toward understanding the post collisional evolution of an orogen influenced by convergence at adjacent plate margins late cretaceous tertiary thermotectonic history of the apuseni mountains 1 the relationship between syn to post collisional orogenic shortening and stresses transmitted from other neighboring plate boundaries is important for understanding the kinematics of mountain belts but has received little attention so far the apuseni mountains are an example of an orogen in the interference zone between two other subduction systems located in the external carpathians and dinarides this interference is demonstrated by the results of a combined thermochronological and structural field study that quantifies the post collisional latest cretaceous tertiary evolution the exhumation history derived from apatite fission track and u th he thermochronology indicates that the present day topography of the apuseni mountains originates mainly from latest cretaceous times modified by two tectonic pulses during the paleogene the latter are suggested by cooling ages clustering around 45 ma and 30 ma and the associated shortening recorded along deep seated fault systems paleogene exhumation pulses are similar in magnitude 3 5 km and are coeval with the final collisional phases recorded in the dinarides and with part of the carpathian rotation around the moesian promontory these newly quantified paleogene exhumation and shortening pulses contradict the general view of tectonic quiescence subsidence and overall sedimentation for this time interval the miocene collapse of the pannonian basin did not induce significant regional exhumation along the western apuseni flank nor did the subsequent carpathian collision this is surprising in the overall context of pannonian basin formation and its subsequent inversion in which the apuseni mountains were previously interpreted as being significantly uplifted in both deformation stages

a diode laser system for heating minerals for u th he chronometry we have developed a diode laser 25 w 808 nm system for he extraction from minerals for u th he chronometry the laser beam is delivered via a 600 m fiber cable and focused using a binocular microscope temperatures necessary for he release from apatite 500 600 c and zircon 1100 1300 c encapsulated in pt foil tubes are attained by heating to 0 5 w for 30 s and 1 25 2 5 w for 20 min respectively using a defocused beam heating at these powers does not result in measurable u and or th loss from apatite as noted by the preservation of the distinct th u in multiple splits of two different durango apatite crystals analyses of durango and the california institute of technology internal standard apatite 97mr22 yield u th he ages of 32 8 1 8 ma 1 n 11 and 4 6 0 5 1 n 5 respectively well within accepted ages the u th he age and th u of five fish canyon tuff zircon aliquots yield 29 3 2 2 ma 1 and 0 6 0 03 respectively and are indistinguishable from ages produced by resistance furnace he extraction heating of unencapsulated minerals shows that the diode laser couples well with optically opaque minerals e g hornblende biotite muscovite garnet and basalt groundmass suggesting that diode lasers offer a cheap small low maintenance alternative to nd yag and ar ion lasers for 40ar 39ar cosmogenic noble gas and stable isotope studies

dem analyses and morphotectonic interpretation the plio quaternary evolution of the eastern ligurian alps italy abstract the ligurian alps italy straddle a complex and ill defined tectonic transition that accommodates eurasia adria shortening driving concurrent growth of the western alps and northern apennines we focus on the plio quaternary landscape evolution of the eastern part of the ligurian alps with the goal of defining the active tectonics through an analysis of topography drainage networks and river long profiles the ligurian alps have a steep seaward facing escarpment with topographic features reminiscent of the geomorphic markers preserved on both actively uplifting coastlines and passive margins for example there are seaward facing benches that are thought to be uplifted marine terraces common to active margins but the drainage divide of the seaward escarpment shows clear evidence of recent northward migration into the po foreland a process consistent with escarpment retreat characteristic of passive or subsiding margins this study explores the active tectonics consistent with these diverse landscape evolution pathways our analysis reveals that rock type strongly throttles the development of topographic relief drainage networks and northward migration of the drainage divide however we also identify segments of the escarpment that indicate recent base level falls through an analysis of modeled channel steepness and comparison with mean hillslope gradient the base level falls are consistent with numerous barbed tributaries that are best explained as recent stream captures no significant correlation among the stream captures at the drainage divide suspected marine terraces at the coast ligurian sea bathymetry and active seismicity indicates that the escarpment is the footwall of a segmented normal fault this normal fault is embedded in a regionally subsiding margin where actively uplifting segments lead to a straightened pinned drainage divide whereas relatively inactive segments permit divide migration into the footwall block these results are broadly consistent with rock uplift increasing eastward toward genova across the long suspected alps apennine sestri voltaggio fault zone they highlight the respective roles of legacy structures rock type and localized rock uplift in constructing a landscape in an otherwise extending and subsiding crustal retrowedge of an active subduction plate boundary

oligocene to present kilometres scale subsidence and exhumation of the ligurian alps and the tertiary piedmont basin nw italy revealed by apatite u th he thermochronology correlation with regional tectonics the ligurian alps segment of the alpine apennine orogen in nw italy is unconformably covered by upper eocene to holocene sediments in the tertiary piedmont basin tpb and po plain these sediments dip towards the north demonstrating the erosional nature of the southern border of the succession and implying that the adjacent orogenic belt formed the substratum rather than the margin of the sedimentary basin apatite u th he and fission track thermochronology shows that the orogen first subsided and was buried at 4 km from 30 to 26 ma and began its exhumation thereafter from 26 ma to present this upward movement was contemporaneous with subsidence in the northern tpb the couple exhumation in the s and subsidence in the n migrated northwards through time vertical movements in the area are similar to those reconstructed in corsica in both cases the onset of exhumation b

geological and industrial implications of extensive dilatancy anisotropy extensive dilatancy anisotropy is the hypothesized distribution of stress aligned fluid filled microcracks pervading most rocks in the earth s crust the geometry of the cracks and the aligning stress field can be monitored by analysing the waveforms of shear waves propagating through the rockmass the ability to estimate some of the parameters of the crack and stress geometry by analysing shear wave particle displacements has widespread implications

evidence of marine isotope stage 5 5 highstand in liguria italy and its tectonic significance abstract the quaternary shoreline displacements in liguria are still poorly known this paper completely revises and reinterprets the literature on this topic taking into account only those markers that allow precise estimates of altitude and age of sea level highstands among the sites showing geomorphological evidence of mis 5 5 present in liguria three were considered reliable in eastern liguria a beach deposit with a terrace inner margin at 28 m a s l villa monteverde was dated by osl in western liguria in a site close to the french border balzi rossi a notch present inside two caves indicating a sea level altitude of 12 m is associated with a deposit containing a faunal assemblage with strombus bubonius this gastropod appeared in the italian seas only during the last interglacial highstand and provides a unique marker of the mis 5 5 horizon eastward near imperia another site madonna dell arma shows similar evidence but in this case the notch is not preserved because the cave is carved in a very soft oligocene conglomerate late quaternary tectonic movements along the different tracts of the ligurian coast seem to have occurred apparently with different although rather low uplift rates the connection between the alpine and apennine chains sestri voltaggio line divides the ligurian arch into two parts the alpine sector can be considered stable whereas the apennine relief displays in its central part an uplift rate of 0 16 mm yr

