surface wave mapping of the crust and upper mantle in the arctic region pure path rayleigh wave group velocities for 24 regional grids inside the arctic have been obtained from 74 mixed path measurements the vertical shear wave velocity structures under these 24 grids were then determined according to their pure path group velocity dispersion data this result indicates that the crustal shear wave velocity in the arctic region is generally lower than the worldwide average in addition a typical mid ocean ridge structure was clearly shown under the nansen ridge we also found an abnormally high upper mantle shear wave velocity under the alpha ridge and makarov basin and low velocity beneath the canadian arctic islands in general our inversion result agrees with the known tectonics in the arctic region to further check the validity of our result we have computed synthetic rayleigh waves and a comparison with our observations shows very good agreement

thermochronological investigation of fault zones abstract the timing of faulting episodes can be constrained by radiometric dating of fault zone rocks fault zone material suitable for dating is produced by tectonic processes such as 1 fragmentation of host rocks followed by grain size reduction and recrystallization to form mica and clay minerals 2 secondary heating melting of host rocks by frictional fault motions and 3 mineral vein formation as a result of fluid advection associated with the fault motions the thermal regime of fault zones consists primarily of the following three factors a regional geothermal structure across the fault zone and background thermal history of studied province bounded by fault systems b frictional heating of wall rocks by fault motions and c heating of host rocks by hot fluid advection in and around the fault zone thermochronological methods widely applied in fault zones are k ar 40ar 39ar fission track and u th methods for which methodological principles as well as analytical procedures are briefly described the thermal sensitivities of individual thermochronological systems are then reviewed which critically control the response of each method against the thermal processes based on the knowledge above representative examples as well as key issues are highlighted to date fault gouges pseudotachylytes mylonites and carbonate veins placing new constraints upon geological geomorphological and seismological frames finally the nojima fault is presented as an example for multiple applications of thermochronological methods in a complex fault zone

experimental study for noble gas release and exchange under high speed frictional melting abstract isotope ratios of noble gases in certain minerals are believed to be modified easily by their ambient reservoirs when the minerals reach temperatures that are higher than their closure temperatures the thermal history of a rock or a geologic event even a fault movement can therefore be determined quantitatively by application of radiometric dating methods to different minerals however neither traditional k ar nor ar ar dating methods are readily applicable to faulted rocks because in the case of faulting it is difficult to prove that the temperature of an event was greater than the closure temperatures of minerals frictional melting experiments performed on fine grain homogeneous gabbroid with high temperatures induced by frictional heating using a high velocity friction apparatus were performed to test whether rapid fault movement can reset the noble gas isotope ratio of fault rocks the temperature on the artificial fault plane is much higher than the closure temperature of the k ar system as inferred from the calculated cooling age the anticipated rapid equilibration of volatiles during the frictional melting of rocks implies that the noble gas isotope composition ratio was reset to an atmospheric value during this experiment we measured noble gas isotopes in a gabbroid sample using laser fusion analysis the resetting of noble gases is only observed in glass that had melted completely rejuvenation and or apparent increases in the k ar ages were only observed in a narrow 3 mm wide zone around the fault plane which appears to be thermally altered and mechanically fractured in thin sections because of frictional heating such glassy materials called pseudotachylytes sometimes form along the fault plane in natural faults as a result of complete melting of rock induced by frictional heating thus these results suggest that k ar ages of fault activity can be quantitatively obtained from the analysis of pseudotachylytes

surface wave dispersion crustal structure and sediment thickness variations across the barents shelf summary rayleigh and love wave group velocities were determined for 21 paths across the barents shelf those group velocities exhibit regional variations of 1 0 km or more at short periods depending upon the location of the path within the shelf only two different crustal shear velocity models beneath sedimentary layers are required however to explain all of the group velocity data one model pertains to most of the shelf from a longitude near the eastern coast of svalbard to novaya zemlya the other pertains to a 200 or 300km wide region at the western edge of the shelf shear velocities in the upper crust of the western region are significantly higher and the crust is much thinner than they are for the rest of the shelf that region is known to have moved to its present prosition from a point several hundred kilometres to the north during the caledonian orogeny surface wave group velocities within each of the two regions are strongly influenced by sediments which have accumulated in basins within the barents shelf some of these basins in the southern portion of the shelf may be 10 km or more in thickness

mapping of muslim bagh ophiolite complex pakistan using new remote sensing and field data abstract tethys is a relational gis database that combines geophysical remote sensing geochemical and geochronological data developed as a flexible resource for studying magmatic and geodynamic responses to continental collisions in this paper we demonstrate utility of our database by integrating field remote sensing and structural data for detailed mapping and tectonic emplacement of muslim bagh ophiolite of western pakistan this ophiolite forms the uppermost part of a nappe pile which accreted onto the indian continental margin during the closure of the neo tethys during a pre terminal collision that predated the final closure of tethys during the major collision between india and eurasia utilizing the tethys landsat aster imagery and a digital elevation model developed from the aster data are used to characterize the lithology and structure of the area use of image processing techniques improved the geologic map of the area for a better understanding of the tectonic emplacement of the muslim bagh ophiolite for the first time we report that the dikes in the muslim bagh ophiolite are cutting the metamorphic sole our preliminary geochemical data for sheeted dike complex suggest chemical affinities with arc related rocks this observation suggests that dikes were intruded in an island arc environment soon after the ophiolite was formed

fundamentals of fission track thermochronology fission track ft analysis has developed into one of the most useful techniques used throughout the geologic community to reconstruct the low temperature thermal history of rocks over geological time the ft method is based on the accumulation of narrow damage trails i e fission tracks in uranium rich mineral grains e g apatite zircon titanite and natural glasses which form as a result of spontaneous nuclear fission decay of 238u in nature price and walker 1963 fleischer et al 1975 the time elapsed since fission tracks began to accumulate is estimated by determining the density of accumulated tracks in a particular material in relation to the uranium content of that material chemical etching can be used to enlarge fission tracks that have formed within a mineral in order to make them readily observable under an ordinary optical microscope price and walker 1962 if a host rock is subjected to elevated temperatures fission tracks that have formed up to that point in time are shortened progressively and eventually erased by the thermal recovery i e annealing of the damage fleischer et al 1975 because thermal diffusion basically governs the annealing process the reduction in ft length is a function of heating time and temperature importantly fission tracks are partially annealed over different temperature intervals within different minerals this characteristic allows for the construction of time temperature paths of many different rock types by a plotting ft and other isotopic ages from different minerals versus their closure temperatures which is applicable in the case of a monotonous cooling history e g wagner et al 1977 zeilter et al 1982 and or by b the inverse modeling of observed ft age and confined track length data e g corrigan 1991 lutz and omar 1991 gallagher 1995 ketcham et al 2000 see also ketcham 2005

