self excitation process due to local seismic amplification responsible for the reactivation of the salcito landslide italy on 31 october 2002 1 an integrated numerical and geophysical approach was used to investigate the role of local seismic amplification in the reactivation of the salcito landslide italy after the molise earthquake of 31 october 2002 numerical stress strain analysis with flac 5 0 fdm software performed in dynamic configuration showed that the 1 hz frequency was consistent with landslide instability conditions the fourier spectrum of the triggering earthquake showed two main peaks occurring at 1 and 2 hz respectively which could be related to local effects the analysis of h v spectral ratios of ambient noise records obtained in the landslide area evidenced amplification effects in the 1 3 hz range on the basis of an engineering geology model numerical modeling of both 1 d and 2 d seismic wave propagation was conducted using linear and nonlinear solutions the simulation outputs showed 1 a 1 hz amplification ascribable to 2 d effects due to a landslide mass lying within a basin like geological structure 2 a double peak amplification at about 2 and 3 hz respectively ascribable to 1 d resonance of the landslide mass and 3 1 d plus lateral wave effects within the landslide mass in the 2 5 3 5 hz frequency range these findings suggest that local amplification of ground motion by the salcito landslide mass may generate a self excitation process responsible for its reactivation

using ambient noise to characterise seismic slope response the case of qiaozhuang peri urban hillslopes sichuan china abstract the mw 7 9 wenchuan earthquake of may 12th 2008 shattered and induced failures on hillslopes surrounding the centre of the town of qiaozhuang located 250 km ne of the mainshock epicentre this motivated investigations on the possible occurrence of site amplification phenomena the initial efforts involved a temporary accelerometer monitoring carried out between april and october 2009 on weigan hill and mount dong located sw and ne of the qiaozhuang centre respectively the monitoring results revealed that the local geological setting characterised by silurian phyllites with sub vertical schistosity at weigan and by fractured precambrian limestones at dong exert major influence on the slopes resonance phenomena with a secondary contribution due to the topographic setting to extend the investigation on local slope response a series of ambient noise recordings were conducted at several sites of the two hills as well as at mount shizi located nw of the town centre which is topographically and geologically similar to mount dong the focus was on the sites monitored by accelerometer stations whose seismic records provided the opportunity to validate the outcomes of ambient noise analysis noise data were analysed using two approaches the standard nakamura s method and a new technique based on analysis of instantaneous polarization properties aimed at estimating ellipticity of rayleigh waves data interpretation was hampered by a contingent factor i e environmental conditions characterised by a strong persistent e w polarized noise at low frequencies below 1 hz and by the complex of geologic and geomorphic conditions the latter particularly in the case of weigan hill appear responsible for a considerable amplification of vertical ground motions the repeated recordings and the comparison of the outcomes of the two techniques of noise analysis with the accelerometer data showed that the new technique provides more stable and consistent results furthermore the new technique was able to reveal site resonance properties that nakamura s method fails to recognise because of transient overlapping of different type waves overall the ambient noise analysis provided evidence of i low frequency resonance 1 hz acting at the scale of the entire relief on weigan hill ii directional amplifications at intermediate frequencies 4 hz affecting ridge crests made of fractured limestone on mounts dong and shizi and iii higher frequency resonances 7 20 hz which vary at a very local scale this information is relevant for inferring the susceptibility of local slopes to earthquake induced failures and hence for the collateral seismic hazard assessment in the qiaozhuan peri urban areas

active thrusting and folding along the northern tien shan and late cenozoic rotation of the tarim relative to dzungaria and kazakhstan we have studied geometries and rates of late cenozoic thrust faulting and folding along the northern piedmont of the tien shan mountain belt west of urumqi where the m 8 3 manas earthquake occurred on december 23 1906 the northern range of the tien shan rising above 5000 m overthrusts a flexural foredeep filled with up to 11 000 m of sediment of the dzungarian basement our fieldwork reveals that the active thrust reaches the surface 30 km north of the range front within a 200 km long zone of neogene quaternary anticlines fault scarps are clearest across inset terraces within narrow valleys incised through the anticlines by large rivers flowing down from the range in all the valleys the scarps offset vertically the highest terrace surface by the same amount 10 2 0 7 m inferring an early holocene age 10 2 kyr for this terrace which is continuous with the largest recent fans of the piedmont yields a rate of vertical throw of 1 0 0 3mm yr on the main active thrust at the surface a quantitative morphological analysis of the degradation of terrace edges that are offset by the thrust corroborates such a rate and yields a mass diffusivity of 5 5 2 5 m 2 kyr a rather fresh surface scarp 0 8 0 15 m high that is unlikely to result from shallow earthquakes with 6 m 7 in the last 230 years is visible at the extremities of the main fold zone we associate this scarp with the 1906 manas earthquake and infer that a structure comprising a deep basement ramp under the range gently dipping flats in the foreland and shallow ramps responsible for the formation of the active fault propagation anticlines could have been activated by that earthquake if so the return period of a 1906 type event would be 850 380 years the small size of the scarp for an earthquake of this magnitude suggests that a large fraction of the slip at depth 2 3 is taken up by incremental folding near the surface comparable earthquakes might activate flat detachments and ramp anticlines at a distance from the front of other rising quaternary ranges such as the san gabriel mountains in california or the mont blanc aar massifs in the alps we estimate the finite cenozoic shortening of the folded dzungarian sediments to be of the order of 30 km and the cenozoic shortening rate to have been 3 1 5 mm yr assuming comparable shortening along the tarim piedmont and minor additional active thrusting within the mountain belt we infer the rate of shortening across the tien shan to be at least 6 3 mm yr at the longitude of manas 85 5 e a total shortening of 125 30 km is estimated from crustal thickening assuming local airy isostatic equilibrium under the same assumption serial n s sections imply that cenozoic shortening across the belt increases westwards to 203 50 km at the longitude of kashgar 76 e as reflected by the westward increase of the width of the belt this strain gradient implies a clockwise rotation of tarim relative to dzungaria and kazakhstan of 7 2 5 around a pole located near the eastern extremity of the tien shan west of hami 96 e 43 5 n comparable to that revealed by paleomagnetism between tarim and dzungaria 8 6 8 7 a 6 mm yr rate of shortening at the longitude of manas would imply a rate of rotation of 0 45 m y and would be consistent with a shortening rate of 12 mm yr north of kashgar taking such values to be representative of late cenozoic rates would place the onset of reactivation of the tien shan by the india asia collision in the early to middle miocene 16 22 9 m y in accord with the existence of particularly thick late neogene and quaternary deposits such reactivation would thus have started much later than the collision roughly at the time of the great mid miocene changes in tectonic regimes denudation and sedimentation rates observed in southeast asia the himalayas and the bay of bengal and of the correlative rapid change in seawater sr isotopic ratio 20 to 15 ma like these other changes the rise of the tien shan might be a distant consequence of the end of indochina s escape

