductivity as compared with bare soils the k h of the non crusted soil were 2 5 times higher than that of the crusted soil the k h decreased with increasing tensions k 60 and k 120 were only 8 4 and 0 89 respectively of k 30 for the vegetated surfaces and were about 30 and 8 7 respectively of k 30 for both rock fragment covered surfaces and bare soils suggesting that pores in the 0 5 to 1 mm diameter range dominate flow under unsaturated conditions there were significant differences in k h among the different topographic units of the dolines and k h tended to be higher in the upper position than in the lower position of the doline

mantle dynamics beneath the gibraltar arc western mediterranean from shear wave splitting measurements on a dense seismic array 1 controversial evolutionary models have been proposed for the gibraltar arc system a complex interaction zone between the eurasia and african plates here we derive new mantle anisotropic constraints from sks splitting measurements on a dense network of about 90 broad band stations deployed over south iberia and north morocco the inferred fast polarization directions fpd clearly show a spectacular rotation along the arc following the curvature of the rif betic chain while stations located at the south and south east edges show distinct patterns these results support geodynamical processes invoking a fast retreating slab rather than convective removal and delamination models the fpd variations along the gibraltar arc can be explained by fossil anisotropy acquired during the western mediterranean eocene subduction while changes to the south and south east of the rif betic chain could be the imprint of a flow episode around an alboran high velocity slab during its miocene fragmentation from the algerian slab

active surface deformation and sub lithospheric processes in the western mediterranean constrained by numerical models we present the results of dynamic modeling of the western mediterranean that accounts for observed global positioning system gps surface deformation of the alboran sea and surrounding rif and betic mountains as the result of the combined effects of relative motion of the eurasian and nubian plates low strength in the alboran sea region and sub lithospheric processes occurring beneath the external rif domain assuming that the lithosphere behaves elastically over the short time period of the gps observations an elastic plate model is considered in our study including an area of weak lithosphere factor of 10 centered on the alboran sea and in which lateral boundary conditions consist of the nubia eurasia oblique convergence sub crustal processes are modeled by application of a horizontal traction on a small area patch at the base of the elastic plate our modeling studies demonstrate the need for sub crustal or sub lithospheric southwestward directed forcing to account for observed southwestward motion of the rif and betic domains based on the location orientation and small area of the traction patch we hypothesize that forcing is associated with delamination and rollback of the subducted african continental lithospheric mantle beneath the external rif zone due to the pull of the oceanic part of the western mediterranean slab a dynamic process that may be similar to that where the over riding plate is driven toward the subduction zone during slab rollback

evolution of retreating subduction boundaries formed during continental collision retreating subduction boundaries formed where the rate of subduction exceeds the rate of overall plate convergence appear to be commonly developed features within regions of early or incomplete continent continent collision they are characterized by regional extension within the overriding plate and at their leading edge by thin skinned arcuate thrust belts that are concave towards the overriding plate as is illustrated by examples from the mediterranean region the formation of retreating subduction boundaries is intimately related to the process of continental collision during the early stages of collision retreating subduction boundaries are commonly formed by lateral ejection from zones of crustal shortening along the main collision boundary retreating plate boundaries can also form before the main collision and the associated thrust belts emplaced as precollisional accretionary assemblages because the driving mechanism for retreating subduction boundaries appears to be gravity acting on a dense subducted slab slab pull subduction usually ceases when and only when thick buoyant continental crust enters the subduction zone thus differences in the evolution and duration of retreating subduction systems can be largely attributed to the size and configuration of the deep water regions available to be subducted in some cases retreating subduction boundaries may escape into the open ocean where they form nearly isolated local tectonic systems in these systems the rate of subduction is approximately compensated by the rate of upper plate extension and migration of the system across the oceanic region may be very rapid for example the horseshoe seamounts located about 800 km offshore in the eastern north atlantic may be the active expression of an east dipping westwardly migrating retreating subduction boundary that has evolved from the betic cordillera rif system active in miocene time and may now be progressing across the atlantic at approximately 50 mm yr an analogous situation may be represented by the scotia arc system a westward dipping retreating subduction system located between the south american and antarctic plates which may have escaped into the south atlantic ocean from a zone of crustal shortening in the andes and is now progressing across the atlantic at a rate of about 80 mm yr

