morphotectonic structure of the western part of the north aegean basin based on swath bathymetry abstract the morphotectonic structure of the north aegean basin is studied on the basis of a new detailed swath bathymetric survey the resulting bathymetric map is presented in reduction with 20 m isobaths the slope analysis gives an accurate scheme of the geometry of the basin and distinction of several sub basins approximately 20 the overall basin geometry is a rectangular tetrahedron shaped by the major slope discontinuity separating the continental platform from the continental slope the area distribution with depth shows a maximum at depths between 300 and 450 m along the sub horizontal edge of the continental platform and at depths between 1000 and 1200 m at the basinal areas of the sub basins the separation of the western part of the north aegean basin from the eastern part saros bay is very clear in the area between limnos and thasos with a maximum depth of 490 m the 3 2 of the basin area is characterized by slope values 20 which correspond to active fault zones their trend is ne sw n46 and nw se n136 some secondary e w faults are also present within the basin with morphological expression only on the orientation of slopes

building the pamirs the view from the underside the pamir mountains are an outstanding example of extreme crustal shortening during continental collision that may have been accommodated by formation of a thick crust much thicker than is currently thought and or by continental subduction we pre sent new petrologic data and radiometric ages from xenoliths in miocene volcanic rocks in the southeastern pamir mountains that suggest that gondwanan igneous and sedimentary assemblages were underthrust northward buried to 50 80 km during the ear ly stage of the india asia collision and then heated and partly melted during subsequent thermal relaxation before finally being blasted to the surface these xenoliths the deepest crustal samples recovered from under any active collisional belt provide direct evidence for early cenozoic thickening of the pamirs and lower crustal melting during collision the xenoliths also suggest that the present mountain range was a steady state elevated plateau for most of the cenozoic

probing the basement of southern tibet evidence from crustal xenoliths entrained in a miocene ultrapotassic dyke abstract a variety of felsic and mafic granulites and ultramafic rocks occur as xenoliths within a 12 7 ma ultrapotassic dyke intruding xigaze flysch immediately to the north of the yarlung tsangpo suture zone in southern tibet garnet clinopyroxene plagioclase quartz thermobarometry on mafic granulite xenoliths gives temperatures of 1130 1330 c and pressures between 22 and 26 kbar indicating equilibration in the high pressure and ultrahigh temperature granulite field and defining a geotherm of c 16 c km 1 ultramafic xenoliths consist mainly of hornblende and biotite probably of restitic crustal rather than mantle origin and attained peak metamorphic conditions of 920 1130 c and 17 24 kbar whereas felsic granulites equilibrated at 870 900 c at an inferred pressure of 17 kbar in situ u th pb laser ablation inductively coupled plasma mass spectrometry dating of zircons shows that protoliths may include proterozoic basement rocks late cretaceous calc alkaline tonalites of the gangdese batholith root and or remnants of a neo tethyan oceanic arc certain zircons from a felsic granulite and an ultramafic xenolith have mean 206 pb 238 u ages of 16 8 0 9 ma and 15 6 0 6 ma respectively and monazites from a micaceous xenolith yielded a mean 208 pb 232 th age of 14 4 0 4 ma these results show that the southern tibet basement reached a thickness of c 80 km by 17 14 ma at the latest and has remained unchanged until the present day supplementary material mineral analyses used for pressure temperature estimations and results of 40 ar 30 ar laser single grain fusion experiments are available at http www geolsoc org uk sup18325

crustal strain in central greece from repeated gps measurements in the interval 1989 1997 summary a 66 station gps network spanning central greece first observed in 1989 has been occupied fully on three occasions june 1989 october 1991 and may 1993 subsets of this network bounding the gulf of korinthos have also been occupied in june 1995 october 1995 may 1996 and september october 1997 the first three occupations were processed using a fiducial gps methodology whereas later surveys were processed using code precise orbits combination of data from different surveys to yield smooth site velocities requires global network translations at each epoch to compensate for errors in the realization of the reference frame this method provides a posteriori estimates of the relative coordinate errors and reference frame noise only one earthquake the 1995 june 15 egion event has caused significant local coseismic displacement and its effects on the interseismic velocity field are removed using an elastic dislocation model we constrain the orientation of the 100 yr triangulation gps velocity estimates of davies et al 1997 using 14 sites common to the two networks the goodness of fit of this transformation indicates that the short term and 100 yr geodetic estimates of deformation are highly compatible we infer that short term geodetic studies are capable of determining longer term deformation rates provided that transient local effects can be modelled from the combined velocity field we estimate principal strains and rigid body rotation rates at points on a regular grid using data from neighbouring sites strain rates are high within the gulf of korinthos and much lower elsewhere the extension rate across the gulf of korinthos increases from east to west comparison of the extension rate with historical and recent rates of seismic release of strain reveals significant medium term seismic hazard in the western gulf of korinthos and may also indicate long term aseismic strain

neogene recent extension on the eastern flank of mount olympus greece abstract the olympus massif of ne greece comprises metamorphosed and deformed triassic and cretaceous eocene carbonates considered to represent part of the passive southwestern margin of neotethys which separated the apulia plate of mainland greece from southern europe in the mesozoic ocean closure in the early tertiary led to subduction of this passive margin as a result of which the olympus carbonates were tectonically overridden in the eocene by a series of thrust sheets consisting of locally high p t blueschist metamorphosed continental margin sediments basement granitoid gneisses and ophiolitic rocks following collision uplift of the olympus carbonates by 6 8 km was accomplished by early neogene ductile and late neogene recent brittle normal faulting which exposed the carbonates in the form of a structural window through the overriding thrust stack the focus of this exhumation occurred on the eastern flank of the massif where a thick calc mylonite with down to the east sense of shear indicators and a prominent zone of nnw to nw trending brittle normal faults separate the carbonates from telescoped structurally overlying units published 40 ar 39 ar microcline ages that indicate a thermal perturbation close to the contact zone in excess of 100 150 c at 16 23 ma early miocene are taken to date the onset of ductile extension and imply long term uplift rates of 0 4 to 1 km m y degradation of pleistocene glacial features on the olympus massif and the presence on its eastern piedmont of deeply incised streams erosional terraces and fault scarps that offset the sedimentary deposits of three cycles of pleistocene glacial deposition units 1 3 testify to its continuing uplift a prominent frontal fault offsets unit 2 by 150 m and several subsidiary nw trending normal faults with a cumulative displacement of 130 m offset a paleosol developed on unit 1 kinematic indicators indicate normal dip slip movement cumulative fault displacement for unit 1 exceeds 277 m yielding a minimum uplift rate of 1 3 mm yr given the oxygen isotope stage 7 mindel riss age of 210 ka proposed for the unit 1 paleosol cumulative offset of 196 m for the paleosol developed on unit 2 yields an uplift rate of 1 6 mm yr given its proposed isotope stage 5e riss wurm age of 125 ka this estimate is supported by longitudinal valley profile data that document 200 m of stream incision since unit 2 deposition and show the offset as reflecting uplift of the olympus massif rather than subsidence of the adjacent gulf of thermaikos assuming 1 8 ma for the base of the pleistocene these rates yield a total uplift range for the quaternary of 2 3 4 1 km consistent with the present 2 6 km height of olympus above the exposed frontal fault neogene uplift of olympus was likely facilitated by extension accompanying the opening of the aegean back arc basin during the miocene as a result of the southward retreat of the hellenic subduction zone for the pliocene recent uplift was likely facilitated by extension linked to the termination of dextral motion at the western end of the north anatolian fault associated with the westward tectonic escape of anatolia

mechanical basis for low angle normal faulting in the basin and range province low angle normal faults seem to violate the criterion that relates fault dip to stress orientation to explain such faults one must postulate a 45 rotation of principal stress directions at mid crustal depths which is difficult to understand on the basis of previous elastic crust models such a stress rotation is shown to be a natural consequence of a low viscosity lower crust

miocene volcanism in the lhasa block tibet spatial trends and geodynamic implications miocene ultrapotassic up shoshonitic p and calc alkaline ca volcanism is recognized widely over the tibetan plateau this volcanism occurred after the end of india s oceanic lithosphere subduction beneath the plateau ambiguities about the distribution and significance of this volcanism arise in part from a paucity of geochronologic and geochemical data we have sampled two volcanic fields in the lhasa block 1 the eastern edge of the zabuye salt lake central part of the block 2 the southwestern edge of the yangbajin graben major and trace elements display high k2o 6 06 6 54 over a wide range of sio2 75 03 55 30 na2o 1 32 3 30 and lree hree enrichment with a significant rare earth element fractionation 266 la yb n 6 42 as well as negative nb ta and ti anomalies these features indicate that our samples are chemically identical to the post collision miocene up to p volcanic rocks already identified all over the tibetan plateau and the southern plateau specifically but distinct from the ca rocks found in the lhasa block the miocene volcanics found in the lhasa block present greater chemical variation than the rest of the tibetan plateau 40 ar 39 ar ages on both sanidine and biotite gave ages ranging from 16 16 g 0 12 ma to 16 01 g 0 12 ma and 10 60 g 0 14 ma to 10 88 g 0 17 ma 2 c excluding systematic errors relative to fish canyon sanidine at 28 02 ma for zabuye salt lake and yangying geothermal field volcanics respectively these results are consistent with the range of previously published ages from this part of the tibetan plateau the presence of n s trending dikes and the location of the volcanic fields suggest that local e w extension in the lhasa block was coeval we propose that the synchronous up p and ca volcanism in the lhasa block between 23 and 8 ma is the result of progressively deepening northward subduction of indian continental lithosphere producing asthenospheric upwelling convective thinning delamination of lithospheric mantle fueled by the hot asthenosphere induced partial melting of an enriched sub continental mantle lithosphere as well as eclogitic lower crust this mechanism could also explain the local e w extension observed in the same period 18 10 ma we also propose that lateral migration of the deepening indian continental lithosphere mantle slab could explain the observed younger volcanism in the eastern part of the lhasa terrane

