cone penetration test calibration for erksak beaufort sea sand interpretation of the cone penetration test in sands is generally based on empirical calibrations from tests in large diameter calibration chambers although interpretation of these calibration data for clean sands in terms of the state parameter is expected to be broadly applicable to other sands material specific correlations are desirable for many projects this paper describes a series of calibration chamber tests carried out on a sand dredged from the beaufort sea for construction of artificial islands this erksak sand is a uniformly graded subrounded medium grained sand with a fines content of 3 6 the testing chamber described is 1 4 m in diameter and allows independent control of vertical horizontal and back pressures on the sand sample samples of the sand were prepared by moist compaction to preserve the fines content and then back pressure saturated the chamber test data are presented and confirm that the erksak sand fits the general trends observed for other sands very well a method i

a gravity current model of cooling mantle plume heads with temperature dependent buoyancy and viscosity gravity currents are a ubiquitous fluid dynamical phenomenon which involve the horizontal spreading of fluid masses under their own weight or buoyancy a theoretical model is developed to account for the effects of bulk cooling on the dynamics and morphology of geological gravity currents with particular focus on mantle plume heads spreading beneath the lithosphere as many geological gravity currents e g plume heads and lava flows spread they cool and thereby become more viscous and dense all gravity currents initially spread at the same rate as the isothermal currents predicted by huppert 1982 however currents with temperature dependent viscosity and or buoyancy eventually go to a much slower spreading rate than the isothermal currents moreover unlike the isothermal gravity currents cooling variable viscosity and or variable buoyancy currents do not conserve shape as they spread both constant volume and constant volume flux currents with strongly temperature dependent viscosity develop steep sided flat topped plateau shapes which become more rounded once the currents lose most of their heat currents with temperature dependent buoyancy develop inflections or even extensive swelling at their flow fronts the surface expression of the edge steepening effect in mantle plume heads is likely to be filtered by lithospheric flexure but may contribute to the flattened plateau shape inferred by wessel 1993 for the hawaiian swell the frontal inflation effect due to variable buoyancy may contribute to the dual lobe structure of the hawaiian swell gravity anomaly and suggests an alternate physical mechanism for forming the torus or horseshoe shaped geochemical patterns in the galapagos and the marquesas hotspots perhaps most significantly the gravity current model also predicts the thermal i e degree of melting pattern for galapagos and marquesas hotspots more readily than the traditional entrainment models

volcanic vent self similar clustering and crustal thickness in the northern main ethiopian rift 1 the spatial distribution of volcanic vents in the northern ethiopian rift has been analysed in terms of their self similar clustering the fractal distribution of vents has been computed for the monogenetic vents cones domes and maar occurring along the rift valley and in the rift margin the self similar clustering of vents has been computed through the analysis of vent centres coordinates by means of the two point correlation method the vents of the northern main ethiopian rift display a self similar clustering characterised by a correlation coefficient of 1 41 0 02 with a size range defined by a lower cut off of 1 1 km and an upper cut off of 26 5 km this analysis indicates a probable crustal thickness of 27 km as indicated by the value of the computed upper cut off this value compares well with other estimates for the crustal and lithosphere thickness in the ethiopian rift

hotspot volcanism close to a passive continental margin the canary islands the canarian archipelago is a group of volcanic islands on a slow moving oceanic plate close to a continental margin the origins of the archipelago are controversial a hotspot or mantle plume a zone of lithospheric deformation a region of compressional block faulting or a rupture propagating westwards from the active atlas mountains fold belt have been proposed by different authors however comparison of the canarian archipelago with the prototypical hotspot related island group the hawaiian archipelago reveals that the differences between the two are not as great as had previously been supposed on the basis of older data quaternary igneous activity in the canaries is concentrated at the western end of the archipelago close to the present day location of the inferred hotspot this is the same relationship as seen in the hawaiian and cape verde islands the latter archipelago associated with a well defined but slow moving mantle plume shows anomalies in a plot of island age against distance which are comparable to those seen in the canary islands these anomalies cannot therefore be used to argue against a hotspot origin for the canaries individual islands in both archipelagoes are characterized by initial rapid growth the shield building stages of activity followed by a period of quiescence and deep erosion erosion gap which in turn is followed by a post erosional stage of activity the absence of post shield stage subsidence in the canaries is in marked contrast with the major subsidence experienced by the hawaiian islands but is comparable with the lack of subsidence evident in other island groups at slow moving hotspots such as the cape verdes comparison of the structure and structural evolution of the canary islands with other oceanic islands such as hawaii and reunion reveals many similarities these include the development of triple mercedes star rift zones and the occurrence of giant lateral collapses on the flanks of these rift zones the apparent absence of these features in the post erosional islands may in part be a result of their greater age and deeper erosion which has removed much of the evidence for their early volcanic architecture we conclude that the many similarities between the canary islands and island groups whose hotspot origins are undisputed show that the canaries have been produced in the same way

