reassessment of the rifting process in the western corinth rift from relocated seismicity the seismic activity in the western part of the corinth rift greece over the period 2000 2007 monitored by a dense network of three component stations is analysed in terms of multiplets and high precision relocation using double difference techniques this detailed analysis provides new insights into the geometry of faults at depth the nature and the structure of the active zone at 6 8 km depth previously interpreted as a possible detachment and more generally into the rifting process the seismicity exhibits a complex structure strongly varying along the rift axis the detailed picture of the seismic zone below the rift indicates that its shallower part at depths of 6 8 km is 1 1 5 km thick with a complex microstructure and that its deeper part at depths of 9 12 km gently dipping to the north 10 20 is 0 1 0 3 km thick with a microstructure consistent with the general slope of the structure although the nature of this seismic zone remains an open question the presence of seismicity beneath the main active area the strong variability of the structure along the rift over short distances and the complex microstructure of the shallower part revealed by the multiplet analysis are arguments against the hypothesis of a mature detachment under the rift this active zone more likely represents a layer of diffuse deformation the geometry of the mapped active faults is not well defined at depth as no seismicity is observed between 0 and 4 km except for the aigion fault rooting in the seismic layer at 6 km depth with a dip of 60 a distinct cloud of seismicity may be associated with the antithetic kalithea fault on which the 1909 fokis earthquake m s 6 3 may have occurred the link between the 1995 rupture m s 6 2 and the faults known at the surface has been better constrained as the relocated seismicity favours a rupture on an offshore blind fault dipping at 30 rather than on the deeper part of the east helike fault consequently the 1995 event is expected to have decreased the coulomb stress on the east helike fault to explain these seismic observations along with the geodetic observations a new mechanical model for the rifting process in this region is proposed involving non elastic mostly aseismic uniform ns opening below the rift axis coupled with the downward and northward growth of a yet immature detachment the reported gps rates would mainly result from this deep silent source and the seismicity would reveal the detachment position not yet connected to the ductile lower crust in such a model the strong fluctuations of microseismicity would result from small strain instabilities undetected by continuous gps and possibly related to pore pressure transients

litho1 0 an updated crust and lithospheric model of the earth we present the litho1 0 model which is a 1 tessellated model of the crust and uppermost mantle of the earth extending into the upper mantle to include the lithospheric lid and underlying asthenosphere the model is parameterized laterally by tessellated nodes and vertically as a series of geophysically identified layers such as water ice sediments crystalline crust lithospheric lid and asthenosphere litho1 0 is created by constructing an appropriate starting model and perturbing it to fit high resolution surface wave dispersion maps love and rayleigh group and phase over a wide frequency band 5 40 mhz we examine and discuss the model with respect to key lithospheric parameters such as average crustal velocity crustal thickness upper mantle velocity and lithospheric thickness we then compare the constructed model to those from a number of select studies at regional and global scales and find general consistency it appears that litho1 0 represents a reasonable starting model of the earth s shallow structure crust and uppermost mantle for the purposes in which these models are used such as traveltime tomography or in efforts to create a 3 d reference earth model the model matches surface wave dispersion over a frequency band wider than the band used in the inversion there are several avenues for improving the model in the future by including attenuation and anisotropy as well as making use of surface waves at higher frequency

persistent scatterer interferometric synthetic aperture radar for crustal deformation analysis with application to volcan alcedo galapagos 1 while conventional interferometric synthetic aperture radar insar is a very effective technique for measuring crustal deformation almost any interferogram includes large areas where the signals decorrelate and no measurement is possible persistent scatterer ps insar overcomes the decorrelation problem by identifying resolution elements whose echo is dominated by a single scatterer in a series of interferograms existing ps methods have been very successful in analysis of urban areas where stable angular structures produce efficient reflectors that dominate background scattering however man made structures are absent from most of the earth s surface furthermore existing methods identify ps pixels based on the similarity of their phase history to an assumed model for how deformation varies with time whereas characterizing the temporal pattern of deformation is commonly one of the aims of any deformation study we describe here a method for ps analysis stamps that uses spatial correlation of interferogram phase to find pixels with low phase variance in all terrains with or without buildings prior knowledge of temporal variations in the deformation rate is not required for their identification we apply stamps to volcan alcedo where conventional insar fails because of dense vegetation on the upper volcano flanks that causes most pixels to decorrelate with time we detect two sources of deformation the first we model as a contracting pipe like body which we interpret to be a crystallizing magma chamber the second is downward and lateral motion on the inner slopes of the caldera which we interpret as landsliding

earthquake mechanisms of the adriatic sea and western greece implications for the oceanic subduction continental collision transition summary we present 21 focal solutions magnitude 5 5 reliably computed by body wave modelling for the western hellenic arc from yugoslavia to the southern peloponnese mechanisms located within the aegean show normal faulting the t axis trending n s in the centre and parallel to the active boundary in the external part mechanisms associated with the keffalinia fault are consistent with dextral strike slip motion reverse mechanisms located along the active boundary are remarkably consistent and do not depend on the nature of the active boundary continental collision or oceanic subduction the consistency in azimuth of the slip vectors and of the gps velocity relative to africa all along the active boundary suggests that the deformation is related to the same motion the discrepancy between seismic energy release and the amount of shortening confirms that the continental collision is achieved by seismic slip on faults but the oceanic subduction is partially aseismic the northward decrease in velocity between continental collision and oceanic subduction suggests the continental collision to be a recent evolution of the active subduction

speleothem architectural analysis integrated approach for stalagmite based paleoclimate research this work was supported by the r d i program of spain cgl2013 43257 r and the universidad complutense de madrid research group 910198

origin timing and temperature of secondary calcite silica mineral formation at yucca mountain nevada the origin of secondary calcite silica minerals in primary and secondary porosity of the host miocene tuffs at yucca mountain has been hotly debated during the last decade proponents of a high level nuclear waste repository beneath yucca mountain have interpreted the secondary minerals to have formed from cool descending meteoric fluids in the vadose zone critics citing the presence of two phase fluid inclusions argued that the minerals could only have formed in the phreatic zone from ascending hydrothermal fluids understanding the origin temperature and timing of these minerals is critical in characterizing geologically recent fluid flux at the site and has significant implications to whether waste should be stored at yucca mountain petrographic and paragenetic studies of 155 samples collected from the exploratory studies facility esf and repository block cross drift ecrb tunnels indicate that heterogeneously distributed calcite with lesser chalcedony quartz opal and fluorite comprise the oldest secondary minerals these are typically overgrown by intermediate aged calcite often exhibiting distinctive bladed habits the youngest event recorded across the site is the deposition of mg enriched up to 1 wt and depleted growth zoned calcite intergrown with u enriched opal the cyclical variation in mg enrichment and depletion is probably related to climate changes that have occurred during the last few million years the distribution of secondary minerals is consistent with precipitation in the vadose zone fluid inclusion petrography of sections from the 155 samples determined that 96 of the fluid inclusion assemblages fias contained liquid only inclusions that formed at ambient temperatures 35 c however 50 of the samples n 78 contained relatively rare fia that contain both liquid only and liquid plus vapor inclusions herein termed two phase fias that formed at temperatures above 35 c virtually all of these two phase fias occur in paragenetically old calcite rare two phase inclusion assemblages were also observed in early fluorite and quartz and early intermediate calcite homogenization temperatures trapping temperatures across yucca mountain are generally 45 to 60 c but higher temperatures reaching 83 c were recorded in calcite from the north portal and ramp of the esf cooler temperatures of 35 to 45 c were recorded in the intensely fractured zone multiple populations of two phase fias from lithophysal cavities in the esf and ecrb cross drift indicate early fluid cooling with time from temperatures 45 c in early calcite to 35 to 45 c in paragenetically younger calcite freezing point depressions range from 0 2 to 1 6 c indicating trapping of a low salinity fluid the majority of intermediate calcite and all outermost mg enriched calcite contains rare all liquid inclusions and formed from ambient temperature 35 c fluids carbon and oxygen isotope data reveal a consistent trend of decreasing 13 c from 9 5 to 8 5 and increasing 18 o from 5 2 to 22 1 values from paragenetically early calcite to mg enriched growth zoned calcite depleted d values 131 to 90 of inclusion fluids from intermediate and the youngest mg enriched calcite indicate derivation from surface meteoric fluids recalculation of 18 oh2o values of 12 to 10 is consistent with derivation from paleometeoric fluids results of integrated u pb dating opal and chalcedony and fluid inclusion microthermometry indicate that two phase fias that trapped fluids of 50 c are older than 6 29 0 30 ma two phase fias in parage netically later calcite which formed from fluids of 35 to 45 c are older than 5 32 0 02 ma there is no evidence for trapping of fluids with elevated temperatures during the past 5 32 my the youngest mg enriched calcite intergrown with opal began to precipitate between about 1 9 to 2 9 ma and has continued to precipitate within the past half million years the presence of liquid only inclusions and the consistent occurrence of mg enriched calcite and opal as the youngest event indicate a minor but chemically distinct ambient temperature 35 c fluid flux during the past 2 to 3 my copyright 2003 elsevier science ltd

seismicity deformation and seismic hazard in the western rift of corinth new insights from the corinth rift laboratory crl this paper presents the main recent results obtained by the seismological and geophysical monitoring arrays in operation in the rift of corinth greece the corinth rift laboratory crl is set up near the western end of the rift where instrumental seismicity and strain rate is highest the seismicity is clustered between 5 and 10 km defining an active layer gently dipping north on which the main normal faults mostly dipping north are rooting it may be interpreted as a detachment zone possibly related to the phyllade thrust nappe young active normal faults connecting the aigion to the psathopyrgos faults seem to control the spatial distribution of the microseismicity this seismic activity is interpreted as a seismic creep from gps measurements which shows evidence for fast continuous slip on the deepest part on the detachment zone offshore either the shallowest part of the faults is creeping or the strain is relaxed in the shallow sediments as inferred from the large ns strain gradient reported by gps the predicted subsidence of the central part of the rift is well fitted by the new continuous gps measurements the location of shallow earthquakes between 5 and 3 5 km in depth recorded on the on shore helike and aigion faults are compatible with 50 and 60 mean dip angles respectively the offshore faults also show indirect evidence for high dip angles this strongly differs from the low dip values reported for active faults more to the east of the rift suggesting a significant structural or rheological change possibly related to the hypothetical presence of the phyllade nappe large seismic swarms lasting weeks to months seem to activate recent synrift as well as pre rift faults most of the faults of the investigated area are in their latest part of cycle so that the probability of at least one moderate to large earthquake m 6 to 6 7 is very high within a few decades furthermore the region west to aigion is likely to be in an accelerated state of extension possibly 2 to 3 times its mean interseismic value high resolution strain measurement with a borehole dilatometer and long base hydrostatic tiltmeters started end of 2002 a transient strain has

