crustal structure of the western new england appalachians and the adirondack mountains we present an interpretation of the crustal velocity structure of the new england appalachians and the adirondack mountains based on a seismic refraction wide angle reflection experiment in eastern north america extending from the adirondacks in new york state through the northern appalachians in vermont and new hampshire to central maine modeling of the eastern portion of the profile within the new england appalachians shows a subhorizontal layered crust with upper crustal velocities ranging from 5 5 to 6 2 km s a midcrustal velocity of 6 4 km s and a lower crustal velocity of approximately 6 8 km s crustal thickness increases from 36 km beneath maine to 40 km in vermont little evidence is seen for structures at depth directly related to the white mountains or the green mountains a major lateral velocity change in the upper and mid crust occurs between the appalachians and the adirondacks this boundary projecting to the surface beneath the champlain valley dips to the east beneath the green mountains and extends to a depth of 25 km below the eastern edge of the connecticut valley synclinorium in vermont the tahawus complex a series of strong horizontal reflections at 18 24 km depth beneath the adirondack highlands is seen to dip eastward beneath vermont upper crustal rocks in the adirondack mountains have poisson s ratios of 0 28 0 01 that can be correlated with the marcy anorthosite pois son s ratios of 0 24 0 01 calculated for rocks of the connecticut valley synclinorium indicate a siliceous upper crust in vermont the lower crust is considered to be best represented by intermediate to mafic granulites a high poisson s ratio 0 26 0 27 tends to support a mafic lower crust in the new england appalachians this seismic refraction wide angle reflection experiment provides further evidence for the obduction of the allochthonous western appalachian units onto grenvillian crust above a zone of detachment that penetrates at least to midcrustal depths and was the locus of successive paleozoic thrusting

vertical cyclic loading response of shallow skirted foundation in soft normally consolidated clay skirted foundations are a potential foundation solution for a range of offshore structures including hydrocarbon and renewable energy platforms and subsea structures offshore foundations can be s

response of normally consolidated kaolin clay under irregular cyclic loading and comparison with predictions from the accumulation procedure the accumulation procedure on contour diagrams of shear strain is used in geotechnical design to account for the effect of cyclic loading on offshore foundations in this paper contour diagrams of

the role of premagmatic rifting in shaping a volcanic continental margin an example from the eastern north american margin both magmatic and tectonic processes contribute to the formation of volcanic continental margins such margins are thought to undergo extension across a narrow zone of lithospheric thinning 100 k

formation of immature asphalt from organic rich carbonate rocks i geochemical correlation abstract the formation of low maturity asphaltic oils immature asphalts from carbonate source rocks was investigated the senonian bituminous rocks sbr in israel are organic rich carbonate rocks that were deposited in a high productivity environment and they are part of a sedimentary sequence that also contains cherts and phosphorites the sbr were studied in different basins and the samples are from outcrops and three deep drillholes the bitumen contents of the rocks are exceptionally high up to 700 mg g c org and immature asphalts are found to be associated with them geochemical analysis indicates that the bitumens are indigenous to the host sbr and the associated asphalts are bitumens that have migrated a short distance with negligible chemical fractionation the high heteroatom content of the kerogens up to 30 in the sbr is suggested as a possible cause of the generation of asphaltic oils in an early stage of maturation

comparison of truly undrained and constant volume direct simple shear tests the paper describes a chamber for the norwegian geotechnical institute s direct simple shear device that enables undrained tests with pore pressure measurements to be run the results of undrained

