palaeomagnetic evidence for block rotations in the western greek rhodope summary the rhodope massif has been traditionally considered to be a pre mesozoic element that remained stable during the tertiary this idea has been partly supported by previous palaeomagnetic results on plutonic and volcanic rocks ranging in age from palaeocene to oligo miocene however new palaeomagnetic data from additional sites on tertiary magmatic rocks of the western greek rhodope show declination values indicating in most cases a clockwise rotation whereas inclinations are systematically lower than those corresponding to the actual latitudinal position of the rhodope our results together with previously published ones are discussed in the light of recent ideas proposed for the rhodope and the north aegean region we suggest that at least the western part of the greek rhodope has been clockwise rotated after the oligocene north south to ne sw extension tilted the formations towards the north or north east producing apparently high inclinations if the alternative pole position for eurasia proposed by westphal 1990 is adopted

spatial and temporal relationships between mid tertiary magmatism and extension in southwestern arizona cenozoic magmatism in southwestern arizona which is within the basin and range tectonic province occurred almost entirely between 15 and 25 ma volcanic rocks typically consist in ascending order of 1 a thin sequence of mafic to intermediate lava flows 2 voluminous felsic lava flows and pyroclastic rocks with minor to moderate amounts of intermediate to mafic lava flows and 3 basalt and andesite volcanic rock sequences rest disconformably on pre tertiary bedrock in most areas but locally overlie substantial coarse clastic debris that was deposited immediately before and during earliest magmatism prevolcanic clastic debris is interpreted as a consequence of local early normal faulting in most regions tilting related to extension began later and occurred during or after eruption of felsic volcanic rocks and before the end of younger mafic volcanism extension generally ended before about 17 ma except in a northwest trending belt adjacent to the relatively unfaulted and topographically elevated transition zone tectonic province which is adjacent to the colorado plateau rapid cooling of metamorphic core complexes and tilting of young basalts and coarse clastic rocks continued in this belt until as recently as 11 ma extension was extreme in this belt whereas it was generally moderate to slight in other parts of southwestern arizona large magnitude extension was not associated with areas of greatest igneous activity and rapid cooling and exhumation of core complexes postdated local magmatism these relationships are inconsistent with theories that relate genesis of metamorphic core complexes to magma intrusion in the upper crust except for young extension in this northwest trending belt there are no apparent regional migration trends for either magmatism or extension within southwestern arizona lack of substantial extension before magmatism and general lack of magmatism during youngest extension are inconsistent with the hypothesis that magmatism was the product of decompression melting during lithospheric extension the long duration and large magnitude of extension adjacent to the transition zone tectonic province and within an area of earlier crustal thickening are consistent with the hypothesis that extension was driven by the gravitational potential energy of elevated land mass and crustal roots regional magmatic heating apparently weakened the lithosphere and triggered extension but did not control extension locally

guided wave propagation in laterally varying media ii lg waves in north western europe summary lg wave observations at norsar from a sequence of explosions straddling the central graben in the north sea show that the phase is almost extinguished by passing through this structure for models of the graben structure based on seismic refraction experiments with crustal thinning beneath a zone of thickened sediments numerical modelling of lg propagation shows very poor transmission the inclusion of attenuation simulating the effects of scattering from faults and other complex structures further diminishes the transmittivity the theoretical effect of a crustal pinch is to redistribute s energy over a wide range of groups velocities a pattern that fits well with the observations three components recordings at norsar of explosive charges fired in water covering a wide range of azimuths show significant transverse components to the seismograms the transverse energy builds up with travel time and for lg is of the same order as the vertical component these results are consistent with the theoretical prediction of progressive net transfer of energy from rayleigh to love modes as the wavetrain propagates through a three dimensionally heterogeneous medium

a study of the regional variation of low frequency around the korean peninsula we studied regional graphic 1 at 1 hz graphic 2 around the korean peninsula based on broadband vertical component seismic records of six incorporated research institutions for seismology iris global seismographic network stations and 19 korean stations of the korea institute of geoscience and mineral resources kigam using 177 seismic events with magnitudes between 5 3 and 5 7 and depths less than 50 km the reversed two station method was applied and 94 high quality interstation paths were selected from 869 possible pairs these results show high graphic 3 paths around the sea of japan east sea reflecting the typical oceanic structure and low graphic 4 paths around northeastern china related to inactive seismicity assigning these path values into 193 cells around south korea with a size of 1 by 1 we observed that the regional graphic 5 decreased gradually from east to west between 2 and 1 10 3 1 embed inline graphic 2 gif 2 embed inline graphic 3 gif 3 embed inline graphic 4 gif 4 embed inline graphic 5 gif 5 embed inline graphic 6 gif

timing kinematics and cause of aegean extension a scenario based on a comparison with simple analogue experiments abstract since the early 1970s most geodynamic models proposed for the eastern mediterranean consider that the initiation of extension in the aegean during the late middle miocene or later was a direct consequence of the westward extrusion of anatolia away from the arabia eurasia collision front in the late 1990s a few models have taken into account the increasing evidence for an earlier initiation of aegean extension arising mostly from the analysis of deformation within the various alpine metamorphic complexes of the area based largely on our own investigations we first present a review of the data that reliably constrain the minimum age for the initiation of extension in these complexes it shows that regional scale extension with a pattern of stretching orientations similar to that of the pliocene pleistocene was already strongly active in the aegean before the onset of arabian indentation into eurasia lower miocene vs middle or upper miocene this implies that the initiation of aegean extension did not result from the lateral extrusion of anatolia instead extension may have started owing to a process of gravity spreading of the continental lithosphere that had previously been thickened during alpine collision the main arguments favouring this interpretation are presented and a preliminary scenario is proposed for the neogene evolution of the eastern mediterranean in which lateral extrusion of anatolia occurred lately during southward spreading of the aegean lithosphere in order to test this hypothesis further physical experiments simulating the horizontal spreading of a continental lithosphere toward a free boundary have been carried out the analysis of various elements of the deformation field displacements strain rotations fault pattern and kinematics both in the experiments and in the aegean domain reveals an excellent agreement between the two not only do early stages of aegean extension appear to fit the gravity spreading hypothesis but so does the recent to present internal deformation of the aegean transverse e w active shortening observed in the northern aegean is commonly taken as one of the most striking pieces of evidence that aegean extension results from the lateral extrusion of anatolia the experiments indicate that such transverse shortening may equally develop as a result of pure gravity spreading associated with a pattern of faults and rotations that compares well with that of the northern aegean pure dextral shearing along some strands of the north aegean trough fault system and the related development of an asymmetric pattern of faults in the northern aegean are eventually the only features that evidently arise from the extrusion of anatolia since less than 3 ma finally we argue that during the early stages of aegean extension since at least 21 ma and until ca 11 ma the distribution of extensional strain on a regional scale has been controlled by the distribution of earlier thickening post thickening thermal weakening through partial melting of deep levels of the crust probably accounts for the localization of extensional strain within the areas of thick crust restoring the aegean in its most likely configuration at the onset of bulk crustal extension suggests that 1 the extensional strain rate remained roughly constant or has eventually decreased since the onset of aegean extension and 2 the amounts of extension before and after 16 ma have been roughly equal

dextral rotations and tectonomagmatic evolution of the southern rhodope and adjacent regions greece abstract palaeomagnetic measurements deduced from eocene oligocene miocene and pliocene formations exposed in the greek rhodope and surrounding areas reveal significant clockwise rotations displaying an apparent systematic increase in magnitude from thrace westwards and a decrease northwards the pelagonian zone in the west has suffered no rotation at least since the late miocene a transition from rotated to unrotated regions seems to exist close to the western boundary of the vardar zone no rotations are apparent earlier than the mid oligocene parts of the rhodope may have been rotated clockwise by 12 during the late oligocene additional clockwise rotations occurred after the early miocene it is proposed that at least the post early miocene rotations were the result of plate tectonic motions in the north aegean area initiated by middle miocene times and continuing to the present day southward stretching and bending of the ductile part of the lithosphere was accomplished at brittle upper crustal levels by the detachment translation and rotation of the upper plate of the rhodope core complex the serbomacedonian element possibly followed by further fragmentation and rotation of individual blocks

cretaceous tertiary structures and kinematics of the serbomacedonian metamorphic rocks and their relation to the exhumation of the hellenic hinterland macedonia greece the kinematic pattern and associated metamorphism of the predominant ductile deformation and the subsequent deformational stages of the serbomacedonian metamorphic rocks and granitoids are presented in terms of peri tethyan tectonics a systematic record of structural and metamorphic data gives evidence of a main top to ene to ese ductile flow of cretaceous age 120 90 ma associated with a crustal stretching and unroofing a subordinate wsw to wnw antithetic sense of movement of the tectonic top is observed in places the associated metamorphic conditions are estimated at 4 5 7 5 kbar and 510 580 c during eocene to miocene times these fabrics were successively deformed by low angle extensional de ductile shear zones with top to ne and sw sense of movement and brittle shear zones of similar kinematic pattern suggesting a transition from ductile to brittle deformation de deformation was accompanied during its later stages by nw se directed shortening we also discuss the relation of this cretaceous tertiary deformation of the serbomacedonian metamorphic rocks with the eocene to miocene ductile top to southwestward crustal shear of the adjacent rhodope crystalline rocks we regard the serbomacedonian and the rhodope metamorphic rocks to represent related metamorphic provinces the most recent exhumation and cooling history of which is bracketed between the eocene and neogene

