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

systematic comparisons of earthquake source models determined using insar and seismic data abstract robust earthquake source parameters e g location seismic moment fault geometry are essential for reliable seismic hazard assessment and the investigation of large scale tectonics they are routinely estimated using a variety of data and techniques such as seismic data and more recently interferometric synthetic aperture radar insar comparisons between these two datasets are frequently made although not usually in a comprehensive way this review compares source parameters from global and regional seismic catalogues with those from a recent database of insar parameters which has been expanded with 18 additional source models for this study we show that moment magnitude mw estimates agree well between the two datasets with a trend for thrust events modelled using insar to have slightly larger mw estimates earthquake locations determined using insar agree well with those reported in regional catalogues with a median difference of 6 3 km between them which is smaller than for global seismic catalogues we also investigate the consistency of source parameters and source directivity by comparing isc hypocentres with gcmt and icmt centroid locations for earthquakes with mw 6 5 in some cases the source directivity is qualitatively comparable with previous studies especially when comparing isc and icmt locations the average difference between insar determined depths and those in the ehb catalogue is reduced if a layered half space is used in the inversion of insar data overall faulting geometry strike dip and rake angles remain in good agreement with values from the gcmt catalogue and any large discrepancies can be attributed to tradeoffs between parameters with continued investment in satellites for radar interferometry insar is a valuable technique for the estimation of earthquake source parameters the observed trends and discrepancies between insar and seismically determined source parameters are the result of issues with the data different inversion techniques and the assumed earth structure model

evidence for magmatic underplating and partial melt beneath the canary islands derived using teleseismic receiver functions abstract in recent years an increasing number of studies have focussed on resolving the internal structure of ocean island volcanoes traditionally active source seismic experiments have been used to image the volcano edifice here we present results using the analysis of compressional to shear p to s converted seismic phases from teleseismic events recorded by stations involved in an active source experiment tom teidevs ibanez et al 2008 on the island of tenerife canary islands we supplement this data with receiver function rf analysis of seismograms from the canary islands of lanzarote and la palma applying the extended time multitaper frequency domain cross correlation estimation method helffrich 2006 we use the neighbourhood inversion approach of sambridge 1999a sambridge 1999b to model the rfs and our results indicate magmatic underplating exists beneath all three islands ranging from 2 to 8 km but showing no clear correlation with the age of the island beneath both la palma and tenerife we find localized low velocity zones lvzs which we interpret as due to partial melt supported by their correlation with the location of historical earthquakes la palma and recent earthquakes tenerife for lanzarote we do not sample the most recently volcanically active region and find no evidence for a lvz instead we find a simple gradational velocity structure with discontinuities at 4 10 and 18 km depth in line with previous studies

volcanic history and 40ar 39ar and 14c geochronology of terceira island azores portugal abstract seven new 40ar 39ar and 23 new radiocarbon ages of eruptive units in support of new geologic mapping improve the known chronology of middle to late pleistocene and holocene volcanic activity on the island of terceira azores and define an east to west progression in stratovolcano growth the argon ages indicate that cinco picos volcano the oldest on terceira completed its main subaerial cone building activity by about 370 380 ka collapse of the upper part of the stratovolcanic edifice to form a 7 9 km caldera occurred some time after 370 ka postcaldera eruptions of basalt from cinder cones on and near the caldera floor and trachytic pyroclastic flow and pumice fall deposits from younger volcanoes west of cinco picos have refilled much of the caldera the southern portion of guilherme moniz volcano in the central part of the island began erupting prior to 270 ka and produced trachyte domes flows and minor pyroclastic deposits until at least 111 ka the northern part of guilherme moniz caldera is less well exposed than the southern part but reflects a similar age range the northwest portion of the caldera was formed sometime after 44 ka several well studied ignimbrites that blanket much of the island likely erupted from guilherme moniz volcano the pico alto volcanic center a tightly spaced cluster of trachyte domes and short flows is a younger part of guilherme moniz volcano stratigraphic studies and our new radiocarbon ages suggest that most of the pico alto eruptions occurred during the period from about 9000 to 1000 years bp santa barbara volcano is the youngest stratovolcano on terceira began erupting prior to 29 ka and has been active historically

site amplification in the los angeles basin from three dimensional modeling of ground motion it is well established that sedimentary basins can significantly amplify earthquake ground motion however the amplification at any given site can vary with earthquake location to account for basin response in probabilistic seismic hazard analysis therefore we need to know the average amplification and intrinsic variability standard deviation at each site given all earthquakes of concern in the region due to a dearth of empirical ground motion observations theoretical simu lations constitute our best hope of addressing this issue here 0 0 5 hz finite difference finite fault simulations are used to estimate the three dimensional 3d response of the los angeles basin to nine different earthquake scenarios amplifi cation is quantified as the peak velocity obtained from the 3d simulation divided by that predicted using a regional one dimensional 1d crustal model average ampli fication factors are up to a factor of 4 with the values from individual scenarios typically differing by as much as a factor of 2 5 the average amplification correlates with basin depth with values near unity at sites above sediments with thickness less than 2 km and up to factors near 6 above the deepest 9 km and steepest dipping parts of the basin there is also some indication that amplification factors are greater for events located farther from the basin edge if the 3d amplification factors are divided by the 1d vertical sh wave amplification below each site they are lowered by up to a factor of 1 7 the duration of shaking in the 3d model is found to be longer by up to more than 60 seconds relative to the 1d basin response the simu lation of the 1994 northridge earthquake reproduces recorded 0 0 5 hz particle velocities relatively well in particular at near source stations the synthetic and observed peak velocities agree within a factor of two and the log standard deviation of the residuals is 0 36 this is a reduction of 54 and 51 compared to the values obtained for the regional 1d model and a 1d model defined by the velocity and density profile below a site in the middle of the basin dow respectively this result suggests that long period ground motion estimation can be improved consid erably by including the 3d basin structure however there are uncertainties con cerning accuracy of the basin model model resolution the omission of material with shear velocities lower than 1 km s and the fact that only nine scenarios have been considered therefore the amplification factors reported here should be used with caution until they can be further tested against observations however the results do serve as a guide to what should be expected particularly with respect to increased amplification factors at sites located above the deeper parts of the basin

crustal seismic velocity structure near faial and pico islands azores from local earthquake tomography the azores archipelago portugal is located on an oceanic plateau in a geodynamic environment prone to intense seismic and volcanic activity in order to investigate the crustal structure in this region we have conducted a local earthquake tomography study in the area of the islands of faial pico and s jorge using data recorded in july 1998 the july 9th 1998 earthquake near faial island triggered an aftershock sequence of thousands of events that lasted for several months and were recorded by a total of 14 stations located on the three islands surrounding the epicentral area in the upper crustal layers consistency is seen between the tomographic results and the islands surface volcanic units beneath the faial central volcano a low vp b6 0 km s anomaly roughly located at 3 7 km depth suggests a connection to the plumbing system possibly the presence of a magma chamber in ne faial a high vp n6 3 km s body was found located at mid lower crust most likely an intrusion of gabbroic composition that is bordered by the registered seismic activity its shape suggesting a tectonic controlled mechanism the relocated hypocenters together with the overall analysis of the tomographic model suggest a tectonic segmentation of faial island the crustal thickness under the islands volcanic buildings of the faial pico area was estimated at around 14 km 2007 elsevier b v all rights reserved

the isostatic compensation of the azores plateau a 3d admittance and coherence analysis the compensation of the azores plateau is re examined by means of a 3d admittance study involving computations of the admittance between the bathymetry and 1 the geoid 2 the free air gravity and 3 the mantle bouguer anomalies the geoid to bathymetry relationship rather than being analysed in the space domain is studied in the spectral domain in this way the information related to the flexural response of the lithosphere is retained in the geoid to bathymetry signal and can be compared to that of the gravity to bathymetry we find that the anomalously shallow depths of the azores plateau are not due to dynamic forces sustained by mantle upwelling the plateau is supported by a thickened crust which mainly results from large volumes of accreted extrusives and consequent deflection of the underlying elastic plate both the free air gravity and the mantle bouguer admittance point to a flexural isostatic model with a moho depth of 12 km and an elastic thickness in the range of 3 6 km however the analysis of the coherency between bathymetry and the mantle bouguer anomaly indicates that buoyant material at the base of the crust partially accounts for the uplift of the plateau in our best fitting model the average elastic thickness is 4 km and the amplitude of the buoyant load at the moho is 1 3 of that of the surface volcanic load buoyancy forces at the moho may arise from underplated material resulting from subcrustal plutonism