receiver function images of the base of the lithosphere in the alboran sea region summary we analyse data from seismic stations surrounding the alboran sea between spain and north africa to constrain variations of the lithosphere asthenosphere boundary lab in the region the technique used isthereceiver function technique which usess to pconverted teleseismic waves at the lab below the seismic stations we confirm previous data suggesting a shallow 60 90km lab beneath the iberian peninsula and we observe a similarly shallow lab beneath the alboran sea where the lithosphere becomes progressively thinner towards the east a deeper lab 90 100km is observed beneath the betics the south of portugal and morocco the structure of the lab in the entire region does not seem to show any indication of subduction related features we also observe good p receiver function signals from the seismic discontinuities at 410 and 660km depth which do not indicate any upper mantle anomaly beneath the entire region this is in agreement with the sparse seismic activity in the mantle transition zone suggesting the presence of only weak and regionally confined anomalies

the quest for the africa eurasia plate boundary west of the strait of gibraltar the missing link in the plate boundary between eurasia and africa in the central atlantic is presented and discussed a set of almost linear and sub parallel dextral strike slip faults the swim1 faults that form a narrow band of deformation over a length of 600 km coincident with a small circle centred on the pole of rotation of africa with respect to eurasia was mapped using a new swath bathymetry compilation available in the area offshore sw portugal these faults connect the gloria fault to the rif tell fault zone two segments of the plate boundary between africa and eurasia the swim faults cut across the gulf of cadiz in the atlantic ocean where the 1755 great lisbon earthquake m 8 5 8 7 and tsunami were generated providing a new insight on its source location

geodynamic evolution of the lithosphere and upper mantle beneath the alboran region of the western mediterranean constraints from travel time tomography an edited version of this paper was published by the american geophysical union copyright 2000 agu see also http www agu org pubs crossref 2000 2000jb900024 shtml http atlas geo cornell edu morocco publications calvert2000 htm

geophysical model of the lithosphere across the variscan belt of sw iberia multidisciplinary assessment abstract a multidisciplinary geophysical study along a large seismic transect in the sw iberian peninsula has been carried out this study integrates the crustal structure geometry and composition obtained from normal incidence and wide angle seismic reflection data with other observables geoid gravity and topography the internal architecture of the lithosphere across the variscan orogen of sw iberia is constrained by the 300 km long high resolution deep normal seismic reflection iberseis transect the most prominent feature imaged by the seismic survey is the iberseis reflective body irb a 140 km long high amplitude reflective body located in the middle crust of the northern half of the transect the seismic velocity vp distribution within the crust and the upper mantle is constrained by two wide angle seismic transects acquired in the same area the velocity models show a complex crust with a specially complex middle crust which features higher velocities than the average continental crust also the wide angle data revealed that the irb is characterized by high velocities this feature was then interpreted as sill like structure built up by a series of mafic intrusions therefore a key issue is to study if this relatively mafic crust is consistent with other geophysical observables based on the velocity models two lithospheric density models have been derived along the iberseis wide angle transects the geoid gravity and topography response of these models have been calculated using a finite elements code that solves simultaneously the geopotential lithostatic and heat flow equations the resulting values are then compared with the measured observables and the crustal and lithospheric mantle geometry and density is modified until the best fit is obtained the initial density models calculated from the seismic data adjust quite well to the real potential field data however minor modifications have been required in order to properly fit the observables the final density models are consistent with the existence of relatively high density bodies in the mid crust providing further support to the seismic interpretation in addition they place new constraints on the location of the lithosphere asthenosphere boundary and on the tectonic evolution of sw iberia

seismic anisotropy beneath southern iberia from sks splitting abstract seismic anisotropy of the south iberian upper mantle is investigated using shear wave splitting of sks phases we analyzed teleseismic events recorded by sixteen permanent broadband stations installed on the southern iberian peninsula and in northern africa and we determined fast polarization directions and delay times t between fast and slow components the area of investigation extends across two important geological structures in the variscan iberian peninsula the variscan iberian massif in its center and the gibraltar arc in the southeast that represents the most westerly alpine belt in the western mediterranean shear wave splitting measurements from stations in the betic domain show homogeneous ene wsw fast directions nearly parallel to the trend of the mountain belt and smooth spatial variations stations in the north toward the southern part of the variscan iberian massif show homogeneous fast directions however trending ns to ne sw different from those recorded in the betic these observations may reflect a post hercynian variscan deformation of the ossa morena zone related to the main stages in the tectonic evolution of this part namely transpressional stage transtensional stage and shortening episode or a deformation related to the posterior alpine orogeny along the gibraltar arc we observe a smoothly varying trend changing from ene wsw in the eastern betics to ns in the area of gibraltar and ceuta following more or less the general trend of the mountain belt around the alboran sea and the coastline since a similar rotation is also visible in results from pn anisotropy this suggests that the anisotropy is vertically coherent starting from just below the moho comparing the anisotropy pattern expected from various geodynamic models with the observed sks splitting suggests that the anisotropy is best explained by a model of slab rollback rather than by delamination models