earthquake prediction a new physical basis summary subcritical crack growth in the laboratory occurs slowly but progressively in solids subjected to low stresses at low strain rates the cracks tend to grow parallel to the maximum compressive stress so that when this stress is aligned over a large enough region the cracks will also be aligned and possess effective seismic anisotropy it is suggested that such subcritical crack growth produces extensive dilatancy anisotropy eda throughout earthquake preparation zones this process is a possible driving mechanism for earthquake precursors observed at substantial distances from impending focal zones and provides in the shear wave splitting which has been observed in several seismic regions a possible technique for monitoring the build up of stress before earthquakes

river incision and migration deduced from 36cl cosmic ray exposure durations the clue de la cerise gorge in southern french alps abstract we estimate recent 20 ka incision and lateral migration rate on a spectacular n s striking gorge cross cutting n dipping limestones in a fold and thrust belt of the external southern french alps upstream of the gorge the river makes a right angle turn and follows the limestone surface parallel to the bedding direction ew eighteen samples were gathered along two vertical river polished profiles and three others on the denuded north dipping surface layer in order to determine river incision and lateral migration timing and rates surface age exposures of polished river cliff and bedding surface have been obtained from 36cl cosmogenic nuclide dating and allow us to constrain the rate of vertical incision and of surface denudation of the jurassic limestone layer fifteen 36cl exposure ages have been obtained and range from 21 ka to 3 ka samples clearly define two age height linear trends which slopes correspond to incision rates of 1 and 0 3 mm yr respectively the transition from low to high incision rate occurs at about 12 ka i e during the younger dryas glacial phase data also indicate that the vertical incision of the n s branch of the gorge is coeval with the lateral northward river migration of its e w branch associated with the denudation of the limestones surface extrapolating incision rates deduced from 36cl exposure ages through time suggests that the incision of the clue and denudation of the jurassic limestones started about 500 600 ka ago

shear wave polarizations near the north anatolian fault i evidence for anisotropy induced shear wave splitting summary the turkish dilatancy projects tdp1 in 1979 and tdp2 in 1980 recorded small earthquakes near the north anatolian fault with closely spaced networks of three component seismometers in order to investigate the possibility of diagnosing dilatancy from its effects of shear wave propagation this paper examines the polarizations of shear wavetrains recorded in the shear wave window immediately above the earthquake foci abrupt changes in the orientation and or ellipticity of the shear wave polarizations are almost always observed during the first few cycles following the initial shear wave arrival on each seismogram the horizontal projections of the polarizations of the first shear wave arrivals at any given station show nearly parallel alignments with approximately the same orientations at each of the recording sites with one exception it is difficult to explain this uniform alignment over a wide area in terms of scattering at the irregular surface topography or by earthquake focal mechanisms we demonstrate that the shear wave splitting is likely to be the result of anisotropy in the region above the earthquake foci which could produce polarizations displaying the observed alignments the temporal change of the azimuth of alignment observed at one locality between 1979 and 1980 may be due to the release of a local stress anomaly by a very near earthquake

solving the production diffusion equation for finite diffusion domains of various shapes part 2 application to cases with alpha ejection and non homogeneous distribution of the source abstract in this paper numerical methods derived in part i chem geol 2002 are expanded to accommodate the effects of emission and zonation of u and th as relevant for u th he thermochronology expressions for the required coefficients are derived for spheres finite and infinite cylinders and rectangular blocks for parent nuclide distributions which are either uniform or have stepwise zoning we show that the effects of emission and zonation on the he retention in a nonspherical crystal of modest aspect ratio can be approximated by a sphere of identical surface to volume ratio s v if the zonation is transposed on to the sphere the currently usual correction method is to perform first a diffusive calculation without considering emission and zonation and to multiply afterward with a correction factor that has been derived originally for nondiffusive calculations our results demonstrate that more accurate calculations yield different results and that the differences are often too large to be ignored in practice especially for thermal histories that include a protracted residence in the partial retention zone the difference between the usual correction and our correction can be as high as 20 for homogeneous sources for zoned crystals the difference can be even larger

observation and modelling of fault zone fracture seismic anisotropy i p sv and sh travel times summary three component vsp borehole seismograms taken in the vicinity of an active normal fault in california show strong systematic shear wave splitting that increases with proximity to the fault using cerven s method of characteristics for ray tracing in anisotropic heterogeneous media and hudson s formulation of elastic constants for media bearing aligned fractures we have fitted a suite of p sv and sh hanging wall and foot wall travel times with a simple model of aligned fractures flanking the fault zone the dominant fracture set is best modelled as parallel to the fault plane and increasing in density with approach to the fault the increase in fracture density is non uniform power law or gaussian with respect to distance to the fault although the hanging wall and the foot wall rock are petrologically the same unit the fracture halo is more intense and extensive in the hanging wall than in the foot wall upon approach to the fault plane the fracture density or fracture density gradient becomes too great for the seismic response to be computed by hudson cerven procedures the maximum fracture density that can be modelled is about 0 08 within this 25 m fracture domain it appears more useful to model the fault and near field fractures as a low velocity waveguide we observe production of trapped waves within the confines of the intense fracture interval

effects of the free surface on shear wavetrains summary the behaviour of shear waves is of great importance in identifying and investigating seismic anisotropy in the earth however shear wavetrains recorded at the earth s surface do not always reflect the motion at depth introducing practical problems of interpretation shear wavetrains incident on the surface of an isotropic half space at angles less than critical about 35 are broadly preserved but at greater angles substantial distortions can occur for stations situated close to the source as in local earthquake studies the local sp phase a radially polarized precursor to s may occur the behaviour at the surface of an anisotropic half space is further complicated by the divergence of phase and energy propagation vectors all of these complications suggest that detailed seismogram modelling is essential to any study of shear wave propagation in the earth and in particular to investigations of anisotropy induced shear wave splitting

late stages of exhumation constrained by structural fluid inclusion and fission track analyses sesia lanzo unit western european alps in metamorphic areas paleogeothermal gradients are difficult to properly estimate leading to great uncertainty in exhumation rate calculations based on fission track analysis in this work a new multidisciplinary approach based on fluid inclusion analysis structural analysis and fission track dating has proven to be able to constrain the late stages of exhumation of metamorphic rocks the study area is located in the sesia lanzo unit of the western european alps along the hone shear zone kinematic analysis at different scales unraveled a polyphase postmetamorphic deformation history constrained in the p t space thanks to laboratory investigation of kinematically referenced fluid inclusions coupled with the analysis of the rheological behavior of quartz and feldspar inside syn kinematic veins the resulting p t path points to an increasing paleogeothermal gradient from 18 to 30 c km 1 after greenschist facies metamorphic conditions and provides a reference framework for a quantitative interpretation of fission track data in terms of exhumation rates and fault throws according to fission track data throws accommodated by the hone shear zone between 33 and 30 ma are on the order of 4 5 km and would be underestimated by 25 if a normal steady gradient was assumed for the whole post metamorphic history of the area the deepest portions of this structure were exhumed thanks to the activity of the e w fault system that accommodated a throw of 4 km between 28 and 20 ma and a throw of 0 8 km during the last 20 myr

