atmospheric methane flux from bubbling seeps spatially extrapolated quantification from a black sea shelf area bubble transport of methane from shallow seep sites in the black sea west of the crimea peninsula between 70 and 112 m water depth has been studied by extrapolation of results gained through different hydroacoustic methods and direct sampling ship based hydroacoustic echo sounders can locate bubble releasing seep sites very precisely and facilitate their correlation with geological or other features at the seafloor here the backscatter strength of a multibeam system was integrated with single beam data to estimate the amount of seeps m2 for different backscatter intensities resulting in 2709 vents in total direct flux measurements by submersible revealed methane fluxes from individual vents of 0 32 0 85 l min or 14 5 37 8 mmol min at ambient pressure and temperature conditions a conservative estimate of 30 mmol min per site was used to estimate the flux into the water to be 1219 1355 mmol s the flux to the atmosphere was calculated by applying a bubble dissolution model taking release depth temperature gas composition and bubble size spectra into account the flux into the atmosphere 3930 4533 mol d or into the mixed layer 6186 6899 mol d from the 21 8 km2 large study area is three times higher than independently measured fluxes of dissolved methane for the same area using geochemical methods 1030 2495 mol d the amount of methane dissolving in the mixed layer is 2256 2366 mol d this close match shows that the hydroacoustic approach for extrapolating the number of seeps m2 and the applied bubble dissolution model are suitable to extrapolate methane fluxes over larger areas

geotechnical characterization and strain analyses of sediment in the mauritania slide complex nw africa mass wasting processes are a common phenomenon along the continental margin of nw africa located on the high upwelling regime off the mauritanian coastline the mauritania slide complex msc is one of the largest events known on the atlantic margin with an affected area of not vert similar30 000 km2 understanding previous failure events as well as its current hazard potential are crucial for risk assessment with respect to offshore installations and tsunamis we present the results of geotechnical measurements and strain analyses on sediment cores taken from both the stable and the failed part of the msc and compare them to previously published geophysical and sedimentological data the material originates from water depths of 1500 3000 m and consists of detached slide deposits separated by undisturbed hemipelagic sediments while the hemipelagites are characterized by normal consolidation with a downward increase in bulk density and shear strength from 1 68 to 1 8 g cm3 2 10 kpa the slid deposits of the uppermost debris flow event preserve constant bulk density values 1 75 and 1 8 g cm3 with incisions marking different flow events these slid sediments comprise three different matrix types with normal consolidation at the base ocr 1 04 strong overconsolidation ocr 3 96 in the middle and normal consolidation to slight overconsolidation at the top ocr 0 91 1 28 however the hemipelagic sediments underlying the debris flow units which have been 14c dated at 24 ka bp show strong to slight underconsolidation ocr 0 65 0 79 with low friction coefficients of 0 18 fabric analyses show deformation intensities r 4 ratio 1 3 in several of the remobilized sediments such high deformation is also attested by observed disintegrated clasts from the underlying unit in the youngest debrites 14c age of 10 5 10 9 ka bp these clasts show strong consolidation and intense deformation implying a pre slide origin and amalgamation into the mass transport deposits while previous studies propose an emplacement by retrogressive failure for thick slide deposits separated by undisturbed units our new data on geotechnical properties strain and age infer at least two different source areas with a sequential failure mechanism as the origin for the different mass wasting events

empirical predictive models for earthquake induced sliding displacements of slopes earthquake induced sliding displacement is the parameter most often used to assess the seismic stability of slopes the expected displacement can be predicted as a function of the characteristics of the slope yield acceleration and the ground motion e g peak ground acceleration yet there is significant aleatory variability associated with the displacement prediction using multiple ground motion parameters to characterize the earthquake shaking can significantly reduce the variability in the prediction empirical predictive models for rigid block sliding displacements are developed using displacements calculated from over 2 000 acceleration time histories and four values of yield acceleration these empirical models consider various single ground motion parameters and vectors of ground motion parameters to predict the sliding displacement with the goal of minimizing the standard deviation of the displacement prediction the combination of peak ground acceleration and peak ground velocity is the tw