a geophysical study of the earth s crust in central virginia implications for appalachian crustal structure a regional seismic reflection line i 64 across the virginia piedmont has provided a stacked section suitable for an integrated interpretation of geophysical data in the region a highly reflective upper crust an allochthonous blue ridge province underlying thrust sheets including the blue ridge master decollement and a basal decollement at a depth of about 9 km 3 s are confirmed on the seismic data immediately east of the blue ridge province appalachian structures plunge to as much as 12 km 4 s depth the evington group hardware terrane and chopawamsic metavolcanic rocks carolina terrane crop out in the piedmont province and numerous eastward dipping reflections originate from these rocks in the subsurface these eastward dipping reflectors overlie a gently west dipping 10 15 highly reflective zone that varies in depth from 1 5 s 4 5 km beneath the goochland terrane to 4 s 12 km beneath the rocks of the evington group some of the overlying eastward dipping reflections apparently root in this zone the zone may include decollement surfaces along which the overlying rocks were transported relatively few reflections originate from within autochthonous grenville basement at the western end of the profile the goochland granulite terrane is interpreted to be a westward thrust nappe structure that has overridden a portion of the chopawamsic metavolcanic rocks a broad zone of east dipping 20 45 reflections bounds the goochland terrane on the east these reflections may originate from deformation zones and continue to moho depths they appear to be correlative with similar events seen on other appalachian lines the pervasiveness of the zone of east dipping events on other seismic reflection lines and the continuity of the adjacent piedmont gravity high suggest continuity of crustal features along the length of the appalachians a major conclusion of this study is that crustal thinning is responsible for the main components of the gravity field in virginia that is the appalachian gravity gradient and the piedmont gravity high the crust thins from about 52 km beneath the appalachian mountains to about 35 km beneath richmond virginia and then rethickens by up to 10 km beneath the zone of east dipping reflections mylonites east of richmond the i 64 seismic data also contain a sequence of reflections at about 9 12 s indicative of lower crustal layering the base of this zone of reflections coincides almost exactly with the mohorovicic discontinuity interpreted from earlier refraction work the layering extends about 70 km west from richmond virginia and is interpreted as a lower crustal transition zone that is believed to persist across most of virginia

stability threshold for cyclic loading of saturated clay this paper presents the results of an experimental investigation performed to study the stability threshold under cyclic repeated loading and the postcyclic static strength of a sensitive clay from the hudson bay region the strain rate and structure effects were also studied by carrying out monotonic and cyclic triaxial tests at both slow and rapid strain rates or frequencies and at confining pressures above and below the apparent preconsolidation pressure the stability threshold for both structured and normally consolidated grande baleine clay is about 60 65 of the original undrained shear strength measured at the same strain rate as that used in the repeated loading test the undrained shear strength and the failure envelope remain essentially unchanged if the repeated preloading is kept below the threshold the clay structure remains unaltered by this preloading key words clay stability threshold cyclic loading earthquake postcyclic strength

offshore extent of gondwanan paleozoic strata in the southeastern united states the suwannee suture zone revisited abstract the recognition of the suwannee terrane in southeastern north america was a critical step in advancing our current understanding of the tectonic evolution of ocean basins unfortunately further clarification of the boundaries of the suwannee terrane has proven difficult due to the thick coastal plain cover limited well log analyses and a paucity of seismic reflection data onshore we present the results from a new compilation and analysis of legacy marine seismic reflection refraction and well data from offshore the southeastern united states which reveals in the subsurface a previously unmapped lower paleozoic sedimentary section spanning the continental shelf from florida to north carolina previously only identified in two deep offshore wells cost ge 1 and transco 1005 1 this paleozoic platform sequence is identified in seismic reflection profiles as a package of low frequency sub horizontal laterally continuous reflectors which are clearly discordant with and distinct from the overlying mesozoic and cenozoic stratigraphy above the post rift unconformity pru the inferred base of the paleozoic sequence is marked by the downward diminution of parallel seismic reflectors as well as an increase in seismic velocities to 6 km s observed on numerous offshore seismic refraction surveys while clearly deformed in some areas these paleozoic strata are generally sub horizontal range in thickness from 4 to 6 km and can be mapped continuously over an area in excess of 130 000 km 2 similar sedimentary rocks have been recognized from onshore exploration wells in florida since the 1930s and were subsequently identified to be part of the suwannee basin within the larger exotic suwannee terrane of gondwanan affinity recognition of the presence and extent of these gondwanan strata offshore implies 1 the inferred position of the suwannee suture zone offshore lies 200 km further north approximately along the boundary between the carolina terrane and the charleston terrane 2 previously identified terranes brunswick charleston suwannee northern florida are likely distinct crustal blocks but their amalgamation predates deposition of the overlying paleozoic section of the suwannee basin 3 collectively this crust represents the gondwanan continent based on the size and presence of a stable platform stratigraphy nominally doubling the size of the last sutured terrane the suwannee terrane