quantification of spatial gradation of slope positions transition between slope positions e g ridge shoulder slope back slope foot slope and valley is often gradual quantification of spatial transitions or spatial gradations between slope positions can increase the accuracy of terrain parameterization for geographical or ecological modeling especially for digital soil mapping at a fine scale current models for characterizing the spatial gradation of slope positions based on a gridded dem either focus solely on the parameter space or depend on too many rules defined by topographic attributes which makes such approaches impractical the typical locations of a slope position contain the characteristics of the slope position in both parameter space and spatial context thus the spatial gradation of slope positions can be quantified by comparing terrain characteristics spatial and parametrical of given locations to those at typical locations based on this idea this paper proposes an approach to quantifying the spatial gradation of slope positions by using typical locations as prototypes this approach includes two parts the first is to extract the typical locations of each slope position and treat them as the prototypes of this position and the second is to compute the similarity between a given location and the prototypes based on both local topographic attributes and spatial context the new approach characterizes slope position gradation in both the attribute domain i e parameter space and the spatial domain i e geographic space in an easy and practicable way applications show that the new approach can quantitatively describe spatial gradations among a set of slope positions comparison of spatial gradation of a horizon sand percentages with the quantified spatial gradation of slope positions indicates that the latter reflects slope processes confirming the effectiveness of the approach the comparison of a soil subgroup map of the study area with the maximum similarity map derived from the approach also suggests that the quantified spatial gradation of slope position can be used to aid geographical modeling such as digital soil mapping c 2009 elsevier b v all rights reserved

regional seismic wave propagation lg and sn and pn attenuation in the arabian plate and surrounding regions an edited version of this paper was published by blackwell publishing copyright 2004 blackwell publishing see also http www blackwell synergy com doi abs 10 1111 j 1365 246x 2004 02246 x http atlas geo cornell edu middleeastnorthafrica publications al damegh2004 htm

is there a relationship between magmatic fabrics and brittle fractures in plutons a view based on structural analysis anisotropy of magnetic susceptibility and thermo mechanical modelling of the tanvald pluton bohemian massif abstract the present study focuses on the thermal and mechanical aspects of cooling of plutonic systems with respect to their internal structure analysis of the tanvald pluton and the nearby liberec granite the krkonose jizera plutonic complex bohemian massif using the anisotropy of magnetic susceptibility ams method indicates the decoupled magnetic fabrics formed by different processes in these two plutons two regional sets of vertical fractures cut across the plutons and their host rocks they are interpreted as having been formed as opening mode fractures joints after emplacement and cooling our thermo mechanical finite element modelling indicates that the thermal stresses within the tanvald pluton were compressive and that fracture criteria were not met during pluton cooling these results imply that the emplacement depth and confining pressure significantly affect the state of stress within a pluton during cooling and may play a crucial role in the formation of early fractures in plutons consequently the formation of early fractures during pluton cooling is driven by external conditions overriding the role of internal magmatic fabrics we argue that no genetic geometric or temporal correlation can exist between magmatic fabrics and fractures in granitoid plutons and thus that the original concept of hans cloos based on fabric joints relationships should be reconsidered instead an alternative classification of fractures in plutons should include cooling fractures syntectonic fractures uplift fractures and post uplift fractures

mesozoic tertiary structural evolution of an extensional gneiss dome the kesebir kardamos dome eastern rhodope bulgaria greece the tectonic evolution of the rhodope massif involves mid cretaceous contractional deformation and protracted oligocene and miocene extension we present structural kinematic and strain data on the kesebir kardamos dome in eastern rhodope which document early tertiary extension the dome consists of three superposed crustal units bounded by a low angle nne dipping detachment on its northern flank in bulgaria the detachment separates footwall gneiss and migmatite in a lower unit from intermediate metamorphic and overlying upper sedimentary units in the hanging wall the high grade metamorphic rocks of the footwall have recorded isothermal decompression direct juxtaposition of the sedimentary unit onto footwall rocks is due to local extensional omission of the intermediate unit structural analysis and deformational metamorphic relationships give evidence for several events the earliest event corresponds to top to the sse ductile shearing within the intermediate unit interpreted as reflecting mid late cretaceous crustal thickening and nappe stacking late cretaceous palaeocene eocene late tectonic to post tectonic granitoids that intruded into the intermediate unit between 70 and 53 ma constrain at least pre latest late cretaceous age for the crustal stacking event subsequent extension related deformation caused pervasive mylonitisation of the footwall with top to the nne ductile then brittle shear ductile flow was dominated by non coaxial deformation indicated by quartz c axis fabrics but was nearly coaxial in the dome core latest events relate to brittle faulting that accommodated extension at shallow crustal levels on high angle normal faults and additional movement along strike slip faults radiometric and stratigraphic constraints bracket the ductile then brittle extensional events at the kesebir kardamos dome between 55 and 35 ma extension began in paleocene early eocene time and displacement on the detachment led to unroofing of the intermediate unit which supplied material for the syn detachment deposits in supra detachment basin subsequent cooling and exhumation of the footwall unit from beneath the detachment occurred between 42 and 37 ma as indicated by mica cooling ages in footwall rocks and extension proceeded at brittle levels with high angle faulting constrained at 35 ma by the age of hydrothermal adularia crystallized in open spaces created along the faults this was followed by late eocene oligocene post detachment overlap successions and volcanic activity crustal extension described herein is contemporaneous with the closure of the vardar ocean to the southwest it has accommodated an earlier hinterland directed unroofing of the rhodope nappe complex and may be pre cursor of and or make a transition to the aegean back arc extension that further contributed to its exhumation during the late miocene this study underlines the importance of crustal extension at the scale of the rhodope massif in particular in the eastern rhodope region as it recognizes an early tertiary extension that should be considered in future tectonic models of the rhodope and north aegean regions

syn metamorphic nappe complex in the rhodope massif structure and kinematics mylonitic gneisses of the bulgarian and greek rhodope were deformed under medium pressure type metamorphism the kinematic information contained in these gneisses shows that shear deformation occurred during development of a nappe complex lithologies and metamorphic histories allow a lower footwall and an upper hanging wall terrane to be distinguished that define a crustal scale duplex as oceanic crust is involved collision between two continental units with subsequent crustal thickening is inferred the blocks would be moesia to the north and the lower rhodope promontory to the south which collided in the mesozoic to early cenozoic the nappe complex is characterized by south to southwestward foreland directed piling up and is associated with both coeval and subsequent extension the late extension is associated with the establishment of a high temperature low pressure metamorphic gradient and plutonism that predates but makes a transition to the lithospheric extension of the aegean arc

u pb and 40ar 39ar geochronology of the symvolon granodiorite implications for the thermal and structural evolution of the rhodope metamorphic core complex northeastern greece north aegean continental lithosphere was thickened by southwest vergent thrusting and continental subduction within the alpine collisional orogen but has subsequently been greatly extended on a northeast southwest axis in the back arc of the hellenic subduction zone crosscutting relationships with two granodiorite bodies emplaced at 31 33 ma the xanthi and eastern vrondou plutons constrain a pre mid oligocene origin of alpine convergent structures in northeastern greece post alpine thinning of the north aegean nappe pile began in earliest miocene time and has been accommodated by a succession of distinct structural systems the earliest of these the symvolon shear zone appears to represent a midcrustal coaxial rupture of the falakron marble series a carbonate platform 5000 m thick that was subducted northeastward beneath high grade rocks of the rhodope metamorphic province in late alpine time zircon and titanite u pb dates and hornblende 40ar 39ar dates obtained in this study constrain the intrusion and incipient mylonitization of the symvolon or kavala granodiorite within the symvolon shear zone at 21 22 ma following its emplacement the symvolon body resided at temperatures between 300 c and 500 c for 5 7 m y during which coaxial deformation may have continued within a widening symvolon rupture the strymon valley detachment a regionally south west dipping low angle normal fault succeeded the symvolon shear zone in middle miocene time southwestward displacement of the serbo macedonian gneiss complex by as much as 80 km in the hanging wall of this detachment facilitated the unroofing of the rhodope metamorphic core complex including the falakron marble series and several tertiary plutons in its footwall biotite and k feldspar 40ar 39ar dates from 11 1 0 2 ma to 15 5 0 3 ma yielded by symvolon granodiorite samples document the cooling of the rhodope core complex below 150 c 300 c during its southwestward progressive exhumation in the footwall of the strymon valley detachment

tectonometamorphic evolution of the rhodope orogen 1 this study combines new data on tectonostratigraphy macrostructures and microstructures petrology and geochronology to propose a comprehensive model for the tectonometamorphic evolution of the rhodope orogen from the jurassic to the early paleogene rocks from two study areas in the central and eastern greek rhodope represent a continental suture zone rhodope suture zone with the included material most likely forming an extensional allochthon south of the european continent during permo triassic times that was subsequently subducted beneath europe in the early jurassic 180 ma on the basis of comparable metamorphic ages and coherent structures but differences in metamorphic conditions and lithologies the rocks of the rhodope suture zone are subdivided into an upper and a lower part the prograde history is linked with subduction related structures in the lower part uniaxial stretching deformation stage d1 in metapelites the earliest stage of metamorphism recorded at circa 180 ma occurred at least under ultrahigh pressure metamorphic conditions the rocks of the upper part experienced isothermal decompression with partial anatexis exhumation paths of both parts differ in temperature because of the relative tectonic position within the exhuming wedge exhumation was forced by the nestos shear zone that controlled the early phase of normal displacement by sw shearing at the base lower part and ne shearing on top upper part from the late jurassic to the late cretaceous deformation stage d2 an intervening stage of mineral recrystallization and thermal reequilibration in the upper part was followed by a common exhumation history of both parts at pressures lower than about 12 kbar 35 40 km depth during this stage exhumation was controlled by southwest directed shearing and folding deformation stage d3 slab retreat to the south led to subsequent extension deformation stage d4 and final exhumation coeval with the formation of basement domes thus making the rhodope a classic core complex juxtaposed with former structurally higher units

