ambient vibration analysis of an unstable mountain slope summary a field experiment with small aperture seismic arrays was performed on the unstable rock slope above the village of randa in the southern swiss alps the aim of this experiment was to constrain the seismic response of a potential future rockslide using ambient vibration recordings weak seismic events were identified on the recordings and site to reference spectral ratios were calculated using a reference site located on the stable part of the slope spectral ratios of up to 30 were observed at sites located within the unstable portion of the slope a strong variation of spectral ratios with azimuth indicates a directional site effect neither amplification nor directionality were observed at sites located in the stable part of the slope furthermore time frequency polarization analysis of the ambient noise was performed to provide robust estimates of frequency dependent directions of the maximum polarization it was found that the unstable part of the slope vibrates within a narrow range of directions 130 10 for the frequency range centred around 5 hz the polarization directions estimated from ambient seismic vibrations are in good agreement with the deformation directions obtained by geodetic and in situ measurements no directionality of ambient vibrations was observed at sites within the stable part of the slope

the 36cl 36ar 40k 41k records and cosmic ray production rates in iron meteorites this is the first contribution towards a reevaluation of exposure histories of iron meteorites and of the constancy of the cosmic ray flux over the last billion years as recorded in these fossil detectors we have performed new 36cl 26al 10be and noble gas measurements including determination of the shielding parameter s 4he 21ne in samples with published k data the k isotopic data coupled to 36ar and 36cl concentrations permit selection of meteorites which have only experienced simple constant geometry irradiation histories these objects can be used for the calibration of shielding dependent production rates within these metallic detectors in order to carry out production rate calibrations based on 40k 41k data we assume constancy of the cosmic flux during the interval 150 to 700 my ago we note that meteorites with very old potassium ages cannot be included in this calibration as these meteorites require distinct parameter sets a calibration data set representing a total of 13 meteorites was used to compute long term 0 5 gy average production rates these average production rates of 36cl from this particular calibration set are significantly 28 lower than those determined for the recent 10 my cosmic ray flux we also document here the quality of the resulting potassium production rate parameter m0 s with a calculated isochron for irons of group iva

the cosmic ray exposure history of the twannberg iron meteorite iig the twannberg iron meteorite is one out of only six members of the group iig the combined noble gas and radionuclide data obtained in this new systematic study indicate that twannberg with its 570 recently recovered specimens was a large object with a preatmospheric radius in the range of 2 m which corresponds to 250 9 10 kg the cosmic ray exposure age for twannberg is 182 45 ma the most surprising result is the long terrestrial age of tterr 202 33 34 ka which is unexpected considering the humid conditions in switzerland however this age is in accord with glaciation events indicating that the less shielded samples from mt sujet were found close to the position of the original strewn field whereas the samples from gruebmatt and twannbach which are from more shielded positions were glacially transported to the east northeast during the second last ice age 185 130 ka ago from an original position west of mt sujet

a combined inversion of rayleigh wave dispersion and 2 d resonance frequencies summary shear wave velocities of the sediment fill of a deep alpine valley are estimated from ambient noise recorded on linear and circular arrays we propose a combined inversion of 2 d reso nance frequencies identified from site to reference spectral ratios and rayleigh wave dispersion curves obtained from frequency wavenumber analysis the method is tested on synthetic noise data and on noise recorded at three sites in the rhone valley in southern switzerland previous studies have shown that 2 d resonance dominates the ambient vibration wavefield at low fre quencies at the investigated sites inversion techniques which assume that the noise wavefield consists mainly of horizontally propagating surface waves will therefore fail to resolve shear wave velocities at depths below around 500 m we show that standard techniques lead to an overestimation of shear wave velocities at depth when applied to synthetic and observed am bient noise the combined inversion is able to resolve the shear wave velocities in the initial velocity model when applied to synthetic noise records application of the method to observed ambient noise improves resolution at depth and yields realistic shear wave velocities for the lower part of the sediment fill

