an anomaly in the amplitude ratio of skks sks in the range 100 108 from portable teleseismic data we have examined the amplitude ratio skks sks from two deep focus events recorded by the apt89 portable seismic experiment for one of the events beneath the solomon islands we obtain a profile of 18 stations in the distance range 99 108 we observe large systematic variations in this ratio as a function of distance from 99 to 106 the ratio is fairly constant and in the range 0 1 to 0 5 but it then rapidly increases to the range 0 5 3 5 between 106 and 108 such variations are in fact predicted by standard earth models such as prem although this feature of the wavefield has not previously been observed it is due to the momentary drop in sks amplitude at the ray parameter where the reflected phase scp is critically reflected because ray theory is not valid in this distance range we use full wave theory to model the amplitudes we have been able to match the distance pattern reasonably well if we use a model with the p velocity at the base of the mantle reduced by 1 5 compared to prem although fewer stations are available the second event shows the same basic distance pattern except that the abrupt increase in the ratio occurs at a closer distance this suggests an even lower p velocity for this region about 3 5 slower than prem and is consistent with lateral heterogeneity at the base of the mantle of a few percent

late cenozoic stress field in the cameli basin sw turkey a history of deformation has been determined for the cameli basin located in the western part of the major fethiye burdur fault zone interpreted as the on land continuation of pliny strabo fault system e g eastern boundary of the hellenic arc inversion of fault slip vectors affecting mio pliocene to quaternary formations in the cameli basin in the southwestern segment of the transtensional fethiye burdur fault zone yields two different normal faulting stress regimes characterized by a roughly orthogonal set of extensional axes a nw se n129 19 e 3 axis and a ne sw n50 16 e 3 axis the orientation of fault sets is predominantly around the ne sw direction in the major fethiye burdur fault zone making the extension nw se the mean r values are 0 74 and 0 69 for both extensions indicating a triaxial stress state which is clearly different from radial extension and from transitional to strike slip stress state the nw se extension is probably responsible for the formation of the cameli basin during mio pliocene time in contrast the inversion of focal mechanism solutions of shallow earthquakes occurring within the cameli basin identifies a present day predominantly extensional stress regime characterized by an approximately n s n184 e 3 axis which has an r value of 0 637 indicating a triaxial stress state the nearly orthogonal extensional stress regimes seem to have been acting contemporaneously with each other at different intensities from the mio pliocene onwards in sw turkey this may be attributed to the geodynamic effects related to the subduction of the african plate beneath anatolia diffusing along hellenic and cyprus arcs and in the west southwestward extrusion of anatolia our hypothesis is that the cause of the early nw se extension is the slab pull force due to the subduction process along the cyprus arc considered to be dominant up to plio quaternary the later ne sw to present day n s extension dominant since the plio quaternary is related to the combined forces of the anatolian extrusion and the subduction process along the hellenic arc

seismotectonics of western anatolia regional stress orientation from geophysical and geological data abstract available fault plane solutions of shallow earthquakes occurring in the central part of western anatolia were reviewed in order to determine the stress directions active in this region data on 66 shocks were used for numerical analysis with the p and t dihedra method some of these data being used in further determination of stress tensors through numerical methods despite uncertainties on depth determinations results were found consistent and in agreement with those of geological analyses independently carried out on recent and active faults selections from the data were adopted on the basis of areal distribution magnitude and depth of earthquakes variations in stress axes orientation with depth seem significant and related to increasing influence of crustal anisotropy near the surface the dominant trend of the present day extension in this region as indicated by the analysis of available earthquake mechanisms is nne ssw with a corresponding azimuth of the 3 axis n25 e the stress regime is extensional with dominant normal fault motions and increasing importance of strike slip faults from south to north this pattern of stress in western turkey is consistent with kinematic reconstructions indicating a westward and southwestward motion of anatolia and aegea relative to eurasia

tectonic analysis of fault slip data sets using data that include the direction and the sense of motion on individual fault surfaces determined by slickenside lineations it is possible to reconstruct reduced stress tensors that correspond to the orientation of stress axes and to the ratio 2 3 1 3 between principal stress values 1 2 3 compression being positive no assumption is made concerning the orientation of fault planes relative to stress axes so that reactived faults are taken into account as well as newly created ones qualitative and quantitative methods for analysis of fault slip data were developed during the last 10 years the practical limitation of the methods and the necessity for critical field observations are emphasized these methods can be applied to focal mechanisms of earthquakes a more complex analysis of heterogeneous data sets involving an iterative separation of different stress systems is also discussed this analysis enables one to distinguish successive faulting events careful qualitative study in the field is in all cases essential