crustal structure of northern italy from the ellipticity of rayleigh waves abstract northern italy is a diverse geological region including the wide and thick po plain sedimentary basin which is bounded by the alps and the apennines the seismically slow shallow structure of the po plain is difficult to retrieve with classical seismic measurements such as surface wave dispersion yet the detailed structure of the region greatly affects seismic wave propagation and hence seismic ground shaking here we invert rayleigh wave ellipticity measurements in the period range 10 60 s for 95 stations in northern italy using a fully non linear approach to constrain vertical v s v p and density profiles of the crust beneath each station the ellipticity of rayleigh wave ground motion is primarily sensitive to shear wave velocity beneath the recording station which reduces along path contamination effects we use the 3d layering structure in mambo a previous model based on a compilation of geological and geophysical information for the po plain and surrounding regions of northern italy and employ ellipticity data to constrain v s v p and density within its layers we show that ellipticity data from ballistic teleseismic wave trains alone constrain the crustal structure well this leads to mambo e an updated seismic model of the region s crust that inherits information available from previous seismic prospection and geological studies while fitting new seismic data well mambo e brings new insights into lateral heterogeneity in the region s subsurface compared to mambo it shows overall faster seismic anomalies in the region s quaternary pliocene and oligo miocene layers and better delineates the seismic structures of the po plain at depth two low velocity regions are mapped in the mesozoic layer in the western and eastern parts of the plain which seem to correspond to the monferrato sedimentary basin and to the ferrara romagna thrust system respectively

new observations of ambient inclusion trails aits and pyrite framboids in the ediacaran doushantuo formation south china ambient inclusion trails aits are intriguing microtubular structures that commonly occur in association with pyrite in precambrian organic rich cherts and phosphorites they are thought to be created by the migration of pyrite or other crystal grains through a lithified substrate driven by pressure solution from the in situ thermal decomposition of organic matter new phosphorite samples of the ediacaran doushantuo formation south china contain abundant aits exhibiting diverse morphotypes which may be distinguished from filamentous microfossils and endolithic microborings with a suite of morphological criteria based on optical microscopy and scanning electron microscopy sem black shales of the baizhu section contains abundant pyrite framboids whose size distributions reveal significant temporal variations of redox conditions in shallow marine waters that probably promoted the formation of the doushantuo phosphorites aits in the phosphorites are categorized into three types and further into five subtypes i a i b ii a ii b and iii based on their morphologies and observed or interpreted associations with various kinds of terminal pyrite crystals among these subtype ii a single striated microtubes 2 10 m wide are interpreted to have resulted from migration of intact pyrite framboids those of subtype ii b dense clusters of outward radiating microtubes with consistent widths and inward facing cuspate ridges likely have formed by explosive disintegration and propulsion of pyrite framboids due to highly concentrated carbon dioxide gas during the oxidation of organic matter during early diagenesis formation of euhedral and framboidal pyrites involve a suite of biogeochemical and physical processes including non biological oxidation of organic matter and reduction of sulfate in the presence of ferrous iron following the burial of pyrites further oxidative degradation of organic matter produced abundant co2 gas which drives the pyrites to move through the solid but not yet fully lithified phosphatic gel composing granules this model explains the formation of previously reported but unexplained star burst type aits and it may be tested by experimental studies our new observations provide evidence for the widespread occurrence of aits in the doushantuo phosphorites and urge careful petrographic examinations and differentiation between aits and morphologically similar biogenic microstructures

magmatic underplating of crust beneath the laccadive island nw indian ocean summary we investigate the crust and uppermost mantle velocity structure beneath the laccadive island through the inversion of teleseismic receiver functions following the neighbourhood algorithm the velocity structure suggests that the 16 km thick oceanic crust is underplated by 8 km thick high velocity layer vs 4 25 4 4 km s 1 vp 7 35 7 6 km s 1 the uppermost mantle shear velocity is 4 6 km s 1 vp 8 18 km s 1 the moho at 24 km is possibly formed due to underplating of mantle derived picritic melt at the base of oceanic crust produced during the interaction of the indian plate with the reunion hotspot continuity of crustal underplated material beneath the laccadive could be traced to the laxmi ridge in the north and to the reunion island in the south suggesting this to be possible trace of the reunion hotspot

variations in thickness of layer 3 dominate oceanic crustal structure abstract seismic refraction studies have determined that while much of the crust underlying the world s oceans is about 7 km thick it also occurs in lesser and considerably greater thicknesses here we show that vastly different thicknesses of oceanic crust formed at ridges by seafloor spreading are generally characterized by the two gradient velocity structure recognized as typical of 6 7 km thick oceanic crust adopting a standard we study ninety published seismic velocity structures of oceanic crust ranging in thickness from 2 to 37 km several structures formed in midplate settings ocean islands and seamounts are also considered for comparison regardless of origin ridge or midplate we find that the percentage of the whole crust formed by layer 2 systematically decreases with increasing total crustal thickness while the average velocity of layer 2 varies widely for all crust the average velocity of layer 3 increases systematically with increases in the average whole crustal thickness and velocity crust formed in midplate settings differs in that the thickness of layer 2 velocity crust is generally two to three times that of crust formed at ridges residual depths were calculated for oceanic crust by removing the effects of sediment loading and subsidence due to lithospheric cooling most of the data fall close to a model whereby different crustal thicknesses result from different extents of partial melting of oceanic upper mantle the crustal sections were restored to zero age assuming the average depth of emplacement for 7 km thick oceanic crust is 2 5 km below sea level from this restoration it appears that the depth to the top of layer 3 at the time it was formed is 4 25 1 25 km below sea level regardless of whole crustal thickness or spreading rate these results suggest that the mechanism of construction of oceanic crust is in many ways remarkably uniform despite very large changes in the total thickness of the crust produced very basic questions remain it is for instance not at all clear why layer 2 and layer 3 exist in the proportions they do while neutral buoyancy or melt trapping at the base of a brittle lid may account for local properties of the layer 2 3 boundary they do not seem adequate to account for the global phenomenon

predatorial borings in late precambrian mineralized exoskeletons the late precambrian tube forming cloudina the earliest known animal to produce a mineralized exoskeleton shows evidence of having been attacked by shell boring organisms of more than 500 tubes from shaanxi province china 2 7 have rounded holes 40 to 400 micrometers in diameter the relation between the size of the holes and the width of the bored tubes suggests that the attacking organism was a predator selecting its prey for size if true this would be the oldest case of predation in the fossil record and would support the hypothesis that selection pressures from predation was a significant factor in the evolution of animal skeletons around the precambrian cambrian boundary

crustal structure beneath portugal from teleseismic rayleigh wave ellipticity up until now portugal lacked a countrywide shear velocity model sampling short length scale crustal structure which limits interpretations of seismicity and tectonics and predictions of strong ground motion in turn such interpretations and predictions are important to help mitigate risk of destruction from future large on and offshore earthquakes similar to those that portugal has experienced in the past e g the mw 8 5 8 7 tsunamigenic event in 1755 in this study we measured teleseismic rayleigh wave ellipticity rwe from 33 permanent and temporary seismic stations in portugal with wave periods between 15 s and 60 s and inverted it for 1 d models of shear wave velocity vs structure beneath each station using a fully non linear monte carlo method because rwe is strongly sensitive to the uppermost few kilometres of the crust both rwe measurements and vs models are spatially correlated with surface geology in portugal for instance we find that sedimentary basins produced by rifting that had begun in the mesozoic such as the lusitanian basin lb and the lower tagus sado basin ltsb are characterised by higher rwe lower vs interestingly we observe similar rwe and vs values in the interior of the central iberian zone ciz which is a metamorphic belt of paleozoic age together with reduced crustal thickness previously estimated for the same parts of the ciz this suggests that the ciz might have experienced an episode of extension possibly simultaneous to mesozoic rifting the galicia tras os montes zone gtmz that has undergone polyphased deformation since the paleozoic is characterised by the lowest rwe highest vs in portugal ossa morena zone and the south portuguese zone exhibit intermediate vs values when compared to that of basins and the gtmz our crustal vs model can be used to provide new insights into the tectonics seismicity and strong ground motion in portugal