tethys atlantic interaction along the iberia africa plate boundary the betic rif orogenic system abstract initial se dipping slow subduction of the ligurian tethys lithosphere beneath africa from late cretaceous to middle oligocene twisting to a later faster e dipping subduction of the subcrustal lithosphere is proposed as an efficient geodynamic mechanism to structure the arcuate betic rif orogenic system this new subduction related geodynamic scenario is supported by a kinematic model constrained by well dated plate reconstructions tectonic sedimentary and metamorphic data sets the slow initial se dipping subduction of the ligurian tethys realm beneath the malaguide upper plate unit is sufficient to subduct alpujarride and nevado filabride rocks to few tens of kilometers of depth in middle eocene times the shift from se to e dipping subduction during latest oligocene early miocene was possibly caused by both the inherited geometry of the highly segmented ligurian tethys domain and by the fast roll back of the subducted lithospheric slab the early miocene rather synchronous multiple crustal and subcrustal processes comprising the collision along the betic front the exhumation of the hp lt metamorphic complexes the opening of the alboran basin its flooring by hp alpujarride rocks and subsequent ht imprint can be explained by the fast nw and w directed roll back of the ligurian tethys subcrustal lithospheric slab the w retreat of the ligurian tethys lithosphere in middle late miocene times could partly explain the initiation of its lateral tear and consequent subcrustal processes from latest miocene onward the betic rif system evolved under both the northerly push of africa resulting in tightening at crustal and subcrustal levels and by the distinct current dynamics of the steep lithospheric slab the sw directed scape of the rif fold belt is one of the most striking evidences linked to the recent evolution of the squeezed betic rif system between africa and iberia

geophysical evidence of a mantle derived intrusion in sw iberia 1 deep seismic reflection data acquired as part of the sw iberia europrobe project across the transpressional variscan orogen sample three tectonic terranes the south portuguese zone the ossa morena zone and the central iberian zone the seismic data reveal the existence of a mid crustal reflective body 140 km long and of variable thickness up to 5 km the iberian reflective body the conductivity image provided by coincident mt soundings the amplitude characteristics of the seismics mineralization studies related to magmatic ore deposits and the surface geology suggest that the irb is a mantle derived mafic intrusion the geophysical geological and petrological data suggest that the irb is most probably an early carboniferous approximately at 350 340 ma mantle derived intrusion possibly linked to plume activity that took place in europe in the carboniferous and permian

a rapid method to map the crustal and lithospheric thickness using elevation geoid anomaly and thermal analysis application to the gibraltar arc system atlas mountains and adjacent zones we present a method based on the combination of elevation and geoid anomaly data together with thermal field to map crustal and lithospheric thickness the main assumptions are local isostasy and a four layered model composed of crust lithospheric mantle sea water and the asthenosphere we consider a linear density gradient for the crust and a temperature dependent density for the lithospheric mantle we perform sensitivity tests to evaluate the effect of the variation of the model parameters and the influence of rms error of elevation and geoid anomaly databases the application of this method to the gibraltar arc system atlas mountains and adjacent zones reveals the presence of a lithospheric thinning zone sw ne oriented this zone affects the high and middle atlas and extends from the canary islands to the eastern alboran basin and is probably linked with a similarly trending zone of thick lithosphere constituting the western betics eastern rif rharb basin and gulf of cadiz a number of different even mutually opposite geodynamic models have been proposed to explain the origin and evolution of the study area our results suggest that a plausible slab retreating model should incorporate tear and asymmetric roll back of the subducting slab to fit the present day observed lithosphere geometry in this context the lithospheric thinning would be caused by lateral asthenospheric flow an alternative mechanism responsible for lithospheric thinning is the presence of a hot magmatic reservoir derived from a deep ancient plume centred in the canary island and extending as far as central europe