glacial demise and methane s rise the historical sciences geology archeology and cosmology test hypotheses differently than the experimental laboratory sciences when the process or event being investigated took place long ago or at a great distance from the investigators hypotheses are tested by assembling key data that can support or refute the likelihood of the proposed explanation in this way we have developed understanding and agreement on many major events in earth history such as the cretaceous tertiary extinction or the glacial interglacial cycles of the pleistocene epoch a consilience of findings is required and in a mechanistic causative model timing is of critical importance if a key factor in the explanation can be shown to have occurred at a time inconsistent with the model too early or too late the hypothesis has to be modified or rejected in pnas reyes and cooke 1 apply a refined dating approach to assess the timing of deglacial environmental change across the high latitude circumpolar arctic and its relation to increases in a major atmospheric greenhouse gas methane in their study these investigators use improved methods for presentation and interpretation of the initiation dates for a very large dataset of arctic peatland tundra and thermokarst sites to demonstrate that their development occurred too late to be the principal cause of impressively abrupt and large methane increases in atmospheric methane abundance at the beginning of the bolling and the end of the younger dryas climatic intervals of the last deglaciation 2

hypothesis for increased atmospheric methane input from hydrocarbon seeps on exposed continental shelves during glacial low sea level natural marine hydrocarbon seeps on continental margins today represent a small source of methane in the global atmosphere budget which is dominated by anthropogenic sources and contributions from wetlands in the tropics and northern high latitudes in glacial times with lowered sea level exposed seeps must have vented directly to the atmosphere and the portion of methane that was formerly dissolved and oxidized in the ocean contributed to the global atmospheric methane budget we estimate that during lowered sea level 40 100 10 12 g yr of methane were added to the atmosphere from gas seeps on the exposed shelves this source could account for much of the atmospheric methane during glacial episodes because major wetlands were largely absent prior to the holocene q 2005 elsevier ltd all rights reserved

effects of confining stress density and initial static shear stress on the cyclic shear response of fine grained unclassified tailings a constant volume direct simple shear apparatus was used to investigate the effects of confining stress initial static shear stress and void ratio on the liquefaction resistance of fine grained tailings the cyclic resistance ratio also expressed as the overburden stress correction factor was found to decrease with increasing confining stresses in the range 100 400 kpa and to gradually increase from 400 kpa onwards when samples were tested at the same initial void ratio the presence of an initial static shear stress decreased the liquefaction resistance a key outcome of the work was to reveal the critical importance of density on liquefaction susceptibility of compressible tailings thus a combined correction factor to account for overburden stress and density on cyclic resistance was proposed

decrease in natural marine hydrocarbon seepage near coal oil point california associated with offshore oil production prolific natural hydrocarbon seepage occurs offshore of coal oil point in the santa barbara channel california within the water column above submarine vents plumes of hydrocarbon gas bubbles act as acoustic scattering targets using 3 5 khz sonar data seep distribution offshore of coal oil point was mapped for august 1996 july 1995 and july 1973 comparison of the seep distributions over time reveals more than 50 decrease in the areal extent of seepage accompanied by declines in seep emission volume in a 13 km 2 area above a producing oil reservoir declines in reservoir pressure and depletion of seep hydrocarbon sources associated with oil production are the mechanisms inferred to explain the declines in seep area and emission volume

relationships between the loch ailsh and borralan alkaline intrusions and thrusting in the moine thrust zone southern assynt culmination nw scotland

balanced cross sections and their implications for the deep structure of the northwest alps reply abstract the structure of the northwest external french alps around the internal belledonne and mont blanc massifs in the beaufortain area can be explained by foreland wnw propagating thrust tectonics the internal belledonne massif is interpreted as having developed by imbrication of an originally thin skin of basement with a mesozoic cover above this massif all thrusts tend to climb lateral sections to the south to converge with the frontal pennine thrust the southern termination of the mont blanc massif is merely a spectacular example of such a lateral ramp

