isostatic response of the alula fartak and owen transforms in the eastern gulf of aden and the adjoining arabian sea summary the alula fartak and owen transforms are the active parts of major fracture zones with a distinct topographic expression in the eastern gulf of aden and the arabian sea respectively while the alula fartak transform offsets the sheba ridge by about 180 km and is associated with a broad steep sided valley with a relief of nearly 3 5 km the owen transform offsets the carlsberg ridge by nearly 300 km and is associated with a broad step like valley surrounded by deeper water depths the gravity and topography data along several profiles selected across these two transforms have been analysed using cross spectral analysis in order to investigate their isostatic compensation the observed admittance estimates have been compared with three theoretical isostatic compensation models two local compensation models airy i and ii and one regional compensation plate model comparing the longer wavelength admittance estimates suggests that the regional compensation model gives the best fit for both the alula fartak transform and the owen transform with effective elastic thickness te of 5 km and slightly less than 10 km respectively for the alula fartak transform the airy ii model might also be acceptable though with large scatter in the observed values it suggests a mean value of 9 km for the mantle layer with a 6 km thick crust for the owen transform on the other hand the two local compensation models failed the difference in te estimate between the two transforms could be ascribed to differences in thermal structure arising from their varied tectonic history a comparison with the isostatic response estimates of transform fracture zones along the slow spreading mid atlantic ridge suggests that the regional compensation model is generally applicable for transform fracture zone topography along such mid ocean ridges

central gulf of aden conjugate margins yemen somalia tectono sedimentary and magmatism evolution in hybrid type margins abstract magma rich and magma poor passive margins are generally studied separately yet the spatial evolution from one type to another is not well understood central gulf of aden margins are at the transition between these two types of margins based on new seismic data published wells and gravity data we determine seismic stratigraphy and structural patterns we map the distinct crustal domains continental ocean continent transition oct oceanic domains and propose a tectonic evolution of the yemeni and somalian conjugate margins in an oblique rifting context the most striking results are the significant segmentation narrowness and asymmetry of conjugate margins as well as the gradual eastward decrease in the intensity of magmatic activity of these hybrid type margins west of bosaso hami fracture zone bhfz the hami ahl medo segment presents magmatic type margin features in the distal yemeni margin related to the strong influence from the afar plume seaward dipping reflectors develop since the late syn rift stage 21 18 ma near the xiis al mukalla fracture zone conversely east of bhfz the bosaso sayhut margins segment is characterized by magma poor margins for which the exhumation stage is characterized by the unroofing of mantle along multiple detachment faults in the oct and shortly followed by diachronous volcanism 18 ma the central gulf of aden is affected by a major uplift during the final syn rift stage and up to oct formation this event is associated with the formation of erosional surfaces in the east and with gravitational deformation taking place on decoupling surfaces at the base of the syn rift sequence lower ghaydah fm that lead to the sliding of syn rift units on top of the exhumed mantle rocks in the oct

field evidences from northern dead sea fault zone south turkey new findings for the initiation age and slip rate abstract the left lateral strike slip dead sea fault zone dsfz extends from the red sea in the south to the east anatolian fault zone eafz in the north this study examines the northern part of the dsfz around amik basin and presents surface and subsurface geological evidence for the quaternary activity and initiation age of the northernmost dsfz the dsfz extends n s in the south of the amik basin where clear geological and morphological evidence exists for faulting geological observations around amik basin analyses of borehole data and electrical resistivity profiles within the amik basin indicate that the activity of the northern dsfz started after pliocene in the amik basin subsurface data in the basin suggest that the dsfz offsets a pre quaternary basin sinistrally by about 7 9 km the offset pre quaternary basin suggests at least 4 94 0 13 mm year slip rate for the northern part of the dsfz the karasu fault zone kfz extends in an en echelon pattern along the western margin of the karasu valley and it transfers the significant amount of slip from dsfz to the eafz

seismic gravity and magnetic surveys in the central part of the red sea their interpretation and implications for the structure and evolution of the red sea abstract while there is unanimous agreement that the axial part of the red sea has witnessed seafloor spreading since the early pliocene opinions diverge considerably with regard to the situation in the main trough and shelves new high precision data comprising palaeomagnetic seismic gravity magnetic and bathymetric measurements from the central and northern parts of the red sea have been examined to discriminate between the earlier proposed hypotheses and to formulate an evolutionary model for the red sea the results show that oceanic crust extends for about 80 km at 19 n on each side of the spreading axis symmetrical seafloor spreading magnetic anomalies are recognized out to anomaly 3a 6 m y b p between 18 30 and 19 45 n anomaly 2a between 19 45 and 20 n and near 21 n anomaly 2 near 22 n and only anomaly 1 near 23 30 n although anomaly 3a is the oldest recognizable magnetic anomaly the extent and configuration of the oceanic basement as determined from seismic measurements indicate that spreading has started and continued without a hiatus since 10 12 m y b p prior to the initiation of oceanic accretion an extension of 40 55 km i e 50 70 has taken place in the proterozoic continental lithosphere whereas a separation of 70 160 km has occurred during the seafloor spreading phase several lines of evidence indicate that the shelves and the marginal parts of the main trough are of continental nature

statistical tests of additional plate boundaries from plate motion inversions we have investigated the application of the f ratio test a standard statistical technique to the results of relative plate motion inversions the method tests whether the improvement in fit of the model to the data resulting from the addition of another plate to the model is greater than that expected purely by chance this approach appears to be useful in determining whether additional plate boundaries are justified we confirm previous results favoring separate north american and south american plates with a boundary located between 30 n and the equator using chase s global relative motion data we show that in addition to separate west african and somalian plates separate west indian and australian plates with a best fitting boundary between 70 e and 90 e can be resolved these results are generally consistent with the observation that the indian plate s internal deformation extends somewhat westward of the ninetyeast ridge the relative motion pole is similar to minster and jordan s and predicts the nw se compression observed in earthquake mechanisms near the ninetyeast ridge

earthquakes in the davie ridge madagascar region and the southern nubian somalian plate boundary the largest earthquake sequence mb up to 6 4 and m0 up to 5 1018 nm to have struck eastern africa within the past 60 years occurred in may and june of 1985 off the coast of the tanzania mozambique border the epicenters are located on the northern extension of the davie ridge a prominent north south trending bathymetrie feature accompanied by distinct gravity anomalies a joint hypocenter location of the 14 largest events in this sequence appears as a cluster of epicenters with no apparent lineation al teleseismic distances p and sh waves generated by the two largest events of this sequence have nearly identical waveforms on the long period records of the worldwide standard seismograph network a formal inversion of the data shows a pure normal faulting mechanism on nodal planes striking slightly west of north at least two point sources are necessary to model each event one at a depth of 40 10 km and the other at about 20 5 km on a regional scale normal faulting seems to characterize the scattered seismicity throughout the region between madagascar and the eastern arm of the east african rift zone even though oceanic lithosphere dominates part of the region and no topographic expression of a rift system can be identified since normal faulting events of up to 25 5 km deep also characterize the scattered seismicity west of the topographic expression of the western arm of the rift zone at about the same latitude we propose that the southern termination of the nubian somalian plate boundary consists of a diffuse zone of east west extension up to 2000 km wide

oblique slip deformation in extensional terrains a case study of the lakes tanganyika and malawi rift zones the east african rift system ear is the archetypal continental rift and a widely proposed analogue for the early stages of evolution of passive continental margins the three dimensional structure of parts of the ear has been recently elucidated by a multifold seismic mfs survey of lakes tanganyika and malawi project probe analysis of fault geometries displayed on the probe mfs data coupled with the more extensive 28 khz echosounder data has improved understanding of the geometry and kinematics of the linked fault systems that underlie the lakes in particular it has been recognized that profiles across i e at high angles to the rift elongation commonly display fault geometries that are not readily retrodeformable there must therefore be significant displacement out of the plane of what would conventionally be regarded as dip lines that is perpendicular to rift elongation and parallel to the tectonic transport or extension direction careful determination of fault plane dip and the dip of synrift reflectors in the hanging wall demonstrates that the dip directions of the shallowest faults and the steepest hanging wall sediment dips are oriented either nw or se this defines the direction of maximum fault block rotation and therefore the direction of extension or tectonic transport as nw se oblique to the trend of the regional rift axis and to the apparent strike of many of the major border faults in the survey area the border faults and many other faults imaged on the probe mfs data must therefore have significant components of strike slip motion and the tanganyika and malawi rift zones have undergone extension oblique to and not perpendicular to their axes near dip slip normal faults steeply dipping oblique slip faults and subvertical strike slip or transfer faults have all been recognized in a complex linked fault system that accomplishes the extension the overall orientation of the rift lakes and their internal segmentation are influenced by major preexisting subvertical fault zones within the basement complex accommodation zones act principally as transfer zones that allow switches in gross polarity of the border fault system the detailed geometries of the accommodation zones result from the specific relations between juxtaposed half graben and the strike and internal geometry of the influencing basement structure the variations in fault geometry subsidence water depth and basin or rift morphology can be better explained by an oblique slip extensional model influenced by basement structures than by a simple orthogonal extensional model