the geohydrologic setting of yucca mountain nevada abstract this paper provides a geologic and hydrologic framework of the yucca mountain region for the geochemical papers in this volume the regional geologic units which range in age from late precambrian through holocene are briefly described yucca mountain is composed of dominantly pyroclastic units that range in age from 11 4 to 15 2 ma the principal focus of study has been on the paintbrush group which includes two major zoned and welded ash flow tuffs separated by an important hydrogeologic unit referred to as the paintbrush non welded ptn the regional structural setting is currently one of extension and the major local tectonic domains are presented together with a tectonic model that is consistent with the known structures at yucca mountain streamflow in this arid to semi arid region occurs principally in intermittent or ephemeral channels near yucca mountain the channels of fortymile wash and amargosa river collect infrequent runoff from tributary basins ultimately draining to death valley beneath the surface large scale interbasin flow of groundwater from one valley to another occurs commonly in the region regional groundwater flow beneath yucca mountain originates in the high mesas to the north and returns to the surface either in southern amargosa desert or in death valley where it is consumed by evapotranspiration the water table is very deep beneath the upland areas such as yucca mountain where it is 500 750 m below the land surface providing a large thickness of unsaturated rocks that are potentially suitable to host a nuclear waste repository the nature of unsaturated flow processes which are important for assessing radionuclide migration are inferred mainly from hydrochemical or isotopic evidence from pneumatic tests of the fracture systems and from the results of in situ experiments water seeping down through the unsaturated zone flows rapidly through fractures and more slowly through the pores of the rock matrix although capillary forces are expected to divert much of the flow around repository openings some may drip onto waste packages ultimately causing release of radionuclides followed by transport down to the water table

genesis and microstratigraphy of calcite coralloids analysed by high resolution imaging and petrography abstract the genesis of calcite coralloid speleothems from lamalunga cave southern italy is here investigated from a purely petrographic perspective which constitutes the basis for any subsequent chemical investigation lamalunga cave coralloids formed on bones and debris on the floor of the cave they consist of elongated columnar crystals whose elongation progressively increases from the flanks to the tips of the coralloid forming a succession of lens shaped layers which may be separated by micrite or impurity rich layers organic molecules are preferentially concentrated toward the centre of convex lenses as highlighted by epifluorescence their occurrence on cave floor lens shaped morphology and concentration of impurities toward the apex of the convex lenses supports the hypothesis that their water supply was hydroaerosol generated by the fragmentation of cave drips evaporation and degassing preferentially occurred on tips enhancing the digitated morphology and trapping the organic molecules and impurities carried by the hydroaerosol between the growing crystals which became more elongated micrite layers that cap some coralloid lenses likely identify periods when decreasing in hydroaerosol resulted in stronger evaporation and higher supersaturation with respect to calcite of the parent film of fluid this interpretation of coralloid formation implies that these speleothems can be used to extract hydroclimate information

continuing evolution of the pacific juan de fuca north america slab window system a trench ridge transform example from the pacific rim abstract many subduction margins that rim the pacific ocean contain complex records of cenozoic slab window volcanism combined with tectonic disruption of the continental margin the series of slab windows that opened beneath california and mexico starting about 28 5 ma resulted from the death of a series of spreading ridge segments and led to piecewise destruction of a subduction regime the timing and areal extent of the resultant slab window volcanism provide constraints on models that depict the subsequent fragmentation and dispersal of the overlying continental margin the initial pioneer slab window thermally weakened the overlying western transverse ranges and california borderlands region starting about 28 5 ma a second thermal pulse occurred in the same region starting about 19 ma during growth of the monterey slab window this additional heating combined with the capture of a partially subducted monterey plate fragment by the cocos plate initiated the pulling apart and rotation of the adjacent continental margin similarly the capture of guadalupe and magdalena plate fragments by the pacific plate and initiation of the guadalupe magdalena slab window about 12 5 ma are coeval with baja california pulling away from the mexico continental margin with the break along the comondu arc in crust already thermally weakened by about 10 my of volcanism in coastal california distributed crustal extension and subsidence accompanied the new transform plate boundary and continued until the slab windows cooled and plate motion coalesced along a through going system of strike slip faults the transform boundary continues to evolve and forward modeling predicts an instability with the current configuration as a result of convergence between the sierra nevada and peninsular ranges batholiths starting about 2 my in the future the instability may be resolved by a shift in the locus of transform motion from the san andreas fault to the eastern california shear zone or by breaking off another fragment of the mojave or southern sierra nevada crustal blocks and translating it northward

subduction of the south chile active spreading ridge a 17 ma to 3 ma magmatic record in central patagonia western edge of meseta del lago buenos aires argentina abstract the chile triple junction is a natural laboratory to study the interactions between magmatism and tectonics during the subduction of an active spreading ridge beneath a continent the mlba plateau meseta del lago buenos aires is one of the neogene alkali basaltic plateaus located in the back arc region of the andean cordillera at the latitude of the current chile triple junction the genesis of mlba can be related with successive opening of slabs windows beneath patagonia within the subducting nazca plate itself and between the nazca and antarctic plates detailed 40ar 39ar dating and geochemical analysis of bimodal magmatism from the western flank of the mlba show major changes in the back arc magmatism which occurred between 14 5 ma and 12 5 ma with the transition from calc alkaline lavas cerro plomo to alkaline lavas mlba in relation with slab window opening in a second step at 4 3 ma alkaline felsic intrusions were emplaced in the western flank of the mlba coevally with the mlba basalts with which they are genetically related these late oib like alkaline to transitional basalts were generated by partial melting of the subslab asthenosphere of the subducting nazca plate during the opening of the south chile spreading ridge related slab window these basalts differentiated with small amounts of assimilation in shallow magma chambers emplaced along transtensional to extensional zones the close association of bimodal magmatism with extensional tectonic features in the western mlba is a strong support to the model of patagonian collapse event proposed to have taken place between 5 and 3 ma as a consequence of the presence of the asthenospheric window scr 1 segment of south chile ridge below the mlba area

along strike changes in the structural evolution over a brittle detachment fault example of the pleistocene corinth patras rift greece abstract the patras corinth and northern saronic gulfs occupy a 200 km long n120 trending pleistocene rift zone where peloponnese drifts away from mainland greece the axes of patras and corinth basins are 25 km apart and linked by two transfer fault zones trending n040 the older one defines the western slope of panachaikon mountain and the younger one limits the narrow rion patras littoral plain between these two faults the ca 4 km thick rion patras series dips 20 30 ssw it is part of the patras gulf synrift deposits which pile in an asymmetric basin governed by a fault dipping ca 25 35 nne located in the southern gulf of patras mapping of this fault to the east in northern peloponnese shows that it is an inactive north dipping low angle normal fault 0 to 30 n called the northern peloponnese major fault npmf the structural evolution of the npmf was different in the gulfs of patras and corinth in the gulf of patras it is still active in northern peloponnese footwall uplift and coeval southward tilting flattened the fault and locked its southern part steeper normal faults formed north of the locked area connecting the still active northern part of the npmf to the surface after several locks the presently active normal faults psathopyrgos aigion helike trend along the southern shore of the gulf of corinth this migration of faults caused the relative 25 km northward shift of the corinth basin and the formation of ne sw trending transfer faults between the corinth and patras gulfs

improved spatial resolution for u series dating of opal at yucca mountain nevada usa using ion microprobe and microdigestion methods two novel methods of in situ isotope analysis ion microprobe and microdigestion were used for 230th u and 234u 238u dating of finely laminated opal hemispheres formed in unsaturated felsic tuff at yucca mountain nevada proposed site for a high level radioactive waste repository both methods allow analysis of layers as many as several orders of magnitude thinner than standard methods using total hemisphere digestion that were reported previously average growth rates calculated from data at this improved spatial resolution verified that opal grew at extremely slow rates over the last million years growth rates of 0 58 and 0 69 mm m y were obtained for the outer 305 and 740 m of two opal hemispheres analyzed by ion microprobe and 0 68 mm m y for the outer 22 m of one of these same hemispheres analyzed by sequential microdigestion these pleistocene growth rates are 2 to 10 times slower than those calculated for older secondary calcite and silica mineral coatings deposited over the last 5 to 10 m y dated by the u pb method and may reflect differences between miocene and pleistocene seepage flux the microdigestion data also imply that opal growth rates may have varied over the last 40 k y these data are the first indication that growth rates and associated seepage in the proposed repository horizon may correlate with changes in late pleistocene climate involving faster growth during wetter cooler climates glacial maximum slower growth during transition climates and no growth during the most arid climate modern data collected at this refined spatial scale may lead to a better understanding of the hydrologic variability expected within the thick unsaturated zone at yucca mountain over the time scale of interest for radioactive waste isolation

velocity and deformation fields in the north aegean domain greece and implications for fault kinematics derived from gps data 1993 2009 abstract gps rates based on data of an extended continuous and campaign type gps network in the north aegean domain are presented the data processed for the time period 1993 2009 is used to analyze the complex kinematic and deformation fields in the north aegean sea and adjacent regions the presence of slowly deforming areas is investigated southern bulgaria eastern macedonia and thrace move uniformly southward relative to eurasia 1 5 3 5 mm yr western macedonia epirus thessaly and central greece rotate rather coherently clockwise the region comprising the islands of limnos agios efstratios and alonnisos moves like a counterclockwise rotating slowly deforming block the new gps rates allow a quantification of the spatial change of strike slip motion and locking depth along the north aegean trough dextral strike slip motion diminishes from east toward west amounting to 21 2 mm yr along the saros basin and 12 5 mm yr south of the chalkidiki peninsula less than 5 mm yr 50 nstrain yr shear strain rate is transferred from the sporades islands pelion toward northern evia the locking depth is shallow for the ganos fault and the western saros basin 5 6 8 9 km it is deeper between the sporades islands and pelion 17 7 km corresponding to a more diffuse shear zone an elementary finite element model is applied to derive slip rates of the three main ene wsw to ne sw trending dextral strike slip faults in the north aegean large scale n s to nne ssw extension in the north aegean domain is analyzed by employing finite element and gps based strain rate analyses pronounced extension 100 nstrain is associated with known tectonic structures e g mygdonian graben northern gulf of evia in offshore areas such as the sporades basin the correspondence between gps derived extension rates and active fault structures is not entirely evident however important constraints are provided for seismotectonic interpretations

