rate of dune reddening in a humid tropical climate the formation of red beds has long interested geologists and pedologists1 3 it has been suggested that the nature and degree of reddening in dune sands can be a useful indicator of the relative age and environmental history of the sands several authors have concluded that dune sands undergo progressive reddening with time4 7 and james and stanley8 considered that coastal dunes might actually be mapped on the basis of colour however quantitative data regarding the rate of reddening in different environmental conditions are generally lacking i present here radiocarbon evidence from north east australia which suggests that red weathering profiles have developed in stabilized dunes of holocene age in humid tropical conditions within the past 7 500 yr

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

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 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

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 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

palaeoenvironment of braided fluvial systems in different tectonic realms of the triassic sherwood sandstone group uk abstract fluvial successions comprising the fills of sedimentary basins occur in a variety of tectonic realms related to extensional compressional and strike slip settings as well as on slowly subsiding passive basin margins a major rifting phase affected nw europe during the triassic and resulted in the generation of numerous sedimentary basins in the uk much of the fill of these basins is represented by fluvial and aeolian successions of the sherwood sandstone group additionally regions that experienced slow rates of mesozoic subsidence unrelated to triassic rifting also acted as sites of accumulation of the sherwood sandstone group one well exposed example being the eastern england shelf the fluvial depositional architecture of deposits of the sherwood sandstone group of the eastern england shelf a shelf edge basin is compared with similar fluvial deposits of the st bees sandstone formation eastern irish sea basin a half graben the two studied successions represent the preserved deposits of braided fluvial systems that were influenced by common allogenic factors climate sediment source delivery style differences in preserved sedimentary style principally reflect their different tectonics settings analysis of lithofacies and architectural elements demonstrates that both studied successions are characterized by amalgamated channel fill elements that are recorded predominantly by downstream accreting sandy barforms the different tectonic settings in which the two braided fluvial systems accumulated exerted a dominant control on preserved sedimentary style and long term preservation potential on the eastern england shelf the vertical stacking of pebbly units and the general absence of fine grained units reflect a slow rate of sediment accommodation generation 18 19 4 m myr in this shelf edge basin successive fluvial cycles repeatedly reworked the uppermost parts of earlier fluvial deposits such that only the lowermost channel lags tend to be preserved by contrast in the eastern irish sea basin of west cumbria the rate of sediment accommodation generation was substantially greater 119 m myr such that space was available to preserve complete fluvial cycles including silty drape units that cap the channelized deposits

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

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

ichnology paleosols and palimpsests surfaces in the tinat member of the nuayyim formation unayzah group subsurface saudi arabia trace fossils and genetic stratigraphy in continental settings abstract the nuayyim formation of the unayzah group is widespread in subsurface central saudi arabia and constitutes a laterally variable stratigraphic unit with a complex mosaic of facies sedimentation for the tinat member took place majorly in a continental setting dominated by aeolian processes that resulted in dunes interdunes ephemeral stream deposits terminating with regional development of paleosols facies ichnofacies and palynological analysis suggest an arid to semi arid setting with biogenic activity in the form of continental fauna and plants in deposits associated with pedogenetical alteration in paleosol horizons therein burrowing exhibits elements of the scoyenia ichnofacies in beds with sparse to abundant bioturbation tectonic uplift and subaerial exposure resulted in the exhumation of previously buried substrates leading to the formation of burrowed palimpsests surfaces associated with paleosols at the end of unayzah deposition prior to the onset of the khuff formation progressive thermal updoming is interpreted to have occurred during the latest portion of the unayzah group sedimentation cycle in the arabian plate culminating in the regional pre khuff unconformity at the top of this megacycle recognized in this study by biogenically demarcated diastems ichnological and sedimentological observations outlined in this study are significant because they i refine existing interpretations of the paleoenvironmental history in the study area ii document diastems marking breaks in sedimentation and iii outline several soil forming cycles that allowed the establishment of a trace fossil suite with continental affinities thus demarcating the end of an entire sedimentation cycle the recognition and delineation of burrowed horizons associated with paleosols provides a tool to understand the tectono stratigraphic evolution of similar successions in the rock record

