tracking holocene glacial and high altitude alpine environments fluctuations from minerogenic and organic markers in proglacial lake sediments lake blanc huez western french alps holocene palaeoenvironmental evolution and glacial fluctuations at high altitude in the western french alps are reconstructed based on a multiproxy approach within lake blanc huez 2550 m a s l drainage basin the combination of seismic profiling 3 5 khz piston coring and radiocarbon dating in proglacial lacustrine sediments together with a detailed organic analysis of autochthonous and allochthonous supply allows documenting the evolution of glacier activity during the holocene over the last 9700 years the holocene lake record has a bimodal pattern whose transition is progressive and occurring between 5400 and 4700 cal bp during the early holocene the organic lacustrine facies reflects reduced glacial activity in the catchment this major glacial retreat seems to result from solar forcing and high summer insolation after 5400 cal bp lacustrine sedimentation is marked by the gradual increase both of minerogenic supply and soil erosion suggesting a progressive transition to wetter climatic conditions this climate change is synchronous both from the gradual decrease of summer insolation and the gradual reorganization of oceanic and atmospheric circulations characterizing the beginning of the neoglacial period both colder temperature and humid climate induced significant glacier advance since 4700 cal bp over this global trend three periods are particularly associated with higher runoff processes and higher soil erosion interpreted as wetter time intervals resulting from enhanced northern westerlies regimes across the north atlantic and western europe they are dated from 8700 to 7000 4700 to 2500 and 1200 to 200 cal bp these wetter phases drastically contrast with periods of reduced glacial activities dated from the early bronze age ca 3870 3770 cal bp the iron age ca 2220 2150 cal bp the roman period ca ad115 330 and the medieval warm period ca ad760 1160 in addition these dryer periods are associated with mining activities at high altitude

reconstructing recent environmental changes from proglacial lake sediments in the western alps lake blanc huez 2543 m a s l grandes rousses massif france abstract the evolution of high altitude glaciers and human activities in the grandes rousses massif is documented by high resolution seismic reflection profiling and multiproxy analysis of short sediment cores in proglacial lake blanc huez these lacustrine data are compared with historical chronicles geomorphological features and glaciological studies in this region of the western alps and they allow the documentation of recent environmental changes the specific geometry of high amplitude reflections in the uppermost seismic unit the lithology of short cores and the available limnological data in the lake suggest that clastic particles eroded by the glaciers and transported in suspension by glacial melt waters in early summer essentially develop homopycnal flood events in the lake a conceptual model linking fluctuations of glacier equilibrium line altitudes in the catchment area with sedimentary facies retrieved in the lake basin is proposed this approach allows reconstructing continuous glacier fluctuations since ad1820 1850 and suggests several phases of glacier fluctuations during the little ice age lia these reconstructions are based on changes in lacustrine sediment laminations density magnetic susceptibility reflectance spectra organic matter and arsenic content the age depth model of short sediment cores is provided by 210 pb 137 cs and 241 am radionuclide dating this chronology is further supported by identifying in lacustrine sediments the impact of i the nearby m 5 3 correncon earthquake in ad 1962 ii the development of the ski resort at high altitude close to the lake and iii the last advance of glaciers during the lia in ad1820 1850 and the following phase of glacier retreat observed in the alpine region at the end of the lia in ad 1880 frequent sandy layers enriched in organic matter and associated with fluctuations in the arsenic concentrations may result from hydraulic remobilisation of middle age mine tailings at the lake shore by snow melt or heavy rain fall events during the lia

seismic hazard on the french riviera observations interpretations and simulations summary we present here a detailed analysis of a seismic data set recorded by a dense seismological network installed over 6 months in the southeast of france this experiment was set up at the boundary between the ligurian basin and the southern subalpine thrust belt the nice arc which is a complex tectonic region that undergoes low to moderate seismicity we recorded more than 500 microearthquakes among which 348 occurred exactly in the centre of the network during a very active seismic sequence that lasted mainly over 2 months we performed an absolute location of all of the events and calculated the magnitudes then we applied a cross correlation technique to gather similar events and to relocate relatively few of them this method revealed a very clear alignment of 19 events in a direction n120 oblique to the n20 general trend of seismicity focal mechanisms were determined for the four largest events and composite solutions for 32 smaller ones both the alignments of the earthquakes and the focal solutions revealed that two oblique segments of the fault were activated during the crisis the main segment 8 km long that was oriented nne with a left lateral strike slip movement is called the blausasc fault taking into account the tectonic evolution and the relationships between surface structures and the distribution of earthquakes and through a paleaoreconstruction of the tectonic evolution we propose that the blausasc fault is the hidden root of the peille laghet fault which has a mapped length of at least 15 km the smaller segment 0 6 km long that was activated during the crisis could be interpreted as an antithetic riedel fracture the active blausasc fault is located in a densely populated zone at only 10 km from the crowded cities of monaco and nice it is thus particularly interesting to analyse it for hazard assessment in the last section we present a simulation that is aimed at predicting what the ground motion in the city of nice would be like if an earthquake of magnitude 5 7 occurs on this fault for this we used the recordings of the largest event of the seismic sequence ml 3 2 and an empirical green s function summation scheme to simulate the ground motion at two stations situated in urban environments the values obtained show that especially on soft soil sites the effects of such an earthquake would be considerable in the city of nice

allochthony of the chartreuse subalpine massif explosion seismology constraints abstract the deep structure of the chartreuse subalpine massif has been investigated with explosionseismology techniques involving several longitudinal and fan profiles the main results obtained suggest evidence of a refraction level at shallow depth 2 km and three deep seated reflectors 4 5 8 and 10 km the shallow level could be the urgonian limestone slab the three deep reflectors could be associated with autochthonous and parautochthonous pre triassic basements the discussion of these results mainly concerns the tectonic significance of the shallow unambiguous refractor detailed balanced cross sections of the massif request the presence of a new major overthrust in the sedimentary filling of the subalpine chains with an extent of at least 15 km it opens up wide possibilities for oil traps in the tertiary molasse underneath

oxygen isotope studies of carbonaceous chondrites abstract the carbonaceous chondrites display the widest range of oxygen isotopic composition of any meteorite group as a consequence of the interaction of primordial isotopic reservoirs in the solar nebula these isotopic variations can be used to identify the reservoirs and to determine conditions and loci of their interactions we present a comprehensive set of whole rock analyses of cv co ck cm cr ch and ci chondrites as well as selected components of some of these meteorites a simple model is developed which describes the isotopic behavior during parent body aqueous alteration processes the process of thermal dehydration also produces a recognizable effect in the oxygen isotopic composition

slip parallel seismic lineations on the northern hayward fault california a high resolution relative earthquake location procedure is used to image the fine scale seismicity structure of the northern hayward fault california the seismicity defines a narrow near vertical fault zone containing horizontal alignments of hypocenters extending along the fault zone the lineations persist over the 15 year observation interval implying the localization of conditions on the fault where brittle failure conditions are met the horizontal orientation of the lineations parallels the slip direction of the fault suggesting that they are the result of the smearing of frictionally weak material along the fault plane over thousands of years