a comparison and test of various site response estimation techniques including three that are not reference site dependent abstract we compare various site response estimation techniques using after shock data of the 1989 loma prieta earthquake collected in oakland california because of recent interest in comparing results from weak and strong motion to infer any nonlinearity and between direct s and coda waves we pay particular attention to the uncertainties first sediment to bedrock spectral ratio estimates between pairs of sites are compared with those obtained from various generalized inversion approaches where the source and site effects of multiply recorded events are solved for simultaneously we find that the site amplification factors are very similar among these approaches but that the uncertainties can be significantly different depending on how the data are weighted we also examine and test three site response estimation techniques that do not rely on a reference site to estimate source and path effects the first involves a parameterized source and path effects inversion even when the bedrock data are excluded from consideration this approach is found to reveal the frequency dependence of site response at each of the sediment sites the second technique involves taking horizontal to vertical component spectral ratios receiver function type estimates of shear wave aftershock data these are also found to reveal the frequency dependence of site response at the sediment sites and the results for the bedrock site are relatively flat and near unity the third estimate is formed by taking horizontal to vertical component ratios of ambient seismic noise and these are shown to reveal the fundamental resonant frequency of the sediment sites unfortunately discrepancies exist among all of the site response estimates and with one dimensional predictions with respect to a frequency independent scaling factor nevertheless the highly frequency dependent character of site response is well constrained and the fact that non reference site dependent methods are capable of revealing this is promising for site specific hazard assessments in regions that lack adequate reference sites

the origin of the upper palaeozoic chanaral melange of n chile the fragmented and mixed strata of the chanaral melange extend for some 220 km from n to s in the coastal ranges of n chile 26 20 to 28 20 s the melange was produced in an accretionary wedge resulting from the ne subduction of the ancestral pacific oceanic plate beneath the gondwana land margin during carboniferous times the melange consists essentially of blocks of sandstone in a pelitic matrix these sediments were deposited as deep sea basin plain turbidites prior to their fragmentation other blocks in the melange include mafic volcanic rocks with the geochemical characteristics of oceanic island basalts and rare shallow marine limestones structures in the melange suggest an origin by two distinct deformation processes involving unlithified sediments initial boudinage and break up of the strata was apparently accomplished by intrastratal movement resulting from imbricate thrusting within the accretionary wedge the second process produced cross cutting zones of breccia which are interpreted as fluid escape conduits resulting from the high pore pressures produced during underthrusting

palaeogene and neogene cold seep communities in barbados trinidad and venezuela an overview palaeogene and neogene fossiliferous carbonates from barbados trinidad and northern venezuela are interpreted to have formed at ancient cold seep sites the hydrocarbon seepage that fuelled these chemosymbiotic ecosystems was related to tectonic activity in the southern caribbean region particularly the subduction of the caribbean plate beneath the north atlantic plate the carbonates and fossils from the scotland district north eastern barbados are eocene miocene in age and are associated with two distinct tectonic units the sub oceanic fault zone and a diapiric melange the sub oceanic fault zone is the tectonic junction between accretionary prism sediments and over lying thrust sheets of fore arc basin sediments the loading of the thrust sheets caused methane rich fluids to be expelled from the accretionary prism sediments and channelled to the sea floor via the sub oceanic fault zone where it supported chemosymbiotic invertebrate communities containing vesicomyid lucinid thyasirid solemyid and nuculanid bivalves a variety of gastropods and possibly vestimentiferan tube worms the diapiric melange is considered to represent sediment that failed under pressure in the accretionary prism and was remobilised as a diapir that extruded onto the sea floor providing a conduit for methane and other hydrocarbons that sustained a chemosynthesis based community of vesicomyid lucinid and nuculanid bivalves and various gastropods the geological setting of fossiliferous carbonates known as freeman s bay limestone in southwest trinidad has been less fully investigated the freeman s bay limestone is a member of the miocene lengua formation which is believed to have formed in a fore deep basin on lapping onto an accretionary prism formed by the subduction of proto caribbean crust beneath the south american plate the carbonates and fossils of the fbl including the bivalves pleurophopsis unioides van winkle 1919 and thyasira adoccasa van winkle 1919 lucinids nuculanids and bathymodiolins and provannid and other gastropods are interpreted to have formed at palaeo seep sites on the accretionary prism little is currently known about the geological setting of the fossils collected from the miocene huso member of the pozon formation from northern venezuela but a seep origin is strongly suspected based on the taxa present like the fossil assemblages from barbados and trinidad the venezuelan material is dominated by vesicomyid bivalves together with lucinid thyasirid bathymodiolin and solemyid bivalves and various gastropods these taxa are characteristics of modern cold seep communities most comparisons between the fossil caribbean and modern seep fauna are necessarily at the generic or family level although in some cases individual species are found at both ancient and modern seep sites for example the gastropod cataegis meroglypta is found in seep carbonate from the sofz of barbados and the fbl of trinidad as well as at modern seeps on the barbados prism at the generic level this study has revealed the first fossil occurrences of abyssochrysos and provanna in the caribbean such temporal and spatial links further the understanding of both local and global patterns of biogeographic distribution of cold seep fauna