a drying upward aeolian system of the bohdasin formation early triassic sudetes of ne czech republic record of seasonality and long term palaeoclimate change abstract the record of aeolian processes was studied in early triassic sandstones of the upper part of the bohdasin formation ne bohemia an isolated erosional relict of a triassic fluvial aeolian succession in the sudetes block of the bohemian massif central europe the aeolian system exposed in the dev t k i quarry near cerven kostelec provides a significant addition to the generally poorly preserved record of early triassic palaeoclimate and palaeowind regime in central europe two mutually interbedded facies occur in the aeolian succession 1 dune facies comprising cross strata that show interdune reactivation and superimposition bounding surfaces and 2 interdune facies formed by horizontally stratified commonly mud draped sandstones which display a number of indicators of damp to wet conditions and fluctuations in water table the succession of the dev t k i sandstones is interpreted as a record of migration and climb of dunes with intervening interdune flats which replaced an underlying fluvial system it is likely that a coeval fluvial system existed near the dev t k i dune field providing available sand in dry periods and flooding in wet periods dominant palaeowind directions are southwestward and northward in present day coordinates repeated reversals of palaeowind direction interpreted as seasonal are recorded in changes in the internal structure of the cross strata reworking and reactivation in the dune migration direction at least some episodes of dune reworking occurred simultaneously with episodes of water table rise a drying upward trend in the aeolian succession is interpreted from evidence for increased availability of sand through time the upward transition from a braided fluvial to a wet drying upward aeolian system within the bohdasin formation represents a shift toward maximum aridity of the palaeoenvironment which marks also the peak arid conditions in the long term palaeoclimatic evolution of the carboniferous triassic succession of the sudetes region and correlates with the establishment of aeolian settings in other regions of central europe during the early triassic the record of changing palaeowind directions documented in several cases to have been coupled with episodes of rapid rise in water table is taken as evidence for pronounced climatic seasonality and brings additional support to the models predicting strong monsoonal circulation during the early triassic affecting particularly the eastern subequatorial coast of pangaea and adjoining regions

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

holocene development of an episodic transgressive dune barrier ramsay bay north queensland australia abstract an investigation of the stratigraphy and sedimentological properties of a tombolo barrier at ramsay bay north queensland has indicated that the barrier consists largely of aeolian sands which in places extend more than 30 m below present sea level two major episodes of dune activity are recognized on morphological and pedogenic criteria radiocarbon dating of organic muds associated with the barrier sands suggests the older dunes were partly drowned during the early holocene marine transgression 9500 6000 c 14 yrs b p the later generation of dunes formed in the late holocene probably within the last 900 c 14 yrs the ultimate causes of the aeolian episodes are not certain but appear to be related to periods of rapid shoreface erosion

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

high resolution stratigraphy and depositional model of wind and water laid deposits in the ordovician guaritas rift southernmost brazil abstract the upper portion of the pedra pintada alloformation includes about 100 m of mostly eolian deposits this paper emphasizes the vertical succession and lateral association of sedimentary facies based on analysis of outcrop data and aerial photographs as well as the hierarchy and origin of bounding surfaces it aims to propose a high resolution stratigraphic and depositional model that may be useful to exploitation of eolian reservoirs the succession has been preserved due to basin subsidence and is described in terms of four facies associations that constitute three dominantly eolian units these units are sharply bounded by major flooding surfaces super surfaces that in turn are overlain by 1 to 2 m thick dominantly water laid facies lacustrine fluvial deltaic and eolian both their internal organization and boundaries were controlled by changes in the base level rise rate the basal eolian unit is composed of crescentic eolian dunes and damp interdune deposits ascribed to a wet eolian system on the other hand eolian units ii and iii also characterized by crescentic eolian dunes simple and compound deposits were related to dry eolian systems since they comprise dry eventually wet interdune facies eolian unit iii is truncated by basinwide unconformity which is then overlain by the ephemeral fluvial deposits varzinha alloformation this second type of super surface is related to climate induced wind erosion deflation down to the water table level regional stokes surface followed by fluvial incision linked to tectonic activity

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

stratigraphic evolution and preservation of aeolian dune and damp wet interdune strata an example from the triassic helsby sandstone formation cheshire basin uk new and previously published models of wet aeolian system evolution form a spectrum of types that may be explained in terms of aeolian dune dynamics rate of water table rise and or periodicity of interdune flooding this is illustrated with an example from the mid triassic anisian helsby sandstone formation cheshire uk lenses of damp and wet interdune strata exhibit an intertonguing transitional relationship with the toe sets of overlying aeolian dune units this signifies dune migration that was contemporaneous with water table controlled accumulation in adjacent interdunes downwind changes in the geometry and facies of the interdune units indicate periodic expansion and contraction of the interdunes in response to changes in the elevation of the groundwater table and episodic flooding during which accumulation of dune strata continued relatively uninterrupted this contrasts with other models for accumulation in wet aeolian systems where interdune flooding is associated with a cessation in aeolian bedform climbing and the formation of a bypass or erosional supersurface architectural panels document the detailed stratigraphy in orientations both parallel and perpendicular to aeolian transport direction enabling a quantitative three dimensional reconstruction of genetically related aeolian dune and interdune elements sets of aeolian dune strata are composed of grainflow and translatent wind ripple strata and are divided by a hierarchy of bounding surfaces originating from oblique migration of superimposed dunes over slipfaceless sinuous crested parent bedforms together with lee slope reactivation under non equilibrium flow conditions silty mudstone and sandstone interdune units are characterized by wind ripple wavy and subaqueous wave ripple laminae desiccation cracks mud flakes raindrop imprints load casts flutes intraformational rip up clasts and vertebrate and invertebrate footprint impressions and trackways these units result from accumulation on a substrate that varied from dry through damp to wet surface conditions interdune ponds were flooded by either fluvial incursions or rises in groundwater table and were periodically subject to gradual desiccation and reflooding red silty mudstone beds of subaqueous origin pass laterally into horizontally laminated wind ripple beds indicating a progressive transition from wet through damp to dry surface conditions within a single interdune