the chromium isotopic composition of almahata sitta abstract nine ureilitic fragments of the anomalous polymict ureilite almahata sitta have been analyzed for their cr isotopic compositions all the samples including both nonmagnetic and magnetic portions show essentially the same e54cr deficit 0 77 0 10 relative to the terrestrial cr standard this contrasts with the variable positive 54cr anomalies observed for carbonaceous chondrites but agrees with the values measured for eucrites diogenites and mesosiderites trinquier et al 2007 this implies that contrary to previous suggestions based on o isotopes ureilites were not derived from any known carbonaceous chondrite parent body instead the almahata sitta parent body may have accreted in a nebular region environment similar to that of the howardite eucrite and diogenite hed parent body in addition the lack of variation in e54cr combined with variable o isotopic compositions in the meteorite fragments suggests that whatever process es caused the o isotopic heterogeneity of the solar system was probably not responsible for heterogeneity in e54cr the samples show resolvable variations in e53cr 0 15 0 41 that are correlated with mn cr ratios suggesting that live 53mn was present at the time of formation of almahata sitta the isochron yields an initial 53mn 55mn value of 3 1 1 1 10 6 corresponding to an age of 4563 6 2 2 ma when related to u pb and mn cr data for the d orbigny angrite this age is consistent with the mn cr and al mg ages of two other polymict ureilites goodrich et al 2010 magmatic activity on the ureilites parent body seems to have postdated the formation of refractory inclusions by approximately 4 5 ma

optical characteristics of graptolite bearing sediments and its implication for thermal maturity assessment abstract graptolite reflectance was thought to be one of the most useful thermal maturity indicators for graptolite bearing sediments however the relationship between graptolite reflectance and vitrinite reflectance is not well established graptolites especially in the wufeng longmaxi formations from the ordovician to silurian of south china have been mistaken for vitrinite like particles or solid bitumen which results in inconsistent data on the thermal maturity in this paper we have employed optical microscope techniques to describe the detailed optical characteristics of graptolites and solid bitumen in the wufeng longmaxi formations laboratory simulation of maturation was used to determine the relationship between graptolite reflectance and vitrinite reflectance the organic constituents in the wufeng longmaxi formations are mainly composed of graptolites and solid bitumen granular and non granular graptolites were observed in the wufeng longmaxi formations with non granular as the most common texture solid bitumen can be distinguished from non granular graptolites by its coarse surface weaker anisotropy and lower random reflectance the combination of non polarized and polarized light is very helpful to distinguish solid bitumen from graptolite for comparison organic material from the early ordovician alum shale formation of sweden and estonia was also studied the macerals of the alum shales are mainly composed of lamalginites mineral bituminous groundmasses graptolites and solid bitumen the major textures of the graptolites in the sweden and estonia sediments are non granular and granular respectively both non granular graptolite and vitrinite reflectances display a systematic increase with the increase of heating temperature and time the granular graptolites in the estonian sample were gradually changed to non granular graptolites following laboratory simulated maturation indicating that granular graptolites can transform into non granular graptolites with maturation solid bitumen in the wufeng longmaxi formations was derived from the solid residue of kerogen and or post oil bitumen the graptolite random reflectance is a better thermal maturity indicator than graptolite maximum reflectance and is more precise due to the smaller standard deviation several equations are proposed to determine the thermal maturity of the graptolite bearing sediments based on graptolite random reflectance graptolite maximum reflectance and solid bitumen random reflectance

constraining recent fault offsets with statistical and geometrical methods example from the jasneuf fault western alps france we propose two new approaches regarding recent fault offset measurements by studying the seismogenic potential of the jasneuf fault the ne trending right lateral strike slip jasneuf fault is the southwestern extension of the belledonne fault system in the vercors massif this fault which is located in an intraplate domain does not show strongly associated seismicity but displays morphological anomalies that are related to recent faulting right lateral offset of late cenozoic cliffs recent talwegs and post ganz scarps the two methods that we use to quantify fault slip are as follows 1 recursive measurements of stream offsets are conducted this analysis reveals that a stream network can display characteristic distances between streams that can be mistakenly interpreted as long term cumulative fault offsets a comparison of the apparent stream offset values and stream spacing values is necessary to identify the true offsets 2 we propose a new method that enables us to determine the fault offset and kinematics by using recursive measurements of topographic apparent offsets to counter the lack of morphologic features that are used to determine piercing points or lines this method enables us to define each possible slip vector for numerous artificial piercing points along a fault the slip vector that is shared by these piercing points is the true slip vector by applying these methodologies we determine that the jasneuf fault has accumulated slip since the messinian which corresponds to an average slip rate of 0 13 0 03 mm year the extension of the fault is poorly constrained nevertheless if we do not consider the potential aseismic creep slip component of the faulting we calculate that this fault could generate mw 5 7 earthquakes every similar to 500 years according to wells and coppersmith s scaling laws and by assuming that the faulting is limited to the sedimentary cover and the vercors plateau c 2016 elsevier b v all rights reserved

origin of ureilites inferred from a sims oxygen isotopic and trace element study of clasts in the dar al gani 319 polymict ureilite secondary ion mass spectrometer sims oxygen isotope analyses were performed on 24 clasts representing 9 clast types in the dar al gani dag 319 polymict ureilite with precisions better than 1 olivine rich clasts with typical ureilitic textures and mineral compositions have oxygen isotopic compositions that are identical to those of the monomict ureilites and plot along the ccam carbonaceous chondrite anhydrous mineral line other igneous clasts including plagioclase bearing clasts also plot along the ccam line indicating that they were derived from the ureilite parent body upb thus we suggest that some of the plagioclase bearing clasts in the polymict ureilites represent the missing basaltic component produced by partial melting on the upb trace element concentrations mg k sc ti v cr mn fe co ni cu rb sr and ba in ureilitic plagioclase and glass from 13 clasts were obtained by using the sims high mass resolution method the trace element contents of the plagioclase generally show monotonic variations with anorthite content mol that are consistent with partial melting and fractional crystallization incompatible trace element concentrations k ti and ba are low and variable for plagioclase with an 40 indicating that the parental magmas for some clasts were derived from a depleted source we performed partial melt modeling for ci and cm precursor compositions and compared the results to the observed trace element k ba and sr abundances in the plagioclase our results indicate that 1 the upb evolved from a alkali rich carbonaceous chondritic precursor 2 parent melts of porphyritic clasts could have formed by 5 20 equilibrium partial melting and subsequent fractional crystallization and 3 parent melts of the incompatible trace element depleted clasts could be derived from fractional melting where low degree 10 partial melts were repeatedly extracted from their solid sources thus both the oxygen isotopic and trace element compositions of the plagioclase bearing clasts in dag 319 suggest that the upb underwent localized low degree partial melting events the partial melts could have been repeatedly extracted from the precursor resulting in the formation of the olivine pigeonite monomict ureilites as the final residue

analysis of rock fall and rock fall avalanche seismograms in the french alps this study reviews seismograms from 10 rock fall events recorded between 1992 and 2001 by the permanent seismological network sismalp in the french alps a new seismic magnitude scale was defined which allowed us to compare and classify g round motion vibrations generated by these alpine rock falls each rock fall has also been cha racterized by its ground motion duration t30 at an epicentral distance of 30 km no relation was found between rock fall parameters fall height runout distance volume potential energy and rock fall s eismic magnitudes derived from seismogram amplitudes on the other hand the signal duration t30 shows a rough correlation with the potential energy and the runout distance highlighting the co ntrol of the propagation phase on the signal length the signal analysis suggests the existence of at le ast two distinct seismic sources one corresponding to the initial rupture associated with an elastic r ebound during the detachment and the other one generated by the rock impact on the slope although the fall phenomenon includes other complex processes fragmentation of the block interaction with topography plastic deformation during and after impact 2d finite element simulations of thes e two seismic sources are able to retrieve the main seismogram characteristics