quaternary oblique extensional tectonics in the ethiopian rift horn of africa abstract the ethiopian rift extends in a northeasterly direction from southern ethiopia to the afar region it shows a complex fault pattern characterised by the interplay of a n30 e n40 e trending border fault system with the quaternary wonji fault belt which is constituted by right stepping en echelon n s to n20 e trending faults the wonji fault belt affects mainly the rift floor but it also overlaps with some segments of the margins its en echelon arrangement indicates a left lateral component of displacement along the rift trend the general fault pattern of the ethiopian rift as well as mesoscopic fault analyses and structural features of some key areas indicate the occurrence of a roughly e w extension which is compatible with the sinistral shear component of motion along the rift this paper proposes that oblique rifting related to the e w direction of extension has been active since the beginning of the quaternary and that it came after an earlier phase of roughly pure extension orthogonal to the rift trend

tectonic evolution of the southwest indian ocean since the mid cretaceous plate motions and stability of the pole of antarctica africa for at least 80 myr summary the southwest indian ridge is the boundary where seafloor is being created between the african and antarctic plates east of the newly recognized du toit fracture zone at 27 e it trends north easterly and is cut by a series of six deep near north south clefts marking transform faults this series starts with the dual prince edward fracture zone near 35 e and includes discovery i1 also dual at 42 e indomed at 46 e and gallieni at 52 e terminating with the spectacular atlantis i1 and melville fracture zones at 57 30 e and 60 30 e respectively the trend of these fracture zones is compatible with an instantaneous pole of relative motion for antarctica africa at 8 4 n 42 4 w between 35 e and 55 e the development of the southwest indian ridge has separated the elevated madagascar ridge from the discontinuous crozet plateau that was contiguous to it prior to eocene time in this entire sector the ocean floor overall is elevated with respect to ocean floor of equivalent age elsewhere between these features anomalies 0 22 0 53 ma have been identified north and 13 26 35 60 ma south of the ridge axis these anomalies and 0 34 0 80 ma located just to the west in the mozambique basin lie at the same distance from the ridge axis as a similar sequence east of the bouvet triple junction the similarity in distance from the ridge axis of these anomaly sequences is evidence that africa and east antarctica have been separated by a single plate boundary from 80ma to the present the pole representing the motion of these two plates at the present has not moved in totality far from the position it occupied in the late cretaceous 80 ma furthermore calculation of intermediate finite rotation poles for four intervals within this span reveals only minor 15 excursions from the present pole the spatial reconstruction of the southwest indian ridge at 80ma anomaly 34 places the ridge midway between africa and eastern antarctica and lying at right angles to the north trending mozambique ridge the separation of antarctica from africa following initial opening in the jurassic may have been as straightforward as it appears to have been from 80 ma to the present

the somalia plate and the east african rift system present day kinematics summary the motion of the somalia plate relative to the nubia africa arabia and antarctica platcs is re evaluated using a new inversion method based on a monte carlo technique and a least absolute value misfit criterion a subset of the nuvel 1 data set with additional data along the levant fault and in the red sea is used the results confirm that the motion of arabia with respect to africa is significantly different from the motion relative to somalia it is further shown that the data along the sw indian ridge are compatible with a pole of relative motion between africa and somalia located close to the hypothetical diffuse triple junction between the ridge and thc east african rift the resulting africa somalia motion is then compatible with the geological structures and seismological data along the east african rift system assuming a separate somalia plate thus solves kinematic and geological problems around the afar triple junction and along the east african rift

kinematics of the asal rift djibouti determined from the deformation of fieale volcano because of its subaerial exposure the asal rift segment provides an exceptional opportunity to quantify the deformation field of an active rift and assess the contribution of tectonics and volcanism to rifting processes the present topography of the asal rift results from the tectonic dismemberment during the last 100 000 years of a large central volcanic edifice that formed astride the rift zone 300 000 to 100 000 years ago three dimensional deformation of this volcano has been quantified from the combined analysis of the topography and geology the analysis indicates that spreading at 17 to 29 millimeters per year in a n40 5 e direction accounts for most of the separation between arabia and somalia the small topographic subsidence relative to extension suggests that tectonic thinning of the crust has been balanced by injection and underplating of magmatic material of near crustal density the methodology developed in this study could also be applied to quantify deformation in relatively inaccessible areas where the main available information is topography or bathymetry

seismic velocity and poisson s ratio tomography of the crust beneath east anatolia abstract eastern anatolia is a region in the early stages of continent continent collision and so provides a unique opportunity to study the early development of continental plateau located within the alpine himalayan fold thrust fault belt the anatolian plateau is geologically very complex with over half of the surface area covered with late cenozoic volcanics of diverse composition the plateau is also seismically active and is dissected by numerous seismogenic faults predominantly of strike slip motion in this study we determine 3 d tomographic images of the crust beneath eastern anatolia by inverting a large number of arrival time data of p and s waves from the obtained p and s wave velocity models we estimated the poisson s ratio structures for a more reliable interpretation of the obtained velocity anomalies our tomographic results are generally consistent with the major tectonic features of the region high p and s wave velocity anomalies are recognized near the surface while at deeper crustal layers low seismic wave velocities are widely distributed poisson s ratio exhibits significant structural heterogeneities compared to the imaged velocity structure the seismic activity is intense along highly heterogeneous zones and is closely associated with pre existing faults in the central and western parts of the study area results of the checkerboard resolution test indicate that the imaged anomalies are reliable features down to a depth of about 40 km the low velocity high poisson s ratio zones in the middle to lower crust are consistent with many geophysical observations such as strong sn attenuation low pn and sn velocity and the absence of mantle lid implying the presence of partial melt in the uppermost mantle

quaternary volcano tectonic activity in the soddo region western margin of the southern main ethiopian rift 1 we present an analysis of the distribution timing and characteristics of the volcano tectonic activity on the western margin of the southern main ethiopian rift in the soddo area latitudes between 7 10 n and 6 30 n the margin is characterized by the presence of numerous normal faults with limited vertical offset and often sigmoidal in shape which accommodate a gentle transition from the rift floor to the ethiopian plateau new radiocarbon dating indicates post 30 ka fault activity pointing to a significant late pleistocene holocene tectonic activity of the soddo margin comparison of the fault architecture with analog models suggests that deformation has been controlled by a sub e w roughly n100 e extension direction resulting in an oblique extension with respect to the roughly ne sw trending rift this well accords with inversion of fault slip data collected on faults with pleistocene holocene activity and is also in good agreement with recent gps data from the southern main ethiopian rift our data support a close correlation between the recent volcanic activity and deformation in the study area with eruptive vents located along the recent border faults the axial tectono magmatic activity is subordinate in the area these findings support a transition from axial tectono magmatic deformation in the northern main ethiopian rift to marginal deformation in the central and southern main ethiopian rift in turn indicating an along axis north to south decrease in rift maturity

intraplate deformation and closure of the australia antarctica africa plate circuit to determine the current motion between the australian antarctic and african plates and to test whether this plate circuit obeys closure all plate motion data available along the southeast southwest and central indian ridges are analyzed and reduced to 67 spreading rates 38 transform fault azimuths and 135 earthquake slip vectors carlsberg ridge data were excluded because they record india africa not australia africa motion new data include 10 new transform azimuths along the southwest indian ridge many slip vectors and a dense aeromagnetic survey along the southeast indian ridge all published and many unpublished magnetic profiles are modeled to determine rates consistently over a 3 m y time averaging interval for three reasons 1 magnetic profiles from the southeast and central indian ridges suggest recent spreading rate changes 2 some published rates differ for identical profiles and 3 prior studies have not used identical criteria and time scales to determine spreading rates the new rates differ from published rates by as much as 5 mm yr transform fault azimuths are estimated from bathymetry seasat altimetric data epicenter distributions and offsets of magnetic lineations azimuths of plate motion are also estimated from the horizontal projections of slip vectors from the centroid moment tensor solutions and other focal mechanism studies our new australia antarctica and australia africa euler vectors differ from all prior euler vectors at the 95 confidence level along the southeast and central indian ridges our model gives rates differing by 4 7 mm yr from those of prior models from a systematic analysis of the plate motion data we find no evidence for a nubia somalia antarctica triple junction along the southwest indian ridge we also find no evidence for a triple junction previously proposed to be at 80 e along the southeast indian ridge any deformation within this seismically active region of the australian plate adds up to less than a few millimeters per year along each boundary data are fit well by a single euler vector except for a 5 systematic misfit to azimuthal data along the eastern southeast indian ridge near a seismically active region of the australian plate south of tasmania although seismicity and the azimuthal misfit suggest the australian plate is deforming measurably possibly by distributed deformation or by the westward motion of a small microplate southeast of tasmania the significance of the misfit is marginal and is small enough that systematic errors may cause it these alternative explanations could be distinguished by surveying these transform faults with modern seafloor mapping techniques prior studies found that enforcing plate circuit closure causes systematic misfits to rates along the southeast indian ridge here we find that enforcing closure causes no systematic misfits to any data moreover only insignificant nonclosure is found by an f ratio test which numerical experiments suggest could detect deformation exceeding 2 mm yr we conclude that indian ocean plate circuit nonclosure and the deformation it suggests are much smaller than thought before the absence of significant nonclosure argues against the usefulness of a model of deformation distributed throughout an indo australian plate but favors a model in which the significant deformation occurs in a diffuse plate boundary along the equatorial indian ocean between the central indian ridge and the sumatra trench