frictional melt pulses during a 1 1 ma earthquake along the alpine fault new zealand our understanding of frictional melting that occurs during large earthquake slip events has been hampered by the extremely fine grain size of frictionally fused rock and the lack of detailed high resolution microscopy studies that describe features at the crystal lattice scale in such a study we here report the complex nature of melting and crystallization in a symmetrically layered pseudotachylyte vein from the alpine fault new zealand two melt pulses are recognized attributed to successive but rapid injections of frictionally generated material the initial injection preserved at the vein margins was proximally derived and contains a high concentration of clasts and a si rich glass this was quickly followed by a second generation of a more distally derived melt dominated fraction which was injected into the weak vein center whereas fragments of wall rock biotite are preserved in the marginal zones neocrystallized microlitic biotite characterizes both margins and center the vein biotite is different in composition microstructure and polytypism from the metamorphic biotite of the wall rock in all melt layers newly formed biotite shows notable signs of syn flow crystallization strain features and erosion at crystal glass contacts with breakdown of neocrystallized microlites along both crystal edges and faces these characteristics imply cyclic pulses of heating melting and crystallization occurred during a single large earthquake episode and probably reflects the stick slip propagation properties of coseismic faulting 40 ar 39 ar total gas ages from the vein center give a 1 11 0 04 ma date for cyclic melting which based on current exhumation rates occurred at a crustal of depth v11 km 2003 elsevier science b v all rights reserved

introduction to tethys an interdisciplinary gis database for studying continental collisions abstract the tethys gis database is being developed as a way to integrate relevant geologic geophysical geochemical geochronologic and remote sensing data bearing on tethyan continental plate collisions the project is predicated on a need for actualistic model templates for interpreting the earth s geologic record because of their time transgressive character tethyan collisions offer actualistic models for features such as continental escape collision induced upper mantle flow magmatism and marginal basin opening associated with modern convergent plate margins large integrated geochemical and geophysical databases allow for such models to be tested against the geologic record leading to a better understanding of continental accretion throughout earth history the tethys database combines digital topographic and geologic information remote sensing images sample based geochemical geochronologic and isotopic data for pre and post collision igneous activity and data for seismic tomography shear wave splitting space geodesy and information for plate tectonic reconstructions here we report progress on developing such a database and the tools for manipulating and visualizing integrated 2 3 and 4 d data sets with examples of research applications in progress based on an oracle database system linked with arcims via arcsde the tethys project is an evolving resource for researchers educators and others interested in studying the role of plate collisions in the process of continental accretion and will be accessible as a node of the national geosciences cyberinfrastructure network geon via the world wide web and ultra high speed internet2 interim partial access to the data and metadata is available at http geoinfo geosc uh edu tethys and http www esrs wmich edu tethys htm we demonstrate the utility of the tethys database in building a framework for lithospheric interactions in continental collision and accretion

apatite and zircon fission track dating from the hirabayashi nied borehole nojima fault japan evidence for anomalous heating in fracture zones abstract fission track ft analysis using apatite and zircon was performed on samples from two fracture zones fz at the depths of 1140 and 1310 m within the 1838 m borehole core penetrating the ryoke granitic rocks in the nojima fault at nojima hirabayashi awaji island japan drilled just after the 1995 hyogo ken nanbu earthquake clear discordance in apatite and zircon ft age was found for two samples located at 2 m below the central part of each fzs where the presence of pseudotachylyte and or fault gouge would predict the largest amount of slip asymmetric distribution was identified by discordant ages with respect to the central part of fzs these very local discordant ages in the fault reflect thermal anomalies caused by secondary heating with an inferred maximum temperature in the region between apatite and zircon closure temperatures at a time post 48 ma as a source of the secondary heating heat transfer or dispersion via geothermal fluids caused presumably the observed similarity in asymmetric distribution of discordant ft ages at two different fzs other samples yield concordant ft zircon and apatite ages and these indicate rapid cooling within the bounds of two closure temperatures of these minerals at 60 ma of the ryoke granitic rocks

pn velocities beneath continental collision zones the turkish iranian plateau summary tomographic imaging of the uppermost mantle velocity in the middle east shows normal pn velocities 8 0 8 2 kms beneath the black sea and the southern caspian sea in contrast low pn velocities 7 9 km s i are found beneath the aegean sea and much of the turkish iranian plateau a region of exceptionally low pn velocities c7 6 km s beneath the lesser caucasus mountains and along the turkish iranian border coincides with a region of high sn attenuation and extensive neogene volcanism all these features suggest that near solidus conditions exist within the uppermost mantle beneath the turkish iranian plateau such conditions may result either from the decompression melting associated with upwelling convection cells or by the infiltration of water released from subducted lithosphere into the mantle above the presence of a partially melted uppermost mantle weakens the lithosphere beneath the turkish iranian plateau thus allowing it to become the locus of deformation in the arabian eurasian collision zone

synthetic seismogram and surface wave constraints on crustal models of spitsbergen abstract seismic refraction data collected on spitsbergen in 1978 are used to obtain a crustal model assuming plane horizontal layering the observed travel times and wave forms are compared with those of synthetic seismograms computed for various published crustal models the more detailed models adequately explain some but not all of the features of the synthetics these models are adjusted utilizing travel times and wave form amplitudes until a satisfactory fit is achieved the best fitting model consists of a 4 layer crust having thicknesses of 4 1 10 0 7 4 and 5 8 km and compressional velocities of 4 65 6 21 6 30 and 6 65 km sec with increasing depth the uppermost mantle has a velocity of 7 90 km sec a comparison of observed and synthetic p n waveforms supports the existence of a thin low velocity zone beginning at a depth of about 5 km beneath the moho boundary an inversion of seismic surface wave group velocity data yields a shear wave model which is compatible with the compressional wave model

exploring the ar isotope record of an early miocene pseudotachylyte in an early oligocene intrusion rieserferner pluton eastern alps abstract we investigate the influence of unmelted clasts on the 40ar 39ar age record of a miocene pseudotachylyte within the early oligocene riesenferner pluton eastern alps this case study is ideal to investigate the effect of inherited ar retained in survivor clasts because although seismic faulting was only slightly younger 39ar laser analyses of low k microlitic domains free of discernable clasts yield slightly but significantly older ages than those from the high k matrix results suggest that older ages up to 4 on average from low k domains are due to contamination by plagioclase clasts and suggest an age of 17 12 0 22 ma for coseismic slip this age dates the last stage of activity of the giudicarie fault during tectonic indentation of the dolomites block of the southern alps against the nappe stack of the eastern alps

early proterozoic activity on archean faults in the western superior province evidence from pseudotachylite major transcurrent faults in the superior province developed in the late archean at the close of the kenoran orogeny reactivation of some of these faults late in the early proterozoic is indicated by rb sr analyses of pseudotachylite from the rainy lake seine river and quetico faults in the rainy lake region of minnesota and ontario fault veins of pseudotachylite and immediately adjacent country rock at two localities yielded subparallel isochrons that are pooled for an age of 1947 23 ma k ar and rb sr biotite ages register earlier regional cooling of the terrane at about 2500 ma with no evidence of younger thermal overprinting at temperatures exceeding 300 c accordingly the 1947 23 ma age is interpreted as dating the formation of the pseudotachylite reactivation of existing faults at this time was caused by stresses transmitted from margins of the superior province where compressional tectonic events were occurring

fission track dating of faulting events accommodating plastic deformation of biotites we performed fission track ft analyses to constrain the timing of fault slip events associated with plastic deformation of biotite grains formed at high temperature higher than 200 300 c apatite ft ages of 49 6 16 7 ma were obtained from late cretaceous granites near the fault with younger ages near a basaltic dike that intruded at 19 ma by comparing the distribution of apatite ft ages using forward thermal and ft annealing calculations we interpreted the younger ages as being explained by basaltic intrusion we concluded that the plastic deformation of the biotite grains could have occurred associated with the following events 1 primal cooling of the granitic body at 68 50 ma and or 2 basaltic intrusion at 19 ma a combination of detailed observation of microscale deformation structures and dense ft measurements successfully constrained timing of fault events distributed in bedrock without covering layers