fault block rotations at the edge of a zone of continental extension southwest turkey the ne sw trending burdur acigol and baklan basins of southwest turkey are bounded by normal faults which became active in quaternary times prior to this a more widely spaced system of pliocene basins had existed each of the quaternary basins has a half graben geometry with a major nw dipping fault on its southeast side previous studies of the 1971 burdur earthquake caused by movement on the fault bounding the burdur basin have shown this fault to flatten slightly at depth deformation in the hangingwall of the fault controlling the pliocene basin in the burdur region suggests a planar fault geometry it is suggested that the pliocene fault rotated to its present shallow orientation then became inactive and acted as a detachment at depth for the more recent quaternary fault quaternary faults bounding the burdur acigol and baklan basins have a sinistral strike slip component with slip vectors indicating extension in an nw se direction this is at variance with regional n s extension in western turkey a solution for this contrast is found by invoking block rotations about vertical axes in a deforming zone between the rapidly extending aegean region to the west and the stable unstretched anatolian plateau to the east

a numerical method for determining the state of stress using focal mechanisms of earthquake populations application to tibetan teleseisms and microseismicity of southern peru the numerical method described in this paper enables the study in terms of stress of the kinematics of seismic faults provided by focal mechanisms this method assumes a mean state of stress in the source region and is based on the simple mechanical model used for fault population analysis which supposes slip in the direction of the resolved shear stress acting on the fault plane the proposed algorithm first defines compressional and tensional zones resulting from superimposition of the compressional and tensional quadrants limited by the nodal planes this enables one to test the data homogeneity furthermore this restricts the space where the principal stress axes have to be searched then for each principal stress reference whose location is constrained by above confined zones the r value chosen equal to 2 1 3 1 is computed which fits the slip vector on each nodal plane this permits one to select a set of preferred seismic fault planes from a set of auxiliary planes finally a state of stress is computed from the preferred seismic fault plane set using the non linear simplex method already applied to fault populations this algorithm is constructed so as to avoid two major difficulties misleading estimation of the deviatoric stress tensor which may result from excessive emphasis by minimizing the residuals by a least squares method if some of the data are wrong and a lengthy prospection of the stress references over all the space of directions this calculation does not take into account possible changes of the strike and dip of the nodal planes however we use rotations of nodal planes in agreement with the first arrival data to test the compatibility of these data with the computed state of stress tibetan teleseisms and southern peruvian microseisms are analyzed and results are compared with kinematics of superficial recent and active faults measured in field in the same regions this suggests that major seismic events may give a good evaluation of the regional mean state of stress focal mechanisms of the small events are also modelled by a mean stress deviator but this differs significantly from the regional state of stress in southern peru deduced from quaternary faulting this may be due to imprecise location of the small events however some movements are strongly different from those predicted by the computed mean stress deviator this suggests that small fault kinematics surely depend on the regional state of stress but that local effects may control the small deformations

accretionary processes at subduction zones in the eastern mediterranean abstract the tectonic history of the eastern mediterranean as well as the present tectonic style are affected by the collision and accretion of oceanic plateaus at subduction zones small but distinct oceanic plateaus exist today in the eastern mediterranean away from the plate boundary many other oceanic plateaus crowd the plate boundary particularly in the hellenic arc area their presence results in the unusual complexity of this subduction zone as is evidenced by the seismicity and bathymetry patterns the present two arcs system in this region the hellenic and cyprean arcs is probably the consequence of the collision of a large continental plateau with an older arc this plateau has been thrusted over the continental mass of anatolia and pieces of it are to be found in the region between the two arcs active subduction in the hellenic arc takes place in the outer trenches particularly in the ionian and strabo trenches subduction of mediterranean lithosphere in the pliny and ptolemy trenches is limited to their western parts inner segments of these trenches served as the main subduction trenches before the subduction zones migrated outward following the collision of oceanic plateaus

metamorphic history suggested by garnet growth chronologies in the isua greenstone belt west greenland abstract compositional maps for garnets from the five tectonic domains of the isua greenstone belt in west greenland are used to identify episodes of garnet growth during the metamorphism of the greenstone belt three distinct episodes of garnet growth are recorded in domains iii v two in domain ii and one in domain i a wide variety of garnet textures are observed including growth zoning post growth homogenisation replacement rim resorption and oscillatory zoning there is no simple correlation of garnet growth events among domains indicating that at least some events are related to localised metasomatic processes in the greenstone belt however the relative growth chronology combined with the available geochronology indicates that the observed metamorphic processes span both the early and late archaean