source side shear wave splitting and upper mantle flow in the chile ridge subduction region the actively spreading chile ridge has been subducting beneath patagonian chile since the middle miocene after subduction continued separation of the faster nazca plate from the slow antarctic plate has opened up a gap a slab window between the subducted oceanic lithospheres beneath south america we examined the form of the asthenospheric mantle flow in the vicinity of this slab window using s waves from six isolated unusual 2007 earthquakes that occurred in the generally low seismicity region just north of the ridge subduction region the s waves from these earthquakes were recorded at distant seismic stations but were split into fast and slow orthogonally polarized waves at upper mantle depths during their passage through the slab window and environs we isolated the directions of fast split shear waves near the slab window by correcting for upper mantle seismic anisotropy at the distant stations the results show that the generally trench parallel upper mantle flow beneath the nazca plate rotates to an ene trend in the neighborhood of the slab gap consistent with upper mantle flow from west to east through the slab window

active tectonics of the north and central aegean sea summary in this paper we examine the connection between the westward motion of turkey relative to europe and the extension in and around the aegean sea the principal new data available since the last attempt to synthesize the tectonics of this region by mckenzie 1978 are much improved focal mechanisms of earthquakes constrained by p and sh body wave modelling as well as by first motions these mechanisms show that the faulting in the western part of the aegean region is mostly extensional in nature on normal faults with a nw to wnw strike and with slip vectors directed nnw to nne there is evidence from palaeomagnetism that this western region rotates clockwise relative to stable europe in the central and eastern aegean and in nw turkey distributed right lateral strike slip is more prevalent on faults trending ne to ene and with slip vectors directed ne palaeomagnetic data in this eastern region is more ambiguous but consistent with very small or no rotations in the northern part and possibly anticlockwise rotations relative to europe in the south the strike slip faulting that enters the central aegean from the east appears to end abruptly in the sw against the nw trending normal faults of greece the kinematics of the deformation is controlled by three factors the westward motion of turkey relative to europe the continental collision between nw greece albania and the apulia adriatic platform in the west and the presence of the hellenic subduction zone to the south as the right lateral slip on the north anatolian fault enters the aegean region it splays out becoming distributed on several parallel faults the continental shortening in nw greece and albania does not allow the rotation of the western margin of the region to be rapid enough to accommodate this distributed e w right lateral shear and thus leads to e w shortening in the northern aegean which is compensated by n s extension as the southern aegean margin can move easily over the hellenic subduction zone the dynamics of the system once initiated is self sustaining being driven by the high topography in eastern turkey and by the roll back of the subducted slab beneath the southern aegean the geometry of the deformation resembles the behaviour of a system of broken slats attached to margins that rotate in spite of its extreme simplicity a simple model of such broken slats is able to reproduce quantitatively most of the features of the instantaneous velocity field in the aegean region including the slip vectors and nature of the faulting in the eastern and western parts the senses and approximate rates of rotation the overall extensional velocity across the aegean and the distribution of strain rates as seen in the seismicity and topography or bathymetry and using geodetic measurements as part of this study we re examined the relation between the surface faulting and the focal parameters determined seismologically for the three large 1981 gulf of corinth earthquakes and reassessed the evidence for associating particular earthquakes in the sequence with observed surface faulting an important result is that in one of the events there is a resolvable discrepancy between the slip vector measured at the surface and that determined from the seismic body waves

evolution of the san jorge basin argentina the san jorge basin although small is the most important hydrocarbon producing basin in argentina remaining untested potential is high because of the presence of good source rock favorable structural complexity and multiple reservoirs reservoir quality is commonly low because of the highly tuffaceous sandstones the sedimentary fill of the basin is closely related to its tectonic history northwest southeast trending grabens formed and filled during a triassic and early jurassic early rift phase climaxing with a pervasive middle jurassic volcanic episode continued growth and filling of the basin occurred during a late jurassic earliest cretaceous late rift phase and cretaceous early and late sag phases late cretaceous early tertiary extension set up many of the present day structural traps along normal faults middle tertiary andean compression produced the narrow north south san bernardo structural belt which exhibits reversed movement on older normal graben bounding faults and on local low angle thrust faults marked early to middle tertiary erosion produced a significant unconformi y within cretaceous beds around basin margins origin of upper jurassic and lowermost cretaceous sedimentary fill is primarily lacustrine or fluvial in origin lacustrine organic rich black shales are fringed by oolitic and other limestones and fluvial deltaic sandstones derived mostly from the north a significant southern source of sand existed during the valanginian interbedded marine shales occur mostly to the west toward a presumed marine seaway connection to the northern magallanes basin middle to upper cretaceous sedimentary rocks sourced mostly from the north are mainly fluvial sandstone shale successions with some minor lacustrine influence reservoir quality glauconitic sands were deposited during a late cretaceous early tertiary marine incursion from the atlantic after development of a lower tertiary regional unco formity relatively undisturbed younger tertiary sediments completed the basin fill lower cretaceous lacustrine shales of the d 129 formation are the best source rocks yet identified however most hydrocarbon production occurs above the source in middle and upper cretaceous sandstones along the basin flanks the most obvious hydrocarbon emplacement mechanism is vertical migration along reactivated graben faults

thermal anomaly near the aigio fault gulf of corinth greece maybe due to convection below the fault a thermal profile has been measured in a 1000 m deep borehole intersecting the active aigio fault corinth rift greece the heat flow is 53 mw m 2 indicating that the rifting process has no effect in heat flow the temperature near the fault is higher than expected from a pure conductive model this discrepancy is not due to fluid flow above the fault as shown by the long term monitoring of downhole pressure neither can it be attributed to the fault slip since the aigio fault is a minor normal fault of the rift with no very recent earthquake we propose that the anomaly is due to the convection within the karst that constitutes the footwall numerical simulations give a correct estimate for the recorded temperature increase this is an extreme case of thermal disturbance induced near a fault by local fluid circulation the occurrence of convection outside geothermal area is very rare

calcite fabrics growth mechanisms and environments of formation in speleothems from the italian alps and southwestern ireland five fabrics were identified in alpine and irish caves on the basis of morphological and microstructural characteristics and re lated to growth mechanisms and growth environment columnar and fibrous fabrics grow when speleothems are continuously wet and from fluids at near equilibrium conditions low supersaturation sicc 0 35 through the screw dislocation mechanism the highly defective microcrystalline fabrics form at the same supersaturation range as co lumnar fabric but under variable discharge and the presence of growth inhibitors dendritic fabrics which have the highest density of crystal defects develop in disequilibrium conditions high supersaturation un der periodic very low flow regime periods that result in prolonged out gassing cave calcareous tufa forms in disequilibrium conditions only the calcite crystals of fabrics formed at low supersaturation seem to precipitate near isotopic equilibrium conditions

traces of epigenetic hydrothermal activity at yucca mountain nevada preliminary data on the fluid inclusion and stable isotope evidence samples of opal quartz calcite crusts from the 7 8 km long tunnel excavated under yucca mountain were studied to determine their origin calcite in these crusts commonly forms relatively large up to 1 5 cm euhedral crystal terminations in some crusts layers of chalcedony and patches of opal alternate with calcite layers chalcedony commonly grades into euhedral quartz crystals quartz also forms microdruses of individual crystals up to 8 mm in size fluorite was identified in four samples fluid inclusion studies on calcite revealed formation temperatures of 35 85 c gas filled inclusions are apparently of low density p 1 bar at room temperature and contain aromatic hydrocarbons in four studied calcite samples values of 18o remain virtually constant across crusts 10 6 to 12 1 v pdb in one sample the earliest part of calcite had 18o of 19 in this part of the sample the highest fluid inclusion temperatures 70 85 c were measured the secondary calcite found at yucca mountain is commonly interpreted as being formed through a pedogenic process from rain waters percolating in the vadose zone and carrying dissolved carbonate from overlying soils e g stuckless j s peterman z e muchs d r 1991 u and sr isotopes in ground water and calcite yucca mountain nevada evidence against upwelling water science 254 551 554 nas nrc 1992 ground water at yucca mountain how high can it rise national academy press washington dc roedder e whelan j f vaniman d t 1994 fluid inclusion studies of calcite veins from yucca mountain nevada tuffs environment of formation high level radioactive waste management proc int conf am nucl soc la grande park il pp 1854 1860 our data indicate that the calcite opal quartz with minor fluorite crusts from the presently unsaturated vadose zone of yucca mountain were formed from low temperature hydrothermal aqueous fluids in the saturated phreatic environment the issue has direct bearing on the suitability of yucca mountain as a site for permanent geological disposal of the high level nuclear waste

testing theoretically predicted stalagmite growth rate with recent annually laminated samples implications for past stalagmite deposition annually laminated stalagmites deposited over the last 30 160 years are analysed to determine their growth rate three natural and artificial cave sites in england france and belgium were chosen for their wide range of variability in growth rate determining variables and multiple samples were taken from each site the annual nature of laminae deposition within the stalagmite calcite was confirmed by comparison to the date of cave void opening 14c analyses or by using dated event horizons measured stalagmite growth rate was determined from annual laminae thickness measurements and compared to that theoretically predicted from the chemical kinetics of the calcite precipitation reaction a good agreement is observed between empirical observations and theoretical predictions although two complicating factors variations in calcite porosity and seasonal cessation of the water supply to the samples both affect the growth rate implications for the extraction of palaeoclimate information from stalagmite growth rate are discussed

understanding the genesis of nonmarine calcite deposits through quadrupole mass spectrometric analysis of fluid inclusion gases abstract quadrupole mass spectroscopy was used to analyze fluid inclusion volatiles in different types of nonmarine calcites including travertines phreatic calcretes hydrothermal vein calcites and pedogenic calcites the objectives of the study were to determine if there were any diagnostic or characteristic differences between the inclusion volatiles from the different calcites and to see if the quadrupole results could be used to understand the processes and environmental conditions that controlled calcite precipitation the calcites formed under saturated conditions have water dominated inclusions with well constrained n 2 ar ratios and either co 2 or n 2 as the dominant inclusion gas some calcretes and travertines were exceptions to the above characteristics but it is likely that these were subjected to secondary precipitation in an environment different from the primary precipitation phase results for the pedogenic calcites are quite different from calcites formed in water saturated systems pedogenic calcites have gas dominated water poor inclusions unexpectedly large ch 4 contents low o 2 contents and highly variable n 2 ar ratios the dominance of ch 4 and low o 2 contents in the pedogenic calcites suggest that anaerobic conditions occurred during at least part of the precipitation process scanning electron microscope sem examination of the pedogenic calcites shows fungal remains bacteria like forms and gels from fungi or plant roots the quadrupole and sem results suggest pedogenic calcite precipitation occurred as a result of aerobic and ultimately anaerobic microbial decay processes