structural and rheological implications of lower crustal earthquakes below northern switzerland abstract a detailed study of the recent seismicity in the northern alpine foreland of switzerland reveals that earthquakes with magnitudes between 0 9 and 4 2 occur not only in the upper part of the crust but contrary to observations in most other intracontinental settings seismicity extends down to depths of about 30 km in the lower crust observed p wave velocities in the focal region of even the deepest earthquakes are less than 6 3 km s 1 the average value of poisson s ratio for the entire focal depth range 6 30 km lies between 0 23 and 0 24 focal mechanisms are mostly a combination of strike slip and normal faults with consistent orientations of p and t axes but without any systematic dependence on focal depth from geological observations regional strain rates are of the order of 10 13 s 1 two dimensional temperature modelling indicates that temperatures in the lower crustal seismogenic zone are well above 450 c under the assumption of a dry environment the observed p wave velocities and poisson s ratios imply either a granitic or quartz rich gneissic composition or possibly a gabbroic quartz free granulite the deformation would be governed either by the rheology of quartz or of plagioclase the onset of ductility observed in laboratory studies lies around 300 c for quartz and around 450 c for plagioclase thus conditions in the lower crust beneath northern switzerland appear to be incompatible with the occurrence of either brittle failure or plastic instabilities as is implied by the existence of earthquakes alternatively lower crustal earthquakes could be a manifestation of the presence of fluids in the lower crust fluids under near lithostatic pressure either evolved in situ from metamorphic reactions or from infiltration from the mantle would tend to decrease the effective stress on pre existing faults and thus allow brittle friction failure to occur at depths where under dry conditions or low fluid pressures only ductile deformation would be expected

seismic evidence of a crustal overthrust in the western alps seismic data provided by the alp75 experiment in the northwestern part of the alpine arc has been re evaluated using ray tracing techniques in a laterally inhomogeneous medium thus improving a previous interpretation the structure of the crust definitely appears to be different in the northern subalpine chains where it is layered with an ese mean dip of 30 and in the inner part of the alpine are where no clear stratification can be derived from the available data

the ml 5 3 epagny french alps earthquake of 1996 july 15 a long awaited event on the vuache fault the ml 5 3 epagny earthquake that occurred on 1996 july 15 in the vicinity of annecy french alps was the strongest event to shake southeastern france in the last 34 years moderate to serious damage in the annecy area is consistent with msk intensities of vii viii this earthquake occurred on the vuache fault a geologically well known morphologically clear nw se trending strike slip fault that links the southern jura mountains with the northern subalpine chains the hypocentre was located in mesozoic limestones at shallow depths 1 3 km the focal mechanism indicates left lateral strike slip motion on a n136 e striking plane dipping 70 to the ne abundant field evidence was gathered in the days following the main shock several hundred aftershocks were recorded thanks to the rapid installation of a 16 station seismic network all aftershocks occurred along the southernmost segment of the vuache fault defining a 5 km long 3 5 km deep n130 e striking rupture zone dipping 73 to the ne the fault plane solutions of 60 aftershocks were found to be consistent with left lateral slip on nw se striking planes at the se tip of the aftershock zone we found ground cracks parallel to the fault close to the annecy meythet airport runway at the nw tip near bromines we observed left lateral displacement of concrete walls in a building we also noticed flow changes in two springs close to that locality geodetic levelling across the fault revealed about 1 cm of uplift for the region north of the fault the recording of aftershocks with a six station accelerometric network showed that lacustrine deposits locally amplified the ground motion up to eight times which explains how this moderate magnitude shock could cause such heavy damage historical records draw attention to the central segment of the vuache fault which has been locked for at least 200 years situated nw of the 1996 aftershock zone between the mandallaz and vuache mountains this segment forms a 12 km long potential seismic gap where other m5 events or one single m6 event might occur

the recent fault scarps of the western alps france tectonic surface ruptures or gravitational sackung scarps a combined mapping geomorphic levelling and 10be dating approach abstract in the western alps some recent scarps were previously interpreted as surface ruptures of tectonic reverse and normal faults that agree with microseismicity and gps measurements our analysis shows that in fact there are hundreds of recent scarps up to 30 m high and 2 1 km long with only pure normal motions they share the same characteristics as typical sackung scarps the scarps are mainly uphill facing parallel to the ridge crests and the contour lines they are relatively short less than 2 1 km with respect to tectonic fault ruptures and organized in swarms they cut screes and relict rock glaciers with a slow commonly 1 mm year average slip rate in the aiguilles grives massif these sackung scarps clearly express the gravitational toppling of sub vertical bedding planes in hard rocks in contrast the belledonne outer crystalline massif exhibits scarps that stem from the gravitational reactivation of conjugate tectonic faults the recent faults extend to about 1600 m beneath the rognier ridge crest but are always above the valley floor the main scarp swarm is 9 2 km long and constitutes the largest sackung ever described in the western alps 10 be dating of a scarp and offset surfaces shows that 4 m slip may have occurred rapidly in less than 3800 years sometimes between the end of the glaciation and 8800 1900 years ago this dating together with the location of some faults far from the deep glacial valleys suggests that sagging might have been triggered by strong earthquakes during a post glacial period of probably enhanced seismicity the belledonne and synclinal median faults just beneath the rognier sackung could have been the sources of this seismicity

tectonic and geomorphic analysis of the belledonne border fault and its extensions western alps in the western alps the ne trending belledonne fault system extends from the mont blanc massifs in the ne to the vercors massif in the sw it includes the belledonne border fault defined by an alignment of micro earthquakes ml 3 5 focal mechanisms and their respective depths indicate a crustal scale ne trending dextral strike slip faulting this study aims at better constraining the geometry the fault kinematics and slip rate of the faults of the belledonne fault system by using a multidisciplinary approach that includes tectonics geomorphology and geophysics new clues of potential quaternary deformations are observed 1 the right lateral offsets of morphologic markers talwegs along the ne trending arcalod fault at the north eastern termination of the belledonne border fault 2 the left lateral offset of the valley carved by the isere glacier along the nw trending brion fault which is consistent with the fault kinematics deduced from the focal mechanisms stream network anomalies along the belledonne border fault are related to glacial erosion processes rather than faulting however fault kinematics analysis along the belledonne border fault allows us to determine a strike slip tectonic regime characterized by horizontal ene trending sigma 1 stress axis it is consistent with the mean trend of the p and t axes deduced from the focal mechanisms we display evidences that this stress state is messinian to quaternary in age and occurred after an oligocene to messinian strike slip tectonic regime characterized by horizontal wnw trending sigma 1 fault slip rates cannot be assessed because of the lack of morphologic features with constrained ages however it is likely that the presented geomorphic markers are older than wurm c 2015 elsevier b v all rights reserved