global positioning system constraints on plate kinematics and dynamics in the eastern mediterranean and caucasus we present and interpret global positioning system gps measurements of crustal motions for the period 1988 1997 at 189 sites extending east west from the caucasus mountains to the adriatic sea and north south from the southern edge of the eurasian plate to the northern edge of the african plate sites on the northern arabian platform move 18 2 mm yr at n25 5 w relative to eurasia less than the nuvel 1a circuit closure rate 25 1 mm yr at n21 7 w preliminary motion estimates 1994 1997 for stations located in egypt on the northeastern part of africa show northward motion at 5 6 2 mm yr also slower than nuvel ia estimates 10 1 mm yr at n2 4 e eastern turkey is characterized by distributed deformation while central turkey is characterized by coherent plate motion internal deformation of 2 mm yr involving westward displacement and counterclockwise rotation of the anatolian plate the anatolian plate is de coupled from eurasia along the right lateral strike slip north anatolian fault naf we derive a best fitting euler vector for anatolia eurasia motion of 30 7 0 8 n 32 6 0 4 e 1 2 0 1 myr the euler vector gives an upper bound for naf slip rate of 24 1 mm yr we determine a preliminary gps arabia anatolia euler vector of 32 9 1 2 n 40 3 1 1 e 0 8 0 2 myr and an upper bound on left lateral slip on the east anatolian fault eaf of 9 1 mm yr the central and southern aegean is characterized by coherent motion internal deformation of 2 mm yr toward the sw at 30 1 mm yr relative to eurasia stations in the se aegean deviate significantly from the overall motion of the southern aegean showing increasing velocities toward the trench and reaching 10 1 mm yr relative to the southern aegean as a whole

p wave tomography of the mantle under the alpine mediterranean area 1 we study the upper mantle p wave velocity structure below the euro mediterranean area down to 1000 km depth by seismic travel time tomography we invert summary residuals constructed with both regional and teleseismic first arrival data reported by the international seismological centre isc 1964 1995 introducing some alternative strategies in the travel time tomographic approach and a new scheme to correct teleseismic data for global mantle structure our high resolution model pm0 5 is parameterized with three dimensional 3 d linear splines on a grid of nodes with 0 5 spacing in both horizontal directions and 50 km vertical spacing we obtain about 26 root mean square rms reduction of residuals by inversion in addition to roughly 31 reduction after summary rays formation and selection sensitivity analyses are performed through several test inversions to explore the resolution characteristics of the model at different spatial scales the distribution of large scale fast anomalies suggests that two different stages of a convection process presently coexist in very close regions the mantle dynamics of western central europe is dominated by blockage of subducted slabs at the 660 km discontinuity and ponding of seismically fast material in the transition zone contrarily in the eastern mediterranean fast velocity material sinks into the lower mantle suggesting that the flow of the cold downwelling here is not blocked by the 660 km discontinuity on a smaller scale the existence of tears in the subducted slab lithospheric detachment all along both margins of the adriatic plate as proposed by some authors is not supported by our tomographic images

fault slip directions in central and southern greece measured from striated and corrugated fault planes comparison with focal mechanism and geodetic data fault slip directions recorded by outcropping striated and corrugated fault planes in central and southern greece have been measured for comparison with extension directions derived from focal mechanism and global positioning system gps data for the last 100 years to test how far back in time velocity fields and deformation dynamics derived from the latter data sets can be extrapolated the fault slip data have been collected from the basin bounding faults to plio pleistocene to recent extensional basins and include data from arrays of footwall faults formed during the early stages of fault growth we show that the orientation of the inferred stress field varies along faults and earthquake ruptures so we use only slip directions from the centers of faults where dip slip motion occurs to constrain regionally significant extension directions the fault slip directions for the peloponnese and gulfs of evia and corinth are statistically different at the 99 confidence level but statistically the same as those implied by earthquake focal mechanisms for each region at the 99 confidence level they are also qualitatively similar to the principal strain axes derived from gps studies extension directions derived from fault slip data are 043 047 for the southern peloponnese 353 for the gulf of corinth and 015 014 for the gulf of evia extension on active normal faults in the two latter areas appears to grade into strike slip along the north anatolian fault through a gradual change in fault slip directions and fault strikes to reconcile the above with 5 myr 1 clockwise rotations suggested for the area we suggest that the faults considered formed during a single phase of extension the deformation and formation of the normal fault systems examined must have been sufficiently rapid and recent for rotations about vertical axes to have been unable to disperse the fault slip directions from the extension directions implied by focal mechanisms and gps data thus in central and southern greece the velocity fields derived from focal mechanism and gps data may help explain the dynamics of the deformation over longer time periods than the 100 years over which they were measured this may include the entire deformation history of the fault systems considered a time period that may exceed 1 2 myr