the l3 6 chondritic regolith breccia northwest africa nwa 869 ii noble gases and cosmogenic radionuclides abstract we measured cosmogenic radionuclides and noble gases in the l3 6 chondrite breccia northwest africa nwa 869 one of the largest meteorite finds from the sahara concentrations of 10be 26al and 36cl in stone and metal fractions of six fragments of nwa 869 indicate a preatmospheric radius of 2 0 2 5 m the 14c and 10be concentrations in three fragments yield a terrestrial age of 4 4 0 7 kyr whereas two fragments show evidence for a recent change in shielding most likely due to a recent impact on the nwa meteoroid approximately 105 yr ago that excavated material up to approximately 80 cm deep and exposed previously shielded material to higher cosmic ray fluxes this scenario is supported by the low cosmogenic 3he 21ne ratios in these two samples indicating recent loss of cosmogenic 3he most nwa samples except for clasts of petrologic type 4 6 contain significant amounts of solar ne and ar but are virtually free of solar helium judging from the trapped 4he 20ne ratio of approximately 7 trapped planetary type kr and xe are most clearly present in the bulk and matrix samples where abundances of 129xe from decay of now extinct 129i are highest cosmogenic 21ne varies between 0 55 and 1 92 10 8 cm3 stp g 1 with no apparent relationship between cosmogenic and solar ne contents low cosmogenic 22ne 21ne c ratios in solar gas free specimens are consistent with irradiation in a large body combined 10be and 21ne concentrations indicate that nwa 869 had a 4 cosmic ray exposure cre age of 5 1 myr whereas elevated 21ne concentrations in several clasts and bulk samples indicate a previous cre of 10 30 myr on the parent body most probably as individual components in a regolith unlike many other large chondrites nwa 869 does not show clear evidence of cre as a large boulder near the surface of its parent body radiogenic 4he concentrations in most nwa 869 samples indicate a major outgassing event approximately 2 8 gyr ago that may have also resulted in loss of solar helium

26al and10be production in iron meteorites abstract we have measured by accelerator mass spectrometry the 26 al contents of 20 and the 10 be contents of 14 iron meteorites the 26 al contents are typically 30 or more lower than values obtained by counting techniques the 10 be contents are 10 15 lower the production rates p of these nuclides decrease by more than a factor of two as the 4 he 21 ne ratio increases with increasing shielding from 200 to 400 for the lighter shielding conditions expected in stony meteorites we estimate p 26 fe as 3 4 dpm kg and p 10 fe as 4 5 dpm kg the average p 10 p 26 activity ratio is close to 1 5 exposure ages calculated from 21 ne 26 al ratios cannot be calibrated so as to agree with both 40 kk ages and ages based on the shorter lived nuclides 39 ar and 36 cl if agreement with the latter is forced then the disagreement with 40 kk ages may signal a 35 increase in the cosmic ray intensity during the last 10 7 a

evidences for strong directional resonances in intensely deformed zones of the pernicana fault mount etna italy 1 in this paper we investigate ground motion properties in the western part of the pernicana fault this is the major fault of mount etna and drives the dynamic evolution of the area in a previous work rigano et al 2008 showed that a significant horizontal polarization characterizes ground motion in fault zones of mount etna both during earthquakes and ambient vibrations we have performed denser microtremor measurements in the ne rift segment and in intensely deformed zones of the pernicana fault at piano pernicana this study includes mapping of azimuth dependent horizontal to vertical spectral ratios along and across the fault frequency wave number techniques applied to array data to investigate the nature of ambient vibrations and polarization analysis through the conventional covariance matrix method our results indicate that microtremors are likely composed of volcanic tremor spectral ratios show strong directional resonances of horizontal components around 1 hz when measurements enter the most damaged part of the fault zone their polarization directions show an abrupt change by 20 to 40 at close measurements between the northern and southern part of the fault zone recordings of local earthquakes at one site in the fault zone confirm the occurrence of polarization with the same angle found using volcanic tremor we have also found that the directional effect is not time dependent at least at a seasonal scale this observation and the similar behavior of volcanic tremors and earthquake induced ground motions suggest that horizontal polarization is the effect of local fault properties however the 1 hz resonant frequency cannot be reproduced using the 1 d vertically varying model inferred from the array data analysis suggesting a role of lateral variations of the fault zone although the actual cause of polarization is unknown a role of stress induced anisotropy and microfracture orientation in the near surface lavas of the pernicana fault can be hypothesized consistently with the sharp rotation of the polarization angle within the damaged fault zone

directivity of slope dynamic response to seismic shaking 1 a four year long accelerometric monitoring of a landslide prone slope area in italy provided evidence of amplifications with systematic directional differences in shaking energy by a factor of 2 3 apparently correlated with the directions of local topographic features the examination of regional scale data revealed similar site response directivity phenomena also on some steep rock slopes not affected by amplification the spectral properties of the site responses were investigated using hvsr analysis and a new approach based on the multiplication of spectra from several events the results suggest that such phenomena are caused by a directional redistribution of spectral energy controlled by a combination of interrelated topographic and geologic factors acting in similar directions

