surface wave tomography of the western united states from ambient seismic noise rayleigh and love wave phase velocity maps summary we present the results of rayleigh wave and love wave phase velocity tomography in the western united states using ambient seismic noise observed at over 250 broad band stations from the earthscope usarray transportable array and regional networks all available threecomponent time series for the 12 month span between 2005 november 1 and 2006 october 31 have been cross correlated to yield estimated empirical rayleigh and love wave green s functions the love wave signals were observed with higher average signal to noise ratio snr than rayleigh wave signals and hence cannot be fully explained by the scattering of rayleigh waves phase velocity dispersion curves for both rayleigh and love waves between 5 and 40 speriod were measured for each interstation path by applying frequency time analysis the average uncertainty and systematic bias of the measurements are estimated using a method based on analysing thousands of nearly linearly aligned station triplets we find that empirical green s functions can be estimated accurately from the negative time derivative of the symmetric component ambient noise cross correlation without explicit knowledge of the source distribution the average traveltime uncertainty is less than 1 s at periods shorter than 24 s we present rayleigh and love wave phase speed maps at periods of 8 12 16 and 20 s the maps show clear correlations with major geological structures and qualitative agreement with previous results based on rayleigh wave group speeds

accurate relocation of izmit earthquake mw 7 4 1999 aftershocks in cinarcik basin using double difference method 1 we relocated part of the aftershock activity in cinarcik basin and surrounding areas that are associated with the 1999 izmit earthquake mw 7 4 double difference relocation algorithm is used to relocate the aftershocks the data set was obtained from a temporary seismic network deployed 10 days after the main shock by cooperation between bogazici university kandilli observatory and earthquake research institute lgit grenoble and ipgp paris for a better station coverage additional data set was obtained from a network operated by tubitak marmara research center differential travel times were calculated using both arrival time readings and waveform cross correlation method we relocated 1145 of the aftershocks and interpreted the results with emphasis on the yalova and tuzla cluster located within the marmara sea the results show better focused seismicity patterns for the yalova cluster providing clear evidence for the proposed models we present a revised location of the 1963 cinarcik earthquake which took place in area of yalova cluster finally we propose that the activity of tuzla cluster represents a parallel subsidiary fault of the main marmara fault

variscan intra orogenic extensional tectonics in the ossa morena zone evora aracena lora del rio metamorphic belt sw iberian massif shrimp zircon u th pb geochronology

seismic imaging of the three dimensional architecture of the cinarcik basin along the north anatolian fault the cinarcik basin is a transtensional basin located along the northern branch of the northern north anatolian fault naf in the sea of marmara the eastern half of which has been identified as a seismic gap during the seismarmara 2001 experiment a dense grid of multichannel seismic reflection profiles was shot covering the whole cinarcik basin and its margins the new seismic images provide a nearly three dimensional view of the architecture of the basin fault system at depth and sedimentary infill and provide insight into its tectonic evolution along both northern and southern margins of the basin seismic reflection data show deep penetrating faults hence long lived features which have accommodated a large amount of extension there is no indication in the data for a single throughgoing strike slip fault neither a cross basin fault nor a pure strike slip fault running along the northern margin faster opening is presently observed in the eastern part of the basin the cinarcik basin seems to have developed as a transtensional basin across strike slip segments of the northern naf for the last few million years

dislocation creep of polycrystalline dolomite the field of dislocation creep and rheological parameters for coarse grained d 240 m natural dolomite has been determined through experiments performed at temperatures of 700 1000 c effective pressures of 300 900 mpa and strain rates of 10 4 s to 10 7 s at low strain 7 dolomite aggregates deform homogeneously and define a power law between strain rate and differential stress with a stress exponent of 3 0 0 1 but at higher strains through going fine grained 10 m shear zones develop in the dolomite aggregates concomitant with strain weakening recrystallization is limited at low strain and microstructures observed in the low strain samples include undulatory extinction twins grain boundary bulging limited recrystallization along twins and fluid inclusion trails these same microstructures are present outside of the narrow through going shear zones in high strain samples however within the shear zones the grain size is small 10 m with some larger porphyroclasts 20 50 m shear zones nucleate at fine grained zones formed at twin boundaries twin twin intersections and fluid inclusion trails and is likely due to a switch in deformation mechanism due to the large strength contrast between the fine grained zones deforming by diffusion creep and the coarse grained protolith the activation energy q for creep of coarse grained dolomite at low strain is 145 kj mol in contrast to other activation energies for dislocation and diffusion creep of minerals q for dislocation creep of dolomite is considerably less than that for diffusion creep 248 kj mol the results of this study indicate that coarse grained dolomite will initially deform by dislocation creep at natural strain rates and temperatures between 200 and 550 c but due to limited recovery mechanisms fine grained shear zones will nucleate and diffusion creep may control the rheology of these fine grained shear zones in nature at temperatures above 300 c