the basis for earthquake prediction summary recent advances in understanding the behaviour of shear waves propagating in the crust make the routine prediction of earthquakes seem practicable accumulating evidence suggests that most of the earth s crust is pervaded by distributions of fluid filled cracks and microcracks that are aligned by the contemporary stress field so that the cracked rockmass is effectively anisotropic to seismic waves this causes shear waves to split and shear wave splitting is observed whenever shear waves propagating along suitable raypaths in the crust are recorded by three component instruments these distributions of cracks are known as extensive dilatancy anisotropy or eda many characteristics of the crack and stress geometry can be monitored by analyzing shear waves propagating through the cracked rockmass observations of temporal variations of the behaviour of shear wave splitting in seismic gaps confirm these hypotheses and suggest that stress changes before earthquakes may be monitored by analyzing shear waves in particular monitoring earthquake preparation zones with three component shear wave vertical seismic profiles could lead to techniques for the routine prediction of earthquakes

estimating the internal structure of reservoirs with shear wave vsps in the past 10 years vertical seismic profiles vsps have played an increasingly important role in identifying and delineating in situ layers such vsps have usually recorded p wave data three component shear wave trains carry three or four times more information about the source and structure of the rocks along the raypath than the equivalent p wave train so in principle shear wave vsps should be a particularly valuable technique for examining in situ layers

shear wave polarizations near the north anatolian fault iii observations of temporal changes summary almost all shear waves from local earthquakes recorded on closely spaced three component seismometer networks deployed near the north anatolian fault turkey in two experiments in 1979 and 1980 display shear wave splitting the observations are consistent with the presence of eda extensive dilatancy anisotropy distributions of fluid filled cracks and microcracks aligned by the regional stress field temporal changes in the stress field which may occur before an earthquake may modify the geometry and possibly the orientation of the eda microcracks and lead to corresponding changes in the behaviour of the split shear waves a third experiment was undertaken in 1984 to investigate eda further and to search for possible temporal variations of the polarization of the leading split shear wave and the time delay between split shear waves observations indicate that the polarization alignments which are parallel to the strike of the parallel vertical eda cracks are unaltered between 1979 and 1984 implying that the direction of the regional stress field has not changed significantly temporal changes in the stress field are more likely to cause changes in the crack density and or aspect ratio which would result in a corresponding change in time delay between the split shear waves we examine observations of time delay in relation to their propagation path with respect to the crack geometry since it is then possible to separate the effects of changes in crack density and changes in aspect ratio with this procedure a small temporal variation of time delays is found between 1979 and 1984 consistent with a decrease in crack density and consequently a relaxation of stress in this time period no evidence was found for any observable variation of time delay over a six month observation span in 1984 we suggest that analysis of repeated shear wave vsps offers a technique for monitoring stress changes before earthquakes

tectono thermal evolution of a distal rifted margin constraints from the calizzano massif prepiedmont brianconnais domain ligurian alps the thermal evolution of distal domains along rifted margins is at present poorly constrained in this study we show that a thermal pulse most likely triggered by lithospheric thinning and asthenospheric rise is recorded at upper crustal levels and may also influence the diagenetic processes in the overlying sediments thus representing a critical aspect for the evaluation of hydrocarbon systems the thermal history of a distal sector of the alpine tethys rifted margin preserved in the ligurian alps case tuberto calizzano unit is investigated with thermochronological methods and petrologic observations the studied unit is composed of a polymetamorphic basement and a sedimentary cover providing a complete section through the prerift synrift and postrift system zircon fission track analyses on basement rocks samples suggest that temperatures exceeding 240 25 c were reached before 150 160 ma upper jurassic at few kilometer depth neoformation of green biotite stable at temperatures of 350 to 450 c was synkinematic with this event the tectonic setting of the studied unit suggests that the heating cooling cycle took place during the formation of the distal rifted margin and terminated during late jurassic 150 160 ma major crustal and lithospheric thinning likely promoted high geothermal gradients 60 90 c km and triggered the circulation of hot deep seated fluids along brittle faults causing the observed thermal anomaly our results suggest that rifting can generate thermal perturbations at relatively high temperatures between 240 and 450 c at less than 3 km depth in the distal domains during major crustal thinning preceding breakup and onset of seafloor spreading

presence of a long term lithospheric thermal anomaly evidence from apatite fission track analysis in northern new england abstract apatite fission track aft ages from 56 samples of paleozoic and mesozoic crystalline rocks in new hampshire northeastern vermont and western maine range from 70 to 140 ma and reflect widespread early to late cretaceous cooling the regional aft age distributions determined in this study suggest that reactivation of preexisting orogen parallel faults and the presence of a long lived thermal anomaly in the lithospheric mantle controlled the late unroofing history of this part of the northern appalachians a northeast trending zone of young dominantly late cretaceous aft ages 70 118 ma extends from southwestern new hampshire through the central white mountain region and continues into northern new hampshire northeastern vermont and western maine providing evidence for regional nw se extension and cooling at this time significantly older aft ages 125 140 ma in the region bounded by the bill little ammonoosuc and northey hill faults in northwestern new hampshire suggest a normal sense r

climatically versus tectonically forced erosion in the alps thermochronometric constraints from the adamello complex southern alps italy abstract we apply u th sm he dating and fission track thermochronometry of apatites to the adamello complex located in the southern european alps our goal is to constrain exhumation rates since the miocene in particular to determine whether the increase in sedimentation documented in the foreland basins since 5 ma is recorded in cooling rates of the southern alps thermochronometry provides a cooling rate for rocks which can be converted to an exhumation rate through thermal modeling thereby quantifying the amount of rock exhumed at different time scales apatite fission track and u th sm he analyses all record miocene ages we find no evidence for an increase in exhumation rate during the plio pleistocene the results of our exhumation rate estimates and tectono geomorphic modeling suggest that unroofing during thrust propagation of the southern alps in the late miocene drove most of the exhumation while changes in relief mainly associated with plio pleistocene climate change likely did not affect the adamello complex the findings from this study combined with other studies highlight that there appears to be a gradient across the alps with more intensive plio pleistocene erosion in the western and central alps compared to the eastern and southern alps

neotectonics of the marmara sea region of turkey seismological investigations in western anatolia nw turkey have identified linear patterns of earthquake epicentres outlining a wedge shaped block in the area of the marmara sea this block shows different seismic characteristics from the rest of western anatolia and appears to act as a separate tectonic unit earthquake fault plane mechanisms show that the marmara block is being rotated and sheared in order to accommodate the right lateral motion of the north anatolian fault and the extensional tectonics of the southwestern anatolia investigations of the behaviour of seismic shear waves suggest that neotectonic stress aligns water filled microcracks throughout the upper brittle 10 20 km of the crust and that in situ stress directions can be monitored by analysis of shear waves recorded on three component instuments

analysis of records of local earthquakes the turkish dilatancy projects tdp1 and tdp2 summary this is the introduction to a series of papers analysing records from three component seismometers immediately above a swarm of small earthquakes near the north anatolian fault in turkey the networks were set up to investigate the possibility of estimating dilatancy induced adisotropy by monitoring shear wave splitting in shear waves from local earthquakes as suggested by the hypothesis of extensive dilatancy anisotropy eda these networks were among the first closely spaced digital three component seismometers to be deployed in the shear wave window immediately over a seismic source zone where the polarizations of incident shear waves can be recognized from surface recordings consequently the seismograms display several new phenomena that have not been previously observed 1 the polarizations of almost all shear waves arriving within the shear wave window showed abrupt changes in direction characteristic of shear wave splitting in synthetic seismograms modelling wave propagation through anisotropic rocks 2 the polarizations of the faster split shear waves are in patterns characteristic of propagation through distributions of cracks aligned by the principal axes of stress but not characteristic sf shear waves propagating through isotropic rock from a double couple source oriented by the same stress axes 3 many characteristics of the observed polarization patterns are similar to synthetic polarization diagrams for wave propagation through vertical parallel cracks 4 the orientation of the anisotropy derived from the shear wave polarizations is consistent with the common axes of stress of the fault plane mechanisms 5 the orientation of the shear wave anisotropy is also similar to the orientation of the anisotropy derived independently from inverting p and s wave arrival times and 6 there is some indication of a temporal change in polarization in one locality such as might be expected if a change in a local stress anomaly altered the crack geometry