10be and36cl depth profiles in an apollo 15 drill core cosmic ray produced10be t1 2 1 6 106 years and36cl t1 2 3 0 105 years have been measured in the apollo 15 long core for study of galactic cosmic ray production profiles using tandem accelerator mass spectrometry from these experiments the half attenuation length for10be production and36cl production were calculated to be 120 g cm2 and 132 g cm2 150 400 g cm2 region the measured half attenuation length for10be is slightly longer than that predicted by the reedy arnold theoretical model the flatter and somewhat deeper maximum seen in the36cl profile compared to the10be 26al and53mn profiles can be explained by production from secondary thermal neutrons on35cl

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

contributors to chromium isotope variation of meteorites we report the results of a comprehensive high precision survey of the cr isotopic compositions of primitive chondrites along with some differentiated meteorites to ensure complete dissolution of our samples they were first fused with lithium borate tetraborate at 1050 1000 c relative to the nist cr standard srm 3112a carbonaceous chondrites exhibit excesses in 54cr 52cr from 0 4 to 1 6e 1e 1 part in 10 000 and ordinary chondrites display a common 54cr 52cr deficit of 0 4e analyses of acid digestion residues of chondrites show that carbonaceous and ordinary chondrites share a common 54cr enriched carrier which is characterized by a large excess in 54cr 52cr up to 200e associated with a very small deficit in 53cr 52cr 2e we did not find 54cr anomalies in either bulk enstatite chondrites or in leachates of their acid digestion residues this either requires that the enstatite chondrite parent bodies did not incorporate the 54cr anomaly carrier phase during their accretion or the phase was destroyed by parent body metamorphism chromium in the terrestrial rocks and lunar samples analyzed here show no deviation from the nist srm 3112a cr standard the eucrite and martian meteorites studied exhibit small deficits in 54cr 52cr the 54cr 52cr variations among different meteorite classes suggest that there was a spatial and or temporal heterogeneity in the distribution of a 54cr rich component in the inner solar system we confirm the correlated excesses in 54cr 52cr and 53cr 52cr for bulk carbonaceous chondrites but the new data yield a steeper slope 6 6 than that reported in shukolyukov and lugmair 2006 the correlated excesses may affect the use of the mn cr chronometer in carbonaceous chondrites we could not confirm the bulk carbonaceous chondrite mn cr isochron reported by shukolyukov and lugmair 2006 and moynier et al 2007 mostly because we find much smaller total variations in e53cr 0 2 all bulk chondrites have small e53cr excesses up to 0 3 relative to the earth most likely reflecting the sub chondritic mn cr ratio of the earth the e53cr variations in chondrites do seem to grossly correlate with mn cr and yield an initial solar system 53mn 55mn value of 5 4 2 4 10 6 corresponding to an absolute age of 4566 4 2 2 ma nuclear interactions with cosmic rays result in coupled excesses in e54cr and e53cr with a 4 1 ratio in phases with high fe cr these are most dramatically demonstrated in the iron meteorite carbo showing excesses in e54cr of up to 140e these new results show that the mn cr chronometer should be used with caution in samples minerals with high fe cr and long cosmic ray exposure ages

site effect analysis around the seismically induced ananevo rockslide kyrgyzstan in 1911 the surface wave magnitude 8 2 kemin earthquake hit northeastern tien shan kyrgyzstan close to the cities of bishkek and almaty the capitals of kyrgyzstan and kazakhstan respectively several hundreds of people were killed by the earthquake some by indirect effects such as landslides and mudflows a particular but nonfatal landslide triggered by the kemin event was a rockslide in the vicinity of ananevo north of lake issyk kul kyrgyzstan rockslide located above the fault zone activated in 1911 in the summer of 1999 a geophysical seismological field trip was organized to study geology and to record seismic ground motions on and around the ananevo rockslide the work was part of project assessing seismogenic landslide hazard in northern kyrgyzstan based on various case studies of slope failures in connection with site specific ground motion dynamics the geophysical investigations consisted of seismic refraction tests processed as 2d seismic tomographies and surface wave inversion which were combined to build a 3d geophysical model of the landslide site ground motions from small earthquakes were analyzed using several techniques to define site effects over the mountain massif both h v and standard spectral ratios indicated lower dominant frequencies with stronger amplification in the crest region with respect to the mountain slope these effects could be partially simulated by 1d 2d and 3d finite element modeling by comparing the numerical results with the experimental data the presence of a surficial low velocity layer of varying thickness appeared to be the key factor controlling the ground motion around the rockslide