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

late quaternary evolution of coastal sand barriers port stephens myall lakes area central new south wales australia abstract the geomorphic and stratigraphic history of six coastal embayments has been studied in the vicinity of newcastle new south wales n s w australia in order to determine modes of deposition and the degree to which marine and estuarine deposits can be correlated and dated each embayment possesses its own distinctive suite of landforms ranging from those dominated by coastal dunes to those in which beach ridges occur in four of the bays dual sand barriers comprising an inner barrier and an outer barrier provide the framework for correlation between embayments six stages are recognized in the deposition of late quaternary sediments in this area i pre last interglacial involving accumulation of separate composite units consisting of estuarine clays and transgressive dune complexes ii last interglacial stage during which inner barriers were formed iii last glacial reworking of barrier and dune sands by westerly winds iv postglacial marine transgression during which the outer barriers were initiated v mid holocene stage following cessation of sea level rise ca 6000 6500 yr b p on this coast and involving progradation of outer barriers in some embayments and vi late holocene episodic eolian reworking of dune complexes and outer barriers the relatively high wave and wind energy as well as the tectonic setting of the central n s w coast results in somewhat different geomorphic histories from barrier island coasts in north america and europe

the action of wind and water in a mid cretaceous subtropical erg margin system close to the variscan iberian massif spain aeolian processes and ephemeral water influx from the variscan iberian massif to the mid cretaceous outer back erg margin system in eastern iberia led to deposition and erosion of aeolian dunes and the formation of desert pavements remains of aeolian dunes encased in ephemeral fluvial deposits aeolian pods demonstrate intense erosion of windblown deposits by sudden water fluxes the alternating activity of wind and water led to a variety of facies associations such as deflation lags desert pavements aeolian dunes pebbles scattered throughout dune strata aeolian sandsheets aeolian deposits with bimodal grain size distributions mud playa ephemeral floodplain pebble sand and cobble sand bedload stream pebble cobble sand sheet flood sand bedload stream debris flow and hyperconcentrated flow deposits sediment in this desert system underwent transport by wind and water and reworking in a variety of sub environments the nearby variscan iberian massif supplied quartzite pebbles as part of mass flows pebbles and cobbles were concentrated in deflation lags eroded and polished by wind driven sands facets and ventifacts and incorporated by rolling into the toesets of aeolian dunes the back erg depositional system comprises an outer back erg close to the variscan highlands and an inner back erg close to the central erg area the inner back erg developed on a structural high and is characterized by mud playa deposits interbedded with aeolian and ephemeral channel deposits in the inner back erg area ephemeral wadis desiccated after occasional floods were mud cracked and overrun episodically by aeolian dunes subsequent floods eroded the aeolian dunes and mud cracked surfaces resulting in largely structureless sandstones with boulder size mudstone intraclasts floods spread over the margins of ephemeral channels and eroded surrounding aeolian dunes the remaining dunes were colonized occasionally by plants and their roots penetrated into the flooded aeolian sands upon desiccation deflation resulted in lags of coarser grained sediments a renewed windblown supply led to aeolian sandsheet accumulation in topographic wadi depressions synsedimentary tectonics caused the outer back erg system to experience enhanced generation of accommodation space allowing the accumulation of aeolian dune sands ephemeral water flow to the outer back erg area supplied pebbles eroded aeolian dunes and produced hyperconcentrated flow deposits fluidization and liquefaction generated gravel pockets and recumbent folds dune damming after sporadic rains the case of the namib desert monsoonal water discharge thar desert and meltwater fluxes from glaciated mountains taklamakan desert are three potential non exclusive analogues for the ephemeral water influx and the generation of hyperconcentrated flows in the cretaceous desert margin system an increase in relief driven by the aptian anti clockwise rotation of iberia led to an altitude sufficient for the development of orographic rains and snowfall which fed melt water fluxes to the desert margin system quartzite conglomerates and sands dominantly consisting of quartz and well preserved feldspar grains which are also observed in older cretaceous strata indicate an arid climate and the mechanical weathering of precambrian and palaeozoic metamorphic sediments and felsic igneous rocks unroofing of much of the cover of sedimentary rocks in the variscan iberian massif must therefore have taken place in pre cretaceous times