lg magnitudes and yield estimates for underground novaya zemlya nuclear explosions abstract lg wave amplitudes of 30 novaya zemlya underground nuclear explosions as recorded by short period seismographs in denmark finland germany norway spitsbergen and sweden are used to determine m b lg values assuming that the m b lg versus explosion yield relation derived from nevada test site data applies to all continental areas the yields of the explosions are estimated they cover a large range of values from 2 5 to 4900 kt the largest explosion since april 1976 had an estimated yield of 145 kt the m b lg values when subtracted from the m b p values can be used to estimate the m b p bias between two test sites in this way the m b p bias between novaya zemlya and the nevada test site is estimated to be 0 20 magnitude units

seismicity and present day tectonics of the svalbard region summary data collected by temporary seismic networks and individual stations over a 7 yr period in the svalbard archipelago are integrated and used to study the seismicity and present day tectonics of the archipelago and surrounding regions most of the continental seismic activity occurs in three concentrated zones one in heer land near the eastern coast of the island of spitsbergen and two in close proximity to one another on the island of nordaustlandet all three zones are in regions which have been devoid of major orogenic activity since the late devonian the heer land zone and at least one of the zones in nordaustlandet define active faulting which has not been identified by surface mapping the other zone in nordaustlandet occurs in the region of a mapped system of faults all branches of which are relatively minor a number of smaller concentrations and individual earthquakes occur throughout much of the archipelago and surrounding continental shelves seismicity is currently low in the region of tertiary orogenic activity in western spitsbergen a roughly linear pattern of minor activity in southern spitsbergen occurs west of the heer land zone and extends at least 50km southward the major n s faults in spitsbergen which are thought to have accomodated large displacements in devonian time are currently inactive except perhaps at the southern termini of the billefjorden and lomfjorden fault zones where they approach the heer land seismic zone earthquakes located near the western continental margin of spitsbergen may occur on segments of rifting and shearing which reflect the opening of the greenland sea during the tertiary the limited extent of the currently active zones of activity their spatial stability over several years and the lack of activity on the major faults of svalbard argue against the existence of plate boundaries along which motion is currently occurring in the svalbard region all fault plane solutions on svalbard are consistent with a stress field characterized by e w compression whereas previously published fault plane solutions for the ridge system west of svalbard indicate e w extension the magnitude of the compressive stress increases from small values near the ridge system to values sufficiently large to dominate the regional seismicity of svalbard over distances of 200 300 km

tomographic imaging of deep velocity structure beneath the eastern and southern carpathians romania implications for continental collision the vrancea seismic zone located beneath the elbow of the eastern and southern carpathians is characterized by intermediate depth seismicity associated with subduction and plate collision among many strong earthquakes that have occurred in the region the 1977 vrancea earthquake march 4 1977 ms 7 1 depth of 86 km caused extensive damage and fatalities the vrancea seismic zone is defined by a tabular region of seismicity that extends from the surface to a depth of 200 km the small size about 80 km in length and 40 km in width and geometry of the seismic zone have made it difficult to interpret the kinematics of subduction and continental collision in the romanian carpathians to better understand the collision subduction environment body wave seismic tomography was used to image the deep structure beneath the eastern and southern carpathians in romania a total of 7837 p and 2292 s arrival times from 433 shallow and intermediate depth earthquakes recorded by local and regional seismic stations were inverted for the three dimensional 3 d seismic velocity structure the travel times and ray paths were calculated by an efficient 3 d ray tracing technique by utilizing the lsqr algorithm p and s wave velocity perturbations were determined from the surface down to a depth of 200 km the high resolution p wave tomographic images reveal a pattern of broad heterogeneity in the velocity structure of the region one of the most important features is a high velocity body existing beneath the carpathian arc at depths between 100 and 170 km this high velocity body outlines a slab dipping near vertically where most of the intermediate depth earthquakes occur beneath the transylvanian basin a high velocity zone is dipping toward the se and may represent the base of lithosphere which is in convergence with the subducted slab low velocity bodies are found along the forearc of the carpathian foredeep down to depths of 70 to 80 km these low velocity bodies may be correlated with the shallow sedimentary layer in the foreland and may represent crustal materials wedged and underthrust along with the subducted lithosphere

thermal evolution of a sheared continental margin insights from the ballenas transform in baja california mexico abstract the ballenas transform margin in central baja california offers an unparalleled opportunity to study the thermal behaviour of a sheared continental margin during various stages of its evolution apatite fission track and u th he results from two transects perpendicular to the coast reveal a pronounced latest pliocene to pleistocene 1 8 ma heating event related to the neogene opening of the gulf of california proximity to a regional pre rift unconformity indicates that samples remained at near surface levels since paleogene unroofing despite having experienced reheating to maximum paleotemperatures within or above the fission track partial annealing zone in general maximum paleotemperatures during overprinting decrease from 100 120 c near the coast to below 60 c ca 5 8 km further inland suggesting lateral heat flow from a source within the gulf of california heat sources related to the structural development of the ballenas transform fault located approximately 1 5 4 5 km offshore from the two sample transects most likely controlled the observed reheating overprinting patterns do not support conductive reheating due to reburial magmatism or frictional shear instead a pronounced thermal spike in between much less overprinted neighbouring samples strongly favours convective heating by hydrothermal fluids as the dominant overprinting process hydrothermal activity may be caused by either deep fluid circulation along newly formed shear zones of the transform fault or more likely magmatic leaking along the transform fault latest pliocene to pleistocene 1 8 ma activity on the ballenas transform fault is closely linked to extension in the lower and upper delfin basins and provides a minimum age for the structural reorganisation and the relocation of extension in the northern gulf of california this study shows that hydrothermal activity can cause significant thermal events in a transform margin before the passage of the spreading centre paleotemperatures from the ballenas transform are similar to those of other transform margins after passage of a spreading centre which suggests that hydrothermal fluids may have an important thermal buffering effect moderating the maximum temperatures of the ridge segments near their intersection with a continental transform margin

fluidization and melting of fault gouge during seismic slip identification in the nojima fault zone and implications for focal earthquake mechanisms 1 the record of physical processes that occur during seismic slip events is well preserved in fault rocks from the active nojima fault in japan the fault rocks formed at about 3 km depth and comprise thin alternating layers of very fine gouge and pseudotachylyte derived from granite each layer is thinner than a few millimeters and corresponds to one seismic slip event the very thin slip zone width suggests that some mechanisms of slip weakening operated and our studies of the fault rocks suggest that fluidization and melting of gouge were particularly important fluidized and nonfluidized gouges were distinguished using the detection probability of fragmented counterparts method it is known from granular material science that the phase transition from a grain friction regime to fluidization of granular materials can occur only by a very small decrease in volume fraction of solid grains once fluidization occurs the frictional resistance decreases abruptly to nearly zero even before thermal pressurization reaches its extreme state when fault gouge is melted frictional resistance is governed by the viscosity of melt which depends mainly on temperature chemical composition h2o concentration and the volume fraction of unmelted grains for each pseudotachylyte layer we estimated the temperature of melt using various temperature indices and measured volume fraction of unmelted grains we synthesized these data to reconstruct the change in viscosity during seismic slip events the melt viscosity is very high 107 9 pas during initial melting due to the combined effect of low temperature 750 800 c and large volume fraction of solid grains thus seismic slip is inevitably restrained instantaneously once this mechanical barrier is overcome the viscosity reduces continuously and dramatically as slip increases at 1000 c the viscosity reduces to 104pas and eventually to 10pas at 1280 c thus stress drops almost completely and rupturing tends to run away