reconstructing the architectural evolution of volcanic islands from combined k ar morphologic tectonic and magnetic data the faial island example azores the morpho structural evolution of oceanic islands results from competition between volcano growth and partial destruction by mass wasting processes we present here a multi disciplinary study of the successive stages of development of faial azores during the last 1 myr using high resolution digital elevation model dem and new k ar tectonic and magnetic data we reconstruct the rapidly evolving topography at successive stages in response to complex interactions between volcanic construction and mass wasting including the development of a graben we show that 1 sub aerial evolution of the island first involved the rapid growth of a large elongated volcano at ca 0 85 ma followed by its partial destruction over half a million years 2 beginning about 360 ka a new small edifice grew on the ne of the island and was subsequently cut by normal faults responsible for initiation of the graben 3 after an apparent pause of ca 250 kyr the large central volcano cv developed on the western side of the island at ca 120 ka accumulating a thick pile of lava flows in less than 20 kyr which were partly channelized within the graben 4 the period between 120 ka and 40 ka is marked by widespread deformation at the island scale including westward propagation of faulting and associated erosion of the graben walls which produced sedimentary deposits subsequent growth of the cv at 40 ka was then constrained within the graben with lava flowing onto the sediments up to the eastern shore 5 the island evolution during the holocene involves basaltic volcanic activity along the main southern faults and pyroclastic eruptions associated with the formation of a caldera volcano tectonic depression we conclude that the whole evolution of faial island has been characterized by successive short volcanic pulses probably controlled by brief episodes of regional deformation each pulse has been separated by considerable periods of volcanic inactivity during which the faial graben gradually developed we propose that the volume loss associated with sudden magma extraction from a shallow reservoir in different episodes triggered incremental downward graben movement as observed historically when immediate vertical collapse of up to 2 m was observed along the western segments of the graben at the end of the capelinhos eruptive crises 1957 58

morpho structural evolution of a volcanic island developed inside an active oceanic rift s miguel island terceira rift azores the evolution of volcanic islands is generally marked by fast construction phases alternating with destruction by a variety of mass wasting processes more specifically volcanic islands located in areas of intense regional deformation can be particularly prone to gravitational destabilisation the island of s miguel azores has developed during the last 1 myr inside the active terceira rift a major tectonic structure materializing the present boundary between the eurasian and nubian lithospheric plates in this work we depict the evolution of the island based on high resolution dem data stratigraphic and structural analyses high precision k ar dating on separated mineral phases and offshore data bathymetry and seismic profiles the new results indicate that 1 the oldest volcanic complex nordeste composing the easternmost part of the island was dominantly active between ca 850 and 750 ka and was subsequently affected by a major south directed flank collapse 2 between at least 500 ka and 250 ka the landslide depression was massively filled by a thick lava succession erupted from volcanic cones and domes distributed along the main e w collapse scar 3 since 250 kyr the western part of this succession furnas area was affected by multiple vertical collapses associated plinian eruptions produced large pyroclastic deposits here dated at ca 60 ka and less than 25 ka 4 during the same period the eastern part of the landslide scar was enlarged by retrogressive erosion producing the large povoacao valley which was gradually filled by sediments and young volcanic products 5 the fogo volcano in the middle of s miguel is here dated between ca 270 and 17 ka and was affected by at least one southwards flank collapse 6 the sete cidades volcano in the western end of the island is here dated between ca 91 and 13 ka and experienced mutliple caldera collapses a landslide to the north is also suspected from the presence of a subtle morphologic scar covered by recent lava flows erupted from alignments of basaltic strombolian cones the predominance of the n150 and n75 trends in the island suggest that the tectonics of the terceira rift controlled the location and the distribution of the volcanism and to some extent the various destruction events

inversion of the hz ratio of microseisms for s wave velocity in the crust summary s wave velocity in the shallow crust is an important controlling parameter for ground motion amplification it is a key parameter for prediction of ground motion and thus for earthquake hazard mitigation in general shallow s wave velocity structure has often been obtained from phase velocity of microtremors and microseisms we present a new approach which directly inverts the ratio of horizontal to vertical amplitudes of microseisms which is referred to as the hz ratio in this paper our approach consists of i isolation of rayleigh wave dominant portions in seismograms by using the 90 degree phase shift between horizontal and vertical component ii measurement of the hz ratios as a function of frequency and iii iterative inversion for s wave velocity structure in the crust depth sensitivity kernels of the hz ratios for density p wave velocity and s wave velocity are derived by a numerical method examples of the application of this method to data in southern california show that the hz ratio data require modification of the standard seismic velocity model in this region southern california earthquake center community velocity model 3 0 or scec cvm in the upper 10 15 km the derived models show amplification of incident sh waves by factors of 2 8 relative to the prediction by the scec cvm the proposed approach has promise for applications to other regions in the world because microseisms are observed everywhere in the world the method may become even more powerful if it is combined with phase velocity data

global compilation of interferometric synthetic aperture radar earthquake source models 1 comparisons with seismic catalogs 1 while many earthquakes have now been studied using interferometric synthetic aperture radar insar data a full assessment of the quality and additional value of insar source parameters compared to seismological techniques is still lacking we compile a catalog of source models obtained using insar and estimate the corresponding centroid moment tensor cmt parameters we refer to this compilation as the icmt archive we compare source parameters from over 70 insar studies of 57 global earthquakes with those in the global cmt gcmt international seismological centre isc and engdahl hilst buland ehb seismic catalogs we find an overall good agreement between fault strike dip and rake values in the gcmt and icmt archives likewise the differences in seismic moment between these two archives are relatively small and we do not find support for previously suggested trends of insar leading to larger moments than seismic data however epicentral locations show substantial discrepancies which are larger for the gcmt median differences of 21 km than for the ehb and isc catalogs median differences of 10 km since insar data have a high spatial resolution and thus should map epicentral locations accurately this allows us to obtain a first independent estimate of epicentral location errors in the seismic catalogs earthquake depths from insar are systematically shallower than those in the ehb catalog with a median of differences of 5 km while this trend may be partly due to unmodeled crustal complexity it is also compatible with the observation that the rupture of crustal earthquakes tends to propagate upward in the seismogenic layer

factors affecting cold air outbreaks east of the rocky mountains abstract a two layer isentropic model is used to examine the parameters controlling the severity of cold air outbreaks east of the rocky mountains and in particular the channeling effect of the mountain range the case that is scrutinized is the cold air outbreak of early february 1989 the parameters investigated include a the baro clinicity expressed as the ratio of upper to lower layer zonal scale velocities b the rossby number c the height of the topography d the initial longitudinal position of the cold air mass relative to the mountain ridge and e the presence of a wave in the upper level flow it is found that the rossby number determines the intensity of a cold air outbreak whereas the baroclinicity as well as the height of the orography and the initial position of the cold air mass control the extent to which the outbreak is channeled by the mountain range an upper level trough over the central united states favors the evolution of an outbreak