lateral and vertical changes of deformation style in the osen roa thrust sheet oslo region abstract changes in deformation style and amounts of shortening in the osen roa thrust sheet of the oslo region occur vertically and laterally approaching the thrust front in the south deformation in the cambromiddle ordovician sequence passes laterally from closely spaced imbricates in the north 50 60 shortening through triangle pop up and imbricate zones toward the south 20 37 shortening to widely spaced zones of deformation up to 20 shortening approaching the thrust front changes in deformation style are attributed to changing boundary conditions across the klekken thrust declining end of orogenic forces and an increase in thickness of competent units in the ordovician rocks to the south vertical changes in deformation style are attributed to the increasing percentage of competent units upward in the cambro silurian sedimentary rocks in the north the accompanying decrease in shortening upwards requires a structurally necessary upper detachment horizon to separate folded late middle ordovician silurian sediments from imbricated early cambro middle ordovician sediments below while southward in the oslo area the upper detachment needs to be placed between silurian and cambro ordovician units finally in eiker with less than 20 shortening the whole cambrosilurian sequence appears to have deformed as a single unit in the northern oslo region the upper detachment probably has a backthrust sense of motion above an imbricate stack passive roof duplex further south the upper detachment is probably directed toward the foreland

evolution of the triangle zone in the rocky mountain foothills near coalspur central alberta a triangle zone which commonly occurs along the external margin of a foreland thrust and fold belt with a buried thrust front is underlain by a subhorizontal blind foreland verging thrust that ends against a foreland dipping hinterland verging thrust these contemporaneous thrusts active towards the end of orogenesis enclose an intercutaneous wedge that moved towards the foreland during orogenesis a triangle zone evolves through periodic replacement of faults bounding the active wedge replacements occur in cycles during each of which a lower fault tends to be replaced by one in a lower stratigraphic horizon an upper fault by one farther away from the foreland each cycle ends with the lower fault moving to a younger horizon where it joins a new more external upper fault near coalspur the triangle zone exposes the remnants of several wedges involving upper cretaceous and paleocene molasse most of these wedges developed during the last cycle but one and have a combined displacement of about 5

grain boundary contact effects during faulting of quartzite an sem ebsd analysis abstract during low temperature faulting of cambrian quartzite assynt nw scotland stress concentrations develop at grain contacts either at the onset of deformation prior to the establishment of a through going fault plane or within the damage zone remote from the main displacement segment such concentrations contribute to the development of intragranular microfractures cataclastic microstructures and fault rocks this contribution considers the progressive deformation sequence that precedes microfracturing and cataclasis the complexity of this deformation is revealed by scanning electron microscope sem electron backscattered diffraction ebsd dauphine twinning is a widespread feature associated with grain contact stress concentration and forms distinctive ebsd microstructures automatic sem ebsd analysis reveals that whilst initial indentation causes dauphine twinning of many grains continued indentation results in the formation of an arcuate array of subgrains via low temperature plasticity and or microcracking which overprint the dauphine twins these observations are consistent with transmission electron microscopic analysis of quartz crystals used for microhardness indentation tests which reveal that indentation causes an intensely deformed region to develop comprising a high density of microfractures and a submicron scale blocky microstructure that accommodates any plastic deformation deformation mechanisms and associated microstructures develop sequentially with progressive indentation and may provide sites of microfracture nucleation via low temperature ductile fracture the new microstructures assist diffusive mass transfer dmt processes by the formation of a cellular or subgrain array that represents a reduction of several orders of magnitude in apparent grain size and hence in diffusion path length concomitantly associated microfracturing perturbs local thermodynamic equilibrium leading to enhanced dmt crack healing and cementation overgrowths together these processes form the aseismic creep and sealing components of fault zone development

tectonic processes in a surge type glacier the 1982 1983 surge of variegated glacier involved the development growth and downglacier propagation of a velocity peak associated with rapid basal sliding facilitated by high subglacial water pressures passage of the velocity peak through the glacier was preceded by an episode of longitudinal shortening and followed by an episode of elongation the deformation history of the glacier ice was dependent upon location relative to the surge nucleus and the final position reached by the propagating velocity peak ice above the surge nucleus experienced continuous and cumulative elongation ice below the final position of the velocity peak experienced continuous and cumulative shortening ice between these two points experienced shortening followed by elongation and low cumulative strain the large scale pattern of ice structure development reflects these deformation histories surging is equivalent to thrust sheet emplacement by a combination of gravity gliding over a weakened basal layer and push from behind with the gravity driven motion of the surging part of the glacier providing the push which allows the surge front to propagate the relationships established between the deformation history of surging glaciers and the development of ice structures may facilitate the interpretation of structures in thrust sheets