statistical analysis of irregular wave guide influences on regional seismic discriminants in china short period regional phases play an important role in identifying low magnitude seismic events in the context of monitoring the comprehensive test ban treaty amplitude ratios of regional phases comprised mainly of p wave energy pn pg to those comprised mainly of s wave energy sn lg effectively discriminate between explosions and earthquakes in many regions particularly at frequencies higher than 3 hz at lower frequencies discrimination is usually poor due to large scatter that causes overlapping of event populations scatter in regional discriminant measures such as pg lg ratios is caused by both source and propagation effects and reducing the scatter imparted by the latter is essential to improving the discriminant performance when events do not share identical paths regional phases experience distance dependent amplitude variations due to effects such as critical angle ampli fication geometric spreading and attenuation discriminant measures are usually corrected for empirically determined distance trends for a given region but large scatter persists after such corrections this study seeks to develop more sophisticated empirical corrections for path properties in order to further reduce the scatter in regional discriminant measures caused by propagation effects broadband seismic waveforms recorded at station wmq in western china demonstrate that regional pg lg ratios show significant distance dependence for frequencies less than 6 hz however variations in crustal structure cause additional path specific amplitude fluc tuations that are not accounted for by regionally averaged distance corrections blockage of lg phases on paths traversing the margins of the tibetan plateau is one such effect regression analysis demonstrates that pg lg ratios measured at wmq display significant correlations with path specific properties such as mean elevation topographic roughness basement depth and crustal thickness multiple regressions using optimal combinations of parameters yield corrections that reduce variance in pg lg measurements for frequencies less than 3 hz by a factor of 2 or more relative to standard distance corrections this should systematically enhance the performance of the pg lg discriminant at low frequencies the method presented here can be used for all regions and all short period regional discriminants it is likely that the extraor dinary crustal heterogeneity in western china represents an extreme case of path dependent effects

on the nature of regional seismic phases ii on the influence of structural barriers summary the blockage of the lg wave by crustal barriers such as continental margins and graben structures has long been recognized as providing a very useful tool for mapping large scale lateral crustal variations along the propagation path numerical simulation of lg wave propagation in complex anelastic media using the pseudospectral method provides insight into the nature of the propagation process using both snapshots of the wavefield and synthetic seismograms a variety of 2 d structures have been investigated including the influence of sediments crustal thickness and attenuation thick sedimentary basins covering a graben structure can have a major influence since they remove lg energy by generating p conversion and scattering the principal mechanisms for strong lg attenuation across a graben the reduction of the lg energy is reinforced by anelastic attenuation in the sediments as well as the influence of the gradually thinning crustal waveguide associated with an elevated moho the extinction of lg in a sequence of explosions fired across the central graben of the north sea can be simulated by numerical calculations for the structure derived from refraction experiments

are long period body wave coda caused by lateral heterogeneity summary data from two broad band arrays in western europe nars and grf are used to study the character of long period body wave coda the events studied are at epicentral distances of 40 to 60 in the hindu kush region and on the mid atlantic ridge sampling the upper mantle to a depth of about lo00 km the periods studied are 5 50 s the long period coda of p at grf interstation distance about 10 km are strongly coherent whereas the long period coda of pp ppp and s waves are incoherent this indicates that the latter coda consists of scattered waves to investigate the nature of the scattering process the data of grf are analysed for slowness and azimuth variations in the coda intervals a new beamforming algorithm is presented to deal with the low frequences and relatively short time intervals the method is based on backus gilbert inverse theory the results show that the incoherent long period coda intervals almost entirely consist of surface waves these waves are scattered from the preceding body waves some calculations with linearized theory for body wave to rayleigh wave conversion at topography at the surface or at the moho show that realistic scatterers can account for the observed constant coda level the beamforming results show that the phases in the p coda all arrive along the great circle as scattering calculations point out that body wave to body wave scattering is inefficient it is concluded that the long period p coda does not contain a significant amount of scattered energy synthetic seismograms obtained with the reflectivity method show that spherically symmetric upper mantle models can explain these coda waves for events in the hindu kush region an upper mantle with a thick lid overlying a pronounced low velocity zone lvz is necessary to explain the character of the p coda at grf such an upper mantle agrees with previous studies of similar great circle paths the strong coherence of the p coda at grf is lost on the scale of nars station separation about 200 km this suggests lateral variations in the upper mantle at a scale of about 200 km it appears from previous studies of the upper mantle under europe that these variations must be sought in the lvz it is shown that the long period p coda is sensitive to variations in the p velocity structure of the lvz this suggests the p coda i e pdp phases as a tool for monitoring lateral variations in the lvz and possibly to prove the existence or absence of a lvz in the p velocity

spectral characteristics of the excitation and propagation of lg from underground nuclear explosions in central asia the nonlinear inverse method of xie 1993 is applied to analyze lg spectra from many recent underground nuclear explosions in central asia the analysis simultaneously determines lg seismic moments m0 and corner frequencies fc of events as well as path variable lg q values and their frequency dependences at 1 hz lg q at 1 hz estimated for many paths from the lop nor and balapan test sites to various broadband incorporated institution for seismology chinese digital seismic network and kyrghizstan network stations agree well with path averaged lg coda q values from previously obtained tomographic maps for eurasia this suggests that the lg q values obtained in this inversion have not been significantly affected by focusing defocusing or other effects of three dimensional structural complexities the logarithms of lg m0 values obtained in this study correlate linearly with a slope of about 1 2 with international seismological centre isc body wave magnitudes mb the linear relationship is consistent with a previous empirical relationship found between the logarithm of p wave seismic moments and isc mb values the slope of the linear relationship also suggests that the logarithm of lg m0 is a more direct measure of event size than is mb which for larger events is affected by high frequency amplitude falloff another important finding of this study is that the m0 values for the explosions scale with fc 4 rather than with fc 3 as would be expected if stress drops were constant this is consistent with previous scaling relations derived using lg from earthquake sources and suggests that the difference between lg and local s excitation by the same source types explosion or earthquake may overwhelm that between the excitation of lg by different source types a comparison between lg m0 and fc values obtained using an explosion source model with those obtained using an earthquake source model suggests that the m0 values estimated using the explosion source model are systematically lower by a factor of 0 27 than those estimated using the earthquake source model this occurs even though the data used are the same in the inversions with the two types of source model the factor of 0 27 is therefore due to the source model dependence of the m0 fc estimates the overshoot and lower spectral levels at lower frequencies in the explosion source model tend to reduce both the estimated m0 and fc values this suggests that in any nuclear monitoring program the same type of source model either an earthquake or explosion should always be used to discriminate explosions using lg the source model dependence also suggests that more effort should be made to estimate the amount of overshoot in the lg excitation caused by various source types

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

complex rotational deformations in the serbo macedonian massif north greece structural and paleomagnetic evidence abstract structural data concerning the neotectonic deformation of the serbo macedonian massif suggest a possible counterclockwise rotation of the stress field which corresponds to a clockwise rotation of the geological structures such a rotation is confirmed by paleomagnetic data providing a new alternative interpretation of the geodynamic evolution of this area

the distance dependence of regional phase discriminants abstract amplitude ratios of p and s phases recorded at regional distances have been suggested as potential discriminants for the character of seismic sources because of the differences expected in the radiation patterns of earthquakes and well contained explosions the most useful reference phase for p waves beyond 200 km from the source is pn and for s possible choices are the mantle phase sn and the crustally guided wave lg each of these phases has a different interaction with the seismic structure of the crust and mantle and such structural effects will impose their own patterns on the radiation characteristics from the source the range dependent component in lg pn and sn pn ratios have been investigated for a dense set of three component records covering the distance range out to 700 km for an explosive shot in water in southern sweden which formed part of the 1979 fennolora experiment a stable measure of amplitudes and amplitude ratios is provided by using the vector resultant of ground motion the square root of the total energy however even for a common source there are significant variations in the amplitude ratios for lg pn and sn pn of a factor of three or more as a function of range three component record sections allow a detailed examination of the way in which individual records relate to the whole wavefields the role of multiple reflections in building the pg and lg phases can be clearly seen as well as the complex substructure of the pn and sn phases returned from the uppermost mantle

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

emplacement and fabric forming conditions of the alous en tides granite eastern border of the tin seririne tin mersoi basin algeria magnetic and visible fabrics analysis abstract the alous en tides pluton intruded within one of the most important late panafrican n s shear zones the 7 30 shear zone in the southern hoggar shield a magnetic fabric study points out strong preferred orientations of the magnetite grains the orientation is coherent in the whole massif however it cannot be correlated with any of the visible structures in the field or in thin section strongly oriented magnetites are thus disseminated within all the rock the main rock forming minerals in this pluton were not preferably oriented during their crystallization showing that magma was emplaced without strongly oriented stresses magnetite orientations on the contrary reflect a strong stress field strike slip movements along the 7 30 shear zone probably generated local relative distension allowing pluton emplacement during the last magmatic phase they put the intrusion under the regional compressional stress field causing orientation of the magnetite the magnetic fabric then reveals the regional ene wsw stress field during late panafrican times in part of the pluton which was later affected by very intense solid state deformation during dextral movement the magnetic fabric remains mainly in connection with this initial magnetite fabric