imaging the upper crust of the korean peninsula by surface wave tomography cross correlation of seismic background motions campillo and paul 2003 shapiro et al 2005 is applied to observations from the korean meteorological administration seismic network to estimate the short period rayleigh and love wave dispersion characteristics of the region standard processing procedures are applied to the cross correlation except that signal whitening is used in place of one bit sampling to equalize power in signals from different times multiple filter analysis is used to extract the group velocities from the estimated green s functions which are then used to image the spatially varying dispersion at periods between 0 5 and 20 sec the tomographic inversion technique used inverts all periods simultaneously to provide a smooth dispersion curve as a function of period in addition to the usual smooth spatial image for a given period the gyeongsang basin in the southeastern part of the peninsula is clearly resolved with lower group velocities

the crustal structure of the eastern marmara region turkey by teleseismic receiver functions summary we study the crustal structure of eastern marmara region by applying the receiver function method to the data obtained from the 11 broad band stations that have been in operation since the 1999 earthquake the stacked single event receiver functions were modelled by an inversion algorithm based on a five layered crustal velocity model to reveal the firstorder shear velocity discontinuities with a minimum degree of trade off we observe crustal thickening from west 29 32 km to east 34 35 km along the north anatolian fault zone nafz but we observe no obvious crustal thickness variation from north to south while crossing the nafz the crust is thinnest beneath station ter 29 km located near the black sea coast in the west and thickest beneath station tar 35 km located inland in the southeast the average crustal thickness and s wave velocity for the whole regions are 31 2 km and 3 64 0 15 km s 1 respectively the eastern marmara region with its average crustal thickness high heat flow value 101 11 mw m 2 and with its remarkable extensional features seems to have a basin and range type characteristics but the higher average shear velocities 3 64 km s 1 and crustal thickening from 29 to 35 km towards the easternmost stations indicate that the crustal structure shows a transitional tectonic regime therefore we conclude that the eastern marmara region seems to be a transition zone between the marmara sea extensional domain and the continental anatolian inland region

c slip in quartz from subsolidus deformed granite abstract the slip behaviour of quartz from a granite and granitic veins during subsolidus high temperature conditions 700 800 c of deformation is studied by lattice preferred orientation lpo and microstructural techniques lpos with a point maximum of c axes parallel to the shear direction which is close to the stretching lineation are presented and interpreted with the aid of light and electron microscopy in terms of c as the dominant slip direction during plastic deformation microscopy of such samples reveals the presence of 0001 tilt boundaries and free 0001 burgers vector dislocations in edge orientations a change in lpo in a decreasing temperature environment from c axes parallel to the shear direction to c axes normal to the shear direction documents a fabric transition from the rare c slip to the more common a slip fabric it is concluded that conditions of high temperature and partial pressure of water are required to initiate dominant c slip during deformation at geological strain rates

shear wave velocity imaging of the avignonet landslide france using ambient noise cross correlation 1 the avignonet landslide affects a 2 by 2 km area covered by clayey deposits this paper presents the use of the seismic ambient noise cross correlation technique to retrieve a 3 d model of the shear wave velocity of the area seismic ambient noise was recorded during 15 days at 13 stations located on the landslide cross correlations computed between the vertical components of all station pairs allow the retrieval of the rayleigh wave green s functions and the estimation of their group velocity dispersion curves in the 1 7 5 hz frequency range at frequencies lower than 1 5 hz the anisotropy of the wavefield strongly influences the apparent rayleigh wave velocities moreover the analysis of the convergence of the cross correlations shows that at frequencies higher than 5 hz the recording time length was not sufficient for the cross correlation to be stable these 1 7 5 hz passive group dispersion curves are complementary to the ones computed from shot signals in the 3 7 hz frequency range a tomographic inversion of the resulting 1 7 7 hz rayleigh wave group dispersion curves provides local group dispersion curves at each cell of the tomographic grid these are inverted with a neighborhood algorithm to retrieve the 3 d model of the landslide despite the complex wave propagation in the eastern part of the landslide and the sparse ray coverage estimated velocities and first order features are in good agreement with previous investigations

crustal anisotropy in the eastern sea of marmara region in northwestern turkey abstract the north anatolia fault zone nafz is a transform zone 1600 km in length representing the plate boundary between the westward moving anatolian plate and stable eurasia almost the entire fault zone has failed during the last century except for the sea of marmara section which is located in direct vicinity to the city of istanbul in this study we investigate the crustal anisotropy along the eastern marmara section of the nafz based on shear wave splitting we measure seismic anisotropy parameters namely the fast polarization direction pd and time delay td by analyzing local seismicity recorded at selected seismographs operated throughout the eastern sea of marmara region our shear wave splitting sws observations indicate a predominant northwest southeast oriented pd which is sub parallel to both the orientation of the regional s hmax in northwest turkey and the local nafz strike along the princes islands segment toward the south at the armutlu peninsula we find a different pd pattern reflecting local fault strikes s hmax as well as strain asymmetry between different crustal blocks across the fault zone applying strict quality criteria enables us to identify robust preferred fast pds which suggests that initially observed pd heterogeneities are sometimes caused by second order effects in the data rather than by varying pds comparing td and hypocentral depth distribution we find the depth extent of the anisotropy is confined to the uppermost 10 km depth of crust we combine our sws results with those from previous studies conducted along the san andreas fault saf and nafz in order to investigate the relation of angular deviations of the pds from regional s hmax and local fault strikes with fault zone distance we find that fast pds are mainly controlled by the local fault structure in close proximity to a fault zone 5 and 10 km while they are controlled by crustal stress at off fault locations 5 and 10 km