neoproterozoic to early cambrian small shelly fossil assemblages and a revised biostratigraphic correlation of the yangtze platform china abstract small shelly fossils ssfs occur widely on the yangtze platform and have great potential for biostratigraphic subdivision of pre trilobitic early cambrian strata based on the ssf record of the shallow water realm five biozones can be recognized for the meishucunian stage in ascending order the biozones are anabarites trisulcatus protohertzina anabarica assemblage zone paragloborilus subglobosus purella squamulosa assemblage zone watsonella crosbyi assemblage zone formerly heraultipegma yunnanensis zone poorly fossiliferous interzone sinosachites flabelliformis tannuolina zhangwentangi assemblage zone in addition one ssf biozone is recognized for the overlying qiongzhusian stage pelagiella subangulata taxon range zone the formerly used siphogonuchites triangularis paragloborilus subglobosus zone and heraultipegma yunnanensis zone are discussed and redefined approximately 80 species of ssfs were screened for their spatial and temporal distribution on the yangtze platform variations in lithofacies and biofacies can be recognized throughout the yangtze platform extending over an area of 2000 900 km in a deeper water shelf setting the first zone is represented by the protohertzina anabarica kaiyangites novilis assemblage zone while younger zones are not recognized in the southern region at the northern platform margin the qiongzhusian is represented by the ninella tarimensis cambroclavus fangxianensis assemblage zone and the rhombocorniculum cancellatum taxon range zone the southeastern shaanxi western hubei region followed a slightly different lithological and faunal development than the rest of yangtze platform indicating a stronger similarity with parts of east gondwana some taxa such as w crosbyi p subangulata r cancellatum microdictyon effusum a trisulcatus protohertzina unguliformis and p anabarica occur nearly worldwide and support an international correlation of early cambrian sequences between the yangtze platform and smaller west gondwanan blocks siberia newfoundland and australia the six investigated zones of the yangtze platform comprise an interval spanning the early nemakit daldynian to the late atdabanian early botoman stage on the siberian platform palaeobiogeographic analysis revealed a strong taxic similarity between the yangtze platform and the tarim platform a smaller number of species are shared with other west gondwanan platform fragments such as india and iran palaeobiogeographic results do not support the previously reported position of the south china block between australia and siberia during the early cambrian

seismic imaging of hotspot related crustal underplating beneath the marquesas islands volcanism in active continental rift zones1 2or on rifted continental margins3is frequently associated with unusually high lower crustal seismic velocities indicating the presence of large igneous intrusions at the base of the crust the only comprehensive investigation of crustal underplating at an oceanic hotspot beneath hawaii4 6 has yielded controversial results7 here we report the results of seismic refraction experiments across the marquesas islands hotspot trace which show that the island chain is underlain by crust 15 17 km thick and that a large lower crustal region 275 km wide and 2 8 km thick has seismic velocities 7 3 7 75 km s 1 indicative of crustal underplating wide angle reflections occur near the base of the normal lower crustal velocities and at the base of the underplating complex we interpret these reflectors as the relict pre hotspot moho and the current post hotspot moho respectively the high velocity material may be purely intrusive or may consist of a mixture of intrusive and preexisting rocks the volume of the high velocity body is impressive amounting to nearly twice the volume of volcanics erupted at the surface

the potential failure of monte nuovo at ischia island southern italy numerical assessment of a likely induced tsunami and its effects on a densely inhabited area ischia is the emergent top of a large volcanic complex that rises more than 1 000 m above the sea floor at the north western end of the gulf of naples caldera resurgence in the central part of the island has resulted in the formation of differentially displaced blocks among which mt epomeo 787 m a s l is the most uplifted deformation and slope instability have been recognised as common features induced by a block resurgence mechanism that causes uplift and favours gravitational loading and flank failure the monte nuovo block a topographic high on the north western flank of mt epomeo has recently been interpreted as a block affected by deep seated gravitational slope deformation this block may undergo a catastrophic failure in the case of renewal of magmatic activity this paper investigates the potential failure of the monte nuovo block as a rockslide debris avalanche the consequent tsunami generation and wave propagation and discusses the catastrophic effects of such an event mobilization prone volume has been estimated at about 160 106 m3 and would move from a maximum elevation of 400 m a s l the landslide itself would sweep away a densely populated territory as large as 3 5 km2 the highest waves generated by the tsunami on which this paper is mainly focussed would hit the northern and western shores of ischia however the high coast would prevent inundation and limit devastation to beaches harbours and surrounding areas most of the tsunami energy would head towards the north east hitting the campania coast severe inundation would affect an area of up to 20 km2 around the mouth of the volturno river including the urban area of castel volturno in contrast less energy would travel towards the south and the gulf of naples would be perturbed by long persisting waves of limited damaging potential

precambrian endoliths discovered the earliest known microborings have now been found in late precambrian ooids upper riphean1 vendian2 570 700 myr of the eleonore bay group of eastern greenland the ooids were originally carbonaceous and underwent silicification after boring occurred the finding establishes that the habit of microbial boring evolved before the appearance of skeleton bearing metazoans in the geological record

vertical movements of ocean island volcanoes insights from a stationary plate environment abstract uplift reconstructions based on the cape verde s geological record provide a unique opportunity to study the long term isostatic movements associated with hotspot activity on a stationary plate environment the archipelago is considered stationary with respect to its melting source so the hotspot driven isostatic effects affecting the ocean islands are expected to be enhanced in this study ar ar and u th geochronology techniques were used to date a set of palaeo markers of sea level from santiago s and sao nicolau s edifices two of the main cape verde islands a comparison between relative sea level and eustatic sea level from a modern eustatic curve was established to extract the vertical displacement undergone by the markers and to reconstruct the uplift subsidence history of each island the resulting uplift reconstructions confirm that both santiago and sao nicolau experienced a general uplift trend over the last 6 ma seemingly synchronous with the vigorous volcanic activity that built their exposed edifices these islands however exhibit different uplift histories despite their common uplift trend several uplift mechanisms were tested and a local rather than regional mechanism is proposed as the main cause of uplift generally unrelated with far field effects of surface loading this mechanism is probably associated with magmatic additions at crustal level

40ar 39ar ages and paleomagnetism of sao miguel lavas azores we present new 40 ar 39 ar ages and paleomagnetic data for sao miguel island azores paleomagnetic samples were obtained for 34 flows and one dike successful mean paleomagnetic directions were obtained for 28 of these 35 sites 40 ar 39 ar age determinations on 12 flows from the nordeste complex were attempted successfully ages obtained are between 0 78 ma and 0 88 ma in contrast to published k ar ages of 1 ma to 4 ma our radiometric ages are consistent with the reverse polarity paleomagnetic field directions and indicate that the entire exposed part of the nordeste complex is of a late matuyama age the duration of volcanism across sao miguel is significantly less than previously believed which has important implications for regional melt generation processes and temporal sampling of the geomagnetic field observed stable isotope and trace element trends across the island can be explained at least in part by communication between different magma source regions at depth the 40 ar 39 ar ages indicate that our normal polarity paleomagnetic data sample at least 0 1 myr 0 0 1 ma and up to 0 78 myr 0 0 78 ma of paleosecular variation and our reverse polarity data sample approximately 0 1 myr 0 78 0 88 ma of paleosecular variation our results demonstrate that precise radiometric dating of numerous flows sampled is essential to accurate inferences of long term geomagnetic field behavior negative inclination anomalies are observed for both the normal and reverse polarity time averaged field within the data uncertainties normal and reverse polarity field directions are antipodal but the reverse polarity field shows a significant deviation from a geocentric axial dipole direction 1998 elsevier science b v all rights reserved

vertical movements of ocean island volcanoes insights from a stationary plate the origin of hotspot swells is still controversial and their development is at present poorly constrained and strongly model dependent however since islands are built on top of these structures the role of swell development in island uplift subsidence should be assessed