erratum to reply to the comment on physical and stable isotope evidence for formation of secondary calcite and silica in the unsaturated zone yucca mountain nevada by y v dublyansky s e smirnov and g p palyanova applied geochemistry 19 2004 1879 1889

time dependent land uplift and subsidence in the santa clara valley california from a large interferometric synthetic aperture radar data set 1 we invert 115 differential interferograms derived from 47 synthetic aperture radar sar scenes for a time dependent deformation signal in the santa clara valley california the time dependent deformation is calculated by performing a linear inversion that solves for the incremental range change between sar scene acquisitions a nonlinear range change signal is extracted from the ers insar data without imposing a model of the expected deformation in the santa clara valley cumulative land uplift is observed during the period from 1992 to 2000 with a maximum uplift of 41 18 mm centered north of sunnyvale uplift is also observed east of san jose seasonal uplift and subsidence dominate west of the silver creek fault near san jose with a maximum peak to trough amplitude of 35 mm the pattern of seasonal versus long term uplift provides constraints on the spatial and temporal characteristics of water bearing units within the aquifer the silver creek fault partitions the uplift behavior of the basin suggesting that it acts as a hydrologic barrier to groundwater flow while no tectonic creep is observed along the fault the development of a low permeability barrier that bisects the alluvium suggests that the fault has been active since the deposition of quaternary units

pedogenesis of siliceous calcretes at yucca mountain nevada abstract siliceous calcretes in faults near yucca mountain nevada have been interpreted by some observers as evidence of seismically triggered eruptions of deep water such an origin could have important consequences if yucca mountain is developed as an unsaturated site for disposal of high level nuclear waste at odds with this hypothesis are the absence of features that should be present at fault fed springs e g fissure ridge mounds with microterraces and the preservation within root casts of delicate pedogenic microfossils such as calcified filaments and needle fiber calcites chemical evidence of pedogenic origin is found in fe and sc enrichments that require prior weathering of detritus in the calcretes as opposed to direct incorporation of adjacent unweathered bedrock carbonate and silica abundances and accumulation rates are well within the scope of pedogenic processes sources of carbonate are eolian whereas silica is derived in part by dissolution of local volcanic glasses but also by extensive dissolution of unstable silica minerals tridymite and cristobalite that are abundant in the local tuffs the siliceous calcretes at yucca mountain are pedogenic and provide no evidence in support of conjectured spring activity

scattered wave imaging of the lithosphere asthenosphere boundary several recent studies have imaged discontinuities interpreted as the lithosphere asthenosphere boundary using receiver function methods these are exciting results since this boundary is fundamental and yet relatively elusive its location is not well imaged nor are its properties well understood the receiver function method provides high depth resolution and the multitude of studies using this method have increased lateral resolution a better global understanding of the location and nature of the boundary is developing which ultimately will have implications for mantle dynamics and planetary evolution however these new results do not all form a clear and consistent picture and in some cases introduce new complexities and questions some apparent contradictions may represent unmodeled earth structure overall interpretation and synthesis requires careful consideration of the approaches and sensitivities of individual studies

limited hydrologic response to pleistocene climate change in deep vadose zones yucca mountain nevada abstract understanding the movement of water through thick vadose zones especially on time scales encompassing long term climate change is increasingly important as societies utilize semi arid environments for both water resources and sites viewed as favorable for long term disposal or storage of hazardous waste hydrologic responses to pleistocene climate change within a deep vadose zone in the eastern mojave desert at yucca mountain nevada were evaluated by uranium series dating of finely layered hyalitic opal using secondary ion mass spectrometry opal is present within cm thick secondary hydrogenic mineral crusts coating floors of lithophysal cavities in fractured volcanic rocks at depths of 200 to 300 m below land surface uranium concentrations in opal fluctuate systematically between 5 and 550 g g age calibrated profiles of uranium concentration correlate with regional climate records over the last 300 000 years and produce time series spectral peaks that have distinct periodicities of 100 and 41 ka consistent with planetary orbital parameters these results indicate that the chemical compositions of percolating solutions varied in response to near surface climate driven processes however slow micrometers per thousand years relatively uniform growth rates of secondary opal and calcite deposition spanning several glacial interglacial climate cycles imply that water fluxes in the deep vadose zone remained low and generally buffered from the large fluctuations in available surface moisture during different climates

the galaxidi earthquake of 18 november 1992 a possible asperity within the normal fault system of the gulf of corinth greece the galaxidi earthquake that occurred in the gulf of corinth on 18 november 1992 was not followed by a noticeable aftershock sequence a fact that was also observed for the 1965 eratini event in the same area the temporary network of 35 stations that we installed 5 days after the mainshock did not help to identify a cluster of activity related to the mainshock in a section across the epicentral zone the focal mechanism of the mainshock and the distribution of a few aftershocks define a plane dipping north consistent with the nearby helike fault we propose that the galaxidi earthquake was related to an asperity located between the helike and xilo kastro faults

episodic caldera volcanism in the miocene southwestern nevada volcanic field revised stratigraphic framework 40ar 39ar geochronology and implications for magmatism and extension the middle miocene southwestern nevada volcanic field swnvf is a classic example of a silicic multicaldera volcanic field in the great basin more than six major calderas formed between 15 and 7 5 ma the central swnvf caldera cluster consists of the overlapping silent canyon caldera complex the claim canyon caldera and the timber mountain caldera complex active from 14 to 11 5 ma and centered on topographic timber mountain locations of calderas older than the claim canyon caldera source of the tiva canyon tuff are uncertain except where verified by drilling younger peralkaline calderas black mountain and stonewall mountain formed northwest of the central swnvf caldera cluster we summarize major revisions of the swnvf stratigraphy that provide for correlation of lava flows and small volume tuffs with the widespread outflow sheets of the swnvf new laser fusion 40 ar 39 ar isotopic ages are used to refine and revise the timing of eruptive activity in the swnvf the use of high sensitivity mass spectrometry allowed analysis of submilligram sized samples with analytical uncertainties of 0 3 1 permitting resolution of age differences as small as 0 07 ma these results confirm the revised stratigraphic succession and document a pattern of episodic volcanism in the swnvf major caldera episodes belted range crater flat paintbrush timber mountain and thirsty canyon groups erupted widespread ash flow sheets within 100 300 k y time spans and pre and post caldera lavas erupted within 100 300 k y of the associated ash flows peak volcanism in the swnvf occurred during eruption of the paintbrush and timber mountain groups when over 4500 km 3 of metaluminous magma was erupted in two episodes within 1 35 m y separated by a 750 k y magmatic gap peralkaline and metaluminous magmatism in the swnvf overlapped in time and space the peralkaline tub spring and grouse canyon tuffs erupted early and the peralkaline thirsty canyon group tuffs and stonewall flat tuff erupted late in the history of the swnvf flanking the central volumetrically dominant peak of metaluminous volcanism magma chemistry transitional between peralkaline and metaluminous magmas is indicated by petrographic and chemical data particularly in the overlapping grouse canyon and area 20 calderas of the silent canyon caldera complex volcanism in the swnvf coincided with the miocene peak of extensional deformation in adjoining parts of the great basin although regional extension was concurrent with volcanism it was at a minimum in the central area of the swnvf where synvolcanic faulting was dominated by intra caldera deformation significant stratal tilting and paleomagnetically determined dextral shear affected the southwestern margin of the swnvf between the paint brush and timber mountain caldera episodes larger magnitude detachment faulting in the bullfrog hills southwest of the central swnvf caldera cluster followed the climactic timber mountain caldera episode postvolcanic normal faulting was substantial to the north east and south of the central swnvf caldera cluster but the central area of peak volcanic activity remained relatively unextended in postvolcanic time volcanism and extension in the swnvf area were broadly concurrent but swnvf area were broadly concurrent but in detail they were episodic in time and not coincident in space

renewal models and coseismic stress transfer in the corinth gulf greece fault system 1 we model interevent times and coulomb static stress transfer on the rupture segments along the corinth gulf extension zone a region with a wealth of observations on strong earthquake recurrence behavior from the available information on past seismic activity we have identified eight segments without significant overlapping that are aligned along the southern boundary of the corinth rift we aim to test if strong earthquakes on these segments are characterized by some kind of time predictable behavior rather than by complete randomness the rationale for time predictable behavior is based on the characteristic earthquake hypothesis the necessary ingredients of which are a known faulting geometry and slip rate the tectonic loading rate is characterized by slip of 6 mm yr on the westernmost fault segment diminishing to 4 mm yr on the easternmost segment based on the most reliable geodetic data in this study we employ statistical and physical modeling to account for stress transfer among these fault segments the statistical modeling is based on the definition of a probability density distribution of the interevent times for each segment both the brownian passage time bpt and weibull distributions are tested the time dependent hazard rate thus obtained is then modified by the inclusion of a permanent physical effect due to the coulomb static stress change caused by failure of neighboring faults since the latest characteristic earthquake on the fault of interest the validity of the renewal model is assessed retrospectively using the data of the last 300 years by comparison with a plain time independent poisson model by means of statistical tools including the relative operating characteristic diagram the r score the probability gain and the log likelihood ratio we treat the uncertainties in the parameters of each examined fault source such as linear dimensions depth of the fault center focal mechanism recurrence time coseismic slip and aperiodicity of the statistical distribution by a monte carlo technique the monte carlo samples for all these parameters are drawn from a uniform distribution within their uncertainty limits we find that the bpt and the weibull renewal models yield comparable results and both of them perform significantly better than the poisson hypothesis no clear performance enhancement is achieved by the introduction of the coulomb static stress change into the renewal model

geometry of continental normal faults seismological constraints teleseismic body waves from large earthquakes are used to study the downdip geometry of continental normal faults in the aegean waveform modeling techniques together with rigorous statistical tests are applied to put firm bounds on the amount of downdip curvature of these faults and the role of coseismic slip on a basal detachment synthetic modeling shows that good azimuthal station coverage and inclusion of sh waves are necessary to resolve fault curvature the data indicate ruptures of the aegean events occurred on planar faults extending across the entire brittle portion of the crust no seismogenic low angle detachment faulting at the base of the upper crust was detected for these events decoupling of the brittle upper crust from the plastic lower crust probably occurs aseismically in a ductile fashion