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

periodic accumulation and destruction of aeolian erg sequences in the permian cedar mesa sandstone white canyon southern utah usa the permian cedar mesa sandstone represents the product of at least 12 separate aeolian erg sequences each bounded by regionally extensive deflationary supersurfaces facies analysis of strata in the white canyon area of southern utah indicates that the preserved sequences represent erg centre accumulations of mostly dry though occasionally water table influenced aeolian systems each sequence records a systematic sedimentary evolution enabling phases of aeolian sand sea construction accumulation deflation and destruction to be discerned and related to a series of underlying controls sand sea construction is signalled by a transition from damp sandsheet ephemeral lake and palaeosol deposition through a phase of dry sandsheet deposition to the development of thin chaotically arranged aeolian dune sets the onset of the main phase of sand sea accumulation is reflected by an upward transition to larger scale ordered sets which represent the preserved product of climbing trains of sinuous crested transverse dunes with original downwind wavelengths of 300 400 m regularly spaced reactivation surfaces indicate periodic shifts in wind direction which probably occurred seasonally compound co sets of cross strata record the oblique migration of superimposed slipfaced dunes over larger slipfaceless draa each aeolian sequence is capped by a regionally extensive supersurface characterized by abundant calcified rhizoliths and bioturbation and which represents the end product of a widespread deflation episode whereby the accumulation surface was lowered close to the level of the water table as the sand sea was progressively cannibalized by winds that were undersaturated with respect to their potential carrying capacity aeolian sequence generation is considered to be directly attributable to cyclical changes in climate and related changes in sea level of probable glacio eustatic origin that characterize many permo carboniferous age successions sand sea construction and accumulation occurred during phases of increased aridity and lowered sea level the main sand supply being former shallow marine shelf sediments that lay to the north west sand sea deflation and destruction would have commenced at or shortly after the time of maximum aridity as the available sand supply became exhausted restricted episodes of non aeolian accumulation would have occurred during humid interglacial phases accumulation and preservation being enabled by slow rises in the relative water table subsidence analysis within the paradox basin together with comparisons to other similar age successions suggests that the climatic cycles responsible for generating the cedar mesa erg sequences could be the product of 413 000 years so called long eccentricity cycles by contrast annual advance cycles within the aeolian dune sets indicate that the sequences themselves could have accumulated in just a few hundred years and therefore imply that the vast majority of time represented by the cedar mesa succession was reserved for supersurface development

facies control on seismites in an alluvial aeolian system the pliocene dunefield of the teruel half graben basin eastern spain abstract the recognition of seismically induced soft sediment deformation structures ssds in sedimentary successions characterized by different facies and hence by different rheology is challenging this is the case for high porosity and high permeability aeolian facies interbedded with muddy wet interdune deposits and alluvial conglomerates and sandstones several types of ssds have been studied in two exposures of the upper pliocene 2 9 2 6 ma sediments of a fault bounded intracontinental aeolian dune field in the teruel basin iberian chain eastern spain among ssds load and fluid escape structures apart from several animal tracks have been recognized those structures show an irregular distribution through the studied stratigraphic sections being scarce in homogenous aeolian sands and frequent in water related facies a detailed study of the distribution and geometry of ssds and their relationships with respect to the stratigraphic architecture and facies has allowed a critical discrimination of trigger mechanisms i e biological or physical overloading vs earthquakes the seismically induced structures are concentrated into seven deformed beds showing an uneven lateral distribution and geometry closely controlled by the hosting sedimentary facies and their rheology these seismites resulted from liquefaction during moderate earthquakes estimated magnitude from 5 0 to 6 8 the most probable seismogenic source was the sierra del pobo normal fault zone located 2 km to the east results show how an appropriate recognition of sedimentary facies is crucial to understand the lateral variability of seismites in sedimentary environments characterized by sharp facies changes

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

a stratigraphic model to account for complexity in aeolian dune and interdune successions wet aeolian systems in which the water table or its capillary fringe are in contact with the accumulation surface such that moisture influences sedimentation are well known from modern aeolian systems and several ancient preserved successions are recognized from outcrop one common mechanism by which accumulation of wet aeolian system deposits occurs is via a progressive rise in the relative water table level that is coincident with ongoing dune and interdune migration the angle of dune climb being determined by the ratio between the rate of relative water table rise and the rate of downwind migration of the bedforms accumulations of wet aeolian system deposits tend to be characterized by units of climbing dune strata separated by units of damp or wet interdune strata for simple geometric configurations where the size of the dune and interdune units the rate of bedform migration and the rate of aggradation all remain constant over space and time the resulting accumulation has a simple architecture characterized by sets of uniform thickness inclined at a constant angle however the dynamic nature of most aeolian dune systems means that such simple configurations are unlikely in nature the complexity inherent in these systems is accounted for here by a numerical model in which key controlling parameters including dune and interdune wavelength and spacing migration rate and aggradation rate are allowed to vary systematically both spatially from a dune field centre to its margin and temporally in response to changes in sediment availability or water table level the range of synthetic stratigraphic architectures generated by the model accounts for all the best known examples of aeolian dune and interdune stratigraphic configurations documented from the stratigraphic record modelling results have enabled the erection of a scheme for the classification of dune system type whereby the many elaborate stratal architectures known to exist in nature can effectively be accounted for by only four parameters that are allowed to vary over space and time dune and interdune wavelength and spacing rate of bedform migration and rate of accumulation results have applied implications including the modelling of reservoir heterogeneity and the prediction of fluid flow pathways of hydrocarbons water co2 and contaminants in subsurface reservoirs and aquifers in which low permeability interdune units might act as baffles or barriers