new cocorp profiling in the southeastern united states part ii brunswick and east coast magnetic anomalies opening of the north central atlantic ocean new cocorp profiles on the coastal plain of georgia and northern florida support the hypothesis that the brunswick anomaly marks a late paleozoic suture they do not support the alternate view that this anomaly is caused by a mesozoic rift basin the trend of the brunswick anomaly relative to the appalachian gravity gradient indicates that in westernmost georgia and adjacent alabama african basement suwannee terrane is in proximity to autochthonous north american basement grenville farther east one or more paleozoic accreted terranes intervene between the north american and african sides of the orogen offshore the brunswick anomaly closely parallels the east coast magnetic anomaly this relationship implies that the east coast magnetic anomaly marks not only the present continental oceanic crustal transition but also the northward continuation of the late paleozoic suture between north america and africa transitional crust beneath the carolina trough baltimore canyon trough and correlative parts of the african atlantic margin is thus likely to have formed within a preexisting suture zone the dramatic change in character of the u s atlantic margin southward from the carolina trough to the blake plateau probably reflects the fact that two different types of prerift crust are juxtaposed in this region

source rock evaluation by well log analysis lower toarcian hils syncline abstract the feasibility of conducting petroleum source rock evaluations from well log data was examined using three continuously cored sections immature mature and postmature stages of the lower toarcian posidonia shale northern germany logs depicting natural gamma emission k u th bulk density sonic travel time and resistivity were utilised as was the borehole televiewer for fracture control selected data from these logs were correlated with parameters of source richness hydrocarbon content and maturity the resulting three dimensional cross plot shows at a glance well by well comparison of facies maturity and hydrocarbon content a simple correlation between organic geochemical and petrophysical parameters is of course not perfect since log response is complex and affected by mineralogical and pore fluid properties of the rock as well as by organics however source rock characterization by wireline logging is still a fast and therefore economical method relative quick look comparisons from well to well are possible without calibration to core data and can easily be performed at once at the drill site the present application is limited to clastic source rocks in basins with simple geologic histories

deep velocity structure of rifted continental crust u s mid atlantic margin from wide angle reflection refraction data we present new ocean bottom wide angle seismic data collected during the 1990 edge mid atlantic multichannel seismic experiment which provide a measurement of the deep velocity structure of rifted appalachian continental crust beneath the u s east coast continental margin reflections from the entire crust and moho are visible from offsets of zero to 100 km one dimensional inverse traveltime modeling reveals a 34 km thick crust consisting of four layers beneath the post rift sediments with velocities of 5 9 6 3 6 4 and 6 85 km s this velocity structure is indistinguishable from that found beneath several appalachian terranes in the northern appalachians of new england the average velocity of 6 85 km s in the lower crust limits the landward extent of the high velocity 7 2 7 4 km s lower crust found farther seaward and supports the interpretation of that layer as the result of rift related magmatic underplating rather than as thinned pre existing lower continental crust

structure of the lower crust beneath the carolina trough u s atlantic continental margin data from three large offset seismic profiles provide information on the crustal structure beneath the carolina trough the profiles obtained by the u s geological survey the naval oceanographic research development agency and the scripps institution of oceanography in 1985 were oriented parallel to the trough and were located 1 seaward of the east coast magnetic anomaly ecma which is generally thought to represent the boundary between oceanic and continental crust 2 along the axis of the trough between the ecma and the hinge zone which is thought to reflect the landward limit of highly stretched and altered transitional crust and 3 along the carolina platform landward of the basement hinge zone on crust thought to have been thinned only slightly during rifting these data constrain the velocity structure of the lower crust and provide evidence for a thick lens of high velocity 7 1 km s lower crustal material that extends beneath the carolina trough and the adjacent ocean basin this lens reaches a maximum thickness of about 13 km beneath the deepest part of the trough thins to about 5 km seaward of the ecma and is either very thin or absent landward of the hinge zone it is interpreted to represent material that was underplated beneath and or intruded into the crust during the late stage of continental rifting and that led to an anomalously thick plutonic layer during the early seafloor spreading phase these data thus support the recent conclusions of white et al 1987b and mutter et al 1988 that the initiation of seafloor spreading is attended in many if not most cases by the generation of an anomalously large volume of melt

relation between source rock properties and wireline log parameters an example from lower jurassic posidonia shale nw germany abstract the relationships between source rock quality and wireline log parameters were established for the lower jurassic posidonia shale the most prolific petroleum source rock of central europe wireline logs used are the gamma ray spectrometry density sonic and various resistivity logs the organic geochemical parameters considered include the organic carbon content hydrogen index and the hydrocarbon potential expressed by pyrolysis yield the case history presented is based on a continuous core through the entire posidonia shale interval from a location where this source rock is immature care was taken to detect and to avoid samples and log values influenced by bore hole roughness and fractures fair correlations were observed only between uranium content from gamma ray spectrometry log and organic carbon content no correlation was recognized between uranium content and kerogen type as defined by hydrogen indices for various reasons density sonic and resistivity logs did not provide useful data in this study three rock units with irregular high and low uranium contents could be differentiated possible causes for this tripartition are different environments during deposition and postdepositional redistribution of uranium during early diagenesis and in association with fractures