volcano spacing and plate rigidity in plane stresses which accompany the flexural deformation of the lithosphere under the load adjacent volcanoes may govern the spacing of volcanoes in hotspot provinces specifically compressive stresses in the vicinity of a volcano prevent new upwelling in this area forcing a new volcano to develop at a minimum distance that is equal to the distance in which the radial stresses change from compressional to tensile the inflection point if a volcano is modeled as a point load on a thin elastic plate then the distance to the inflection point is proportional to the thickness of the plate to the power of 3 4 compilation of volcano spacing in seven volcanic groups in east africa and seven volcanic groups of oceanic hotspots shows significant correlation with the elastic thickness of the plate and matches the calculated distance to the inflection point in contrast volcano spacing in island arcs and over subduction zones is fairly uniform and is much larger than predicted by the distance to the inflection point reflecting differences in the geometry of the source and the upwelling areas

the role of lithospheric processes on the development of linear volcanic ridges in the azores abstract linear volcanic ridges lvrs are widespread along the azores plateau and are often used as a tectonic marker of the surface stress field nevertheless the mechanisms that drive the emplacement and development of these structures are not well established and they have been attributed to the plateau diffuse deformation off rift extension or the result of the interaction between a hotspot and the brittle lithosphere this study hypothesizes that linear volcanic ridges are the result of magma emplacement into pre existing damaged lithosphere using a 3d finite element representation of the brittle lithosphere and underlying ductile mantle and assuming that the deformation is driven by plate boundary forces applied at the edges as describe by global plate kinematic models the brittle layer is described by an elastoplastic rheology with progressive damage where fractures are assumed to be analogous to localized shear bands the ductile mantle underneath is modeled as a viscoelastic layer that exerts a shear drag at the base of the brittle layer the modeling shows that lithospheric processes alone can justify the spatial distribution of linear volcanic ridges and even the development of the faial ridge the factors controlling the fracturing pattern are the plate geometry and velocity boundary conditions the shearing introduced at the east azores fracture zone gloria fault limit and the interaction between the viscous mantle and the spatially varying brittle plate thickness along the terceira rift the predicted fractures match the orientation of the lvrs in the second n135 n140 and third n150 to n s sectors and provide an explanation for the arcuate shape of the rift itself the brittle plate thickness variations are crucial for the development of the more recent lvrs which are predicted to occur along the faial ridge in the best fit model the top mantle viscosity is 1 10 22 pa s at 5 15 km depth and the present day fracture network takes 3 ma to develop

melting dehydration and the geochemistry of off axis plume ridge interaction 1 we present results from a series of two dimensional numerical experiments in which synthetic melt compositions are calculated for a system in which a thermally buoyant off axis mantle plume interacts with a nearby ridge axis spatial gradients in synthetic melt properties are compared to observed spatial gradients in geochemistry from the easter salas y gomez system in an effort to constrain the dynamics of mantle flow in off axis plume ridge systems results indicate that observed gradients in radiogenic isotopic ratios between the ridge axis and the plume require significant heating of the ambient mantle adjacent to the plume this heating allows ambient mantle to melt off axis but also attenuates the flow from the plume to the ridge when increases in viscosity due to dehydration during melting are considered spatial gradients in the geochemical properties of synthetic melts become extremely sharp at odds with the observational data this may indicate that viscosity increases due to dehydration are not significant in off axis plume ridge systems

the influence of elastic thickness non uniformity on viscoelastic crustal response to magma emplacement application to the kutcharo caldera eastern hokkaido japan