velocity and deformation fields in the north aegean domain greece and implications for fault kinematics derived from gps data 1993 2009 abstract gps rates based on data of an extended continuous and campaign type gps network in the north aegean domain are presented the data processed for the time period 1993 2009 is used to analyze the complex kinematic and deformation fields in the north aegean sea and adjacent regions the presence of slowly deforming areas is investigated southern bulgaria eastern macedonia and thrace move uniformly southward relative to eurasia 1 5 3 5 mm yr western macedonia epirus thessaly and central greece rotate rather coherently clockwise the region comprising the islands of limnos agios efstratios and alonnisos moves like a counterclockwise rotating slowly deforming block the new gps rates allow a quantification of the spatial change of strike slip motion and locking depth along the north aegean trough dextral strike slip motion diminishes from east toward west amounting to 21 2 mm yr along the saros basin and 12 5 mm yr south of the chalkidiki peninsula less than 5 mm yr 50 nstrain yr shear strain rate is transferred from the sporades islands pelion toward northern evia the locking depth is shallow for the ganos fault and the western saros basin 5 6 8 9 km it is deeper between the sporades islands and pelion 17 7 km corresponding to a more diffuse shear zone an elementary finite element model is applied to derive slip rates of the three main ene wsw to ne sw trending dextral strike slip faults in the north aegean large scale n s to nne ssw extension in the north aegean domain is analyzed by employing finite element and gps based strain rate analyses pronounced extension 100 nstrain is associated with known tectonic structures e g mygdonian graben northern gulf of evia in offshore areas such as the sporades basin the correspondence between gps derived extension rates and active fault structures is not entirely evident however important constraints are provided for seismotectonic interpretations

neogene extension and volcanism in the kunlun fault zone northern tibet new constraints on the age of the kunlun fault 1 the geology of the jingyu basin north tibet provides constraints on the relationship between localized e w extension in the qiangtang block and strike slip motion along the kunlun fault eocene to oligocene sw ne compression formed topographic relief in the present western kunlun shan pull apart basins started forming in the western kunlun ranges around 15 ma possibly coincident with the initiation of subduction of the tarim qaidam lithosphere under the kunlun shan extensional tectonism is still active and the jingyu basin is extending as a normal fault connected with the kunlun fault was recently active localized extension allows tertiary and quaternary shoshonitic magmas to reach the surface from crustal depths of 50 to 60 km miocene strike slip faulting indicates that the initiation of the kunlun strike slip fault is early neogene in age and that the total amount of horizontal movement that occurred along the fault has to be reconsidered

pressure temperature time paths of regional metamorphism i heat transfer during the evolution of regions of thickened continental crust the development of regional metamorphism in areas of thickened continental crust is investigated in terms of the major controls on regional scale thermal regimes these are the total radiogenic heat supply within the thickened crust the supply of heat from the mantle the thermal conductivity of the medium and the length and time scales of erosion of the continental crust the orogenic episode is regarded as consisting of a relatively rapid phase of crustal thickening during which little temperature change occurs in individual rocks followed by a lengthier phase of erosion at the end of which the crust is at its original thickness the principal features of pressure temperature time ptt paths followed by rocks in this environment are a period of thermal relaxation during which the temperature rises towards the higher geotherm that would be supported by the thickened crust followed by a period of cooling as the rock approaches the cold land surface the temperature increase that occurs is governed by the degree of thickening of the crust its conductivity and the time that elapses before the rock is exhumed sufficiently to be affected by the proximity of the cold upper boundary for much of the parameter range considered the heating phase encompasses a considerable portion of the exhumation decompression part of the ptt path in addition to the detailed calculation of ptt paths we present an idealized model of the thickening and exhumation process which may be used to make simple calculations of the amount of heating to be expected during a given thickening and exhumation episode and of the depth at which a rock will start to cool on its ascent path an important feature of these ptt paths is that most of them lie within 50 c of the maximum temperature attained for one third or more of the total duration of their burial and uplift and for a geologically plausible range of erosion rates the rocks do not begin to cool until they have completed 20 to 40 per cent of the total uplift they experience considerable melting of the continental crust is a likely consequence of thickening of crust with an average continental geotherm a companion paper discusses these results in the context of attempts to use metamorphic petrology data to give information on tectonic processes 1984 oxford university press

active tectonics of the north and central aegean sea summary in this paper we examine the connection between the westward motion of turkey relative to europe and the extension in and around the aegean sea the principal new data available since the last attempt to synthesize the tectonics of this region by mckenzie 1978 are much improved focal mechanisms of earthquakes constrained by p and sh body wave modelling as well as by first motions these mechanisms show that the faulting in the western part of the aegean region is mostly extensional in nature on normal faults with a nw to wnw strike and with slip vectors directed nnw to nne there is evidence from palaeomagnetism that this western region rotates clockwise relative to stable europe in the central and eastern aegean and in nw turkey distributed right lateral strike slip is more prevalent on faults trending ne to ene and with slip vectors directed ne palaeomagnetic data in this eastern region is more ambiguous but consistent with very small or no rotations in the northern part and possibly anticlockwise rotations relative to europe in the south the strike slip faulting that enters the central aegean from the east appears to end abruptly in the sw against the nw trending normal faults of greece the kinematics of the deformation is controlled by three factors the westward motion of turkey relative to europe the continental collision between nw greece albania and the apulia adriatic platform in the west and the presence of the hellenic subduction zone to the south as the right lateral slip on the north anatolian fault enters the aegean region it splays out becoming distributed on several parallel faults the continental shortening in nw greece and albania does not allow the rotation of the western margin of the region to be rapid enough to accommodate this distributed e w right lateral shear and thus leads to e w shortening in the northern aegean which is compensated by n s extension as the southern aegean margin can move easily over the hellenic subduction zone the dynamics of the system once initiated is self sustaining being driven by the high topography in eastern turkey and by the roll back of the subducted slab beneath the southern aegean the geometry of the deformation resembles the behaviour of a system of broken slats attached to margins that rotate in spite of its extreme simplicity a simple model of such broken slats is able to reproduce quantitatively most of the features of the instantaneous velocity field in the aegean region including the slip vectors and nature of the faulting in the eastern and western parts the senses and approximate rates of rotation the overall extensional velocity across the aegean and the distribution of strain rates as seen in the seismicity and topography or bathymetry and using geodetic measurements as part of this study we re examined the relation between the surface faulting and the focal parameters determined seismologically for the three large 1981 gulf of corinth earthquakes and reassessed the evidence for associating particular earthquakes in the sequence with observed surface faulting an important result is that in one of the events there is a resolvable discrepancy between the slip vector measured at the surface and that determined from the seismic body waves

late cenozoic extension in northeastern greece strymon valley detachment system and rhodope metamorphic core complex the strymon valley detachment system accommodated at least 25 km of extension at the northern margin of the aegean extensional province from middle miocene through early pliocene time the primary detachment surface is exposed as a gently southwest dipping low angle normal fault similar to those widely known in core complex settings of the u s basin and range province for more than 150 km along strike from the aegean sea coast in northeastern greece northward into the struma valley of southern bulgaria hanging wall rocks in the strymon valley detachment system moved in a s53 w direction relative to the footwall resulting ultimately in the tectonic unroofing of the rhodope metamorphic core complex several segments of the strymon valley detachment have previously been interpreted as thrust faults formed during a miocene compressional event our results negate the principal evidence for this event and imply instead that extensional deformation has characterized the northern aegean region since at least middle miocene time displacement ceased on the strymon valley detachment with the late pliocene development of the strymon and drama basins we propose that those basins together with the other principal basins of the northern aegean region are subsiding above an active northeast dipping extensional detachment zone that forms a unified kinematic system with the western offshore continuation of the dextral north anatolian strike slip fault the north aegean trough if this hypothesis is correct then the north aegean trough the western strands of the north anatolian fault and the principal modern depocenters of the northern aegean region may all have originated no earlier than late pliocene time

single bubble marine source offers new perspectives for lithospheric exploration abstract we present deep penetration seismic time sections obtained in the last two years with the single bubble pulse generating method using marine seismic airguns whole crustal penetration and resolution have been obtained on the ionian quasi oceanic basin and its margin on the continental crust of the aegean sea on the continental margins and oceanic basin of the gulf of biscay we show that this method is more efficient than others in radiating the lower frequencies returned by deep structure without loosing resolution hence it allows deep crustal imaging from relatively low power academic ships and if the method is applied to powerful industrial vessels it may open the subcrustal lithosphere to imaging

subsidence of the north aegean trough an alternative view the north aegean trough is a zone of deep water trending from northeast to southwest across the n aegean sea the western part of the trough the sporadhes basin contains a thick sequence of late cenozoic sediments le pichon et al 1984 suggested that the sporadhes basin coincides with a zone of extreme lithospheric stretching and that the crustal thickness is locally reduced to only 15 km we argue that the geophysical evidence cited by le pichon et al can be equally well explained by a crustal model involving a much smaller amount of local crustal thinning