zagros orogeny a subduction dominated process this paper presents a synthetic view of the geodynamic evolution of the zagros orogen within the frame of the arabia eurasia collision the zagros orogen and the iranian plateau preserve a record of the long standing convergence history between eurasia and arabia across the neo tethys from subduction obduction processes to present day collision from 150 to 0 ma we herein combine the results obtained on several geodynamic issues namely the location of the oceanic suture zone the age of oceanic closure and collision the magmatic and geochemical evolution of the eurasian upper plate during convergence as testified by the successive sanandaj sirjan kermanshah and urumieh dokhtar magmatic arcs the p t t history of the few zagros blueschists the convergence characteristics across the neo tethys kinematic velocities tomographic constraints subduction zones and obduction processes together with a survey of recent results gathered by others we provide lithospheric scale reconstructions of the zagros orogen from 150 to 0 ma across two sw ne transects the evolution of the zagros orogen is also compared to those of the nearby turkish and himalayan orogens in our geotectonic scenario for the zagros convergence we outline three main periods regimes 1 the mid to late cretaceous 115 85 ma corresponds to a distinctive period of perturbation of subduction processes and interplate mechanical coupling marked by blueschist exhumation and upper plate fragmentation 2 the paleocene eocene 60 40 ma witnesses slab break off major shifts in arc magmatism and distributed extension within the upper plate and 3 from the oligocene onwards 30 0 ma collision develops with a progressive sw migration of deformation and topographic build up sanandaj sirjan zone 20 15 ma high zagros 12 8 ma simply folded belt 5 0 ma and with partial slab tear at depths 10 ma to present our reconstructions underline the key role played by subduction throughout the whole convergence history we finally stress that such a long lasting subduction system with changing boundary conditions also makes the zagros orogen an ideal natural laboratory for subduction processes

the first u th he thermochronology of pseudotachylyte from the median tectonic line southwest japan abstract to constrain the thermal and its spatial conditions of pseudotachylyte formation and cooling we dated zircons from a pseudotachylyte in the ryoke belt obtained about 100 m north from the median tectonic line in the taki area southwest japan and its host rock the hatai tonalite by the u th he method the ages obtained are 60 3 2 7 and 55 5 4 5 1se ma respectively which are essentially the same within the error this is the first u th he age directly measured for a pseudotachylyte the coincidence between these ages indicates that the pseudotachylyte formed at ca 60 ma under the ambient temperature of about 180 c the closure temperature of zircon u th he method the fish canyon tuff zircon one of the most well known geological age standards was also dated to confirm the validity of our analyses which yielded the weighted mean age of 29 6 1 5 1se ma consistent with other reported ages the average cooling rates and denudation rates of the host rock were calculated based on these ages reported zircon fission track ages ca 70 ma and apatite fission track ages ca 40 ma as about 12 c myr and about 0 6 mm yr from 70 to 60 ma and about 4 c myr and about 0 2 mm yr from 60 to 40 ma respectively assuming that the closure temperatures of zircon and apatite ft methods are 300 c and 110 c respectively and a geothermal gradient of 20 c km one possible reason of this slow down of denudation rates is the decrease of convergent rate and change in the movement direction of the pacific plate relative to the eurasian plate along the southwest japan in the paleogene

dating pseudotachylyte of the nojima fault using the zircon fission track method 1 the zircon fission track analysis of pseudotachylyte answered how old the nojima fault is which was activated during the 1995 kobe earthquake in japan the time of seismic fault motions at the crustal interior can be constrained by dating pseudotachylyte formation we succeeded in separating zircons from the pseudotachylyte layer of the fault as well as in dating them by the fission track method here we show that the layer has a significantly younger age 56 4 ma than the initial cooling age of the host rock suggesting that the fault was already initiated at 56 ma much older than the previous estimate based on the spatial distribution of sediments around the fault

towards zircon fission track thermochronology reference framework for confined track length measurements abstract horizontal confined track hct lengths and angles to the crystallographic c axis were measured for both unannealed spontaneous and induced fission tracks ft in zircons to establish a reference framework of hct length measurement induced track lengths were analysed on eleven zircon separates from various rock types including four age standards and spontaneous lengths on three zircon standards were analysed in general the observed hct lengths in each sample are slightly anisotropic with shorter tracks having greater angles to the c axis in addition all samples show large anisotropy in the number of observed hct s particularly for induced tracks as an observed mean hct length is controlled by the combined influence of these two anisotropies selective measurement of tracks that have specified azimuth angles to the c axis e g 60 90 is recommended in annealing studies or thermochronological applications mean spontaneous and induced hct lengths of 60 90 are approximately concordant for individual age standards although slightly controlled by the difference in overetching effects due to the different etching criteria adopted this indicates that natural track annealing at an ambient surface temperature at geological timescales is negligible in zircon in contrast to the case in apatite mean lengths of induced hct s do not differ significantly between the zircons analysed therefore the overall mean and standard deviation values of hct lengths for 60 90 azimuth angles i e 10 50 0 04 1 standard error m and 0 76 0 03 m for spontaneous tracks and 10 73 0 04 and 0 63 0 03 m for induced tracks respectively offer reliable references for hct length measurement in zircon ft thermochronology

sedimentary basins and the blockage of lg wave propagation in the continents the phenomenon of lg blockage where lg is strongly attenuated by crustal heterogeneities poses a serious problem to ctbt monitoring because lg is an important seismic phase for discrimination this paper examines blockage in three continental regions where the lg blockages may be caused by large enclosed sedimentary basins along the propagation path the barents sea basin blocks lg propagation across the barents sea from the russian nuclear test sites at novaya zemlya to scandinavian stations also early lg waves are observed in sn codas on norsar noress and arcess recordings of novaya zemlya explosions where direct lg is blocked early lg waves may have resulted from sn to lg mode conversion at the contact between the barents basin and the kola peninsula the northern and southern caspian sea basins also block lg waves from pnes and earthquakes perhaps due to thick low velocity low q sediments replacing the granitic layer rocks in the crust lg blockage has also been observed in the western mediterranean levantine basin due to low q sediments and crustal thinning a basin capture model is proposed to explain lg blockage in sedimentary basins in this model shear waves that reverberate in the crust and constitute the lg wave train are captured delayed and attenuated by thick low velocity sediments that replace the granitic layer rocks of the upper crust along part of the propagation path sn waves which propagate below the basin would not be blocked and in fact the blocked lg waves may be diverted downward into sn waves by the low velocity sediments in the basin