in situ sand state from cpt evaluation of a unified approach at two canlex sites cet article est consacre a l analyse des donnees de cpt dans les sables afin de deduire l indice des vides a partir des resistances a la penetration au cone l on a etudie a l interieur d un nouveau cadre de reference deux sites de canlex l un appele site syncrude comprenant un depot de sable de steriles relativement homogenes a fort mcmurray alberta et l autre qui est un des sites de la phase ii constitue d un depot de sable naturel dans le delta du fleuve fraser pres du tunnel massey en colombie britannique l approche proposee considere que la resistance en pointe normalisee des sables est reliee a un parametre d etat normalise au niveau initial de contrainte et a la contrainte a l etat critique la methode d interpretation fournit l etat in situ d un depot de sable donne et requiert la connaissance des parametres a l etat critique qui peuvent etre determines en laboratoire sur des echantillons reconstitues cependant il est essentiel d obtenir ces parametres sur une plage etendue de contraintes incluant les contraintes pour lesquelles le broyage des grains est produit par cisaillement une concordance etroite a ete obtenue sur le site de syncrude qui est un depot relativement jeune cependant l analyse des donnees de cpt du site de massey suggere que le vieillissement et ou la cimentation influencent la resistance a la penetration au cone donc l etat in situ si les valeurs non corrigees du cpt sont utilisees

trade off in production between adjacent seamount chains near the east pacific rise bathymetric data and side scan sonar images collected near the southern east pacific rise between 15 and 19 s1 2 have revealed many seamounts on the west flank of the rise most of which are organized into chains running perpendicular to the rise axis the number of seamounts of 5 km diameter is at least twice that expected for average east pacific sea floor3 the formation of numerous small 5 myr linear seamount chains and the tendency for fresh lava flows to be found primarily at the near ridge ends of the chains suggest that there are plume like sources in the upper mantle which are relatively stationary active for extended periods and affected by adjacent sources

imaging rapidly deforming ocean island volcanoes in the western galapagos archipelago ecuador using local body wave arrival time tomography methods to determine 3 d seismic velocity structure we imaged the plumbing system of sierra negra volcano galapagos this hot spot volcanic chain includes some of the fastest deforming volcanoes in the world making this an ideal location to study shield volcano plumbing systems we inverted p and s wave arrivals recorded on a 15 station temporary array between july 2009 and june 2011 using an a priori 1 d velocity model constrained by offshore refraction studies with local seismicity from nearby volcanoes as well as the ring fault system the model resolution is good between depths of 3 and 15 5 km the propagation of s waves throughout this volume argues against any large high melt accumulations although a shallow melt sill may exist above 5 km we image a broad low velocity region 25 km laterally below sierra negra at depths 8 15 km no large regional velocity increase is found within the limits of good resolution suggesting that crust is thicker than 15 km beneath the western galapagos archipelago our results are consistent with crustal accretion of mafic cumulates from a large volume magma chamber that may span the boundary between preplume and accreted crust the similarity between our results and those of hawaii leave open the possibility that the crust has also been thickened by under plating

the cone penetration test in sands part ii general inference of state the state parameter concept provides a new method of characterizing sand behaviour but the utility of the concept relies on the ability to measure the state parameter in situ part i of this paper demonstrated a relationship between normalized cone resistance and state parameter for monterey sand in this paper the state parameter approach is applied to data from calibration chamber tests on several sands it is shown that this approach leads to a common relationship for all the data that includes the effects of material type quantified by the slope of the steady state line the state parameter for a sand can therefore be determined in situ with a reasonable precision using a general framework of interpretation which applies to all uncemented sands la notion de parametre d etat fournit une nouvelle methode pour caracteriser le comportement des sables mais son utilite depend de la possibilite de mesurer le parametre d etat in situ la premiere partie de cet article demontre une relation entre la resist