rift structure evolution and earthquakes in the gulf of corinth from reflection seismic images abstract continental extension is forming the gulf of corinth across the strike of earlier alpine evolution here we present the first deep reflection sections with pre stack depth migration processing across the deep basin of the corinth active rift which image structures unpredicted by current models resolving the infill as a pile of layers that are broken by faults allows one to follow their subsidence and deformation history variation among the profiles suggests that southern normal faults control the rift in a time progression from the east towards its western tip on the central derveni itea transect a 3 km widening of the basin accrued since the initiation of this control that is marked by an unconformity between the two main sedimentary units this is estimated to have occurred 0 5 0 6 myr ago assuming the glacio eustatic sea level changes have controlled the stratigraphy of sediments deposited as a succession of layers on the subsiding hangingwall as they did on the southern footwall in forming the famous flight of marine terraces of corinth a roll over anticline and crestal collapse graben are diagnostic of the control by a normal fault of dip varying with depth the deeper low angle part of this bi planar fault is indeed imaged as a reflector in the basement the occurrence of the collapse with a breakaway at the steep southern basin bounding fault of the hangingwall slab can be estimated 0 12 0 2 myr ago with a marked increase in extension rate that brought it to its present fastest value over 10 mm yr the low angle part of the active fault might also have controlled earlier evolution upslope and in the basin when compared with inferences from earthquake studies this low angle active fault may not appear to be seismogenic but may participate to the seismic cycle possibly in a conditionally stable regime active faults seen as sea bottom scarps merely accommodate deformation of its subsiding hangingwall the footwall of the low angle faults which current seismicity shows to be in extension appears then as being pulled out from beneath the rift in a motion towards the rolling back slab that causes the hellenic subduction retreat

mechanics of low angle extensional shear zones at the brittle ductile transition corresponding to low values of the velocity ratio ve vs the 2 d solution for ve vs 1 0 3 reveals the development of a periodic system of extensional shear bands dipping at 30 toward the shearing direction at a depth of 12 to 14 km shear bands are formed after less than half a million years at the base of the reaction zone defined by the region where feldspar to mica reaction is completed shear bands do not propagate to greater depths because the pressure prevents the feldspar from fracturing and thus the reaction to occur the periodic system of shear bands defines a midcrustal flat weakened zone within which the equivalent shear stress is enhanced by at least a factor of three at the shear band tips brittle fracture could thus occur within the midcrustal flat weakened zone explaining therefore the microseismicity monitored at these depths in regions of active extension index terms 8109 tectonophysics continental tectonics extensional 0905 8159 tectonophysics rheology crust and lithosphere 8164 tectonophysics stresses crust and lithosphere 7218 seismology lithosphere and upper mantle 3230 mathematical geophysics numerical solutions keywords continental extension strain localization detachment fault rheology reaction softening numerical model

the north cycladic detachment system low angle normal faults accommodate a large part of continental post orogenic extension besides the intrinsic rheological characteristics of the continental crust that may lead to the formation of shallow dipping shear zones at the brittle ductile transition the role of pre existing low angle structures such as large thrusts has been proposed by several authors we explore this question with the example of the north cycladic detachment system ncds that is composed of a series of distinct detachments cropping out on the islands of andros tinos and mykonos separating the cycladic blueschists in the footwall from the upper cycladic nappe in the hanging wall we show that these extensional structures are part of a single large scale structure more than 200 km along strike that reactivates the vardar suture zone it extends eastward on ikaria and westward offshore evia and thessalia where it probably connects to recent shallow dipping normal faults evidenced on published seismic reflection profiles the ncds started its activity in the oligocene concommitantly with the aegean extension and was still active in the late miocene it has exhumed a series of metamorphic domes from southern evia to mykonos below low angle detachment systems made of low angle normal faults and low angle ductile shear zones the ductile shear zones and the faults were created with a low dip and they kept the same attitude throughout their exhumation we identify three main detachments that are part of a continuum of extension on the ncds tinos detachment livada detachment and mykonos detachment a fourth detachment vari detachment is the reactivation of an eocene exhumation related structure deformation in the footwall is characterized by intense stretching and flattening using the spatial evolution observed along strike from andros to mykonos we construct a history of formation of the ncds starting with the reactivation of former thrusts leading to the exhumation of high temperature metamorphic domes the aegean example shows that reactivation of earlier shallow dipping discontinuities can play a fundamental role in continental post orogenic extension

accurate relocation of seismicity along the north aegean trough and its relation to active tectonics abstract the tectonics of northern aegean are affected by the westward push of anatolia and the gravitational spreading of the aegean lithosphere that promote transtensional deformation in the area this regime is also responsible for the creation of a series of pull apart basins collectively known as the north aegean trough this work accurately relocates a total of 2300 earthquakes that were recorded along the north aegean trough during 2011 2016 by stations of the hellenic unified seismic network husn and strong motion sensors absolute locations for these events were obtained using a nonlinear probabilistic algorithm and utilizing a minimum 1d velocity model with station corrections the hypocentral depth distribution of these events shows a peak at 8 km diminishing gradually down to 20 km a systematic overestimation of hypocentral depths is observed in the routine locations provided by the national observatory of athens where the majority of events appear to be deeper than 15 km in order to obtain more accurate relative locations these events were relocated using the double difference method a total of 1693 events were finally relocated with horizontal and vertical uncertainties that do not exceed 0 11 km and 0 22 km respectively well defined clusters of seismicity can be observed along the saros and sporades basins as well as the kassandra and sithonia peninsulas these clusters either occur along the well known ne sw strike slip faults bounding the basins or along normal faults whose strike is perpendicular to the regional minimum stress axis locking depth along the north aegean trough is found to be remarkably stable between 13 and 17 km this is likely a consequence of simultaneous reduction along the sw direction of heat flow from 89 to 51 mw m 2 and strain rate from 600 to 50 nstrain yr whose opposite effects are canceled out precluding any sharp changes in locking depth

extension and dynamics of the andes inferred from the 2016 parina huarichancara earthquake the mw 6 1 2016 parina earthquake led to extension of the south peruvian andes along a normal fault with evidence of holocene slip we use interferometric synthetic aperture radar seismology and field mapping to determine a source model for this event and show that extension at parina is oriented ne sw which is parallel to the shortening direction in the adjacent sub andean lowlands in addition we use earthquake source models and gps data to demonstrate that shortening within the sub andes is parallel to topographic gradients both observations imply that forces resulting from spatial variations in gravitational potential energy are important in controlling the geometry of the deformation in the andes we calculate the horizontal forces per unit length acting between the andes and south america due to these potential energy contrasts to be 4 8 1012 n m along strike of the mountain range normal faulting at parina implies that the andes in south peru have reached the maximum elevation that can be supported by the forces transmitted across the adjacent foreland which requires that the foreland faults have an effective coefficient of friction urn x wiley jgrb media jgrb53009 jgrb53009 math 00010 2 additionally the onset of extension in parts of the central andes following orogen wide compression in the late miocene suggests that there has been a change in the force balance within the mountains we propose that shortening on weak detachment faults within the andean foreland since 5 9 ma reduced the shear tractions acting along the base of the upper crust in the eastern andes leading to extension in the highest parts of the range

visible infrared spectral properties of iron bearing aluminate spinel under lunar like redox conditions remote sensing observations have identified aluminate spinel in the absence of measureable olivine and pyroxene as a globally distributed component of the lunar crust earlier remote sensing observations and returned samples did not indicate the presence of this component leaving its geologic significance unclear here we report visible to mid infrared v ir reflectance 300 25 000 nm and mossbauer spectra of aluminate spinels synthesized at lunar like oxygen fugacity o2 that vary systematically in fe abundance reflectance spectra of particulate 6 fe although the 2000 and 2800 nm bands are assigned to fe 2 iv electronic transitions spectra of aluminate spinels with excess al2o3 demonstrate that the strengths of the 1000 nm bands are related to the abundance of fe 2 vi the abundance of fe 2 vi depends on bulk fe content as well as factors that control the degree of structural order disorder such as cooling rate consequently the strength of the 1000 nm bands are useful for constraining the fe content and cooling rate of remotely sensed spinel controlling for cooling rate particle size and o2 we conclude that spinels with 12 fe 88 mg have observable 1000 nm bands under ambient lunar conditions and that only very mg rich spinels lack 1000 nm bands in their spectra this links remote observations of spinel anorthosite to mg suite magmatism the combined effects of fe oxidation state abundance of coexisting plagioclase and space weathering have not been explored here and may add additional constraints the relative strengths of the distinctive 1000 and 2000 nm bands of the spinels associated with pyroclastic deposits at sinus aestuum suggest fast cooling rates possibly in the absence of an extensive vapor cloud

on the origin of orogens in order to understand how orogens work a quantitative approach demonstrating proof of concept is essential our goal is to reconcile the diverse array of tectonic features observed in natural orogens in the context of working numerical models that are consistent with both the underlying physics and first order geological constraints we present a simple conceptual temperature magnitude t m framework for orogenesis in terms of the progression from small cold to large hot orogens and we use forward numerical models to test hypotheses corresponding to specific stages along the t m spectrum small cold orogens are analyzed using crustal scale singularity s point models in which suborogenic mantle lithosphere is kinematically subducted beneath crust that deforms by critical wedge mechanics the transition from oceanic subduction to continental collision and the subsequent evolution of large hot orogens has been investigated using both crustal and upper mantle scale models the latter including dynamic subduction of suborogenic mantle lithosphere large hot orogens with thick crust are characterized by elevated plateaus with a strong superstructure underlain by hot weak lower crustal infrastructure beneath plateaus tectonic processes are dominated by ductile flow of weak crust in response to differential pressure while plateau flanks form external thrust sense wedges we discuss four topical issues in orogenic tectonics including the response of the suborogenic mantle lithosphere to convergence the interaction of climate and tectonics the current debate concerning wedge versus channel flow models to explain the himalayan tibetan system and the interpretation of metamorphic architecture in terms of orogenic processes we conclude that collisional orogenesis is driven largely by subduction and accretion of material at convergent margins accompanied by shortening thickening and heating of deformed crust