crustal structure of the transpressional variscan orogen of sw iberia sw iberia deep seismic reflection profile iberseis 1 iberseis a 303 km long 20 s deep seismic reflection profile was acquired across the variscan belt in sw iberian peninsula the acquisition parameters were designed to obtain a high resolution crustal scale image of this orogen the seismic profile samples three major tectonic terranes the south portuguese zone the ossa morena zone and the central iberian zone which were accreted in late paleozoic times these terranes show a distinctive seismic signature as do the sutures separating them late strike slip movements through crustal wedges are apparent in the seismic image and have strongly modified the geometry of sutures the upper crust appears to be decoupled from the lower crust all along the seismic line but some deformation has been accommodated at deeper levels a sill like structure is imaged in the middle crust as a 1 2 s thick and 175 km long high amplitude conspicuous reflective band it is interpreted as a great intrusion of mafic magma in a midcrustal decollement taking into account surface geological data and the revealed crustal architecture a tectonic evolution is proposed for sw iberia which includes transpressional collision interacting during early carboniferous with a mantle plume the moho can be identified along the entire transect as subhorizontal and located at 10 to 11 s indicating a 30 35 km average crustal thickness its seismic signature changes laterally being very reflective beneath the south portuguese zone and the central iberian zone but discontinuous and diffuse below the ossa morena zone

elastic anelastic regional structures for the iberian peninsula obtained from a rayleigh wave tomography and a causal uncoupled inversion the elastic and anelastic structure of the lithosphere and asthenosphere of the iberian peninsula is derived by means of tomographic techniques applied to local phase and group velocities and local attenuation coefficients of rayleigh wave fundamental mode the database consists of surface wavetrains recorded at the broadband stations located in the iberian peninsula on the occasion of the iliha project path averaged phase and group velocities and attenuation coefficients were previously obtained by standard filtering techniques of surface wavetrains and subsequently local dispersion curves were computed according to the yanovskaya ditmar formulation first a principal component analysis pca and the average linkage al clustering algorithm are applied to these local values in order to classify the iberian peninsula in several rather homogeneous domains from the viewpoint of the similarity of the corresponding local dispersion curves without previous seismotectonic constraints second averaged phase and group velocities and attenuation coefficients representing each homogeneous region are used to derive the respective elastic and anelastic models of the lithosphere and asthenosphere this purpose is achieved by using the uncoupled causal inversion of phase and group velocities and attenuation coefficients the main features of the homogeneous regions are discussed by taking as reference the hercynic alpine and neogene domains of the iberian peninsula and two questions affecting the reliability of the elastic anelastic models are revised first the coherence of the shear velocity and q 1 models obtained by causal uncoupled inversion for each region is analysed second the influence of the causal phase and group velocities on the shear velocity models is evaluated by comparing elastic and anelastic models derived from causal uncoupled inversion with those deduced from non causal inversion

delamination in collisional orogens thermomechanical modeling 1 modes of mantle delamination in collision zones are discussed in the light of 2d numerical modeling freely evolving thermomechanical models take into account phase changes in the mantle and melting in the crust distinct modes are identified in which orogens undergo mantle delamination concurrently or after collision delamination propagates along the moho of the subducted plate together with the retreating trench provided that slab pull is sufficient and that the meta stability of the crust lithospheric mantle interface is overcome topography is an instantaneous response to delamination and migrates with the focused and localized separation between crust and lithospheric mantle delamination front early exhumation of high pressure rocks is followed by exhumation of high temperature partially molten rocks convective stabilization of delamination outlasts slab break offs and impedes renewed build up of mechanically strong lithospheric mantle by static cooling parameter studies investigate the sensitivity of delamination to the age of the subducted oceanic plate the collision rate the mantle rheology and explore the effects of melting and sedimentation mantle flow patterns that form around delamination and subduction are sensitive to and often limited by the semi permeable 670 km spinel perovskite transition demonstrating that phase changes are essential factors delamination may account for the formation of complex boundary zones between continents such as between africa and europe in the mediterranean where transient compression and extension the lack of mantle lithosphere and the exhumation of high grade metamorphic core complexes are features also obtained in our modeling results

seismic sources on the iberia african plate boundary and their tectonic implications the plate boundary between iberia and africa has been studied using data on seismicity and focal mechanisms the region has been divided into three areas a the gulf of cadiz b the betics alboran sea and northern morocco and c algeria seismicity shows a complex behavior large shallow earthquakes h 30 km occur in areas a and c and moderate shocks in area b intermediate depth activity 30 h 150 km is located in area b the depth earthquakes h 650 km are located to the south of granada moment rate slip velocity andhvalues have been estimated for shallow shocks and show similar characteristics for the gulf of cadiz and algeria and quite different ones for the central region focal mechanisms of 80 selected shallow earthquakes 8 mb 4 show thrust faulting in the gulf of cadiz and algeria with horizontal nnw sse compression and normal faulting in the alboran sea with e w extension focal mechanisms of 26 intermediate depth earthquakes in the alboran sea display vertical motions with a predominant plane trending e w solutions for very deep shocks correspond to vertical dip slip along n s trends frohlich diagrams and seismic moment tensors show different behavior in the gulf of cadiz betic alboran sea and northern morocco and northern algeria for shallow events the stress pattern of intermediate depth and very deep earthquakes has different directions vertical extension in the nw se direction for intermediate depth earthquakes and tension and pressure axes dipping about 45 o for very deep earthquakes regional stress pattern may result from the collision between the african plate and iberia with extension and subduction of lithospheric material in the alboran sea at intermediate depth the very deep seismicity may be correlated with older subduction processes