a three dimensional crustal velocity model of the southwestern alps from local earthquake tomography a temporary network of 65 short period seismological stations was installed in the southwestern alps during the second half of 1996 it complemented the permanent monitoring networks obtaining an average interstation distance of 10 km travel time data from 446 local earthquakes and 104 quarry blasts were inverted simultaneously for hypocenter parameters and three dimensional velocity structure the p wave velocity model displays strong lateral contrasts both at shallow and deeper levels a low velocity anomaly stands out at shallow depths beneath the digne and castellane nappes in the southwestern part of the investigated area farther east the monviso ophiolitic massif appears to have a much larger extension at depth than previously assumed the largest and strongest anomaly is located under the dora maira massif and the westernmost po plain it correlates with the well known ivrea body which is classically interpreted as a wedge of adriatic upper mantle at the best resolved depths 10 and 15 km it appears as a rather thin 10 to 15 km north south elongated high velocity 7 4 to 7 7 km s 1 anomaly with very sharp edges extending to the south as far as 10 km north of the surface trace of the frontal penninic thrust special care was taken with regard to the quantitative estimation of the resolution for the main anomalies using the inversion of synthetic travel time data

high altitude varve records of abrupt environmental changes and mining activity over the last 4000 years in the western french alps lake bramant grandes rousses massif abstract two twin short gravity cores and a long piston core recovered from the deepest part of proglacial lake bramant grandes rousses massif french alps under and overlying a large slump identified by high resolution seismic profile allow the investigation of holocene natural hazards and interactions between human activity and climatic changes at high altitude annual sedimentation throughout the cores glacial varves is identified on photographs itrax high resolution continuous microfluorescence x and cat scan computerized axial tomography analyses and is supported by 1 the number of dark and light laminations between dates obtained by radionuclide measurements 137cs 241am 2 the correlation of a slump triggered by the nearby ad 1881 allemond earthquake msk intensity vii and of a turbidite triggered by the ad 1822 chautagne regional earthquake msk intensity viii 3 the number of laminations between two accelerator mass spectrometry ams 14c dates and 4 archaeological data in lake bramant dark layers are coarser contain less detrital elements but more neoformed elements and organic matter content these darker laminations result from calm background sedimentation whereas the lighter layers are finer and rich in detrital elements and reflect the summer snowmelt traces of mining activity during the roman civilization apogee ad 115 330 and during the early bronze age 3770 3870 cal bp are recorded by lead and copper content in the sediments and probably result from regional and local mining activity in the nw alps warmer climate during the bronze age in this part of the alps is suggested by 1 two organic deposits 4160 3600 cal bp and 3300 2850 cal bp likely reflecting a lower lake level and smaller glaciers and 2 evidence of a different vegetation cover around 2500 m a s l the onset of clastic proglacial sedimentation between 3600 3300 cal bp and since 2850 cal bp is synchronous with periods of glacier advances documented in the alps and high lake levels in west central europe this major change in proglacial sedimentation highlights the development of a larger st sorlin glacier in the catchment area of lake bramant

widespread extension in the core of the western alps revealed by earthquake analysis the western alps are an active collision belt whose current stress field is inhomogeneous muller et al 1992 we report new seismological data which significantly improve our knowledge of this stress field about 1600 earthquakes which occurred in the western alps during the last 10 years were precisely located and 79 new focal solutions were computed the analysis of this database shows that widespread extension affects all the internal zones of the belt to better constrain the associated stress regime six stress tensors were computed using the gephart and forsyth 1984 method they show that the current tectonics of the western alps are contrasted with close variation in the stress regime transpression to the front of the belt contrasting with extension in the core of the belt the extensional direction is radial to the arcuate geometry of the belt and bounded outboard by the former thrust of the internal zones onto the external zone suggesting extensional reactivation of this inherited crustal discontinuity such widespread extension within the inner part of an actually ongoing collision belt cannot be explained by simple collision related tectonics we propose that intrabelt buoyancy forces such as those produced by a slab retreat or slab break off interfere with the boundary forces driven by the ongoing europe africa convergence

exhumation and relief development in the pelvoux and dora maira massifs western alps assessed by spectral analysis and inversion of thermochronological age transects 1 we have used dedicated sampling and analysis of apatite fission track aft and apatite u th he ahe thermochronological data sets in an attempt to quantify relief evolution and exhumation rates in the pelvoux and dora maira massifs western european alps a dual approach comparing spectral analysis and thermal kinematic model inversion was applied we sampled age elevation relationships at a range of topographic wavelengths along two north south transects crossing these massifs for the 40 km long pelvoux transect we report 35 new aft ages that range between 3 0 0 4 ma and 12 6 1 0 ma and 8 new ahe ages between 3 5 1 5 and 4 7 0 7 ma the dora maira transect spans a distance of 60 km and includes 28 23 new and 5 previously published significantly older aft ages which vary between 13 1 0 2 and 27 3 0 3 ma inferred exhumation rates of 0 7 km m y 1 since 8 ma in the pelvoux and only 0 1 km m y 1since 20 ma in dora maira are consistent between methods as well as with previous estimates although they are associated with large uncertainties due to imperfect sampling and analytical errors neither massif displays clear evidence for relief change during the intervals constrained by the data data from the dora maria massif suggest moderate recent relief increase whereas the results from the pelvoux are inconclusive but could imply relief decrease our study highlights the difficulties of applying thermochronology techniques to constrain relief changes we show that an unreasonable number of samples is needed to perform reliable spectral analysis of age elevation transects and discuss the overall limitations of both techniques to address relief evolution we suggest that a more efficient approach would be to apply thermal kinematic model inversion to relatively small study areas using spatially distributed sampling and multiple thermochronometer analyses per sample

cre dating on the head scarp of a major landslide sechilienne french alps age constraints on holocene kinematics cosmic ray exposure cre dating applied to the active sechilienne landslide romanche valley belledonne massif french alps provides information about its holocene dynamics from initiation to present day activity glacier retreat at 1100 m a s l is estimated at 16 6 0 6 10be ka from glacially polished bedrock samples with total deglaciation of the valley achieved at least by 13 3 ka application of the cre method along vertical profiles sampled with a high spatial resolution of 3 m on the head scarp yields 1 an initiation of the rock slope failure at 6 4 1 4 10be ka and 2 a continuous rock slope failure activity with a mean head scarp exposure rate of 0 6 cm yr the data suggest an increase of the head scarp exposure rate between 2 3 and 1 0 ka after this acceleration phase the exposure rate is similar to that obtained by the present day monitoring data over 20 years in the depletion zone 1 3 cm yr since the failure initiation occurred more than 5400 yr after the total deglaciation of the valley the slope failure does not appear as an immediate consequence of debutressing in the romanche valley this result is consistent with studies of other large alpine rockslides in the alps failure initiation of the sechilienne landslide occurred during the holocene climatic optimum a hot and wet period the temperature and precipitation changes of this climatic optimum seem to have a worsening effect at the regional scale to trigger large mass wasting in this glacial alpine valley