array estimators and the use of microseisms for reconnaissance of sedimentary basins a natural field seismic technique is possible to attain by observing microseisms with a suitably designed array and by digitally processing the data to obtain estimates of the phase velocities of rayleigh waves wavelengths of interest in detecting depth to the basement of sedimentary basins are in the range 2 to 20 km and correspond to wave periods from 1 to 7 s an array of five or seven seismometers deployed as an expanding cross configuration simplifies field procedures and is adequate for phase velocity measurements of rayleigh waves in the required wavelength range provided high resolution frequency wavenumber spectral analysis is used this analysis can be implemented on a minicomputer in the field results obtained from observation in a sedimentary basin of known structure show predominantly fundamental mode rayleigh wave propagation the scatter of velocity estimates is small enough to allow inversion by curve matching and depth to the basement can be computed to an accuracy of 30 percent w

palaeogeographical evolution of the thrace neogene basin and the tethys paratethys relations at northwestern turkey thrace abstract the thrace neogene basin situated in northwestern turkey was initiated by strike slip faulting that was active from the early miocene until the end of the pliocene during the early miocene it began to form under the control of the thrace eskisehir fault zone initiated by continental collision in northwestern anatolia late oligocene early miocene during the late early miocene the basin was a site of mainly fluviatile and limnic sedimentation to the west and marine sedimentation via the paratethyan transgression in the north with the onset of the middle miocene the thrace block started to rotate in a counterclockwise sense and escaped westward with respect to the strandja istanbul block owing to rejuvenation of fossil fault systems within it in this period warm marine conditions were also established around the gulf of saros through a mediterranean originated transgression during the middle late miocene fluviatile and limnic conditions were created over the western thrace by the westerly propagation of the thrace eskisehir fault zone one of the principal results of the early middle miocene tectonics is the tilting of the strandja istanbul block to the south severing the tethys and the paratethys during the latest miocene early pliocene period the thrace eskisehir fault zone was deactivated because of the evolution of the north anatolian fault zone to the south the resurrected ganos fault zone situated on the dissected fossil suture zone in the sea of marmara also joined the north anatolian fault zone uplifting the gelibolu peninsula and thus severing the connection that existed between the sea of marmara and the paratethys the sea of marmara eventually became an endemic basin by the activity of the north anatolian fault zone

recalculated probability of m 7 earthquakes beneath the sea of marmara turkey 1 new earthquake probability calculations are made for the sea of marmara region and the city of istanbul providing a revised forecast and an evaluation of time dependent interaction techniques calculations incorporate newly obtained bathymetric images of the north anatolian fault beneath the sea of marmara le pichon et al 2001 armijo et al 2002 newly interpreted fault segmentation enables an improved regional a d 1500 2000 earthquake catalog and interevent model which form the basis for time dependent probability estimates calculations presented here also employ detailed models of coseismic and postseismic slip associated with the 17 august 1999 m 7 4 izmit earthquake to investigate effects of stress transfer on seismic hazard probability changes caused by the 1999 shock depend on marmara sea fault stressing rates which are calculated with a new finite element model the combined 2004 2034 regional poisson probability of m 7 earthquakes is 38 the regional time dependent probability is 44 18 and incorporation of stress transfer raises it to 53 18 the most important effect of adding time dependence and stress transfer to the calculations is an increase in the 30 year probability of a m 7 earthquake affecting istanbul the 30 year poisson probability at istanbul is 21 and the addition of time dependence and stress transfer raises it to 41 14 the ranges given on probability values are sensitivities of the calculations to input parameters determined by monte carlo analysis 1000 calculations are made using parameters drawn at random from distributions sensitivities are large relative to mean probability values and enhancements caused by stress transfer reflecting a poor understanding of large earthquake aperiodicity index terms 7223 seismology seismic hazard assessment and prediction 7230 seismology seismicity and seismotectonics 8150 tectonophysics plate boundary general 3040 keywords earthquake probability sea of marmara seismic hazard turkey stress interaction north anatolian fault

geodynamic evolution of the sw variscides orogenic collapse shown by new tectonometamorphic and isotopic data from western ossa morena zone sw iberia 1 the pre mesozoic geodynamic evolution of sw iberia has been investigated on the basis of detailed structural analysis isotope dating and petrologic study of high pressure hp rocks revealing the superposition of several tectonometamorphic events 1 an hp event older than circa 358 ma is recorded in basic rocks preserved inside marbles which suggests subduction of a continental margin the deformation associated with this stage is recorded by a refractory graphite fabric and noncoaxial mesoscopic structures found within the host metasediments the sense of shear is top to south revealing thrusting synthetic with subduction underthrusting to the north 2 recrystallization before circa 358 ma is due to a regional scale thermal episode and magmatism 3 noncoaxial deformation with top to north sense of shear in northward dipping large scale shear zones is associated with pervasive hydration and metamorphic retrogression under mostly greenschist facies this indicates exhumation by normal faulting in a detachment zone confined to the top to north and north dipping shear zones during postorogenic collapse soon after 358 ma ago inversion of earlier top to south thrusts 4 static recrystallization at circa 318 ma is due to regional scale granitic intrusions