avalon terrane in eastern coastal maine seismic refraction wide angle reflection data a 145 km long seismic refraction line recorded parallel to the eastern coastline of maine within the avalon terrane provides information about the crustal velocity structure within the avalon block and its relation to other appalachian terranes a crustal velocity model for the upper 8 km determined by using two dimensional ray tracing accounts for all first arrivals on the traveltime curves for each of the shots recorded and shows that except for a thin surficial layer of velocity 5 0 5 3 km s upper crustal granites and country rocks have velocities in the range 6 0 6 3 km s and gabbros have a 6 5 km s velocity to determine the lower crustal structure deep reflections were analyzed by applying normal moveout corrections routinely used in reflection data processing major reflective boundaries at approximately 3 4 7 and 10 11 s two way traveltime are easily distinguished and are similar to those observed in a near vertical seismic reflection survey crossing the refraction profile at its southwestern end the deepest reflections correspond to the crust mantle boundary at a depth of 34 35 km

threshold shear strain for cyclic pore water pressure in cohesive soils threshold shear strain for cyclic pore water pressure t is a fundamental property of fully saturated soils subjected to undrained cyclic loading at cyclic shear strain amplitude c larger than t residual cyclic pore water pressure changes rapidly with the number of cycles n while at c t such changes are negligible even at large n to augment limited experimental data base of t in cohesive soils five values of t for two elastic silts and a clay were determined in five special cyclic norwegian geotechnical institute ngi type direct simple shear ngi dss constant volume equivalent undrained tests threshold t was also tested on one sand with the results comparing favorably to published data the test results confirm that t in cohesive soils is larger than in cohesionless soils and that it generally increases with the soil s plasticity index pi for the silts and clay having pi 14 30 t 0 024 0 06 was obtained limited data suggest that t in plastic silts and clays practically

simultaneous inversion of reflection and refraction seismic data and application to field data from the northern rio grande rift summary an inversion scheme that determines a velocity model simultaneously from normalincidence reflection and refraction wide angle reflection seismic data has been developed tested and applied to real seismic data simultaneous inversion minimizes the non uniqueness of inversion results a common midpoint cmp stacked reflection section provides a detailed image of the structural configuration in time refraction or wide angle reflection data can be used to derive a velocity model if both refraction data and normal incidence reflection data are available along coincident profiles simultaneous inversion of the data sets can produce an improved model with the extra control of the interface depth provided by reflection data it is also possible to avoid ambiguity of phase identification the commonly used damped least squares dls inversion method often results in significant inversion artefacts we provide effective methods for reducing inversion artefacts using both damping and smoothing from tests using synthetic data we conclude that the simultaneous inversion scheme can improve resolution and can be applied to velocity models with a reasonably complex structure the simultaneous inversion scheme has been successfully applied to coincident seismic reflection and refraction data recorded by the sage program in 1990 1991 in the western boundary area of the rio grande rift near abiquiu new mexico in this example the simultaneous inversion derived a velocity model in which stratigraphic units and extensional fault blocks can be resolved

deep crustal seismology of continental margins this review discusses results from recent seismic experiments at continental margins conducted by u s investigators as well as those by non u s investigators necessary to place the results of u s workers into context continental margins may be characterized as either rifted transform or convergent rifted or passive margins form where continents are torn apart during continental drift transform margins accommodate transform plate motions along strike slip faults such as the san andreas fault at convergent margins oceanic crust is being thrust beneath or subducted under the continental crust all three types of margins are found in north america