new constraints from seismology and geodesy on the mw 6 4 2008 movri greece earthquake evidence for a growing strike slip fault system the 2008 mw 6 4 movri earthquake ruptured a nne right lateral strike slip fault about 30 km south of the city of patras although some strike slip activity on minor faults was known there was no tectonic evidence of large scale ns striking fault and such a large event was not anticipated following the event a network of six stations was installed for 4 months in the epicentral area in order to monitor aftershocks and in particular the northern part of the rupture area closest to the city of patras we combine these new aftershock observations with gps measurements of an already existing geodetic network in the area performed just after the earthquake as well as with sar interferograms together with already published source studies in order to refine already proposed models of this event the combined data set allows defining much more accurately the lateral and vertical limits of the rupture its length inferred from geodesy is 15 km and its modelled upper edge 17 km the seismic moment then constrains the lower edge to coincide within a few kilometres with the moho interface the absence of seismicity in the shallow crust above the co seismic fault is interpreted as a result of the decoupling effect of possible presence of salt layers above the rupture area near 14 to 16 km in depth which favours our interpretation of an immature strike slip fault system compatible with the absence of surface ruptures the immature character of this large crustal fault is further suggested by the high variability of focal mechanisms and of fault geometries deduced from aftershock clusters in the strike direction its geometry and mechanism is consistent with the crustal shear striking nne revealed by gps in this region this shear and faulting activity might be generated by the differential slip rate on the subduction interface 50 km to the south leading to a north northeastward propagating strike slip fault zone the wide extension of the aftershock distribution forming a nne alignment beyond the rupture area towards the north suggests a localization process of the shear strain which could be the preliminary stage of fault propagation further to the nne an alternative speculative model for this regional stress could be the existence of a well developed nne striking shear zone within the uppermost mantle marking at depth the southward propagation of the northern branch of the north anatolian fault both models may not be exclusive of each other and in fact their sources may be mechanically interdependent

dynamics of microseismicity and its relationship with the active structures in the western corinth rift greece we analyse the complete earthquake archive of the western corinth rift using both cross correlations between pairs of event waveforms and accurate differential traveltimes observed at common stations in order to identify small scale fault structures at depth the waveform database was generated by the dense corinth rift laboratory network and includes about 205 000 events between 2000 and 2015 half of them are accurately relocated using double difference techniques the novelty of this relocated catalogue is the integration of the recent westernmost earthquakes due to the extension of the network in 2010 to the western extremity of the corinth rift and the consideration of the whole database over more than 15 yr the total relocated seismicity exhibits well defined clusters at the root of the main normal faults mainly between 5 and 10 km depth in the middle of the gulf and illuminates thin active structure planes dipping north about 20 under the northern coast some seismicity is observed in the footwall of the main active faults along the west and east helike faults we also built a multiplet database based on waveform similarity taking into account cross correlation coefficients weighted by signal to noise ratios short term multiplets are concentrated in the middle of the gulf along the kamarai fault system in a 1 2 km thick layer at 6 8 km depth interpreted as a highly fractured geological layer they are often associated to slow seismic migration velocities occurring in this zone during strong swarm episodes and are thus likely to be triggered by pore pressure variations on the other hand most long term and regular multiplets are located deeper 7 10 km under the northern coast within a layer less than 0 3 km thick they occur at the border of nearly planar structures with low seismicity rate which we identify as fault planes and they may be explained by aseismic slip on the fault surface around them this supports the existence of an immature structure growing downdip towards the north at the base of the active geological layer which possibly connects to the ductile middle crust around 15 km depth as suggested by the occurrence of deeper events in the continuity of the 1995 fault plane the different migration velocities from 0 05 km d 1 to several km d 1 highlighted during the western 2014 swarms indicate that both pore pressure and creep diffusion are operating in the fault zone the fast migrations observed in the psathopyrgos fault zone where a slow slip event was detected by dilatometers in 2002 compare with that for creeping faults to the west from spatial distribution of events we show that the rion patras fault connecting the western extremity of the corinth rift fault system to the patras rift is dipping around 60 north west with a rake angle of 115 finally we identified two new areas within the central active zone which may correspond to large scale locked asperities on active fault surfaces similar in size to the main asperity broken during the 1995 mw 6 3 aigion earthquake

nonlinear subsidence rate estimation using permanent scatterers in differential sar interferometry discrete and temporarily stable natural reflectors or permanent scatterers ps can be identified from long temporal series of interferometric sar images even with baselines larger than the so called critical baseline this subset of image pixels can be exploited successfully for high accuracy differential measurements the authors discuss the use of ps in urban areas like pomona ca showing subsidence and absidence effects a new approach to the estimation of the atmospheric phase contributions and the local displacement field is proposed based on simple statistical assumptions new solutions are presented in order to cope with nonlinear motion of the targets

the three dimensional thermo mechanical signature of ridge subduction and slab window migration we present a series of three dimensional numerical models investigating possible thermal and mechanical effects of ridge subduction and slab window migration ridge subduction is a fundamental process of plate tectonics and the geologic manifestations in the overriding lithosphere have been investigated in many convergent margin settings many of the geologic effects of slab window migration e g anomalous high t metamorphism in the forearc non arc like magmatism in the volcanic arc are explained primarily by the introduction of a region of hot upwelling asthenospheric mantle in the subduction zone environment using end member boundary conditions and idealized geometries our models address the thermal and corresponding mechanical manifestations of slab window migration and our results provide a general agreement with observations from interpreted regions of slab window migration our models show that protracted heating in the forearc region should result in protracted high temperature metamorphism associated rheologic weakening and strain partitioning and changes in the topographic uplift pattern in regions affected by slab window migration although these models are idealized they do provide valuable insight into the geodynamics of slab window environments and provide a valuable starting point for further exploration

neogene kinematic history of nazca antarctic phoenix slab windows beneath patagonia and the antarctic peninsula article i nfo the patagonian slab window is a subsurface tectonic feature resulting from subduction of the nazca antarctic spreading ridge system chile rise beneath southern south america the geometry of the slab window had not been rigorously defined in part because of the complex nature of the history of ridge subduction in the southeast pacific region which includes four interrelated spreading ridge systems since 20 ma first the nazca phoenix ridge beneath south america then simultaneous subduction of the nazca antarctic and the northern phoenix antarctic spreading ridge systems beneath south america and the southern phoenix antarctic spreading ridge system beneath antarctica spreading ridge paleo geographies and rotation poles for all relevant plate pairs nazca phoenix antarctic south america are available from 20 ma onward and form the mathematical basis of our kinematic reconstruction of the geometry of the patagonia and antarctic slab windows through neogene time at approximately 18 ma the nazca phoenix antarctic oceanic ridge ridge ridge triple junction enters the south american trench we recognize this condition as an unstable quadruple junction heat flow at this junction and for some distance beneath the forearc would be considerably higher than is generally recognized in cases of ridge subduction from 16 ma onward the geometry of the patagonia slab window developed from the subduction of the trailing arms of the former oceanic triple junction the majority of the slab window s areal extent and geometry is controlled by the highly oblique near parallel subduction angle of the nazca antarctic ridge system and by the high contrast in relative convergence rates between these two plates relative to south america the very slow convergence rate of the antarctic slab is manifested by the shallow levels achieved by the slab edge b45 km thus no point on the antarctic slab is sufficiently deep to generate normal mantle derived arc type magmas upwelling beneath the region may have contributed to uplift and eastward transfer of extension in the scotia sea

evolution of the offshore western gulf of corinth the young gulf of corinth rift in central greece is an ideal place to study processes occurring during the initiation and early stages of continental extension at the east end of the 100 km long e w rift holocene extension on n dipping faults equates to geodetic extension rates at the western end however estimated extension rates on n dipping onshore faults account for only 20 40 of the geodetically measured rates 10 15 mm yr we use high quality multichannel seismic reflection and swath bathymetry data to investigate the tectonics of the western gulf and quantify the contribution of offshore fault activity toward total rift extension five major offshore faults generate the variable basement topography and a ca 0 4 ma unconformity separates stratigraphy into two main packages basin fill geometry indicates that during the early stages of subsidence of the offshore western gulf s dipping faults were the dominant border fault structure this is still the case at the western end of the western gulf however elsewhere n dipping faults on the south margin are now relatively more dominant and cause stratigraphy to tilt south the temporally and spatially varying rift structure contrasts with the simple consistently n dipping border fault half graben geometry of the east gulf of corinth combined west gulf offshore and onshore holocene fault extension rates total 5 14 5 mm yr within the range calculated geodetically and render enhanced slip on a low angle detachment surface beneath the western gulf unnecessary

u and sr isotopes in ground water and calcite yucca mountain nevada evidence against upwelling water hydrogenic calcite and opaline silica deposits in fault zones at yucca mountain nevada have created considerable public and scientific controversy because of the possible development of a high level nuclear waste repository at this location strontium and uranium isotopic compositions of hydrogenic materials were used to test whether the veins could have formed by upwelling of deep seated waters the vein deposits are isotopically distinct from ground water in the two aquifers that underlie yucca mountain indicating that the calcite could not have precipitated from ground water the data are consistent with a surficial origin for the hydrogenic deposits

u pb ages of secondary silica at yucca mountain nevada implications for the paleohydrology of the unsaturated zone abstract uranium th and pb isotopes were analyzed in layers of opal and chalcedony from individual mm to cm thick calcite and silica coatings at yucca mountain nevada usa a site that is being evaluated for a potential high level nuclear waste repository these calcite and silica coatings on fractures and in lithophysal cavities in miocene age tuffs in the unsaturated zone uz precipitated from descending water and record a long history of percolation through the uz opal and chalcedony have high concentrations of u 10 to 780 ppm and low concentrations of common pb as indicated by large values of 206pb 204pb up to 53 806 thus making them suitable for u pb age determinations interpretations of u pb isotope systems in opal samples at yucca mountain are complicated by the incorporation of excess 234u at the time of mineral formation resulting in reverse discordance of u pb ages however the 207pb 235u ages are much less affected by deviation from initial secular equilibrium and provide reliable ages of most silica deposits between 0 6 and 9 8 ma for chalcedony subsamples showing normal age discordance these ages may represent minimum times of deposition typically 207pb 235u ages are consistent with the microstratigraphy in the mineral coating samples such that the youngest ages are for subsamples from outer layers intermediate ages are from inner layers and oldest ages are from innermost layers 234u and 230th in most silica layers deeper in the coatings are in secular equilibrium with 238u which is consistent with their old age and closed system behavior during the past 0 5 ma the ages for subsamples of silica layers from different microstratigraphic positions in individual calcite and silica coating samples collected from lithophysal cavities in the welded part of the topopah spring tuff yield slow long term average growth rates of 1 to 5 mm ma these data imply that the deeper parts of the uz at yucca mountain maintained long term hydrologic stability over the past 10 ma despite significant climate variations u pb ages for subsamples of silica layers from different microstratigraphic positions in individual calcite and silica coating samples collected from fractures in the shallower part of the uz welded part of the overlying tiva canyon tuff indicate larger long term average growth rates up to 23 mm ma and an absence of recently deposited materials ages of outermost layers are 3 5 ma these differences between the characteristics of the coatings for samples from the shallower and deeper parts of the uz may indicate that the nonwelded tuffs ptn located between the welded parts of the tiva canyon and topopah spring tuffs play an important role in moderating uz flow