radiometric discrimination of pre variscan amphibolites in the ediacaran serie negra ossa morena zone sw iberia new results on the geochronology of metabasites hosted by the neoproterozoic late ediacaran serie negra of the ossa morena zone iberian massif are presented these rocks record a protracted subduction at least since the latest cryogenian followed in a continuum by early cambrian rifting the serie negra country rocks are continental crust forearc segments of the thinned continental margin of gondwana the metabasite suite exhibits e and n morb as well as volcanic arc signatures and discloses the existence of a diverse late ediacaran early cambrian magmatism across the ossa morena zone protoliths of the e morb metabasites are clearly ediacaran they exhibit geochemical characteristics typical of younger island arcs notably of their forearc zones affected by extension soon after the initiation of subduction radiometric dating of n morb metabasites shows that these rocks are significatively younger than their country rocks whose age has been stratigraphically and paleontologically constrained as ediacaran they record early cambrian rifting developed in a continuum after a protracted subduction metabasite petrological zonation permits to reconstruct a single ediacaran subduction zone located to the s of the current omz and dipping towards the n in present day geographical coordinates

ambient noise analysis in the eastern sea of marmara region in northwest turkey lateral variations of the crustal velocity field abstract we analyze the ambient seismic noise field in order to investigate the crustal structure at the north anatolian fault zone nafz in northwest turkey we focus on the eastern sea of marmara section where the nafz is in the final phase of the seismic cycle prior to an expected major m 7 earthquake we apply cross correlation analysis of the seismic ambient noise to determine the spectral dependence of the seismic velocity in order to image the crustal structure at seismogenic depth time domain cross correlations are calculated for available station pairs in the target area interstation distances span 0 3 90 km here the vertical component is analyzed in order to recover fundamental mode rayleigh waves in the 0 05 1 1 hz frequency range group velocity dispersion curves are obtained for selected correlation paths in particular to address the azimuthal dependence of the velocity field in the frequency band of interest average group velocities range between 1 8 and 3 5 km s dispersion curves corresponding to the north south trending paths crossing the main nafz fault branch below the eastern sea of marmara show low group velocities between 1 5 and 1 8 km s which is well explained by the 3 4 km deep cinarcik basin located between the two major fault branches the princes islands and armutlu fault segments in contrast ray paths restricted to within the mainland of istanbul and the armutlu peninsulas primarily trending east west show higher group velocities up to 3 2 km s by averaging the dispersion curves we determine an optimized 1d s wave velocity model for the eastern sea of marmara region allowing for a significant improvement in hypocenter determination for local seismicity

tectonometamorphic evolution of the aracena metamorphic belt sw spain resulting from ridge trench interaction during variscan plate convergence 1 the aracena metamorphic belt is a high temperature low pressure ht lp band located at the southern end of the european variscan chain it marks a suture between armorica and avalonia this belt is characterized by 1 the presence of mid ocean ridge basalt derived metabasites that were affected by an inverted ht lp metamorphism related to sw verging thrusting whose thermal peak diachronously migrated eastward 2 the occurrence of a ht lp metamorphism related to an extensional event affecting continental rocks belonging to the ossa morena zone with peak temperatures that are 150 c higher than that recorded in the oceanic metabasites and 3 the presence of near trench magmatism with high mg andesite composition these and other characteristics can be interpreted in terms of a ridge trench trench triple junction that migrated along the armorican margin during variscan oblique convergence

spatiotemporal earthquake clusters along the north anatolian fault zone offshore istanbul we investigate earthquakes with similar waveforms in order to characterize spatiotemporal microseismicity clusters within the north anatolian fault zone nafz in northwest turkey along the transition between the 1999 izmit rupture zone and the marmara sea seismic gap earthquakes within distinct activity clusters are relocated with cross correlation derived relative travel times using the double difference method the spatiotemporal distribution of microearthquakes within individual clusters is resolved with relative location accuracy comparable to or better than the source size high precision relative hypocenters define the geometry of individual fault patches permitting a better understanding of fault kinematics and their role in local scale seismotectonics along the region of interest temporal seismic sequences observed in the eastern sea of marmara region suggest progressive failure of mostly nonoverlapping areas on adjacent fault patches and systematic migration of microearthquakes within clusters during the progressive failure of neighboring fault patches the temporal distributions of magnitudes as well as the number of events follow swarmlike behavior rather than a mainshock aftershock pattern