surge zones in the moine thrust zone of nw scotland abstract the caledonian thrust zones of assynt show several examples of large fault bounded structures surge zones up to 8 km 2 in extent which have moved further than adjacent rocks extensional faults can be traced into strike slip faults and then to contractional imbricate faults there are also zones of extensional and contractional flow as shown by strained bioturbation marks in the cambrian pipe rock several other low angle extensional fault zones have been recognized along the length of the moine thrust zone notably in the kinlochewe district recognition of these extensional faults and local surge zones has solved several local problems such as the lack of continuity of the glencoul thrust and the out of sequence character of some of the large low angle faults though the thrust propagation direction was generally from east to west in the transport direction several of the eastern faults have been reactivated later and locally cut down as extensional faults the so called moine thrust shows extensional fault movement at several localities along its length the extensional structures and the surge zones suggest that body forces have been important in driving the faults rather than just a push from the rear the moines and moine thrust zone were presumably driven to the wnw by gravity spreading and thinning of the main scottish caledonides

liquefaction resistance of undisturbed and reconstituted samples of a natural coarse sand from undrained cyclic triaxial tests the paper deals with an experimental study of the undrained cyclic behavior of a natural coarse sand and gravel deposit located in gioia tauro a town situated on the continental side of the messina strait in italy the study was conducted through cyclic undrained triaxial tests carried out on both undisturbed and reconstituted samples undisturbed samples were recovered by an in situ freezing technique and the sample quality was carefully assessed reconstituted samples were prepared by using two different reconstitution methods namely air pluviation ap and water sedimentation ws and tested under the same in situ initial relative density and effective overburden stress tests were carried out on both isotropically and anisotropically consolidated specimens the results obtained from this study provide direct evidence that cyclic liquefaction resistance obtained from water sedimented samples closely approximates that exhibited by undisturbed samples in both isotropically and anisotropically consolidated tests conversely ap leads to a marked underestimation since the investigated deposit is considered to have been formed by the marine water environment these results can be regarded as proof that ws closely replicates the in situ fabric of the investigated deposit allowing the substitution of the expensive undisturbed samples with their reconstituted counterparts anisotropically consolidated specimens respectively exhibit cyclic liquefaction or cyclic mobility depending on whether or not they are loaded under the shear stress reversal mode

syn orogenic alkaline magmatism and its relationship to the moine thrust zone and the thermal state of the lithosphere in nw scotland the alkaline complexes of nw scotland lie in a zone sub parallel to the moine thrust and represent the nw edge of the otherwise overwhelmingly calc alkaline late orogenic magmatism of the caledonian fold belt the emplacement of intrusives in assynt overlapped the thrust movements and new u pb zircon ages for the loch ailsh intrusion 439 4 ma provide are liable bracket when combined with existing age data for the loch borralan intrusion 430 4 ma for the main movements on the ben more thrust plane a detailed history of the main tectonic and igneous events in the moine thrust zone is tabulated zircons from the undeformed cnoc nan cuilean syenite emplaced in moine rocks near loch loyal give an age of 426 9 ma in contrast to the deformed glen dessary syenite for which earlier work gave 456 5 ma the linear distribution of the alkaline complexes to the west of the calc alkaline plutons and the ultra potassic character of the loch borralan complex the most westerly are consistent with but do not prove generation related to a w dipping subduction zone the persistence of the magmatism over 30 ma in a belt being shortened by thrusting suggests a source in the mantle lithosphere the absence of magmatism further to the nw and the production of calc alkaline magmas to the se of this zone is compatible with a model in which the thermal state of the lithosphere exercises the most important control on the nature of late caledonian magmatism