crustal structure along a traverse across the middle and high atlas mountains derived from seismic refraction studies in 1986 explosion seismic investigations have been carried out along a traverse of about 350 km length running from nnw to sse crossing the high and middle atlas two further profiles run e w through the middle and nw se through the high atlas

imaging the colliding indian and asian lithospheric plates beneath tibet 1 a high resolution image of the base of the lithosphere from s to p converted seismic waves revealed the collision architecture of the indian and asian continental plates beneath the tibetan plateau the base of the indian lithosphere dips northward from a depth of 160 km beneath the himalayas to a depth of 220 km just south of the bangong suture the base of the asian lithosphere is nearly horizontal at the depth of 160 180 km from central to northern tibet there is a vertical gap of about 50 km between indian and asian lithospheres our observation of a well defined thick lithosphere throughout the entire plateau is not consistent with models of wholesale convective instability of a thickened mantle lithosphere which would predict a very thin asian lithosphere the hypothesized sequential southward subduction of tibetan and asian continental lithospheres leading to the growth of the tibetan plateau if correct cannot be occurring below 180 km depth our results along with available geological and geophysical data strongly support that the plateau is predominantly formed by a relatively coherent north dipping subducted indian continental lithosphere in the south which presently can be traced to the middle of the plateau and a south dipping subducted asian lithosphere in the north at a shallower depth

the s receiver functions synthetics and data example summary recently the s receiver function method has been successfully developed to identify upper mantle interfaces s receiver functions have the advantage of being free of s wave multiple reflections and can be more suitable than p receiver functions for studying mantle lithosphere however because of specific ray geometry and interference of diverse phases the s receiver function method has some technical difficulties and limitations we use synthetic seismograms to demonstrate the feasibility and limitations of s receiver functions for studying mantle structures full wavefield seismograms were calculated using the reflectivity method and processed to generate synthetic s receiver functions for s sks and scs waves results show that s receiver functions can be obtained from waveforms of s sks and scs waves the synthetic s receiver functions for these incident waves show s to p converted phases at all discontinuities in the crust and upper mantle useful ranges of epicentral distances for calculation of s receiver functions are 55 85 for s 85 for sks and 50 75 for scs waves we apply both the s and p receiver function methods to data recorded at broadband station ykw3 in northwest canada the study shows that there is significant agreement among different receiver function methods and demonstrates the usefulness of s receiver functions for imaging the mantle lithosphere

discussion of origins of hinterland basins to the rif betic cordillera and carpathians abstract the hinterland basins of the rif betic cordillera western alboran sea and the carpathians pannonian basin are in part composed of a thick in excess of 3 4 km thermal sag basin sequence the underlying crust has been thinned to 25 km in parts of the pannonian basin and to 15 km in parts of the alboran sea modern tectonic models for these areas envision tectonic collision and thickening of the crust followed by crustal thinning either by gravitational collapse back arc extension or a combination of the two contemporaneous with thrusting basin and range type extension has been envisioned for parts of these extensional collapse systems extensional features are common and they interact in a complex way with strike slip systems flexural cantilever modelling agrees with earlier mckenzie type pure shear modelling of the extensional systems in suggesting that extension alone cannot generate sufficient thermal decay to explain the great thickness of the sag basins associated with the alboran sea and pannonian basin consequently it is suggested that uplift of the asthenosphere accompanying subduction roll back is an important factor in the evolution of these basins roll back of the mantle lithosphere permits hot asthenospheric mantle to upwell and lie close to the base of the crust initially uplift and erosion of the crust overlying the asthenosphere occurs as the thermal perturbation cools the crust thermally subsides to produce a large sag basin