53mn 53cr and 26al 26mg ages of a feldspathic lithology in polymict ureilites abstract we report 53 mn 53 cr and 26 al 26 mg isotopic data obtained by in situ sims analysis for feldspathic clasts in polymict ureilites dag 319 and dag 165 the analyzed clasts belong to the albitic lithology the most abundant population of indigenous feldspathic materials in polymict ureilites and are highly fractionated igneous assemblages of albitic plagioclase fe rich pyroxenes phosphates ilmenite silica and fe mn k p ti enriched glass glass in dag 165 clast 19 has extremely high and variable 55 mn 52 cr ratios 500 58 000 and shows correlated 53 cr excesses up to 1500 clearly indicating the presence of live 53 mn at the time of formation the slope of the well correlated isochron defined by glass and pyroxenes from this clast corresponds to 53 mn 55 mn 2 84 0 10 10 6 2 data for less 55 mn 52 cr enriched glasses from dag 319 clast b1 as well as phosphates from several other clasts are consistent with this isochron the 53 mn 55 mn ratio obtained from the isochron implies that these clasts are 0 70 0 18 ma younger than the d orbigny angrite corresponding to the absolute age of 4563 72 0 22 ma plagioclase in dag 319 clast b1 has a fairly constant 27 al 24 mg ratio of 900 and shows resolvable 26 mg excesses of 2 the slope of the isochron defined by pyroxene and plagioclase in this clast is 3 0 1 1 10 7 2 corresponding to a time difference of 5 4 0 3 0 5 ma after cai assuming the canonical initial 26 al 27 al ratio of 5 10 5 and an age 0 5 0 3 0 5 ma younger than d orbigny its absolute age relative to d orbigny is 4563 9 0 4 0 5 ma in agreement with the 53 mn 53 cr age from clast 19 these data provide the first high precision age date 5 4 ma after cai for ureilites giving a minimum estimate for the age of differentiation of their parent asteroid interpretation of this age for the thermal and physical history of that asteroid depends on a number of currently unknown or model dependent parameters including its size bulk composition and oxidation state and the petrologic relationship between the feldspathic clasts and main group ureilites

seismic monitoring of sechilienne rockslide french alps analysis of seismic signals and their correlation with rainfalls 1 in the french alps sechilienne rockslide is one of the natural phenomena that presents one of the highest levels of risk in terms of socioeconomical outcomes this rockslide has been active for a few decades and has been instrumented since 1985 the current very active volume of this rockslide is estimated to be up to 5 million m3 located on the border of a slowly moving mass reaching 50 100 million m3 the velocity of the most active zone reached 1 4 m yr in 2008 about twice the value of 2000 a seismic network was installed on this rockslide in may 2007 to supplement the monitoring system it has now recorded several thousand events mostly rockfalls but also hundreds of local and regional earthquakes which can be distinguished and classified from their signal characteristics rockfalls and microseismicity which occur in bursts of activity are found to be weakly but significantly correlated with rainfall rockfall occurrence increases linearly with precipitation with however strong fluctuations of the numbers of rockfalls per day for the same rainfall intensity no threshold was found for rainfall triggering with even 1 mm of rain being enough to trigger rockfalls rockfall activity starts almost immediately during a rainfall episode and lasts for several days after the rainfall rain also induces strong accelerations of the rockslide movement which also start quasi instantaneously and last for about a month

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

continuous gps measurements across the western alps 1996 1998 summary global positioning system gps data are analysed from three permanent sites two in the western alps grasse france and zimmerwald switzerland and the third in the po basin torino italy for the 2 5 year period from 1 january 1996 to 1 july 1998 an analysis of the stochastic properties of the position time series reveals a significant amount of spatially and temporally correlated noise which best fits a model combining white noise and flicker noise the coloured noise is drastically reduced by spatially filtering the time series suggesting that it is not due to site specific evects such as monument motion but rather to noise sources common to the three sites such as reference frame satellite orbit or earth orientation errors we find velocity uncertainties 95 per cent confidence interval of 2 7 mm yr 1 at gras 2 3 mm yr 1 at zimm and 2 9 mm yr 1 at tori the residual velocity in the eurasian reference frame is statistically greater than zero at zimm only with 2 4 2 3 mm yr 1 of motion in a nw direction these uncertainties place an upper bound on the expected deformation in the western alps velocities relative to stable eurasia do not exceed 3m m yr 1 corresponding to a maximum strain rate of 0 03 mstrain yr 1 over the gras tori zimm triangle

inversion of thermochronological age elevation profiles to extract independent estimates of denudation and relief history ii application to the french western alps abstract thermochronologic data collected along age elevation profiles are commonly interpreted as recording temporally variant but spatially constant exhumation rates however thermochronologic age elevation relationships are known to be perturbed by topographic effects and potential changes in relief which are neglected in the inherently 1 d interpretation commonly applied such data thus potentially record both the denudation and relief history of the sampled region but extracting this information is challenging in a companion paper we develop a methodology for rigorously interpreting thermochronologic age elevation profiles in terms of exhumation rates and relief development through time and to independently quantify the resolution of these constraints here we test this approach using a thermochronological dataset consisting of apatite and zircon fission track and u th he data collected at la meije peak in the pelvoux ecrins massif french western alps our data and models suggest a three phase exhumation history in the pelvoux ecrins massif including a pulse of rapid exhumation at 6 5 5 ma preceded and followed by more moderate rates of denudation in the order of 0 3 0 4 km myr 1 this rapid exhumation event appears to occur coevally in other external crystalline massifs in the alps but is not detected by qualitative inspection of the age elevation relationships both our synthetic results and inversion of the la meije data strongly suggest that apatite fission track age elevation relationships alone cannot resolve both denudation and relief histories independently and that multiple thermochronometers are required combining apatite fission track and u th he ages and particularly including fission track length data greatly improves the resolution of the inferred exhumation histories although denudation rates through time and the timing of rate changes are generally well resolved our data have insufficient resolution to satisfactorily constrain the relief history synthetic results reported in the companion paper suggest that the reason for this limitation is that relief increase through valley carving has been insufficient with respect to the regional denudation rates to be unambiguously extracted from the data

deep geophysical investigation of the large sechilienne landslide western alps france and calibration with geological data a geophysical imaging campaign including four 950 m electrical profiles and four 470 m long seismic profiles was performed on the large sechilienne landslide with the objective of constraining the depth and the volume of the affected zone compared to the undisturbed ground the moving area exhibits lower velocity and higher resistivity values comparison with existing geodetic geomorphic and geological data investigation gallery and borehole allowed showing that these geophysical parameter variations result from intense fracturing and the progressive development of air filled voids within the moving mass a maximum thickness of 150 m to 200 m was found in the most deconsolidated zones locally near vertical very low resistivity anomalies were evidenced related to cataclasis zones filled with clayey material applying the wyllie s experimental law rock mass porosity images were derived from seismic tomography profiles porosity between 30 and 4 was found from the top to the bottom of the deconsolidated zone explaining the deep water table considering a porosity threshold of 3 7 for the sound bedrock the total volume of the sechilienne landslide was estimated to about 60 10 106 m3 a more precise bracket than the previous estimations 20 106 to 100 106 m3

aseismic deformation in the alps gps vs seismic strain quantification neotectonics of the western and central alps is characterized by ongoing widespread extension in the highest zones of the chain and transcurrent compressive tectonics at the external limits of the belt the overall geodetically measured deformations also indicate extension across the western alps there is a good qualitative coherency between seismotectonic and geodetic approaches here we attempt to quantify the seismic part of the deformation the seismic strain is compared to the deformation derived from geodesy in sub areas of homogeneous seismic stress strain we computed the total seismic moment tensor and related strain tensor this study provides new quantitative elements about the ongoing geodynamic processes in the alpine belt the important discrepancies obtained between seismic strains and geodetically measured deformations raise the issue of aseismic deformation in the alps which could be related to elastic loading creeping and or a slower ductile style deformation