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

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

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

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

comment on the permian triassic transition and the onset of mesozoic sedimentation at the northwestern peri tethyan domain scale palaeogeographic maps and geodynamic implications by s bourquin a bercovici j lopez gomez j b diez j broutin a ronchi m durand a arche b linol and f amour palaeogeography palaeoclimatology palaeoecology 299 2011 265 280 abstract the recent paper by bourquin et al 2011 describes the regional palaeogeographic evolution of the late permian to middle triassic on a pan european scale whilst useful data and interpretations are provided for their southern and intra variscan belt domains additional well and seismic data from the central and northern north sea and the atlantic margin region together with results from recent publications allow us to refine and improve their interpretation of their northern domain the presence of a regional unconformity at the permian triassic boundary with only localised induan sedimentation is less clear in the northern region where multiple extensional events through late permian and triassic time led to the development of localised footwall and rift flank unconformities as arctic rifting propagated southwards and entered the north sea and the atlantic margin regions the hardegsen unconformity may be locally identifiable in the southern portion of the northern domain but again forms one of a number of unconformities marking the onset of rifting data from the northern domain suggest that early triassic aeolian activity was ubiquitous on the distal fringes of terminal fluvial systems but with no evidence of the discrete episode of increased aridity in the smithian identified in the south the onset of vegetation cover in the northern domain was also more diachronous in this region appearing in the central north sea at approximately the same time as muschelkalk flooding of the adjacent southern permian basin and later in basins further to the north in most cases the middle triassic fluvial systems in the north were terminal in nature failed to discharge into marine basins and were not exorheic in character their advance and retreat was independent of sea level fluctuations or the presence of a marine water body and fluvial expansion and retreat aeolian reworking and vegetation cover appear to have been linked to catchment runoff the disconnect with the observations to the south may be in part a product of the more northern latitudinal position of these systems or at least that of the headwaters of the fluvial drainage

aeolian dune field development in a water table controlled system skeiđararsandur southern iceland aeolian dune fields characterized by partly vegetated bedforms undergoing active construction and with interdune depressions that lie at or close to the water table are widespread on skei ararsandur southern iceland the largest aeolian dune complex on the sandur covers an area of 80 km2 and is characterized by four distinct landform types i spatially isolated aeolian dunes ii extensive areas of damp and wet flooded interdune flat with small fluvial channels iii small aeolian dune fields composed of assemblages of bedforms with simple morphologies and small predominantly damp interdune corridors and iv larger aeolian dune fields composed of assemblages of complex bedforms floored by older aeolian dune deposits that are themselves raised above the level of the surrounding wet sandur plain the morphology of each of these landform areas reflects a range of styles of interaction between aeolian dune interdune and fluvial processes that operate coevally on the sandur surface the geometry scale orientation and facies composition of sets of strata in the cores of the aeolian dunes and their relationship to adjoining interdune strata have been analysed to explain the temporal behaviour of the dunes in terms of their mode of initiation construction pattern of migration style of accumulation and nature of preservation seasonal and longer term flooding induced changes in water table level have caused episodic expansion and contraction of the wet interdune ponds most of the dunes are currently undergoing active construction and migration and although sediment availability is limited because of the high water table substantial aeolian transport must occur especially during winter months when the surface of the wet interdune ponds is frozen and sand can be blown across the sandur without being trapped by surface moisture bedforms within the larger dune fields have grown to a size whereby formerly damp interdune flats have been reduced to dry enclosed depressions and dry aeolian system accumulation via bedform climb is ongoing despite regional uplift of the proximal sandur surface in response to glacial retreat and unloading over the past century sediment compaction induced subsidence of the distal sandur is progressively placing aeolian deposits below the water table and is enabling the accumulation of wet aeolian systems and increasing the likelihood of their long term preservation wet dry and stabilizing aeolian system types all co exist on skei ararsandur and the dunes are variously undergoing coeval construction accumulation bypass stabilization and destruction as a result of interactions between localized factors

effects of sand supply on the morphodynamics and stratigraphy of active parabolic dunes bigstick sand hills southwestern saskatchewangeological survey of canada contribution 20060654 sand supply is a major controlling factor on parabolic dune form and stratigraphy in inland settings in this study aerial photographs ground penetrating radar gpr and stratigraphic analysis d