structural interpretation of the marmara region nw turkey from aeromagnetic seismic and gravity data abstract the seismically active marmara region located in nw turkey lies on the westward end of the north anatolian fault naf the naf is well defined on land previous investigations of its extension in the marmara sea include marine bathymetry seismological activity and seismic profiles in this study faults and their configurations identified inland are extended into the marmara sea by means of aeromagnetic anomalies as well as seismic and gravity profiles the deep structure was resolved by constructing a map of the tertiary bottom shallow curie isotherm was determined by spectral analysis indicating a thinner crust in the northern marmara depression area with respect to the continental crust a combination of the geophysical data allows us to propose the existence of subsidence and isostatic equilibrium in the northern marmara sea a less active zone identified in the central high zone dividing the marmara sea into two parts may also be deduced from the seismic data this structural arrangement may play a key role in earthquakes that will affect the surrounding regions

development of preferred orientation in plane strain deformed limestone experiment and theory carbonate rocks deform preferentially by twin gliding on e 01 18 and slip on r 10 14 and f 02 21 in polycrystalline aggregates strong textures develop we report on experimentally produced textures in triaxial plane strain geometry with orthorhombic symmetry at 200 c and 400 c pole figure of the experimentally deformed specimens are compared quantitatively with theoretical simulations based on the taylor theory using both slip and mechanical twinning as mechanisms agreement at low and high temperature is satisfactory and documents that models developed for f c c metals can be applied to low symmetry minerals provided that deformation mechanisms are known and that mechanical twinning is properly accounted for comparison with experimental results indicates that strain was nearly homogeneous at the conditions considered and the same may apply to many geological textures three texture types are described which are differentiated mainly by the relative importance of e twinning

asymmetric slip partitioning in the sea of marmara pull apart a clue to propagation processes of the north anatolian fault between 1939 and 1999 the north anatolian fault naf experienced a westward progression of eight large earthquakes over 800 km of its morphological trace the 2000 km long north anatolian transform fault has also grown by westward propagation through continental lithosphere over a much longer timescale 10 myr the sea of marmara is a large pull apart that appears to have been a geometrical mechanical obstacle encountered by the naf during its propagation the present paper focuses on new high resolution data on the submarine fault system that forms a smaller pull apart beneath the northern sea of marmara between two well known strike slip faults on land izmit and ganos faults the outstandingly clear submarine morphology reveals a segmented fault system including pull apart features at a range of scales which indicate a dominant transtensional tectonic regime there is no evidence for a single continuous purely strike slip fault this result is critical to understanding of the seismic behaviour of this region of the naf close to istanbul additionally morphological and geological evidence is found for a stable kinematics consistent both with the long term displacement field determined for the past 5 myr and with present day anatolia eurasia motion determined with gps however within the sea of marmara region the fault kinematics involves asymmetric slip partitioning that appears to have extended throughout the evolution of the pull apart the loading associated with the westward propagation process of the naf may have provided a favourable initial geometry for such a slip separation

seismic noise tomography in the chile ridge subduction region summary we used cross correlation of ambient seismic noise recorded in the chile triple junction ctj region to estimate interstation surface wave time domain green s functions and then inverted traveltimes to obtain crustal surface wave velocity models interstation distances within the chile ridge subduction project crsp temporary seismic network ranged from 40 to 100 km we selected 365 d and cross correlated and stacked 24 hr of vertical component data at 38 stations pairs resulting in nominally 703 traveltimes along assumed straight interstation paths velocities in 2 d cells of 30 km 30 km were calculated using a linear least squares inversion of the rayleigh wave group velocity traveltimes furthermore we performed a rayleigh wave group velocity dispersion analysis to estimate the sensitivity of different period waves at depth and to calculate a 3 d shear velocity model of the patagonian crust the process was applied to cross correlation pairs determined in two period bands 5 10 s corresponding to shallow crustal velocities down to approximately 10 km depth and 10 20 s for velocities down to around 20 km our results show that cell velocities correlate well with known geological features we find high crustal velocities where the patagonian batholith outcrops or is likely present at depth and low velocities correlate with the active volcanic arc of the southern volcanic zone and the subducted chile ridge in taitao peninsula where thermal activity of hot springs is present high velocities in the mountainous portions of the southeastern study area appear to correlate with outcropping older metamorphic units low velocity in the east correlate with sequences of volcaniclastic deposits

the influence of dolomite on the plastic flow of calcite rheological microstructural and chemical evolution during large strain torsion experiments abstract aggregates composed of calcite and dolomite have been deformed and annealed at high temperature 700 800 c and high pressure 300 mpa to investigate the mutual effects of deformation and chemical reaction strain partitioning fabric development and phase segregation in a polyphase rock samples deformed in torsion displayed an almost newtonian creep with stress exponent of 1 7 0 3 specimens were deformed up to a maximum shear strain of 10 and developed a clear texture documented by electron back scatter diffraction measurements in both calcite and dolomite both the texture and the foliation created during the large strain experiments display a monoclinic symmetry closely reproducing that of naturally deformed carbonate marbles with the preferred orientation of the c axes inclined against the sense of shear detailed microstructural investigation shows that grains are internally strain free and that grain boundaries are preferentially aligned in straight segments implying that deformation occurred through a combination of grain boundary sliding and diffusion processes accommodated by dislocation activity chemical investigations performed on both statically annealed and torsion samples indicate that deformation may have an important influence on the phase equilibrium of a reacting system calcite grains deformed with excess of dolomite with respect to the equilibrium were able to incorporate higher amounts of mg within the calcite lattice than the static samples as documented by electron probe microanalysis moreover the above analysis documented that reaction rate was faster in torsion than in static experiments at the same conditions of pressure and temperature