viscoelastic analysis of transversely isotropic multilayered porous rock foundation by fractional poyting thomson model abstract this paper presents a numerical solution to the problem of a transversely isotropic multilayered viscoelastic porous rock foundation under vertical circular loadings a fractional poyting thomson model is proposed to elaborate the rheological characteristics of the rock mass the viscoelastic solution of the rock foundation in the transformed domain is deduced by using the elasticity viscoelasticity correspondence principle the actual solution is obtained by the integral inverse transform the reliability and correctness of the fractional viscoelastic model are verified with the experimental data numerical examples are conducted to further verify the accuracy and precision of the presented theory the influence of viscoelastic and transversely isotropic parameters and the rock mass stratification on the time dependent behavior of a rock foundation is further explored

evolution of individual snowflakes during metamorphism 1 the morphological changes of individual snowflakes evolving within a dry snow aggregate have been studied using x ray computed microtomography micro ct fresh dry snow was collected during a snowfall sealed and stored in a 5 c cold room between periodic observations using micro ct time series 3 d images were used to examine the structural evolution of an individual snowflake within the aggregate over a 2 month period after which the snowflake had lost its original dendritic structure analysis of the aggregate showed that the fraction of large ice particles increased over this period while the total number of particles decreased presumably to lower the free energy of the snow specimen this approach enables the study of metamorphism of individual snowflakes in a local environment close to that found in nature the evolution of structural parameters including the volume fraction of ice the surface to volume ratio of the ice matrix the thickness and separation of the ice structure determined by the distance transform of the ice and pore space were monitored and analyzed using coarsening theories the computed growth exponent was smaller than the values obtained in the earlier work by legagneux et al 2004 and kaempfer and schneebeli 2007 who also interpreted the isothermal metamorphism in terms of coarsening theories

mid holocene erosive episodes in tufa deposits from trabaque canyon central spain as a result of abrupt arid climate transitions during the holocene a series of tufa sediments were deposited from a karstic spring along the trabaque canyon central spain a long term lowering of the water table caused the location of the spring to be displaced from the upper sector of the canyon during the early holocene to the lower sector in the late holocene this progressive shift was in response to decreased precipitation in the region the depositional environments and their geomorphologic relationships were characterized thus five morphosedimentary units msus were identified within the holocene tufa deposits erosive episodes were recognized between msus and as most of the msus partially overlap the older ones are perched in relation to the younger ones the chronology of the msus is based on 14c dates and stable isotopes and total organic carbon content provided environmental information during the period of tufa sedimentation the successive dissection episodes in the trabaque canyon tufa deposits took place during transitioning climate conditions from the relatively wet early holocene to the more arid late holocene during this transitional period in the mid holocene wet phases alternated with more arid conditions causing the largest hydrological regime gradients in the holocene thus the four erosive episodes causing tufa dissection in trabaque during the holocene are interpreted as the result of abrupt transitional periods towards arid conditions

assessment of the collapse mechanisms of tufa deposits abstract this research assesses the collapse mechanisms of tufa deposits the city of antalya located on the mediterranean coast of turkey has been settled on tufa deposits by the end of 1980s the area behind the tufa cliffs became the site of high rise residential buildings some of these buildings have suffered from foundation instabilities which have given rise to cracking and fissuring of the walls and overall tilting the collapsible behaviour upon loading and or wetting of some tufa deposits has caused foundation settlement voids bonding of grains and grain properties of the collapsible tufa were investigated using optical and scanning electron microscopes our studies indicate that the collapse behaviour of tufa is affected mainly by depositional environment and microfabric laboratory tests have been performed in order to determine the index properties and the collapse potential of tufa samples young tufa deposits near the surface are weakly bonded with thin films of carbonate cement giving rise to high void ratios analysis of geotechnical parameters has shown that the collapse potential of tufa is closely related to the natural void ratio and the amount of cement binding the grains

internal structure of the dead sea leaky transform rift in relation to plate kinematics abstract the structures along the dead sea transform rift are related to the motions of the sinai and arabia plates which border it and to the irregularities of their boundaries the total slip was 105 km left lateral but the present structures were formed mainly during the last 40 km of slip which probably occurred in the plio pleistocene along the southern half of the transform the strike slip motion takes place on en echelon faults this produces rhomb shaped grabens or pull aparts which are sometimes composite and in which there is local crustal separation thus much of the transform is leaky these structures occur in a morpho tectonic rift valley delimited by normal faults which express a small component of transverse extension along a few segments the shape of the transform is such that lateral motion produces local transverse compression the geometric relations of the structures along the transform define an eulerian pole of relative plate motions at 32 8 n 22 6 e 0 5 the older motion was somewhat different and is described by a pole located about 5 west of the above then the component of transverse extension and crustal separation was much smaller than now while local transverse compression was more important the northern half of the dead sea transform has an irregular shape and the bordering plates did not remain rigid as lateral motion continued here transverse compression is often important

moment tensor solutions estimated using optimal filter theory global seismicity 1988 1989 moment tensor solutions estimated using optimal filter theory are listed for 201 moderate to large earthquakes occurring from 1988 to 1989

a reappraisal of earthquake focal mechanisms and active shortening in the zagros mountains of iran summary the zagros mountains of sw iran are one of the most seismically active intra continental fold and thrust belts on earth and an important element in the active tectonics of the middle east surface faulting associated with earthquakes is extremely rare and so most information about the active faulting comes from earthquakes we use long period teleseismic p and sh body waves to determine the orientation and depth of faulting in 16 new earthquakes and then evaluate and synthesize all the available teleseismic data on earthquake source parameters in the zagros we use this information to investigate the style and distribution of active faulting in the zagros and how it contributes to the n s shortening of the arabia eurasia collision when the data are ranked in quality and carefully evaluated simple patterns are seen that are not apparent when routine catalogue data are taken at face value an important change in the fault configuration occurs along strike of the belt in the nw overall convergence is oblique to the trend of the belt and the surface anticlines and is achieved by a spatial separation partitioning of the orthogonal strike slip and shortening components on separate parallel fault systems by contrast in the se overall convergence is orthogonal to the regional strike and achieved purely by thrusting in the central zagros between these two structural regimes deformation involves parallel strike slip faults that rotate about vertical axes allowing extension along the strike of the belt the overall configuration is similar to that seen in other curved shortening belts such as the himalaya and the java sumatra trench all the zagros earthquakes we have been able to check have centroids shallower than 20 km and are confined to the upper crust many of the larger earthquakes are likely to occur in the basement beneath the sedimentary cover which is active even beneath areas of known shallow structural decollement such as the dezful embayment the dominant style of shortening is high angle reverse faulting with dips 30 though some lower angle thrusting occurs in places active thrust and reverse faulting is relatively confined to the lower topography on the sw edge of the belt today and only strike slip faulting affects the higher topography profound vertical changes in structural and stratigraphic level indicate that a similar style of deformation was once active across the width of the simple folded belt but has progressively migrated sw over the last 5 ma there is no evidence for a seismically active structural decollement such as a low angle thrust beneath the zagros nor is there any seismic evidence for active subduction either beneath the zagros or beneath central iran instead the arabian margin seems to have shortened by distributed thickening of the basement only in the syntaxis of the oman line at the se end of the zagros is there any evidence for a low angle thrust of regional extent here earthquakes continue 50 km north of the zagros thrust line the geological suture between the arabian margin and central iran reaching depths of 30 km and may represent thrusting of arabian basement beneath central iran to this extent

orientation of absolute african plate motion revealed by tomomorphometric analysis of the ethiopian dome the ethiopian dome comprising the ethiopian and yemeni plateaus formed as a result of the uplift of red sea gulf of aden and ethiopian rift shoulders the uplift was essentially due to a mantle plume activity a digital elevation model of this region before rifting constructed by using the rotation of its constituent plates and pulling down the rift shoulders reveals that important high areas existed before rifting these highs are interpreted to be the result of mantle plume activity a fast fourier transform was used to smooth the digital elevation model prerift dome before a tomomorphometric analysis was applied to quantify the orientation of each digital elevation model horizontal slice this procedure allowed us to determine a bearing of n30 e for absolute african plate motion since the paleogene

a new kinematic approach for the danakil block using a digital elevation model representation abstract data from the literature are integrated in a regional digital elevation model dem in order to analyse the motion of the danakil block with regard to the arabian and somalian plates the application of the poles and angles of rotation taken from the literature induces a superposition of the danakil block on the arabian plate and the formation of a gap in the afar region the determination of new poles of rotation using a best fitting procedure allows one to avoid these drawbacks in all cases calculations are carried out keeping the nubian plate stationary the present approach shows that the danakil block is an independent entity and is not related to the nubian and arabian plates between the oligocene and the miocene it has been submitted to a n20 e sinistral strike slip motion anterior to the rotation itself that was started in the middle miocene this rotation is directed by a mechanical couple due to the combination of the red sea and north afar extensions

oblique extensional tectonics in the malawi rift africa the malawi rift is the southern segment of the western branch of the east african rift system there has been little agreement as to whether this rift is opening perpendicularly or obliquely to its north south axis and little agreement on a mechanism for the formation of the asymmetric basins that make up the rift our analysis combines landsat image interpretation and field measurement of the latest slip direction on faults to produce a kinematic model of rift evolution the fault slip data are consistently compatible with a late cenozoic northwest southeast directed divergence between the nubian and somalian blocks plates across the rift the northwest striking livingstone fault at the northern limit of the malawi rift and the northwest striking zambezi fault zone to the south serve as dextral intracontinental transform zones between left stepping segments of the western branch of the east african rift system within the rift second order northwest striking transfer faults separate adjacent asymmetric basins the transform and transfer faults form a pattern that is similar to overlapping right stepping strike slip faults with a releasing geometry fault surfaces with two sets of striations indicate a progression from predominantly strike slip toward oblique normal faulting we hypothesize that during initial rift formation most northwest striking faults were dextral and that fault interaction between these structures resulted in curved stress trajectories and a pull apart component arcuate north to northeast striking border faults and subsiding basins then formed between these northwest striking faults in response to the right stepping dextral shear the maximum distance over which fault interaction is significant may control basin dimensions as opening of the rift proceeds slip partitioning and gravity failure result in increasing normal slip perpendicular to major escarpments and decreasing strike slip parallel to them