10be ages reveal 12 ka of gravitational movement in a major sackung of the western alps france abstract the rognier sackung which extends ne sw for more than 9 km is a major gravitational morpho structure located in the western alps we used the 10 be cosmic ray exposure dating method on 23 samples to unravel its history and better understand its genetic mechanism we found that the average slip rate on sackung faults varies from 0 3 to 3 2 mm yr 1 conjugate sackung faults are contemporaneous in agreement with a model in which the whole mountain ridge is involved in the gravitational deformation 600 m thick multiple samples on single faults suggest that the development of this sackung started before 12 ka and that it is still active we cannot exclude the possibility that the dissolution of the underlying triassic evaporites participated in the sagging of mt rognier however the age of this sackung and the presence of the lauziere sackung on the other side of the arcs valley support glacial erosion and debuttressing following the retreat of the valley glacier as the main causes of these large gravitational structures the long and permanent activity of the rognier sackung contrasts with that of the neighbouring arcs sackung which we previously dated using the same method and showed that it is a result of flexural toppling along with the proximity of the rognier sackung to the belledonne border active fault its long history suggests that earthquake shaking contributed to maintain its activity additionally two ages confirm that in the western alps rock glaciers formed mainly during the younger dryas this study allowed the determination of the best sampling strategy for future cre dating of these types of gravitational structures

the oxygen isotope composition of almahata sitta abstract eleven fragments of the meteorite almahata sitta ahs have been analyzed for oxygen isotopes the fragments were separately collected as individual stones from the meteorite s linear strewn field in the nubian desert each of the fragments represents a sample of a different and distinct portion of asteroid 2008 tc3 ten of the fragments span the same range of values of 18o 17o and 17o and follow the same trend along the carbonaceous chondrite anhydrous minerals ccam line as monomict and polymict members of the ureilite family of meteorites the oxygen isotope composition of fragment 25 is consistent with its resemblance petrographically to an h5 ordinary chondrite our results demonstrate that a single small asteroidal parent body asteroid 2008 tc3 only 4 m in length encompassed the entire range of variation in oxygen isotope compositions measured for monomict and polymict ureilites

reconstructing historical seismicity from lake sediments lake laffrey western alps france sediment archives from a mountain lake are used as indicators of seismotectonic activity in the grenoble area french western alps 45n sedimentological analysis texture and grain size characteristics exhibits several layers resulting from instantaneous deposits in lake laffrey six debris flow events up to 8 cm thick can be attributed to slope failure along the western flank of the basin dating with 210 pb and 137 cs gamma counting techniques and the reconnaissance of historical events provide a constrained age depth model over the last 250 years five of such debris flow deposits could be related to historical earthquakes of msk intensities greater than vi over an area of 60 km one debris flow deposit triggered at the beginning of the last century can be related to an historical landslide possibly triggered by the artificial regulation of the lake level

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

site effect study in urban area experimental results in grenoble france three methods are used to determine the site effect in the town of grenoble located in the western alps first we use the classical spectral ratio method in 14 sites to calculate the transfer function of the basin we find an amplification of 10 in the frequency range of 0 25 to 10 hz second we compare these results with the h over v spectral ratio method and propose a map of resonance frequency of the basin we find a lower resonance frequency in the center of the basin than on the edge that is consistent with the structure deduced from a gravity bouguer anomaly map finally we use the empirical green s function method to simulate a m w 5 5 earthquake at a distance of 20 km from the town the simulated acceleration reaches the level of 2 m s2 in the center of the basin compared to 0 2 m s2 on the edges the simulated ground motion we compute is smaller than the french seismic codes on the edge of the valley but significantly larger in the center

on the limitation of the h v spectral ratio using seismic noise as an exploration tool application to the grenoble valley france a small apex ratio basin the h v spectral ratio method based on seismic noise hvsrn was used in the grenoble basin france an alpine valley characterized by a small apex ratio the resonance frequencies obtained in the experiments were compared to the thickness of the sediments deduced from a microgravimetric survey and to the 1 d theoretical assessment of site responses given the abundance of data on the sediments and depth of the basin the values of the theoretical resonance frequency fo can be determined quite accurately however it has been observed that the effects of basin geometry can disturb fo measurements using the hvsr method in particular for a case like the grenoble basin which has a small apex ratio w h and strong suspected 2 d and or 3 d effects interpretation of fo values in terms of bedrock depth gives rise to estimation errors of about 10 in certain cases with the most significant errors 50 occurring on the edges of the basin where subsurface layers are characterised by larger heterogeneities and where the basin topography is accentuated this study suggests that great care must be taken when using the hvsrn method as an exploration tool at least in valleys with a small apex ratio

manganese chromium isotope systematics of carbonaceous chondrites abstract in this article we present the results of cr isotope investigations of different types of carbonaceous chondrites and of the pallasite eagle station the 53 cr 52 cr ratios in the bulk samples of carbonaceous chondrites are correlated with 55 mn 52 cr ratios the slope of the correlation line yields a 53 mn 55 mn ratio of 8 5 1 5 10 6 at the time of mn cr fractionation mapping this ratio onto an absolute time scale yields a time for this event of 4568 1 0 8 1 1 ma ago this time is very similar to the formation age of efremovka cais of 4567 2 0 6 ma y amelin a n krot i d hutcheon a a ulyanov lead isotopic ages of chondrules and calcium aluminum rich inclusions science 297 2002 1678 1683 to a time of the chondrule formation of 4568 1 ma ago l e nyquist d lindstrom d mittlefehldt c y shih h wiesmann s wentworth r martinez manganese chromium formation intervals for chondrules from the bishunpur and chainpur meteorites meteorit planet sci 36 2001 911 938 which most likely constrains early global high temperature mn cr fractionation in a nebular setting the bulk samples of carbonaceous chondrites exhibit clear 54 cr excesses 54 cr that are correlated with the 53 cr excesses 53 cr and also with mn cr ratios one possible explanation of this correlation is that 54 cr is also radiogenic like 53 cr and was formed by the decay of the short lived parent radionuclide 54 mn the very short half life of 54 mn of 312 days would require that both short lived radionuclides 53 mn and 54 mn were generated locally in spallation reactions during the early period of an active sun the alternative and possibly more plausible explanation is the heterogeneous addition of presolar material the presolar component enriched in 54 cr is mostly contained in the matrix of carbonaceous chondrites the relative amount of matrix decreases in the sequence ci cm co cv a large proportion of mn is associated with the matrix while cr preferentially resides in the chondrules thus the mn cr ratio also follows the sequence ci cm co cv and is correlated with 54 cr the acid resistant residues of carbonaceous chondrites are characterized by relatively large excesses of 54 cr and moderate deficits of 53 cr the magnitude of these excesses and deficits decreases in the sequence ci cm cv and may imply that cr in the cm and cv residues is increasingly more equilibrated with cr from the rest of the meteorites the 53 cr 52 cr and 54 cr 52 cr ratios in the residues are anti correlated indicating that there are at least two cr components of possibly presolar origin all residues have large excesses of the most neutron rich ti isotope 50 ti the pattern of 50 ti does not exactly follow that observed for 54 cr but it is generally similar the cr isotope systematic of the pallasite eagle station indicates that the precursor of this meteorite was a cv type material the 53 mn 53 cr system indicates that the cr isotopes equilibrated in this meteorite 4557 5 0 6 ma ago