45 m y of aegean crust and mantle flow driven by trench retreat the available seismic anisotropy data in the aegean shallow mantle and their relationship with crustal deformation are used for deciphering the lithosphere scale flow pattern driven by rollback of the hellenic subduction slab in the north and central aegean the directions of mantle seismic anisotropy trend parallel to stretching lineations in core complexes of the overlying crust suggesting that crust and mantle have undergone the same direction of flow at the scale of the entire aegean crustal extension is controlled by dextral rotation around a pole located at scutary pec albania that is related to the hellenic trench retreat the intensity of mantle anisotropy increases as a function of distance from the pole and of amount of rotation surface geology reveals that this rotating flow pattern resulted in strains accumulated since 45 ma a slab tear model is suggested to integrate the observed variations of geological events in time and space to subduction dynamics

late cenozoic stress evolution along the karasu valley se turkey abstract this study defines the mio pliocene to present day stress regime acting at the northeastern corner of the eastern mediterranean region along the karasu valley i e the amanos range taking in the antakya osmaniye and kahramanmaras provinces the inversion slip vectors measured on fault planes and chronologies between striations indicate that the stress regime varied from transpressional initially to transtensional having consistent nw and ne trending hmax 1 and hmin 3 axes respectively there are significantly different mean stress ratio rm values however the older mean stress state is characterized by n151 11 e trending 1 and n59 12 e trending 3 axes and by a mean arithmetic rm value of 0 76 indicating that the regional stress regime is transpressional the younger stress regime is characterized by n154 8 e trending 1 and n243 8 e trending 3 axes and by a mean arithmetic rm value of 0 17 indicating a transtensional character for this regional stress regime the low r values of the stress deviators related to the recent stress state reflect normal component slips the earthquake focal mechanism inversions confirm that the younger stress regime continues into the recent the inversion identifies a transtensional stress regime representing strike slip and an extensional stress state with a consistent ne trending hmin 3 axis these stress states are characterized by n66 e and n249 e trending 3 axes respectively both significant regional stress regimes induce left lateral displacement along the southern part of the east anatolian fault eaf or amanos fault the temporal change probably in quaternary time within the regional stress regime from transpression to transtension resulted from the coeval influences of subduction processes in the west southwest i e along the cyprus arc continental collision in the east and westward escape of the anatolian block

exhumation of high pressure rocks driven by slab rollback rocks metamorphosed under high pressure hp and ultra high pressure uhp conditions in subduction zones come back to the surface relatively soon after their burial and at rates comparable to plate boundary velocities in the mediterranean realm their occurrence in several belts related to a single subduction event shows that the burial exhumation cycle is a recurrent transient process using the calabria apennine and aegean belts as examples we show that the exhumation of hp rocks is associated in time and space with the subduction of small continental lithosphere blocks that triggers slab rollback creating the necessary space for the exhumation of the buoyant continental crust that was deeply buried just before the buoyancy force of the subducted crust increases until this crust detaches from the downgoing slab it then exhumes at a rate that depends directly on the velocity of trench retreat to become part of the overriding plate heated from below by the asthenosphere that flows into the opening mantle wedge the exhumed crust weakens and undergoes core complex type extension responsible for a second stage of exhumation at a lower rate the full sequence of events that characterizes this model crust mantle delamination slab rollback and trench retreat hp rock exhumation asthenosphere heating and core complex formation arises entirely from the initial condition imposed by the subduction of a small continental block no specific condition is required regarding the rheology and erosion rate of hp rocks the burial exhumation cycle is transient and can recur every time a small continental block is subducted

an improved method for determining the regional stress tensor using earthquake focal mechanism data application to the san fernando earthquake sequence the orientations of fault planes and slip directions indicated by a population of earthquake focal mechanisms can be used to determine best fit regional principal stress directions and r 2 1 3 1 a measure of relative stress magnitudes under the assumption of uniform stress in the source region this analysis allows for the possibility that failure occurs on preexisting zones of weakness of any orientation in the inversion we perform a grid search of stress models to find the one which requires the smallest total rotation of all the fault planes that is needed to match the observed and predicted slip directions the method allows for errors in orientations of both the fault planes and slip directions we have an objective means for identifying the more likely of the two possible fault planes from each focal mechanism relative to a given stress model thus we do not face the problem of ambiguity of nodal planes which plagues other analyses of this kind by using a grid search of stress models rather than a linearization scheme we are able to perform a realistic error analysis and thus establish confidence limits for the preferred regional stresses the method can be used to investigate possible stress inhomogeneities during earthquake sequences by analyzing subsets of the data population the technique has been applied to 76 events from the san fernando earthquake sequence for which we have found best fit stresses plunge and azimuth 1 7 187 2 27 281 3 62 84 and r 0 65 the average misfit between this stress model and all the data is about 8 and all but eight of the aftershocks have misfits of less than 20 these values are considerably less than the uncertainty of the focal mechanism determinations therefore significant stress inhomogeneities are not required by the data our analysis does not support the suggestion of a change in stresses during the aftershock sequence as proposed by others on the basis of an apparent change in focal mechanisms