regionalized versus single station wave guide effects on seismic discriminants in western china regional seismic signals play an important role in identifying low magnitude explosion and earthquake sources for monitoring the comprehensive test ban treaty ctbt to enhance the performance of seismic discriminants regional phases need to be corrected for propagation effects of large and intermediate scale crustal wave guide heterogeneity multivariate regression analysis using parametric path characteristics has shown promise for reducing the propagation induced scatter in short period regional phase amplitude ratios while path length is an important parameter for most seismic phase amplitudes other parametric features of crustal wave guide structure are often significantly correlated with regional amplitude ratios of p wave energy pn pg to s wave energy sn lg as demonstrated by our prior work on station wmq a question remains as to whether these effects can be regionalized so that they apply to all observations in a given region we explore the viability of regionalization of wave guide effects on regional seismic discriminants for frequencies of 0 75 to 6 hz in central asia and southwest china by analyzing single and multi station data linear regressions for single station data indicate that the significance of specific path parameters extracted from available crustal models varies from one station to another and from one subregion to another in general corrections for optimal combinations of wave guide parameters obtained from multivariate regression reduce the data variance more than conventional corrections for path length alone for both single station and multi station data however in central asia several stations show path dependence on certain variables with opposite signs so regionalization with multi station data does not perform well this is due to highly path specific effects in southwest china there is greater commonality in behavior among stations and fairly good regionalization can be achieved however the resulting variance reduction is still less than that for individual stations because some path effects appear to be direction dependent our results indicate that individual station calibration is the preferred procedure but this should include corrections for path effects beyond simple distance correction

palaeomagnetism in greece cenozoic and mesozoic components and their geodynamic implications abstract an important number of palaeomagnetic data have been obtained in greece during the last 20 years these data can be schematically divided into two groups according to their age when plate movements are fairly well constrained the cenozoic provides a dense network of palaeomagnetic directions the general pattern displays eastward declinations broadly distributed over a large distance from the ionian islands to the western greek rhodope and westward declinations less accurately constrained in space and time in the southern and eastern aegean and in western anatolia emphasis is given to the evaluation of this dataset by comparing it with new concepts of the regional tectonics in the mesozoic palaeozoic more scarcely covered reliable information is provided about latitudinal movements resulting in a suggested palaeolatitude of 15 20 n for almost all studied areas a model proposing prevailing counterclockwise rotations in the internal hellenides and strong clockwise rotations for the external hellenides appears plausible finally issues for future research are outlined for example mio pliocene formations from central greece the pindos ophiolites and palaeocene upper cretaceous data should receive further attention

progressive deformation of a zone of magma transfer in a transpressional regime the variscan merens shear zone pyrenees france the ew striking variscan merens shear zone msz located on the southern border of the aston dome pyrenees corresponds to variously mylonitized gneisses and plutonic rocks that are studied using the anisotropy of magnetic susceptibility ams technique the plutonic rocks form ew striking bands with from south to north gabbro diorites quartz diorites and granodiorites the msz underwent a mylonitic deformation with an intensity progressively increasing from the mafic to the more differentiated rocks the foliations are ew to nw se striking and subvertical a first set of lineations shows a moderate wnw plunge with a dextral reverse kinematics more recent subvertical lineations correspond to an uplift of the northern compartment to the east the msz was cut by a n120 e striking late shear band separating the msz from the querigut pluton the different stages of mylonitization relate to late variscan dextral transpression this regime allowed the ascent of magmas along tension gashes in the middle crust we interpret the msz as a zone of magma transfer which fed a pluton now eroded that was similar to the querigut and millas plutons located to the east we propose a model of emplacement of these plutons by successive pulses of magmas along en echelon transfer zones similar to the msz

azimuthal anisotropy of lg attenuation in eastern tibetan plateau 1 the q of seismic phase lg is measured to approach the crustal q which can be used to infer crustal rheology a reverse two station event method is used to measure the interstationqlg which theoretically eliminates effects from the source and site response strong azimuthal anisotropy of 1 qlg in northern tibet is observed which approximately correlates with the seismic velocity anisotropy observed using both surface waves and teleseismic s waves both the intrinsic and scattering attenuation contribute the isotropic q whereas the anisotropic q may be associated with the fractures and faults in the crust strong 1 qlgis observed in the northwestern songpan ganzi fold belt where the high qdirections correspond with the orientations of major strike slip faults intrinsic and scatteringq values are estimated for different tectonic terranes in eastern tibetan plateau the intrinsic qvalues are approximately 500 in the northern tibetan plateau which suggests a hot 700 c crust consistent with low seismic velocity measurements our result suggests that the crust of northwestern songpan ganzi fold belt may be hotter than that of the qiangtang terrane which may be related to the strain heating along the major strike slip fault zones that dominate the northernmost tibet

p sv wave field connection technique for regional wave propagation simulation a boundary element be method is developed to calculate the two dimensional p sv elastic response for crustal wave guides with irregular topographic features to simulate long range propagation of regional waves a connection technique is proposed to avoid large matrix inversions that become formidable for long range high frequency problems by using this technique a long crustal wave guide can be divided into relatively shorter sections and the be method can be used section by section to model the effects of rough topography on wave propagation at extended regional distances the validity of the technique is tested by comparison with a direct calculation numerical simulations with this scheme show that rough topography can scatter the p and rayleigh waves and attenuate the energy propagating in the wave guide this method can be used in computing the site effects on sites such as canyons mountains and valleys the connection technique expands this method to deal with large earth models with irregular topography

characteristics of short period wave propagation in regions of fennoscandia with emphasis on lg abstract wave propagation of crustal phases in particular lg near the arcess array in northern norway is examined and compared to propagation characteristics near the noress array in southern norway relying on array analysis we show that ray theory explanations of arrivals in local and regional seismograms are very useful in deducing the composition of the crustal wave trains frequency wavenumber analysis is applied to the array data to identify the arrivals then a composite of array beams is used to approximate each event record sections of composite seismograms are constructed for different directions from arcess to study propagational characteristics with distance and azimuth and then compared to composite seismogram record sections from noress to study different regional characteristics to model the observed character of lg and rg synthetic record sections are constructed by wavenumber integration in velocity models representative of structure in the different regions the results show that rg propagation distance varies significantly between regions and that the velocity gradient in the lower crust is the dominant factor in specifying lg characteristics in the baltic shield region lg is dominated by several discrete arrivals representing multiple moho reflections or by multiple moho reflections and turning waves with each multiple confined to a small distance range so that only one multiple set dominates at each distance furthermore we demonstrate that incomplete knowledge of the propagation characteristics leads to mislocations of local and regional events and inhibits source depth discrimination of events we identify three earthquakes in the arcess data set based on source depths these are constrained by phase velocities and depth phases none of which were properly identified by the automatic array detection software

characteristics of lg attenuation in the tibetan plateau 1 lg a regional seismic wave comprised of multiple shear wave reverberations trapped in the crustal waveguide is important for magnitude estimation and source discrimination for monitoring nuclear testing treaties in stable continental regions lg propagates with a group velocity of about 3 5 km s and can often be observed at distances up to 4000 km to better understand the absence of high frequency lg arrivals for paths traversing the northern boundary of the tibetan plateau we investigate spatial variations of broadband 0 15 5 0 hz energy in the lg group velocity window 3 6 3 0 km s using regional waveforms recorded at the chinese digital seismic network station wmq vertical component seismograms are analyzed for 90 events with magnitudes of 4 4 mb 6 4 that occurred between 1987 and 1999 in the tibetan plateau and around its margins the lg amplitude spectra for events located near the northern margin of the plateau have apparent corner frequencies of 1 2 hz nearly identical to those for comparable size events at similar distances outside the plateau high frequency 1 hz lg energy recorded at wmq decreases rapidly as a function of source distance into the plateau a path length of 300 400 km within the northern plateau suffices to eliminate 2 5 hz lg energy for events in southern tibet with paths crossing the central portion of the tibetan plateau almost total lg extinction occurs even for energy in the low frequency band of 0 2 1 hz corresponding apparent corner frequencies of the lg amplitude spectra range between 0 2 and 0 4 hz the corner frequency shift is found to vary systematically with path length across the plateau linear regressions demonstrate that the shift in apparent corner frequency of lg amplitude spectra is negatively correlated with features of the tibetan plateau such as mean elevation along the paths or travel distance within the plateau above specified elevation thresholds the systematic variations in the amplitude and frequency content of energy in the lg window as a function of path length within the plateau indicate that strong crustal attenuation plays an important role in lg extinction for paths traversing central and northern tibet superimposed on any structural blockage effects associated with abrupt thinning of the crust near the northern boundary of the plateau spectral ratios of many event pairs along great circle paths give estimates of frequency dependent lg attenuation for paths crossing western central and eastern sectors of tibet the region of strong sn attenuation in northern central tibet also has strong lg attenuation with qlg for 1 hz on the order of qo 80 90 while in southern central tibet qo increases to about 316 and in eastern and western tibet qo is on the order of 120 200 for paths traversing the entire plateau the strong lg attenuation in northern central tibet is responsible for the so called lg blockage and may be associated with partial melting in the crustal low velocity layer in northern tibet our qlg values for tibet are significantly lower than most earlier estimates primarily as a result of not excluding blocked observations along with allowing for lateral variations within tibet index terms 7203 seismology body wave propagation 7255 seismology surface waves and free oscillations 7205 seismology continental crust 1242 keywords lg tibetan plateau nuclear event discrimination crustal attenuation lg blockage crustal partial melting

distribution anisotropy the cause of ams in igneous rocks understanding of ams in pristine basic igneous rocks in terms of flow orientation of ellipsoidal magnetite grains is thwarted by the fact that these grains 1 typically are irregularly equant or skeletal rather than distinctly ellipsoidal and 2 usually crystallize interstitially and late after magma flow has ceased however the distribution of such grains will be relatively anisotropic if they grew in residual liquid volumes within a preferredly oriented by flow silicate template this constraint may impose a slight preferred shape orientation to the irregular magnetite grains during their growth but in addition we suggest it is the anisotropic magnetic interaction between the grains which is the basic cause of ams experiments involving the casting of magnetite epoxy mixtures in various foliated or lineated glass templates have yielded samples with the expected ams symmetry i e k3 perpendicular to glass plates or k1 parallel to glass rods slicing of near isotropic synthetic blank and natural rock cores and interleaving with glass slides showed a progressive increase in anisotropy of the blank from 0 4 to 2 and the natural rock from 0 9 to 2 9 in both the k3 axis migrates to be perpendicular to the glass slides