ice age terrestrial carbon changes revisited n shackleton 1977 first proposed that changes in the marine 13 c record 13 c could be used to infer ice age changes in carbon storage on land the previously published best estimate from the marine record is equivalent to about 490 gt 0 32 13 c however adams et al 1990 utilized a pollen database to estimate a 1350 gt change in carbon storage which would cause a 13 c of about 0 90 the nearly trillion ton difference in estimates amounts to almost half of the total carbon stored on land to address the nature of this discrepancy i have reexamined the terrestrial carbon record based on a new pollen database compiled by r webb and the cooperative holocene mapping project cohmap group i estimate about 750 1050 gt glacial interglacial change in terrestrial carbon storage with the range reflecting uncertainties in carbon storage values for different biomes additional uncertainties apply to rainforest and wetland extent and presence of c4 plants which have a significantly different isotopic signature than c3 plants although some scenarios overlap a new estimate of carbon storage based on the oceanic 13 c record revised to 0 40 and 610 gt most estimates seem to fall outside the envelope of uncertainty in the marine record several possible explanations for this gap involve 1 a missing sink may be involved in land sea carbon exchange e g continental slopes 2 the geochemistry of the exchange process is not understood 3 carbon storage by biome may have changed under ice age boundary conditions or 4 the standard interpretation of whole ocean changes in the marine 13 c record requires reevaluation this latter conclusion receives some support from comparison of the 13 c records for 18 o stages 2 and 6 for the stage 6 glacial the 13 c changes are 50 60 larger than for the stage 2 glacial yet implications of increased aridity are not supported by longterm trends in atmospheric dust loading to summarize the above analysis implies that despite the uncertainties remaining in estimates of terrestrial carbon storage changes a case can be made that our understanding of the transfer process is incomplete and that the eventual explanation may require clarification of factors affecting the marine 13 c record

contributions to atmospheric methane by natural seepages on the uk continental shelf natural gas seepages occur on the united kingdom s continental shelf and although published reports suggest that they are very rare the petroleum industry has identified but not publicly reported many more there is also very little data on the flux of gas from seabed seepages and even less on the contribution of seepages to atmospheric concentrations of gases such as methane potential gas source rocks include quaternary peats as well as petroliferous source rocks such as the carboniferous coal measures and the upper jurassic kimmeridge clays there are also other organic rich sediments which are potential source rocks together these cover a considerable part of the u k continental shelf analogue seismic reflection pinger profiles acquired during the british geological survey s regional mapping programme have been reviewed to identify water column targets including fish and plumes of gas bubbles the ability to distinguish targets is critical to an assessment of the distribution of gas seepages both theoretical predictions of target identity and the habits of shoaling fish have been investigated in order to identify a method of distinction data from seabed seepages and measurements of seepage rates have been used to establish likely ranges of gas flux rates and the sizes of gas bubbles the likelihood that a rising bubble will survive and escape into the atmosphere is determined primarily by bubble size and water depth methane the principal constituent of seepage gas is relatively unreactive and sparingly soluble the studies have enabled a new estimate of the distribution of gas seepages on the u k continental shelf and of the contribution to atmospheric methane levels the results suggest that natural gas seepages are significantly more important as a source of methane than had hitherto been established it is estimated that between 120 000 and 3 5 mtonnes of methane per year come from a continental shelf area of about 600 000 km2 this represents between 2 and 40 of the total united kingdom methane emission it is suggested that similar contributions arise from other continental shelf areas worldwide and that geological sources of atmospheric methane are more significant than is generally acknowledged

unified thixotropic fluid model for soil liquefaction the geotechnical earthquake engineering profession has struggled with the inherent complexity of the multiphase soil response to cyclic loading owing to the progressive nature of the generation of

the internal geometry of nappes criteria for models of emplacement summary the geometric and stratigraphic properties of thrust sheets and fold nappes are controlled by the mechanisms by which they were initiated and emplaced thrust sheets that have developed by gravity gliding have their internal stratigraphies truncated by the basal thrusts which cut up section at the trailing edges in contrast thrust sheets that have developed by gravitational spreading have their internal stratigraphies truncated by the overlying thrust sheets and their basal thrusts cut up section at the leading edges fold nappes have complicated geometries and correlation of stratigraphy between successive nappes is difficult the basic geometric and stratigraphic properties of thrust sheets and fold nappes developed by different mechanisms may be used as criteria for testing the applicability of these mechanisms to particular areas of orogenic belts the valley and ridge province of the appalachians has geometric and stratigraphic properties consistent with thrust sheet development by gravitational spreading the western nappes of the central scandinavian caledonides are more complex but have properties suggesting development by buoyant upwelling of the orogen infrastructure there is however a lack of detailed cross sections of orogenic belts based on geophysical and or borehole data in addition to the geological data the interpretation of geological data in isolation is often too dependent on subjective information coloured by the mechanism preferred by the individual concerned