the complex exposure histories of the pitts and horse creek iron meteorites implications for meteorite delivery models the concentrations of cosmogenic radionuclides and noble gases in pitts iab and horse creek ungrouped provide unambiguous evidence that both irons have a complex exposure history with a first stage irradiation of 100 600 myr under high shielding followed by a second stage exposure of 1 myr as small objects the first stage exposure ages of 100 myr for horse creek and 600 myr for pitts are similar to cosmic ray exposure ages of other iron meteorites and most likely represent the yarkovsky orbital drift times of irons from their parent bodies in the main asteroid belt to one of the nearby chaotic resonance zones the short second stage exposure ages indicate that collisional debris from recent impact events on their precursor objects was quickly delivered to earth the short delivery times suggests that the recent collision events occurred while the precursor objects of horse creek and pitts were either very close to the chaotic resonance zones or already in earthcrossing orbits since the cosmogenic noble gas records of horse creek and pitts indicate a minimum radius of a few meters for the precursor objects but do not exclude km sized objects we conclude that these irons may represent fragments of two near earth asteroids 3103 eger and 1986 da respectively finally we used the cosmogenic nuclide concentrations in horse creek which contains 2 5 wt si to test current model calculations for the production of cosmogenic 10be 26al and neonisotopes from iron nickel and silicon

dynamic response of the chamousset rock column western alps france 1 this paper investigates the variation of the first resonance frequency of the chamousset limestone column 21 000 m3 vercors french alps before its collapse in november 2007 the site was instrumented with seismometers and extensometers during a 4 month period with some gaps in the measurements experimental results and numerical modeling showed that the resonance frequency of a prone to fall column can be derived from the spectra of continuous seismic noise records at the chamousset site the evolution of the resonance frequency appeared to be strongly controlled by the temperature when temperatures were positive slight resonance frequency variations correlated well with thermal fluctuations irreversible damage can occur during freeze thaw cycles and to a lesser extent during strong wind it coincided with a significant drop in resonance frequency which was interpreted as the result of rock bridge breakage this hypothesis is supported by fresh rupture observations after the collapse seismic event records and numerical modeling this study suggests that seismic noise recording could be used for assessing the potential failure of unstable columns in rigid rocks

cosmogenic radionuclides in l5 and ll5 chondrites from queen alexandra range antarctica identification of a large l ll5 chondrite shower with a preatmospheric mass of approximately 50 000 kg the collection of approximately 3300 meteorites from the queen alexandra range que area antarctica is dominated by more than 2000 chondrites classified as either l5 or ll5 based on concentrations of the cosmogenic radionuclides 10 be 26 al 36 cl and 41 ca in the metal and stone fraction of 16 que l5 or ll5 chondrites we conclude that 13 meteorites belong to a single meteorite shower que 90201 with a large preatmospheric size and a terrestrial age of 125 kyr members of this shower have properties typical of l e g pyroxene composition and ll chondrites e g metal abundance and composition as well as properties intermediate between the l and ll groups e g olivine composition and is thus best described as an l ll5 chondrite based on comparison with model calculations the measured radionuclide concentrations in the metal and stone fractions of que 90201 indicate irradiation in an object with a preatmospheric radius of approximately 150 cm representing one of the largest chondrites known so far based on the abundance of small l5 and ll5 chondrites at que and their distinct mass distribution we conclude that the que 90201 shower includes up to 2000 fragments with a total recovered mass of 60 70 kg 1 of the preatmospheric mass of approximately 50 000 kg the mass distribution of the que 90201 shower suggests that the meteoroid experienced catastrophic atmospheric fragmentation s either because it was a fragile object or it had a high entry velocity

instrumental evidence of normal mode rock slope vibration summary a unique field experiment was performed to constrain the seismic response of a large potentially unstable rock slope in the southern swiss alps small aperture seismic arrays were deployed to record ambient vibrations both inside and outside of the mapped instability boundary the recordings were analysed by means of the high resolution f k method site to reference spectral ratios and time frequency dependent polarization analysis all three methods indicated that the wavefield within the potentially unstable rock mass is dominated by normal mode motion standing waves rather than horizontal propagation of seismic waves both fundamental frequency and relative amplification could be recovered from ambient noise data the observed amplification is strongly directional and the maximum amplification is oriented perpendicular to open tension cracks mapped at the ground surface our results highlight site response characteristics relevant for analysis of earthquake triggered rock slope failures