kinematic constraints on distributed lithospheric deformation in the equatorial indian ocean from present motion between the australian and indian plates from an expanded accurate and up to date data set comprising 110 spreading rates 46 transform azimuths and 151 earthquake slip vectors from the indian ocean and gulf of aden we determine a new rigid plate model describing the motion since 3 ma between india and australia the euler vector 0 313 m y about 5 s 78 e lies near the middle of the equatorial diffuse plate boundary dividing the indian from the australian plate and predicts a rate of north south shortening along 85 e of 4 3 mm yr only 30 as fast as predicted by our prior model the new model also predicts north south extension of 6 2 mm yr at 68 e along the western segment of the diffuse plate boundary where our prior model predicted north south contraction using data only along the carlsberg and central indian ridges and no other plate boundaries we show that plate motion data cannot be fit by a single euler vector however the data are well fit by two euler vectors when an east west striking india australia plate boundary is assumed to intersect the central indian ridge near the equator the best location along the central indian ridge for this triple junction is 6 s 3 s with 95 confidence limits of 9 s 4 n just west of a region of intense seismicity the sense of deformation as recorded in earthquake focal mechanisms reverse faults mapped with reflection seismic data and undulations in basement topography surface gravity and the geoid agrees well with the north south extension predicted in the western part and the north south shortening predicted in the eastern part of the india australia boundary the predicted rate of north south shortening between 79 e and 86 e is consistent with the rate of shortening inferred from observed faulting and folding shortening taken up by faulting is 6 to 100 times greater than that taken up by the spectacular basement folds little of the rapid north south shortening predicted east of 86 e is taken up by crustal thickening instead lithosphere is transported northeastward toward the sumatra trench through strike slip faulting and possible clockwise rotation the failure of the convergent segment of the diffuse plate boundary to form a subducting trench provides some new observations that must be satisfied by models for the initiation of subduction a model of separate rigid indian and australian plates divided by a diffuse plate boundary appears to be valid and useful because the predictions of the model agree with independent data and because the predicted velocity of relative motion is statistically significant and comparable with that across other plate boundaries

segmentation and along strike asymmetry of the passive margin in socotra eastern gulf of aden are they controlled by detachment faults on the island of socotra the southern passive margin of the gulf of aden displays along its strike two different types of asymmetric structures western socotra is made up of a series of southward tilted blocks bounded by consistently northward dipping normal faults eastern socotra consists of a broad asymmetric anticline with a steep northern limb and a gently dipping southern limb a zone of ne sw striking strike slip and normal faults separates the two areas the overall structure is interpreted as representing two rift segments separated by a transfer zone the along strike juxtaposition of crustal scale asymmetric structures on the southern margin of the gulf of aden is complemented by the asymmetry of the conjugate margins on either side of the gulf whereas the western socotra margin is narrow and characterized by oceanward dipping normal faults the conjugate oman margin is broader and dominated by horsts and graben considering that asymmetric structures in the upper crust are often associated with synthetic shear zones at deeper ductile levels we propose that the western and eastern socotra margin segments were controlled at depth by two detachment faults with opposite dips and senses of shear the normal faults of western socotra would sole out into a top to the north ductile shear zone whereas the asymmetric anticline of eastern socotra would be associated with a top to the south detachment fault

seismic behaviour of the dead sea fault along araba valley jordan the dead sea fault zone is a major left lateral strike slip fault south of the dead sea basin the wadi araba fault extends over 160 km to the gulf of aqaba the dead sea fault zone is known to have produced several relatively large historical earthquakes however the historical events are unequally distributed along the fault and only four events have been reported in the araba valley over the last few thousands of years magnitudes estimated from the historical record are probably slightly smaller than that of the m w 7 3 earthquake that struck the gulf of aqaba in 1995 the fault cuts straight across pleistocene to holocene alluvium and shows morphologic evidence for essentially pure strike slip motion regional seismic monitoring reveals little microseismicity along the fault except around the dead sea and gulf of aqaba where the fault splays into complex pull apart basin fault systems we have investigated the fault zone at several sites selected from spot images and the study of aerial photography at the site of the now destroyed tilah castle a well preserved wall dated to be about 1200 yr bp 14 c age on charcoal is cut by the fault and offset by 2 2 m comparison with offset gullies at a nearby site 3 km to the north and at three other sites respectively 25 50 and 65 km to the south reveals that this specific fault displacement is probably related to the last seismic event that ruptured that fault segment possibly in ad 1458 moreover the offset gullies suggest a characteristic slip behaviour with recurring slip of about 1 5 m on average given the 4 2 mm yr 1 slip rate derived for this fault segment we infer that the fault should produce m w 7 earthquakes along some segment in the araba valley about every 200 years the historical period with only four well documented large earthquakes in ad 1068 ad 1212 ad 1293 and ad 1458 thus appears to have been relatively quiescent with a 20 per cent deficit of m w 7 earthquakes however our data do not exclude the possibility of larger m w 7 6 earthquakes or time clustering of earthquakes over longer timespans an alternative seismic behaviour involves m w 7 6 earthquakes about every 6000 years and m w 7 earthquakes about every 250 years the historical catalogue would then appear to be complete for m w 7 earthquakes

lithospheric structure of a nascent spreading ridge inferred from gravity data the western gulf of aden the aden spreading ridge somalia arabia plate boundary does not connect directly to the red sea spreading ridge it propagates toward the east african rift through the afar depression where the presence of a hot spot has been postulated from seismological and geochemical evidence the spreading direction n37 e is highly oblique to the overall trend n90 e of the ridge we present and interpret new geophysical data gathered during the tadjouraden cruise r v l atalante 1995 in the gulf of aden west of 46 e these data allow us to study the propagation of the ridge toward the afar and to discuss the processes of the seafloor spreading initiation we determine the lithospheric structure of the ridge using gravity data gathered during the cruise with the constraint of available refraction data a striking bouguer anomaly gradient together with the identification of magnetic anomalies defines the geographical extent of oceanic crust the inversion of the bouguer anomaly is performed in terms of variations of crustal thickness only and then discussed with respect to the expected thermal structure of the mantle lithosphere which should depend not only on the seafloor spreading but also on the hot spot beneath east africa our results allow us to define three distinct lithospheric domains in the western gulf of aden east of 44 45 e the lithosphere displays an oceanic character thermal subsidence recorded for the last 10 ma and constant crustal thickness between 43 30 e and 44 10 e the lithosphere is of continental type but locally thinned beneath the axial valley the central domain defined between 44 10 e and 44 45 e is characterized by a transitional lithosphere which can be seen as a stretched continental crust where thick blocks are mixed with thinned crust it displays en echelon basins that are better interpreted as extension cells rather than accretion cells

a theory of intraplate tectonics the theory of plate tectonics assumes a rigid behavior of tectonic plates and therefore fails to account for observed intraplate deformation a new theory of intraplate tectonics is developed to calculate the first order intraplate deformation induced by horizontal displacement of deformable plate boundaries it is based on simple assumptions that link the well established directions of relative plate motion to the displacement and deformation fields within a plate interior adjacent to three types of deformable plate boundaries inward outward and tangential displaced boundaries the theory predicts the direction of intraplate displacement displacement rate strain and stress fields in terms of small circles great circles and 45 loxodromes around the pole of rotation of two adjacent plates the 45 loxodromes are two orthogonal sets of directions clockwise and counterclockwise that intersect both small and great circles at 45 the principal axis of the maximum horizontal stress follows small circles for inward displaced boundaries great circles for out ward displaced boundaries and loxodromes for tangential displaced boundaries the theoretical predictions are systematically compared with more than 4000 reliable observed directions of maximum horizontal stress provided by the world stress map project zoback 1992 the theory indicates that the first order intraplate deformation is predominantly induced by horizontal forces acting on plate boundaries and by buoyancy forces that arise from lateral density variations between mid ocean ridges and plate interiors ridge push the simplicity of the predictions and their good agreement with observations suggests that intraplate deformation should be investigated in the pole of rotation spherical coordinate system

thermal conductivity and heat transfer through the snow on the ice of the beaufort sea 1 eighty nine point measurements of the thermal conductivity ks of the snow on the sea ice of the beaufort sea were made using a heated needle probe average values ranged from 0 078 w m 1 k 1 for new snow to 0 290 w m 1 k 1 for an ubiquitous wind slab ks increased with increasing density consistent with published equations but could also be reliably estimated from the metamorphic state of the snow using measured values of ks and snow stratigraphy the average bulk value for the full snowpack was 0 14 w m 1 k 1 in contrast ks inferred from ice growth and temperature gradients in the snow was 0 33 w m 1 k 1 the mismatch arises in part because the second estimate is based on measurements from an aggregate scale that includes enhanced heat flow due to two and three dimensional snow and ice geometry a finite element model suggests that the complex geometry produces areas of concentrated heat loss at the snow surface these hot spots however increase the apparent conductivity only by a factor of 1 4 not enough to fully explain the mismatch nonconductive heat transfer mechanisms like natural and forced air convection may also be operating in the snowpack though the ubiquitous presence of low permeability wind slabs potentially limits their effectiveness the relative contributions of effects due to snow and ice geometric and nonconductive processes within the snowpack remain uncertain