enso variability reflected in precipitation oxygen isotopes across the asian summer monsoon region abstract oxygen isotope signals 18 o from paleo archives are important proxies for past asian summer monsoon asm climate reconstruction however causes of interannual variation in the 18 o values of modern precipitation across the asm region remain in argument we report interannual 18 o variation in southern tibetan plateau precipitation based on long term observations at lhasa these data together with precipitation 18 o records from five global network of isotopes in precipitation gnip stations and two ice core 18 o records were used to define a regional metric of asm precipitation 18 o asmoi back trajectory analyses for rainy season precipitation events indicate that moisture sources vary little between years with relatively high and low 18 o values a result that is consistent for the south lhasa southeast bangkok and east asm regions hong kong in contrast 18 o values at these three locations are significantly correlated with convection in the estimated source regions and along transport paths these results suggest that upstream convection rather than moisture source change causes interannual variation in asm precipitation 18 o values contrasting values of the asmoi in el nino and la nina years reveal a positive isotope el nino southern oscillation enso response e g high values corresponding to warm phases which we interpret as a response to changes in regional convection we show that the isotope enso response is amplified at high elevation sites and during la nina years these findings should improve interpretations of paleo 18 o data as a proxy for past asm variation and provide new opportunities to use data from this region to study paleo enso activity

broadband ambient noise surface wave tomography across the united states 1 this study presents surface wave dispersion maps across the contiguous united states determined using seismic ambient noise two years of ambient noise data are used from march 2003 through february 2005 observed at 203 broadband seismic stations in the us southern canada and northern mexico cross correlations are computed between all station pairs to produce empirical green functions at most azimuths across the us coherent rayleigh wave signals exist in the empirical green functions implying that ambient noise in the frequency band of this study 5 100 s period is sufficiently isotropically distributed in azimuth to yield largely unbiased dispersion measurements rayleigh and love wave group and phase velocity curves are measured together with associated uncertainties determined from the temporal variability of the measurements a sufficient number of measurements 2000 is obtained between 8 and 25 s period for love waves and 8 and 70 s period for rayleigh waves to produce tomographic dispersion maps both phase and group velocity maps are presented in these period bands resolution is estimated to be better than 100 km across much of the us from 8 40 s period for rayleigh waves and 8 20 s period for love waves which is unprecedented in a study at this spatial scale at longer and shorter periods resolution degrades as the number of coherent signals diminishes the dispersion maps agree well with each other and with known geological and tectonic features and in addition provide new information about structures in the crust and uppermost mantle beneath much of the us

surface fault breaks aftershock distribution and rupture process of the 17 august 1999 izmit turkey earthquake the results obtained from field studies of surface fault breaks on land aftershock studies and analysis of complex teleseismic body waves of the 17 august 1999 izmit earthquake m w 7 4 indicate that the northern strand of the north anatolian fault zone had been ruptured between 29 1 e and 31 1 e with a maximum total fault rupture length of about 200 km the 12 november 1999 duzce earthquake m w 7 2 extended the surface fault break an additional 41 km to the east alignment of the aftershocks delineates the fault rupture on land and extends it to the west of the hersek delta well into the marmara sea to 29 1 e longitude we have identified six fault rupture segments two of them are located to the west of the hersek delta and four are located to the east rupture process analysis suggests two stages of rupture separated in space and time with an estimated total scalar seismic moment of 2 42 1020 n m the first stage initiated at the epicenter near izmit and propagated asymmetrically first eastward and then westward with a total scalar moment of 1 6 1020 n m showing predominantly right lateral strike slip faulting followed by a minor subevent extending the rupture further east the second stage took place at the western and eastern ends of the source area rupturing two segments within the marmara sea west of the hersek delta and two segments between akyazi and golyaka the rupture process analysis indicates that six fault segments were ruptured during the mainshock four of them on land and two within the marmara sea the major moment release of 1 2 1020 n m is found on the 64 km long sapanca segments located between the easternmost tip of the gulf of izmit and akyazi with an estimated maximum slip of 5 3 m the moment release on the golcuk segment with a length of 30 km is about 3 7 1019 n m and the estimated slip on this segment is 4 1 m rupture process analysis suggests two 20 km long segments between akyazi and golyaka striking n70 e the scalar moment releases on these segments are 2 7 1019 and 1 9 1019 n m with estimated offsets of 2 2 and 1 6 m respectively the last two subevents took place to the west of the hersek delta on the yalova segment and within the marmara sea with estimated offsets of 1 3 and 1 0 m respectively manuscript received 20 august 2000