interaction between tectonic and erosion processes on the morphogenesis of an alpine valley geological and geophysical investigations in the lower romanche valley belledonne massif western alps in the belledonne massif the steep paleozoic belledonne middle fault bmf separates micaschists displaying numerous landslides from amphibolites the massif is incised by the lower romanche river valley when crossing the bmf the valley widens into a lozenge shaped basin recently interpreted as an active pull apart type structure associated with a major n110 striking quaternary fault multidisciplinary investigations were carried out in the basin to check if this model has implications on the seismic and landslide hazard assessment this study demonstrated the existence of a n80 sinistral strike slip sechilienne fault zone sfz this fault zone is suspected to offset the bmf by 375 m across the basin geophysical experiments revealed that the bedrock depth increases strongly in the basin up to 350 m our study invalidates the active pull apart origin of the basin and suggests it results from quaternary glacial and fluvial erosion processes magnified by the intersection of two inherited structures the bmf and the sfz

location of seismic signals associated with microearthquakes and rockfalls on the sechilienne landslide french alps the sechilienne rockslide in the french alps has recently been instrumented with three seismic arrays this network has recorded numerous rockfalls and local microearthquakes because the media is highly fractured it is difficult to identify and pick first arrivals beam forming methods were therefore used to locate these events the method has been adapted to take into account the heterogeneity of seismic wave velocities the location accuracy has been estimated to be about 50 m for epicenters by applying the method to calibration shots depth is less constrained due to uncertainties on the velocity model and due to the seismic network geometry this method of location has then been applied to rockfalls and microearthquakes most rockfalls initiate in the most active part of the rockslide called les ruines the others are located on a recent eroded area aside from les ruines the network also allows the estimation of the rockfall trajectory and propagation speed finally 55 microearthquakes have been located within two zones microearthquakes are located within the first 250 m below the surface most microearthquakes are located in les ruines the most active part of the rockslide where the velocity has increased from 0 5 m yr in 1996 to 1 4 m yr in 2008 these events are located close to three faults that delimit a mass of about 3 6 million m3 other events are located close to the summital scarp in a zone moving at a few centimeters per year the western part of the rockslide which moves more slowly did not produce any event large enough to be detected simultaneously by all stations this seismic monitoring suggests that only a very small fraction of the deformation is released through seismic events

present day deformation of the dauphine alpine and subalpine massifs se france the positions of 20 geodetic points surveyed in 1946 1952 by the institut geographique national in the grenoble area western alps were remeasured in 1993 1994 using gps we evaluate the displacements of the common points of the networks between the two surveys and calculate the strain rate tensors for different sets of three adjacent points the significant n70 shortening direction observed at the boundary of the belledonne and taillefer massifs suggests that the dextral strike slip motion between the external crystalline massifs ecm and the subalpine domain is still active geological evidence suggests that this deformation which is compatible with the few focal mechanisms available for the area occurred throughout the late neogene our data also suggest a roughly 3 5 mm yr 1 active shortening concentrated at the external front of the subalpine chains this thrust motion results in a principal axis of compression orientated n130 oblique to the direction of shortening observed in the ecm this change in direction is also seen in in situ stress measurements this motion may mark the southward continuation of the active fault observed in the jura mountains by jouanne menard darmendrail 1995

alpine thermal and structural evolution of the highest external crystalline massif the mont blanc 1 the alpine structural evolution of the mont blanc highest point of the alps 4810 m and of the surrounding area has been reexamined the mont blanc and the aiguilles rouges external crystalline massifs are windows of variscan basement within the penninic and helvetic nappes new structural 40ar 39ar and fission track data combined with a compilation of earlier p t estimates and geochronological data give constraints on the amount and timing of the mont blanc and aiguilles rouges massifs exhumation alpine exhumation of the aiguilles rouges was limited to the thickness of the overlying nappes 10 km while rocks now outcropping in the mont blanc have been exhumed from 15 to 20 km depth uplift of the two massifs started 22 myr ago probably above an incipient thrust the alpine sole thrust at 12 ma the ne sw trending mont blanc shear zone mbsz initiated it is a major steep reverse fault with a dextral component whose existence has been overlooked by most authors that brings the mont blanc above the aiguilles rouges total vertical throw on the mbsz is estimated to be between 4 and 8 km fission track data suggest that relative motion between the aiguilles rouges and the mont blanc stopped 4 myr ago since that time uplift of the mont blanc has mostly taken place along the mont blanc back thrust a steep north dipping fault bounding the southern flank of the range the european roof is located where the back thrust intersects the mbsz uplift of the mont blanc and aiguilles rouges occurred toward the end of motion on the helvetic basal decollement hbd at the base of the helvetic nappes but is coeval with the jura thin skinned belt northwestward thrusting and uplift of the external crystalline massifs above the alpine sole thrust deformed the overlying helvetic nappes and formed a backstop inducing the formation of the jura arc in that part of the external alps nw se shortening with minor dextral ne sw motions appears to have been continuous from 22 ma until at least 4 ma but may be still active today a sequential history of the alpine structural evolution of the units now outcropping nw of the pennine thrust is proposed

quantified sensitivity of small lake sediments to record historic earthquakes implications for paleoseismology seismic hazard assessment is a critical but challenging issue for modern societies a key parameter to be estimated is the recurrence interval of damaging earthquakes this requires the establishment of earthquake records long enough to be relevant i e far longer than historical observations we study how lake sediments can be used for this purpose and explore conditions that enable lake sediments to record earthquakes this was achieved i through the compilation of eight lake sediment sequences from the european alps to reconstruct chronicles of mass movement deposits and ii through the comparison of these chronicles with the well documented earthquake history this allowed 24 occurrences of mass movements to be identified of which 21 were most probably triggered by an earthquake however the number of earthquake induced deposits varies between lakes of a same region suggesting variable thresholds of the lake sequences to record earthquake shaking these thresholds have been quantified by linking the mass movement occurrences in a single lake to both intensity and distance of the triggering earthquakes this method offers a quantitative approach to estimate locations and intensities of past earthquake epicenters finally we explored which lake characteristics could explain the various sensitivities our results suggest that sedimentation rate should be larger than 0 5 mm yr 1 so that a given lake records earthquakes in moderately active seismotectonic regions we also postulate that an increasing sedimentation rate may imply an increasing sensitivity to earthquake shaking hence further paleoseismological studies should control carefully that no significant change in sedimentation rates occurs within a record which could falsify the assessment of earthquake recurrence intervals