the continuity of active fault systems in greece summary evidence from geomorphology the distribution of large earthquakes and geodetic measurements suggests that the active faulting in mainland greece and the north aegean sea is concentrated into a small number of discrete linear zones that bound relatively rigid blocks on land the zones are most clearly identified where the faulting is associated with large escarpments particularly in hard footwall rocks the zones can become indistinct and diffuse near their ends sometimes because they enter high unstable topography where landsliding obscures the fault morphology but mostly because the extension rates decrease along strike as a consequence of the relative rotation of the blocks they bound the main graben systems of chalkidiki southern thessaly and the north gulf of evia all seem to connect with the strike slip faulting in the offshore aegean and to die out in the west a configuration related to clockwise rotations in east central greece by contrast the gulf of corinth which is the fastest opening graben system in greece opens more rapidly in the west than the east both these features of the gulf of corinth are consequences of the motion of the south aegean and peloponnese as a single block late pliocene and quaternary geology and geomorphology indicate that the boundaries of the rigid blocks in central greece have changed over that time with faulting migrating into the hanging walls sometimes changing in orientation these changes are probably related to the way faulting in the seismogenic layer adapts to block rotation so as to maintain the general features of a velocity field that is controlled by larger scale effects such as buoyancy forces and the seaward migration of the subducting slab beneath crete the image of greece as a mosaic of rigid blocks whose boundaries change with time is a useful framework for seismic hazard evaluation but we emphasize that some moderate sized earthquakes do occur away from the main fault zones within the relatively rigid blocks and especially near their diffuse ends

speculations on the formation of cratons and cratonic basins abstract surface wave tomography using rayleigh waves has shown that tibet and the surrounding mountain ranges that are now being shortened are underlain by thick lithosphere of similar thickness to that beneath cratons both their elevation and lithospheric thickness can result from pure shear shortening of normal thickness continental lithosphere by about a factor of two the resulting thermal evolution of the crust and lithosphere is dominated by radioactive decay in the crust it raises the temperature of the lower part of the crust and of the upper part of the lithosphere to above their solidus temperatures generating granites and small volumes of mafic alkaline rocks from beneath the moho as well as generating high temperature metamorphic assemblages in the crust thermal models of this process show that it can match the p t estimates determined from metamorphic xenoliths from tibet and the pamirs and can also match the compositions of the alkaline rocks the seismological properties of the upper part of the lithosphere beneath northern tibet suggest that it has already been heated by the blanketing effect and radioactivity of the thick crust on top if the crustal thickness is reduced by erosion alone to its normal value at low elevations without any tectonic extension over a time scale that is short compared to the thermal time constant of thick lithosphere of 250 ma thermal subsidence will produce a basin underlain by thick lithosphere though this simple model accounts for the relevant observations there is not yet sufficient information available to be able to model in detail the resulting thermal evolution of the sediments deposited in such cratonic basins

inferring upper mantle structure by full waveform tomography with the spectral element method summary mapping the elastic and anelastic structure of the earth s mantle is crucial for understanding the temperature composition and dynamics of our planet in the past quarter century global tomography based on ray theory and first order perturbation methods has imaged long wavelength elastic velocity heterogeneities of the earth s mantle however the approximate techniques upon which global tomographers have traditionally relied become inadequate when dealing with crustal structure as well as short wavelength or large amplitude mantle heterogeneity the spectral element method on the other hand permits accurate calculation of wave propagation through highly heterogeneous structures and is computationally economical when coupled with a normal mode solution and applied to a restricted region of the earth such as the upper mantle sem importantly sem allows a dramatic improvement in accounting for the effects of crustal structure here we develop and apply a new hybrid method of tomography which allows us to leverage the accuracy of sem to model fundamental and higher mode long period 60 s waveforms we then present the first global model of upper mantle velocity and radial anisotropy developed using sem our model semum confirms that the long wavelength mantle structure imaged using approximate semi analytic techniques is robust and representative of the earth s true structure furthermore it reveals structures in the upper mantle that were not clearly seen in previous global tomographic models we show that semum favourably compares to and rivals the resolving power of continental scale studies this new hybrid approach to tomography can be applied to a larger and higher frequency data set in order to gain new insights into the structure of the lower mantle and more robustly map seismic structure at the regional and smaller scales

structural evolution of andros cyclades greece a key to the behaviour of a flat detachment within an extending continental crust the continental crust extends in a brittle manner in its upper part and in more distributed ductile manner in its lower part during exhumation of hp metamorphic rocks brittle features superimpose on earlier ductile ones as a result of the progressive localization of deformation the islands of tinos and andros are part of the numerous metamorphic core complexes exhumed in the aegean domain they illustrate two steps of a gradient of finite extension along a transect between mt olympos and naxos this study confirms the main role of boudinage as an initial localizing factor at the brittle ductile transition and emphasizes the continuum of strain from ductile to brittle during exhumation early low angle semi brittle shear planes superimpose onto precursory ductile shear bands whereas steeply dipping late brittle planes develop by progressive steepening of structures or sliding across en echelon arrays of veins the comparison between tinos and andros allows us to propose a complete dynamic section of the aegean extending continental crust and emphasizes that the strain localization process depends on both its rheological stratification and its compositional heterogeneity

creep and locking of a low angle normal fault insights from the altotiberina fault in the northern apennines italy while low angle normal faults have been recognized worldwide from geological studies whether these structures are active or capable of generating big earthquakes is still debated we provide new constraints on the role and modes of the altotiberina fault atf in accommodating extension in the northern apennines we model gps velocities to study block kinematics faults slip rates and interseismic coupling of the atf which is active and accounts with its antithetic fault for a large part of the observed chain normal 3 mm yr tectonic extension a wide portion of the atf creeps at the long term slip rate 1 7 0 3 mm yr but the shallow locked portions are compatible with m 6 5 earthquakes we suggest that positive stress accumulation due to atf creep is most likely released by more favorable oriented splay faults whose rupture may propagate downdip along low angle normal fault surface and reduce the probability of occurrence of a seismic rupture of the shallower locked portion

fault structure and related basins of the north aegean sea and its surroundings 1 fault structure and basin evolution in the northern aegean sea and its surroundings have been investigated using bathymetry available onshore and offshore seismic profiles onshore fault patterns from ne greece nw turkey three islands in the aegean sea surface ruptures associated with the 1978 thessaloniki earthquakes gps measurements from north aegean islands and a number of earthquake focal plane solutions and historic seismicity bathymetric and isopach data show that the north aegean trough can be divided into the sporades basin and the saros trough post miocene sediment thickness differences in these basins offset of distinct horizons and frequent seismicity along basin bounding faults indicate that sediment accumulation in the area is fault controlled offshore seismic profiles show that the basin bounding faults are dominantly characterized by apparent normal components as well as strike slip components inferred from typical fault zone profiles additional evidence for existence of strike slip faulting comes from earthquake focal plane solutions we refined the pattern and kinematics of the faults controlling the basins and classified them into two major groups the faults in the first group trend ne sw and ene wsw and are here interpreted to be dominantly right lateral strike slip with normal or reverse components these faults accommodate a similar amount of deformation like the ganos fault and thus represent the westernmost extension of the north anatolian fault zone the faults in the second group trend nw se and are dominantly normal faults with an occasional left lateral component these faults are believed to manifest the termination of the north anatolian fault zone because of the segmentation of the right lateral strike slip faults and the preexisting ne trending tectonic grain the basins are compartmentalized into smaller depocenters basins are orientated with their long axes either parallel to the ne sw to ene wsw trending echelon strike slip faults or in the zone north of the strike slip faults parallel to the nw se trending normal faults the interpretations regarding the kinematics of the faults are consistent with the data compiled from the islands near the faults and from the land in ne greece and nw turkey the northern aegean basins and their spatial relationships to the fault architecture representing the diffused termination of the north anatolian fault system are consistent with the mechanical principles of the strike slip tectonics

westward propagation of the north anatolian fault into the northern aegean timing and kinematics we present new evidence for the propagation processes of the north anatolian fault folding in the dardanelles straits region allows us to document the timing of the deformation preceding and the finite displacement after the passage of the propagating tip of the fault the accuracy of the observations is due to interplay between deformation and the sea level changes in the mediterranean the well known messinian regression followed by the pliocene transgression the long term kinematics around the sea of marmara pull apart total displacement of about 85 km over the past 5 m y is similar to the present day kinematics deduced from space geodesy at a larger scale westward propagation of the north anatolian fault over nearly 2000 km in the past 10 m y appears to be associated with strain recovery suggesting that the continental lithosphere retains long term elasticity