interaction between the mid atlantic ridge and the azores hot spot during the last 85 myr emplacement and rifting of the hot spot derived plateaus 1 multiple and single beam bathymetric data are compiled over the azores plateau to produce a 1 km 1 km grid between latitudes 32 n and 49 n and longitudes 22 w and 43 w mantle bouguer anomalies are then calculated from this grid and the satellite derived gravity these grids provide new insights on the temporal and spatial variations of melt supply to the ridge axis the elevated seafloor of the azores plateau is interpreted as resulting from the interaction of a mantle plume with the mid atlantic ridge mar the presence of a large region of elevated seafloor associated with a thick crust between the great meteor seamounts and the azores platform on the africa plate and less developed conjugate structures on the north america plate favors genetic relations between these hot spot derived structures this suggests that a ridge hot spot interaction has occurred in this region since 85 ma this interaction migrated northward along the ridge axis as a result of the sse absolute motion of the africa plate following a direction grossly parallel to the orientation of the mar kinematic reconstructions from chron 13 35 ma to the present allow a proposal that the formation of the azores plateau began around 20 ma and ended around 7 ma a sharp bathymetric step is associated with the beginning of important melt supply around 20 ma the excess of melt production is controlled by the interaction of the ridge and hot spot melting zones the geometry and distribution of the smaller scale features on the plateau record episodic variations of the hot spot melt production the periodicity of these variations is about 3 5 myr following the rapid decrease of widespread volcanism the plateau was subsequently rifted from north to south by the mid atlantic ridge since 7 ma this rifting begins when the mar melting zone is progressively shifted away from the 200 km plume thermal anomaly these results bear important consequences on the motion of the africa plate relative to the azores hot spot they also provide an explanation to the asymmetric geochemical signature of the azores hot spot along the mid atlantic ridge

episodic swell growth inferred from variable uplift of the cape verde hotspot islands ocean islands formed over hotspots can uplift and subside as the hotspots evolve the history of the cape verde islands reveals large scale uplift owing to growth of the hotspot swell but also variable uplift of individual islands resulting from the local intrusion of magma

the zh ratio method for long period seismic data sensitivity kernels and observational techniques summary amplitude ratio between vertical and horizontal components of rayleigh waves is controlled by structure beneath a seismic station this ratio measured as a function of frequency has been extensively analysed for shallow crustal structure study in earthquake engineering and applied seismology this quantity termed the zh ratio in this paper may be useful for deep earth structure study and its feasibility for the frequency range between 0 004 and 0 05 hz period 20 250 s is explored in this paper for depth sensitivity kernels we demonstrate that a numerical approach is practical and provides sufficient accuracy for structural inversion depth extent of sensitivity kernels are about half of depth extent in phase velocity kernels indicating that the zh ratio is useful for studying the lithospheric structure two observational approaches for measurement of the zh ratio are presented the first approach uses simple envelope amplitude ratio and the second approach uses waveform correlation technique between vertical and horizontal components the zh ratio data alone only constrains structure beneath seismic stations but recent densification of seismic networks may make it possible to extend the analysis to regional scale structure a greater opportunity may exist in combination of the zh ratio method and the phase and group velocity measurements

40ar 39ar constraints on the temporal evolution of graciosa island azores portugal lava flows spanning the eruptive record of graciosa island azores archipelago and a gabbro xenolith were dated by 40ar 39ar in order to constrain the pleistocene and holocene volcanic evolution of the island the results range from 1 05 ma to 3 9 ka whereas prior published k ar and 14c ages range from 620 to 2 ka the formation of the serra das fontes shield volcano started at minimum 1 05 ma and the magmatic system was active for ca 600 ky as suggested by the formation of the gabbro xenolith by magmatic differentiation evolved magmas making up the serra das fontes serra branca composite volcano were generated at ca 450 ka after a period of ca 110 ky of volcanic inactivity and erosion of volcanic edifices volcanism was reactivated with the formation of the vitoria unit nw platform later the development of the vulcao central unit started with the formation of monogenetic cones located to the south of the serra das fontes serra branca vitoria unit this volcanism became progressively more evolved and was concentrated in a main eruptive center forming the vulcao central stratovolcano with an age older than 50 ka the caldera related to this stratovolcano is older than 47 ka and was followed by effusion of basaltic magmas into the caldera resulting in the formation of a lava lake which ultimately spilled over the caldera rim at ca 11 ka the most recent eruptions on graciosa formed two small pyroclastic cones within the caldera and the pico do timao cone within the vitoria unit at ca 3 9 ka

emergence and evolution of santa maria island azores the conundrum of uplifted islands revisited the growth and decay of ocean island volcanoes are intrinsically linked to vertical movements while the causes for subsidence are better understood uplift mechanisms remain enigmatic santa maria island in the azores archipelago is an ocean island volcano resting on top of young lithosphere barely 480 km away from the mid atlantic ridge like most other azorean islands santa maria should be experiencing subsidence yet several features indicate an uplift trend instead in this paper we reconstruct the evolutionary history of santa maria with respect to the timing and magnitude of its vertical movements using detailed field work and 40ar 39ar geochronology our investigations revealed a complex evolutionary history spanning 6 m y with subsidence up to ca 3 5 ma followed by uplift extending to the present day the fact that an island located in young lithosphere experienced a pronounced uplift trend is remarkable and raises important questions concerning possible uplift mechanisms localized uplift in response to the tectonic regime affecting the southeastern tip of the azores plateau is unlikely since the area is under transtension our analysis shows that the only viable mechanism able to explain the uplift is crustal thickening by basal intrusions suggesting that intrusive processes play a significant role even on islands standing on young lithosphere such as in the azores

joint inversion of rayleigh wave phase velocity and ellipticity using usarray constraining velocity and density structure in the upper crust rayleigh wave ellipticity or h v ratio observed on the surface is particularly sensitive to shallow earth structure in this study we jointly invert measurements of rayleigh wave h v ratio and phase velocity between 24 100 and 8 100 sec period respectively for crust and upper mantle structure beneath more than 1000 usarray stations covering the western united states upper crustal structure in particular is better constrained by the joint inversion compared to inversions based on phase velocities alone in addition to imaging vs structure we show that the joint inversion can be used to constrain vp vs and density in the upper crust new images of uppermost crustal structure 3 km depth are in excellent agreement with known surface features with pronounced low vs low density and high vp vs anomalies imaged in the locations of several major sedimentary basins including the williston powder river green river denver and san juan basins these results demonstrate not only the consistency of broadband h v ratios and phase velocity measurements but also that their complementary sensitivities have the potential to resolve density and vp vs variations

constraining s wave velocity using rayleigh wave ellipticity from polarization analysis of seismic noise we develop a new method for measuring ellipticity of rayleigh waves from ambient noise records by degree of polarization dop analysis the new method named dop e shows a good capability to retrieve accurate ellipticity curves separated from incoherent noise in order to validate the method we perform synthetic tests simulating noise in a 1 d earth model we also perform measurements on real data from antarctica and northern italy observed curves show a good fit with measurements from earthquake records and with theoretical ellipticity curves the inversion of real data measurements for vs structure shows a good agreement with previous models in particular the shear wave structure beneath concordia station shows no evidence of a significant layer of liquid water at the base of the ice the new method can be used to measure ellipticity at high frequency and therefore it will allow the imaging of near surface structure and possibly of temporal changes in subsurface properties it promises to be useful to study near surface processes in a wide range of geological settings such as volcanoes fault zones and glaciers

microbial infestation a pathway of fluorine enrichment in bone apatite fragments negev phosphorites israel backscattered electron bse imaging and electron probe coupled analysis of bone debris in the negev phosphorites israel show that f concentrations vary considerably in these components and that these variations are driven by microbial activity the bone debris are microbially tunneled commonly with a micritic carbonate fluorapatite cfa phase filling the tunnels and gradually replacing the bone matrix as a rule the micritic cfa within the microbial tunnels is significantly much more fenriched f p2o5 0 106 0 125 than the bone matrix f p 2o5 0 083 0 104 similar results are obtained in bones at final stages of microbial infestation and micrite phosphate replacement the infested replacing envelope invading the bone debris is much f enriched enrichment factor of about 1 27 on average than the surviving bone that escaped boring these results are explained by redeposition as cfa of the microbially bored and dissolved hydroxyapatite presumably fostered by microbial f transfer from porewaters to the sites of cfa precipitation in bone microborings this pathway of f enrichment driven by microbial activity may also explain the enigmatic differential u enrichment previously observed in negev phosphorite bones q 2000 elsevier science b v all rights reserved