late orogenic vertical movements within the arc of the sw alps and ligurian alps abstract mainly on the basis of seismic data we reconstruct magnitude and timing of miocene to present vertical movements in the region of the savigliano basin an up to 4 km thick succession of neogene to quaternary sediments accumulated inside the alpine arc at the western termination of the po plain we focus in particular on the margins of the basin which are the link between the mountain range and the subsiding basin seismic data from these regions allow for the definition of upward and downward vertical movements uplift exhumation and subsidence with a spatial and temporal resolution which cannot be attained by other methods the eastern southern and western margins of the savigliano basin display very different geometries of the sedimentary bodies and therefore document different vertical movements during miocene to present times the eastern part of the savigliano basin and the regions to the e experienced subsidence followed by exhumation the southern margin of the basin in the cuneo area was much more stable with miocene to present formations all pinching out close to the present day outcropping position of the basement sedimentary cover contact in the w seismic sections record a stage of tilting until the burdigalian followed by generalized subsidence which affected also the adjacent regions of the sw alps the overall pattern of vertical movements is essentially controlled by the nw ward migration of a syncline anticline couple with the synclinal axis presently located in the center of the savigliano basin the width of the folds is in the order of 30 60 km 1 2 wavelength in map view the trace of the fold axes changes from n s in the savigliano basin to e w in the alessandria basin

miocene lateral extrusion in the inner western alps revealed by dynamic fault analysis 1 from early miocene to the present day the core parts of the western european alps experienced brittle extensional deformations mostly in a strike parallel direction here we present new data constraining the brittle deformation of the vanoise area french alps and a synthesis of 312 paleostress tensors in the whole arc of the internal western alps the data show a continuous change in the direction of extension from n065 simplon area to n s vanoise area and to nnw sse briancon area the abundance of orogen perpendicular 3 axes increases from the north to the south in the brianconnais area an extensional reactivation of the basal penninic thrust seems to be the origin of the e w to ne sw oriented 3 in light of these new data and the regional paleostress synthesis we propose a predominant orogen parallel extension in the internal zone as a whole this orogen parallel extension is related to the indentation rotation of the apulian microplate and to the opening of the ligurian sea during the lower middle miocene the locally observed orogen perpendicular extension is interpreted as an effect of the exhumation of the internal crystalline massifs the uplift of the external crystalline massifs and or the present day geodynamics postorogenic gravitational collapse some transcurrent tectonics older than the extension in the valais area and younger than the extension farther south is observed in the entire inner western alps strike slip movements are correlated with the apulian rotation and local permutation of stress axes

extensional neotectonics around the bend of the western central alps an overview the western alps active tectonics is characterized by ongoing widespread extension in the highest parts of the belt and transpressive compressive tectonics along its borders we examine these contrasting tectonic regimes using a multidisciplinary approach including seismotectonics numerical modeling gps morphotectonics fieldwork and brittle deformation analysis extension appears to be the dominant process in the present day tectonic activity in the western alps affecting its internal areas all along the arc shortening in contrast is limited to small areas located along at the outer borders of the chain strike slip is observed throughout the alpine realm and in the foreland the stress orientation pattern is radial for 3 in the inner extensional zones and for 1 in the outer transcurrent tranpressional ones extensional areas can be correlated with the parts of the belt with the thickest crust quantification of seismic strain in tectonically homogeneous areas shows that only 10 20 of the geodesy documented deformation can be explained by the alpine seismicity we propose that alpine active tectonics are ruled by isostasy buoyancy forces rather than the ongoing shortening along the alpine europe adria collision zone this interpretation is corroborated by numerical modeling the neogene extensional structures in the alps formed under increasingly brittle conditions a synthesis of paleostress tensors for the internal parts of the west alpine arc documents major orogen parallel extension with a continuous change in 3 directions from ene wsw in the simplon area to n s in the vanoise area and to nnw sse in the briancon area minor orogen perpendicular extension increases from n to s this second signal correlates with the present day geodynamics as revealed by focal plane mechanisms analysis the orogen parallel extension could be related to the opening of the ligurian sea during the early middle miocene and to compression rotation of the adriatic indenter inducing lateral extrusion

apatite u th he age constraints on the development of the great escarpment on the southeastern australian passive margin the southeast australian margin like other high elevation passive margins is characterised by a steep escarpment that separates a dissected coastal plain from a low relief inland plateau quantitative constraints on the generation of escarpments can be provided by apatite u th he ages here we use a coast perpendicular traverse across the coastal lowlands escarpment and plateau to test the three prevailing models of se australian escarpment formation namely retreat into a downwarped rift shoulder escarpment retreat and down wearing on high elevation rift shoulder with flexural rebound apatites from the coastal plain have he ages of between 87 and 112 ma suggesting that the coastal lowlands developed very rapidly after rifting and continental break up at 85 100 ma the he age data are inconsistent with the erosion of a downwarped rift margin and cannot be explained by a constant post break up rate of lateral escarpment retreat across the coastal plain or by constant down wearing the data require either rapid escarpment retreat or rapid in place excavation of the escarpment soon after break up in response to rifting and the lowering of base levels on the margin of the new continent at break up followed by a period of landscape stability and low erosion combined with the existing apatite fission track record the he data are consistent with erosion of 3 4 km within a maximum of 28 myr of break up at a minimum vertical erosion rate of 130 m myr 1 along the coast the rapid denudation period across the coastal plain in this region took less than 48 myr from the coast to the escarpment base which corresponds to an average vertical erosion rate of 45 m myr 1 this is equivalent to a mean escarpment retreat rate of 5 10 km myr 1 apatite he ages from the plateau 183 247 ma indicate that the highlands remained stable throughout continental break up experiencing average erosion rates of less than 10 m myr 1 since the late palaeozoic early mesozoic

modeling of the temperature sensitivity of the apatite u th he thermochronometer apatite u th he apparent ages will generally reflect residence for extended periods at temperatures where helium is neither quantitatively retained nor lost by diffusion to characterize the response of apatite he ages to thermal histories involving partial he retention we explored solutions to the he production diffusion equation under thermally static conditions the analytical solution to this equation coupled with published diffusivity data demonstrates that the zone of partial he retention extends from about 40 c to 85 c this zone lies at temperatures 35 c cooler than the analogous fission track partial annealing zone he ages within the partial retention zone ultimately achieve a balance between he production and loss yielding a steady state age both the ultimate age and the time it takes to achieve this age are temperature dependent for example an apatite held at 75 c equilibrates to an age of 2 ma after 17 myr regardless of whether equilibrium is approached from a higher or a lower initial he age for representative dynamic thermal histories we evaluated apatite he ages using a numerical solution to the ingrowth diffusion equation the results illustrate the sensitivity of he ages to various geologic histories and are useful for understanding he age elevation relationships and for testing time temperature paths derived from apatite fission track length distributions in addition although he diffuses rapidly from apatite at shallow crustal temperatures modeling of ambient temperature fluctuations indicates that he ages are nearly unaffected by surficial processes