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

giant calcite concretions in aeolian dune sandstones sedimentological and architectural controls on diagenetic heterogeneity mid cretaceous iberian desert system spain aeolian dune sandstones of the iberian erg system cretaceous spain host giant calcite concretions that constitute heterogeneities of diagenetic origin within a potential aeolian reservoir the giant calcite concretions developed in large scale aeolian dune foresets at the transition between aeolian dune toeset and damp interdune elements and in medium scale superimposed aeolian dune sets the chemical composition of the giant concretions is very homogeneous they formed during early burial by lowmg calcite precipitation frommeteoric pore waters carbonate componentswith yellow orange luminescence form the nuclei of the poikilotopic calcite cement these cements postdate earlier diagenetic features characterized by earlymechanical compaction fe oxide cements and clay rims around windblown quartz grains resulting from the redistribution of aeolian dust over the grain surfaces the intergranular volume igv in friable aeolian sandstone ranges from 7 3 to 15 3 whereas in cemented aeolian sandstone it is 18 6 to 25 3 the giant calcite concretions developed during early diagenesis under the influence of meteoric waters associated with the groundwater flow of the desert basin although local e g activity of fluid flow through extensional faults and or other regional controls e g variations of the phreatic level associated with a variable water influx to the erg system and varying sea level could have favoured the local development of giant calcite concretions the spatial distribution pattern of carbonate grains and the main bounding surfaces determined the spatial distribution of the concretions in particular the geometry of the giant calcite concretions is closely associated with main bounding aeolian surfaces thus interdune superimposition and reactivation surfaces exerted a control on the concretion geometries ranging fromflat and tabular ones e g bounded by interdunes towedge shaped concretions at the dune foresets e g bounded by superimposition and reactivation surfaces determining the spatial distribution of the heterogeneities of diagenetic origin in the aeolian reservoir

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

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

high resolution stratigraphic architecture and lithological heterogeneity within marginal aeolian reservoir analogues marginal aeolian successions contain different lithological units with variable geometries dimensions and spatial distributions such variations may result in considerable heterogeneity within hydrocarbon reservoirs developed in successions of this type which poses a high risk to their efficient development here such heterogeneity is described and characterized at inter well 1 km scales using two well exposed outcrop analogues of end member marginal aeolian deposits from the permian cedar mesa sandstone and jurassic page sandstone of south central utah usa the sedimentology and stratigraphic architecture of the cedar mesa sandstone was studied in a 1 2 km2 area in the indian creek region of southern utah where the interval consists of interbedded fluvial and aeolian deposits representative of a fluvial dominated erg margin the page sandstone was studied in a 4 3 km2 area near escalante close to the utah arizona border where it consists of interbedded sabkha and aeolian deposits representative of a transitional marine erg margin the three dimensional stratigraphic architectures of both reservoir analogues have been characterized in order to establish the dimensions geometries and connectivity of high permeability aeolian sandstones facies architecture of the aeolian sabkha deposits is characterized by laterally continuous aeolian sandstone layers of relatively uniform thickness that alternate with layers of heterolithic sabkha deposits aeolian sandstones are thus likely to form vertically unconnected but laterally widespread flow units in analogous reservoirs facies architecture in the aeolian fluvial deposits is more complex because it contains alternating intervals of aeolian sandstone and fluvial heterolithic strata both of which may be laterally discontinuous at the studied length scales aeolian sandstones encased by fluvial heterolithic strata may form small isolated flow units in analogous reservoirs although the limited continuity of fluvial heterolithic strata results in vertical connectivity between successive aeolian sandstones in other locations these architectural templates may be used to condition zonation schemes in models of marginal aeolian reservoirs

cementation and blackening of holocene sands by peat derived humates a case study from the great dune of pilat landes des gascogne southwestern france abstract the base sand layers of the aeolian great dune of pilat which stretches along the coast of arcachon bay have been locally impregnated with a dark brown to black amorphous organic substance of humate composition the humate cemented sand forms a well indurated horizon 40 50 cm in thickness that developed immediately beneath the holocene peaty layer p1 paleosoil the humate identified by means of ft ir and raman micro spectroscopy acted both as a cementing agent and as a coloring agent it formed thin coats and meniscus cements between individual sandstone grains which in turn caused the dark asphaltic like appearance of the sandstone field observations combined with geochemical analyses and the presence of identical geochemical compounds recognized in the peat and sandstone humate cement suggest that the peat containing low coalified rr 0 2 fragments of higher submerged and floating plants and marine algae deposited in a saline and reducing environment served as an obvious source rock for the humate the humate derived from decaying organic remains that descended from the peat into the permeable sand where it indurated irreversibly over a period shorter than 3500 years the present day actions of waves and tides contribute to the erosion of the frontal parts of the humate impregnated sandstone horizon resulting in the formation of the dark rounded sandstone slabs and pebbles that are deposited on nearby beaches this process provides a fine example of recent black pebble formation that derived from pre existing organic matter impregnated source rocks in contrast to their tropical carbonate counterparts however the humate induced blackening of the sandstone pebbles appears to be relatively unstable as the impregnated fragments bleach when exposed to air and seawater for a few seasons