seismic response of a hill the example of tarzana california the northridge california earthquake that strongly shook the city of los angeles in january 1994 produced one of the highest ground accelerations ever recorded in an earthquake at a site located on top of a small hill in tarzana about 6 km south of the epicenter the subsequent study of aftershock recordings obtained by a dense seismic array deployed on the hill a few days after the earthquake showed the existence of a strong amplification at stations located at the top of the hill relative to stations near the base spudich et al 1996 resonances and polarization rotations were also observed we investigate in this study the role that the topography of the site played on the observed ground motions and accelerations to this aim we perform numerical simulations and study the response of the three dimensional topography of the site to incident shear waves polarized in different directions the method used is a boundary integral equation scheme in which the green s functions are calculated by the discrete wavenumber method the results obtained show that the topography of the site though quite gentle the hill is less than 20 m high strongly affects the ground motions in the frequency range between 2 and 15 hz many of the observed characteristics of the seismic response at tarzana are explained in part by its topography the consistent amplification of ground motion at and near the top of the hill the directional seismic response of the hill that results in a strong amplification of the ground motion transverse to the direction of elongation of the hill the existence of a fundamental transverse oscillatory resonance mode of the hill at 3 to 5 hz the rotation of the polarization of ground motion and the spatial variation of amplification over the hill at the fundamental resonance mode the seismic response of the topography however does not fully explain the amplitude of the effects observed the three dimensional geological structure of the site must in some way amplify the effect of the topography to produce the observed seismic response in spite of not being as strong as the observed effect the topographic effect of the site is considerable the ground motion is amplified by factors ranging from 30 to 100 at some locations in the frequency range from 2 to 15 hz rapid spatial variations of ground shaking intensities can take place over distance scales of a few tens of meters at high frequency finally the results of the simulation indicate that the topography of the site amplified the large east west accelerations recorded there during the northridge mainshock by 30 to 40

ambient vibration classification of unstable rock slopes a systematic approach abstract in this paper we are comparing the seismic response of 25 different rock slope instabilities with diverse geological properties activity level failure mechanism fracturing and volumes we classify them according to their dynamic behaviour in the dataset we found two main classes of unstable rock slopes depth controlled sites and volume controlled sites for depth controlled instabilities the seismic wavefield is controlled by horizontally propagating surface waves in the highly fractured and weathered material at such sites surface wave dispersion curves can be retrieved and inverted into velocity profiles of the underground the lateral borders of depth controlled instabilities are not obvious and the seismic properties mainly change with depth the seismic response of volume controlled sites is dominated by the eigenvibrations of the rock mass itself such instabilities have clear lateral and vertical borders and show highly amplified ground motion in limited frequency bands the observed polarisation of the ground motion is perpendicular to deep open fractures that do not allow surface waves to propagate a special case of the volume controlled sites is represented by tower like rock masses showing strong amplification and directionality their dynamic behaviour might not only be related to the internal structure but also to their geometry that is similar to high rise buildings another type of rock instabilities is represented by block structures which are difficult to identify by the proposed ambient vibration methods a clear relation between geological properties and seismic response was not found

evidences of landslide earthquake triggering due to self excitation process the basin like setting of stiff bedrock combined with pre existing landslide masses can contribute to seismic amplifications in a wide frequency range 0 10 hz and induce a self excitation process responsible for earthquake triggered landsliding here the self excitation process is proposed to justify the far field seismic trigger of the cerda landslide sicily italy which was reactivated by the 6th september 2002 palermo earthquake ms 5 4 about 50 km far from the epicentre the landslide caused damage to farm houses roads and aqueducts close to the village of cerda and involved about 40 106 m3 of clay shales the first ground cracks due to the landslide movement formed about 30 min after the main shock a stress strain dynamic numerical modelling performed by fdm code flac 5 0 supports the notion that the combination of local geological setting and earthquake frequency content played a fundamental role in the landslide reactivation since accelerometric records of the triggering event are not available dynamic equivalent inputs have been used for the numerical modelling these inputs can be regarded as representative for the local ground shaking having a pga value up to 0 2 m s2 which is the maximum expected in 475 years according to the italian seismic hazard maps a 2d numerical modelling of the seismic wave propagation in the cerda landslide area was also performed it pointed out amplification effects due to both the structural setting of the stiff bedrock at about 1 hz and the pre existing landslide mass in the range 3 6 hz the frequency peaks of the resulting amplification functions a f fit well the h v spectral ratios from ambient noise and the h h spectral ratios to a reference station from earthquake records obtained by in situ velocimetric measurements moreover the fourier spectra of earthquake accelerometric records whose source and magnitude are consistent with the triggering event show a main peak at about 1 hz this frequency value well fits the one amplified by the geological setting of the bedrock in correspondence with the landslide area which is constituted of marly limestones and characterised by a basin like geometry