contrasting styles of seafloor spreading in the woodlark basin indications of rift induced secondary mantle convection the woodlark basin in the southwest pacific is a young ocean basin which began forming by 6 ma following the rifting of continental and arc lithosphere the n s striking moresby transform divides the oceanic basin into eastern and western parts which have contrasting characteristics seafloor spreading west of moresby transform began after 2 ma and although spreading rates decrease to the west the western basin has faster spreading characteristics than the eastern basin these include 1 500 m shallower seafloor 2 bouguer gravity anomalies that are 30 mgals lower 3 magnetic anomaly and modeled seafloor magnetization amplitudes that are higher 4 a spreading center with an axial high in contrast to the axial valleys of the eastern basin 5 smoother seafloor fabric and 6 exclusively nontransform spreading center offsets in contrast to the eastern basin which has transform faults and fracture zones that extend across most of the basin overall depth contrasts and bouguer anomalies can be matched by end member models of thicker crust 2 km or thinner lithosphere 1 3 in the western basin correlated with these contrasts the surrounding rifted margins abruptly thicken westward of the longitude of moresby transform we examine alternative explanations for these contrasts and propose that rift induced secondary mantle convection driven by thicker western margin lithosphere is most consistent with the observations although rift induced convection has been cited as a cause for the voluminous excess magmatism at some rifted margins the observations in the woodlark basin suggest that this mechanism may significantly affect the morphology structure and geophysical characteristics of young ocean basins in alternate ways which resemble increased spreading rate

the crustal structure in central maine from coherency processed refraction data in 1984 the u s geological surcvey and the canadian department of energy mines and resources conducted an extensive seismic refraction experiment the quebec maine transect project as part of this project a 180 km long seismic refraction profile was recorded along the axis of the central maine synclinorium high near surface velocities of 6 0 6 2 km s made a conventional refraction analysis including first arrivals uninformative below about 10 km peak signal frequencies around 30 hz recorded at all offsets and a trace spacing of 800 m led to severe spatial aliasing effects for secondary arrivals on the record sections to allow a reliable deep structural interpretation a coherency processing technique was applied to the data to enhance phase coherent secondary arrivals in addition interpretation of a coincident wide angle reflection study provided constraints on the deep crustal velocities and structure the crust beneath the central maine synclinorium can be described by three major structural units the upper crust is interpreted as the metasedimentary rocks of the central maine synclinorium with velocities that range from 6 2 to 6 3 km s regions of relative lower velocity 6 0 6 1 km s within the upper crust are interpreted as granitic intrusions low velocity regions modeled at 2 7 km depth with velocities around 5 4 km s are interpreted as seismic evidence for folding and doubling within the upper crustal metasedimentary sequence at 12 15 km depth the base of the synclinorium appears alternately as a strong reflector indicating the presence of layering and also as a weak reflector especially ne of the sebago pluton a 4 km thick boundary layer at 24 km depth is interpreted as a major intracrustal shear zone in which the velocity increases from 6 4 to 6 8 km s the crust thickens from 36 to 40 km going from refraction experiment the quebec maine transect project as part of this project a 180 km long seismic refraction profile was recorded along the axis of the central maine synclinorium high near surf ace velocities of 6 0 6 2 km s made a conventional refraction analysis including first arrivals uninformative below about 10 km peak signal frequencies around 30 hz recorded at all offsets and a trace spacing of 800 m led to severe spatial aliasing effects for secondary arrivals on the record sections to allow a reliable deep structural interpretation a coherency processing technique was applied to the data to enhance phase coherent secondary arrivals in addition interpretation of a coincident wide angle reflection study provided constraints on the deep crustal velocities and structure the crust beneath the central maine synclinorium can be described by three major structural units the upper crust is interpreted as the metasedimentary rocks of the central maine synclinorium with velocities that range from 6 2 to 6 3 km s regions of relative lower velocity 6 0 6 1 km s within the upper crust are interpreted as granitic intrusions low velocity regions modeled at 2 7 km depth with velocities around 5 4 km s are interpreted as seismic evidence for folding and doubling within the upper crustal metasedimentary sequence at 12 15 km depth the base of the synclinorium appears alternately as a strong reflector indicating the presence of layering and also as a weak reflector especially ne of the sebago pluton a 4 km thick boundary layer at 24 km depth is interpreted as a major intracrustal shear zone in which the velocity increases from 6 4 to 6 8 km s the crust thickens from 36 to 40 km going from the ne to the sw end of the profile surface rocks at the sw end of the profile have a metamorphic depth of burial of at least 15 km indicating that the crust below the central maine synclinorium may have been thickened to at least 55 km during paleozoic collisions