characteristics and significance of some humate cemented sands humicretes at cape flattery queensland australia humate cemented sands humicretes are exposed at several locations along the foreshore and in gullies near cape flattery north queensland australia three broad types of humate accumulation are recognized a pedogenetic b groundwater and c aquatic pedogenetic and groundwater humicretes usually have a grain supported fabric in which quartz represents 99 of the framework grains hand specimens of humicrete are brittle but disintegrate rapidly in 0 1 n naoh concentration of humate is considered to have occurred by vertically and laterally migrating groundwater while induration has probably been caused by irreversible drying of the humic substances during periods of seasonal water table lowering radiocarbon dating of an in situ root embedded in indurated humate near cape flattery has indicated a background age of 48000 c 14 years

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

karst subsidence as a control on the accumulation and preservation of aeolian deposits a pleistocene example from a proglacial outwash setting ebro basin spain meltwater flows emanating from the pyrenees during the pleistocene constructed a braided outwash plain in the ebro basin and led to the karstification of the neogene gypsum bedrock synsedimentary evaporite dissolution locally increased subsidence rates and generated dolines and collapses that enabled the accumulation and preservation of outwash gravels and associated windblown deposits that were protected from erosion by later meltwater flows in these localized depocentres maximum rates of wind deceleration resulted from airflow expansion enabling the accumulation of cross stratified sets of aeolian strata climbing at steep angles and thereby preserving up to 5 m thick sets the outwash plain was characterized by longitudinal and transverse fluvial gravel bars channels and windblown facies organized into aeolian sand sheets transverse and complex aeolian dunes and loess accumulations flat lying aeolian deposits merge laterally to partly deformed aeolian deposits encased in dolines and collapses synsedimentary evaporite dissolution caused gravels and aeolian sand deposits to subside such that formerly near horizontal strata became inclined and generated multiple internal angular unconformities during episodes when the wind was undersaturated with respect to its potential sand transporting capacity deflation occurred over the outwash plain and coarse grained lags with ventifacts developed subsequent high energy flows episodically reached the aeolian dune field leading to dune destruction and the generation of hyperconcentrated flow deposits composed in part of reworked aeolian sands lacustrine deposits in the distal part of the outwash plain preserve rhythmically laminated lutites and associated gilbert type gravel deltas which developed when fluvial streams reached proglacial lakes this study documents the first evidence of an extensive pleistocene proglacial aeolian dune field located in the ebro basin 41 50 n south of what has hitherto been considered to be the southern boundary of pleistocene aeolian deposits in europe a non conventional mechanism evaporite karst related subsidence for the preservation of aeolian sands in the stratigraphic record is proposed

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

formation of quartz silt during humid tropical weathering of dune sands abstract quartz dune sand grains in northeast australia break down in situ under humid tropical weathering conditions to form substantial amounts of silt fragmentation appears to occur primarily due to silica solution along microfractures and dislocation structures in grains which have experienced tectonic deformation prior to deposition the surface textures of quartz grains viewed with the sem exhibit a close dependency on crystallographic properties in the b and c horizons of some weathered late pleistocene dunes silt forms up to 10 of the bulk sediment local remobilisation of such deposits by wind allows selective removal of the silt which is later deposited as a thin surficial sheet in more sheltered areas downwind these observations provide further evidence that weathering processes provide a major mechanism of silt formation and are an important factor to be considered in relation to the origin of loess and siltstones

lithological heterogeneity in a back barrier sand island implications for modelling hydrogeological frameworks abstract sediment mineralogy quartz grain surface textures grain size analysis bore hole logging and ground penetrating radar are combined to develop a three dimensional stratigraphic model of a back barrier sand island in southeast queensland australia the island consists of an unconsolidated sedimentary pile above an erosional bounding surface at the top of the underlying bedrock the stratigraphy is complex recording the shift in depositional environments from fluvio deltaic to strandplain via estuarine stages of evolution the back barrier island deposits are correlated with the stratigraphy of the adjacent coastal plain to the west and the barrier island to the east extrapolation of optically stimulated luminescence dates obtained from the barrier island combined with direct dating of the back barrier island sediments is used to constrain the depositional age and chronology of the back barrier island stratigraphy the modern depositional environment evolved from a chenier plain into a barrier island system by the flooding of an interdune swale and development of a shore parallel back barrier tidal lagoon the lithological heterogeneity of the back barrier island succession was controlled by the presence of a bedrock incised palaeovalley and changes in relative sea level sedimentary facies associations constrain the spatial distribution of hydraulic properties controlled by lithological heterogeneity post depositional alteration horizons are integrated with the facies model to account for the effects of weathering and diagenesis on hydraulic behaviour the derived hydrostratigraphy describes a vertically stacked dual aquifer island groundwater system consisting of a semi confined palaeovalley aquifer overlain by an unconfined strand plain aquifer hydrostratigraphic analysis based on sedimentary facies associations integrated with post depositional alteration characteristics reveals great complexity of groundwater systems within small island settings the facies modelling approach employed in this study more accurately estimates the distribution of lithological heterogeneity and the associated variations in hydraulic properties in the sedimentary pile