chronology causes and progression of the messinian salinity crisis the messinian salinity crisis is widely regarded as one of the most dramatic episodes of oceanic change of the past 20 or so million years 1 3 earliest explanations were that extremely thick evaporites were deposited in a deep and desiccated mediterranean basin that had been repeatedly isolated from the atlantic ocean1 2 but elucidation of the causes of the isolation whether driven largely by glacio eustatic or tectonic processes have been hampered by the absence of an accurate time frame here we present an astronomically calibrated chronology for the mediterranean messinian age based on an integrated high resolution stratigraphy and tuning of sedimentary cycle patterns to variations in the earth s orbital parameters we show that the onset of the messinian salinity crisis is synchronous over the entire mediterranean basin dated at 5 96 0 02 million years ago isolation from the atlantic ocean was established between 5 59 and 5 33 million years ago causing a large fall in mediterranean water level followed by erosion 5 59 5 50 million years ago and deposition 5 50 5 33 million years ago of non marine sediments in a large lago mare lake sea basin cyclic evaporite deposition is almost entirely related to circum mediterranean climate changes driven by changes in the earth s precession and not to obliquity induced glacio eustatic sea level changes we argue in favour of a dominantly tectonic origin for the messinian salinity crisis although its exact timing may well have been controlled by the 400 kyr component of the earth s eccentricity cycle

the messinian diatomite deposition in the mediterranean region and its relationships to the global silica cycle abstract diatomites constitute a widely represented lithology in the messinian sections of the circum mediterranean neogene marginal basins although traditionally interpreted as genuine evidence of the gradually restricted conditions that characterized the mediterranean just before the messinian salinity crisis their coeval occurrence with a global intensification of the opaline production in the world oceans late miocene early pliocene biogenic bloom suggests that an integrative analysis of the origins of these sediments is necessary a comprehensive analysis of the geological and paleontological records suggests that the synergistic intervention of abiotic tectonic and climate reconfigurations and biotic expansion of grass dominated opal rich biomes controlling factors may have promoted a remarkable enhancement of silica flux from continents to oceans which in turn can explain the opaline burst that occurred during the late miocene at both the global and mediterranean scale the finely laminated pattern and the rich fossil content of diatomaceous deposits that are usually considered to be byproducts of anoxic conditions are briefly discussed some studies seem to indicate that instead of anoxia the aggregation and sedimentation of diatom tests may play a critical role in these processes the lower messinian diatomites of the mediterranean region are generally interbedded with organic rich sediments sapropels clearly attesting prolonged precessionally controlled periods of basin stratification and bottom water anoxia or hypoxia a causal relationship between sapropel and diatomite deposition in the mediterranean is proposed considering the possible interplay between stratification adapted diatoms and anaerobic bacteria and their respective role in influencing the marine silica cycle

tsunami mapping related to local earthquakes on the french italian riviera western mediterranean the ligurian coast located at the french italian border is densely populated as well as a touristic area it is also a location where earthquakes and underwater landslides are recurrent the nature of the local tsunamigenesis is therefore a legitimate question because no tsunami warning system can resolve tsunami arrival times of a few minutes which is the case for the area as far as the seismicity of the area is concerned the frequent recurrent earthquakes are generally of moderate magnitude most of them are lower than mw 5 however the relatively large mw 6 9 earthquake larroque et al in geophys j int 2012 doi 10 1111 j 1365 246x 2012 05498 x that occurred on the february 23 1887 offshore of imperia italian riviera is quite emblematic this unusual event for the region merits a complete study the quantification of its rupture mechanism is essential 1 to understand the regional active deformation but also 2 to evaluate its tsunamigenesis potential by deriving relevant rupture scenarios obtained from our knowledge of the event for that purpose the event is extensively described here the first point has been the subject of quite a few studies based on the seismotectonics of the area the last documented approach has been completed by larroque et al geophys j int 2012 doi 10 1111 j 1365 246x 2012 05498 x who proposed a rupture scenario involving a reverse faulting along a north dipping fault and favoring a mw 6 9 magnitude in the present paper 1 we study the accuracy of their solutions in relation to the computational grid spacing and the dispersive nondispersive parameterization 2 based on an uncertainty on the recorded wave amplitude of the genoa tide gauge they used we propose a mw 6 7 earthquake magnitude solution for the event the kinematics is unchanged co existing with the mw 6 9 3 we evaluate the tsunami coastal impact of the 1887 event and 4 we test a range of possible ruptures that local faults may undergo in order to propose a synoptic mapping of the tsunami threat in the area the spatial distribution of the maximum wave height mwh is provided with a tentative identification of the processes that are responsible for it this latter issue is imperative in order to make our mapping as generic as possible in the framework of our deterministic approach based on realistic scenarios and not on ensemble statistics the predictions suggest that the wave impact is mostly local considering the relatively moderate size of the rupture planes although the present day seismicity in this region is moderate stronger earthquakes m 6 5 have occurred in the past the studied scenarios show that for such events specific localities along the french italian riviera may experience very significant mwh related to the shallow focal depth tested for such scenarios we may reasonably conclude that the tsunami threat is relatively significant and uniform at the italian side of the riviera from ventimiglia to imperia while it is more localized sporadic at the french side from antibes to menton with however higher local level of inundation e g nice city center

a closing ligurian sea two earthquakes occurred in the ligurian sea in december 1989 and april 1990 both were widely felt along the french and italian rivieras thus reminding us of the seismic risk in this region the significant increase in the number of seismic stations in the area facilitated the study of these two shocks and their related aftershocks using different techniques absolute and relative hypocentral locations doublet analysis and waveform modeling we computed accurate hypocentral locations and estimated the location error range for earthquakes in this area we also computed the focal mechanisms for both mainshocks and we present here a synthesis that integrates previous data the reactivation in compression of the ligurian sea sphenochasm is confirmed which would eventually result in the closing of an aborted oceanic domain as the seismic activity is clearly restricted to the northern margin we suggest it locally results from the lateral expulsion of the south western alps along the apulian indenter