application of geophysical methods for the investigation of the large gravitational mass movement of sechilienne france several geophysical techniques electromagnetic profiling electrical tomography seismic refraction tomogra phy and spontaneous potential and seismic noise measurement were applied in the investigation of the large gravita tional mass movement of sechilienne france the aim of this study was to test the ability of these methods to characterize and delineate the rock mass affected by this complex movement in mica schists whose lateral and vertical limits are still uncertain a major observation of this study is that all the zones strongly deformed previously and at present by the movement are characterized by high electrical resistivity values 3 k m in contrast to the undis turbed mass which exhibits resistivity values between a few hundred and 1 k m as shown by the surface observa tions and the seismic results this resistivity increase is due to a high degree of fracturing associated with the creation of air filled voids inside the mass other geophysical techniques were tested along a horizontal transect through the movement and an outstanding coherency appeared between the geophysical anomalies and the displacement rate curve these preliminary results illustrate the benefits of combined geophysical techniques for characterizing the rock mass in volved in the movement results also suggest that monitoring the evolution of the rock mass movement with time lapse geophysical surveys could be beneficial resume plusieurs techniques geophysiques profil electromagnetique tomographie electrique tomographie sismique et potentiel spontane et bruit de fond sismique ont ete appliquees pour la reconnaissance du grand mouvement de ter rain de sechilienne france situe dans des micaschistes l objectif de cette etude etait de tester ces methodes geophy siques afin de caracteriser et de delimiter la masse de roche affectee par ce mouvement complexe dont la limite laterale reste incertaine l etude a montre que toutes les zones tres deformees encore actuellement et dans le passe par le mouvement sont caracterisees par de fortes valeurs de resistivite electrique superieur ea3k m tandis que dans la zone non perturbee les valeurs de resistivite sont de quelques centaines de m a1k m comme le montrent les observations de surface et les profils de tomographie sismique cette augmentation de resistivite est due a une frac turation importante associee a la creation de vides remplis d air au sein du massif les techniques electromagnetiques ps et de mesure de bruit ont ete testees le long d un profil transversal recoupant le mouvement une correlation remar quable est obtenue entre les anomalies geophysiques et le taux de deplacement ces resultats preliminaires soulignent l interet de combiner les methodes geophysiques pour caracteriser la masse de roche impliquee dans le mouvement et pour determiner l evolution du mouvement par un suivi temporel des parametres geophysiques mots cles mouvement gravitaire methodes geophysiques sechilienne meric et al 1115

the 4 56 ga upb age of the met 780058 ureilite the u th pb and sm nd isotopic systematics of mineral separates from the ca rich ureilite met 78008 are reported extensive acid leaching procedures were used to eliminate terrestrial contamination because the amounts of u th pb sm and nd are extremely low in the meteorite the three residues without terrestrial pb contamination yield a pb pb age of 4 563 0 021 ga on a u pb concordia diagram the residue data corrected for an initial lead isotopic composition calculated with 11 7 for 3 ma from starting canon diablo troilite pb in indicate a 2o7pb 206pb model age of 4 563 ga the sm nd isotopic data are scattered around the 4 56 ga chondritic isochron however the sm nd model age for handpicked augite is 4 573 0 029 ga assuming an initial chur composition two separates show a positive 142nd anomaly similar to those found in other meteorites of the same age 4 5 4 6 ga these sm nd isotopic results support the pb pb and u pb ages of this meteorite therefore it is very likely that the formation age of ureilites is consistent with the so called 4 56 ga canonical age of meteorites it is also possible that extensive igneous processes for generating the ultramatic mineralogy of ureilites took place in the parent body within a few million years after formation of the solar nebula

new approach for coupling k 2 and empirical green s functions application to the blind prediction of broad band ground motion in the grenoble basin summary we present a new approach for performing broad band ground motion time histories 0 1 30 hz of a future earthquake in a sedimentary basin synthetics are computed with an hybrid scheme combining reciprocity based 3 d spectral element method simulations at low frequencies and empirical green s functions egf at high frequencies the combination between both deterministic and empirical parts results in a set of hybrid green s functions summed according to a new k 2 kinematic model algorithm the summation technique enables to remove the high frequency artefacts that appear above the egf corner frequency the ground motion variability is assessed by generating a variety of source parameter sets selected from ap rioriprobability density functions this leads to a population of response spectra from which the median spectral acceleration and standard deviation values are derived the method is applied to simulate a m w 5 5 event in the deep grenoble basin french alps the comparison with ec8 regulations suggests the need of specific design spectra in the grenoble valley

the october november 2010 earthquake swarm near sampeyre piedmont region italy a complex multicluster sequence during one month in october and november 2010 the region of sampeyre western alps italy was struck by a seismic activity of several hundred events the location of 287 events recorded at least by three stations showed a diffuse swarm ranging between 8 and 13 km depth the number of earthquakes in the database was increased thanks to a detailed analysis of the continued recordings of the nearest station doi which allowed identifying 2612 earthquakes the temporal distribution of the seismicity is characterized by the alternation of active and quiescent periods moment magnitude was computed for 730 events by a p wave spectral analysis of the doi station data the estimated magnitudes range between 0 7 and 3 15 the b value of the cumulated frequency magnitude distribution is around 1 4 spatio temporal analysis of the located earthquakes highlighted an overall northward migration of the seismicity from spatio temporal criteria the seismicity was divided in three clusters each cluster is characterized by its own focal mechanism family the stress tensor determined from the focal mechanisms indicates probable stress heterogeneities at small spatial scale the observed migration of the seismicity could be compatible with earthquake triggering by fluid diffusion processes

u pb ages of angrites abstract precise u pb ages determined with double spike 202 pb 205 pb thermal ionization m1ass spectrometry are reported for angrites angra dos reis ador lewis cliff 86010 lew and d orbigny nineteen of 23 acid washed pyroxene fractions from these meteorites and whole rock fractions from d orbigny contain between 0 5 and 1 3 pg of total common pb indistinguishable from analytical blank measured 206 pb 204 pb ratios in these fractions are between 6300 and 14 100 for ador 1160 4500 for lew and 608 8500 for d orbigny blank corrected 206 pb 204 pb ratios for all three meteorites vary from 2160 to over 100 000 these fractions yielded precise and reproducible 207 pb 206 pb dates with the average values of 4557 65 0 13 ma for ador 4558 55 0 15 ma for lew and 4564 42 0 12 ma for d orbigny pb pb isochrons including data with slightly elevated common pb and u pb upper concordia intercepts yield similar dates the implications of these new pb isotopic ages of angrites are threefold first they demonstrate that ador and lew are not coeval and the group of slowly cooled angrites is therefore genetically diverse second the new age of lew suggests an upward revision of 53 mn 53 cr absolute ages by 0 7 ma third a precise age of d orbigny allows consistent linking of the 53 mn 53 cr and 26 al 26 mg extinct nuclide chronometers to the absolute lime scale

the belledonne border fault identification of an active seismic strike slip fault in the western alps summary in the french western alps east of grenoble we identify the belledonne border fault as an active seismic fault this identification is based on the seismic monitoring of the grenoble area by the sismalp seismic network over the past 12 yr 1989 2000 we located a set of earthquakes with magnitudes ranging from 0 to 3 5 along a 50 km long alignment which runs in a n30 e direction on the western flank of the belledonne crystalline massif available focal solutions for these events are consistent with this direction n36 e strike slip fault with right lateral displacement these events along the belledonne border fault have a mean focal depth of 7 km in the crystalline basement with a probably very low slip rate the belledonne border fault has never been mapped at the surface where the otherwise heavily folded and faulted mesozoic cover makes this identification difficult historical seismicity also shows that over the past two and a half centuries a few events located mainly along the southern part of the belledonne border fault caused damage with the magnitude 4 9 1963 monteynard earthquake reaching intensity vii the most recent damaging event in the study area is the magnitude 3 5 1999 laffrey earthquake intensity v vi although its epicentre lies at the southern tip of the belledonne border fault there is clear evidence that aftershocks were activated by the left lateral slip of a n122 e striking fault the length of the belledonne border fault which could easily accommodate a magnitude 6 event as well as the proximity to the isere valley with its unlithified quaternary deposits up to 500 m thick known to generate marked site effects make the identification of the belledonne border fault an important step in the evaluation of seismic risk in the grenoble area besides the activity observed on the fault will now have to be taken into account in future geodynamic models of the western alps