multimode rayleigh wave attenuation and qβ in the crust of the barents shelf the multimode method of cheng and mitchell 1981 is used to study the attenuation properties of the crust throughout the barents shelf the sensitivity of the spectra to various source factors and to propagation factors which might characterize a shelf region are thoroughly studied for plane layered models the method is very sensitive to q in the upper crust and to q of sedimentary layers if those layers are thick and highly attenuating it is far less sensitive to q in the lower crust and to q the spectra for shallow strike slip earthquakes are very insensitive to changes in strike slip and dip angles of the fault throughout the entire period range of interest but are very sensitive to variations in focal depth except in the long period range of the fundamental mode and the short period range of the higher modes the fundamental mode but not the higher mode spectra for one path across the barents shelf are apparently distorted at short periods by lateral heterogeneities along the travel path simple two layer trial and error inversions yield a model of the barents shelf with an upper crustal q value of about 80 three layer inversions with a sedimentary layer however yield an upper crustal q of about 250 if the sediments are 1 km thick and are characterized by q values of 40 shear velocity models for the barents shelf show variations between about 3 0 and 3 6 km s in the upper crust along different paths the lower crust shows smaller regional differences but velocities vary between 3 5 and 4 0 km s through the depth range 25 35 km the variation of shear velocities in the upper mantle may correlate with those of the upper crust and vary regionally between about 4 3 and 4 8 km s

thermobarometric data from a fossil zircon partial annealing zone in high pressure low temperature rocks of eastern and central crete greece abstract a fossil partial annealing zone of fission tracks in zircon is described from high pressure low temperature hp lt rocks of the phyllite quartzite unit pq on the island of crete greece correlation of regional trends in fission track age populations with independent thermobarometric and microstructural data and with new experimental annealing results allows a calibration of this low temperature thermochronological method to a degree hitherto not available from other field examples the zircon fission track ft ages of samples from the pq across crete range from original detrital signature through reduced to completely reset the annealing is the result of a single heating period related to the hp lt metamorphism with near peak temperatures lasting for only a few million years some time between 24 1 and 20 1 ma in eastern crete where rocks have experienced temperatures of 300 50 c and pressures of 0 8 0 3 gpa zircon ft ages range from 414 24 to 145 10 ma ages above 300 ma occur mostly near the east coast of the island in rocks which have not been heated to above ca 280 c and probably represent a pre variscan source track lengths are already indicative of a substantial annealing at this temperature most of the zircon ft ages from eastern crete scatter within error around the stratigraphic age samples with apparent zircon ft ages significantly younger than the depositional age are only observed in areas where temperatures exceeded ca 320 c towards the west a sudden decrease to very young ages ranging from 17 2 to 18 1 ma reflects a complete resetting at ca 350 c short tracks however are still observed throughout the central and western part of the island ages are consistently below 22 ma thermobarometric data for this area indicate maximum temperatures of 400 50 c and pressures of 1 0 3 gpa only samples from western crete which have been exposed to 400 50 c show exclusively long tracks consequently the high temperature limit of the zircon partial annealing zone zpaz appears to be between 350 and 400 c a significant influence of elevated confining pressure on the stability of fission tracks in zircon is ruled out by the results of annealing experiments at 0 5 gpa and at different temperatures which fit the curves previously obtained by other authors at ambient pressure

transpression and the build up of the cordillera the example of the bucaramanga fault eastern cordillera colombia widespread wrench tectonics have been described along the northern andes the bucaramanga fault described as sinistral strike slip bounds the high santander massif we combine structural and thermochronological data from the central southern portion of the fault to investigate the vertical displacement the structural survey data show old phases of activity preserved in the host rocks along the fault trace with the superimposition of different generations of slickenlines and both strike slip and dip slip kinematics indicators new and previous thermochronological data show that differential exhumation of the fault walls has been ongoing for the last 50 ma the hanging wall the santander massif records in the central portion decreasing exhumation rates from the early miocene to the mid to late miocene and in the southern portion constant rates from the late oligocene to the pliocene combining such observations the thermochronological offset resulting from the relative motion of the two fault walls is comparable with the observed drop in elevation across the fault suggesting that the present topography of the santander massif is related to vertical movement along the bucaramanga fault we infer that the fault has a significant neogene reverse component consistent with the present day horizontal global positioning system vector data long term exhumation rates and the structural assemblage supplementary material the supplementary materials contain methodological information on the thermochronological procedures a compilation of the previously published data used in this study and the structural geology dataset https doi org 10 6084 m9 figshare c 4620140

natural long term annealing of the zircon fission track system around a granitic pluton we measured 24 ages and 14 length distributions of fission tracks in zircons separated from basement sandstones around a granitic pluton to investigate natural long term annealing behaviors of the zircon fission track zft system samples were collected from three cretaceous coherent units of the shimanto accretionary complex shikoku japan along an eastward traverse at distances of between 1 6 and 10 6 km from the intrusion contact of 15 ma takatsukiyama granite exposing about 5 km in diameter sampling was carried out around the expected position of the transition zone of track retention i e the fossil partial annealing zone fpaz based on previous regional zft age distributions approaching the contact original zft ages of 100 ma show a continuous reduction to 15 ma at 3 km distance their single grain age distributions accordingly change from widespread multimodal patterns reflecting provenance ages to unimodal ones characterizing the secondary heating by the granite intrusion mean and distributions of zft lengths also show notable variations within the fpaz as a result of mixing both preexistent tracks that were shortened by the miocene heating and unannealed ones having original long lengths that have been formed and accumulated after the cooling of the pluton these facts along with observed track segmentation and annealing anisotropy suggest that the shortening patterns of tracks in nature a heating duration of 105 106 years estimated from thermal modeling are indistinguishable from those previously demonstrated at laboratory timescales this basically validates the conventional approach of extrapolating laboratory based kinetic parameters to geologic timescales the observed fpaz and thermal modeling results in conjunction with laboratory heating data previously reported and recent constraints from an ultradeep borehole favor a relatively narrow temperature range for the partial annealing zone i e 230 to 330 c for a heating duration of 106 years

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

apatite fission track dating of fault related rocks along the nojima and kusumoto faults and its tectonic significance 1 the tectonic history of the nojima fault a 10 km long active fault whose movement caused the disastrous 1995 kobe earthquake was studied by the apatite fission track aft dating method aft ages of 63 83 ma from a thermally undisturbed uplifted block indicate relatively minor uplift since 65 ma with an estimated total exhumation of 3 6 km assuming a geothermal gradient of 25 c km aft ages of 44 54 ma and the nature of the track length distribution from fault related rocks indicate that fault related hydrothermal minerals such as laumontite and chlorite and foliated cataclasite were formed by ancient fault activity that occurred before 44 ma it is inferred that the quaternary fault activity of the nojima fault is a relatively major phase in the entire tectonic history of the nojima fault