the east anatolian fault an oblique collisional belt abstract the tectonic setting for the area around the arabia africa anatolia triple junction is described from combined landsat spot satellite image analysis and field observations since the late miocene the motion along the east anatolian fault generated major structures corresponding to shortening with a sinistral slip component the 150 km wide area of the triple junction is highly deformed by folding and thrusting distributed mainly on the border of the anatolian block in addition kinematic reconstructions confirm that the arabia anatolia relative motion is both sinistral and convergent the sinistral strike slip faults of the east anatolian fault zone are of second order and local consequences of the n s arabia anatolia collision

the state of stress in an overriding plate situated above a flat slab the andes of central peru in the andes of central peru that are situated above a flat dipping slab analysis of both structural data collected in the field and available focal mechanisms show that the quaternary and recent state of stress is characterized by n s trending extension in the western cordillera and along the pacific coast whereas e w trending compression prevails in the sub andean lowlands and at the contact between the nazca and south american plates the eastern cordillera deformations suggest an intermediate state of stress i e strike slip faulting characterized by e w trending compression and n s trending extension thus major fault zones striking nw se i e parallel to the central peruvian andes are normal with a sinistral component in the western cordillera e g cordillera bianca and reverse sinistral in the eastern cordillera e g cordillera de huaytapallana this state of stress displays similarities with that of southern peru and may be also interpreted as an effect of compensated high topography in this model the vertical stress zz increases with the topography and hmax is considered as fairly constant trending e w roughly parallel to the convergence on both edges of the andes tectonics being compressional zz is 3 and hmax is 1 in the high andes zz becomes 1 then hmax is 2 allowing hmin striking n s to be 3 along the pacific coast tectonics is not compressional as expected and a nearly neutral state of stress may be due to a topographical effect related to the nearby deep peru chile trench however a conspicuous difference occurs in the andes of central peru in respect to the southern peru andes compressional strike slip tectonics is observed in the eastern cordillera indeed the mean elevation of the eastern cordillera is 3 7 km whereas that of the western cordillera is 4 2 km allowing an intermediate state of stress to occur therefore in central peru a lower mean andean topography and a stronger coupling consequence of the flat subduction seems to explain that compressional tectonics is distributed in a more widespread area than in southern peru superficial deformations related to the subduction of the aseismic nazca ridge are restricted to the coastal domain opposite to this ridge they support the fact that submarine topography of large extension may subduct without producing compressional deformation in the overriding plate which can be reminiscent of a collisional setting

pattern of normal faulting in the gediz graben sw turkey hanging wall deformation of the fault systems controlling the southern margin of the gediz graben were investigated separately within the plio quaternary and neogene predominantly miocene deposits of the graben fill fault styles observed in both packages share many similarities in terms of geometry and comprise conjugate fault sets that show clustering of strike orientations predominantly around wnw ese but also sw ne and nw se directions the main difference between the two units is observable in terms of fault dips and rake of the slickenside lineations measured on the exposed fault planes both measurements show a uni modal distribution for the plio quaternary deposits but a tri modal distribution for the neogene deposits this variation is probably related to the geometrical modification of the older faults by the process of domino style back rotation in the hanging wall of higher order faults similarities among the two units are not limited to geometrical aspects of the fault systems but also counts for the orientation of the principal stress axes that controlled the deformation during the deposition of each sedimentary package inversion of the fault slip data showed that approximately n s oriented extension which varies in the range of nnw sse and nne ssw controlled the faulting during the accumulation of the entire graben fill with almost no evidence of change in the state of stress during the graben evolution however some heterogeneity in terms of stress field is observable among the fault systems formed within the same time frame this heterogeneity is probably related to poorly defined direction of extension in the graben indeed low ratio in the order of 0 25 suggests that 2 and 3 are close in magnitudes and the direction of extension is not well constraint with a potential of 2 3 axes permutations local stress field anomalies related to fault segment interaction could also contribute to the observed heterogeneity