a new method for measuring deformation on volcanoes and other natural terrains using insar persistent scatterers 1 we present here a new insar persistent scatterer ps method for analyzing episodic crustal deformation in non urban environments with application to volcanic settings our method for identifying ps pixels in a series of interferograms is based primarily on phase characteristics and finds low amplitude pixels with phase stability that are not identified by the existing amplitude based algorithm our method also uses the spatial correlation of the phases rather than a well defined phase history so that we can observe temporally variable processes e g volcanic deformation the algorithm involves removing the residual topographic component of flattened interferogram phase for each ps then unwrapping the ps phases both spatially and temporally our method finds scatterers with stable phase characteristics independent of amplitudes associated with man made objects and is applicable to areas where conventional insar fails due to complete decorrelation of the majority of scatterers yet a few stable scatterers are present

inorganic calcite morphology roles of fluid chemistry and fluid flow abstract evaluation of calcite crystal habits and fabric and their relation to precipitating fluids in spelean environments indicates that habit variations are controlled primarily by degree of supersaturation at less than 6 times supersaturation crystal habits are limited to those with shallow to steep rhombohedral forms i e 1011 4041 with increasing supersaturation scalenohedrons extremely steep rhombohedrons pinacoids and hexagonal prisms are developed slight elongation due to differences in crystal dimensions of these forms may arise i e scalenohedrons versus shallow rhombohedrons at extreme supersaturation 12 times curvature of crystal faces or curved surfaces appear the development of fibrous versus equant fabrics is the result of changes or modification of reactant supply rates and the number of crystallites nuclei present under rapid flow conditions growth rates are accelerated and greater numbers of nuclei are present thus compromise boundaries parallel to c axis and perpendicular to flow and substrate are rapidly attained in the absence of flow fewer crystallites are present and larger well developed crystals or branching forms dictated by saturation conditions arise in the absence of flow at low supersaturation elongate composite crystals and hence fibrous fabrics may result from migration of the fluid crystal interface as a result of changing or oscillating water levels a flow control mechanism can be applied to numerous geological conditions in which transitions from fibrous to equant crystal morphologies are observed

subduction of diverging plates and the principles of slab window formation consumption of an ocean basin by subduction commonly brings a sea floor spreading ridge toward a deep sea trench if plate divergence and convergence continue after the ridge intersects the subduction zone a slab window forms between the subducted parts of the diverging oceanic plates producing anomalous thermal physical and chemical effects in the surrounding asthenospheric mantle in turn these conditions alter the tectonic and magmatic evolution of the overriding plate usually disturbing ordinary fore arc and arc regimes differential lithospheric stresses on opposite sides of the triple junction contribute to disturbances in the overriding plate anomalous magmatism from fore arc to back arc may be accompanied by fore arc metamorphism strike slip faulting uplift extension and in extreme cases rifting the shape and size of the window are controlled mainly by the pre subduction ridge transform trench configuration slab dip angles and vectors of plate convergence subducted ridge segments expand into windows whose margins approximately parallel the motion vectors between the triple junction and the subducting plates subducted transform faults continue to be active usually as oblique slip faults until the plates separate as transform faults subduct they become longer on the plate which occupies the acute angle between ridge and trench and shorter on the other plate trains of isolated windows produced by subduction of a segmented ridge transform system progressively expand during descent commonly merging together to form a composite slab window oblique subduction of a highly segmented ridge is likely to produce two or more fraternal slab windows one at each site of ridge trench intersection above a slab window arc volcanism diminishes and may be replaced by volcanism of mid ocean ridge or rift affinity the change in chemical character reflects various processes including elevated heat flow decreasing hydration of the upper mantle juxtaposition of supra and sub slab mantle reservoris asthenospheric upwelling and melting of the trailing plate edges if the slab window migrates the anomalous magmatic regime may be replaced by renewed arc volcanism identifying the effects of slab windows in ancient convergent margin assemblages requires an understanding of slab window principles and implications

physical and stable isotope evidence for formation of secondary calcite and silica in the unsaturated zone yucca mountain nevada abstract calcite and silica form coatings on fracture footwalls and cavity floors in the welded tuffs at yucca mountain the potential site of a high level radioactive waste repository these secondary mineral deposits are heterogeneously distributed in the unsaturated zone uz with fewer than 10 of possible depositional sites mineralized the paragenetic sequence compiled from deposits throughout the uz consists of an early stage assemblage of calcite fluorite zeolites that is frequently capped by chalcedony quartz intermediate and late stage deposits consist largely of calcite commonly with opal on buried growth layers or outermost crystal faces of the calcite coatings on steep dipping fractures usually are thin 3 mm with low relief outer surfaces whereas shallow dipping fractures and lithophysal cavities typically contain thicker more coarsely crystalline deposits characterized by unusual thin tabular calcite blades up to several cms in length these blades may be capped with knobby or corniced overgrowths of late stage calcite intergrown with opal the observed textures in the fracture and cavity deposits are consistent with deposition from films of water fingering down fracture footwalls or drawn up faces of growing crystals by surface tension and evaporated at the crystal tips fluid inclusion studies have shown that most early stage and some intermediate stage calcite formed at temperatures of 35 to 85 c calcite deposition during the past several million years appears to have been at temperatures 18 o values although others have interpreted the elevated temperatures as evidence of hydrothermal activity and flooding of the tuffs of the potential repository the authors conclude that the temperatures and fluid inclusion assemblages are consistent with deposition in a uz environment that experienced prolonged heat input from gradual cooling of nearby plutons the physical restriction of the deposits and therefore fluid flow to fracture footwalls and cavity floors and the heterogeneous and limited distribution of the deposits provides compelling evidence that they do not reflect flooding of the thick uz at yucca mountain the textures and isotopic and chemical compositions of these mineral deposits are consistent with deposition in a uz setting from meteoric waters percolating downward along fracture flow paths

aragonite calcite speleothems identifying original and diagenetic features despite the increasing use of speleothems as high resolution archives of past climate proxies few efforts have been made to improve understanding of diagenetic pathways affecting this material and to assess the degree of postdepositional transformation of initial features including associated geochemical signatures to provide criteria for distinguishing primary spelean growth history and secondary spelean diagenetic history features this study documents a process based approach combining mineralogical textural and geochemical data at different scales to characterize various diagenetic processes undergone by aragonite and calcite speleothems from the pont de ratz cave herault s france results show that the initial precipitation of carbonate minerals forming the stalagmites vadose precipitation is represented alternatively by aragonite and calcite and consists of two types of primary aragonite and a primary columnar calcite four different types of growth interruption and inclusion horizons are evident and attest to the discontinuous growth of stalagmites in this cave postdepositional diagenetic processes include void filling calcite cementation selective dissolution of either aragonite or calcite and recrystallization recrystallization processes include 1 textural change of original aragonite precipitates isomineralogical recrystallization and 2 two distinct types of aragonite to calcite recrystallization these results highlight the diversity of potential synformational and postformational processes controlling the formation and evolution of speleothems and their impact on the geochemical properties of the primary and secondary carbonate phases and the potential importance in paleoclimatic interpretation

the january 2010 efpalio earthquake sequence in the western corinth gulf greece abstract the january 2010 efpalio earthquake sequence provides some key elements to enhance our view on the western corinth gulf tectonics the sequence lasted almost six months and included two mw 5 strong events both exhibiting normal faulting along e w trending planes this paper attempts to construct a unified seismotectonic model of the sequence jointly interpreting earthquake locations moment tensors and slip inversions in terms of the possible activated fault planes previous studies have connected the prevailing microseismic activity to a major low angle north dipping structure under the corinth gulf and the efpalio sequence favors such a general trend moreover it clearly shows the significance of the shallow activity so far less recognized and possibly connected to the relatively steep faults outcropping on the northern coast the first 18 january 2010 mw 5 event had almost no on fault aftershocks and most likely it occurred on a 55 south dipping nodal plane the early off fault aftershocks formed two clusters roughly e w trending both of which are connected with normal faulting cross sections revealed that the northernmost cluster is connected with a north dipping structure where the second 22 january 2010 mw 5 event occurred in addition the very shallow parts of the faults

influence of continental roots and asthenosphere on plate mantle coupling the shear tractions that mantle flow exerts on the base of earth s lithosphere contribute to plate driving forces and lithospheric stresses we investigate the sensitivity of these tractions to sub lithospheric viscosity variations by comparing shear tractions computed from a mantle flow model featuring laterally varying lithosphere and asthenosphere viscosity with those from a model with layered viscosity lateral viscosity variations generally do not change the direction of shear tractions but deeply penetrating continental roots increase traction magnitudes by a factor of 2 5 compared to 100 km thick lithosphere a low viscosity asthenosphere decreases traction magnitudes by a smaller amount and is important only if 100 km thick increased plate mantle coupling beneath thick continental lithosphere may increase plate driving forces surface deformation and mantle derived lithospheric stresses in these regions by contrast a low viscosity asthenosphere does not decouple the lithosphere from mantle flow highlighting the geological importance of mantle tractions on the lithosphere

geodetic estimate of seismic hazard in the gulf of korinthos the recent 15 june 1995 m0 6 0 1018 n m aigion earthquake in the western gulf of korinthos has focussed attention on the seismic hazard of the region although there have been few large earthquakes in the region during this century the historical record suggests that there may have been many large earthquakes there in the interval 1750 1900 we present geodetic data that give estimates of the rate of extension of the gulf of korinthos during this century and which suggest that less than half of the elastic strain in the central and western gulf of korinthos has been released by earthquakes during this century in contrast the seismic and geodetic strains in the eastern gulf of korinthos are in agreement with each other if the discrepancy between seismic and geodetic strains in the western gulf of korinthos that has accumulated during this century is removed in earthquakes the moment release will be equivalent to several ms 6 5 earthquakes