the lithosphere below the rockall trough wide angle seismic evidence for extensive serpentinisation abstract the longer range data from wide angle seismic reflection experiments along an axial and transverse profile determined the seismic properties of the shallow mantle lithosphere beneath the rockall trough in the north atlantic two subcrustal p and s wave reflections are observed the first defines a layer 3 10 km thick below the moho where p wave velocities vary from 7 5 to 7 8 km s v p v s ratios increase within this layer from 1 80 in the north to 1 83 in the south of the basin along the axial profile the second reflection from approximately 34 km depth identifies a layer 15 20 km thick with a vp velocity of approximately 8 1 km s and a v p v s ratio of 1 73 these values are typical for normal mantle peridotites both p and s wave velocities and v p v s ratios constrain the possible composition of the first layer which is interpreted as a zone of partially serpentinised peridotites below the moho about 15 volume alteration of the parent mantle peridotite is required to produce the observed seismic properties this degree of alteration accounts for a systematic deficit in total tectonic subsidence when compared with that predicted from the variation in bulk crustal stretching along the axis of the basin syntectonic cooling occurred during differential lithospheric stretching as the upper to mid crust became more extended over a narrower region than the mantle lithosphere this served to rheologically couple the lower crust to the mantle near the final stage of deformation as the primary brittle ductile transition zone in the crust migrated downwards into the mantle lithosphere the resultant fracturing generated the permeability necessary to facilitate the seawater circulation which hydrated the cold mantle

the transition between the erris and the rockall basins new evidence from wide angle seismic data abstract the rockall trough is a deep water basin west of britain and ireland the origin of the basin and the nature of the crust beneath it is controversial a series of seismic wide angle experiments carried out during 1988 and 1990 help to clarify the crustal and upper mantle structure in the region results for the crustal structure from a profile which straddles the shelf break between the basin and the irish shelf are discussed here these data together with the available geological information indicate that the basin probably formed in the late palaeozoic to early mesozoic as part of a regionally linked basin assemblage which includes the hatton basin and the shallow sea basins surrounding ireland and britain good data quality has allowed the transition between the relatively unstretched crust of the irish and british mainland defined by previous onshore seismic refraction experiments to be well resolved the erris trough one of the small late palaeozoic to early mesozoic basins which fringe the mainland shelf region north of the porcupine basin is a half graben its major bounding fault is located on its western margin and the basin is divided from the rockall trough by a narrow horst the erris ridge the shelf trajectory along the western flank of the horst deepens smoothly towards the trough centre where the crust thins to 5 km near the trough margin below a sedimentary and water column 8 km thick surprisingly the crustal thickness is slightly greater over a 150 km broad zone at the trough centre i e ca 6 km this change in crustal thickness may be due to lateral strain migration to the warmer basin margins as its centre cooled during the deformation the crustal structure beneath the sediment pile at the trough centre is two layered as opposed to the three layered seismic refraction structure found onshore however the basic character of the lower crust present in onshore ireland in particular the presence of a gradient zone defining the crust mantle transition is still preserved in the trough this similarity in structure precludes the presence of magmatic underplating the crustal structure observed in the rockall trough can be formed by differential stretching of the lithosphere in this model the lower ductile crust and mantle lithosphere are stretched over a wide region by 2 2 3 strain focusing into a much narrower region of brittle upper crust generates severe amounts of crustal thinning 1 8 10 and is responsible for the fusing of the upper and mid crustal seismic refraction layers found beneath onshore ireland and britain mediating detachment surfaces sited at the brittle ductile transition at any time served to relay the strain from the lower lithosphere into the upper crust syntectonic heat loss plays an important role in controlling the deformation pattern

a practical model for organic richness from porosity and resistivity logs a practical method the delta log r technique for identifying and calculating total organic carbon in organic rich rocks has been developed using well logs the method employs the overlaying of a properly scaled porosity log generally the sonic transit time curve on a resistivity curve preferably from a deep reading tool in water saturated organic lean rocks the two curves parallel each other and can be overlain since both curves respond to variations in formation porosity however in either hydrocarbon reservoir rocks or organic rich non reservoir rocks a separation between the curves occurs using the gamma ray curve reservoir intervals can be identified and eliminated from the analysis the separation in organic rich intervals results from two effects the orosity curve responds to the presence of low density low velocity kerogen and the resistivity curve responds to the formation fluid in an immature organic rich rock where no hydrocarbons have been generated the observed curve separation is due solely to the porosity curve response in mature source rocks in addition to the porosity curve response the resistivity increases because of the presence of generated hydrocarbons the magnitude of the curve separation in non reservoirs is calibrated to total organic carbon and maturity and allows for depth profiling of organic richness in the absence of sample data this method allows organic richness to be accurately assessed in a wide variety of lithologies and maturities using common well logs