metamorphic equilibria in the siliceous dolomite system 6 kbar experimental data and geologic implications hydrothermal experiments with h2o co2 fluids at pfluid 6 kbar yielded the following quilibrium conditions for reactions important in metamorphosed siliceous dolomites t c x xco2 3 dolomite 2 quartz diopside 2 co2t 620 8x 0 73 0 03 5 5 dolomite 8 quartz h2o tremolite 3 calcite 7 co2t 600 5 550 5 540 5 500 5x 0 66 0 03 0 21 0 03 0 21 0 04 0 06 0 02 7 3 dolomite 4 quartz h2o talc 3 calcite 3 co2t 550 5 500 5 450 5x 0 25 0 05 0 07 0 02 0 03 0 02 8 2 dolomite talc 4 quartz tremolite 4 co2t 550 5 540 5 500 5x 0 22 0 03 0 21 0 02 0 06 0 02 a thermodynamically self consistent 6 kbar t xco2 topology results by extrapolating equilibria from experimental brackets using a modified redlich kwong equation for activities in h2o co2 mixtures this topology restricts the assemblage talc calcite to a narrow stability band in t xco2 space at xco2 0 55 and t 590 c accordingly the occurrence of talc calcite in pure siliceous dolomites metamorphosed at pfluid 6 kbar implies correspondingly water rich fluids

a tomographic image of the shallow crustal structure in the eastern marmara 1 we present a 2 d tomographic seismic velocity image in eastern marmara region along a n s trending 120 km long seismic refraction profile which traverses the northern branches of north anatolian fault naf and tectonically active cinarcik basin in the sea of marmara the 2 d velocity model which is constrained down to upper crustal depth of 7 km shows significant heterogeneities in the upper crust displayed by well constrained velocity anomalies the seismicity observed following the 17 august 1999 izmit earthquake concentrates in three distinct zones and takes place near the inferred low velocity zones and below high velocity anomalies obtained from tomographic inversion this correlation is interpreted as a result of intensely sheared zones of deformation imposed by strike slip motion of the northern branches of the north anatolian fault

velocity structure under the trans mexican volcanic belt preliminary results using correlation of noise summary prediction of ground motion in central mexico is of great consequence not only for mexico city but also for several other cities in the region however the geometry and velocity distribution of the geological structures in central mexico is unknown in this paper the velocity structure in central mexico is investigated using seismic noise records from three different arrays one permanent and two temporary distances between stations span 3 300 km seismic noise is analysed using time domain cross correlation to estimate the green s function between stations only the fundamental mode of rayleigh waves is recovered in the cross correlation of vertical component records between 5 and 10 s period at smaller periods we obtain no correlation even between closely spaced stations this suggests that the heterogeneity of the trans mexican volcanic belt tmvb hampers the propagation of rayleigh waves smaller than 9 km we observe a large velocity contrast between the guerrero terrain and the tmvb this velocity contrast measured here for the first time at this scale explains the appearance of regional amplification in central mexico and the origin of the diffracted waves behind the long duration of ground motion observed in mexico city in the large scale average rayleigh wave group velocity at 5 s period is about 2 5 km s 1 in the tmvb and larger than 3 6 km s 1 outside it significant lateral heterogeneity is evident in the stations of the dense meso american subduction experiment array we analysed we observe in addition a significant increase in velocity from north to south in the central portion of the tmvb our results are part of ongoing studies with the final objective of building a model of tmvb that may be used to simulate ground motion in central mexico from subduction zone earthquakes

kinematic analysis of the southern iberian shear zone and tectonic evolution of the acebuches metabasites sw variscan iberian massif 1 the acebuches metabasites constitute a slice of oceanic crust located at the variscan suture between the ossa morena and the south portuguese zones iberian massif the emplacement of the metabasites onto the accretionary prism was associated with the activity of the southern iberian shear zone careful measurements of the fabrics and structures related to this shear zone show consistent kinematic criteria pointing to the presence of a simple shear component with an oblique predominantly left lateral sense of displacement the data are consistent with existing models of triclinic or oblique shear zones considering coeval simple shear and pure shear components these models provide a satisfactory explanation of the observed spatial variations in the foliation lineation and fold hinge data the kinematics of other shear deformations older and younger than the southern iberian shear zone have also been established these results offer new insights into the tectonic evolution of this suture of the variscan belt and show how complex transpressional strains can arise during oblique crustal deformation associated with the motions of tectonic plates

calcite fabrics in a natural shear environment the helvetic nappes of western switzerland the aim of this contribution is to describe and interpret the crystallographic orientations and microstructures of calcite in the upper jurassic limestones of the helvetic nappes between the mont blanc and aar massifs over a distance along strike of about 180 km the c axis preferred orientation pattern which could be inferred is regionally very constant the c axis point maxima are everywhere subperpendicular to the regional strike of the chain there is an obliquity between the orientation of the macroscopically dominant cleavage and the microscopically visible long axes of individual grains the c axis maxima in most specimens are parallel to the axis of shortening of the microscopic grain shape fabric this fabric geometry indicates either continuous shear deformation or alternatively a two stage deformation history the obliquity of the grain shape fabric may be due to the fact that the flattening plane of the individual grains reflects only the last increment of a continuous shear process or it may represent a later finite deformation which has led to the formation of a regionally developed second cleavage there is a systematic relationship between the direction of these late shear movements and the main overthrust direction as given by the finite strain pattern this suggests that the microfabric of the rocks was acquired during a progressive rotation with time of the main overthrust direction the observed pattern of preferred orientation has been correlated by several authors with intracrystalline deformation mechanisms a combination of slip on r and twinning on e however the e twinning observed in the specimens investigated is younger than the development of the crystallographic fabric a new method for stress determination from e twinning is proposed