the origins of granulites a metamorphic perspective although many recent reviews emphasize a uniformity in granulite pressure temperature p t conditions and paths granulites in reality preserve a spectrum of important petrogenetic features which indicate diversity in their modes of formation a thorough survey of over 90 granulite terranes or occurrences reveals that over 50 of them record p t conditions outside the 7 5 1 kbar and 800 50 c average granulite regime preferred by many authors in particular an increasing number of very high temperature 900 1000 c terranes are being recognized both on the basis of distinctive mineral assemblages and geothermobarometry petrogenetic grid and geothermobarometric approaches to the determination and interpretation of p t histories are both evaluated within the context of reaction textures to demonstrate that the large range in p t conditions is indeed real and that both near isothermal decompression itd and near isobaric cooling ibc p t paths are important amphibolite granulite transitions promoted by the passage of co 2 rich fluids as observed in southern india and sri lanka are exceptional and not representative of fluid related processes in the majority of terranes it is considered on the contrary that fluid absent conditions are typical of most granulites at or near the time of their recorded thermal maxima itd granulites are interpreted to have formed in crust thickened by collision with magmatic additions being an important extra heat source erosion alone is not however considered to be the dominant post collisional thinning process instead the itd paths are generated during more rapid thinning 1 2 mm yr exposure related to tectonic exhumation during moderate rate or waning extension ibc granulites may have formed in a variety of settings those which show anticlockwise p t histories are interpreted to have formed in and beneath areas of voluminous magmatic accretion with or without additional crustal extension ibc granulites at shallow levels very rapid 5 mm yr extensional thinning subsequent to collision it is suggested that the preservation of ibc paths rather than itd paths in many granulites is primarily related to the rate and timescale of extensional thinning of thickened crust and that hybrid itd to ibc paths should also be observed most ibc granulites and probably many itd granulites have not been exposed at the earth s surface as a result of the tectonic episodes which produced them but have resided in the middle and lower crust for long periods of time 100 2000 ma following these events the eventual exhumation of most granulite terranes only occur through their incorporation in later tectonic and magmatic events unrelated to their formation

average lithospheric structure of southern africa summary we present a new 1 d earth model for the crust and upper mantle beneath the archaean core of southern africa the crustal structure is constrained by published seismic refraction reflection data and by the modelling of teleseismic receiver function data the mantle structure is constrained by traveltime measurements for p and s waves by waveform inversion of multimode surface waves and by forward modelling of p waveforms for regional earthquakes the 42 km thick crust of southern africa consists of four layers a 2 km thick 5 05 km s surface layer a 5 km thick 6 08 km s upper crust a 20 km thick 6 30 km s l mid crust and a 15 km thick 6 73 km s lower crust below the crust there is an 80 km thick upper mantle lid v and v are 8 09 and 4 62 km s l respectively at the top of the lid and the compressional and shearvelocity gradients through the lid are 0 0008 s l and 0 0013 s respectively below the lid there is a substantial shear wave lvz with the shear wave velocity dropping from 4 72 km s l in the lower part of the lid to 4 32 km s at 250 km depth the shear wave lvz is required to fit both the v measurements and the regional surface waveforms forward modelling of p suggests that no upper mantle p wave lvz exists there is an increase in the p wave velocity gradient at 125 km depth to 0 0015 s and a second increase at 250 km depth to 0 0035 s velocities and densities in the seismic model of the lid agree closely with velocity and density estimates from the geochemical analysis of garnet periodotite nodules from kimberlites of the kaapvaal craton implying that the estimates from kirnberlites are representative of a wider region of the archaean core of southern africa not just of the restricted region beneath which the kimberlites are found a comparison of the southern african seismic model with seismic models for other shield regions where nodule data are not available shows that the nodule results may also be representative of the upper mantle in those regions

fault parameters of the 1980 mw 6 5 volos central greece earthquake from inversion of repeated leveling data the 1980 volos almyros seismic sequence the last of an unusual clustering of earthquakes with surface magnitude 6 0 7 0 which hit thessaly central greece between 1930 and 1980 is among the least studied recent earthquakes in greece repeated measurement of three first order spirit leveling traverses crossing the meizoseismal area of the seismic sequence indicates that between 1970 1971 and 1988 1989 a subsidence of about 35 cm is observed at the almyros neogene quaternary graben the observed displacements are significant against random and systematic errors and can be assigned to the 1980 earthquake sequence inversion of leveling data using an elastic dislocation model constrained by structural and seis mological data indicates that the mainshock mw 6 5 and the largest aftershock mw 6 1 were probably associated with reactivation of two subparallel homothetic nor mal faults marking the northern margin of the almyros neogene quaternary graben

lateral variations in the crustal structure of the indo eurasian collision zone we thank michael ritzwoller and two anonymous reviewers for constructive comments that have helped improve the manuscript the majority of the seismic data used in this study were downloaded from iris dmc data for the ngri stations in india were provided by s s rai and zahid ra provided the pmd pakistan data kajal borah provided the ambient noise cross correlations for the uttaranchal network figures were prepared using generic mapping tools gmt software wessel and smith 1998 we thank robert herrmann for making the computer programs in seismology freely available

evolution of hydrothermal regime along a crustal shear zone tinos island greece 1 structural cathodoluminescence and sims 18o analyses of quartz calcite veins are combined to constrain the evolution in space and time of fluid infiltration in an exhuming detachment shear zone tinos island cyclades greece careful description of vein arrays shows that the plumbing system evolved into an interconnected network just beneath the ductile to brittle transition microtextures of quartz and calcite infilling veins display deformed relics and newly precipitated grains high resolution 18o mapping in relics yields a steady quartz calcite fractionation of 2 at 400 c whereas fractionation increases in neograins from 2 to 5 in 190 m toward the fault or a 150 c temperature fall cooling is associated with a shift of fluid stable isotope signature from 15 to 0 beneath the detachment results are interpreted as advective removal of heat by massive infiltration of surface derived fluids over depths of 10 15 km fluid penetration was promoted by the coalescence of late ductile early brittle veins as the exhuming footwall crossed the ductile brittle transition only small amounts of fluids penetrated the ductile crust beneath the transitional rheology

interaction between trench retreat and anatolian escape as recorded by neogene basins in the northern aegean sea the evolution of the north aegean sea is studied through the development of three deep basins the north aegean trough the north skyros basin and the ikaria basin bathymetric data a 2d seismic dataset and the well investigated stratigraphic records of the onshore deep basins of northern greece and western turkey were used to make structural and seismic stratigraphic interpretations the study area shows two sharp unconformities that correspond to the eocene oligocene transition and the miocene pliocene shift these discontinuities were used as marker horizons for a more detailed structural and seismic stratigraphic interpretation resulting in the identification of several seismic units a general seismic signature chart was established using onshore basin stratigraphy and well data which was then used to constrain the ages of the different seismic units the main features observed in the basins are interpreted as 1 trans tensional growth patterns in pliocene and quaternary sediments that combine ne sw trending and steeply dipping fault zones that likely correspond to strike slip corridors and e w wnw ese trending normal faults 2 regional erosional truncations of miocene sediments likely related to the messinian salinity crisis msc 3 thick delta turbidite deposits of neogene age only the north aegean trough shows evidence of earlier development and polyphase deformation through inversion structures and additional seismic units extension processes in the aegean region have been driven by the hellenic slab rollback since the middle eocene the widespread development of neogene basins at the whole aegean scale attests to a major tectonic change due to an acceleration of the trench retreat in the middle miocene the present study shows that the neogene basins of the north aegean sea developed in dextral transtension with the northward migration of the associated ne sw trending strike slip faults at regional scale this tectonic pattern indicates that the westward escape of anatolia started to interact with the trench retreat in the middle miocene around 10 myr before the arrival of the north anatolian fault in the north aegean sea

a critical discussion of the subduction collision model for the neoproterozoic aracuai west congo orogen abstract the neoproterozoic aracuai west congo orogen in brazil and congo represents a branch of the brasiliano pan african orogenic system that is considered to terminate northward into a confined cratonic environment defined by the horseshoe shaped pre atlantic sao francisco congo craton the prevailing interpretation is that this orogen formed as a result of 50 m y of subduction leading to a classical continent continent collision this subduction collision model hinges on interpretation of 630 580 ma granitoids in the core of the orogen as being arc related and of locally exposed mafic and ultramafic metamorphic rocks as being ophiolitic we show that when tested beyond geochemical signature the model has fundamental problems that cannot be accounted for in particular there is an insurmountable oceanic space problem in this confined setting that is overlooked in most of the current literature there are also problems with subduction initiation lack of unambiguous evidence for oceanic crust no trace of any high p metamorphism and the abrupt termination of an ocean with no realistic way to transfer the large amount of oceanic opening displacement and subsequent convergence required by the model we conclude that the prevailing subduction collision model cannot possibly work and argue that the existing data are more consistent with hot intracontinental orogeny we stress the importance of building tectonic models on more than one type of data making realistic restorations and palinspastic reconstructions and taking into account modern geotectonic knowledge

brasiliano crustal structure and the tectonic setting of the parnaiba basin of ne brazil results of a deep seismic reflection profile a 1430 km deep crustal seismic reflection profile of the parnaiba basin shows an asymmetric structured western margin and a gently dipping eastern margin the 3 km thick phanerozoic sedimentary section overlies a pronounced planar regional unconformity that crosses three precambrian blocks with differing seismic facies the amazonian araguaia block the parnaiba block and the borborema block the blocks are separated by steep crustal scale boundaries across which seismic facies change abruptly in the west the ophiolitic metasedimentary rocks of the araguaia group overlie the amazonian craton both craton and metasediments terminate eastward against a steep east dipping fault zone defining the amazonian araguaia block and parnaiba block boundary reactivation of this neoproterozoic margin in the late triassic and late jurassic early cretaceous folded and elevated basement and basin over 2 km a second crustal boundary defines the eastern margin of the parnaiba block with the neoproterozoic borborema block this boundary is interpreted as the extension of the transbrasiliano shear zone these data demonstrate that the basement of the parnaiba basin was formed during brasiliano orogenesis by west directed collision related thrusting succeeded by lateral accretion along steep crustal scale boundaries after formation of a post brasiliano peneplain the parnaiba basin developed seamlessly across three very different crustal blocks and appears to have been significantly larger than its present outline no extensive underlying rift system is evident suggesting that basement structure had little to do with basin formation but that episodic reactivation of the boundary zones and basement fabric has controlled the structuring and preservation of the basin