classification and environmental models of cool freshwater tufas abstract tufa deposits are common in the quaternary record facies developments are dependent upon localised carbonate precipitation generally these take the form of phytoherm build ups together with associated detrital deposits derived from disagragation of the former phytoherm cements differ from speleothems and floe calcite accumulations in being biologically mediated or modified this paper recognises the following five types perched spring line cascade fluviatile paludal and lacustrine facies each type is composed of distinctive constructional and detrital sediment associations these unique sediment combinations are the product of an interplay between angle of slope water discharge rate standing water bodies phytal and microbial colonization and ambient temperature the proposed models will be of value in the interpretation of ancient and partially exposed tufas

centroid depths and mechanisms of mid ocean ridge earthquakes in the indian ocean gulf of aden and red sea we have determined the centroid depths and source mechanisms of 14 earthquakes along spreading centers in the indian ocean gulf of aden and red sea the earthquakes are all characterized by normal faulting on planes dipping at about 45 and generally striking parallel to the local trend of the spreading center for the ridge axis earthquakes in the indian ocean gulf of aden and central red sea seismic moments range from 3 to 9 1024 dyn cm source time functions are all of simple form and centroid depths of events with adequate azimuthal coverage are all very shallow between 1 and 4 km beneath the seafloor if the centroid depth typically marks the mean depth of fault slip then earthquake faulting extended to 2 8 km beneath the seafloor during these earthquakes the centroid depths for two earth quakes near the mouth of the gulf of suez support the view that seismic faulting accompanying continental rifting generally extends to greater depth than does seismic faulting along the axes of oceanic spreading centers when these findings are combined with our earlier results from the mid atlantic ridge the greatest centroid depths of earthquakes with well constrained source mechanisms tend to shoal with increasing spreading rate this result supports a general decrease with spreading rate in the maximum thickness of the zone of brittle behavior for slow spreading ridges

unusually deep earthquakes in east africa constraints on the thermo mechanical structure of a continental rift system shudofsky 1985 has established that earthquakes associated with the east african rift system have well constrained focal depths as great as 25 30 km using published heat flow measurements as a guide to the local geotherm we find through simple stress envelope calculations that the deepest earthquakes probably occur in the lower crust in a region where the lithosphere is strong these results are at odds with the commonly held idea that seismicity in zones of continental extension is limited to the shallow upper crust because of elevated temperatures accompanying lithospheric thinning any model of the rifting process in east africa must account for the fact that these regions exhibit considerable strength down to lower crustal levels

active faulting in the dead sea rift abstract manifestations of late quaternary and holocene faulting were studied in a 500 km long segment of the dead sea transform rift most prominent are left slip faults whose characteristic physiographic features are recognizable along most of the studied segment where these faults bend or are stepped to the left rhomb shaped grabens or pull aparts are produced forming depressions in the reverse situation compressional features such as pressure ridges domes and folds form positive topographic features such structures are combined on a variety of scales ranging from a few hundred meters long to tens of kilometers normal faults sub parallel to the left slip faults produce a trough like valley along much of the dead sea transform but are most prominent along the margins of the large rhomb grabens e g the dead sea trough they apparently record a small component of transverse extension generally their motion is slow young slip did not occur along some segments during the last few 10 4 y elsewhere throws of 10 20 m at least occurred in this period the dead sea transform is seismically active the instrumental and historic records indicate a seismic slip rate of 0 15 0 35 cm y during the last 1000 1500 y while estimates of the average pliocene pleistocene rate are 0 7 1 0 cm y either much creep takes place or the slip rate varies over periods of a few 10 3 y

a seismically active section of the southwest indian ridge the section of the southwest indian ocean ridge west of the prince edward fracture zone has a large ridge axis offset and a complicated ridge transform morphology we have determined the source mechanisms of transform earthquakes along this portion of the ridge from an inversion of long period p and sh waveforms the seismicity is characterized by anomalous faulting mechanisms source complexity and an unexpectedly large seismic moment release several earthquakes with dip slip components of faulting have been recognized on the central section of the andrew bain and 32 e transforms suggesting geometrical complexity along the transform this region has experienced a mw 8 0 transform earthquake in 1942 yet we observe a seismic slip rate during the last 20 years that is still comparable to the predicted spreading rate 1 6 cm yr the calculated slip rate over a period of 60 years is three times greater than the expected rate of spreading

displacements strains and rotations within the afar depression djibouti from restoration in map view within the afar depression djibouti the stratiform basaltic lava flows emplaced between 4 ma and 1 ma cover the two thirds of the depression because of the desert climate they are almost non eroded the topography can then be used as a reference surface to measure the vertical offset of younger faults using a detailed map the southeastern part of the depression showing the fault pattern and the vertical offset on each fault obtained from stereoparts of spot images we have restored the topography in map view we have computed the fields of finite displacement rotation and strain the field of horizontal displacements shows vectors trending to the ne on average this direction is compatible with the displacement to the ne of the arabian plate with reference to the african plate in detail however displacement vector trend from nne ssw to ne sw major axes of strain ellipse trend ne sw suggesting that major faults n120 are dominantely extensional strain intensities and magnitudes of block rotations are increasing from southwest to northeast of the restored area magnitudes of block rotations are very small compared with those obtained from paleomagnetic measurements therefore we computed a second restoration that covers a smaller area where the true vertical offset of the major faults taking into account the sedimentary fill of basins were avalaible this second model gives rotation magnitudes in better agreement with paleomagnetic data but still underestimates we discuss these results with the available kinematic models of the southeastern part of the depression

seaward extension of the east african rift the continental margin of northern mozambique is edged by a north south trending alignment of submarine peaks forming the davie ridge fig la from earlier studies1 5 the ridge has been interpreted as a remnant transform fault that controlled the late jurassic early cretaceous drift of madagascar and the opening of the somali basin6 8 during md40 macamo cruise june 1984 7 500 km of water gun seismic reflexion lines have been implemented throughout the region where two flat bottomed troughs the north south trending kerimbas and lacerda deep grabens interrupt the continental slope alongside the ridge these grabens cut into tertiary sediments correspond westward to a miocene tilting or a recent normal fault and eastward to an old discontinuity several times reactivated and located above an abrupt uplift of the moho the two grabens are separated from each other by a rigid region of thickened crust affected by intense seismicity and supporting volcanoes we report here that the eastern branch of the east african rift joins the submerged grabens across the tanzanian continental shelf fig 1b

active tectonics and late cenozoic strain distribution in central and eastern iran 1 right lateral shear between central iran and afghanistan is accommodated on n s right lateral strike slip faults surrounding the aseismic dasht e lut north of 34 n the right lateral shear is accommodated on left lateral faults that rotate clockwise about vertical axes little is known of the late tertiary and younger offsets and slip rates on the active fault systems results that are important for understanding the regional tectonics we use observations from satellite imagery to identify displaced geological and geomorphological markers which we use in conjunction with the overall morphology and orientation of the active fault systems to estimate the total cumulative right lateral shear estimates of cumulative fault movements from offset features and inferred vertical axis rotation of fault bounded blocks suggest that the late cenozoic strain is concentrated toward the eastern margin of iran along the sistan shear zone where bedrock offsets of at least 70 km are observed across the active faults the geomorphology of the deh shir anar and great kavir strike slip faults in central iran suggest that although little shortening is accommodated across this region they might still be active and hence capable of producing earthquakes present day activity on these faults in central iran would not be expected from distributions of instrumental and historical earthquakes although speculative the late tertiary strain distribution described in this paper is consistent with what we know of the present day rates of shear in eastern iran and provides a framework to which later more detailed work can be added

the afar depression interpretation of the 1960 2000 earthquakes summary we studied the seismic activity of the afar depression ad and adjacent regions during the period 1960 2000 we define seven distinct seismogenic regions using geological tectonic and seismological data based on the frequency magnitude relationships we obtain b values of about 1 for the different regions the pattern of the distribution of the location of epicentres fits with the known active fault zone in the ad and the axial volcanic ridges the bab el mandab area and the danakil aysha a blocks are less active for 125 intermediate to strong earthquakes the seismic moment and source parameters were calculated the results of the fault plane solutions for the afar depression indicate mainly strike slip and normal sense of movement originating from fault planes striking nw se these results indicate a clockwise block rotation described previously as a bookshelf model in central ad there are a few rightlateral faults east of massawa with e w striking fault planes at the southern red sea north of the danakil block the mixed focal mechanisms with axial plane striking nw se comprise several reverse faulting strike slip motion and normal faulting right lateral movement was also calculated for a cluster of seismic events between the manda hararo and alyata volcanic ridges along nw se striking faults along the n s striking faults in the escarpment at the western afar margins there are two distinct clusters of epicentres the strong earthquakes at the southern cluster exhibit normal or strike slip motions the intermediate to small earthquakes in the northern cluster exhibit reverse and strike slip motions mainly normal faults were calculated along ne sw striking faults of the ethiopian east african rift estimates of the seismic efficiency suggest that the maximal values are about 50 per cent or less implying that most of the motion is taken aseismically