tomographic imaging of lg and sn propagation in the middle east observations based on relatively limited data recorded by sparsely distributed stations have indicated that regional seismic phase propagation lg and sn is very complex in the middle east accurate characterization of regional seismic wave propagation in this region necessitates the use of a large number of seismic stations we have compiled a large data set of regional and local seismograms recorded in the middle east this data set comprises approximately four years of data from national short period networks in turkey and syria data from temporary broadband arrays in saudi arabia and the caspian sea region and data from gsn mednet and geofon stations in the middle east we have used this data set to decipher the character and pattern of regional seismic wave propagation we have mapped zones of blockage as well as inefficient and efficient propagation for lg pg and sn throughout the middle east two tomographic techniques have been developed in order to objectively determine regions of lithospheric attenuation in the middle east we observe evidence of major increase in lg attenuation relative to pg across the bitlis suture and the zagros fold and thrust belt corresponding to the boundary between the arabian and eurasian plates we also observe a zone of inefficient sn propagation along the dead sea fault system which coincides with low pn velocities along most of the dead sea fault system and with previous observations of poor sn propagation in western jordan our observations indicate that in the northern portion of the arabian plate south of the bitlis suture there is also a zone of inefficient sn propagation that would not have been predicted from prior measurements of relatively low pn velocities mapped high attenuation of sn correlates well with regions of cenozoic and holocene basaltic volcanism these regions of uppermost mantle shear wave attenuation most probably have anomously hot and possibly thin lithosphere

upper mantle seismic discontinuities and the thermal structure of subduction zones the precise depths at which seismic velocities change abruptly in the upper mantle are revealed by the analysis of data from hundreds of seismometers across the western united states the boundary near 410km depth is locally elevated that near 660 km depressed the depths of these boundaries which mark phase transitions provide an in situ thermometer in subduction zones the observed temperature contrasts require at least moderate thickening of the subducting slab near 660 km depth in addition a reflector near 210 km depth may mark the bottom of the aesthenosphere

the effect of magnetic anisotropy on paleomagnetic directions in high grade metamorphic rocks from the juiz de fora complex se brazil the juiz de fora complex is mainly composed of granulites and granodioritic migmatite gneisses and is a cratonic basement of the ribeira fold belt which was formed during the last stage of brasiliano orogeny samples widely distributed over the studied region se brazil rio de janeiro state were collected for paleomagnetic and magnetic anisotropy determinations after measurement of anisotropy of low field magnetic susceptibility ams the same specimens were submitted to both alternating field for anisotropy of remanent magnetization arm determinations and thermal demagnetization for paleomagnetic analyses demagnetization processes allowed isolating an eastern steep positive inclination characteristic remanent magnetization chrm direction from the rocks the studied specimens are strongly heterogeneous at sample scale regarding the amount of magnetic minerals even for specimens from the same core rock magnetism indicates that there is a complex mixture of magnetic minerals with both low and high coercivity which are associated with coarse grained titano magnetite and either fine grained titano magnetite or titanohematite grains respectively these magnetic minerals are responsible for both remanent direction and magnetic anisotropies even though for some specimens paramagnetic minerals are the carriers of ams fabric the chrm direction found for the rocks should represent the cooling phase of the brasiliano event in the area and it was acquired after the magnetic fabric was formed the ams and arm fabrics are coaxial and tectonic in origin and compare favorably with the mesoscopic scale fabrics in the adjacent areas however arm measurements have reached only low coercivity grains and it could be determined in few specimens then only an estimate of arm effect on chrms correction is shown the rocks are strongly magnetically anisotropic 50 and foliated the paleomagnetic directions from each specimen within a site tend to approach its ams or arm foliation kmax kint or armmax armmin plane these directions were corrected specimen by specimen from the sites taking into account the pole of ams or arm foliation kmin or armmin and the value of the degree of anisotropy p results show that even for specimens with high p the angular difference between corrected and uncorrected magnetization direction may be insignificant if the geomagnetic field at the time of acquired magnetization was approximately parallel to the magnetic foliation of the specimens our data set suggests that ams is a powerful tool to correct the chrm deviation from paleofields in rocks with complex magnetic mineralogy such as those from the juiz de fora complex

constraining the prograde and retrograde p t t path of eocene hp rocks by shrimp dating of different zircon domains inferred rates of heating burial cooling and exhumation for central rhodope northern greece ion microprobe shrimp dating was carried out on different zircon domains from metamorphic rocks of the hp ht terrane of central rhodope northern greece to constrain the timing of prograde and retrograde stages within a single tectono metamorphic cycle a well determined p t t relative path for the metamorphic rocks of this terrane was used as a petrological basis for the geochronological investigations ion microprobe work was assisted by cathodoluminescence cl images of the zircon crystals the geochronological results revealed that hercynian continental crust was subducted during the eocene several stages of the eocene tectono metamorphic cycle including both the prograde and retrograde parts of the p t path above ca 300 c 0 3 gpa were dated using zircons from the following rock types 1 a deformed quartz vein probably formed at ca 300 c 0 3 gpa zircons in this vein precipitated from a hydrothermal fluid they yielded an age of 45 3 0 9 ma which corresponds to the time of a low t prograde stage of metamorphism 2 in kyanite eclogites zircons were entirely reset during eclogite facies metamorphism resetting was very probably enhanced by the presence of fluids derived by h2o liberating reactions close to the p peak they yielded an age of 42 2 0 9 ma 3 orthogneisses surrounding the kyanite eclogites contained zircons with magmatic oscillatory zoned cores which yielded hercynian ages of 294 8 ma age of granitic protolith formation whereas cl bright metamorphic rims yielded like the eclogite zircons ages of 42 0 1 1 ma therefore both the eclogites and orthogneisses are interpreted to have approached maximum depth at around 42 ma 4 in a leucosome of a migmatized orthogneiss oscillatory zoned zircons yielded an age of 40 0 1 0 ma at this time the rocks reached maximum temperatures during early decompression 5 a late pegmatite crosscutting the schistosity of amphibolites contained oscillatory zoned zircons that yielded a crystallization age of 36 1 1 2 ma thus the whole tectono metamorphic cycle above ca 300 c 0 3 gpa lasted from 45 3 0 9 ma to 36 1 1 2 ma that is 9 2 ma with an extreme error value of 2 1 ma based on combined shrimp and petrological data the average rates of heating and burial during subduction above ca 300 c 0 3 gpa are 94 c ma and 15 mm a respectively rates of cooling and exhumation also above 300 c 0 3 gpa are calculated to be 128 c ma and 7 7 mm a the eocene age of metamorphism in central rhodope implies that the terrane of at least central rhodope and the cyclades very probably was part of the same continental crust

a fuzzy logic slope form system for predictive soil mapping of a landscape scale area with strong relief conditions abstract we studied an improved slope form system using a fuzzy logic method to assess and map soil fertility of a mountain region in northern vietnam that has strong relief conditions the lack of good soil mapping techniques in vietnam has brought about insufficient soil information which often leads to false recommendations for land use and crop planning the reviewed literature describes soil mapping techniques using fuzzy logic method but all of them are applied for mapping areas that have gentle relief conditions that are unlikely to be applicable to the mountainous soils in our study area in this paper we introduce a detailed slope form system that significantly describes the complexity of terrain characteristics of the area to be mapped and provides more detail about the variability of the soil fertility of the area nine basic slopeforms were used to characterize for each of upper middle and foot slope positions making the list 27 slopeforms together with crest and valley the total unit number is 29 we investigated soils of the area and classified them into the major soil groups and calculated soil property indices for all of them we identified four major environmental parameters affecting soil formation and soil quality geology elevation slope inclination and land use the findings indicated that soil fertility differs at slope positions soils located at upper slope positions where agricultural activity only started recently are more fertile than those found at middle slope positions soils located at foot slope positions where eroded sediments accumulate also have high levels of fertility compared to those on the middle slope the improved slope form system then became an important additional environmental parameter for this soil mapping work at a same comparable category i e slope position geology soil group elevation slope gradient straight slopeforms are an indicator for better soil fertility compared to convex and concave forms although the findings could not specify soil fertility variability for all 29 slopeforms they did emphasize the major differences in soil fertility and soil formation based on three major forms of convex straight and concave with other factors taken into account such as slope inclination geology and elevation we expect our results to be used by scientists and local authorities in deriving more effective land use and crop options for land use management strategies for the northern vietnam s mountain regions

variations in regional phase propagation in the area around japan the high level of seismicity and dense network of short period stations in japan allows a detailed characterization of regional phase propagation there are substantial differences depending on the location of the source and stations despite the structural complexity lg is clearly seen in many parts of japan lg is particularly well developed in the western part of the main island honshu and will propagates through some volcanic zones with loss of high frequency components there are also zones of lg blockage in northeastern honshu and for subduction zone events with significant oceanic paths for which the mantle phases pn and sn are particularly clear the oceanic region in the sea of japan blocks lg propagation paths for events in mainland asia at many stations but there are clear lg propagation corridors through korea to stations in the west kyushu western honshu and in the north into hokkaido the lg phase carries substantial energy for large events and the differences in efficiency of propagation influences the intensity of ground shaking thus the 1995 hyogo ken nanbu kobe earthquake shows intensity contours extended to the west in the region of efficient lg wave propagation the rg phase and the fundamental mode of love waves are very significant for the shallow 2000 tottori ken seibu event and the effect of the combination of lg with these slightly lower frequency surface waves would help to explain the discrepancy between the japan meteoro logical agency magnitude from regional stations mj 7 3 and the moment magnitude from distant observations m w 6 6