propagation and termination of a strike slip fault in an extensional domain the westward growth of the north anatolian fault into the aegean sea abstract geometry and kinematics of the active submarine faults over the north aegean trough a complex and highly deforming boundary zone between the eurasian and the anatolian aegean micro plates were examined to investigate how a strike slip motion propagates through an extensional domain the bathymetric and seismic reflection data analysis show that the investigated area is affected from east to west by three sets of active faults striking ene wsw ne sw and wnw ese the ene wsw and ne sw striking faults are right lateral strike slip faults and are considered strands of the northern branch of the north anatolian fault into the north aegean sea the former set bounds the saros basin and the latter set occupies the eastern and central part of the sporades basin in the eastern and western parts of the north aegean trough respectively the wnw ese striking faults are normal low angle faults and develop at the western parts of the sporades basin it is suggested that the strike slip fault system advances westwards and when it reaches the 23 8 e meridian its right lateral motion is transferred to the wnw ese normal faults system forming a 70 km wide normal faulting zone through which the shear is distributed the interaction between the strike slip and normal faults probably started with the arrival of the northern branch of the north anatolian fault into the western part of the sporades basin since 430 ka bp marine isotopic stage 12 the described fault architecture and their spatial distribution in the north aegean trough are consistent with i the earthquake fault plane solutions and ii the stress and strain pattern prevailing across the area furthermore all these three provide evidence that the northern branch of the north anatolian fault terminates at the western end of the nat and does not continue to central greece

rifting and shallow dipping detachments clues from the corinth rift and the aegean the corinth rift is superimposed on the hellenic nappe stack that formed at the expense of the apulian continental crust above the subducting african slab extension started in the pliocene and the major steep normal faults that control the geometry of the present day rift were born very recently some 600 kyr ago only they root into a shallow dipping zone of microseismicity recorded near the base of the upper crust the significance of this seismogenic zone is debated considering the northward dip of the zone of microseismicity the depth of microearthquakes and their focal mechanisms we observe a strong similarity with the northern cycladic detachments in terms of expected pressure temperature conditions and kinematics we herein show 1 that the formation of the corinth rift can be considered a part of a continuum of extension that started some 30 35 ma in the aegean and that was recently localised in a more restricted area 2 that the present day structure and kinematics of the corinth rift can be explained with a series of decollements relayed by steeper ramps that altogether formed a mechanically weak crustal scale detachment and 3 that the deformation fluid behaviour and metamorphic features seen in the northern cycladic metamorphic core complexes can be good analogues of the processes at work below the corinth rift

north aegean crustal deformation an active fault imaged to 10 km depth by reflection seismic data three multichannel seismic profiles imaged a normal fault to at least 10 km depth in the north aegean trough and thermaikos basin the fault is active and recent forming a scarp at sea bottom and crossing the quaternary deltaic front on the northern slope of the trough controlled to the south by the north anatolian fault prestack depth migration imaged the fault as a seismic reflector cutting steeply across the sedimentary rocks and flattening in the basement from the seismic image the n100 e strike of the fault scarp and the orientations of the three profiles the true fault dip is constrained to an average 20 in the basement a low angle dip the throw and age estimated from the geometry in the sedimentary rocks document recent onset of the motion that must have occurred at a high rate both the direction and the rate of slip are consistent with the instantaneous motion as measured by space based geodesy which shows the fault to be forming by pure normal slip large earthquakes that have occurred in the basin may relate to such normal faults whereas the north anatolian fault with its current strike slip earthquakes appears to slip here under low resolved shear stress

observations of frequency dependent sn propagation in northern tibet summary we present new observations of the frequency dependent propagation efficiency of the seismic phase sn over the tibetan plateau our measurements are the ratio of the sn amplitude to the pg coda amplitude on tibetan regional seismograms and we map the lateral variation in the maximum and mean values of this ratio across the plateau good path density and azimuthal coverage allow the area of sn blockage identified by previous studies to be better constrained an important result is that at low frequencies 0 2 hz sn propagates efficiently over the entire plateau whereas at higher frequencies 1h z sn is blocked for a region of the northern plateau as we take measurements at higher frequencies we find that the southern boundary of the region of inefficient propagation migrates to the south the observation that low frequency sn propagates efficiently across the whole plateau suggests that at the length scales sampled by these waves the upper mantle has an overall positive shear velocity gradient which could indicate that the high velocity seismic lid or seismic lithosphere beneath tibet is still intact and has not delaminated as some researchers have previously proposed the observation that high frequency sn does not propagate beneath northern tibet suggests that at the shorter length scales sampled by the higher frequency waves the upper mantle has a negative shear velocity gradient this could indicate that at shallow depths the sub moho upper mantle is hot and may contain some melt

low angle normal faults and seismicity a review although large low angle normal faults in the continental crust are widely recognized doubts persist that they either initiate or slip at shallow dips 30 because 1 global compilations of normal fault focal mechanisms show only a small fraction of events with either nodal plane dipping less than 30 and 2 andersonian fault mechanics predict that normal faults dipping less than 30 cannot slip geological reconstructions thermochronology paleomagnetic studies and seismic reflection profiles mainly published in the last 5 years reinforce the view that active low angle normal faulting in the brittle crust is widespread underscoring the paradox of the seismicity data for dip slip faults large enough to break the entire brittle layer during earthquakes m w 6 5 consideration of their surface area and efficiency in accommodating extension as a function of dip suggests average recurrence intervals of earthquakes r tan assuming stress drop rigidity modulus and thickness of the seismogenic layer do not vary systematically with dip if the global distribution of fault dip normalized to total fault length is uniform the global recurrence of earthquakes as a function of dip is shown to be r tan sin this relationship predicts that the frequency of earthquakes with nodal planes dipping between 30 and 60 will exceed those with planes shallower than 30 by a factor of 10 in good agreement with continental seismicity assuming major normal faults dipping more than 60 are relatively uncommon revision of andersonian fault mechanics to include rotation of the stress axes with depth perhaps as a result of deep crustal shear against the brittle layer would explain both the common occurrence of low angle faults and the lack of large faults dipping more than 60 if correct this resolution of the paradox may indicate significant seismic hazard from large low angle normal faults

continental rifting and initial sea floor spreading in the woodlark basin our understanding of the processes by which continents rift and sea floor spreading initiates is derived primarily from studies either of old passive margins and oceanic crust or of young regions of intra continental extension where spreading has not yet started it has been thought that continental rifting ceases when sea floor spreading begins1 2 that oceanic fracture zones develop from transfer or transform faults within continental rifts3 4 and that linear magnetic anomalies correlate with the onset of sea floor spreading during times of magnetic reversals5 6 here we present a marine geophysical survey of one of the few active examples of continental rifting and spreading initiation the western woodlark basin papuan peninsula region of new guinea which shows that in detail these assumptions do not hold the data confirm models of the rifting to spreading transition that invoke both ridge propagation and nucleation of discrete spreading cells7 10 and provide an unambiguous example of a spreading centre reorienting by synchronous jumping rather than propagation

processing of crust in the root of the caledonian continental collision zone the role of eclogitization segments of the root to the caledonian collision zone are exposed along the west coast of norway allowing the study of processes and petrophysical conditions at the deepest crustal levels p t conditions prevailing in these crustal root zones correspond to eclogite facies eclogitization is associated with marked changes in petrophysical properties notably a density 10 15 and vp increase which may give a mantle signature to an eclogitized crust the observed ductility enhancement may be caused by transformation plasticity reduction in grain size formation of new mineral assemblages and presence of fluid in the western gneiss region and the bergen arcs eclogites form along shear zones interpreted as fluid pathways with sharp boundaries to their metastable protolith this makes eclogite shear zones potential deep crustal reflectors dry crust subducted into roots of continental collision zones will undergo eclogitization only if hydrous fluids are available timing of metamorphic reactions does not depend on crossing of equilibrium boundaries in the p t space but rather on the introduction of fluids into the system eclogites are not only passive recorders of p t t paths illustrating very deep subduction of crust 100 km rapid changes in petrophysical properties make fluid induced eclogitization a dynamic process that influences geodynamics stresses set up by the volume changes or by tectonic forces are released by ductile deformation along shear zones and by seismic faulting as evidenced by syn eclogitic pseudotachylytes in the metastable protolith deformation including seismicity enhances fluid infiltration and further eclogitization dense and rheologically weak eclogites may delaminate and sink into the mantle in the absence of fluids crustal doubling may occur without metamorphic re equilibration the evolution of a collision zone depends on the fluid regime which should be considered in geodynamic modelling in addition to p and t

radiogenic heat production in the continental crust abstract the thermal structure and evolution of continents depend strongly on the amount and distribution of radioactive heat sources in the crust determining the contribution of crustal rocks beneath a superficial layer is a major challenge because heat production depends weakly on major element composition and physical properties such as seismic wavespeed and density enriched granitic intrusives that lie at the current erosion level have a large impact on the surface heat flux but little influence on temperatures in the deep crust many lower crustal rocks that are poor in heat producing elements are restites from ancient orogenic events implying that enrichment of the upper crust was achieved at the expense of deeper crustal levels for the same total heat production concentrating heat sources in an upper layer acts to reduce temperatures in the lower crust thereby allowing stabilization of the crust the present day structure of the crust is a consequence of orogeny and should not be adopted for thermal models of the orogenic event itself this review summarizes information extracted from large data sets on heat flow and heat production and provides estimates of crustal stratification and heat production in several geological provinces analysis of global and regional data sets reveals the absence of a positive correlation between surface heat flow and crustal thickness showing that the average crustal heat production is not constant differences of heat flow between geological provinces are due in large part to changes of crustal structure and bulk composition collating values of the bulk crustal heat production in a few age intervals reveals a clear trend of decrease with increasing age this trend can be accounted for by radioactive decay indicating that thermal conditions at the time of crustal stabilization have not changed significantly for the average crustal thickness of 40 km moho temperatures are near solidus values at the time of stabilization suggesting an intrinsic thermal control on crustal thickness and heat production distribution crustal thickening by more than about 10 km above this mean value induces changes of gravitational potential energy that exceed the strength of the lithosphere for several provinces where strong constraints on heat production are available it is shown that prior to intracrustal fractionation only modest amounts of thickening were needed to generate the conditions of ultra high temperature metamorphism the tell tale signature of crustal heat production is anatectic and metamorphic events that lag the cessation of orogenic activity by several tens of million years crustal heat production is decreasing with time because it is due to the radioactive decay of uranium thorium and potassium its rundown is responsible for the secular cooling of lithospheric roots at a typical rate of about 100 k gy 1 implying complex thermal interactions with a convecting mantle that is not cooling at the same rate