unbiased moment rate spectra and absolute site effects in the kachchh basin india from the analysis of the aftershocks of the 2001 mw 7 6 bhuj earthquake what can be learned about absolute site effects on ground motions with no geotechnical information available in a very poorly instrumented region in addition can reliable source spectra be computed at a temporary deployment these challenges motivated our current study of aftershocks of the 2001 m w 7 6 bhuj earthquake in western india where we decouple the ambiguity between absolute source radiation and site effects by first computing robust estimates of coda derived moment rate spectra of about 200 aftershocks in each of two depth ranges crustal attenuation and spreading relationships based on the same data used here were determined in an an earlier study using our new estimates of source spectra and our understanding of regional wave propagation for direct s waves we isolate the absolute site terms for the stations of the temporary deployment absolute site terms for each station were determined in an average sense for the three components of the ground motion via an l1 norm minimization results for each site were averaged over wide ranges of azimuths and incidence angles the bhuj deployment is characterized by a variable shallow geology mostly of soft sedimentary units vertical site terms in the region were observed to be almost featureless i e flat with amplifications slightly 1 0 within wide frequency ranges as a result the horizontal to vertical h v spectral ratios observed at the deployment mimic the behavior of the corresponding absolute horizontal site terms and they generally overpredict them this differs significantly from results for sedimentary rock sites limestone dolomite obtained by malagnini et al 2004 in northeastern italy where the h v spectral ratios had little in common with the absolute horizontal site terms spectral ratios between the vector sum of the computed horizontal site terms for the temporary deployment with respect to the same quantity computed at the hardest rock station available bac1 are seriously biased by its nonflat nonunitary site response this indicates that occasionally the actual behavior of a rock outcrop may be far from that of an ideal reference site steidl et al 1996

detailed evaluation of site response estimation methods across and along the sedimentary valley of volvi euro seistest using records from the euro seistest area near thessaloniki greece we studied empirically the amplification effects of a sedimentary valley one of the main advantages of this site is the very detailed knowledge of the near subsurface structure due to exhaustive geophysical and geotechnical measurements and data analyses jongmans et al 1998 the uniqueness of the seismological data set is the very dense network 31 stations were installed perpendicular and parallel to the valley axis with minimum interstation distances of 250 m the mean ampli fications along both axes estimated from 13 local events were imaged using the traditional spectral ratio technique variations of the mean amplifications due to the choice of different data subsets were tested by the use of up to 89 local events supplemented by four teleseismic events offering good low frequency resolution results obtained using the traditional spectral ratio technique were compared with results from a generalized inversion technique the h v ratio technique a coda wave technique and nakamura s technique advantages and disadvantages of each method are outlined especially from a practical point of view

petrology of the bitumen manjak deposits of barbados hydrocarbon migration in an accretionary prism abstract bitumen manjak deposits in barbados are located particularly along fracture planes including faults and also in calcite veins as veinlets vug fillings and bedding parallel seams in sandstones and as matrix to diagenetic carbonates they occur particularly near the margins of the diapiric joes river formation and in immediately adjacent rocks reflecting the role of diapirism in the migration of hydrocarbon bearing fluids the larger bitumen veins trend between e w and ne sw following the strike of fault bounded packets of the accretionary prism the predominant fabric in the basal complex of barbados that is hydrocarbon migration followed the structural grain petrographic relationships of bitumen with chemosynthetic diagenetic carbonates suggest that hydrocarbon migration was a multi stage process the host sediments to the bitumens were not well consolidated and appear to have been in an overpressured state hydrocarbon generation may have contributed to overpressuring and buoyancy enhanced diapirism the association of bitumens with faults and decollement surfaces suggests that the lubricating action of the bitumen helped to accommodate deformation during diapirism and other processes related to the evolution of the accretionary prism widespread impregnation of sandstones in the joes river formation suggests that hydrocarbon migration was primarily by intergranular flow in a state of low confining pressure and did not depend on migration along the fault planes which may be of a later date

weathering effects on the geotechnical properties of argillaceous sediments in tropical environments and their geomorphological implications outcrops of young sedimentary argillaceous rocks with well developed fabric display rapid changes in their properties when subject to tropical weathering the change in the materials is often accompanied by mass movement activity and the geomorphological consequence in terms of landforms is usually the development of badlands topography detailed field and laboratory studies have been undertaken on the joe s river formation barbados and the lichi melange taiwan both are sedimentary mudrocks with well developed scaly fabrics physical and geotechnical laboratory tests have been conducted on samples collected from type site locations to elucidate associations between material properties earth surface processes and landform development while the inherent physical properties show little or no difference in the transition from unweathered to highly weathered materials by applying the critical state model the mudrock geotechnical properties can be shown to change significantly as weathering commences material strength surprisingly increases only after a period of more extensive weathering do mechanical properties confirm increasingly incompetent materials the initial strength increase appears to be due to weathering induced modification of the fabric the subsequent strength drop is a product of weathering induced modification of both the fabric and the in situ intact sediment it is suggested that by applying the critical state model a greater consideration can be gained of the geotechnical response of the sediments to weathering

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

characterizing an unstable mountain slope using shallow 2d and 3d seismic tomography as transport routes and population centers in mountainous areas expand risks associated with rockfalls and rockslides grow at an alarming rate as a consequence there is an urgent need to delineate mountain slopes susceptible to catastrophic collapse in a safe and noninvasive manner for this purpose we have developed a 3d tomographic seismic refraction technique and applied it to an unstable alpine mountain slope a significant segment of which is moving at 0 01 0 02 m year toward the adjacent valley floor first arrivals recorded across an extensive region of the exposed gneissic rock mass have extraordinarily low apparent velocities at short 0 2 m to long 100 m shot receiver offsets inversion of the first arrival traveltimes produces a 3d tomogram that reveals the presence of a huge volume of very low quality rock with ultralow to very low p wave velocities of 500 2700 m s these values are astonishingly low compared to the average horizontal p wave velocity of 5400 m s determined from labora