deep seismic reflection data of edge u s mid atlantic continental margin experiment implications for appalachian sutures and mesozoic rifting and magmatic underplating the edge seismic experiment across the virginia continental margin delineated a paleozoic suture buried appalachian terranes and mesozoic rifting and magmatic events the seismic grid revealed that the mesozoic norfolk rift basin exists only in the northern one third of the previously mapped area the north striking listric border fault of the norfolk basin half graben parallels seismic laminations in the basement the jurassic volcanic wedge pinches out just landward of the baltimore canyon trough hinge zone and downlaps on the hummocky oceanic basement under the continental rise under the continental slope the volcanic wedgereaches depths 9 s 20 km two distinct intracrustal reflections at 4 0 5 0 s and at 7 0 s twit two way traveltime dip southeastward at low angles 15 the moho reflection is disrupted where it is intersected by the 7 0 s reflection northwest of this point the moho dips landward seaward it is horizontal seaward of this point the lower crustal boundary laminations exist in a narrow interval 10 5 11 0 s and are of strong amplitude these changes in the moho and lower crust represent the seaward edge of the grenville age north american crust and the landward edge of jurassic magmatic underplating a northwest dipping reflection observed for the first time on the u s atlantic margin may be the top of the jurassic magmatic underplating layer the northwest dipping reflection truncates the southeast dipping 7 0 s twtt reflection landward projection of the 7 0 s reflection yields a north south trace on the postrift unconformity under the center of lower chesapeake bay this trace is near a basement fault between low grade metamorphic rocks carolina slate avalonia on the east and high grade rocks goochland terrane on the west this fault boundary and the southeastdipping 7 0 s reflection probably represent the taconic suture

magmatism at rifted continental margins the intense volcanism and uplift observed on many rifted continental margins forming basaltic seaward dipping reflector sequences is accompanied by the emplacement of a thick igneous section at depth partial melting by decompression of passively upwelling asthenosphere that is hotter than normal because it is near a hotspot explains both the thickness of the new igneous crust and the initial elevation of the rifted margins

the crustal structure of the rockall trough differential stretching without underplating the crustal structure along the axis of the rockall trough in the north atlantic has been studied along a 600 km refraction wide angle reflection transect containing three lines each 200 to 250 km long using explosives and ocean bottom seismometers one dimensional inversions of each section were made using the p method and forward modeling of the observed travel times in the next stage travel times and amplitudes were modeled using ray tracing techniques through two dimensional heterogeneous structures the results indicate that there are three sedimentary layers with velocities ranging from 2 km s to 4 5 km s the whole sedimentary section is up to 6 km thick and interpreted as late paleozoic to tertiary in age a two layer continental crust 5 to 7 km thick occurs along the length of the profile the upper crust 6 0 6 3 km s is circa 2 km thick and the lower crust 6 6 6 9 km s is circa 3 km thick a moho transition zone approximately 1 km thick lies at the base of the crust velocities in this transition zone increase from 6 9 km s up to 7 8 km s along the profile the underlying upper mantle has a laterally variable velocity between 7 6 and 7 8 km s unstretched crust onshore in ireland comprises a three layered crust with each layer approximately 10 km thick and a moho transition zone which is about 3 km thick the two upper layers in the onshore region are interpreted as corresponding to the upper crust in the rockall trough and indicate a stretching factor of 8 10 the velocity pattern in the lower crust in the rockall trough and under ireland are similar suggesting significantly less stretching 2 3 the differential stretching model is supported by the presence of the moho transition zone which is stretched by a similar factor to the lower crust the bulk stretching factor for the crust as a whole is in the range of 4 6 if this represents the lithospheric stretching factor significant underplating would be expected however if the stretching factor for the lower crust in the differential stretching model is more representative of overall lithospheric stretching little or no underplating is predicted the velocity patterns observed in the rockall trough indicate the absence of any significant underplating at the base of the crust such as that observed at the continental margin west of the hatton basin