reconnaissance thermoluminescence dating of northern australian coastal dune systems abstract quaternary lithostratigraphic units in coastal dunes have been dated at three locations in northern australia cobourg peninsula shelburne bay and cape flattery by both radiocarbon dating of shell and organic carbon and thermoluminescence tl sediment dating both coarse fraction and fine fraction tl methods were used seventeen tl dates were measured none of the tl dates contradict the ages given by radiocarbon where multiple tl dates were taken from a unit they overlap within 2 standard deviation giving added confidence in the results a phase of dune emplacement during the late holocene ca 2700 1800 yr b p was identified in two of the dune fields an early holocene phase of dune emplacement ca 8600 7500 yr b p in two of the dune fields and a late pleistocene episode ca 24 000 17 000 yr b p in both the cape york dunefields three older units gave dates of about 29 000 81 000 and 171 000 yr b p but these must be treated with caution

arid climate 2 5 ma in the plio pleistocene valdarno basin northern apennines italy abstract distinctive eolian dominated sandy deposits 35 m thick exposed along the sw margin of the plio pleistocene valdarno basin in the northern apennines italy reflect an unusually arid period in the region paleomagnetic investigation and 40 ar 39 ar dating of a tephra layer 10 m above the eolian sand suggest that the sand was deposited between about 2 7 and 2 4 ma this age is coeval with the global climatic deterioration that occurred at the middle upper pliocene transition eolian sediments are represented by cross bedded sand rippled sand and horizontal bedded sand the alluvial deposits associated with the eolian sediment consist of sheet like beds of coarse sand and erosively based pebbly sand bodies eolian sand together with fluvial sandy deposits was formed in the medial distal portion of an alluvial system and represents the rena bianca sand unit the eolian and alluvial deposits are arranged into sedimentary cycles 2 6 m thick displaying a wetting drying wetting upward trend recording second order climatic oscillations of ca 40 ka each cycle is enclosed between major bounding surfaces defined by iron mineral encrustations these bounding surfaces represent periods of reduced eolian sand accumulation caused by a rising water table during the 2 5 ma global cooling the valdarno basin experienced a period of arid conditions owing to the influence of cold and dry easterly and northeasterly winds in contrast during the pleistocene the uplift of the pratomagno ridge protected the valdarno basin from easterly and northeasterly winds giving rise to relatively warm and wet conditions and mitigating the regional and global climatic changes

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

in situ evidence for an ancient aqueous environment at meridiani planum mars sedimentary rocks at eagle crater in meridiani planum are composed of fine grained siliciclastic materials derived from weathering of basaltic rocks sulfate minerals including magnesium sulfate and jarosite that constitute several tens of percent of the rock by weight and hematite cross stratification observed in rock outcrops indicates eolian and aqueous transport diagenetic features include hematite rich concretions and crystal mold vugs we interpret the rocks to be a mixture of chemical and siliciclastic sediments with a complex diagenetic history the environmental conditions that they record include episodic inundation by shallow surface water evaporation and desiccation the geologic record at meridiani planum suggests that conditions were suitable for biological activity for a period of time in martian history

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

mesoproterozoic erg and sand sheet system architecture and controlling factors galho do miguel formation se brazil abstract aeolian systems of the precambrian time were established in different palaeoclimatic and palaeogeographic conditions than the present different morphologies of dunes draas as linear oblique and star forms are widespread in the recent aeolian systems however the ancient aeolian deposits are rarely interpreted as these types of bedforms and usually referred to as transverse dunes the nature and complexity of bedform morphology in precambrian aeolian systems as well as the factors that allow the construction accumulation and preservation of these environments are still not well defined extensive exposures of galho do miguel formation in southeastern brazil represent a mesoproterozoic erg succession and exhibit a distinct facies architecture which contributed to the understanding of these deposits three architectural elements were identified i tangential cross stratified sandstone with superimposed trough cross bedded sandstone ii planar laminated sandstone and iii extensive flat bedded sandstone dominated by wrinkly laminae these elements are organized into three succession groups representative of simple transverse dune oblique compound draa and sand sheet systems the simple to compound dune draa system corresponds to the most central parts of the erg associated with a higher sediment availability and lower water table level conversely the sand sheet system occurs under low sediment availability and higher water table level in the marginal portions of the erg precambrian climatic oscillations may have changed the aeolian system morphology allowing the alternation of simple and complex aeolian dunes resulting in high frequency changes in sand sheet system and the remobilization of previously accumulated sediments over large geographic areas