neodymium and strontium isotopic constraints on soil sources in barbados west indies abstract neodymium and strontium isotopic compositions and sm nd ratios are used to constrain the sources of silicate rich soils developed on uplifted pleistocene coral reef limestones on barbados west indies the geographic and geologic setting of barbados facilitates the application of these tracers to the evaluation of the following soil sources 1 pleistocene reef limestone regolith 2 tertiary carbonate rocks sandstones and mudstones that are exposed in northeastern barbados 3 volcanic ash erupted from the lesser antilles arc 4 saharan dust transported by trade winds and 5 fertilizer the soils have nd values that range from 6 6 to 1 9 87 sr 86 sr values of 0 70890 to 0 71067 and sm nd ratios of 0 223 0 260 the pleistocene limestone component is the most significant source of sr in the soils and a negligible source of nd comparison of sm and nd concentrations and neodymium isotopic compositions of soil samples that are weathered to varying extents indicates that sm and nd are relatively unfractionated and retained in the soils during weathering nd and sm nd variations in the soils therefore primarily reflect the compositions and proportions of the silicate sources mass balance calculations based on sm nd systematics require that the silicate soil components contain between 30 85 volcanic ash with the remaining silicate fraction comprised of old continentally derived sediment in contrast to sm and nd sr is mobilized and removed from the soils during weathering strontium from volcanic and carbonate sources is preferentially removed relative to continental silicate sources the strontium isotopic compositions of the soils therefore reflect the combined effects of the degree of weathering and the compositions and proportions of the soil sources mass balance calculations indicate that at least 35 60 of the initial sr in the soils has been removed by weathering these results illustrate 1 the utility of radiogenic isotopes in identifying and quantifying soil sources and weathering processes 2 the compositional influence of numerous sources on soils even those developed in a relatively isolated area such as barbados and 3 the domination of barbados soil sm nd systematics by nonregolith eolian components

quartzose turbidites of the accretionary complex of barbados ii variations in bedding styles facies and sequences abstract barbados provides the only subaerial exposures of the barbados ridge an accretionary complex lying outboard of the lesser antilles volcanic arc within nine measured sections of quartzose turbidites five major types of sequences are recognized 1 1 progradational sequences basin plain outer fan of uniformly fine grained flat based base absent turbidites that thicken upward and gradually become coarser grained and base present at the top of the sequence 2 2 a single rejuvenation rapid progradational sequence was identified as an abrupt progradational sequence above abandoned lobe deposits and is not characterized by stacked well developed upward thickening successions as many progradational sequences are 3 3 channelized successions of coarse grained base present turbidites arranged in packets 5 20 or 50 140 m thick which are midfan and inner fan deposits respectively the distinction between predominance of base present and base absent turbidites seems to correspond with the interpreted change from midfan channelized to outer fan sheet flow deposition 4 4 one example of a major retrogradational sequence of midfan deposits above inner fan sandstones has been found on barbados minor sequences of facies retrogradation are relatively common in the outer fan environment where upward thinning sandstone beds overlie upward thickening units to define symmetric sequences 5 5 abandonment successions are major as indicated by massive accumulations of mudstone minor as indicated by abrupt reversals of upward thickening trends in outer fan lobe deposits and cryptic where indicated by thick 4 m bioturbated zones of massive sandstone

source rock and maturation evaluation of the barbados accretionary prism abstract organic material in specimens from surface and downhole sites and samples of oil and gas from barbadian wells were studied for source potential and maturation history the study involved 1 visual examination of the kerogen 2 measurement of total organic carbon content 3 determination of vitrinite reflectance 4 rock eval pyrolysis assay 5 geochemical measurement of pooled and extracted bitumens including carbon isotopic ratios 13 c and 6 gas chromatographic analysis of saturated gaseous hydrocarbons two types of kerogen occur in barbados terrestrial presumably of south american origin and marine planktonic the two types are mixed in most samples the terrestrial kerogens are dominant and occur in all wells in the basal complex and most of its outcrops the planktonic organic matter occurs in exposed melange hemipelagic rocks and rarely in terrigenous turbidites the well specimens do not show significant maturation within the drilled depths suggesting that pooled hydrocarbons originated from deeper levels of the prism and accumulated as a result of migration faults bounding the intraprism thrust sheets probably provided migratory paths for hydrocarbons and water juxtaposed rocks of variable maturity assisted in alteration and biodegradation and led to the formation of structural traps the composition of gases indicates that maturation conditions for gas generation may exist at great depths within the barbados accretionary prism

the ms 7 3 1992 suusamyr kyrgyzstan earthquake 1 constraints on fault geometry and source parameters based on aftershocks and body wave modeling we investigated the suusamyr kyrgyzstan earthquake of 19 august 1992 using aftershock data teleseismic body wave modeling and field observations aftershocks were recorded by the iris kyrgyzstan broadband network a temporary six station aftershock network and a regional network operated by the kyrgyz institute of seismology the aftershocks which range in depth from the surface to 18 km defined a 50 10 km long rupture zone that dips 50 13 to the south and strikes roughly east west the base of the eastern end of the aftershock zone shallowed to the east along strike and may represent a lateral ramp the surface ruptures also had an east west strike and dipped south but the total length less than 4 km was much shorter than the aftershock zone a teleseismic body wave inversion using a point source and a directivity correction yields a focal mechanism with a strike of 221 dip of 46 and a slip of 43 we obtained a moment of 4 1 1019 n m with a centroid depth between 5 and 21 km the rupture propagated along an azimuth of 330 60 which matches the relative location of the mainshock with respect to the aftershock zone the results of the aftershock study and teleseismic inversion yield a clear picture of the fault geometry of a large thrust earthquake

investigating the effect of earthquakes on open pit mine slopes abstract this paper develops a database for studying the circumstances under which dynamic loading of earthquake can cause slope failure in deep open pit mines with a long lifetime the database includes 177 open pit mines hit by earthquake and 95 natural slopes and 37 tailing dams which have been failed by earthquakes both earthquake parameters and geomechanical characteristics involved in each case study are investigated from this information the elements playing role in the earthquake triggered failures in natural slopes and tailing dams are identified and used to indicate conditions that may result in earthquake induced failures in open pit mines the result shows that even though the valley shape geometry and absence of the top weathered layer make open pit mines less prone to earthquake induced failures excessive pore pressure in pit slopes still carries the risk of earthquake triggered failures in open pit slopes only limited numbers of open pit mines have been so far exposed to earthquakes with the same parameters as those causing failure in natural slopes and tailing dams that is the response of open pit mines to higher magnitude shallower and closer earthquakes is still unknown studying the earthquakes that have caused failure in other slopes it is concluded that open pit mines may still experience reportable failures if struck by earthquakes with local depth of less than 40 km epicentral distance of less than 100 km and magnitude of greater than 6 0 the necessity of accounting for seismic loading in slope stability analyses and active dewatering for open pit mines located in seismically active areas are also discussed