ambient inclusion trails in palaeozoic crustaceans phosphatocopina and ostracoda abstract hollow microtubular structures with pyrite grains at their termini have been found in phosphatocopines hesslandona toreborgensis and hesslandona cf angustata from the late cambrian of northern poland and in the metacopine ostracod cytherellina submagna from the early devonian of podolia ukraine the cambrian phosphatocopines are secondarily phosphatised and microtubes 5 20 m in diameter are preserved inside the phosphatized bivalved shield visible on the shield surface as half open microstructures with pyrite grains at their terminal end they are visible only where an external coating layer has peeled off in the devonian ostracod c submagna microtubes c 1 8 m in diameter occur within the phosphatized internal mould steinkern and are visible on the surface of the mould due to the dissolution of the calcite carapace during extraction of the limestone samples these microtubular structures are here interpreted as ambient inclusion trails aits due to the presence of terminal pyrite crystals of equivalent diameter to the microtube polygonal microtube cross sections plus longitudinal striations on the microtube walls that record the movement of the migrating angular pyrite crystal aits are thought to form when mineral crystals typically pyrite are impelled to migrate through a fine grained mineral matrix under increased fluid gas pressure our new materials provide the first record of exceptionally preserved aits occurring in crustaceans and only the third reported occurrence of aits in the palaeozoic the intimate occurrence of aits with phosphatized crustacean body fossils supports the hypothesis that aits are likely driven by increases in gas pressure due the decomposition of soft tissue in the case of cytherellina submagna our calculations suggest that as little as 20 g of organic matter decaying within a volume of 0 06 mm3 encased by an impermeable outer carapace may have been sufficient to produce a large number 100 of aits

the influence of thermal and cyclic stressing on the strength of rocks from mount st helens washington stratovolcanoes and lava domes are particularly susceptible to sector collapse resulting from wholesale rock failure as a consequence of decreasing rock strength here we provide insights into the influence of thermal and cyclic stressing on the strength and mechanical properties of volcanic rocks specifically this laboratory study examines the properties of samples from mount st helens chosen because its strength and stability have played a key role in its history influencing the character of the infamous 1980 eruption we find that thermal stressing exerts different effects on the strengths of different volcanic units increasing the heterogeneity of rocks in situ increasing the uniaxial compressive stress generates cracking the timing and magnitude of which was monitored via acoustic emission ae output during our experiments aes accelerated in the approach to failure sometimes following the pattern predicted by the failure forecast method kilburn 2003 crack damage during the experiments was tracked using the evolving static young s modulus and poisson s ratio which represent the quasi static deformation in volcanic edifices more accurately than dynamic elastic moduli which are usually implemented in volcanic models cyclic loading of these rocks resulted in a lower failure strength confirming that volcanic rocks may be weakened by repeated inflation and deflation of the volcanic edifice additionally volcanic rocks in this study undergo significant elastic hysteresis in some instances a material may fail at a stress lower than the peak stress which has previously been endured thus a volcanic dome repeatedly inflated and deflated may progressively weaken possibly inducing failure without necessarily exceeding earlier conditions

distributed deformation close to the azores triple point abstract terceira rift and the northern and southern branches of the mid atlantic ridge mar form a triple junction close to 39 n known as the azores triple junction new swath bathymetric data are used to investigate the surface expression of faulting close to the triple junction by the systematic mapping of mar generated abyssal hills it is shown that close to the geometrical intersection between the three spreading axes there exists no single transform fault connecting terceira rift to the mar but a distributed tectonic deformation area characterized by mesoscale brittle deformation close to the surface covering approximately 90 km by 100 km and almost no volcanism which links terceira rift to the mar accommodating the relative displacement of the three plates close to the geometrically triple point magnetic chrons are used to compute the spatial variation of spreading velocity at the mid atlantic ridge and confirm the above interpretation they show a progressive increase of spreading velocity along a single mar segment between pure nubian at 38 30 n and pure eurasian at 39 25 n without the development of a transform fault that would integrate the eurasia nubia plate boundary the comparison of similar triple junctions where a slower axis joins two faster ridges shows that the slower arm does not reach the triple point and that there is always a finite triple junction area highly tectonized in which size is dependent on the angle between the two faster arms and consequently on the relative spreading velocity of the slower arm

age spreading rates and spreading asymmetry of the world s ocean crust we present four companion digital models of the age age uncertainty spreading rates and spreading asymmetries of the world s ocean basins as geographic and mercator grids with 2 arc min resolution the grids include data from all the major ocean basins as well as detailed reconstructions of back arc basins the age spreading rate and asymmetry at each grid node are determined by linear interpolation between adjacent seafloor isochrons in the direction of spreading ages for ocean floor between the oldest identified magnetic anomalies and continental crust are interpolated by geological estimates of the ages of passive continental margin segments the age uncertainties for grid cells coinciding with marine magnetic anomaly identifications observed or rotated to their conjugate ridge flanks are based on the difference between gridded age and observed age the uncertainties are also a function of the distance of a given grid cell to the nearest age observation and the proximity to fracture zones or other age discontinuities asymmetries in crustal accretion appear to be frequently related to asthenospheric flow from mantle plumes to spreading ridges resulting in ridge jumps toward hot spots we also use the new age grid to compute global residual basement depth grids from the difference between observed oceanic basement depth and predicted depth using three alternative age depth relationships the new set of grids helps to investigate prominent negative depth anomalies which may be alternatively related to subducted slab material descending in the mantle or to asthenospheric flow a combination of our digital grids and the associated relative and absolute plate motion model with seismic tomography and mantle convection model outputs represents a valuable set of tools to investigate geodynamic problems

crustal structure of the azores archipelago from rayleigh wave ellipticity data determining the crustal structure of ocean island volcanoes is important to understand the formation and tectonic evolution of the oceanic lithosphere and tectonic swells in marine settings and to assess seismic hazard in the islands the azores archipelago is located near a triple junction system and is possibly under the influence of a mantle plume being at the locus of a wide range of geodynamic processes however its crustal structure is still poorly constrained and debated due to the limited seismic coverage of the region and the peculiar linear geometry of the islands to address these limitations in this study we invert teleseismic rayleigh wave ellipticity measurements for 1 d shear wave speed vs crustal models of the azores archipelago moreover we test the reliability of these new models by using them in independent moment tensor inversions of local seismic data and demonstrate that our models improve the waveform fit compared to previous models we find that data from the westernmost seismic stations used in this study require a shallower moho depth 10 km than data from stations in the eastern part of the archipelago 13 16 km this apparent increase in the moho depth with increasing distance from the mid atlantic ridge mar is expected however the rate at which moho deepens away from the mar is greater than that predicted from a half space cooling model suggesting that local tectonic perturbations have modified crustal structure the 1 d vs models obtained beneath the westernmost seismic stations also show higher wave speeds than for the easternmost stations which correlates well with the ages of the islands except santa maria island we interpret the relatively low vs profile found beneath santa maria island as resulting from underplating which agrees with previous geological studies of the island compared to a recent receiver function study of the region the shallow structure top 2 km in our models shows lower shear wave speed which may have important implications for future hazard studies of the region more generally the new seismic crustal models we present in this study will be useful to better understand the tectonics seismicity moment tensors and strong ground motions in the region

early life recorded in archean pillow lavas pillow lava rims from the mesoarchean barberton greenstone belt in south africa contain micrometer scale mineralized tubes that provide evidence of submarine microbial activity during the early history of earth the tubes formed during microbial etching of glass along fractures as seen in pillow lavas from recent oceanic crust the margins of the tubes contain organic carbon and many of the pillow rims exhibit isotopically light bulk rock carbonate 13 c values supporting their biogenic origin overlapping metamorphic and magmatic dates from the pillow lavas suggest that microbial life colonized these subaqueous volcanic rocks soon after their eruption almost 3 5 billion years ago