u s mid atlantic margin structure and early thermal evolution marine seismic experiments have revealed that the u s east coast rifted margin crustal structure is dominated by voluminous volcanics emplaced during continental breakup we present results from seismic data recorded onshore during the 1990 edge mid atlantic onshore offshore seismic experiment that extend the margin crustal profile westward 180 km across the coastal plain and place the offshore results into a broader tectonic context the onshore offshore crustal model defines the crustal thinning profile across the margin enabling calculation of total extension based on direct measurements of crustal thickness we find that the crust beneath the coastal plain is largely unextended has a uniform thickness of 35 km shows no evidence for magmatic additions of sufficient volume to affect seismic velocity and that the total half extension of the crust is 30 to 40 km less than previous estimates by a factor of 3 to 4 we also present results of depth migration of the offshore vertical incidence and wide angle seismic data that yield the most complete and accurate image to date of reflectivity across the u s east coast margin we use this image to analyze margin subsidence by exploiting the stratigraphy of the subaerially extruded basalts beneath the sediments we find that 1 margin subsidence is consistent with a petrogenetic model for initial seafloor spreading magmatism involving high average melting pressures 3 5 4 0 gpa and potential temperatures 1500 c for a present day thermal lid thickness of 225 km 2 it is difficult to explain margin subsidence with a present day lid thickness of much less than 150 km and 3 rapid subsidence following breakup suggests the initially hot mantle underlying the rifting margin cooled very quickly implying a limited and finite initial distribution of hot mantle rather than a continuous upwelling or a ubiquitously warm upper mantle

bearing capacity under cyclic loading offshore along the coast and on land the 21st bjerrum lecture presented in oslo 23 november 2007 le chargement cyclique est important pour la conception de fondations de structures autant en mer sur la cote et sur la terre et pour la stabilite des pentes ceci est illustre a l aide de plusieurs exemples cet article discute du comportement du sol soumis a un chargement cyclique pour la structure et les pentes et demontre que la resistance au cisaillement cyclique et le mode de defaillance sous chargement cyclique dependent fortement du cheminement des contraintes et de la combinaison des contraintes en cisaillement moyennes et cycliques des diagrammes de resistance au cisaillement cyclique pour l argile sable et silt qui peuvent etre utilises pour la conception sont presentes des comparaisons entre les calculs et les essais modelises indiquent que la capacite de la fondation soumise a un chargement cyclique peut etre determinee a partir de la resistance au cisaillement cyclique obtenu par des essais en laboratoire

crustal structure of the southeast georgia embayment carolina trough preliminary results of a composite seismic image of a continental suture and a volcanic passive margin new deep penetration multichannel seismic reflection data combined with refraction results and magnetics modeling support a hypothesis that the carolina trough is a mesozoic volcanic passive margin exhibiting a seaward dipping wedge and associated underplating the structure of carolina platform continental crust is consistent with the late paleozoic continental collision that produced the appalachians but imbrication has had no obvious effect on shallower structures produced by mesozoic extension and volcanism the origin of prominent magnetic anomalies crossing the southeast georgia embayment can be explained by processes attending mesozoic separation of africa and north america and is not related to a paleozoic continental suture as previously postulated

seismic reflection and gravity study of proposed taconic suture under the new jersey coastal plain implications for continental growth a vibroseis seismic reflection line near buena new jersey crosses the linear positive salisbury bouguer gravity and magnetic anomaly that follows the proposed taconic suture two reflections at 1 4 and 1 7 sec under the positive gravity anomaly and beneath the coastal plain basement reflections at 1 1 sec are from interpreted taconic suture rocks with ophiolitic crustal fragments 7 1 7 9 km sec a gently southeast dipping reflection 2 0 2 7 sec is interpreted as the detachment thrust below the allochthonous suture rocks a stratified sequence 5 4 6 3 km sec is interpreted as remnants of parautochthonous lower paleozoic drift stage sedimentary rocks beneath the detachment thrust below 3 0 sec 8 km depth the reflections are subhorizontal or gently dipping 11 all the way to the moho reflection at 11 0 sec on the northwest end of the vibroseis line a northwest tilted mesozoic rift basin basement reflection is seen from 1 1 to 1 5 sec these mesozoic rocks 4 5 4 8 km sec are at least 1 km thick the denser suture rocks with ophiolitic fragments and the less dense mesozoic rocks explain almost all of the salisbury bouguer anomaly no significant lateral density variations are needed below 8 km depth these results are compatible with the taconic suture under the new jersey coastal plain being allochthonous and underlain by parautochthonous grenville age continental crust a deep seated taconic suture at the edge of the grenville north american basement may be southeast of the new jersey coastal plain this implies a greater amount of taconic overthrusting and lesser amounts of accretion of the north american crust than previously proposed