volume loss and defluidization history of barbados the basal complex of barbados island is a tectonic amalgam of eocene strata accreted at an outer deformation front at the end of eocene time the structures and porosity depth function of such sediments give clues to the succession of pore volume loss episodes each of which must have been accompanied by defluidization the basal complex evolved as a perpetually shallow low temperature mass which underwent little or no unroofing in its 36 m y history in the accretionary prism in its early phase of deformation the accretionary structure formed by thrust imbrication perhaps with little concurrent volume loss burial compaction followed tectonic thickening during accretion causing probable large pore volume loss within limits of 0 70 of the initial volume of the imbricate stack a late phase of tectonics has affected barbados and a wide region of the structural high since 20 ma such tectonics reactivated faults in the basal complex which acted as channelways for deep seated and perhaps shallow fluids to emerge from the structural high the late stage tectonics also caused local basins for deposition of sediment cover and emplacement of thrust nappes of forearc basin strata above the basal complex such top loading caused a renewed phase of burial compaction and loss of about 37 or more of the pore volume that existed at the onset of late stage tectonics

mud diapirism and subcretion in the barbados ridge accretionary complex the role of fluids in accretionary processes mud diapirism has recently been recognized in several modern accretionary wedges it provides an important means of dewatering accretionary wedges and should be regarded as an important process for producing the melanges found in both modern and ancient accretionary terranes mud diapirism affects a large area of the barbados ridge accretionary complex the distribution of the mud diapirs appears to be primarily controlled by the presence of underconsolidated terrigenous submarine fan deposits that are being accreted to the complex the frequency of diapir occurrence decreases northward as the fan becomes thinner mud diapirs are absent from the very eastern most part of the complex formed from sediments accreted at its toe with the exception of a few mud volcanoes on the ocean floor in front of the complex the initiation of diapirism appears to be spatially coincident with the onset of subcretion or underplating of sediment to the base of the complex at a ramp between two levels of decollement it is proposed that the release of mud and pore water from the subcreted sediments is a direct or indirect cause of most of the mud diapirism in the accretionary complex there is a range of diapiric form dependent on the viscosity of the mud from mud volcanoes fed by low viscosity mud to higher viscosity mud ridges the diapirs in the eastern areas of the complex are generally mud volcanoes with narrow conduits feeding a surface mound mud ridges are prominent in the western parts of the complex this is interpreted as reflecting a general westward decrease in the fluid content of the accretionary complex bottom simulating seismic reflectors formed by gas hydrate are commonly developed in the areas of mud volcano occurrences the presence of the hydrate indicates that large volumes of methane are being generated at depth in these regions the generation of methane may be contributing to zones of overpressuring in the wedge methane may also be partly responsible for driving the diapiric material to the surface to form mud volcanoes ridges in the subducting oceanic crust beneath the accretionary complex locally enhance diapirism above their crests and southern flanks faults formed later in the development of the complex are more commonly associated with diapirism than those resulting from accretion at the toe of the wedge these later faults play an important role in controlling the sites of individual mud volcanoes chains of mud volcanoes and mud ridges

reconnaissance geophysical methods in landslide investigations abstract landslides are a natural hazard in many countries and often affect civil engineering structures and projects three aspects in particular require examination in a geotechnical appraisal of a landslide s stability in engineering terms 1 the definition of its three dimensional shape with particular reference to shear surfaces and failure planes 2 the definition of the hydrogeological regime with regard to water input to the landslide and its distribution within the slip mass 3 the detection of movement by or within the slip mass and the characterisation of such movements the site investigation costs may be very high since landslides may be extremely large structurally complex and topographically severe it is therefore advantageous in suitable circumstances to carry out reconnaissance geophysical surveys to define the structure and to guide optimum siting of boreholes and pits and ultimately the installation of piezometers inclinometers etc standard surface geophysical techniques including the seismic electrical resistivity acoustic emission and borehole methods have all been applied with varying success to look at a landslide before a major site investigation commences in recent years electromagnetic methods have been the subject of considerable research in this field and significant advances have been made in this paper the application of the above geophysical methods at the reconnaissance stage in a landslide investigation has been reviewed and illustrated with several case histories taken from different geological settings

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

barbados maturation source rock potential and burial history within a cenozoic accretionary complex abstract a number of diagenetic properties were studied in sedimentary rocks exposed along a 25 km across strike transect on barbados the crest of the barbados accretionary complex the island of barbados consists of three structural levels a lower mostly eocene or undated basal complex composed of quartzose turbidites hemipelagites and melange an intermediate level eocene to miocene of nappes composed mostly of calcareous pelagite and a pleistocene coral cap diagenetic studies concentrated on the basal complex although preliminary data from the nappes are also presented the following subjects were studied 1 clay mineralogy illite interlayers in mixed layer clays 2 vitrinite reflectance 3 organic type and maturation by rock eval pyrolysis 4 thermal alteration index of spores and pollen 5 dry bulk density 6 silica mineralogy taken together the data can be interpreted to indicate maximum temperatures attained during diagenesis of less than 80 c based on a uniform palaeogeothermal gradient of 15 c km 1 and a temperature at the sediment water interface of 10 c maximum burial depths of basement complex rocks were about 2 5 km minimum possible burial depths are 1 and are immature organic matter was derived mostly from terrigenous or oxidized sources type iii kerogens although some marine planktonic sources are indicated locally type ii kerogens organic matter is therefore primarily gas prone