deformation of indian ocean lithosphere evidence for a highly nonlinear rheological law the width of diffuse oceanic plate boundaries is determined by the rheology of oceanic lithosphere here we apply thin viscous sheet models which have been successfully applied to deformation in several continental deforming zones to investigate the deformation of oceanic lithosphere in the diffuse oceanic plate boundaries between the india capricorn and australia plates we apply kinematic boundary conditions based on the current motion between these plates we neglect buoyancy forces due to plate thinning or thickening and assume that the thin viscous sheet has the same depth integrated nonlinear viscosity coefficient everywhere our initial models have only one adjustable parameter n the power law exponent with n 1 3 10 30 and 100 the predicted width of the deforming zone decreases with increasing n with n 30 explaining the observations this n value is higher than has been estimated for continental lithosphere and suggests that more of the strength of oceanic lithosphere lies in layers deforming by faulting or by dislocation glide than for continental lithosphere to obtain a stress field that better fits the distribution and type of earthquake focal mechanisms in the diffuse oceanic plate boundary we add a second adjustable parameter representing the effect of slab pull stretching the oceanic plate near the sumatra trench we show that an average velocity increment on this boundary segment of 5 mm a 1 relative to the average velocity of the india and australia plates fits the observed distribution of fault types better than velocities of 3 3 mm a 1 or 10 mm a 1

observation of temperature gradient metamorphism in snow by x ray computed microtomography measurement of microstructure parameters and simulation of linear elastic properties the process of temperature gradient metamorphism in snow strongly affects the microstructure and associated mechanical properties of the snow the purpose of this study was to 1 examine the temporal variations in three dimensional snow microstructure under the influence of a strong temperature gradient for 6 days using x ray computed microtomography mct and 2 numerically simulate the linear elastic properties of snow from microtomographic data using a voxel based finite element technique the temporal changes in the snow structure were analyzed in terms of density specific surface area ssa thickness distribution of ice matrix and pores structure model index and mean intercept length mil fabric tensor the structural indices and orthotropic elastic compliance matrix were computed over several sub volumes within the reconstructed volume to account for statistical uncertainties the mean density increased by about 14 on day 1 and no significant trend was observed thereafter the ssa decreased by 22 whereas both the ice and pore thickness distributions widened with time the computed young s moduli were 1 5 4 times larger than previously published dynamic measurements and found to be significantly correlated with ice volume fraction and mil fabric measures the increasing trend in computed moduli during the experiment is consistent with the observed development of thicker vertical ice structures multiple linear regression models of elastic compliances using fabric tensor formulation and ice volume fraction could explain 89 9 93 0 of the variance our results suggest a strong dependence of elastic properties on both density and microstructural fabric

global seismicity of 1981 centroid moment tensor solutions for 542 earthquakes abstract centroid moment tensor solutions are presented for 542 earthquakes that occurred during 1981

a numerical model to simulate snow cover stratigraphy for operational avalanche forecasting laws of snow metamorphism have been introduced in a numerical model which simulates the evolution of temperature density and liquid water profiles of snow cover as a function of weather conditions to establish these laws the authors have summarized previous studies on temperature gradient and on wet snow metamorphism and they have also conducted metamorphism experiments on dry or wet fresh snow samples an original formalism was developed to allow a description of snow with parameters evolving continuously throughout time the introduction of laws of metamorphism has improved significantly the derivation of the settlement of internal layers and of snow covered albedo which depend on the simulated stratigraphy i e the type and size of snow grains of different layers of the snow cover the model was tested during a whole winter season without any re initialization comparison between the simulated characteristics of the snow cover and the observations made in the field are described in detail the model proved itself to be very efficient in simulating accurately the evolution of the snow cover stratigraphy throughout the whole winter season

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

eocene to recent development of the south west indian ridge a consequence of the evolution of the indian ocean triple junction summary the south west indian ridge the contact between the african and antarctic plates lies between the bouvet triple junction in the south atlantic and the indian ocean triple junction about 2100 km east of madagascar from the vicinity of prince edward island at 40 e it trends north easterly and it is segmented by a suite of deep north south gashes terminating on the north east with two spectacular meridional fracture zones the atlantis ii and the melville at 57 30 e and 60 30 e respectively from there northeast to the indian ocean triple junction at 25 30 s 70 00 e the ridge trends n75 e it is characterized by a triangle of rough topography with the triple junction at the eastern apex from all available data an instantaneous pole of relative motion for africa antarctica was computed it lies at 8 4 n 42 4 w with a rate of 0 15 myr 1 since the marked change in the direction and rate of spreading in the madagascar crozet and central indian basins that occurred in the eocene 44 ma anomaly 19 the poles of relative motion for the african indian and antarctic plates have changed very little we fixed the africa antarctica and africa india poles and computed that for india antarctica we justified this pole by comparisons of predicted isochrons with observed magnetic lineations and determined the tectonic history of the triple junction since the eocene 44 ma anomaly 19 this junction has moved as rapidly east wards with respect to africa as antarctica has moved south the resultant geometry and slow spreading account for the triangle of rough topography produced by the south west indian ridge east of the melville fracture zone the triple junction evolved as a stable ridge ridge ridge type with the south east indian ridge remaining approximately constant in length it was not resolved whether this constancy in length is maintained by frequent ridge jumps or by oblique spreading on the south west and central indian ridges near the triple junction

transverse structures in the central part of the red sea and implications on early stages of oceanic accretion summary transverse structures in the central part of the red sea are mapped according to bathymetric seismic gravity and magnetic data five classes of structures are detected three of these are fractures intertrough zones and transform faults the remaining two are classified as transform zones and pseudo transform faults most structures can be related to ancient lineaments on land intertrough and transform zones are manifestations of unorganized seafloor spreading and their crustal structure is of an oceanic nature that might be similar to quiet magnetic zones

the quaternary travertine deposits of europe and asia minor abstract a summary is provided of the published information relating to all aspects of quaternary travertine formation in europe west of the ural mountains the deposits have been divided into two broad groups the meteogene travertines which result primarily from the degassing of soil borne aqueous co 2 and thermogene deposits resulting from the degassing of thermally generated co 2 meteogene deposits are rare above latitude 58 n and in regions where the mean annual air temperature is below 5 c a significant positive correlation exists between mean air temperature and travertine deposit thickness the combined effects of temperature and rainfall are used to provide a zoned map showing the travertine forming potential of limestones within the region information from 14 c dating indicates that deposition reached a maximum in the period 5 10 ka bp and is currently limited by land and water management practices in the populated areas thermogene deposits occur in regions of high co 2 discharge resulting from tectonic activity such as italy and turkey where there is much vulcanism these travertines are frequently more massive and less readily weathered than meteogene deposits fully referenced information is provided for 320 important mostly well studied sites 227 meteogene 93 thermogene of which 156 are currently active

propagation of an oblique spreading centre the western gulf of aden abstract the east west trending gulf of aden rift between arabia and somalia is spreading along a n35 e direction it propagates westward inside the african continent toward the afar triple junction oblique to the spreading direction these combined propagation and oblique rifting generate a special faulting pattern associated with an irregular distribution of volcanism we analyse this pattern using a structural map derived from the analysis of multibeam bathymetric data and backscattering images from the 1995 tadjouraden cruise in the western gulf of aden the rift valley is bounded by faults trending from n110 e to n130 e in the eastern part of the surveyed area where the valley trends n90 e and by large faults in the central western part where the valley is oriented n70 e the direction of extension deduced from the fault histogram is n37 e 10 over the whole area whatever the rift trend therefore this bend of the plate boundary does not result from a change in the stretching direction this bending increases the rifting obliquity westward and therefore modifies the faulting pattern faults display two distinct patterns either en echelon on the walls indicating a right lateral component of shear or purely normal and parallel to the rift trend inside the valley volcanoes are mostly located in the eastern part of the rift where they are aligned into swarms trending roughly perpendicular to the extension direction deduced from fault directions backscattering images show that recent lava flows fill the axial valley of the eastern part whereas in the central and western parts volcanoes are scattered in the middle part of the valley this distribution is interpreted as a westward propagation of the volcanism and as the direction of deformation migration the thickness of the upper brittle layer of the lithosphere is estimated from the width if the inner graben is inside the rift it indicates a deepening of the brittle ductile transition from east 6 km to west 16 km these values are typical of oceanic and continental systems respectively and consistent with the depth of earthquakes in the western part this points out the existence of a transitional area between 44 e and 45 20 e characterised by the lack of recent volcanism the nature of this mechanical transition is discussed in terms of propagation of an spreading centre into a continental or transitional afar type lithosphere

the thermal conductivity of seasonal snow twenty seven studies on the thermal conductivity of snow k eff have been published since 1886 combined they comprise 354 values of k eff and have been used to derive over 13 regression equation and predicting k eff vs density due to large and largely undocumented differences in measurement methods and accuracy sample temperature and snow type it is not possible to know what part of the variability in this data set is the result of snow microstructure we present a new data set containing 488 measurements for which the temperature type and measurement accuracy are known a quadratic equation where is in g cm 3 and k eff is in w m 1 k 1 can be fit to the new data r 2 0 79 a logarithmic expression can also be used the first regression is better when estimating values beyond the limits of the data the second when estimating values for low density snow within the data set snow types resulting from kinetic growth show density independent behavior rounded grain and wind blown snow show strong density dependence the new data set has a higher mean value of density but a lower mean value of thermal conductivity than the old set this shift is attributed to differences in snow types and sample temperatures in the sets using both data sets we show that there are well defined limits to the geometric configurations that natural seasonal snow can take