lithospheric structure of the aegean obtained from p and s receiver functions combined p and s receiver functions from seismograms of teleseismic events recorded at 65 temporary and permanent stations in the aegean region are used to map the geometry of the subducted african and the overriding aegean plates we image the moho of the subducting african plate at depths ranging from 40 km beneath southern crete and the western peloponnesus to 160 km beneath the volcanic arc and 220 km beneath northern greece however the dip of the moho of the subducting african plate is shallower beneath the peloponnesus than beneath crete and rhodes and flattens out beneath the northern aegean observed p to s conversions at stations located in the forearc indicate a reversed velocity contrast at the moho boundary of the aegean plate whereas this boundary is observed as a normal velocity contrast by the s to p conversions our modeling suggests that the presence of a large amount of serpentinite more than 30 in the forearc mantle wedge which generally occurs in the subduction zones may be the reason for the reverse sign of the p to s conversion coefficient moho depths for the aegean plate show that the southern part of the aegean crustal thickness of 20 22 km has been strongly influenced by extension while the northern aegean sea which at present undergoes the highest crustal deformation shows a relatively thicker crust 25 28 km this may imply a recent initiation of the present kinematics in the aegean western greece crustal thickness of 32 40 km is unaffected by the recent extension but underwent crustal thickening during the hellenides mountains building event the depths of the aegean moho beneath the margin of the peloponnesus and crete 25 28 and 25 33 km respectively show that these areas are also likely to be affected by the aegean extension even though the cyclades crustal thickness of 26 30 km were not significantly involved in this episode the aegean lithosphere asthenosphere boundary lab mapped with s receiver functions is about 150 km deep beneath mainland greece whereas the lab of the subducted african plate dips from 100 km beneath crete and the southern aegean sea to about 225 km under the volcanic arc this implies a thickness of 60 65 km for the subducted african lithosphere suggesting that the aegean lithosphere was not significantly affected by the extensional process associated with the exhumation of metamorphic core complexes in the cyclades

a step fault in central betics associated with lateral lithospheric tearing at the northern edge of the gibraltar arc subduction system abstract we study the crustal and lithospheric mantle structure under central betics in the westernmost mediterranean region by migrating p receiver functions along a dense seismic profile 2 km interstation distance the profile north south oriented probes the crustal structure of different geological units from the alboran domain in the south with metamorphic rocks through the external zones with sedimentary rocks to the variscan terrains of the iberian massif in the north from north to south the moho depth increases from 30 km to 46 km underneath the guadix basin due to the underthrusting of the iberian crust below the alboran crust and suddenly shallows to 30 km underneath the internal zones with a step of 17 km this sharp moho step correlates well with a lithospheric step of 40 km where the thickness of the lithosphere changes abruptly from 100 km in the north to 50 km in the south we interpret this sharp and prominent lithospheric step as the termination of the iberian lithosphere caused by a near vertical step subduction transform edge propagator fault that continues towards the surface as a positive flower tectonic structure of crustal scale this step fault is located at the northern edge of the narrow westernmost mediterranean subduction system facilitating the slab rollback motion towards the west the sharp termination of the iberian lithosphere occurs under the contact between the alpujarride and the nevado filabride complexes of the alboran domain in an ene wsw right lateral transpressive shear zone the thickest crust and lithosphere do not correlate with the highest topography along the profile suggesting that this high topography is a combined effect of the positive flower structure and the push up of the asthenosphere produced by the removal of the iberian lithosphere

topography of the transition zone seismic discontinuities phase transformations in mantle mineralogies probably cause the transition zone seismic discontinuities nominally at 410 520 and 660 km depth thermodynamic principles govern phase transformations making them sensitive to changes in the mantle s ambient conditions through the thermodynamic response changes in temperature or composition shift the transformation to a different pressure creating topography on a level discontinuity with this use as an exploratory tool for the mantle in mind we review the basic seismological and phase equilibrium concepts underlying the detection and interpretation of the seismic wave arrivals associated with the transition zone discontinuities reviewing the evidence for and against the phase transition model we conclude that it is viable and describe how discontinuities have been and can be used to probe the physical and chemical state of the transition zone