multiscale geophysical characterization of an unstable rock mass abstract hazard mitigation from rockfalls and landslides is a priority in densely populated areas a proper characterization of the inner structure of the rock mass is key to the comprehension of the mechanisms enhancing the slope instabilities to this aim multi scale geophysical methods can provide a novel and valuable tool for a high resolution imaging of the internal structure of the rock mass and unique constraints on the physical state of the medium we present here a cross hole seismic tomography survey coupled with laboratory ultrasonic velocity measurements and physical properties determination on rock samples to characterize the damaged and potentially unstable granitic cliff of madonna del sasso nw italy results allowed to obtain i a lithological interpretation of the velocity field obtained at the site ii a systematic correlation of the measured velocities with physical properties density and porosity and macroscopic features of the granite weathering and anisotropy of the cliff the multi scale approach adopted within this study revealed to be crucial for the imaging at depth of the main fractures affecting the cliff site scale seismic tests and for the understanding of the variations in the seismic velocity between altered and intact rock laboratory scale tests similar approaches can be potentially used in further microseismic monitoring studies

multibeam study of the flores backarc thrust belt indonesia using the seamarc ii seafloor mapping tool in conjunction with closely spaced seismic reflection profiles we have mapped a segment of the flores back arc thrust zone structural irregularities along the deformation front of the thrust zone result from changing stratigraphy and basement structure of the lower plate ne trending faults cutting the outer slope of the flores basin are easily mapped because they truncate dense drainage patterns obliquely mud diapirs probably indicating elevated fluid pressures have formed throughout the accretionary wedge but appear to be concentrated as do back arc thrust earthquakes at the ends of thrust faults the overall orientation of the deformation front of the accretionary wedge is 100 suggesting a nne sense of thrust motion and supporting an origin of the thrust zone by collision of the arc with australia rather than by magmatic forcing or gravitational sliding or spreading orientations of faults and folds close to the arc are not consistent with the trends of the frontal thrusts however and the difference may be due to either different initial orientations or to later rotations of structural features as the accretionary wedge grew

the tectonic fabric of the barbados ridge accretionary complex abstract a map showing near surface structure and other surficial geological features on the barbados ridge accretionary complex has been constructed from gloria long range side scan sonographs detailed bathymetric surveys using seabeam and single and multichannel seismic reflection sections the map shows major variations in the size orientation and style of structures across the accretionary complex that are principally related to the increasing thickness of the complex and the sediment drape upon it and variations along the complex that derive from the northward thinning of sediment accreted from the ocean floor and the effects of ridges in the oceanic basement the development of crossfaulting is mainly associated with basement ridges mud diapirism is abundant in the southern part of the complex and is characteristic of that part of the complex into which turbidites from the orinoco submarine fan are accreted slumping on a variety of scales is another feature of the complex the map is presented at a scale of 1 1063415 4 inches per degree of longitude and also shows bathymetry at 200 m contour intervals

microearthquake s wave observations from 0 to 1 km in the varian well at parkfield california abstract high gain three component seismometers from 0 to 1 km deep along the varian a 1 well at parkfield california were used to record the waveforms of nearby microearthquakes despite being in the thick tertiary sediments of the parkfield syncline the s wave amplification at this site is only about a factor of 3 the spectral content and spectral ratios of s waves along the well show that the average qs in the top 1 km at this site is 37 with the qs in different subintervals varying between 8 and 65 based on initial s wave polarizations a complex s wave velocity structure must exist at and below the varian site this structure appears to include position dependent anisotropy as well as steep lateral velocity gradients at a depth of 1 km s wave splitting parallel and normal to the san andreas fault zone is consistently observed this splitting scales at roughly 0 01 sec km subsequent to the split s waves the particle motion seems to be controlled by event focal mechanism above 1 km the upgoing s waves attenuate and change directions of polarization with a new splitting rate of 0 1 sec km uniquely for some events on the san andreas fault immediately below the varian site large post s wave signals with normal dispersion are present we propose that these phases are fault zone guided waves channeled from the san andreas fault to the varian site along the gold hill fault

structure of the accretionary complex of barbados ii bissex hill this is the second of a series concerning the accretionary complex that is exposed on the island of barbados and is thought to represent the lesser antilles fore arc at its structural high two principle tectonostratigraphic elements are present in the bissex hill area a basal complex composed of east northeast striking generally steeply dipping fault bound packages of terrigenous sandstones and mudstones mostly turbidites hemipelagic rocks and melange that complex is overlain by the bissex hill nappe composed of calcareous pelagic rocks crystalline limestone and foraminiferal arenite also present in the basal complex are smaller fault bound packages termed micropackets composed of brecciated basal complex lithologies basal complex faults are cut by the bissex hill nappe except on the southern margin of the bissex hill nappe where melange and hemipelagic lithologies apparently have been faulted over the nappe rocks this youngest faulting may be driven by holocene and older melange diapirism structural evolution of terrigenous and probably hemipelagic rocks in basal complex fault packages is characterized by coaxial deformation about southwest trending axes melange packages possibly experienced greater strain as evidenced by girdled fold axes and axial planes and foliations of constant orientation packet bounding faults probably developed during early folding and probably represent surfaces against which packet contents contracted micropackets are the result of motions after the assembly of major packets and are formed through fault imbrication and or diapiric injection rocks of the bissex hill nappe experienced folding first about a north trending axis followed by folding about a southwest trending axis and gentle folding on the entire nappe about an east northeast trending axis deformation in the basal complex is thought to have occurred by progressive accretion of sediment packets the bissex hill nappe is thought to represent a fore arc basin complex thrust over the accretionary complex quartzose sandstones present in the bissex hill nappe that probably had their source in the basal complex indicate that the accretionary complex probably shoaled by the miocene