the gulf of aden structure and evolution of a young ocean basin and continental margin new marine geophysical data are used to describe the structure and history of the gulf of aden magnetic anomaly data shows seafloor spreading magnetic anomalies of sheba ridge from the axial anomaly to anomaly 5 10 m y b p between the owen fracture zone and 45 sup 0 e and to anomaly 2 3 m y b p or anomaly 3 4 m y b p west of 45 sup 0 e the data does not support the two episodes of seafloor spreading recently proposed landward of the seafloor spreading magnetic anomalies is a magnetic quiet zone of uncorrelatable anomalies the magnetic quiet zone boundary is also a structural boundary effectively marking the edge of sheba ridge with deeper basement lacking a significant topographic gradient found on the landward side a magnetic quiet zone is found not only where sheba ridge splits continental lithosphere but also on east sheba ridge where the ridge splits the old oceanic lithosphre of the owen and somali basins there the position occupied by the continental margin within the gulf is marked by nonmagnetic ridge complexes that stretch from the continents to the owen fracture zone the magnetic quiet zone boundary is not an isochron in either the gulf of aden ormore the red sea suggesting that significant horizontal motions can occur prior to the initiation of seafloor spreading the offset on the dead sea rift is used to estimate that from 80 to 160 km of opening amounting to between 65 and 200 extension of the initial rift valley occurred in the gulf of aden and red sea prior to the establishment of a mid ocean ridge it is suggested that the development of a new ocean basin occurs in two stages the first involves diffuse extension over an area perhaps 10 km wide in a rift valley environment without an organized spreading center this is followed by concentration of the extension at a single axis and the beginning of true seafloor spreading less

the rotation of arabia and the levant fault system abstract we establish the kinematics of the rotation of arabia with respect to africa and show that the rotation rate of africa increased by a factor of about four in late serravallian time about 12 13 ma ago we discuss evidence that oceanic accretion started simultaneously in the gulf of aden and in the red sea at this time it is also at this time that the levant and anatolian fault systems were initiated our initial reconstruction of the red sea rift in late oligocene early miocene time approximately superposes the present shore lines which coincide with the mid point of the zones of rapid crustal thinning the future continental slopes the amount of extension during the early phase of continental rifting is obtained by assuming that the total volume of continental crust is conserved during extension and by checking these estimates through closure around the sinai triple junction in the late miocene the southern evant fault zone was a zone of distributed shear deformation through counterclockwise block rotation extending soul h ward within the northernmost red sea since the early pliocene the shear motion has been localized within the gulf of aqaba changing the tectonic pattern in the northern red sea

active faulting and seismicity of the dasht e bayaz region eastern iran summary the dasht e bayaz left lateral strike slip fault system in ne iran ruptured over a length of ca 120 km during two earthquakes in 1968 and 1979 we constrain source parameters of the 1968 august 31 dasht e bayaz and 1979 november 27 khuli buniabad earthquakes by analysing long period body wave seismograms both earthquakes involved complex rupture processes with at least two subevents in each case coseismic surface ruptures and cumulative scarps in alluvium indicate fault segmentation on numerous short ca 20 km long strands with small pull aparts between them the earthquake subevents seen in the seismograms probably relate to this segmentation the total cumulative offset on the fault system is estimated at ca 4 5 km this is small compared to the total amount of late tertiary deformation expected in this part of iran and indicates that the dasht e bayaz fault may be relatively young distributed strike slip faulting is widespread in the region and there are indications that the dasht e bayaz fault is evolving from several short faults that are coalescing these results are important not only for understanding of the regional tectonics but for the development and evolution of strike slip faults in general

thermobarometry of metamorphosed pseudotachylyte and associated mylonite constraints on dynamic co seismic rupture depth attending caledonian extension north norway abstract the exhumed post caledonian eidsfjord and fiskfjord extensional shear zones of northern norway exhibit evidence of coseismic rupture propagating into the ductile crust as evidenced by the presence of mylonitic and metamorphosed pseudotachylyte geothermobarometric calculations on garnet bearing mineral assemblages in mylonitic gneisses associated with mylonitic pseudotachylyte and in metamorphosed pseudotachylyte permit determination of the depth and ambient temperature of seismogenic low angle ductile extension average pressures from eidsfjord 570 115 mpa at ca 650 c and fiskfjord 1120 220 mpa at ca 650 c correspond to faulting depths of 21 4 km and 41 9 km respectively the fiskfjord results agree with previous thermobarometric calculations on mylonitic cpx grt bearing pseudotachylyte at fiskfjord the calculated depths are 5 25 km below the depth of the standard seismogenic zone these results demonstrate that low angle normal faults may cut through a large portion of continental crust this occurrence of mylonitic pseudotachylyte in an extensional crustal setting is most easily explained by dynamic downward rupture into the ductile regime and or unusually high shear stresses to account for coseismic rupture at such depths implying a direct connection with a seismogenic normal fault in the upper crust

time dependence of snow microstructure and associated effective thermal conductivity this paper presents a sequential evaluation of snow microstructure and its associated thermal conductivity under the influence of a temperature gradient temperature gradients from 28 to 45 k m 1 were applied to snow samples having a density range 180 320 kg m 3 the experiments were conducted inside a cold room in a specially designed heat flux apparatus for a period of 4 weeks a constant heat flux was applied at the base of the heat flux apparatus to produce a temperature gradient in the snow sample a steady state approach was used to estimate the effective thermal conductivity of snow horizontal and vertical thick sections were prepared on a weekly basis to obtain snow micrographs these micrographs were used to obtain snow microstructure using stereological tools the thermal conductivity was found to increase with increase in grain size bond size and grain and pore intercept lengths suggesting a possible correlation of thermal conductivity with snow microstructure thermal conductivity increased even though surface area and area fraction of ice were found to decrease the outcome suggests that changes in snow microstructure have significant control on thermal conductivity even at a constant density

recent kinematics of the tectonic plates surrounding the red sea and gulf of aden this work was funded by the miur prin prot 20125jkany the geodas ship track data used in this study can be found at ngdc http www ngdc noaa gov mgg geodas trackline html

current plate motions across the red sea summary a new objective method is used to estimate precisely 64 rates of seafloor spreading since chron 2a 3 2 ma from all the red sea magnetic profiles available from 15 9 to 26 n the fastest spreading rate 16 mm yr 1 occurs near 18 n whereas the slowest rate 10 mm yr 1 occurs at 25 5 n and is consistent with the rate predicted from arabia nubia data to the south the standard deviation of the spreading rates is 0 8 mm yr 1 much smaller than the median standard deviation of 4 mm yr 1 previously assigned to spreading rates in the global plate motion model nuvel 1 demets et al 1990 the fit to the spreading rates as well as the locations of earthquakes in and near the red sea indicate that spreading south of approximately 17 7 n is less than the full rate of spreading between the arabian and nubian plates the red sea spreading centre is instead usefully interpreted as the boundary between the arabian plate and a danakil microplate that includes the subaerial danakil block and a larger oceanic portion of lithosphere despite the absence of reliable azimuths of transform faults in the red sea all components of the angular velocity of arabia relative to nubia are usefully constrained from just the 45 relevant spreading rates the new compact 95 per cent confidence region of the angular velocity excludes prior estimates based on only four and two spreading rates by chase 1978 and jestin et al 1994 respectively 19 spreading rates in the southern red sea are used to estimate the angular velocity between the danakil microplate and arabia an approach based on singular value decomposition shows that without slip vectors only two of the three components of the angular velocity of the danakil microplate relative to arabia or nubia are usefully constrained but that all three components are usefully constrained if one earthquake slip vector is included

present day motion along the owen fracture zone and dalrymple trough in the arabian sea all plate motion data available for describing the present day motion between the arabian and indian plates are analyzed to understand the present day tectonic role of the presumed plate boundary the owen fracture zone and dalrymple trough in the northern arabian sea all prior plate motion models are shown to be inconsistent with some of the data along the presumed boundary in particular published global plate motion models predict some convergence across the owen fracture zone and dalrymple trough convergence along the owen fracture zone is contradicted by earthquake focal mechanisms which show right lateral strike slip convergence along the dalrymple trough is contradicted by observed normal faulting in the trough and by normal and strike slip focal mechanisms for earthquakes occurring along or near the trough the sense and rate of motion is further constrained by spreading rates along the sheba ridge northwest of the owen fracture zone and along the carlsberg ridge southeast of the owen fracture zone to estimate the present day motion we determine 43 3 m y average spreading rates from sheba ridge carlsberg ridge and central indian ridge magnetic profiles and have combined them with eight transform azimuths and 15 earthquake slip vectors along these ridges and the arabia india boundary we determine an arabia india euler vector that predicts 2 mm yr of right lateral strike slip motion along the owen fracture zone with a 95 confidence interval of 0 7 mm yr which excludes the faster rates of slips predicted by several prior models the direction of motion is 35 50 counterclockwise from that predicted by published global plate motion models if we omit the data along the arabia india boundary the motion differs insignificantly from zero suggesting that magnetic profiles from the carlsberg and sheba ridges give spreading rates too imprecise to detect the slow arabia india motion if the owen fracture zone and dalrymple trough are regarded as a plate boundary it is the slowest slipping plate boundary known on earth with motion about 100 times slower than the fastest slipping faults along the east pacific rise