borehole water and hydrologic model around the nojima fault sw japan abstract the active fault drilling at nojima hirabayashi after the 1995 hyogoken nanbu kobe earthquake mjma 7 2 provides us with a unique opportunity to investigate subsurface fault structure and the in situ properties of fault and fluid the borehole intersected the fault gouge of the nojima fault at a depth interval of 623 m to 625 m the lithology is mostly cretaceous granodiorite with some porphyry dikes the fault core is highly permeable due to fracturing the borehole water was sampled in 1996 and 2000 from the depth interval between 630 and 650 m just below the fault core the chemical and isotopic compositions were analyzed carbon and oxygen isotope ratios of carbonates from the fault core were analyzed to estimate the origin of fluid the following conclusions were obtained 1 the ionic and isotopic compositions of borehole water did not change from 1996 to 2000 they are mostly derived from local ground water as mentioned by sato and takahashi sato t takahashi m 2000 chemical and isotopic compositions of groundwater obtained from the hirabayashi well geological survey of japan interim report no eq 00 1 187 192 2 geochemical speciation revealed that the borehole water was derived from a relatively deep reservoir which may be situated at a depth of 3 to 4 km where the temperature is about 80 90 c 3 the shallower part of the nojima fault shallower than the reservoir depth has not been healed from the hydrological viewpoints 5 years after the event in contrast to the rapid healing detected by s wave splitting tadokoro k ando m 2002 evidence for rapid fault healing derived from temporal changes in s wave splitting geophys res lett 29 10 1029 2001gl013644 4 precipitation of calcite from the present borehole water since drilling supports the idea of precipitation of some calcite in coseismic hydraulic fractures in the fault core boullier a m fujimoto k ohtani t roman ross g lewin e ito h pezard p ildefonse b 2004 textural evidence for recent co seismic circulation of fluids in the nojima fault zone awaji island japan tectonophysics 378 165 181 5 carbon and oxygen isotope ratios of calcite indicated that the meteoric water flux had been localized at the fault core 6 a difference in the carbon isotope ratio between the footwall and the hanging wall suggests that the fault has been acted as a hydrologic barrier although the permeability along the fault is still high

timing of the tsergo ri landslide langtang himal determined by fission track dating of pseudotachylyte abstract fission track dating was carried out on zircon grains from pseudotachylyte associated with a late pleistocene landslide tsergo ri landslide in langtang himal nepal zircon grains were separated from an injection pipe of glassy and vesicular pseudotachylyte about 10 cm in diameter the resulting age of 51 13 ka lies between the two subpeaks 70 and 20 ka of the wurm glacial period and is concordant with the previous age estimate from geomorphological evidence i e older than 25 30 ka this is the first reliable isotopic age for a landslide generated pseudotachylyte excluding the possibility of contamination by an inherited age

healing microstructures of experimental and natural fault gouge 1 the healing of fault gouge was studied by examining microstructures of naturally and experimentally produced granitoid fault rock we performed deformation experiments on intact granitoid rock samples at t 300 500 c pc 500 mpa and 1 2 10 4 1 3 10 7 s 1 with 0 2 wt h2o added healing experiments were carried out on deformed samples at t 200 500 c pc 500 mpa for 4 h to 14 days under hydrostatic and nonhydrostatic conditions the grain size distributions gsd of the deformed samples were quantified using the d value slope of log frequency log radius of the gsd for quartz and feldspar fault gouge healing causes a decrease in the d value from 2 0 to 1 5 the time dependence of the d decrease is described by a hydrostatic healing law of the form d d t df a e t the results of the laboratory experiments were compared to three natural fault systems 1 nojima fault zone japan 2 fault zones in the black forest germany and 3 orobic thrust italian alps natural and experimental gouges have similar d values healing is only observed in monomineralic aggregates polymineralic i e mixed fault gouges retain their high d value after extended healing times because grain growth is inhibited healing under nonhydrostatic conditions is more rapid than hydrostatic healing the low strain rates which were measured during nonhydrostatic healing are temperature dependent and suggest that diffusive mass transfer processes take place during deformation thus fault rocks at upper to midcrustal depth may deform by combined cataclasis and diffusive mass transfer

stability of the regional stress field in central japan during the late quaternary inferred from the stress inversion of the active fault data 1 we analyzed 169 geological fault slip data from 37 active faults in central japan to investigate the late quaternary stress field stability modern stress states have been documented with unprecedented accuracy however their stability over time scales beyond instrumental observations is inadequately understood because the stress field has changed in the geological past we compared present stress conditions in central japan determined from geophysical observations with conditions determined by inverting the fault slip data from active faults that exhibited cumulative displacement for the past 105years the maximum stress axis obtained from fault slip data trends ese wnw this state of stress accounts for 97 of the data and supports the fact that oblique faults with reverse and strike slip senses are interlaced in the region the optimal stress is similar to the present stress state indicating that the stress field in central japan has been uniform and stable over the past 105 years

tomographic inversion of rg wave group velocities for regional near surface velocity structure the tomographic inversion of group velocities of rg waves is a viable technique for mapping lateral variations in the lithology of sedimentary basins in order to determine a velocity structure we first use the moving window maximum entropy spectral analysis to measure the average rg wave group travel times second the group velocities within blocks subregions covering the area sampled by the rg wave propagation paths are determined by tomographic inversion third the vertical shear wave velocity profile within each block is determined from the inversion of group velocities for that block finally a structural cross section is obtained by connecting blocks located along a profile rg waves recorded from mining explosions in alabama were used in a test of the technique by modeling the paleozoic sedimentary rocks in the black warrior basin of northern alabama the high resolution of moving window maximum entropy spectral analysis allows estimation of the rg wave group velocities with a precision of better than 3 the usable frequency range of 0 5 to 1 5 hz allows determination of structures to depths of about 2 4 km with layers of 0 2 km thickness blocks of widths of 20 km or less could be resolved with appropriate data shear wave velocities in the black warrior basin range from 1 6 to 4 0 km s the layering in the velocity structure corresponds to major geologic units within units an increase in velocity to the northeast corresponds to observed facies changes

40ar 39ar geochronometry of pseudotachylytes by vacuum encapsulation north cascade mountains washington usa to determine a reliable means of dating pseudotachylytes we obtained total gas ages plateau ages and argon retention ages on samples from the north cascade mountains washington quartz ampoule vacuum encapsulation analysis of small grains a few milligrams from six samples allowed evaluation of 39 ar loss through recoil during irradiation and laser ablation on four samples allowed textural control in microlitic samples recoil loss 39 ar ranges from 0 2 to 8 4 the total gas ages incorporating this 39 ar are inconsistent but retention ages are much more internally consistent and within analytical error they match or nearly match plateau ages from most of the microlitic samples at 54 55 ma samples analyzed by laser ablation suggest one episode of faulting and pseudotachylyte formation at 55 59 ma and an earlier episode at ca 80 ma the partly glassy pseudotachylyte yielded laser ablation total gas and retention ages of ca 65 ma the microlitic pseudotachylytes indicate formation close to 55 ma with possible older faulting and pseudotachylyte formation at ca 81 84 ma the good consistency among the retention ages the laser ages with highest precision and especially the plateau dates combined with the ages falling within the anticipated time span provides confidence in the geologic reality of the ages nevertheless it is clear that large clasts and crystal fragments within these particular veins did not completely degas or may have an anomalous inherited radiogenic 40 ar component