metallogeny and tectonic development of the tasman fold belt system in tasmania abstract in western tasmania precambrian sedimentary sequences form the basement for narrow trough accumulations of eocambrian and younger sequences the main trough the meridional dundas trough is flanked to the west by the rocky cape region of precambrian rocks within which major apparently stratiform exhalative magnetite pyrite deposits are intercalated with metabasaltic volcanics and ultramafic bodies the eocambrian cambrian troughs apparently developed during extension of precambrian continental crust early shallow water deposition includes thick dolomite units in some troughs deepening of the troughs was accompanied by turbidite sedimentation with minor limestone and submarine basaltic volcanism with associated minor disseminated native copper ultramafic and related igneous rocks were tectonically emplaced in some troughs during a mild compressional phase they contain only minor platinoids copper nickel sulphides and asbestos but are source rocks for tertiary secondary deposits of platinoids chromite and lateritic nickel in the dundas trough eocambrian early cambrian rocks are separated by an inferred erosional surface from structurally conformable overlying middle to late cambrian fossiliferous turbidite sequences the structural conformity continues through overlying ordovician to early devonian terrestrial and shallow marine stable shelf deposits a considerable pile of probable middle cambrian felsic volcanics accumulated between the sedimentary deposits of the dundas trough and the tyennan region of precambrian rocks to the east a lava dominated belt within the volcanics hosts major volcanogenic massive sulphide deposits including those of the exhalative type which in the south are enriched in copper gold and silver whereas in the north they are rich in zine lead copper gold and silver cambrian movements along faults near the margin of the tyennan region resulted in erosion of the mineralized volcanics locally exposing sub volcanic granitoids above the local unconformities occur unmineralized volcaniclastic sequences that pass conformably into ordovician to early devonian shelf deposits ordovician limestone locally hosts stratabound disseminated and veined base metal sulphide deposits pre middle devonian rocks of western tasmania differ for most part from those in the northeast where deeper marine turbidite quartz wacke sequences were deposited during the ordovician and early devonian the eocambrian to early devonian rocks of tasmania were extensively deformed in the mid devonian the precambrian regions of western tasmania behaved as relatively competent blocks controlling early fold patterns in northeastern tasmania folding is of similar age but resulted from movements inconsistent with those affecting rocks of equivalent age in western tasmania the final metallogenic event is associated with high level granitoid masses emplaced throughout tasmania during the middle to late devonian in northeastern tasmania extensive i type granodiorite and s type granite with alkali feldspar granites are associated with mainly endogranitic stanniferous grelsens and wolframite cassiterite vein deposits in contrast scheelite bearing skarns and cassiterite stannite pyrrhotite carbonate replacement deposits are dominant in western tasmania associated mainly with s type granites several argentiferous lead zinc vein deposits occur in haloes around tin tungsten deposits a number of gold deposits are apparently associated with i type granodiorite but some have uncertain genesis the contrasting regions of western and northeastern tasmania have probably been brought together by lateral movement along an inferred fracture flat lying late carboniferous and younger deposits rest on the older rocks and the only known post devonian primary mineralization is gold associated with creta ceous syenite

relatively recent construction of the tien shan inferred from gps measurements of present day crustal deformation rates the tien shan a high seismically active intracontinental mountain belt 1 000 2 000 km north of the himalaya has grown as a result of india s collision with asia1 the crustal shortening 200 50 km refs 2 3 and thickening that gave rise to the tien shan accommodates only a small fraction of india s total penetration into asia 2 000 3 000km and the temporal relationship of deformation in this belt to the india asia collision remains unclear here we report geodetic measurements of the tien shan using the global positioning system gps that indicate that the current crustal shortening rate is nearly half of india s convergence rate with eurasia in this area4 we infer a total shortening rate for the tien shan of 20 mm yr 1 which is approximately twice that inferred previously from the extrapolation of slip rates in the holocene3 and earthquake induced displacements during this century5 suggesting that the rate of mountain building in this region has accelerated several fold since the onset of collision 50 55 myr ago6 7 if as we argue the current shortening rate can be extrapolated to geological timescales then our results suggest that most of the tien shan has been constructed during the past 10 myr perhaps in response to an increased horizontal force following an abrupt rise of the tibetan plateau8 9

fission track evidence for the source of accreted sandstones barbados a part of the accretionary wedge associated with the lesser antilles arc system is exposed in an area of approximately 50 km in northeastern barbados zircon separates from sandstones collected from the scotland district barbados w i were analyzed using the fission track technique in order to assess the spectrum of source areas from which these terrigenous sediments were derived and to better constrain the timing of deposition results yielded a mixture of ages with strong groupings from 25 80 ma 200 350 ma and greater than 500 ma the youngest population indicates that some of the scotland beds previously dated by paleontologic methods as eocene may actually be as young as late oligocene possible source areas include the lesser antilles arc the netherlands venezuelan antilles arc and the caribbean mountains of venezuela the 200 350 ma population may reflect partially annealed cratonic material an andean component and or material associated with a triassic rifting event the oldest zircons 500 ma and metamict zircons were likely derived from the south american craton detrital feldspars separated from sandstone at the base of chalky mount were analyzed by the 40ar 39ar age spectrum technique results yield what is interpreted to be a slow cooling gradient from 1350 ma to 925 ma and provides additional evidence of a cratonic source for the accreted sediments based on results from this study and paleogeographical constraints it is proposed that source areas for the scotland sandstones of barbados may have included the guayana shield central cordillera uplifted areas of coastal south america and the lesser antilles volcanic arc we speculate that in late oligocene time an immense proto orinoco river system flowed in a northeasterly direction from the shield through the northern venezuelan mountain system cordillera de la costa and araya paria finally emerging into the caribbean sea in the area now occupied by unare depression sediments comprising this deltaic complex and deep sea fan were either deposited directly into the trench or onto the sea floor where they were soon after caught up in the accretionary wedge of the lesser antilles arc system this article contains supplementary material