aluminum 26 10be and 36cl depth profiles in the canyon diablo iron meteorite the authors have measured activities of the long lived cosmogenic radionuclides sup 26 al sup 10 be and sup 36 cl in 12 fragments of the iron meteorite canyon diablo and have constructed production rate versus depth profiles of those radionuclides profiles determined using differential particle fluxes calculated with the lahet code system are in good agreement with sup 26 al sup 10 be and sup 36 cl experimental data but the agreement for sup 36 cl was obtained only after neutron induced cross sections were modified profiles calculated with lunar particle fluxes are much lower than experimental canyon diablo profiles the cosmic ray exposure ages of most samples are near 540 m y 34 refs 4 figs 2 tabs

the influence of bays on adjusted sea level over adjacent shelves with application to the labrador shelf we examine how low frequency variations in adjusted sea level over a continental shelf are influenced by an inland sea connected to the shelf through a strait an analytical model shows that free continental shelf waves propagating by the mouth of the strait are strongly modified at a period corresponding to a helmholtz like resonance of the inland sea and strait also near this period atmospheric pressure variations over the inland sea result in relatively strong flow through the strait and the resulting cross isobath flow over the exterior shelf efficiently generates continental shelf waves in the region forward of the strait calculations using a fully nonlinear numerical model with more realistic although still idealized topography verify the predictions of the simpler analytical model we apply this theory to the hudson bay labrador shelf system where we find that this mechanism of shelf wave generation strongly influences the shelf response in the energetic meteorological band 2 6 days data from nain labrador are analyzed using multiple linear regression models and lend further support to the theory

fall classification and exposure history of the mifflin l5 chondrite the mifflin meteorite fell on the night of april 14 2010 in southwestern wisconsin a bright fireball was observed throughout a wide area of the midwestern united states the petrography mineral compositions and oxygen isotope ratios indicate that the meteorite is a l5 chondrite fragmental breccia with light dark structure the meteorite shows a low shock stage of s2 although some shock melted veins are present the u th he age is 0 7ga and the k ar age is 1 8ga indicating that mifflin might have been heated at the time of the 470ma l chondrite parent body breakup and that u th he and k ar ages were partially reset the cosmogenic radionuclide data indicate that mifflin was exposed to cosmic rays while its radius was 3065cm assuming this exposure geometry a cosmic ray exposure age of 25 3ma is calculated from cosmogenic noble gas concentrations the low 22ne 21ne ratio may however indicate a two stage exposure with a longer first stage exposure at high shielding mifflin is unusual in having a low radiogenic gas content combined with a low shock stage and no evidence of late stage annealing this inconsistency remains unexplained less

cosmic ray exposure ages of pallasites we analyzed cosmogenic nuclides in metal and or silicate primarily olivine separated from the main group pallasites admire ahumada albin brahin brenham esquel finmarken glorieta mountain huckitta imilac krasnojarsk marjalahti molong seymchan south bend springwater and thiel mountains and from eagle station the metal separates contained an olivine fraction which although small 1 wt in most cases nonetheless contributes significantly to the budgets of some nuclides e g up to 35 for ne 21 and al 26 a correction for olivine is therefore essential and was made using model calculations and or empirical relations for the production rates of cosmogenic nuclides in iron meteoroids and or measured elemental concentrations cosmic ray exposure cre ages for the metal phases of the main group pallasites range from 7 to 180 ma but many of the ages cluster around a central peak near 100 ma these cre ages suggest that the parent body of the main group pallasites underwent a major break up that produced most of the meteorites analyzed the cre age distribution for the pallasites overlaps only a small fraction of the distribution for the iiiab iron meteorites most pallasites and iiiab irons originated in different collisions probably on different parent bodies a few iiiabs and pallasites may have come out of the same collision but a firm conclusion requires further study cre ages calculated from noble gas and radionuclide data of the metal fraction are higher on average than the ne 21 exposure ages obtained for the olivine samples as the metal and olivine fractions were taken in most cases from different specimens the depth dependency of the production rate ratio be 10 ne 21 in metal not accounted for in our calculations may explain the difference