gps constraints on africa nubia and arabia plate motions summary we use continuously recording gps cgps and survey mode gps sgps observations to determine euler vectors for relative motion of the african nubian arabian and eurasian plates we present a well constrained eurasia nubia euler vector derived from 23 igs sites in europe and four cgps and three sgps sites on the nubian plate 0 95 4 8 n 21 8 4 3 e 0 06 0 005 myr 1 we see no significant 1m m yr 1 internal deformation of the nubian plate the gps nubian eurasian euler vector differs significantly from nuvel 1a 21 0 4 2 n 20 6 0 6 e 0 12 0 015 myr 1 implying more westward motion of africa relative to eurasia and slower convergence in the eastern mediterranean the arabia eurasia and arabia nubia gps euler vectors are less well determined based on only one cgps and three sgps sites on the arabian plate the preliminary arabia eurasia and arabia nubia euler vectors are 27 4 1 0 n 18 4 2 5 e 0 40 0 04 myr 1 and 30 5 1 0 n 25 7 2 3 e 0 37 0 04 myr 1 respectively the gps arabia nubia euler vector differs significantly from nuvel 1a 24 1 1 7 n 24 0 3 5 e 0 40 0 05 myr 1 but is statistically consistent at the 95 per cent confidence level with the revised euler vector reported by chu gordon based on a re evaluation of magnetic anomalies in the red sea 31 5 1 2 n 23 0 2 7 e 0 40 0 05 myr 1 the motion implied in the gulf of aqaba and on the dead sea fault dsf by the new gps nubia arabia euler vector i e ignoring possible sinai block motion and possible internal plate deformation grades from pure left lateral strike slip in the gulf and on the southern dsf with increasing compression on the central and northern dsf with relative motion increasing from 5 6 to 7 5 mm yr 1 1m m yr 1 from south to north along the northern dsf i e north of the lebanon restraining bend motion is partitioned between 6 1m m yr 1 left lateral motion parallel to the fault trace and 4 1m m yr 1 faultnormal compression relative motions on other plate boundaries including the anatolian and aegean microplates derived from the gps euler vectors agree qualitatively with the sense of motion indicated by focal mechanisms for large crustal earthquakes m 6 where data are available on fault slip rates on plate bounding faults north anatolian fault east anatolian fault dead sea fault red sea rift they are generally lower than but not significantly different from the full plate motion estimates suggesting that the majority of relative plate motion is accommodated on these structures

seismic images of the biggest crash on earth in plate tectonics the upper layer of earth the lithosphere consists of rigid plates that shift over geological time scales data from global positioning surveys have estimated that the entire indian subcontinent has moved over the past 50 years about 2 m to the north diving slowly underneath tibet this giant collision has been ongoing for 50 million years and has thrown up the highest mountains as well as the largest and highest plateau on earth not only is the world climate strongly influenced by this massive plateau average elevation of 5000 m but the collision also causes catastrophic earthquakes in southern central and eastern asia

the upper mantle transition zone beneath the ibero maghrebian region as seen by teleseismic pds phases abstract we investigate the upper mantle transition zone thickness beneath the ibero maghrebian region using teleseismic events recorded at 258 seismic stations from the iberarray of the spanish topoiberia project for this purpose the 410 km and 660 km depth discontinuities are mapped through the detection of p to s conversions in order to add consistency and robustness to the detections the final results are based on a joint analysis of receiver functions and two different cross correlation functionals discontinuity depths are determined using time corrections obtained from a 3 d velocity model this study presents the first high resolution topography maps for the 410 and 660 discontinuities which show lateral variations in the transition zone thickness beneath the study area the results are discussed to add new constraints on temperature and composition to seismic velocity anomalies observed in the transition zone beneath the controversial ibero maghrebian region we obtained a thickened transition zone beneath the alboran sea and the north balearic sea suggesting low transition zone temperatures and coinciding with the position of the high velocity anomalies in the tomographic images related to the betic alboran slab and the alpine tethys remnant slab respectively a dominantly thinned transition zone beneath the gulf of cadiz and its surroundings suggest high mantle temperatures we also found evidences of the presence of a low velocity layer atop the 410 discontinuity beneath the study area

active continental subduction beneath the betic cordillera and the alboran sea p and s wave seismic tomography detect a low velocity anomaly in the upper mantle beneath the betic cordillera and the alboran sea region the anomaly is associated with the intermediate depth seismicity h

active tectonics of the western mediterranean geodetic evidence for rollback of a delaminated subcontinental lithospheric slab beneath the rif mountains morocco surface deformation in morocco derived from five years of global positioning system gps survey observations of a 22 station network four continuously recording gps cgps stations and four international gnss service igs stations in iberia indicates roughly southward motion 3 mm yr of the rif mountains morocco relative to stable africa motion of the rif is approximately normal to the direction of africa eurasia relative motion which is predominantly strike slip and results in shortening of the rif and subsequent crustal extension of the adjacent alboran sea region the sense and the n s asymmetry of the observed deformation i e no evidence for north directed shortening in the betic mountains north of the alboran sea cannot be easily explained in terms of crustal plate interactions suggesting that dynamic processes below the crust are driving the recent geologic evolution of the western mediterranean the model that best fits the observations involves delamination and southward rollback of the african lithospheric mantle under the alboran and rif domains