petrofabric of forsterite marbles and related rocks from a low pressure metamorphic terrain almaden de la plata massif ossa morena zone sw spain and its kinematic interpretation abstract a fabric study of forsterite marble and calc silicate rock paragenetic minerals is presented for samples collected in the almaden de la plata massif of sw spain that experienced variscan low pressure metamorphism related to the tectonic evolution of the suture between the ossa morena and south portuguese zones of the iberian massif two tectonically stacked metamorphic units contain marble metacarbonate and variably impure dolomitic rocks that record contrasting thermal conditions of the upper greenschist structuraly upper unit and the upper amphibolite granulite facies structuraly lower unit different reactional paths lead to formation of forsterite marbles in both units dolomite and calcite petrofabrics disclose their contrasting rheological behaviour during syn metamorphic ductile deformation under temperatures between 500 and 700 c dolomite formed harder porphyroclast systems and boudinaged bands whereas weaker calcite underwent dynamic recrystallization in both cases deformation was facilitated by activation of various intracrystalline slip systems complemented by other deformation mechanisms the fabrics of other paragenetic metamorphic minerals also denote crystal plasticity and exhibit close geometrical relationships with respect to the macroscopic foliation and mineral stretching lineation including a systematic asymmetry suggestive of non coaxial deformation components foliations and lineations are interpreted as solid state flow planes and directions bearing a kinematic significance in particular regional sinistral shear at mid deep crustal realms coeval with low pressure metamorphism explains the imbrication of metamorphic units and their exhumation concomitant with the overall wrench tectonic framework ruling the tectonic evolution of the ossa morena south portuguese suture between the late devonian 360 ma and the latest carboniferous 300 ma

rheic ocean ophiolitic remnants in southern iberia questioned by shrimp u pb zircon ages on the beja acebuches amphibolites 1 the rheic ocean was a major oceanic domain between avalonia and gondwana in ordovician silurian times most of the paleozoic plate reconstructions assume that the rheic ocean suture lies within southern iberia coinciding with the contact between the south portuguese zone and the ossa morena zone this paper reports four sensitive high resolution ion micro probe shrimp u pb zircon ages from mid ocean ridge basalt morb featured rocks of the beja acebuches amphibolite unit which crops out along the boundary between the ossa morena and the south portuguese zone and is considered its most conspicuous suture unit the obtained ages range from 332 3 to 340 4 ma corresponding to the crystallization of the mafic protoliths these early carboniferous ages for the beja acebuches amphibolites imply that this unit can no longer be viewed as an ophiolite belonging to the rheic ocean suture since this oceanic domain was presumably closed in devonian times tectonic reconstructions joining in a single suture line the beja acebuches amphibolite unit in southern iberia to either the devonian lizard ophiolite in southern england or the root zone of the devonian ordovician ophiolitic units in northwest iberia must be therefore reconsidered because of the age difference we interpret the beja acebuches amphibolite unit to represent a narrow and very ephemeral realm of oceanic like crust that opened in early carboniferous times after total consumption of the rheic ocean we suggest that a mantle plume underneath southern iberia in early carboniferous times is the most plausible large scale geodynamic scenario for the formation of these morb featured rocks

microseismicity at the north anatolian fault in the sea of marmara offshore istanbul nw turkey 1 the north anatolian fault zone nafz below the sea of marmara forms a seismic gap where a major earthquake is expected to occur in the near future this segment of the fault lies between the 1912 ganos and 1999 izmit ruptures and is the only nafz segment that has not ruptured since 1766 to monitor the microseismic activity at the main fault branch offshore of istanbul below the cinarcik basin a permanent seismic array pires was installed on the two outermost prince islands yassiada and sivriada at a few kilometers distance to the fault in addition a temporary network of ocean bottom seismometers was deployed throughout the cinarcik basin slowness vectors are determined combining waveform cross correlation and p wave polarization we jointly invert azimuth and traveltime observations for hypocenter determination and apply a bootstrap resampling technique to quantify the location precision we observe seismicity rates of 20 events per month for m 2 5 along the basin the spatial distribution of hypocenters suggests that the two major fault branches bounding the depocenter below the cinarcik basin merge to one single master fault below 17 km depth on the basis of a cross correlation technique we group closely spaced earthquakes and determine composite focal mechanisms implementing recordings of surrounding permanent land stations fault plane solutions have a predominant right lateral strike slip mechanism indicating that normal faulting along this part of the nafz plays a minor role toward the west we observe increasing components of thrust faulting this supports the model of nw trending dextral strike slip motion along the northern and main branch of the nafz below the eastern sea of marmara