stratification of the earth beneath the azores from p and s receiver functions abstract seismic recordings of iris ida gsn station cmla and of several temporary stations in the azores archipelago are processed with p and s receiver function prf and srf techniques contrary to regional seismic tomography these methods provide estimates of the absolute velocities and of the vp vs ratio up to a depth of 300 km joint inversion of prfs and srfs for a few data sets consistently reveals a division of the subsurface medium into four zones with a distinctly different vp vs ratio the crust 20 km thick with a ratio of 1 9 in the lower crust the high vs mantle lid with a strongly reduced vp vs velocity ratio relative to the standard 1 8 the low velocity zone lvz with a velocity ratio of 2 0 and the underlying upper mantle layer with a standard velocity ratio our estimates of crustal thickness greatly exceed previous estimates 10 km the base of the high vs lid the gutenberg discontinuity is at a depth of 80 km the lvz with a reduction of s velocity of 15 relative to the standard iasp91 model is terminated at a depth of 200 km the average thickness of the mantle transition zone tz is evaluated from the time difference between the s410p and sks660p seismic phases that are robustly detected in the s and sks receiver functions this thickness is practically similar to the standard iasp91 value of 250 km and is characteristic of a large region of the north atlantic outside the azores plateau our data are indicative of a reduction of the s wave velocity of several percent relative to the standard velocity in a depth interval from 460 to 500 km this reduction is found in the nearest vicinities of the azores in the region sampled by the prfs but as evidenced by srfs it is missing at a distance of a few hundred kilometers from the islands we speculate that this anomaly may correspond to the source of a plume which generated the azores hotspot previously a low s velocity in this depth range was found with srf techniques beneath a few other hotspots

microborings in early cambrian phosphatic and phosphatized fossils abstract a small proportion of phosphatic and phosphatized fossils mostly microfossils extracted from lower cambrian qiongzhusian lime mudstones of deeper water aspect belonging to the yu anshan and shuijingtuo formations of south china is perforated by microborings these microborings are present in bradoriid and phosphatocopine arthropod carapaces lingulid brachiopod valves microdictyon plates and tommotiid sclerites their absence in co occurring phosphatized eodiscid trilobite exoskeletons and palaeoscolecid worm trunk fragments indicates a substrate specificity that suggests the boring microorganism was heterotrophic extracting particular residual organic compounds present in only certain bioclast types microborings occur as meandering tunnels and grooves on bioclast surfaces and most are 10 20 m wide and circular in cross section the euendoliths were thus able to live partly exposed as well as within the substrate tunnel and groove walls bear a distinct longitudinal sculpture of straight striae separated by cuspate ridges 1 2 m apart that parallel the microboring never twisting the microborings accord with the ichnotaxon microptychoites fuquanensis dong in dong et al dong y ji q wang s 1984 the discovery of microscopic trace fossils in the sinian doushantuo formation in southwestern china scientia geologica sinica 346 347 in chinese the fluted sculpture appears to have no modern analogue but may have arisen by localized secretions at the tip of a bundle of filaments this kind of microboring had been previously reported from phosphatic substrates of ediacaran earliest cambrian middle cambrian and probably early devonian age but appears to have no recent counterpart

use of nanosims in the search for early life on earth ambient inclusion trails in a c 3400 ma sandstone ambient inclusion trails ait are enigmatic microtubular structures created by the migration of mineral crystals through a lithified substrate the decomposition of organic material has been suggested as the driving force for the crystal migration but has yet to be rigorously tested ait may hold potential as a biosignature for investigating early life on earth if the associated organic material can be shown to be biological this paper attempts to test the formation mechanism and biogenicity of ait from the c 3400 ma strelley pool sandstone of western australia using nanosims technology in doing so we demonstrate the unique ability of the nanosims to combine sub micron scale imaging with in situ chemical and isotopic data thereby enhancing our ability to evaluate the biogenicity criteria for archaean microstructures enrichments of a suite of major elements c n p s and trace elements co fe ni zn often associated with biological processes are found within several ait in this sandstone c and n enrichments are most common along ait margins and correlate with depletions of si o ca and mg indicating that this material is indeed organic in nature 13 c values of this carbonaceous material average 26 petrographic observations show that some of the ait occur in the centre of detrital sandstone grains where they were sealed from later fluid flow and therefore preserve primary archaean bio geochemistry in contrast ait found around the outer edges of sandstone grains may contain more recent organic material introduced by later fluid migration and are an unreliable biosignature using the petrographic and geochemical data a multi stage model for ait formation and subsequent diagenetic modification is proposed the possible sources of the primary organic material are discussed and we conclude that the data are consistent with a biological origin for these ait an abiogenic origin is more difficult to sustain but cannot yet be completely excluded for ait in general

euendoliths versus ambient inclusion trails from early cambrian kuanchuanpu formation south china abundant microstructures have been discovered in small skeletal fossils ssfs and embryo like fossils collected from the lower cambrian kuanchuanpu formation ca 535 ma in xixiang county shaanxi province china these involve two co occurring structures 1 long unbranched cylindrical filaments which are comparable to phosphatic casts of microborings constructed by euendolithic cyanobacteria endoconchia lata in morphology and preservation pathway and 2 meandering micro tubes or grooves on fossil moulds and steinkerns of a wide range of sizes and morphological diversities perceived as ambient inclusion trails aits herein we also report a new occurrence of organic carbon spherules as ait propelled material which is rare in comparable fossils from direct comparison of endolith fossils and aits we propose a mechanism to account for their notably different preservation and further attempt to offer an explanation for their co occurrence their differential preservation suggests a chronological taphonomic sequence of their formation we interpret that e lata microborings formed prior to phosphate sedimentation whereas aits are likely generated in a later phase of or after phosphorite precipitation but before calcareous re cementation dissecting the sequence of formation of these structures in conjunction with detailed morphological observations assists in distinguishing true biologically produced endoliths from otherwise abiogenically produced microstructures

predictions and observations for the oceanic lithosphere from s to p receiver functions and ss precursors the ocean lithosphere is classically described by the thermal half space cooling hsc or the plate models both characterized by a gradual transition to the asthenosphere beneath scattered waves find sharp seismic discontinuities beneath the oceans possibly from the base of the plate active source studies suggest sharp discontinuities from a melt channel we calculate synthetic s to p receiver functions and ss precursors for the hsc and plate models and also for channels we find that the hsc and plate model velocity gradients are too gradual to create interpretable scattered waves from the base of the plate subtle phases are predicted to follow a similar trend as observations flattening at older ages therefore the seismic discontinuities are probably caused by a thermally controlled process that can also explain their amplitude such as melting melt may coalesce in channels although channels 10 km thick should be resolvable by scattered wave imaging

gravity anomalies and crustal thickness variations along the mid atlantic ridge between 33 n and 40 n multibeam bathymetry and gravity data have been obtained along an 800 km long section of the mid atlantic ridge from just south of the hayes fracture zone at 33 n to the northern edge of the azores platform near 40 n a three dimensional analysis of these gravity and topography data combined with results from earlier seismic refraction studies in this area reveal two different scales of crustal heterogeneity a systematic along axis segment scale 8 9 km near the middle of spreading segments and the thinnest crust 3 4 km near segment offsets the magnitude of this along axis variation in crustal thickness is proportional to the length of the spreading segment and the size of the adjacent ridge offset there also is a distinct asymmetry in crustal structure across the rift valley near large segment offsets with gravity highs inferred to be thinner crust beneath the inside corner highs adjacent to these offsets this segment scale crustal heterogeneity is similar to that reported from the kane to atlantis section of the mid atlantic ridge and from parts of the intermediate spreading southern mid atlantic ridge it is superimposed on a second longer wavelength variation in gravity and crustal thickness associated with the azores hot spot the most pronounced effect of the azores hot spot on the mid atlantic ridge occurs between 38 n and 40 n where the ridge axis rapidly shoals by more than 1000 m the crust thickens by over 2 km and the rift valley largely disappears the absence of a deep axial rift valley on the azores platform and near the midpoints of some ridge segments along the mid atlantic ridge to the south agrees well with the predictions of recent ridge crest thermal and rheological models that suggest a dependence of axial morphology on both crustal thickness and spreading rate the transition from a rift valley to an axial high morphology at these spreading rates 11 mm yr half rate occurs at a crustal thickness of about 9 1km