the formation of mountain range curvature by gravitational spreading this paper presents a mechanism by which mountain ranges can form curved range fronts gravitational spreading of mountain ranges that have been thrust onto rigid lowlands will result in the formation of curvature provided that enough gravity driven flow occurs to dominate the shape of the topography whether this mechanism can operate during the lifetime of a given mountain range depends upon the viscosity of the range the square of the along strike length of the range and the cube of the elevation of the range the curvature of the southern edge of the tibetan plateau is consistent with formation by gravitational spreading provided that the viscosity is similar to that previously estimated using other independent methods the low elevation and young age of the zagros mountains mean that large scale curvature has not had time to develop the short along strike extent and possibly low viscosity of the sulaiman ranges in pakistan may have allowed the ranges to form their distinctive arcuate shape the formation of range front curvature plays an important role in controlling the tectonic evolution of the interiors of the ranges with arc parallel extension becoming progressively more important as range front curvature develops

paleogeography reconstruction of a multi stage modified intra cratonic basin a case study from the jurassic ordos basin western north china craton abstract post depositional modification is commonly found in sedimentary basins particularly in the eastern tethys tectonic domain and is related to special geological settings and evolution processes of the region the chinese continent is composed of numerous small scale blocks that underwent intensive tectonic movements paleogeography reconstruction for a modified basin is fundamental for objectively understanding the basin dynamics and exploration of hydrocarbon sandstone type uranium deposits and other mineral resources as a large scale intra cratonic depression basin in the western part of the north china craton ncc the mesozoic ordos basin underwent multi stage modification as a result only the western part was preserved in this study the paleogeography in bathonian oxfordian ages of the jurassic was reconstructed via integrated approaches including stratigraphic correlation sedimentary facies analysis provenance analysis and fission track analysis the original sedimentary boundary of the ordos basin during this period is approximately outlined we determine that the northern and southern borders reach the cenozoic hetao basin and the cenozoic weihe basin respectively and that the eastern northwestern and southwestern borders lie to the west of taihang mountain at the langshan bayanhot basin kexueshan and to the west of liupan mountain respectively the original sedimentary extent of the ordos basin was almost twice that of the present day residual basin the evolution of this basin in the mesozoic recorded the evolution and destruction processes of the ncc the ncc shows that n s and w e trending compressional setting occurred during the triassic and the jurassic respectively the interactive activities of adjacent tectonic domains played a critical role in subsidence dynamics for the intra cratonic ordos basin this study provides further insights for exploration of hydrocarbon and sandstone type uranium deposits in the ordos basin

recent gravitative mass movements in a highly tectonically active arc system the hellenic arc abstract the hellenic arc system is located within one of the world s most seismically active areas and has experienced extreme tectonism throughout tertiary and quaternary times this paper discusses the various types of gravitative mass movements that have been detected and examines their causative factors in environments of high tectonic and seismic activity the areas surveyed are the sporadhes and corinth grabens in the back arc basin the zante cephalonia shelf on the inner slope of the hellenic trench and the kythera ridge in the outer island arc the various types of gravitative mass movements that have been documented include i sliding of large masses with no or only slight internal deformation ii sliding of masses with disintegration of the sediment fabric to debris flows and iii slow downslope creep the mass movements are associated with fault escarpments delta fronts and well stratified slopes with slope gradients ranging from 2 to 40 earthquakes seem to be the main mechanism initiating mass movement but other mechanisms such as increasing topographic gradient gas in the sediment pores and heavy rain can also independently trigger and or contribute to the initiation of mass movements

moho crustal architecture and deep deformation under the north marmara trough from the seismarmara leg 1 offshore onshore reflection refraction survey abstract understanding further the nature and evolution at lithospheric scale of the sea of marmara on the north anatolian fault needs constraints on the deep crustal and moho spatial variation this has been probed here with offshore onshore and obs ocean bottom seismometer refraction seismics in addition to coincident mcs marine multichannel reflection seismic profiles over the whole north marmara trough the diverse strikes of mcs profiles in a dense grid allow to avoid misinterpretation of late echoes in the deep basin as moho reflections and attribute them to sidesweeps moho is instead positively identified from reversed observations of first arrival head and refracted waves at the top of the mantle obtained at large offset by land stations a significant and sharp reduction in its depth on the order of 5 km occurs beneath both the eastern and western rims of the north marmara trough with a more progressive crustal thinning from the south the wide angle reflections on obs and land stations document in addition to moho the top of a lower crustal reflective layer which is also sampled by mcs profiles and appears to follow moho topography the dense grid of mcs profiles along the southwestern margin of the north marmara trough reveals a dipping reflector through the upper crust with tilted basement blocks on top this low angle fault is suggested as a normal sense detachment extending in depth towards the reflective lower crust the upwarp of the moho and lower crustal layer towards the north marmara trough suggests that crustal thinning occurs mostly in the upper crustal part with lateral transport of the material towards wsw in the footwall of the detachment and possibly other features to the south in the motion of anatolia with respect to stable eurasia oblique to the north marmara trough thinning can be accommodated in an asymmetric partitioning of the displacement on several branching faults at lithospheric scale

quantifying rates of detachment faulting and erosion in the central menderes massif western turkey by thermochronology and cosmogenic 10be exhumation of rocks in extensional tectonic settings results from a combination of normal faulting and erosion but the relative contribution of these processes has rarely been quantified here we present new low temperature thermochronological data and the first 10 be based catchment wide erosion rates from the boz dag region in the central menderes massif which has experienced nne ssw extension since the miocene the slip rate of the shallow dipping gediz detachment fault which defines the northern flank of the boz dag block is 4 3 3 0 1 2 mm a 1 as constrained by zircon u th he ages of c 4 2 ma in the footwall apatite and zircon u th he and fission track ages from the northern flank of the boz dag block yield exhumation rates of 0 6 2 km ma 1 beneath the gediz detachment whereas those on the southern flank are only 0 2 0 6 km ma 1 erosion of catchments on the northern and southern flanks proceeds at rates of 80 180 and 330 460 mm ka 1 respectively this marked contrast is a combined effect of the topographic asymmetry of the boz dag block and differences in rock erodibility if these erosion rates persisted in the past rock exhumation on the northern flank occurred predominantly by tectonic denudation whereas rocks on the southern flank were mainly exhumed by erosion

seismicity and associated strain of central greece between 1890 and 1988 summary we examined the seismicity of central greece between 1890 and 1988 using macroseismic and instrumental data to ask two questions 1 does the seismicity of this period reveal all the major tectonic structures that are known to be active and 2 what are the likely strains associated with the seismicity over this period many known active structures have been effectively aseismic for the last hundred years and even the inclusion of all known large events earlier than 1890 reveals no activity associated with the ne coast of evia gulf of argos or graben ne of mt parnassos it is clear that even 100 years data are inadequate for either a reasonable assessment of seismic risk or for a confident estimation of maximum magnitude however we are aware of no earthquakes in central greece during the last 200 yr that were larger than ms 7 0 it is probable that the maximum magnitude is restricted by the maximum length of fault segments which appears to be around 15 20 km the earthquakes of ms 5 8 during 1890 1988 can account for a n s displacement of around 45 70 cm with maximum and minimum estimates a factor of two greater and smaller than this across part of a 1890 1900 triangulation network in central greece that was resurveyed in 1988 the contribution of smaller events may increase this displacement by about 50 per cent this cumulative seismic displacement is similar to that estimated from the geodetic work about 100 cm but a detailed comparison of the two sets of observations will be reported elsewhere a re evaluation of all the important earthquakes of 1890 1988 in central greece is presented in the appendix which summarizes information of use to both earth scientists and engineers

implications of preliminary subsidence analyses for the parnaiba cratonic basin cratonic sedimentary basins are underlain by thick lithosphere and subside over hundreds of millions of years the driving mechanism for these basins remains enigmatic due to the paucity of crustal scale constraints to address this shortcoming an integrative study of the parnaiba cratonic basin of ne brazil is underway we summarize field observations well log information seismic reflection profiles and subsidence analyses with the objective of shedding light on possible basin forming mechanisms lithological descriptions and borehole logs reveal a stratigraphic succession that consists of interbedded shallow marine and continental deposits on seismic reflection profiles this succession is divided into packages of relatively undisturbed reflections bounded by basin wide disconformities these disconformities are manifest as bright rugose reflections that probably represent buried palaeo landscapes backstripped and water loaded subsidence curves calculated from boreholes distributed throughout the basin show that tectonic subsidence decreases exponentially over c 350 ma a simple model suggests that this subsidence pattern agrees with a thermal time constant of 70 100 ma placing a significant constraint on the likely basin forming mechanism this background trend is punctuated by minor increases in subsidence that follow basin wide erosional disconformities these departures could be indicative of transient epeirogenic uplift events caused by changing patterns of dynamic topography