gulf of aden axial magnetic anomaly and the curie temperature isotherm the main features of magnetic anomalies over ocean ridges have been explained1 as a corollary of seafloor spreading and geomagnetic reversals oceanic crust is formed in a narrow region becoming magnetized in the direction of the earth s magnetic field as its temperature falls through the curie point of the magnetic minerals present the gulf of aden was one of the first places where reversely magnetized sea floor was recognized2 the seafloor spreading direction and latitude are such that the anomaly due to normal magnetization is negative and slightly skewed positive anomalies were also observed suggesting the presence of reverse magnetization a short wavelength magnetic anomaly which frequently occurs superimposed on the axial magnetic anomaly in the gulf of aden is now described various interpretations are considered the preferred involves a dramatic shallowing of the curie temperature isotherm close to the seafloor spreading centre the interpretation has implications for models of the generation of oceanic lithosphere and for locating possible geothermal areas in rifted regions

the accommodation of arabia eurasia plate convergence in iran continental convergence between arabia and eurasia is taken up by distributed deformation in iran at wavelengths large compared with the thickness of the lithosphere this deformation is best described by a continuous velocity field the only quantitative source of information on the spatial distribution of strain rates within iran is the record of earthquakes we find that we can reproduce the style of deformation observed in the seismicity by simply minimizing the rate of work in a continuous viscous medium that has to accommodate the arabia eurasia plate motion between the defined shapes of iran s rigid borders when in addition we specify central iran azerbaijan and the southern caspian basin to be relatively rigid blocks within the deforming zone then the fit to the style of the observed strain rate distribution is even better we conclude that much of the pattern of deformation in iran is predetermined by the shape of its rigid borders and by the disposition of relatively rigid blocks within it this is likely also to have been a common occurrence in older orogenic belts we confirm earlier suggestions that earthquakes between 1909 and 1992 can account for only a small part 10 20 of the total deformation required by the convergence between the arabia and eurasia plates we then show that the whole plate motion can be accommodated by a velocity field with the same orientations and relative magnitudes of principal strain rates seen in the earthquakes but with larger absolute magnitudes there is therefore no requirement that the large proportion of aseismic deformation in iran is substantially different in style orientation or distribution from that released seismically in the earthquakes

preliminary assessments on the modes of instability of the antalya sw turkey coastal cliffs cliff erosion and the consequent instabilities present a significant risk to antalya city sw turkey erosional processes include the chemical action of mixing zone water the mechanical action of waves salt erosion and biological degradation the rock properties lithology stratification strength etc are the controlling factors to this erosion the coastal cliffs of antalya are composed of tufa type carbonate rocks which occur in a wide range from collapsible soil to hard rock the instability problems of the cliffs of antalya tufa commonly involve rock fall cave collapse raveling washout of weakly lithified tufa shear failure and secondary toppling secondary toppling type instabilities culmann type failures and complex failures a combination of these two are widespread on the cliffs the occurrence of large failures are usually associated with heavy rainfall as heavy rainfall causes the saturation of pores increases pore water pressures and reduces the strength of the rock comparison between aerial photographs and topographic maps of different dates do not provide evidence of considerable retreat according to the historical data there has been little or no cliff retreat for 2 000 years therefore the erosion rate of the antalya tufa cliffs is said to be so very slow that retreat is valid only in a geological timescale however in an engineering timescale these cliffs are subjected to instabilities and to local failures causing local retreats

structure and development of the midocean ridge plate boundary in the gulf of aden evidence from gloria side scan sonar a gloria side scan sonar survey along the crest of the midocean ridge in the gulf of aden has provided information on the small scale morphology of its spreading centers and fracture zones spreading center offsets increase in length to the east this is thought to result from changes in the behavior of the mantle with increasing distance from the afar hot spot a 300 km long spreading center in the western gulf of aden is oriented obliquely to the spreading direction nested within the obliquely oriented median valley is an en echelon arrangement of a number of smaller elongated basins each oriented approximately normal to the spreading direction close to the axis of spreading volcanic and closely spaced tectonic structures run approximately normal to the spreading direction higher on the walls of the median valley more widely spaced normal faults have formed subparallel to the valley in the western gulf of aden there are no indications of sonar targets that might represent transform faults parallel to the nne spreading direction in the east spreading center offsets of 15 25 km are made at fracture zones which are best described as narrow zones of highly oblique spreading offsets of greater than 25 km are achieved on single transform faults and the associated tectonic fabric has a spreading direction trend the boundaries between crusts of different ages along inactive transform fault extensions lie along the bases of fracture zone scarps these scarps are situated in the older crust and face the younger this is the opposite of the situation predicted on the basis of simple plate cooling models at some places in the gulf of aden the fracture zone topography is very subdued and this is attributed to the failure of the two slabs of lithosphere at the end of the transform fault to couple completely before the younger lithosphere on the nontransform side of the spreading center completes its ascent of the median valley wall there is evidence of a change of spreading direction 3 5 m y ago from about 040 to 022 it is argued that the small scale morphology of the transform fault spreading center intersections can be understood in terms of the transfer of shear fracture on a transform fault to tensile fracture on a spreading center propagating away from the intersection it is concluded that the transform fault must be weaker than the spreading center

late holocene sea level changes and paleoclimate recorded in lake lungue southern mozambique abstract we report on late holocene paleoenvironmental and sea level changes in southern mozambique based on analysis of diatom stratigraphy mineral magnetic susceptibility saturation isothermal remnant magnetization sirm and organic carbon content in a sediment core from lake lungue located ca 30 km north of xai xai city in the limpopo river floodplain eleven radiocarbon dates performed on terrestrial shells allowed establishment of an age depth model high content of brackish marine taxa especially diploneis suborbicularis and navicula yarrensis suggests that the lake lungue basin was part of the indian ocean coastal zone between ca 740 and 910 ce suggesting higher relative sea level during this phase a similar diatom distribution in older parts of the sequence of unknown age indicates that the site was connected to the indian ocean also at some stage prior to 740 ce between ca 910 and 1130 ce the basin was under a combined effect of sporadic marine water influx and limpopo river actions a freshwater lake was established sometime between 1130 and 1360 ce when the basin became less affected by marine influences due to lower sea levels instead the lake system was more influenced by limpopo river meandering dynamics and flooding events and eventually isolated into a more or less independent lake ecosystem where diatom diversity most likely responded to lake levels fluctuations driven by shifts in relative humidity and rainfall amounts within the floodplain and also from upstream sources during this phase high abundance of freshwater planktonic species i e aulacoseira granulata and a ambigua indicates high lake levels and wetter conditions dated to ca 1360 1560 ce from 1560 ce until present the lake has been subject to drier conditions and higher evaporation as indicated by lower lake levels reported by a decline in freshwater planktonic taxa and increase in brackish taxa e g amphora robusta

recent seismicity of the east african rift system and its implications abstract the seismicity of the east african rift system and southern red sea is studied here location of earthquake epicenters in east africa shows that there is a seismicity gap in space and time between the main ethiopian rift system and the eastern rift however distribution of earthquake epicenters together with the energy mapping suggest a continuity of seismic activity or stress field from the main ethiopian rift system to the western rift system via the southernmost rifts of ethiopia in general except for some earthquakes which occurred at different complex tectonics regions mechanisms of earthquakes studied here show dominantly normal faulting suggesting that the rift system is an extensional zone on the continent the presence of greater focal depth earthquakes to the southern part of the rift system may indicate that softer materials at a shallower depth are present in afar and neighboring regions than in the remaining part of the east african rift system this interpretation is supported by other geophysical studies low electrical resistivity and gravity data performed in afar it is also supported by low and high stress drops found for the northern part afar depression and southern part of the east african rift system respectively

role of regional extension and uplift in the plio pleistocene evolution of the aksu basin sw turkey the aksu basin within the isparta angle area of sw turkey documents plio pleistocene crustal processes at the interface between the tauride mountains and the eastern mediterranean sea basin sedimentation began in the late miocene following an earlier history of emplacement of mesozoic allochthonous units antalya complex miocene basin development and localized late miocene compression aksu phase late miocene early pliocene transtension deformed the aksu basin exploiting pre existing zones of structural weakness during early mid pliocene muddy sediments accumulated in a shallow shelf sea 2 and locally thick up to 250 m cool water antalya tufa deposits then followed prior to glacial times initial localized lacustrine carbonate deposition was followed by development of mainly algal carbonates that are thickest in the west the terraced nature of the tufa terraces at 300 250 100 m above present sea level is explained in terms of fluvial processes regional comparisons suggest a two stage history for the aksu basin first late miocene early pliocene transtension and subsidence secondly late pliocene early pleistocene rifting and marginal uplift the overall tectonic setting reflects interplay between supra subduction zone extension and tectonic escape of anatolia westwards towards the aegean

the miocene to present kinematic evolution of the eastern mediterranean and middle east and its implications for dynamics the present kinematics in the eastern mediterranean and middle east is now well constrained by gps measurements and dominated by a circular counterclockwise motion while arabia rotates rigidly the rotational velocities increase from the levant to aegea causing extension in western anatolia we place the present pattern in light of the post middle miocene geological history and propose that in addition to the effects of the hellenic subduction and zagros collision subduction zones on driving the surface motion an underlying asthenospheric flow is also required this counterclockwise toroidal flow is expected to exist around the eastern edge of the african slab owing to subduction rollback and it helps explain the initiation of the north anatolia fault the extrusion and uplift of anatolia and the mid miocene to recent volcanism in eastern anatolia the afar plume had a similar effect on the acceleration of arabia at 40 mya