insights into the geotectonic evolution of the southern rhodope as inferred from a combined ams microtextural and paleomagnetic study of the tertiary symvolon and vrondou plutons abstract the present study focuses on the tertiary granitoids of the rhodope massif northern greece namely the early miocene symvolon pluton and the composite miocene oligocene vrondou pluton in this paper we provide new anisotropy of magnetic susceptibility ams data from symvolon pluton discussed along with previously published ones from vrondou as well as new paleomagnetic data from samples widely distributed over both studied regions combined with macroscopic observations and microtextural examinations the magnetic fabric study pointed out anisotropic bodies with strong preferred orientations of the magnetic grains however the paleomagnetic vectors corrected for anisotropy effect remain unchanged two groups of magnetic lineations were identified a prevailing ne sw trending linear fabric visible mainly in the early miocene plutons and a second nw se trending fabric clearly imprinted in the mid oligocene eastern part of the vrondou pluton macro and microtextural study revealed the presence of magmatic textures mainly in eastern vrondou and sub solidus plastic deformation textures in symvolon and western vrondou paleomagnetic results displayed a complex pattern with prevailing clockwise rotations reinforcing the existing pattern for n greece and supporting the capacity of granitic bodies to reliably record the earth s magnetic field independently of their anisotropy

elucidation of soil landform interrelationships by canonical ordination analysis abstract this paper examines the robustness of various multivariate ordination methods applied to elucidate the relationship between soil developed on hillslope and the environment in a south australian subcatchment canonical correspondence analyses were found to be less attractive than the linear methods i e principal component analysis and redundancy analysis because interrelations among soil variables and or between soil and the landform attributes are more linear than unimodal among the linear methods standard redundancy analysis following transformation of soil data gave a clearer insight into pedogenetic implications of soil landform interactions gradient angle plan convexity profile convexity and to a lesser extent upslope distance and area account for much of the soil variation in the study area gradient influences the distribution of surficial soil particles which is suggestive of selective removal and deposition of fine materials on the mid to lower slopes higher subsoil clay percentage associated with concave slopes may be ascribed to either increased weathering rate and or flux of fine material due to convergence of water flows solum depth and depth to bedrock also appeared to have controlled some of the contemporary pedo geomorphological processes eluvio illuvial processes are more pronounced in the relatively deep lower slope pedons evidenced by cutans in their subsoil layers soil colours are related to the soil depth attributes slope and upslope distance and area probably through the influence of these attributes on soil drainage condition the extent to which landform and parent material related attributes e g depth to bedrock affect soil development and distribution patterns in the study area is shown quantitatively these findings have considerably improved our understanding of soil genesis in the study area and also point to the importance of land unit delineation to design sampling patterns the enhanced sampling design would be beneficial in terms of reduced extrapolation error and thus misclassification of soil

two stage deformation of the mont louis andorra granite pluton variscan pyrenees inferred from magnetic susceptibility anisotropy the mont louis andorra granodiorite pluton eastern pyrenees france andorra and spain was the subject of a thorough study of its internal structures principally the measurement of the anisotropy of its magnetic susceptibility and the classification of its microstructures regularly spaced sampling 281 sites allowed the precise mapping of the susceptibility magnitudes consistent with mapped rock types the magnetic structures fall into two distinct families which occur in separate parts of the pluton and have different microstructures family i is observed almost everywhere and has close to horizontal lineations remarkably constant in ne sw azimuth magmatic to submagmatic microstructures characterize these rocks in contrast family ii is confined within nw se trending corridors where moderate to steep nw plunges of the lineations are recorded and subsolidus microstructures are observed magnetic structures of family i are argued to equate with the kinematic framework of the deforming magma during its emplacement family ii structures represent a late to post consolidation reworking and therefore record a second stage of deformation in the pluton it is concluded that magma emplacement was related to a ne sw trending strike slip and or thrust fault system coeval with the sw verging thrust episode documented in the pyrenees the second stage corresponds to dextral shear movements with a thrust component on nw se striking planes corridors containing family ii structures are shear zones responsible for dissection of the massif into three blocks the eastern block representing the former base and the western block the top of the pluton restoration of the pluton9s shape along these corridors demonstrates the importance of the early variscan ne sw kinematic direction because the family ii structures that form shear zones affecting the pluton have similar orientation and kinematics as the compressive steep main phase of deformation ubiquitous in the pyrenees the pluton of mont louis andorra was probably emplaced before this main phase of deformation

tertiary granitoids of rhodope northern greece magmatism related to extensional collapse of the hellenic orogen abstract many granites that occur in orogenic belts such as the himalaya the hercynides or caledonides are thought to result from anatexis of the lower parts of over thickened thrust stacked crustal units just preceding termination of the orogenic cycle numerous tertiary granitoids occur in the rhodope zone of northern greece and adjacent regions of bulgaria a belt regarded as an eastern extension of the alpine system these granites could also be regarded as syn or late tectonic crustal melts in that some have been emplaced as sheet like bodies along major alpine thrust planes and show a strong marginal foliation parallel to the pervasive alpine compressional fabrics in detail however the geochemistry of the granitoids their timing and relationships with country rocks suggest they have been emplaced in an extensional regime that is related to the collapse of the hellenic orogen and more particularly to the crustal thinning that the aegean region has suffered since the mid tertiary rather than being products of crustal thickening it is suggested that their petrogenesis is related to the elevation of thermal gradients during the extensional phase which initiated thermal breakdown of hydrous minerals in the lithosphere and lower crust that had existed metastably during compression and the subduction of cool ocean lithosphere beneath the region in the late mesozoic early tertiary

palaeomagnetism and magnetic fabric in the freetown complex sierra leone summary about six separately orientated cores were collected at each of 14 sites distributed throughout the arcuate west dipping 6 km thick freetown layered igneous complex alternating field and thermal demagnetization both isolate a stable component of remanent magnetism which corresponds to a palaeomagnetic south pole from 13 sites nine reverse four normal polarity at 82 9 s 32 7 e a 95 5 6 this is indistinguishable from that reported in 1971 based on alternating field demagnetization of cores from 10 orientated hand samples the diverence between the freetown pole age 193 3 ma and other mid jurassic poles from west africa could be due to its greater age the diverence between the whole west african jurassic pole group and the karoo pole from southern africa however suggests moderate 10 d i verential rotation of west africa relative to the kaapvaal craton a prevalent magnetic foliation fabric coincides generally with the petrological layering as might be expected but a ubiquitous magnetic lineation is predominantly down dip this is compatible with a down dip pyroxene lineation reported to be present in some field outcrops and interpreted in terms of late stage deformation during the slow crystallization and cooling of the large igneous body however a fold test shows that the igneous layering had already achieved its present attitude before the complex cooled to 570 c the maximum blocking temperature of the characteristic remanence

average attenuation of 0 7 5 0 hz lg waves and magnitude scale determination for the region bounding the western branch of the east african rift summary the investigation of lg attenuation characteristics in the region bounding the western branch of the east african rift system using digital recordings from a seismic network located along the rift between lake rukwa and lake malawi is reported a set of 24 recordings of lg waves from 12 regional earthquakes has been used for the determination of anelastic attenuation q lg and regional body wave magnitude m blg scale the events used have body wave magnitudes m b between 4 6 and 5 5 which have been determined teleseismically and listed in isc bulletins the data were timedomain displacement amplitudes measured at 10 diverent frequencies 0 7 5 0 hz q lg and its frequency dependence g in the region can be represented in the form q lg 186 2 6 5 f 0 78 0 05 this model is in agreement with models established in other active tectonic regions the lg wave based magnitude formula for the region is given by m blg log a 3 76 0 38 log d 5 72 1 06 where a is a half peak topeak maximum amplitude of the 1 s lg wave amplitude in microns and d is the epicentral distance in kilometres magnitude results for the 12 regional earthquakes tested are in good agreement with the isc body wave magnitude scale

propagation efficiency of long period lg waves in the south american continent summary we investigate the propagation efficiency characteristics of long period 3 12 s lg waves in continental south america as recorded in the last few years on stations of the gtsn iris usgs irisiida and geoscope networks this paper reports the results of a first look at the available lg data for events with m 5 0 from 1990 to 1995 in this period seven main seismic events and aftershocks along the length of the andes produced a total of 29 usable paths from which preliminary results indicate that 1 long period lg waves are unusually prominent in seismograms of continental paths covering the shield areas of south america and are clearly observed on broad band instruments at epicentral distances exceeding 3500 km 2 lg propagation is substantially attenuated weak or absent for paths along the strike of the andes and along the three active volcanic chains of chile peru and colombia 3 away from the active volcanoes the data show lg propagating more efficiently across than along the strike of the andes and 4 in general the ratio of the transverse to the vertical components of the lg phase decreases with decreasing propagation efficiency these first results also raise a number of exciting questions regarding the exploration of the crustal waveguide in south america such as the potential for lgbased tomography to detect a postulated fossil plume in southeastern brazil or how the propagation efficiency of high frequency lg in volcanically active areas may be used to detect magma chambers consequently we intend to carry out a systematic study of lg in the continent as part of the ongoing surface wave inversion for the south american lithosphere sisal project a collaborative effort vdovin et al 1996 to determine the crustal and lithospheric structure of the south american plate from measurements of surface wave dispersion in the period range 2 200 s