distribution of large pacific seamounts from geosat ers 1 implications for the history of intraplate volcanism we characterize the seamount distribution on the pacific plate using the gridded vertical gravity gradient vgg or geoid curvature derived from geosat and ers 1 satellite altimetry the vgg amplifies short wavelength information and suppresses longer wavelength components making it suitable for seamount detection purposes furthermore the vgg over seamounts has a much more pronounced zero crossing than that of the free air anomaly faa the distance to the zero crossing can be used as a proxy for seamount radius after removing a regional field obtained by robust median filtering we identify seamount amplitudes and locations from local maxima in the vgg grid the radius of a seamount is more difficult to estimate since seamounts tend to cluster and overprint each other s signals individual seamounts are modeled as gaussian axisymmetric objects loading an elastic lithosphere the vgg over such features can be approximated by a simple analytical expression which we use to determine the zero crossing distances for overlapping seamounts by using the vgg the maximum amplitude and distance to the zero crossing become largely independent of the elastic plate thickness and infill density we do forward modeling of gaussian seamounts and their gravimetric response and create a look up table that relates seamount faa in milligals vgg in eotvos and zero crossing distance in kilometers to actual height and radius in kilometers the frequency size distribution of these predicted seamount heights follows a power law for heights between 2 and 8 km the seamount density number of seamounts per area is greatest in the central pacific we confirm earlier results suggesting that the majority of large seamounts are located in the western region of the pacific plate on older crust as crustal age increases so does seamount density peaking on 100 130 m y crust supporting suggestions of high magmatism in the cretaceous we demonstrate that there may be an empirical relationship between the seamount vgg amplitude and the age of the lithosphere at the time of seamount formation and invert this relationship to predict seamount ages from vgg amplitudes these pseudo ages have large uncertainties but nevertheless may be used to investigate temporal fluctuations in pacific intraplate volcanism our results indicate that seamount intraplate volcanism attained a maximum level in the mid cretaceous to late cretaceous about 70 120 ma apparently contemporaneous with the formation of large oceanic plateaus in the pacific

ground freezing and sampling of foundation soils at duncan dam in situ ground freezing to obtain undisturbed samples of a loose sand beneath the duncan dam in british columbia is described this was the first known use of ground freezing to assist in obtaining samples at depth greater than 10 m in canada once frozen the sand was cored and brought to the surface using a cold regions research and engineering laboratory core barrel which is used extensively in permafrost regions the design installation and performance of the liquid nitrogen freezing systems are described in detail the drilling sampling and preparation of the frozen core for transport to the testing facility are also outlined the quality of the core retrieved during the sampling was judged to be excellent and good agreement was found between the void ratios measured using both the frozen core and high quality gamma gamma density logging techniques which were performed adjacent to ground freezing and sampling locations key words ground freezing cohesionless soils undisturbed sampling

lithospheric flexure under the hawaiian volcanic load internal stresses and a broken plate revealed by earthquakes several lines of earthquake evidence indicate that the lithospheric plate is broken under the load of the island of hawai i where the geometry of the lithosphere is circular with a central depression the plate bends concave downward surrounding a stress free hole rather than bending concave upward as with past assumptions earthquake focal mechanisms show that the center of load stress and the weak hole is between the summits of mauna loa and mauna kea where the load is greatest the earthquake gap at 21 km depth coincides with the predicted neutral plane of flexure where horizontal stress changes sign focal mechanism p axes below the neutral plane display a striking radial pattern pointing to the stress center earthquakes above the neutral plane in the north part of the island have opposite stress patterns t axes tend to be radial the m6 2 honomu and m6 7 kiholo main shocks both at 39 km depth are below the neutral plane and show radial compression and the m6 0 kiholo aftershock above the neutral plane has tangential compression earthquakes deeper than 20 km define a donut of seismicity around the stress center where flexural bending is a maximum the hole is interpreted as the soft center where the lithospheric plate is broken kilauea s deep conduit is seismically active because it is in the ring of maximum bending a simplified two dimensional stress model for a bending slab with a load at one end yields stress orientations that agree with earthquake stress axes and radial p axes below the neutral plane a previous inversion of deep hawaiian focal mechanisms found a circular solution around the stress center that agrees with the model for horizontal faults the shear stress within the bending slab matches the slip in the deep kilauea seismic zone and enhances outward slip of active flanks