active deformation at the southwestern alps ligurian basin junction france italy boundary evidence for recent change from compression to extension in the argentera massif abstract several hundred earthquakes of small and moderate magnitude occur each year at the southwestern alps ligurian basin junction in addition the historical seismicity data attests for earthquakes of magnitude close to 6 5 despite the seismic hazard and the vulnerability of this region the present day driving mechanism of deformation and the major structures accommodating these deformations remain unclear this littoral area presents a strong topographic gradient from 3000 masl on the argentera alpine massif to 2500 m u s l in the ligurian basin and a strong structural inheritage resulting from 50 my geological evolution combining different processes such as continental collision and ocean basin opening we present new results about the kinematics of the corsica sardinia continental block with respect to the western alpine belt from 7 years of continuous gps measurements we show that a small part of the nubia eurasia convergence is certainly transferred northward of the maghrebides deformation belts to the corsica sardinia block in the southwesternmost alps from torino to the mediterranean coast the baselines reveal differential motions of lengthening between the po plain and the argentera and shortening between the argentera and the ligurian domain in a region where few focal solutions are available we determine seven new focal mechanisms located in the argentera massif these new data underline a quaternary change from compression to extension in that part of the western alpine belt the focal mechanisms calculated attest for extensional faulting at shallow level between 1 and 11 km depth we add 7 focal mechanisms from the literature to calculate the stress tensor a homogeneous solution indicates a direction of extension broadly perpendicular to the topographic axis culmination of the argentera in contrast the earthquakes recorded below 15 km at the northwestern margin of the po plain testify reverse faulting and a compressional state of stress in the deep crust thus we point out that the stress field is vertically heterogeneous in the crust of the argentera area the ligurian domain is mainly characterized by reverse and strike slip faulting the major earthquakes are located in the northern margin and at the ocean continent transition these earthquakes are assumed to result from the reactivation in a compressional state of stress of the structures formed during the oligo miocene opening of the ligurian basin finally we propose three hypotheses to explain the current deformation at the alps ligurian basin junction taking into account the far field kinematics between the nubia and the eurasia plates the topographic gradient between the argentera massif and the ligurian oceanic floor and the distribution of the deformations

long lasting transcurrent tectonics in sw alps evidenced by neogene to present day stress fields abstract the sw alps are an active orogen undergoing intra mountainous extension and peripheral compression we discuss the significance of syn orogenic extension based on a comparison of paleo stress derived from fault slip data inversion reflecting the long term

tertiary cooling and exhumation history in the maramures area internal eastern carpathians northern romania thermochronology and structural data the tertiary kinematic history of the maramures area is constrained by integrating thermochronological fission track and uth he analysis data with field based structural investigations this study focuses on the tectonic evolution of the northern rim of the tisza dacia block during collision with the european margin cretaceous nappe stacking related metamorphism as well as late cretaceous exhumation are evidenced by zircon fission track data subsequent palaeogene to early miocene sedimentation led to burial heating and annealing of fission tracks in apatite final tectonic uplift was initiated during the convergence of tisza dacia with the european margin associated with transpressional deformation 16 to 12 ma this led to mid miocene exhumation recorded by apatite fission track cooling ages in the western part of the study area transtension between 12 and 10 ma caused brittle deformation along ew trending strike slip faults and swne trending normal faults delimiting blocks that were tilted towards the sw this fragmentation of the crust led to enhanced exhumation at rates of 1 mm a in the central part of the study area as is documented by middle to late miocene cooling ages 13 to 7 ma the outside estimate for the total amount of exhumation since middle miocene times is 7 km

microearthquakes in the tdp swarm turkey clustering in space and time summary the third occupation experiment tdp3 of recording sites above a persistent swarm of microearthquakes near the north anatolian fault with a larger seismic network and over a longer period of time confirms and refines previous observations with greater resolution the greater resolution in earthquake locations has revealed marked clustering in time and space many perhaps most of the earthquakes belong to clusters where successive earthquakes originate in a very small volume and have similar fault mechanisms such studies allow the progression of seismic activity of small earthquakes to be followed in some detail and may reveal features which are hidden in larger and more complex earthquake sequences

the exhumation history of the european alps inferred from linear inversion of thermochronometric data thermochronometric data collected across the alps over the last three decades allows for investigation of the evolution of this orogen which is subject to changes in climate and geodynamics exhumation rates are inferred from the thermochronometric ages using a statistical inversion method based on the fact that the distance a sample traveled since closure is equal to the integral of the exhumation rate from the present day to the age of the sample exhumation rates are assumed to be spatially correlated but are free to vary through time this results in the quantification of exhumation rates across the alps since 32 ma along with assessments of the quality of these inferences we find that exhumation rates are initially fast in the internal arc of the western alps at rates up to 0 8 km myr at 30 ma decreasing at 20 ma to 0 3 km myr to remain slow to the present at the same time around 20 ma rates across the external crystalline massifs of western alps increase to 0 6 km myr we also find that the onset of high exhumation rates in the tauern window and the lepontine dome occurs at around 20 ma a time characterized by major reorganizations in the alpine chain a general increase in exhumation rates at around 5 ma over the entire alps is not confirmed instead we find that the western alps exhibit a 2 to 3 fold increase in exhumation rate over the last 2 ma during a recent event not seen further east in spite of very similar topographic characteristics we attribute this strong signal to detachment of the european slab in the western alps combined with efficient glacial erosion

late miocene to present exhumation in the ligurian alps southwest alps with evidence for accelerated denudation during the messinian salinity crisis detrital apatite u th he and fission track thermochronometry are applied to constrain the exhumation history of the ligurian alps southwest alps exhumation of the ligurian alps is recorded from ca 11 ma and continues until present more than 4 km of exhumation is recorded at an average rate of 0 4 0 2 mm yr exhumation is accommodated along a north dipping thrust at the foot of the ligurian margin combined u th he and fission track thermal modeling show a phase of accelerated denudation between 7 and 5 ma associated with the base level drop during the messinian salinity crisis

testing models of orogen exhumation using zircon u th he thermochronology insight from the ligurian alps northern italy testing models of orogen exhumation requires precise constraint of the time temperature paths of the exhumed rocks the zircon u th he zhe thermochronometer has a closure temperature of 140 210 c and can provide temporal constraints on the exhumation history of rocks through a thermal range which crucially corresponds the onset of brittle behaviour of an exhuming orogen we performed zhe analyses to test the existing contradictory models for the exhumation of the ligurian alps the zhe ages indicate a very rapid 1 3 6 8 mm yr and southward migrating exhumation of the orogen between 32 and 25 ma these high exhumation rates are unique within the alpine belt and cannot be reconciled with existing geodynamic models of the evolution of the ligurian alps we propose a model of tectonic denudation via detachment accomplished in the shallowest crust 5 km as a result of the last orogenic phase of extension

neogene kinematics of the central and western alps evidence from fission track dating zircon and apatite fission track analysis has established the continuation of a zone of rapid change in mineral ages extending from the simplon fault zone in the simplon alps through the rhone valley and along the southeastern side of the mont blanc and belledonne massifs apatite fission track ages to the northwest of this zone generally range from 1 4 to 6 ma whereas those to the southeast range from 6 to 13 ma corresponding values for zircon are 11 13 and 16 26 ma respectively the zone corresponds to the position of the frontal pennine thrust in the mont blanc belledonne region this structure a prominent feature on recent deep seismic profiles may have been reactivated in the neogene with an important normal fault component this is suggested by apatite and zircon fission track ages in the footwall that are younger than those in the hanging wall and by the observed elimination of the lower pennine or simplon nappes along this fault zone in the rhone valley mont blanc belledonne region resulting in the juxtaposition of north penninic and helvetic ultra helvetic nappes at the current erosion level the distribution of fission track ages reflects this movement and the related neogene exhumation of the mont blanc and belledonne external massifs which has continued until less than 1 4 m y ago i e it is almost certainly still active and has tilted the overlying nappe sequence