a major oligo miocene detachment in southern rhodope controlling north aegean extension plutonic and metamorphic rocks of the southwest part of the rhodope massif in greece correspond to ductile lower crust exhumed and deformed along a major detachment during post thickening extensional tectonics extension started during the oligocene and is responsible for the development of miocene quaternary sedimentary basins both brittle and ductile deformations result from gravity collapse of previously thickened lithosphere as proposed for others large extended terranes this interpretation disagrees with the previous models which attributed tertiary ductile deformation to alpine thrusting and brittle extensional deformation to back arc tectonics above a subduction zone

analysis of short period regional phase path effects associated with topography in eurasia propagation of regional seismic phases is highly dependent on path effects but we have a limited understanding of these effects and no general procedure for accounting for path variation influence on regional waveforms thus there is strong regional variability in the effectiveness of regional wave discriminants used to identify small earthquakes and nuclear explosions motivated by many observations of correlation between surface geology and regional phase behavior we empirically explore the relationship between short period regional and upper mantle distance signal energy and statistics of topography along different travel paths using data for underground nuclear explosions at semipalatinsk kazakhstan we find strong linear correlations of the logarithmic rms amplitude ratio sn lg and to a lesser extent p lg with mean altitude rms roughness rms slope and skewness of topography along the paths to receivers in eurasia this indicates that energy partitioning in the regional wave field is controlled by wave guide structure and attenuation variations that are manifested in surface topography this suggests that it is feasible in many cases to directly calibrate regional discriminants for path effects in terms of observable surface topography as a surrogate for overall path properties the relationships also help to understand the nature of regional phase propagation

the effect of 3 d structure on lg propagation patterns the method of ray diagrams based on the constructive interference of multiple s reflections gives a visual measure of the interaction of guided wavetrains with variations in crustal structure the technique is extended to 3 d heterogeneity and by representing the s ray systems in plan view through their basement reflection points a semi quantitative measure of the disruption of lg at different phase velocities can be made in addition the tilt of the ray systems can be used as an indication of the degree of interconversion between rayleigh and love wave energy two simple crustal models are examined to investigate the effects of oblique incidence and transverse topographic gradients on multiple s reflections using ray diagrams the method is then applied to several real earth models of the crust in central asia using topographic data and assuming isostasy interpretations of the ray diagrams for paths across the major tectonic features compare well with many of the observations from previous studies ruzaikan et al 1977 ni barazangi 1983 and suggest that the gross characteristics of lg propagation can be attributed to the shape of the crustal waveguide

contrasts in regional seismic wave propagation to station wmq in central asia summary the varying character of regional seismic phase propagation in central asia is well illustrated by the character of the seismograms at the urumqi station wmq in xinjiang china three different classes of behaviour are seen for propagation across the relatively stable platforms to the north along the tien shan chain and across the tarim basin from tibet these paths demonstrate the influences of the variation in crustal structure on the regional phases particularly the tibetan plateau and its north and south boundaries but also the influence of the pamirs on propagation along the tien shan as an interference phase lg is sensitive to changes in crustal structure and can be used to study crustal heterogeneity lg can propagate along the tien shan chain trapped by the gradients in structure on either side but with a progressive loss in amplitude and frequency however once the northern boundary of tibet is crossed the high frequencies in the lg train are lost and there is little recognizable arrival the amplitude ratios of the different crustal phases pn sn and lg can be used to characterize the behaviour and the different classes of propagation can be further separated when account is made of the frequency content in the lg window the influence of the transitions in crustal structure at the northern edge of the tibetan plateau on propagation to wmq is investigated using numerical modelling with the pseudospectral method for models of crustal variations this demonstrates how the crustal pinch at the northern boundary operates to modify the fairly efficient propagation inside tibet with substantial transfer of energy into the mantle

crustal attenuation within the turkish plateau and surrounding regions the lateral variations of seismic attenuation in the crust of turkey and surrounding regions have been imaged from the inversion of interstation lg q measurements this study develops the first tomographic model for lg q 0 in this region that model is consistent with previous more qualitative lg attenuation models that showed inefficient or blocked lg across the eurasian arabian plate boundary in general the northern arabian platform has low to normal lg q 0 values 250 350 whereas high q 0 values 670 800 occur in the southern arabian plate additionally we have found a dramatic decrease in lg q 0 across the bitlis suture the plate boundary between the arabian and eurasian plates beneath the turkish plateau our high to moderate lg attenuation values q 0 100 200 probably originates from both scattering and intrinsic attenuation due to the tectonic complexity and the widespread young volcanics in the region we conclude that the lowest q 0 values for the east anatolian plateau 70 100 and the portion of western turkey around the menderes massif 60 150 are probably caused by intrinsic attenuation we find low to normal lg q 0 values 150 300 beneath the part of the taurus mountains in western anatolia these higher values may be related to the nature of the crust in the tauride mountain belt we also mapped the lateral variations in lg and observed a fairly consistent negative correlation between and lg q 0 in the northern middle east

tectonic stages along a traverse cross cutting the rhodopian zone greece in a cross section along the rhodopian zone from the greece bulgarian border through the postalpine basins in the xanthi area to thasos island detailed structural mapping and collection of field data enable us to determine a sequence of tectonic stages that affected this area this allows us to propose a model of continental collision during the early eocene ne sw directed movements produced a southwest facing pile of crystalline nappes with internal deformation comprising nw and ne trending isoclinal folds and a ne sw trending stretching lineation after a short time interval nappe movements started again under brittle deformation conditions and produced composite thrust sheets wnw and nne trending chevron folds and thick cataclasite late erogenic uplift and extension caused the formation of nw and ne trending normal faults these faults bounded the oligocene flysch and molasse basins and provided pathways for voluminous magmatic suites this tectonic process was interrupted at the oligocene miocene boundary by a late orogenic compression reflected in nw open folds and dissolution cleavages subsequently differential uplift and subsidence associated with nw and ne trending normal faults has continued up to the present time from the early pliocene new fragmentation and thinning of the crust reflected in wnw listric faults and nne transfer faults has affected the southern parts of the rhodopian zone nappe forming movements are the result of a progressive collisional process involving a kimmerian microcontinent lying between the eurasia and apulia continents in the final stages of this collision uderplating processes led to regional uplift and extension additional extensional movements were related to the formation of the aegean back arc basin caused by the late cenozoic hellenic subduction zone

no significant post eocene rotation of the moesian platform and rhodope bulgaria implications for the kinematic evolution of the carpathian and aegean arcs abstract the region located between the carpathian balkan and aegean arcs the moesian platform and bulgarian rhodope is generally assumed to have been stably attached to the east european craton during the cenozoic evolution of these arcs the kinematic evolution of this region is however poorly constrained by paleomagnetic analysis in this paper we provide new paleomagnetic data 800 volcanic and sedimentary samples from 12 localities showing no significant post eocene rotation of the moesian platform and rhodope with respect to eurasia therefore confirming the stability of this region we compare this result to a provided review of paleomagnetic data from the south carpathians tisza block and the aegean region the tisza block underwent 68 4 16 7 of middle miocene 15 10 ma clockwise rotation with respect to the moesian platform in line with previous rotation estimates based on structural geology the stability of the moesian platform during middle miocene eastward emplacement of the tisza block into the carpathian back arc supports dextral shear along the southern carpathians recorded by 13 6 ma clockwise strike slip related rotations in foreland deposits the new reference direction for the moesian platform and rhodope allows accurate quantification of the rotation difference with the west aegean domain at 38 0 7 2 occurring between 15 and 8 ma to accommodate this rotation we propose that the pivot point of the west aegean rotation was located approximately in the middle of the rotating domain rather than at the northern tip as previously proposed this new scenario predicts less extension southeast of the pivot point in good agreement with estimates from aegean structural geology northwest of the pivot point the model requires contraction or extrusion that can be accommodated by the coeval motion of the tisza block around the northwestern edge of the moesian platform

efficiency of lg propagation from sms dynamic ray tracing in three dimensionally varying crustal waveguides the effects of variations in crustal and basin thicknesses on the efficiency of lg propagation in central asia are investigated by comparing the predictions of ray theoretical modeling of lg as multiple critically reflected sms rays with observations at the knet cnet and ilpa arrays ray modeling predicts that strong spatial gradients in crustal thickness within 10 to 50 km of either the source or receiver can affect lg efficiency over paths exceeding 500 km variations in the efficiency of lg propagation to knet including instances of strong variations across the aperture of the array are consistent with predicted blockage of sms by high slopes of moho topography associated with the hindu kush and pamir mountains at cnet and ilpa the blocking effects of moho slopes associated with the caucausus and zagros mountain belts and black and caspian seas are accentuated by the effects of thick basins thick basins greater than 2000 m are found to have large effects on the efficiency of lg propagation from shallow 1 km crustal sources blocking either a portion or all of the lg phase along paths crossing these basins the basin effects are strongly sensitive to source depth nearly vanishing for sources 15 km and deeper

magnetic fabric shape preferred orientation and regional strain in granitic rocks since granites do not preserve easily mappable foliations lineations and strain markers determining the degree of shape preferred orientation spo in them is challenging the aim of this paper is to present a methodology for determining variation in the degree of spo in granites and to test the feasibility of correlating the same with regional strain the case of the godhra granite located in the southern parts of aravalli mountain belt india is taken as an example degree of spo is determined using two different techniques a anisotropy of magnetic susceptibility ams and b strength of mineral lineation determined by calculating the concentration parameter k of von mises distribution by digital image analysis of biotite kbi and feldspar kf in thin sections prepared parallel to the magnetic foliation plane spo data obtained using the above two techniques from 20 samples distributed across the entire granite are analysed samples with a higher k also have a stronger magnetic fabric magnetic lineation l and degree of magnetic anisotropy p 0 also the degree of spo is greater for granites from the southern parts as compared to the northern parts it is argued that this variation in degree of spo cannot be attributed to rheological differences or strain resulting from difference in aspect ratios regional strain is inferred as the dominant factor since the emplacement of the godhra granite is synchronous with the tectonic rejuvenation along the central indian tectonic zone citz that lies to its south the higher degree of spo in the southern parts is attributed to its proximity to the citz whilst caution needs to be exercised to directly apply magnetic data as a measure of strain intensity on a regional scale it can be a useful guide to select samples for detailed spo analysis using some alternative technique especially for granites and other magmatic rocks that are devoid of mesoscopic strain markers 2006 elsevier ltd all rights reserved