episodic kinematics in continental rifts modulated by changes in mantle melt fraction gps measurements are used to investigate the continental rift system of north island new zealand and to develop a model for short term deformation involving flexing of an elastic upper crust caused by episodic changes in mantle viscosity and melt fraction direct observation of mantle flow dynamics beneath spreading oceanic crusts is difficult but similar processes occur below rifts in the continental crust and so can be inferred from satellite observations of the moving crust simon lamb et al use ten years of continuous gps measurements from a back arc continental rift system in north island new zealand to investigate the dynamics of mantle flow beneath seafloor spreading centres they observe deformation which they conclude to be the result of flexure of an elastic upper crust pulled downwards or pushed upwards along the rift axis by a driving force at depth they propose that this flexure is caused by melt induced episodic changes in mantle viscosity in their model a drop in melt fraction due to melt extraction raises the mantle viscosity and drives subsidence whereas melt accumulation reduces viscosity and allows uplift oceanic crust is created by the extraction of molten rock from underlying mantle at the seafloor spreading centres found between diverging tectonic plates modelling studies have suggested that mantle melting can occur through decompression as the mantle flows upwards beneath spreading centres1 but direct observation of this process is difficult beneath the oceans continental rifts however which are also associated with mantle melt production are amenable to detailed measurements of their short term kinematics using geodetic techniques here we show that such data can provide evidence for an upwelling mantle flow as well as information on the dimensions and timescale of mantle melting for north island new zealand around ten years of campaign and continuous gps measurements in the continental rift system known as the taupo volcanic zone reveal that it is extending at a rate of 6 15 millimetres per year however a roughly 70 kilometre long segment of the rift axis is associated with strong horizontal contraction and rapid subsidence and is flanked by regions of extension and uplift these features fit a simple model that involves flexure of an elastic upper crust which is pulled downwards or pushed upwards along the rift axis by a driving force located at a depth greater than 15 kilometres we propose that flexure is caused by melt induced episodic changes in the vertical flow forces that are generated by upwelling mantle beneath the rift axis triggering a transient lower crustal flow a drop in the melt fraction owing to melt extraction raises the mantle flow viscosity and drives subsidence whereas melt accumulation reduces viscosity and allows uplift processes that are also likely to occur in oceanic spreading centres

a low relief shield volcano origin for the south kaua i swell 1 the south kaua i swell sks is a 110 km x 80 km ovoid bathymetric feature that stands 2 km high and abuts the southern flank of the island of kaua i the origin of the sks was investigated using multibeam bathymetry and acoustic backscatter gravity data radiometric ages and geochemistry of rock samples most of the sks rock samples are tholeiitic in composition with ages of 3 9 5 4 ma indicating they were derived from shield volcanism the ages and compositions of the sks rocks partially overlap with those of the nearby ni ihau kaua i and west ka ena volcano complexes the sks was originally described as a landslide however this interpretation is problematic given the ovoid shape of sks its relatively smooth flat to convex surface and the lack of an obvious source region that could accommodate what would be one of earth s most voluminous 6 x 103 km3 landslides the morphology size and the surrounding gravity anomaly are more consistent with the sks being a low relief shield volcano which was partially covered with a small volume of landside debris from south kaua i and later with some secondary volcanic seamounts a shield origin would imply that hawaiian and possibly other hotspot shield volcanoes can take on a wider variety of forms than is commonly thought ranging from tall island building shields to smaller edifices such as ka ena ridge and mahukona to even lower relief volcanoes represented by the sks and possibly the south west o ahu volcanic field

global distribution of seamounts inferred from gridded geosat ers 1 altimetry using a forward modeling approach based on an axisymmetric gaussian seamount i characterize the global seamount distribution by locating circular maxima in the gridded vertical gravity gradient field derived from altimetry collected by the geosat and ers 1 satellite missions the global seamount distribution is long tailed and resembles a power law distribution for seamounts in the height range 2 7 km smaller seamounts are not well isolated by my technique nor are they well resolved in the gridded data several factors are likely to influence the height of volcanic seamounts such as melt availability magma driving pressure and plate thickness the observed relationship between seamount gravimetric amplitudes and the age of the underlying seafloor implies that there is an upper limit on seamount heights whether a seamount will reach that height depends most likely on supply side factors such as melt availability and magma driving pressure but the limiting height itself seems more likely to be controlled by the strength of the oceanic plate specifically compressional stresses directly beneath the seamount as a consequence of the lithosphere s flexural response to loading may eventually exceed the magma driving pressure and prevent magma from reaching the surface thus limiting the growth of the seamount because oceanic plate strength primarily is controlled by plate age the limit on seamount height is inferred to be a simple function of plate age at the time of seamount emplacement using analytical solutions i present a simple flexural model that predicts the observed global height age relationship