eclogite as a seismic marker in subduction channels seismic velocities anisotropy and petrofabric of cabo ortegal eclogite tectonites spain high pressure sheath like fold nappes made of normal mid ocean ridge basalt n morb eclogites high pressure volcanic arc granulites arc root lithospheric mantle peridotites and shallow crustal volcanosedimentary gneisses were amalgamated at deep realms of an eohercynian orogenic channel and currently crop out in the cabo ortegal complex compressional seismic wave velocity measurements determined in eclogite at confining pressures of 600 mpa range from 8 4 to 7 3 km s whereas anisotropy varies between 0 7 and 3 2 shear wave velocities range from 4 8 to 4 2 km s and the respective anisotropies vary between 0 1 and 3 4 the poisson9s ratios are low 0 25 0 265 independent of the degree of retrogression or deformation seismic velocities and anisotropy are related to the fabric of omphacite and calculated eclogite anisotropy is not symmetrical with respect to the tectonic fabrics calculated seismic reflection coefficients induced by lithological structural and rock petrofabric variations of eclogites show that these can be identified as reflectors imprinting a particular penetrative and dipping fabric to discrete seismic profile segments of paleosubduction settings

crustal structure beneath the iberian peninsula and surrounding waters a new compilation of deep seismic sounding results abstract we present here an updated compilation of crustal parameters beneath the iberian peninsula and surrounding waters inferred from extensive deep seismic exploration performed in the last three decades firstly the more relevant experiments developed in both terrestrial and marine domains are revisited together with the corresponding seismic velocity depth models published that reveal the characteristics of the different tectonic domains sampled including oceanic zones continental margins orogenic and rift belts the results are summarized in three crustal transects sketched along representative directions secondly we compiled the moho depths along all the available seismic profiles to produce a geo referred database this database has then been interpolated using kriging algorithms to obtain a continuous moho depth model in the form of a regular grid file this integrative moho map for a key area in the western mediterranean documenting the interaction between european and african plates can contribute to constrain further regional studies either at crustal lithospheric or mantle scales

evidence for active subduction beneath gibraltar we report on a marine seismic survey that images an active accretionary wedge west of gibraltar ramp thrusts offset the seafloor and sole out to an east dipping decollement indicating ongoing westward vergent tectonic shortening new traveltime tomographic re sults image a slab of oceanic lithosphere descending from the atlantic domain of the gulf of cadiz passing through intermediate depth 60 120 km seismicity beneath the west ernmost alboran sea and merging with a region of deep focus earthquakes 600 660 km below granada spain together these new data provide compelling evidence for an active east dipping subduction zone

seismic receiver functions and the lithosphere asthenosphere boundary abstract the lower boundary of the lithospheric plates has remained as an enigmatic boundary for seismologists since it is relatively poorly observed by seismic means there is traditionally a broad consensus that the asthenosphere is observable as a low velocity zone by seismic surface waves seismic techniques which use shorter period p to s or s to p converted body waves are now far enough developed to be successful in observing such a low velocity zone with a higher resolution the principle of this technique the so called receiver function technique is that a strong teleseismic mother phase e g p s pp or sks incident from below on any seismic discontinuity beneath a station produces a converted phase ps or sp which indicates its depth and properties we discuss details of this technique a sufficient number of such observations exist already to indicate that the top of the low velocity zone is a globally observable discontinuity and it is sharper than previously thought an intriguing observation is that in some cratons the new seismic data indicate that the low velocity zone exists already at shallower depths than obtained from surface waves this confirms earlier results from controlled source observations thybo and perchuc 1997 we discuss possible interpretations of this shallow low velocity zone in cratonic regions

lithospheric thickness estimation beneath northwestern south america from an s wave receiver function analysis we make use of the s to p receiver function technique beneath colombia and neighboring regions to make a first order approximation of the depth of the lithosphere asthenosphere boundary lab and therefore of lithospheric thickness a deconvolution technique was used to calculate the receiver functions and after a moveout correction and a time depth conversion lab depths for different tectonic regions of northwestern south america were obtained results are typically between 65 and 110 km consistent with previous estimates around the world and other regions in south america lithospheric thickness beneath an oceanic island in the caribbean is 80 km whereas for the ecuador colombia trench it is 65 km and around 100 km for the panama arc the transition to the continent is associated with an increase in lab depth where it can reach 110 km with no significant differences among terranes and or tectonic blocks