path corrections for source discriminants a case study at two international seismic monitoring stations improving the performance of short period regional seismic discriminants by applying propagation corrections is explored using observations from two seismic monitoring stations in asia frequency dependent regional phase amplitude ratio measurements at stations nil and zal for earthquakes and underground nuclear explosions were obtained from the prototype international data center pidc that has been established for developing monitoring capabilities of the comprehensive nuclear test ban treaty ctbt the pidc discriminant measurements have large scatter much of which is attributed to wave propagation effects in the heterogeneous crustal waveguide linear regressions indicate that the phase ratios are correlated with topographic characteristics along the individual paths providing an empirical means for correcting for path effects beyond conventional distance corrections kriging a spatial multiple regression algorithm also reveals coherent spatial patterns in the data indicative of regional path effects using available high resolution topography data correction of regional p s ratios for the best models obtained from multivariate regressions systematically reduces the data variance relative to distance corrections alone as has been observed for other data sets the reduced scatter in the measurements increases the separation between earthquake and explosion populations in most cases enhancing the regional discriminant performance the path corrected discriminants isolate explosions better for nil than for zal even though some of the explosion sources are located in a common source area kriging achieves comparable or superior variance reduction for the discriminant measures without requiring knowledge of the path structure although this may not result in improved discriminant performance while always desirable corrections for heterogeneous path effects may prove inadequate in some cases notably when phase blockage occurs or when strong attenuation eliminates the diagnostic high frequency energy

propagation of regional seismic phases lg and sn and pn velocity structure along the africa iberia plate boundary zone tectonic implications we used over 1000 regional waveforms recorded by 60 seismic stations located in northwest africa and iberia to map the efficiency of l g and sn wave propagation beneath the gulf of cadiz alboran sea and bounding betic rif and atlas mountain belts crustal attenuation is inferred from the tomographic inversion of l g pg amplitude ratios upper mantle attenuation is inferred from maps of sn propagation efficiency derived by inversion of well defined qualitative efficiency assignments based on waveform characteristics regions of l g attenuation correlate well with areas of thinned continental or oceanic crust significant sedimentary basins and lateral crustal variations comparison of the sn efficiency results with velocities obtained from an anisotropic pn traveltime inversion shows a fairly good correlation between regions of poor sn efficiency and low pn velocity a low pn velocity 7 6 7 8 km s 1 and significant sn attenuation in the uppermost mantle is imaged beneath the betics in southern spain in sharp contrast to the relatively normal pn velocity 8 0 8 1 km s 1 and efficient sn imaged beneath the alboran sea slow pn velocity anomalies are also imaged beneath the rif and middle atlas in morocco we do not identify any conclusive evidence of lithospheric scale upper mantle attenuation beneath the rif although the crust in the gibraltar region appears highly attenuating making observations at stations in this region ambiguous paths crossing the gulf of cadiz eastern atlantic and the moroccan and iberian mesetas show very efficient sn propagation and are imaged with high pn velocities 8 1 8 2 km s 1 the spatial distribution of attenuation and velocity anomalies lead us to conclude that some recovery of the mantle lid beneath the alboran sea must have occurred since the early miocene episode of extension and volcanism we interpret the low velocity and attenuating regions beneath the betics and possibly the rif as indicating the presence of partial melt in the uppermost mantle which may be underlain by faster less attenuating mantle in the light of observations from other geophysical and geological studies the presence of melt at the base of the betic crust may be an indication that delamination of continental lithosphere has played a role in the neogene evolution of the alboran sea region

numerical simulation of high and low frequency lg wave propagation summary lg waves are sometimes extinguished when traversing geological structures such as mountain ranges or grabens previous investigations have applied numerical full waveform simulations at relatively low frequencies on the order of 1 hz to investigate the relationship of different structural models and the amplitude anomalies of the lg waves these studies often fail to link specific known structures to the amplitude anomalies however the observed waveforms also often contain data of significantly higher frequency than the full waveform simulations we compare such low frequency simulations computed with the boundary integral equation bie technique with synthetic seismograms generated by dynamic ray tracing drt beginning with a plane layered model of the crust in central france we show that the general characteristics of the lg wave train over distances ranging from 100 km to around 500 km can be modelled by computing a relatively small number of rays reflected between the free surface and the moho matching the details of the waveforms is more difficult but can be improved by the addition of reflections between other interfaces in the model considering a one layer model of the crust with a step like change in moho depth that leads to a rapid decrease in crustal thickness we show again that the bie and drt solutions are very similar in character significantly both solutions predict that the lg wave will not be extinguished on traversing the moho step finally we consider a more complete and detailed model of the pyrenees though it is more difficult to match exactly the ray and integral equation solutions the general trends continue to be the same and the lg waves are still predicted to cross the tectonic structures associated with the mountains therefore it appears that observed amplitude changes must be caused by something other than the general structure of the pyrenees such as scattering by smaller scale features within the lower crust

lateral variations of high frequency seismic wave propagation at regional distances across the turkish and iranian plateaus in this study we investigate crustal and uppermost mantle physical properties that characterize some of the continental plateaus of the middle east this is done as part of a larger effort to map and compare high frequency wave propagation at regional distances across the earth s continental plateaus thousands of short period wwssn seismograms recorded at stations located in the middle east and produced by earthquakes with epicentral distances less than about 20 were examined visually in an effort to study lateral variations of high frequency 0 5 2 hz seismic wave propagation across this area particularly to the north of the zone of continental collision between the africa arabian and eurasian plates variations of frequencies and amplitudes of sn and lg relative to p are examined and mapped throughout the region and this work is supplemented by a study of velocities of pn sn and lg sn amplitude variations are very striking in this area an important observation of this study is that sn propagates efficiently beneath a major part of the turkish and iranian plateaus sn is strongly attenuated however in the northernmost portion of the plateaus south of the black and caspian seas and in an area between the two seas these regions are characterized in general by active tectonism including volcanism faulting and folding however this active tectonism is not restricted to the areas of high sn attenuation but appears to extend beneath other parts of the iranian and turkish plateaus patterns of lateral variations in the propagation of lg are not as consistent as those for sn lg propagates efficiently across turkey iran and adjacent regions but the lg waves that cross the turkish and iranian plateaus are weak and have relatively long predominant periods of about 2 5 s the lg phase is not observed when the path of propagation crosses the southern caspian and the black seas consistent with the evidence of oceanic type crustal structure beneath these seas lg is also not observed from subcrustal events located in the hindu kush region the velocity of pn beneath most of the plateau areas and particularly in the regions of sn attenuation ranges between 8 0 and 8 2 km s velocities for sn and lg throughout the middle east are about 4 5 and 3 4 km s respectively it is possible to interpret the efficient sn propagation and the relatively normal uppermost mantle p and s velocities beneath a major part of the turkish iranian plateau as indicating a partial underthrusting of the arabian continental plate beneath the iranian and turkish continental blocks alternatively the mapped regions of efficient sn propagation and high sn attenuation may result from a differential cooling of a past thermal anomaly in this case the isostatic compensation of the plateaus could be due to an anomalously hot uppermost mantle that developed behind the mid to upper tertiary subduction zone s in this region and to a subsequent crustal shortening after the collision of the arabian and eurasian plates our results cannot uniquely confirm the validity of the above proposed models

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

lateral growth of the continental crust through deep level subduction accretion a re evaluation of central greek rhodope abstract the rhodope massif of northern greece and southern bulgaria has been variably interpreted as a fragment of pre alpine possibly hercynian or precambrian age continental crust that was actively involved in european margin convergent tectonics during the mesozoic and tertiary alternatively we propose that for central greek rhodope the lithological associations and tectonothermal history are consistent with progressive south directed mesozoic crustal growth through deep level subduction accretion a process which involved the near continuous transferral of material of oceanic and continental margin affinity from footwall to hanging wall within a north directed palaeotethyan subduction system central greek rhodope comprises a sequence of schists gneisses and migmatites of wide compositional variation that have undergone intense tectonic intermixing extensive occurrences of marble are associated with amphibolites variably retrogressed eclogites meta gabbros and ultramafic rocks quartzo feldspathic gneisses are abundant throughout the area and are associated with psammitic meta greywacke sequences pelites and quartzites the presence of intercalated marble slivers and thin manganiferous and iron rich siliceous bands is significant the various components exposed in the subduction accretion complex were first underthrust northwards to deep crustal levels subjected to high pressure eclogite facies metamorphism and underplated to the base of the overriding eurasian plate this latter accretion event was characterised by intense southwest directed ductile thrusting and pervasive amphibolite facies metamorphic overprinting it was accompanied by migmatisation and intracrustal melt generation and followed by subduction related magmatism deep level subduction accretion leads to southward growth of the continental margin which in turn leads to subduction retreat allowing the encroachment of the magmatic arc from the north subsequent extensional tectonic exhumation brought the complex up to its present position within the southern margin of eurasia this new interpretation may have implications for other high grade terrains within convergent and collisional systems that have been assumed to represent ancient or pre existing continental crust if so then the importance of deep level subduction accretion as a mechanism of continental crustal growth has hitherto been underestimated