the strain rate field in the eastern mediterranean region estimated by repeated gps measurements we use the combined gps velocity field of the eastern mediterranean for the period 1988 to 1996 to determine crustal deformation strain rates in a region comprising the hellenic arc the aegean sea and western anatolia we interpret the velocity field and determine the strain rate tensor by the spatial derivatives of the collocated motion vectors the region following the line marmara sea north aegean trough northern central greece and the central ionian islands is associated with strong right lateral shear motion with maximum shear strain rates of 180 nano strain a 180 10 9 a in the central aegean sea n s oriented extensional processes prevail reaching 100 nano strain a the southern aegean is characterized by relatively small strain rates maximum extensional components of the strain rate tensor reaching 150 nano strain a in a n s direction are found in central greece the hellenic arc is associated with moderate arc parallel extension and strong compression perpendicular to it projections of the strain rates parallel to the major fault zones reveal that the northern aegean is governed by the westward continuation of the north anatolian fault zone which is associated with strong dextral shearing maximum 220 nano strain a accompanied by numerous large earthquakes in this century

continental collisions and the origin of subcrustal continental earthquakes the existence of subcrustal continental earthquakes beneath the alpine himalayan belt was recognised more than 60 years ago there is general agreement that most of those beneath the western part o

seismic hazard scenarios from the longest geologically constrained active fault of the aegean abstract several seismic hazard scenarios are examined concerning the seismic potential of the north aegean basin nab based for the first time purely on geological data detailed analysis of the bathymetry incorporated by seismic reflection profiling has recently revealed the neotectonic structure of the nab and demonstrates that the dominant structure is a 160 km long ne sw trending fault comprising of four major segments this is the longest geologically constrained active fault in the aegean sea following deterministic fault specific analyses six major seismic sources are identified firstly a 55 km oblique normal fault segment towards the southwestern end of the basin that can accommodate a m 7 1 event such an event could produce a maximum vertical offset up to 3 4 m posing also a tsunami threat based on geological data a minimum throw rate of 1 2 0 2 mm yr is estimated for this segment implying a recurrence interval of 1100 350 yrs secondly a sub vertical 70 km long e w dextral trending shear zone northwards the southwestern corner of the n aegean basin that can generate a m 7 2 strike slip event sources 3 and 4 towards the central and eastern segment of the fault are expected to produce seismic strike slip events of m 7 1 whereas the fifth source suggests the simultaneous activation of sources 3 and 4 producing a 105 km long rupture and a m 7 4 event finally the sixth source implies a multi segment rupture involving the entire 160 km long south marginal fault producing a m max 7 6 which represents the worst case scenario this value limits all uncertainties posed on the maximum expected magnitude by other published estimates ranging from m 7 2 up to 8 5 that are based solely on seismological and or geodetic approaches

present day crustal stress field in greece inferred from regional scale damped inversion of earthquake focal mechanisms in this study we utilize regional and teleseismic earthquake moment tensor solutions in order to infer the contemporary crustal stress in the greek region we focus on crustal earthquakes and select only solutions with good waveform fits and well resolved nodal planes a data set of 1614 focal mechanisms is used as input to a regional scale damped stress inversion algorithm over a grid whose node spacing is 0 35 several resolution and sensitivity tests are performed in order to ascertain the robustness of our results our findings show that for most of the greek region the largest principal stress 1 is vertically oriented and that the minimum principal stress axis 3 are subhorizontal with a predominant n s orientation in the sw peloponnese the orientation of 3 axes rotates clockwise and in se aegean counterclockwise these results are in agreement with the generally accepted model that slab rollback combined with gravitational spreading of the aegean lithosphere are the main causes of the extension transitions between different faulting types in nw greece or in the aegean occur within narrow zones in the order of tens of kilometers a visual comparison of the principal horizontal stress axes and the principal strain axes derived from gps observations shows good agreement suggesting that the crust in the greek region behaves largely in an elastic manner

seismicity of the 24 may 2014 mw 7 0 aegean sea earthquake sequence along the north aegean trough abstract the northern aegean sea was hit by a large size mw 7 0 earthquake on 2014 may 24 centroid moment tensor solutions for 40 events with moment magnitudes mw between 3 3 and 7 0 are computed by applying a waveform inversion method on data from the turkish and greek broadband seismic networks the time span of data covers the period between 2014 may 24 and 2014 june 26 the mainshock is a shallow focus strike slip event at a depth of 15 km focal depths of aftershocks range from 6 to 30 km the seismic moment mo of the mainshock is estimated as 4 60 1019 nm the calculated rupture duration of the north aegean sea mainshock is 40 s the focal mechanisms of the aftershocks are mainly strike slip faulting with a minor normal component the geometry of focal mechanisms reveals a strike slip faulting regime with ne sw trending direction of t axis in the entire activated region a stress tensor inversion of focal mechanism data is performed to acquire a more accurate picture of the northern aegean sea stress field along the north aegean trough the stress tensor inversion results indicate a predominant strike slip stress regime with a nw se oriented maximum principal compressive stress 1 in the development of the north aegean trough in aegean sea is in good agreement with the resolved stress tensors with respect the newly determined focal mechanisms the effect of the propagating of the north anatolian fault into aegean sea is very clearly pronounced according to high resolution hypocenter relocation of the north aegean sea seismic sequence three main clusters are revealed the aftershock activity in the observation period between 2014 may 24 and 2014 july 31 extends from the mainshock cluster from ne to the sw direction seismic cross sections indicate that a complex pattern of the hypocenter distribution with the activation of seventeen segments the eastern cluster is associated with a fault plane trending mainly ene wsw and dipping vertical while the western is related to a fault plane trending ne sw and dipping towards nnw the best constrained focal depths indicate that the aftershock sequence is mainly confined in the crust depth 30 km and is operating in the approximate depth range from 1 5 to 30 km consequently coulomb stress analysis is performed to calculate the stress transfer and correlate it with the activated region positive lobes with stress more than 3 bars are obtained indicating that these values are large enough to increase the coulomb stress failure towards ene wsw direction

seismological constraints on the density thickness and temperature of the lithospheric mantle in southwestern tibet h m d thanks h fang d forsyth r g green a holt v levin c yu and especially l royden for helpful discussions and to schlumberger for a scholarship he is also grateful to v levin and s roecker for making all seismo grams from the y2 network freely available through the iris data management centre we also thank three anonymous reviewers for thorough constructive reviews data were processed using obspy all figures were prepared using matplotlib alongside the cartopy library for mapping

high frequency seismic wave propagation beneath the indian shield himalayan arc tibetan plateau and surrounding regions high uppermost mantle velocities and efficient sn propagation beneath tibet summary this paper reports the regional propagation characteristics of high frequhcy p p s and l waves 0 5 to 2hz and p pg and s velocities for several regions in central asia tibet and india an important result is that s waves propagate efficiently in the uppermost mantle beneath most of the tibetan plateau also s transmission in tibet is not affected by crossing many physiographic and tectonic boundaries such as the indus tsangpo suture these observations are similar to observations of s propagation in stable continental and shield regions efficient s propagation is also observed across the stable tarim basin along the tien shan and himalayan mountains and across the indian shield s is strongly attenuated across the northern tibetan plateau chang thang terrane such strong attenuation suggests the existence of a low q zone in the uppermost mantle beneath that region this interpretation is supported by recent geological observations of widespread quaternary to recent basaltic volcanism in the chang thang terrane l propagates efficiently across the tarim basin the indian shield and along the strike of the himalayan mountains l is also observed although less pronounced for paths crossing large portions of the complicated structures of tien shan karakoram and pamir l is not observed for paths crossing the tibetan plateau the southern boundary of the region of inefficient l propagation in tibet lies in the vicinity of the indus tsangpo suture zone the lack of l can be attributed to attenuation within the tibetan crust however other possibilities including scattering by structural discontinuities at the margins of tibet are equally plausible pg and s are the most prominent features on most short period wwssn seismograms at epicentral distances less than about 4 apparent pg velocity determined for the area of the himalayan mountains is 6 0 0 2 km s l apparent velocities of p and s waves that have at least 50 per cent of their paths in the uppermost mantle beneath the tibetan plateau are 8 42 it 0 10 and 4 73 f 0 06 km s respectively these velocities are quite similar to those determined for the himalayan mountains p 8 45 f 0 08 km s i s 4 74 0 05 km s and the indian shield p 8 40 0 08 km s s 4 69 k 0 04 km s p

geodetic determination of the kinematics of central greece with respect to europe implications for eastern mediterranean tectonics we use a new satellite laser ranging global positioning system slr gps solution at seven sites in anatolia and aegea to obtain a better definition of the extrusion motion of the anatolian aegean block with respect to europe we show that this motion can be described in a first approximation by a counterclockwise rotation which transfers most of the motion of arabia to anatolia we combine 78 displacement vectors obtained at common points of two triangulation nets measured in central greece in 1895 and 1975 with the slr gps measurements to compute the velocity field over greece with respect to europe these measurements indicate that central greece is a zone of extension between the anatolian aegean counterclockwise rotation to the south and the northern greece clockwise rotation to the north this extension is principally localized within the gulf of corinth to the east but is distributed to the west we then extrapolate this velocity field to the whole aegea and western anatolia using recently published gps results as well as the slr results the narrow dextral north anatolian fault which limits the velocity field to the north progressively gives way to a much wider boundary zone where extension becomes dominant we show that the collision between the mediterranean ridge and africa began 3 6 ma and we describe the modifications that this collision has produced on the kinematic pattern both in aegea and on the mediterranean ridge