geometry and slip rate of the aigion fault a young normal fault system in the western gulf of corinth the aigion fault is one of the youngest major normal faults in the gulf of corinth greece with an immature displacement profile based on geometry slip rate and comparison with regional faults we estimate the fault system length at 10 km we find the slip rate of the fault system is 3 5 1 mm yr decreasing to 2 5 0 7 mm yr close to its eastern tip complex fault geometry and displacement profiles on the shelf east of aigion are consistent with the latter as the eastern tip location analysis of slip on this fault system and the established fault to the south western eliki fault suggests that slip was transferred rapidly but not homogeneously between the two faults during the period of contemporaneous activity together with a lack of evidence of lateral propagation at the eastern fault tip in the last 10 13 k y we suggest that the fault developed and established its current length rapidly within its 200 300 k y history these results contribute to our understanding of the process of northward fault migration into the rift and the development of new normal faults

thermal history of the unsaturated zone at yucca mountain nevada usa abstract secondary calcite silica and minor amounts of fluorite deposited in fractures and cavities record the chemistry temperatures and timing of past fluid movement in the unsaturated zone at yucca mountain nevada the proposed site of a high level radioactive waste repository the distribution and geochemistry of these deposits are consistent with low temperature precipitation from meteoric waters that infiltrated at the surface and percolated down through the unsaturated zone however the discovery of fluid inclusions in calcite with homogenization temperatures th up to 80 c was construed by some scientists as strong evidence for hydrothermal deposition this paper reports the results of investigations to test the hypothesis of hydrothermal deposition and to determine the temperature and timing of secondary mineral deposition mineral precipitation temperatures in the unsaturated zone are estimated from calcite and fluorite hosted fluid inclusions and calcite 18o values and depositional timing is constrained by the 207pb 235u ages of chalcedony or opal in the deposits fluid inclusion th from 50 samples of calcite and four samples of fluorite range from 35 to 90 c calcite 18o values range from 0 to 22 smow but most fall between 12 and 20 the highest th and the lowest 18o values are found in the older calcite calcite th and 18o values indicate that most calcite precipitated from water with 18o values between 13 and 7 similar to modern meteoric waters twenty two 207pb 235u ages of chalcedony or opal that generally postdate elevated depositional temperatures range from 9 5 to 1 9 ma new and published 207pb 235u and 230th uages coupled with the th values and estimates of temperature from calcite 18o values indicate that maximum unsaturated zone temperatures probably predate 10 ma and that the unsaturated zone had cooled to near present day temperatures 24 26 c at a depth of 250 m by 2 4 ma the evidence of elevated temperatures persisting in ash flow tuffs adjacent to parent calderas for as much as 8 ma is a new finding but consistent with thermal modeling simulations using the heat code demonstrate that prolonged cooling of the unsaturated zone is consistent with magmatic heat inputs and deep seated sub water table hydrothermal activity generated by the large magma body 8 km to the north that produced the 15 11 ma ash flows and ash falls that make up yucca mountain the evidence discussed in this and preceding papers strongly supports unsaturated zone deposition of the secondary minerals from descending meteoric waters although depositional temperatures reflect conductive and possibly vapor phase convective heating of the unsaturated zone related to regional magmatic sources until perhaps 6 ma depositional conditions similar to the present day unsaturated zone have prevailed for at least the past 2 4 ma

heat flow and lithospheric thickness analysis in the patagonian asthenospheric windows southern south america abstract the lithosphere asthenosphere boundary lab is a first order discontinuity essential to understand the earth composition and evolution however its detection has been critical and several regions still lack of coverage southern patagonia in southern most south america is one such area which has been affected by the subduction of a seismic oceanic ridge south chile ridge and formation of an extensive slab window since 12 ma we calculate the lab position by defining the thermal lithospheric thickness of the southernmost patagonia using the thermal conductivity equation to estimate the surface heat flow we used data from seventy five hydrocarbon wells of two from the most productive petroleum basins in argentina the golfo de san jorge and magallanes austral basins our results show the highest heat flow values in the southernmost region over the austral basin and core of the slab window 70 90 mw m2 these values are twice as hot as global average to the north over de golfo de san jorge basin and northern margin of the slab window heat flows are normal 50 60 mw m2 these thermal contrasts from south to north agree with the kinematic reconstructions of the chile ridge and northward widening of the slab window these heat flows values evidence an attenuated lithospheres which thickens eastward from between 25 km to the west trench region to 50 km to the east foreland region

the 2003 2004 seismic swarm in the western corinth rift evidence for a multiscale pore pressure diffusion process along a permeable fault system microseismic multiplets occurring in the western corinth rift greece during a large swarm are analyzed to retrieve their spatiotemporal characteristics these multiplets activated small subfaults at depth 7 km up to 1 km long at the root of two parallel active normal faults the swarm migrates westward nearly horizontally over 10 km at an average velocity of 50 m d with a diffusivity of 0 5 m2 s 1 it successively activates the aigion fault a relay zone in its hanging wall and the fassouleika fault within each multiplet hypocenters also migrate with diffusivities ranging from 0 001 to 0 4 m2 s 1 the largest internal diffusivities appear at the core of the layer defined by the clusters these results are interpreted as a hydroshear process caused by pore pressure migration within permeable corridors resulting from the intersection of the major faults with a brittle geological layer inherited from the hellenic nappe stack

anatomy of the andean subduction zone three dimensional density model upgraded and compared against global scale models summary we present an upgraded version of a previously published 3 d density model of the andean subduction zone between 18 s and 45 s this model consists of 3 d bodies of constant density which geometry is constrained by independent seismic data and is triangulated from vertical cross sections these bodies define the first order morphology and internal structure of the subducted nazca slab and south american plate the new version of the density model results after forward modelling the bouguer anomaly as computed from the most recent version of the earth gravitational model egm2008 the 3 d density model incorporates new seismic information to better constrain the geometry of the subducted slab and continental moho cmh and has a trench parallel resolution doubling the resolution of the previous model as an example of the potential utility of our model we compare the geometry of the subducted slab and cmh against the corresponding global models slab1 0 and crust2 0 respectively this exercise demonstrates that although global models provide a good first order representation of the slab and upper plate crustal geometries they show large discrepancies up to 40 km with our upgraded model for some well constrained areas the geometries of the slab lithosphere asthenosphere boundary below the continent cmh and intracrustal density discontinuity that we present here as supporting information can be used to study andean geodynamic processes from a wide range of quantitative approaches

effects of superficial layers on coseismic displacements for a dip slip fault and geophysical implications summary we study the effect of a superficial layer overlying a half space on the surface displacements created by a dip slip dislocation on a planar rectangular fault using a 2 d finite element model the effect of the density and poisson s ratio is negligible on the other hand the contrast in young s modulus between the top layer and the half space below significantly affects the modelled coseismic displacements the horizontal displacements are more sensitive than the vertical displacements to the existence of the top layer near the fault a low rigidity layer with a young s modulus of 10 gpa can increase the horizontal displacements by up to 40 per cent an analytical 3 d half space model is used to interpret this effect in terms of an equivalent homogeneous model the presence of a top layer can be partly simulated in a homogeneous half space by perturbing the depth and the slip on the fault from their real values to equivalent values for a given displacement field observed at the surface the perturbations in fault depth and slip can reach 1 km and 25 per cent respectively the fault dip angle is not model dependent we conclude that for the accurate estimation of fault depth and slip from coseismic geodetic data rigidity contrasts existing within the upper crust must be taken into account not taking into account the effect of an existing low rigidity layer also leads to an underestimation of seismic moment release this may in part be the cause of apparent discrepancies between seismic and geodetic moment releases in particular areas such as the gulf of corinth greece

neogene patagonian plateau lavas continental magmas associated with ridge collision at the chile triple junction extensive neogene patagonian plateau lavas 46 5 to 49 5 s southeast of the modern chile triple junction can be related to opening of asthenospheric slab windows associated with collisions of chile rise segments with the chile trench at 12 ma and 6 ma support comes from 26 new total fusion whole rock 40ar 39ar ages and geochemical data from back arc plateau lavas in most localities plateau lava sequences consist of voluminous tholeiitic main plateau flows overlain by less voluminous 2 to 5 million year younger alkalic postplateau flows northeast of where the ridge collided at 12 ma most lavas are syncollisional or postcollisional in age with eruptions of both sequences migrating northeastward at 50 to 70 km ma plateau lavas have ages from 12 to 7 ma in the western back arc and from 5 to 2 ma farther to the northeast trace element and isotopic data indicate main plateau lavas formed as larger percentage melts of a garnet bearing oceanic island basalt oib like mantle than postplateau lavas the highest percentage melts erupted in the western and central plateaus in a migrating slab window model main plateau lavas can be explained as melts that formed as upwelling subslab asthenosphere which flowed around the trailing edge of the descending nazca plate and then interacted with subduction altered asthenospheric wedge and continental lithosphere alkaline postplateau lavas can be explained as melts generated by weaker upwelling of subslab asthenosphere through the open slab window thermal problems of high pressure melt generation of anhydrous mantle can be explained by volatiles h2o and co2 introduced by the subduction process into slab window source region s an oib like rather than a mid ocean ridge basalt morb like source region and the lack of magmatism northeast of where ridge collision occurred at 13 to 14 ma can be explained by entrainment of weak plume s or regional variations in an ambient oib like asthenosphere