shear wave splitting above the subducting juan de fuca plate shear wave splitting observed in three component broadband recordings of local earthquakes near southern vancouver island british columbia provide the first constraints on shear wave anisotropy in the continental crust above the subducting juan de fuca plate waveforms of 22 shallow earthquakes 15 30 km depth and 16 deep earthquakes 40 60 km depth were examined for shear wave splitting the fast polarization direction is well defined at 312 19 for the deep earthquakes and 293 27 for the shallow earthquakes these fast polarization directions are approximately parallel to the continental margin and coincide with the orientation of the pressure axes of small crustal earthquakes in this region interpreting this polarization pattern in terms of the extensive dilatancy anisotropy model indicates a margin parallel compressive stress regime comparing the average time delays between the fast and slow shear waves for the deep earthquakes 0 32 s and the shallow earthquakes 0 20 s suggests that the source of the seismic anisotropy is stronger in the upper 20 km of the continental crust here the average differential shear wave anisotropy is estimated at 2 3 these observations support the theory of weak coupling between the downgoing juan de fuca plate and the overlying north america plate as the principal stress is perpendicular to the direction of subduction and the s wave splitting above the subducting plate is nearly perpendicular to the sks splitting direction in the upper mantle beneath the subducting plate

from nappe stacking to out of sequence postcollisional deformations cretaceous to quaternary exhumation history of the se carpathians assessed by low temperature thermochronology 1 apatite fission track aft and u th he ahe thermochronology have been combined to constrain the exhumation history of the se carpathians cooling ages generally decrease from cretaceous for the internal basement nappes aft ages to miocene quaternary aft and ahe respectively for the external sedimentary wedge the aft and ahe data show a paleogene age cluster which confirms a suspected but never demonstrated tectonic event the new data furthermore suggest that the se carpathians have been affected by a middle miocene exhumation phase related to continental collision which occurred at rates of 0 8 mm yr similar to the one previously inferred for the east carpathians the se carpathian tectonic evolution however is overprinted by two younger exhumation events in the pliocene pleistocene the first exhumation phase latest miocene early pliocene occurred at high exhumation rates 1 7 mm yr and is interpreted as a tectonic event and or associated with a sea level drop in the paratethys basins during the messinian low stand the youngest recorded tectonic phase suggests rapid pleistocene exhumation 1 6 mm yr and is interpreted to represent crustal scale shortening different in mechanics from collisional processes the data suggest that the se carpathians did not develop as a typical double vergent orogenic wedge instead exhumation was related to a foreland vergent sequence of nappe stacking during collision and was subsequently followed by a large out of sequence shortening event truncating the already locked collisional boundary

current strain regime in the western alps from continuous global positioning system measurements 1996 2001 four to six years of continuous measurements at 10 permanent global positioning system sites in the western alps show horizontal residual velocities of 2 mm yr with respect to stable europe uncertainties range from 0 3 to 1 4 mm yr these velocities and the associated strain rate field indicate that the central part of the range is currently dominated by east west extension whereas the southern part shows north south to northwest southeast compression the geodetic and seismotectonic data are consistent with a model where strain is essentially controlled by the counterclockwise rotation of the adriatic microplate with respect to eurasia this rotation together with the arcuate shape of the contact between the adriatic microplate and the alps induces dextral shear kinematic boundary conditions across the western alps with an additional divergence component in their central part and in switzerland and a convergence component in their southern part

paleoenvironmental change in a precession paced succession across the onset of the messinian salinity crisis insight from element geochemistry and molecular fossils abstract in marginal mediterranean sub basins the early phase of the messinian salinity crisis msc is recorded by cyclic successions of gypsum and shales which in deeper parts of the sub basins make lateral transition into organic rich shales marls and carbonates the cyclic stacking pattern of the gypsum bearing sequences is assumed to reflect periodic paleoenvironmental change induced by precession driven climate perturbations with the assumption that shales reflect humid climate precession minima while gypsum reflects arid conditions precession maxima however this correlation has not been verified to date mostly because of the scarcity of microfossils the most commonly used tools for the reconstruction of precession driven paleoenvironmental change such change can instead be reconstructed through the study of the deeper water counterparts of gypsum marly and carbonate layers with geochemical indicators major and trace elements molecular fossils which provide insight on climate and aquatic productivity we used this approach to study a section from the piedmont basin nw italy where the onset of the msc is archived in a sequence of organic rich sediments this sequence displays distinct lithological cyclicity evidenced by the repetition of couplets of organic rich shales and marls either bioturbated in the pre msc part of the section or laminated during the msc the influence of orbitally driven precession climate oscillations is demonstrated by fluctuations of ti al si al mg al k al zr al and ba al ratios that are in phase with lithological cyclicity these fluctuations are interpreted to reflect alternation of humid shales deposited during precession minima and arid bioturbated and laminated marls deposited during precession maxima phases dominated by fluvial and aeolian transport of detrital material respectively the cyclicity of the element ratios is mirrored by changes in organic carbon content and molecular fossil inventory in particular the distribution of long chain n alkanes and their degree of preservation reveal that humid phases at times of precession minima were typified by the maximum input of degraded terrestrial organic matter driven by enhanced riverine runoff which promoted water column stratification coeval increase in ba content a common paleoproductivity proxy agrees with enhanced nutrient supply during humid periods promoting phases of eutrophication in the basin lithological and geochemical changes are observed in msc sediments deposited at times of precession maxima evidenced by the replacement of pre msc bioturbated marls by laminated marls rich in filamentous fossils corresponding to the remains of probable colorless sulfide oxidizing bacteria such changes reflect an intensification of water column stratification after the onset of the msc possibly related to the combined effect of persistent freshwater inflow and basin isolation preluding the advent of gypsum precipitation

the syn and post collisional evolution of the romanian carpathian foredeep new constraints from anisotropy of magnetic susceptibility and paleostress analyses abstract the first results of anisotropy of the magnetic susceptibility ams data from the romanian carpathian foredeep reveal compression directions generally perpendicular to the highly bended carpathian orogenic arc the distribution of the present day stress field in the pannonian carpathian region reflects pre imposed plate boundaries that were established during late miocene collision analysis of the ams along the eastern and southern carpathian foredeep at the contacts of the orogenic nappe pile the lower plate and the overlying sedimentary rocks indicates that two factors are critical for the distribution of the stress field during and after collision i e 1 the inherited highly bended plate geometry and 2 the quaternary deformation that lead to differential vertical and horizontal movements in the se carpathians the ams analysis was successfully used in the weakly deformed mio pliocene sedimentary rocks from the carpathian foredeep revealing information about the deformation history of the soft non competent rocks where the poor preservation of traditional kinematic indicators e g faults and folds is difficult

exhumation controlled by transcurrent tectonics the argentera mercantour massif sw alps new apatite fission track aft and u th he ages from the argentera mercantour external crystalline massif of the sw alps document an exhumation history along transcurrent dextral faults significant aft age differences across the strikes of the main faults have been obtained from the ne 12 9 ma to the sw 5 2 ma and are linked to vertical uplifts along these right lateral transpressional structures such segmentation is not observed in ahe ages ahe ages have preserved younger ages 4 5 ma on the eastern hangingwall side of the high durance extensional system such an exhumation history is interpreted to result from a transition of transpressional to transtensional regimes at 8 5 ma during continuing adria europe convergence these data show that recent extensional deformation in the sw alps can be related to the development of a transtensional domain in the ubaye embrunais depression linked to ongoing strike slip deformation along the argentera mercantour