architectural evolution of the nojima fault and identification of the activated slip layer by kobe earthquake 1 evolutionary history of nojima fault zone is clarified by comprehensive examinations of petrological geophysical and geochemical characterizations on a fault zone in deep drilled core penetrating the nojima fault on the basis of the results we reconstruct a whole depth profile of the architecture of the nojima fault and identify the primal slip layer activated by 1995 kobe earthquake the deepest part 8 to 12 km depth of the fault zone is composed of thin slip layers of pseudotachylite 5 to 10 mm thick each 10 cm in total middle depth 4 to 8 km depth of the fault zone is composed of fault core 6 to 10 m thick surrounded by thick 100 m thick damage zone characterized by zeolite precipitation the shallow part of the fault zone 1 to 4 km depth is composed of distributed narrow shear zones which are characterized by combination of thin 0 5 cm thick each 10 cm in total ultracataclasite layers at the core of shear zones surrounded by thicker 1 to 3 m thick damage zones associated with carbonate precipitation an extremely thin ultracataclasite layer 7 mm thick activated by the 1995 kobe earthquake is clearly identified from numerous past slip layers overprinting one of the shear zones as evidenced by conspicuous geological and geophysical anomalies the nojima fault zone was 10 to 100 times thicker at middle depth than that of shallower and deeper depths the thickening would be explained as a combination of physical and chemical effects as follows 1 thickening of fault core at middle depth would be attributed to normal stress dependence on thickness of the shear zone and 2 an extreme thickening of damage zone in middle depth of the crust would result from the weakening of the fault zone due to super hydrostatic fluid pressure at middle depths the high fluid pressure would result from faster sealing with low temperature carbonate at the shallower fault zone

annealing kinetics of fission tracks in zircon an experimental study a series of laboratory annealing experiments on zircon fission tracks has been carried out under heating conditions of 350 750 c for 10 1 103 hr i e 4 5 min 40 days variation in the confined lengths of spontaneous fission tracks was determined using zircon grains from nisatai dacite the fading contours of normalized mean track length r on the arrhenius diagram showed as sets of straight lines we performed a series of model fittings called the parallel and fanning models in order to describe the decrease in r with increasing temperature or heating time the lowest temperature limit of the zircon partial annealing zone zpaz was defined as r 0 95 and the highest as r 0 4 which approximately corresponded to the total fading of surface tracks extrapolation of the results of the laboratory experiments to the geological timescale gives for a heating duration of 106 yr estimated values of the zpaz of 210 320 c 60 c 2 with the parallel model 190 350 c 50 c 2 with the fanning model critical temperature t0 and 170 390 c 50 c 2 with the fanning model t0 the temperatures of the zpaz decrease by 20 c for an annealing duration that is an order of magnitude longer because the estimated closure temperature of zircon fission track analysis approximately corresponds to the middle of the zpaz these results support the previously estimated closure temperature of 240 c by varying the etching time it was revealed that significant removal of radiation damage occurs at r 0 93

40ar39ar dating of pseudotachylite from the vredefort dome south africa a progress report abstract to date six pseudotachylite samples from the vredefort dome have been analysed by the stepheating 40ar 39ar technique the resulting ages ga 2 25 0 04 k ar 2 01 0 06 1 39 0 08 1 44 0 08 1 33 0 04 and 1 09 0 10 may be understood as suggesting several pseudotachylite forming events at vredefort this and other chronological and field evidence may be interpreted as supporting the possibility that vredefort pseudotachylite is not derived from a single catastrophic central shock event but was generated in several local high strain possibly seismic shock events diffusion calculations have shown that it is possible that several thermal spikes could have effectively degassed pseudotachylite at relatively low temperatures and during short periods of time e g at 340 c in 10000 yrs there is however no geological or isotopic evidence directly supporting the existence of these proposed temperature spikes at 2 0 1 3 1 4 and 1 1 ga in the region of the vredefort structure on the contrary field and laboratory observations can be invoked that seem to favour the formation of multiple generations of pseudotachylite in the vredefort dome and in the surrounding witwatersrand basin however it must be noted that likewise no direct geological evidence for local tectonic activity in the region of the witwatersrand basin at those times can be presented with the exception of emplacement of pilanesberg age dykes further tests on the validity of the 40ar 39ar ages on vredefort pseudotachylite are in progress and are discussed

ancient thermal anomaly of an active fault system zircon fission track evidence from nojima gsj 750 m borehole samples 1 to understand better heat generation and transfer along faults fission track ft thermochronologic analysis was performed on zircon separates from cretaceous granitic rocks around the nojima fault activated during the 1995 kobe earthquake samples were collected from the geological survey of japan gsj 750 m borehole and nearby outcrop zircon fts showed reduced mean lengths and ages for samples less than 10 m away from the fault at depth this is interpreted as representing an ancient thermal anomaly by heat transfer or dispersion via fluids at the deep crustal interior because the degree of ft annealing is correlated to that of deformation alteration of borehole rocks from extrapolation of data in the mean ft age length plot as well as from model age calculation it is suggested that last cooling took place at 30 40 ma

experimental study on hydrothermal annealing of fission tracks in zircon abstract increasing temperature causes fading of fission tracks fts in minerals which has been quantified by many laboratory heating experiments in atmosphere in order to elucidate whether or not ft annealing at hydrothermally pressured conditions is the same as that at atmospheric condition we performed zircon heating experiments using a hydrothermal synthetic apparatus for reliable comparison we annealed the same zircon samples using the same temperature monitor and analyzed them using the same experimental procedure as the previous experiment at atmosphere yamada et al chem geol isot geosci sect 122 1995 249 the observed ft annealing characteristics are indistinguishable between atmospheric and hydrothermally heating it is therefore implied that the annealing kinetics of ft in zircon previously established can be applied to thermal history analysis of rocks that were subjected to hydrothermal conditions in nature such as those in fault and subduction zones

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

investigation of teleseismic lg blockage and scattering using regional arrays abstract incoherent beamforming and continuous frequency wavenumber polar scan analysis have been applied to study the characteristics of p coda and lg waves recorded at the regional arrays noress and arcess from presumed explosions on the northwestern russian platform and at test sites of novaya zemlya and eastern kazakh also recordings at the graefenburg array near the new geress regional array of novaya zemlya events and an eastern european platform white sea event have been compared with the norwegian array recordings of the same events the white sea explosion at distances of 14 and 22 from noress and graefenburg respectively exhibits lg rms amplitudes on incoherent beams that exceed those of sn however for explosions at novaya zemlya at 20 from noress and eastern kazakh at 30 from arcess the lg waves have much smaller amplitudes than sn in the case of novaya zemlya the lg wave is almost completely blocked at both noress and arcess but is well recorded at graefenburg this reduction of the lg amplitudes relative to those from events at longer distances cannot be accounted for by anelastic attenuation and spreading comparison of propagation paths suggests that the reduction in amplitudes may be due to blockage and scattering of lg in the barents sea analysis of sn coda waves on incoherent beams and continuous frequency wavenumber analysis polar scans suggests that they can result from lg to sn scattering from the coastline between the barents sea and scandinavia recent geologic studies have revealed significant variations in crustal structure in the barents sea basin which may cause the blockage of lg waves from novaya zemlya in the case of eastern kazakh explosions arcess incoherent beams show much reduced lg amplitudes relative to the p coda waves compared with noress even though the distance to arcess 31 is less than that to noress 38 this reduction in lg amplitude at both noress and arcess is accompanied by enhancement of p and sn coda the timing of the coda waves and the propagation paths suggest that lg waves may be partially blocked and scattered by the ural mountains and that the p and sn coda waves may result from lg to pn pn to sn sn to lg and lg to sn conversions from lateral heterogeneities in the crust beneath the urals the blockage is greater for the eastern kazakh to arcess path because it crosses the middle part of the urals whereas the eastern kazakh to noress path crosses the southern part of the urals chain these blockage effects seem to result from sudden lateral variations in shallow crustal structure such as variations in sediment thicknesses in the sedimentary basins of the russian platform and adjacent to the urals these blockage effects can be predicted from geologic studies and need to be accounted for when using lg amplitudes to estimate absolute yields of explosions and for event identification