18o 16o evidence for an early short lived 10 yr fumarolic event in the topopah spring tuff near the proposed high level nuclear waste repository within yucca mountain nevada usa abstract 18 o 16 o analyses of rock samples from the exploratory studies facility esf and from three other locations in the vicinity of yucca mountain nevada suggest that the uppermost 5 20 m of the 12 8 ma topopah spring tuff displays a characteristic 18 o 16 o pattern that is indicative of short lived 10 yr high temperature 500 c fumarolic meteoric hydrothermal activity hydrothermally altered rock is characterized by 1 3 m thick zones of 18 o depleted groundmass down to 18 o 5 5 located above and locally within the upper vitrophyre as well as complementary 2 4 m thick overlying zones of 18 o enriched as high as 18 o 13 7 mineralogically altered groundmass thirty four samples of the topopah spring tuff collected below the upper vitrophyre are not hydrothermally altered and correspondingly display a more uniform set of 18 o values 18 o 8 6 to 11 1 sanidine phenocrysts from fumarolically altered tuff in the upper cooling unit are petrographically pristine and also display uniform 18 o values 18 o 7 80 0 45 which are in isotopic equilibrium with other phenocryst phases at magmatic temperatures the 18 o 16 o signature displayed by the upper part of the topopah spring tuff is analogous to that produced by short lived 10 25 yr high temperature 500 c fumarolic activity in the bishop tuff and in the 1912 ash flow sheet in the valley of ten thousand smokes alaska the remarkable preservation of a fragile fumarolic 18 o 16 o signature in the upper part of the topopah spring tuff indicates that no subsequent hydrothermal alteration of this part of the tuff has occurred

fractal characteristics of active normal faults an example of the eastern gulf of corinth greece abstract we present a model proposing the evolution of segmented normal faults in a currently extended area allowing an explanation of strong earthquakes hosted by short faults active normal faults accommodating the current extension in the gulf of corinth result from the linkage of smaller component faults well exposed fault zones in the sofiko range are arranged as pairs of graben bounding faults and thus our structural analysis has implications for the evolution of active normal faults as well as graben evolution a basal strip of fresh bedrock at the base of fault scarps suggests continuous seismic or aseismic creep thus the structural analysis of component faults that show a power law length distribution describes an evolved fault zone of particular interest is that faulting in this region is self similar between limits distribution is characterized by a fractal dimension of d 1 and the limits in our study are between 10 m mapping resolution and double the maximum displacement of each fault zone component segments of any compartmentalized fault show a length to maximum displacement ratio of two basin architecture and structural analysis suggest that the nucleation points of faults are detectable over the entire evolution of the fault zone all analyzed faults evolved by an independent nucleation model morphotectonic and kinematic data as well as fractal dimension of trace length population plots all suggest that fault zones defining north and south dipping conjugates are active at least over the late stages of basin evolution although this study was focused on a relatively small area this pattern of fault growth appears to be applicable to the entire fault population in the gulf of corinth and is thus an important model for normal faults

geometry and kinematics of active faults and their seismotectonic significance in the western corinth patras rift greece abstract the western part of the corinth patras rift is formed in an area which is being uplifted rifted domains have subsided relative to the adjacent areas in nw peloponnesus and sterea hellas but subsidence rates rarely exceed uplift rates extension is mainly accomplished by wnw trending active faults with lengths up to 25 km most of these faults show an along strike segmentation and often terminate against transfer faults displacement analysis along 170 mesoscopic faults and 36 mappable faults has been carried out to assess slip rates and to estimate the magnitudes and recurrence time intervals of earthquakes occurring along them earthquake magnitude ranges between 5 and 6 7 only eight faults appear to be capable of producing earthquake magnitudes larger than 6 recurrence times of these large earthquakes vary between 80 and 1690 years upper crustal deformation in the western corinth graben can be described by six large asymmetric grabens which are inferred to bottom out to a n dipping curved ramp the asymmetric shape of most wnw trending rifts in the hellenic peninsula including the corinth patras rift promotes the simple shear model of extension against the pure shear model in the upper crustal layer

the aigion neos erineos coastal normal fault system western corinth gulf rift greece geomorphological signature recent earthquake history and evolution 1 at the westernmost part of the corinth rift greece an area of rapid extension and active normal faulting geomorphological observations reveal the existence and geometry of an active nw se trending coastal fault system which includes the aigion fault we recognize a similar fault pattern on both the coastal range front to the nw of aigion town and the holocene fan deltas in front of it we interpret this as a result of recent migration of faulting to the hanging wall of the fault system differences in the geomorphic expression of the constituent faults provide hints on the possible evolution of the fault pattern during this recent migration a trench excavated across one of the identified coastal fault scarps on a holocene fan delta provides information on the seismic history of the fault system which includes at least four possibly six earthquakes in the past 4000 years a minimum estimate for the slip rate of the trenched fault is 1 9 2 7 mm yr the trench exposed sediments of an uplifted paleolagoon approximate age 2000 years b p inside which the last two earthquakes formed an underwater monoclinal scarp oscillating coastal vertical movements are suggested by the fact that the lagoonal deposits are also uplifted on the trenched fault hanging wall uplift by offshore faults and by the abrupt transition from fluvial to lagoonal deposits subsidence by more landward faults assuming that extensive coastal sediment failure has not taken place in the specific part of the fan delta within the time interval of interest these movements suggest that the proposed migration of activity from the range front faults to those on the fan deltas is probably still ongoing with activity on both sets of faults

cocos nazca slab window beneath central america abstract integration of petrologic and tectonic data favours a model of slab window formation beneath central america in the pliocene pleistocene central america has been the site of voluminous cenozoic arc volcanism the cocos and nazca plates which are subducting beneath central america are diverging along the east trending cocos nazca spreading ridge since 25 ma the americas have advanced about 1800 km west over the ridge transform system since at least 8 ma plate integrity and the ridge transform configuration have been preserved during convergence resulting in subduction of the spreading ridge and development of a slab window the panama fracture zone an active transform fault is the part of the ridge transform system currently being subducted the ridge transform system formerly adjoining the northern end of the panama fracture zone is likely to have been left stepping we use present day plate motions to design a slab window to fit known variations in igneous composition hypocentre distribution and mantle anisotropy the modeling demonstrates that subduction of ridge segments and resultant slab window development began between 6 and 10 ma cessation of ridge subduction occurred between 1 and 3 ma when subduction of the panama fracture zone is considered to have begun the slab window is continuing to expand and migrate northeastward below the central american volcanic arc the absence of a wadati benioff zone from southeastern costa rica through panama corresponds to the position of the slab window within this region dacitic and rhyolitic volcanic rocks have adakitic compositions and are thought to result from anatexis of the young buoyant crust which forms the trailing edges of the slabs bounding the window basalts in this area were derived from an enriched ocean island type mantle source whereas basalts from the rest of the arc in nicaragua el salvador and guatemala are mainly derived from slab modified depleted mantle characteristic of volcanic arcs the presence of ocean island type mantle beneath southern costa rica and panama is explained by eastward flow of enriched asthenosphere from the galapagos plume head through the slab window and into the volcano source region eastward transfer of asthenosphere is consistent with global plate motion studies and seismic anisotropy in the asthenosphere beneath the nazca and caribbean plates the flow of peridotite is a consequence of progressive shrinkage of the pacific mantle reservoir and concurrent expansion of the atlantic mantle reservoir

crustal and upper mantle structure of southernmost south america inferred from regional waveform inversion 1 we determine the crustal and upper mantle structure of southern south america by inverting regional seismograms recorded by the seismic experiment in patagonia and antarctica we present a waveform inversion method that utilizes a niching genetic algorithm the niching genetic algorithm differs from the traditional genetic algorithm in that the inversion is performed in multiple subpopulations thus generating a broader search of the model space and enabling us to examine alternative local error minima the vertical and transverse waveforms were used extending from the p arrival to the surface waves and the inversion was performed at either 0 005 0 06 hz larger events or 0 02 0 06 hz smaller events the inversion included anisotropy by solving for separate sv and sh structures in the upper mantle results indicate that crustal thickness varies from 26 to 36 km with thicker values toward the northeast suggesting that there is little crustal thickening beneath the austral andes the average upper mantle velocities are similar to the preliminary reference earth model prem except that the southernmost region shows velocities of 5 slower than prem the upper mantle has up to 5 polarization anisotropy between the moho and 120 km depth the strongest anisotropy is localized in a lithospheric lid shallower than 65 km depth which overlies a pronounced low velocity zone this shallow limit to anisotropy is consistent with the relatively small shear wave splitting values found in this region these results suggest that the anisotropy is limited to lithospheric depths and may imply the absence of a strong mantle flow pattern in the asthenosphere

magnetic fabric of stalagmites and its formation mechanism 1 speleothems have been regarded as ideal archives for recording variations of the earth s magnetic field because they crystallize rapidly and are seldom modified by post depositional processes and because they can be precisely dated magnetic fabric research on speleothems has potential to reveal details of their interior structure and the distribution of ferrimagnetic minerals which would benefit investigations of geomagnetic field behavior two stalagmites hs4 and wd1 from caves in the middle reaches of the yangtze river were collected for magnetic fabric study the anisotropy of magnetic susceptibility ams of the stalagmites is mainly controlled by calcite crystals and the directions of the minimum axes of ams ellipsoids indicate that their crystallographic orientations are roughly perpendicular to the growth laminae anisotropy of the isothermal remanent magnetization airm indicates that the distributions of ferrimagnetic minerals in the stalagmites are not correlated with stalagmite growth laminae mean directions of the maximum principal axes of airm r1 axes for wd1 are close to that of the natural remanent magnetization which suggests that the orientation of ferrimagnetic minerals in this stalagmite are likely to have been controlled by the geomagnetic field

reply to the comment on physical and stable isotope evidence for formation of secondary calcite and silica in the unsaturated zone yucca mountain nevada by y v dublyansky s e smirnov and g p palyanova

neogene to quaternary tectonic evolution of the patagonian andes at the latitude of the chile triple junction abstract we conducted a preliminary structural and tectonic analysis of the region north and south of the lake general carrera buenos aires lgcba southern patagonian andes chile and argentina in order to study the effects of the subduction of the active south chile spreading ridge scr on the development of the tectonic front of the patagonian andes at the latitude of the chile triple junction ctj here one segment of the scr entered the trench at 6 ma and the corresponding slab window is now located below the study area we emphasize the segmentation of the tectonic front which can be divided into four successive oblique segments a to d trending mainly n170 and right laterally offset this geometrical pattern is consistent with a transpressive stress regime in relation to oblique subduction the four segments of the tectonic front are separated and locally deformed by n170 oriented more recent sinistral strike slip fault zones kinematic analysis of minor fault and striaes confirms the abundance of strike slip faults and suggests rotation of the stress tensor after at least 9 ma a consequence of the subduction of the scr beneath the south american plate at the latitude of the lgcba is a two step history 1 pre ridge subduction oblique to the western margin of the south america plate showing contractional regime with its main axis trending ne sw responsible for dextral transpressive deformation and 2 post ridge subduction more orthogonal convergent regime recent uplift occurred later starting at 3 5 ma and could still be active neotectonic activity has been evaluated in the region from preliminary analysis of river patterns and fluvial lacustrine terraces anomalies in stream development can be found although evidences for recent to active faulting can be shown effects of syn glacial and post glacial related processes cannot be ruled out the evolution of this region during the late cenozoic can be divided into three distinct periods 1 20 15 ma deposition of foreland continental detrital sediments rio zeballos group followed by a major contractional phase leading to the development of the main thrust front sometimes between 15 and 10 9 ma 2 9 4 ma erosion peneplanation and emplacement of voluminous plateau basalts coeval with fluvial glacial sedimentation and 3 3 0 ma renewed orogenic activity uplift and disruption of former erosional surfaces in relation to activation of strike slip fault zones and north trending thrusts onset of the major contractional event in the region of study can be correlated with the initiation of the subduction of the chile ridge at 14 15 ma in southernmost patagonia inducing a different stress regime in the frontal arc region