three dimensional crustal structure of ascension island from active source seismic tomography we present a crustal velocity and moho depth model of the ascension volcanic edifice using one of the most densely sampled 3 d wide angle data sets for volcanic islands currently available we invert traveltimes of first and second arrivals by seeking a layer interface minimum structure model and then test the resulting velocity model by gravity modelling and a 3 d checkerboard resolution test within the shallow extrusive part of the crust two main high velocity regions coincide with the highest topography on land and the gravity maximum off the west coast of the island respectively these features are connected with a high velocity intrusive core that is created either within or on the top of oceanic layer 3 and is interpreted as a possible relic magma chamber the thickness of the surface low velocity region is similar to that observed at hawaii jasper seamount and great meteor seamount suggesting a similar process of edifice construction the mean density of the volcanic edifice is significantly less than that of normal oceanic crust and than load densities typically assumed in studies of flexure as a result of seamount loading there is no simple flexural model that explains the shape of the moho beneath the island perhaps because of the long lived volcanism and the proximity of the island to the mid atlantic ridge mar and the ascension fracture zone there is no evidence for magmatic underplating beneath ascension island

stress change from the 2015 mw 7 8 gorkha earthquake and increased hazard in the southern tibetan plateau abstract we examine the co seismic coulomb stress change induced by the 2015 mw 7 8 gorkha nepal earthquake and investigate its influence on the seismic hazard in the southern tibetan plateau we find that the location of the aftershocks coincides with areas where stress was enhanced this stress enhanced area also covers the west and the shallow fault section updip of the 2015 gorkha earthquake rupture in the main himalayan thrust fault mht signaling the raising hazard of the seismic gaps in the west and south to kathmandu the 2015 gorkha earthquake strongly interacted particularly with the normal and thrust faults in the distance of around 100 250 km from the rupture zone by bringing stress closer to the coulomb failure this fault interaction process increased stress by 12 kpa and 100 kpa at the southern end of the tingkye and the nyalam normal faults respectively triggering the ms 5 9 tingri earhquake on 25 may 2015 and the ms 5 3 nyalam earthquake on 26 may 2015 stress in the main frontal himalaya thrust fault mft the main boundary thrust fault mbt in the lalitpur area of nepal was promoted by 40 100 kpa such stress transfer should facilitate the future rupture on these active faults and raise seismic hazard in the southern tibetan plateau

the volcanotectonic evolution of flores island azores portugal abstract from the study and interpretation of the volcanic products and structures of flores island we infer that its volcanic history was dominated by two major periods 1 proto insular volcanism which includes all the submarine and emergent activities and 2 insular volcanism consisting exclusively of subaerial eruptions the first period includes two phases 1 the oldest 2 2 to 1 5 ma of shallow submarine volcanism 2 the youngest 1 0 to 0 75 ma includes emergent volcanism throughout the second period three volcanic stages are recognized 1 the first one 0 7 to 0 5 ma includes the most voluminous volcanism balanced between effusive and explosive events 2 an intermediate stage 0 4 to 0 2 ma that involves a larger number of small scale feeder centres with effusive eruptions prevailing 3 the third stage is the latest volcanic activity of the island 0 003 ma with strombolian and subsequent phreatic and phreatomagmatic activity centred at four volcanic vents from 1 0 ma to the present the volcanotectonic development of flores island also reflects the operation of two major tectonic processes 1 a marked volcanotectonic uplift during the first stage 1 0 to 0 55 ma and 2 subsidence particularly intensive in the island s central area which led to the subsequent formation of two and perhaps three large calderas during the period 0 55 to 0 4 ma

on the robustness of seismic moment tensor inversions for mid ocean earthquakes the azores archipelago source models of mid oceanic earthquakes are often based only on far field teleseismic data the uncertainties of all source parameters are rarely quantified which restricts our understanding of how these events slip and how oceanic lithosphere is formed here we perform moment tensor inversions for five mw 4 6 5 9 earthquakes that occurred in the azores archipelago near the mid atlantic ridge in 2013 2016 taking advantage of the recently expanded seismic network in the region we assess moment tensor uncertainties due to data and earth model variability as well as the robustness of teleseismic versus local data inversions we find that for the events studied i existing 1 d earth models of the region based on receiver function data lead to a slightly improved data fit of local data compared to a widely used regional model based on active seismic surveys and ii using different 1 d earth models in the local data inversions leads to a variability in the retrieved source parameters of 15 30 in fault strike 5 20 in dip and 20 60 in rake depending on the earthquake s magnitude and location we study in detail the mw 5 9 2013 april 30 povoacao basin earthquake using 1 d and 3 d waveform modelling for which reported values of strike dip and rake in earthquake catalogues differ by 60 35 and 80 we find that our moment tensor solutions show a lower variability than in the catalogues and exhibit a persistent non double couple component of 40 60 per cent which is not due to a volumetric change we suggest that it is potentially due to geometrically complex faulting in the povoacao basin notably curved faults we find that the retrieved moment tensor solutions depend strongly on the earthquake s location if an accurate location is used joint inversions of local and teleseismic data can help to stabilize moment tensor solutions of oceanic earthquakes and reduce parameter trade offs compared to inversions of local data alone

evolution of a volcanic island on the shoulder of an oceanic rift and geodynamic implications s jorge island on the terceira rift azores triple junction abstract the s jorge island in the azores lies on a peculiar setting the southern shoulder of the terceira rift tr which raises a series of questions that we address in this study we first established the main volcanic stratigraphy by recognizing in the field the main unconformities discontinuities and their meaning major erosion surfaces and faults then we collected critical samples and finally dated them by k ar to calibrate the stratigraphy and the age of inferred large scale flank collapses based on field geochronological and marine geophysical data 1 we found much older rocks in s jorge than in previous studies ca 1 85 ma and established a new volcanic stratigraphy from bottom to top old volcanic complex ca 1 9 1 2 ma cropping out in the eastern third of the island intermediate volcanic complex ca 0 8 0 2 ma cropping out in the western two thirds of the island and separated from the underlying complex by a major fault young volcanic complex

the 1980 1997 and 1998 azores earthquakes and some seismo tectonic implications abstract we have studied the focal mechanisms of the 1980 1997 and 1998 earthquakes in the azores region from body wave inversion of digital gdsn global digital seismograph network and broadband data for the 1980 and 1998 shocks we have obtained strike slip faulting with the rupture process made up of two sub events in both shocks with total scalar seismic moments of 1 9 1019 nm mw 6 8 and 1 4 1018 nm mw 6 0 respectively for the 1997 shock we have obtained a normal faulting mechanism with the rupture process made up of three sub events with a total scalar seismic moment of 7 7 1017 nm mw 5 9 a common characteristic of these three earthquakes was the shallow focal depth less than 10 km in agreement with the oceanic type crust from the directivity function of rayleigh lr waves we have identified the nw se plane as the rupture plane for the 1980 and 1998 earthquakes with the rupture propagating to the se slow rupture velocity about of 1 5 km s has been estimated from directivity function for the 1980 and 1998 earthquakes from spectral analysis and body wave inversion fault dimensions stress drop and average slip have been estimated focal mechanisms of the three earthquakes we have studied together with focal mechanisms obtained by other authors have been used in order to obtain a seismotectonic model for the azores region we have found different types of behaviour present along the region it can be divided into two zones zone i from 30 w to 27 w zone ii from 27 w to 23 w with a change in the seismicity and stress direction from zone i in zone i the total seismic moment tensor obtained corresponded to left lateral strike slip faulting with horizontal pressure and tension axes in the e w and n s directions respectively in zone ii the total seismic moment tensor corresponded to normal faulting with a horizontal tension axis trending ne sw normal to the terceira ridge the stress pattern for the whole region corresponds to horizontal extension with an average seismic slip rate of 4 4 mm yr

observations of long period rayleigh wave ellipticity summary we analyse phase shifts and amplitude ratios of horizontal to vertical components of t 150 s fundamental rayleigh waves in the ray picture of surface wave propagation it is expected that at a single station this ratio will be constant being controlled only by the seismic velocity structure beneath the seismic station in contrast we observe substantial variability in the amplitude ratios measured at a number of stations from the global seismic network we discuss possible causes for the anomalous ratios concluding that they probably arise from effects associated with small scale heterogeneity distinctly distributed across different tectonic domains and having scale lengths shorter than a wavelength