modelling low frequency volcanic earthquakes in a viscoelastic medium with topography summary magma properties are fundamental to explain the volcanic eruption style as well as the generation and propagation of seismic waves this study focusses on magma properties and rheology and their impact on low frequency volcanic earthquakes we investigate the effects of anelasticity and topography on the amplitudes and spectra of synthetic low frequency earthquakes using a 2 d finite difference scheme we model the propagation of seismic energy initiated in a fluid filled conduit embedded in a homogeneous viscoelastic medium with topography we model intrinsic attenuation by linear viscoelastic theory and we show that volcanic media can be approximated by a standard linear solid sls for seismic frequencies above 2 hz results demonstrate that attenuation modifies both amplitudes and dispersive characteristics of low frequency earthquakes low frequency volcanic earthquakes are dispersive by nature however if attenuation is introduced their dispersion characteristics will be altered the topography modifies the amplitudes depending on the position of the seismographs at the surface this study shows that we need to take into account attenuation and topography to interpret correctly observed low frequency volcanic earthquakes it also suggests that the rheological properties of magmas may be constrained by the analysis of low frequency seismograms

melt origin of fault generated pseudotachylytes demonstrated by textures a petrographic and electron microprobe study of fault generated pseudotachylytes from the outer hebrides thrust zone scotland demonstrates that the textures have resulted from the primary crystallization of a clast laden melt rather than the devitrification of a glass or by crushing and cataclasis the observations are consistent with these pseudotachylytes having formed by frictional fusion followed by rapid quenching implying faulting at shallow crustal depths

timing of brittle deformation within the nojima fault zone japan abstract k ar ages from clay fault gouges of outcrop and core samples ug500 well from the nojima fault zone awaji island japan are consistent internally with established field constraints and with apatite and zircon fission track ages demonstrating the suitability of this method for dating of brittle deformation six unspiked and thirty conventional k ar data of clay minerals separated from gouge zones were analysed characterized by protoliths of high grade metamorphic and magmatic rocks the samples from the nojima fault zone offer the opportunity to distinct identify newly grown illite in the fault planes all dated sample fractions were characterized by xrd sem and tem k ar ages of 29 separates have an age range from 63 4 1 3 ma early palaeocene danian to 42 2 1 0 palaeogene middle eocene lutetian some

on the inversion of love and rayleigh wave dispersion and implications for earth structure and anisotropy summary various factors can make it difficult to explain observations of love and rayleigh wave dispersion with the same relatively simple isotropic model these factors include systematic errors which might occur in determinations of observed group and phase velocities lateral variations in structure along the path of travel and the attempt to explain observations with a model comprised of only a small number of thick layers the last of these factors is illustrated by an inversion of dispersion data in the central united states where shear wave anisotropy had previously been invoked as one way to explain incompatible love and rayleigh wave velocities it is shown that the data can be satisfied equally well by an isotropic model consisting of several thin layers in cases where the incompatibility of love and rayleigh wave data might be produced by intrinsic anisotropy it is necessary to invert those data using an anisotropic theory rather than by separate isotropic inversions of love and rayleigh waves inversions of fundamental mode data for a region of the pacific assuming anisotropic media in which the layers are transversely isotropic with a vertical axis of symmetry lead to models which are highly non unique even if the inversions solve only for shear velocities in the litho sphere and asthenosphere it is not possible without supplementary information to ascertain the depth interval over which anisotropy occurs or to determine the thickness of the lithosphere or asthenosphere with much precision

transitional continental oceanic structure beneath the norwegian sea from inversion of surface wave group velocity data summary we have analysed the fundamental mode of love and rayleigh waves generated by 12 earthquakes located in the mid atlantic ridge and jan mayen fracture zone using the multiple filter analysis technique we isolated the rayleigh and love wave group velocities for periods between 10 and 50 s the surface wave propagation paths were divided into five groups and average group velocities calculated for each group the average group velocities were inverted and produced shear wave velocity models that correspond to a quasi continental oceanic structure in the greenland norwegian sea region although resolution is poor at shallow depth we obtained crustal thickness values of about 18 km in the norwegian sea area and 9 km in the region between svalbard and iceland the abnormally thick crust in the norwegian sea area is ascribed to magmatic underplating and the thermal blanketing evect of sedimentary layers maximum crustal shear velocities vary between 3 5 and 3 9 km s 1 for most paths an average lithospheric thickness of 60 km was observed which is lower than expected for oceanic type structure of similar age we also observed low shear wave velocities in the lower crust and upper mantle we suggest that high heat flow extending to depths of about 30 km beneath the surface can account for the thin lithosphere and observed low velocities anisotropy coeycients of 1 5 per cent in the shallow layers and 7 per cent in the upper mantle point to the existence of polarization anisotropy in the region

hematite fault rock thermochronometry and textures inform fault zone processes abstract minerals on fault surfaces record fluid rock interaction strain and or heat during fault slip fault hosted hematite is amenable to u th he he thermochronometry hematite he dates reflect fault related processes or exhumation depending on hematite growth above or below the grain size controlled closure temperature and processes that promote open system behavior deconvolving these phenomena requires multi scale hematite textural characterization and constraints on the ambient thermal history from conventional thermochronometry two examples of this approach include investigations of hematite coated fault surfaces from exhumed damage zones in the seismically active wasatch fault zone wfz ut and painted canyon fault pcf paralleling the southern san andreas fault mecca hills ca wfz fault mirrors preserve sub m scale polygonal grain textures and hematite he data patterns that together with host rock apatite he data are consistent with localized friction generated heat hematite he loss and hematite recrystallization during damage zone seismicity

zircon fission track thermochronology and applications to fault studies zircon is one of the most useful minerals used to unravel the earth s history recorded in rocks after the success of etching fission tracks in zircon fleischer et al 1964 naeser 1969 krishnaswami et al 1974 early studies focused primarily on dating young volcanic horizons for stratigraphic purposes e g naeser et al 1973 hurford et al 1976 seward 1979 gleadow 1980 kowallis et al 1986 kohn et al 1992 subsequently fission track analysis of zircon has been extensively employed along with other radiometric dating methods such as u pb and u th he techniques e g davis et al 2003 reiners 2005 to understand the thermochronology of rocks in a variety of geological settings i e thermal history analysis of basement rocks for orogenic studies e g zeilter et al 1982 hurford 1986 kamp et al 1989 sorkhabi 1993 seward and mancktelow 1994 hasebe and tagami 2001 spikings et al 2001 thermochronology using detrital zircon grains in sedimentary rocks for provenance analysis and thermal history analysis in or near faults which will be highlighted below in this present chapter the thermal sensitivity of the zircon fission track thermochronometry is reviewed in the context of laboratory and field studies then laboratory procedures of the zircon fission track analysis using the external detector method are outlined as practiced in the fission track laboratory of kyoto university for basic fundamentals of these fission track analyses including data analysis and graphical displays see the chapter by tagami and o sullivan 2005 finally as an example of recent geological applications of the technique the results of zircon fission track analysis of the nojima fault zone japan are presented these rocks were the target of systematic drilling of an active fault system using five boreholes and a trench applications to other geological settings and the