a procedure for the joint inversion of regional and teleseismic long period body waves a procedure for the joint inversion of regional and teleseismic long period waveforms for source parameters is presented three test cases demonstrate that the inclusion of regional distance seismograms to a data set of teleseismic observations stabilizes the inversion process and adds valuable constraints to the source parameter estimates particularly when the teleseismic green s functions are inadequate the added stability and constraints from regional waveforms can be attributed to the robust nature of regional distance green s functions as well as the added coverage of the focal sphere that regional data provide singular value decomposition is a useful inversion method that is well suited for this study because it provides a measure of the solution dependence on individual observations

plume ridge interaction lithospheric stresses and the origin of near ridge volcanic lineaments 1 in many hot spot ridge systems formation of off axis volcanic chains or lineaments occurs between the hot spot centers and nearby mid ocean ridges in some cases such as galapagos kerguelen and possibly the mid pac mountains and tristan these lineaments appear to meet in a focus zone near the hot spot and fan outward in the direction of the ridge axis the origins of these lineaments are not well known and do not easily fit into typical conceptual models of ridge or hot spot volcanism it has been proposed for the galapagos region that such lineaments are caused by channeling of hot asthenosphere from off axis mantle plumes toward mid ocean ridges where enhanced volcanism initiates island formation morgan 1978 alternatively other workers suggest that these lineaments are controlled by patterns of stress in the lithosphere we examine this latter hypothesis by considering the effects of buoyant uplift and asthenospheric shear on the base of the lithosphere induced by an expanding mantle plume using thin plate theory we calculate the two dimensional plan view pattern of depth integrated stresses in a plate of varying thickness both a straight continuous ridge and a ridge transform ridge system are simulated by a displacement discontinuity boundary element model ridge and transform segments have imposed normal and zero shear tractions and we test different idealized tectonic or far field stress conditions assuming that volcanism is promoted by lithospheric tension and aligns along lineaments parallel to trajectories of least tensile stress calculations reproduce the rough fan shaped pattern of lineaments between the galapagos archipelago and the galapagos spreading center the focus of the fan shape is over the plume center when it interacts with a straight ridge but the fan focus appears closer to a segmented ridge offset by a transform fault if the ridge segments are more tensile than the far field stress this condition provides a plausible explanation for the apparent focus at the galapagos north of the hot spot center the width of the fan pattern along the ridge axis is predicted to increase as the plume ridge separation increases and as the far field stress becomes more tensile parallel to the ridge the observed width along the galapagos spreading center is consistent with a nearly isotropic remote stress models predict the lithospheric tension caused by plumes to promote lineament formation on only young lithosphere in support of this prediction a compilation of data from 23 hot spots shows that lineament formation is common near hot spots with plume ridge separations of 1250 km or on lithosphere of 25 ma but not on older lithosphere

problems with interpretation of sand state from cone penetration test considerable attention has been given to the inference of sand density from indirect tests particularly the cone penetration test cpt data from tests performed in large scale chambers have demonstrated that for a given sand there is an approximately unique relationship between cpt tip resistance density or void ratio and effective stress level data have been presented to support the supposition that cpt tip resistance if normalized by division by the mean effective stress is uniquely related to the difference between the current void ratio and the void ratio at the steady state at the same mean stress level the paper presents a study of chamber test data for the ticino sand and demonstrates that there is no such unique relationship for this sand use of published correlations that fail to recognize this and other potentially important factors could result in interpretations of sand state that if carried through to design could in some circumstances be catastrophic a series of flow slides tha

factors affecting at rest lateral stress in artificially cemented sands this paper presents the results of a laboratory study on the at rest lateral stress and ko of two artificially cemented sands a modified oedometer ring was used to measure the lateral stress of cemented and uncemented sands test materials were no 3 ottawa sand and a marine sand with portland cement the specimens were prepared using the method of undercompaction to minimize the influence of specimen preparation on test results the cement contents were 0 0 5 1 0 2 0 4 0 and 8 0 by the weight of dry sand the water content of the specimens was 4 of the weight of dry sand and cement when the sands were cured under zero confining pressure the test results indicated the following the at rest lateral stress in cemented sands decreases significantly with increasing cement content the relationship between the vertical and at rest lateral stress is nonlinear and the value of ko increases with increasing vertical stress and the lateral stress decreases with sand density and curing period when the s