53mn profiles in four apollo surface cores 53mn data are presented for four apollo cores with an emphasis on the past 107 year history of these samples 1 core 15011 has excess 53mn down to a depth of at least 9 cm which is probably due to the continuous addition of near surface irradiated material high 53mn was also observed at 17 cm which suggests that this might have been the surface at this site 7 10 m y ago the soil found covering the 15011 core tube keeper appears to be surface soil but most likely not from the top of 15011 2 the 53mn profile for 64002 above 12 cm is relatively flat and in excess of that calculated for a static core which suggests that the upper part of this core was deposited rapidly about 2 m y ago as this soil appears to be mature well irradiated local material it seems unlikely that it is ejecta from south ray crater unless south ray crater is much older than 2 m y 3 results for the apollo 17 drill stem show a large excess of 53mn from at least 3 cm downwards some magnetic separates obtained from this core have very high 53mn activities probably due to the presence of agglutinates that were recently irradiated very near the surface these results are consistent with the suggestion of the battelle northwest group that this core sampled a young crater that had partially filled due to the slumping of surface irradiated material 4 the 53mn content of the upper part of 74002 is similar to that of trench samples collected nearby and indicates that the gray orange and black soils at this site have been exposed together near the surface for at least the last 10 m y

cosmogenic nuclides in the brenham pallasite cosmic ray produced cosmogenic nuclides were studied in fragments of the brenham pallasite a large stony iron meteorite the contents of light noble gases he ne and ar and long lived radionuclides 10be 26al 36cl and 53mn produced by nuclear reactions with cosmic rays were measured in the separated metal and olivine phases from numerous samples representing a wide range of shielding conditions in the meteoroid the distribution of cosmogenic nuclide concentrations in the metal follows patterns similar to that observed in large iron meteorites shielding effects were estimated from the relative proportions of low and high energy reaction products the production rates varied from surface to interior by a factor of more than several hundred the 36cl 36ar cosmic ray exposure age of brenham is 156 8 myr this determination is based on a multiple nuclide approach that utilizes cosmogenic nuclide pairs this approach not only yields a shielding independent exposure age but also demonstrates that the production of cosmogenic nuclides occurred in a single stage the depth profiles of 10be in the stone phase and 53mn in the metal phase are shown superimposed on corresponding profiles from the apollo 15 long drill core surprisingly low abundances of lithophile elements such as k u and th provided a unique opportunity to examine the production systematics of those nuclides whose inventories typically have significant contributions from non cosmogenic sources particularly radiogenic contributions the u and th contents of the olivine samples are extremely low allowing detection of cosmogenic 4he production from oxygen magnesium silicon and iron

advances and problems in understanding the seismic response of potentially unstable slopes abstract the influence of site effects on landslide triggering during earthquakes has been inferred in several studies but its evaluation is made difficult by the complexity of factors controlling the dynamic response of potentially unstable slopes and also by the lack of local ground motion instrumental observations this work explores this problem and reports new findings based on an ongoing long term accelerometric monitoring conducted on a landslide prone test area in the apennine mountains italy where the presence of site effects enhancing seismic susceptibility of local slopes has been invoked on the basis of historic accounts of landsliding triggered at large epicentral distance the recordings relative to low to moderate magnitude earthquakes showed significant amplifications affecting hillslope portions covered by thick 5 m colluvia and pronounced amplification maxima oriented along the local maximum slope direction on a recent deep seated landslide while the amplifications seem most likely linked to high impedance contrast between surface materials and underlying substratum the causes of directivity are less clear the case of the monitored test site together with evidence of site response directivity identified on other hillslopes suggest that the directivity phenomena can result from a combination of topographic lithological and structural factors that act together to re distribute shaking energy focusing it on site specific directions thus it is difficult to single out the critical factors controlling such phenomena and no general criterion for the identification of sites affected by directivity is proposed here nevertheless the presence and orientation of site response directivity can be revealed through reconnaissance techniques by using recordings of seismic weak motion and or ambient microtremors and calculating azimuthal variation of shaking energy and horizontal to vertical ground motion spectral ratios a comparison with the recordings obtained during the recent m w 6 3 earthquake that hit the abruzzo region in april 2009 demonstrated that analysis relying on data from low energy events can furnish valid indications for slope behaviour also under stronger shaking provided the data are well differentiated in terms of distance azimuth and source characteristics furthermore the comparative analysis of the abruzzo earthquake recordings at a landslide and reference sites showed that directivity properties of strong shaking had been correctly anticipated using earlier weak motion observations however under the complex slope conditions the identification of resonance frequencies from horizontal to vertical spectral ratios estimated from weak motion accelerometric recordings does not seem reliable and better results have been obtained by velocimetric microtremor recordings