seismic wavefield separation by multicomponent tau p polarisation filtering abstract this paper presents a modified form of controlled direction reception cdr filter to separate p and s waves in a multi component seismic profile the aim of cdr is to enhance the clarity of the section the essence of the method in seeking s wave extinction is to perform a dot product between the signal vector and the polarisation slowness vector during projection of the section into tau p space using the p wave velocity along the array alternatively s waves can be enhanced and all other wave types including background noise suppressed by using a conjugate rotation operator and the s velocity profile in forming the slant stack a two dimensional gain function based on the rectilinearity of particle motion is then applied in tau p space as a non linear boost function in order to enhance strongly polarised arrivals synthetic and physical model examples are used to demonstrate the noise rejection properties of the cdr process and to show how p and s wave seismic sections can be separately obtained

role of topography in isotherm perturbation apatite u th he and fission track results from the malta tunnel tauern window austria 1 apatite u th he and fission track age determinations of samples from a 20 km long near horizontal tunnel in the hochalm ankogel dome eastern tauern window austria are presented in order to determine the role of paleo topography in perturbing isotherms in the shallow crust apatite fission track ages 26 8 ma show no systematic correlation with distance along the tunnel or elevation two age components in the fission track data indicate cooling through 120 c at approximately 20 ma and 80 c at approximately 6 ma surface and tunnel u th he ages 17 9 ma and 13 5 ma respectively are consistently younger than the equivalent fission track ages u th he ages vary systematically along the tunnel with older ages at the northern and southern tunnel portals and younger ages in the central section geological factors faulting lithology appear to have had little effect on this age distribution the u th he age pattern is inconsistent with rock cooling underneath the present day hochalm ankogel dome topography the age minimum is interpreted to coincide with a paleotopographic maximum in the hochalm ankogel dome and suggests that the 40 60 c isotherms were warped sufficiently to affect apatite u th he ages the tunnel apatite u th he ages match synthetic he ages derived from a two dimensional numerical model of landscape evolution integrating the thermal model results with the data allows the relief development to be constrained and we calculate that the present day hochalm ankogel dome topography was formed at 7 to 10 ma

a shear wave polarization study in the wellington region new zealand a month of digital data from two three component seismograph stations near wellington new zealand was analyzed as part of a feasibility study for a major project to investigate shear wave splitting although the total number of earthquakes studies was small 14 some suggestive results were obtained almost all events recorded within the shear wave window showed a phase reversal of the horizontal components after one or two shear wave cycles suggesting that there are actually two shear wave arrivals the measured polarization of the first shear wave arrivals was n 31 plus minus 11 e this polarization alignment cannot be explained by focal mechanisms and it is unlikely to be due to topography because of the station to station correlation the present evidence suggests the most likely cause is crustal anistropy due to the geological structure at shallow depth rather than stress aligned micro cracks

shear wave splitting above small earthquakes in the kinki district of japan abstract we have identified shear wave splitting diagnostic of the effective anisotropy induced by aligned microcracks in the wavetrains of micro earthquakes at four stations of the abuyama network in the kinki district of japan we find that the directions of polarization of the faster split shear waves are nearly parallel for all azimuths of arrival and for all angles of incidence less than the critical angle at three of the four stations these directions of polarization are consistent with the axis of maximum compression obtained from earthquake fault plane mechanisms and also agree with the directions of the general trends of geological structures which represent the orientations of the cleavage or lamination these results suggest that crack induced anisotropy is present in the brittle upper crust beneath japan as has been found elsewhere but we could not distinguish whether this reflects the distributions of cracks induced by the present stress field or results from the general trends of surface geology although the delay times between faster and slower shear waves are difficult to estimate reliably because of their high sensitivity to internal interfaces the delay times can be interpreted as the result of a distribution of parallel vertical cracks with a crack density of about 0 04 the consistency or lack of consistency of the directions of the shear wave polarizations at the four stations demonstrates the effects of surface topography and near surface layering on the shear wave polarizations

western alpine back thrusting as subsidence mechanism in the tertiary piedmont basin western po plain nw italy abstract basin formation dynamics of the tertiary piedmont basin tpb are here investigated by means of cross section numerical modelling previous works hypothesised that basin subsidence occurred due first to extension oligocene and then to subsequent loading due to back thrusting miocene however structural evidence shows that the tpb was mainly under contraction from oligocene until post pliocene time while extension played a minor role furthermore thermal indicators strongly call for a cold flexure induced mechanism but are strictly inconsistent with a hot thermally induced mechanism our new modelling shows that the tpb stratigraphic features can be reproduced by flexure of a visco elastic plate loaded by back thrusts active in the western alps in oligo miocene times far field compression contributed to the tpb subsidence and controlled the basin infill geometry by enhancing basin tilting forebulge uplift and erosion of the southern margin of the basin these results suggest that the tpb subsidence is the result of a combination of mechanisms including thrust loading and far field compressional stresses

solving the production diffusion equation for finite diffusion domains of various shapes part i implications for low temperature u th he thermochronology abstract we propose an accurate fast and easy to use method to derive numerical solutions for production diffusion equations for finite diffusion domains of various shapes and arbitrary cooling histories previous studies provide solutions for spheres infinite cylinders and infinite sheets we extend this range and provide solutions for finite bodies i e finite cylinders and rectangular blocks of any aspect ratio this approach is important as recently it has become clear that for example the physical grain is the diffusion domain for he diffusion in apatite and titanite j geophys res 105 2000 2903 geochim cosmochim acta 63 1999 3845 we discuss the use of the new approach for forward modelling u th he production diffusion in apatite taking results with finite cylinders as a good approximation for apatite crystals it is found that approximating instead with spheres or infinite cylinders having the same radius yields differences in calculated ages that can easily be as large as 20 35 the relative differences are most pronounced in thermal histories that spend significant time at or near the closure temperature on the other hand reasonable agreement is found with spheres having the same surface to volume ratio

shear wave polarizations near the north anatolian fault ii interpretation in terms of crack induced anisotropy summary the polarizations of shear waves recorded by networks of digital thxee component seismometers immediately above small earthquakes near the north anatolian fault in turkey display shear wave splitting on almost all shear wave seismograms recorded within the shear wave window this splitting is incompatible with source radiation patterns propagating through simple isotropic structures but is compatible with effective anisotropy of the internal structure of the rock along the ray paths this paper interprets the phenomena in terms of widespread crack induced anisotropy distributions of stress induced cracks model many features of the observations and synthetic polarization diagrams calculated for propagation through simulated cracked rock are similar to the observed patterns this evidence for widespread crack induced anisotropy lends strong support to the hypothesis of extensive dilatancy anisotropy eda suggested by laboratory experiments in subcritical crack growth the crucial evidence confirming some form of eda would be observations of temporal changes in shear wave splitting as the stress field alters the crack density and crack geometry there is some weak evidence for such temporal changes at one site but further analysis of suitable digital three component seismometer networks in seismic areas is required to confirm eda

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