sizes and ages of seamounts using remote sensing implications for intraplate volcanism satellite altimetry was used to identify and characterize pacific intraplate seamounts the gravimetric amplitudes of seamounts appear to be related to the age difference between the sea floor and seamounts by inverting this relation pseudo ages can be obtained for undated seamounts these pseudo ages imply that excursions in seamount volcanism generally correlate with times of formation of large oceanic plateaus

discrete alternating hotspot islands formed by interaction of magma transport and lithospheric flexure the large scale geometry and age progression of many hotspot island chains such as the hawaiian emperor chain are well explained by the steady movement of tectonic plates over stationary hotspots but on a smaller scale hotspot tracks are composed of discrete volcanic islands whose spacing correlates with lithospheric thickness1 moreover the volcanic shields themselves are often not positioned along single lines but in more complicated patterns such as the dual line known as the kea and loa trends of the hawaiian islands2 3 here we make use of the hypothesis that island spacing is controlled by lithospheric flexure1 to develop a simple nonlinear model coupling magma flow which feeds volcanic growth to the flexure caused by volcanic loads on the underlying plate for a steady source of melt underneath a moving lithospheric plate magma is found to reach the surface and build a chain of separate volcanic edifices with realistic spacing if a volcano is introduced away from the axis of the chain as might occur following a change in the direction of plate motion the model perpetuates the asymmetry for long distances and times thereby producing an alternating series of edifices similar to that observed in the kea and loa trends of the hawaiian island chain

the specific case of the mid proterozoic rapakivi granites and associated suite within the context of the columbia supercontinent abstract rapakivi granites and the associated suite anorthosite mangerite and charnockite that developed during the mid proterozoic escape the global rules that control usual granitic magma formation about 40 points that characterise the proterozoic magmatism confirm the originality of the magmatism rapakivi granites developed without a global orogenic context within the supercontinent columbia the intrusions extend from the east european shield to the western us through fennoscandia greenland and labrador other occurrences in the amazonian shield australia or south china are less well documented they show no definite trend in age or chemistry that would explain large scale mantle plume effects a mantle upwelling of material is contradictory with the re assembly of a supercontinent because it occurred before this magmatic episode 1 9 1 8 ga at 1 7 ga the supercontinent columbia amalgamated with the collision of the yapavai and mazatzal provinces a model is suggested that takes into account the supercontinent re assembly defining a downwelling flow in the mantle that anchors the continent above it in contrast to a material flow heat is still delivered to the base of the continental lithosphere and is focused toward the juvenile suture zone the base of the crust must reach 1200 1300 c before producing anorthosite magmas under such a high temperature gradient lasting over a long time magmas are transferred toward the upper crust giving the thin 5 km and square shape 100 km that the intrusions presently have heat delivery is essentially conductive leading to long time spans for intrusions the presence of the supercontinent immobile over a descending cell poloidal mode of convection developed a tangential force toroidal mode of convection that partly split the continent through strike slip deformation due to plate rotation it developed progressively between 1 57 and 1 3 ga starting from fennoscandia and then passing to amazonia western us and labrador in a clockwise sense the associated rotation induced sinistral shear manifested by small scale shear zones and the orientation of late magmatic facies topaz bearing granites in each province the proterozoic magmatism appears to be unique because it requires a supercontinent with a zone of juvenile crust surrounded by older cratons the present moho still shows remnants of this process having bumpy undulations that may reach 22 km in amplitude over a distance of 200 km

liquefaction and flow failure during earthquakes two aspects of seismically induced liquefaction are discussed which are of vital engineering significance the triggering condition and the consequences of liquefaction the triggering condition is examined with respect to liquefaction analysis note being taken of the onset condition which is governed by cyclic strength consequences of liquefaction are discussed with respect to post seismic stability analysis in which the residual strength plays a major role procedures used for liquefaction analysis based on the results of in situ sounding tests are introduced and the applicability of this method for estimating associated ground settlements is discussed the evaluation of residual strength requires a better understanding of undrained sand behaviour results of extensive laboratory rests on japanese standard sand are examined and new index parameters are proposed to quantify undrained sand behaviour better the results of laboratory tests on silty sands are examined in the same way ah the results are