noble gases in the xinjiang armanty iron meteorite a big object with a short cosmic ray exposure age abstract we measured the concentrations and isotopic ratios of the cosmogenic noble gases he ne and ar in the very large iron meteorite xinjiang iiie the 3he and 4he data indicate that a significant portion of the cosmogenic produced helium has been lost via diffusion or in a recent impact event high 22ne 21ne ratios indicate that contributions to the cosmogenic 21ne from sulfur and or phosphorous are significant by combining the measured nuclide concentrations with model calculations for iron meteorites we were able to determine the preatmospheric diameter of xinjiang to 260 320 cm which corresponds to a total mass of about 70 135 tons the cosmic ray exposure age of xinjiang is 62 16 ma i e relatively short compared to most of the other iron meteorites with the current database we cannot firmly determine whether xinjiang experienced a complex irradiation history the finding of 3he and 4he losses might argue for a recent impact event and therefore for a complex exposure

evidence for ground motion polarization on fault zones of mount etna volcano 1 during local and regional earthquakes an evident amplification of horizontal ground motion is observed at two seismological stations near the tremestieri fault on the southeastern flank of mount etna volcano rotated component spectral ratios show a narrow spectral peak around 4 hz along a n40 e direction a conventional polarization analysis using the eigenvectors of the covariance matrix confirms the very stable directional effect enhancing the approximately ne sw elongation of the horizontal ground motion in the fault zone the effect is evident during the entire seismogram and independent of source back azimuth as well as distance and depth of earthquakes the same polarization is observed in ambient noise as well this consistency allowed us to use microtremors for checking ground motion polarization along and across the tremestieri fault zone with a high spatial resolution the result is a stable polarization of horizontal motion in the entire area that can be observed in a broad frequency band to check whether this ground motion property is recurrent and to understand a possible relationship with fault strike faulting style or orientation of fractures ambient noise was recorded on other mapped faults of the mount etna area the moscarello acicatena and pernicana faults the latter in particular is characterized by different strike and faulting style a systematic tendency of ambient noise to be polarized is found in all of the faults a picture emerges where normal faults of the eastern flank show an e w to ne sw polarization that changes on the pernicana fault which develops approximately e w and is characterized by a prevailing nw se to n s polarization directions of polarization were never parallel to the fault strike moreover polarization persists too far away from the fault trace excluding an effect limited to a narrow low velocity zone hosted between harder wall rocks both these observations rule out an interpretation in terms of fault trapped waves the cause of observed polarizations will be the subject of future studies however the consistency with recent results of velocity anisotropy in a part of the investigated area suggests a possible role of attenuation anisotropy on horizontal amplitude variations versus azimuth

noble gases and cosmogenic radionuclides in the gold basin l4 chondrite shower thermal history exposure history and pre atmospheric size we measured the concentrations of the cosmogenic radionuclides 10be 26al 36cl and 41ca in the stone and metal fractions of 15 fragments of the gold basin l4 chondrite shower as well as noble gases in 18 gold basin fragments a comparison of 10be 26al and 41ca concentrations with calculated production rates from two different models indicates that the gold basin samples came from depths of about 10 cm to more than 150 cm in an object with a radius of 3 5 m as was predicted by recent model calculations the noble gases show a reversal of the 22ne 21ne ratio at very high shielding the 21ne 10be and 21ne 26al ratios in most samples are constant and correspond to a 4 exposure age of 18 2 myr however three gold basin samples show a 30 120 excess of 21ne implying that they were previously exposed close to the surface of the parent body whereas the other samples were buried several meters deeper concentrations of neutron capture 36ar in most samples are consistent with measured concentrations of neutron capture 36cl and an exposure age of 18 myr large excesses of neutron capture 36ar were found in those samples with an excess of 21ne providing additional evidence of a first stage exposure on the parent body the excess of spallation produced 21ne and neutron capture produced 36ar in these samples indicate a first stage exposure of 35 150 myr on the parent body the radiogenic 4he and 40ar concentrations indicate a major impact on the parent body between 300 and 400 myr ago which must have preceded the impacts that brought the gold basin meteoroid to the surface of the parent body and then expelled it from the parent body 18 myr ago