direct dating of mylonite evolution a multi disciplinary geochronological study from the moine thrust zone nw scotland rb sr dating of sub closure temperature syn deformationly crystallized white micas from the moine mylonites knockan and dundonnell has yielded ages which vary from 437 ma to 408 ma morphological and major element analyses of the micas indicate that all the micas within the analysed samples were re crystallized during the moine thrust shearing the ages yielded are therefore interpreted as marking the end of crystal plastic deformation associated with shearing on the moine thrust the variation in ages between samples is significantly greater than the individual analytical errors and may be a product of strain localization within the shear zone alternatively it may indicate flow of strontium rich fluids derived from outside the shear zone implying that feldspars may act as potentially unreliable initial isotopic reservoirs even in very high strain samples within the greenschist facies shear zones however the rb sr age are internally consistent and compatible broadly with existing geological and geochronological data for the region suggesting that even if the feldspars have not acted as perfect initial isotopic reservoirs the resulting errors were minimal the general cessation of ductile deformation at c 430 ma probably dates the general initiation of imbrication within footwall to the moine thrust the age of 430 ma is therefore likely to be a time of significant brittle displacement on the underlying ben more thrust k ar dating of the re crystallized moine mylonite micas yielded anomalously old ages in comparison to rb sr values as a result of incorporation of excess ar during shearing the degree of incorporated excess ar decreases away from the base of the shear zone into the hanging wall becoming indiscernible at c 1 5 km structurally above the base of the shear zone the distance c 1 5 km may represent the distance that fluid can have flowed out of the shear zone during deformation

nature of the moho beneath the scottish highlands from a receiver function perspective abstract the geology of scotland documents a protracted geological history from precambrian basement formation through the caledonian orogeny and to the tertiary opening of the atlantic a temporary deployment of 22 closely spaced broadband seismic stations in scotland traverses many of the major terrane boundaries in the region and provides a unique opportunity to place spatial and temporal constraints on variations in crustal structure with teleseismic p wave receiver functions we use the h method to determine variations in bulk crustal parameters crustal thickness h and v p v s ratio mean crustal thickness is 28 km varying from 23 km in the ne highlands and increasing to 30 km near the highland boundary faultin the southern part of the study area mean v p v s values of 1 76 show no significant variation across the study area an abrupt increase in crustal thickness of 4 5 km nw across the moine thrust is not easily linked to tertiary recent tectonic activity instead it appears that scotland s crust has retained features for hundreds of millions of years since it was first formed despite abundant volcanic activity in tertiary times our work favours the view that the moho is a compositional boundary rather than a mineralogical one defined by a reaction in p t space

geological interpretation of dekorp 2 s a deep seismic reflection profile across the saxothuringian and possible implications for the late variscan structural evolution of central europe abstract a 250 km long deep seismic section the first of its kind in west germany s dekorp project is interpreted in terms of late variscan collisional tectonics the structural model used is based on the intracontinental thrust tectonics concept of modern collision orogens the crustal profile across the saxothuringian zone seems to indicate north facing ramps antiformal stacks and culminations within the crystalline basement of the internal mid european variscides that have been only partially overprinted by permo mesozoic crustal stretching

meltwater pulse 1a from antarctica as a trigger of the bolling allerod warm interval meltwater pulse 1a mwp 1a was a prominent feature of the last deglaciation which led to a sea level rise of 20 meters in less than 500 years concurrent with mwp 1a was the onset of the bolling allerod interstadial event 14 600 years before the present which marked the termination of the last glacial period previous studies have been unable to reconcile a warm northern hemisphere with mwp 1a originating from the laurentide or fennoscandian ice sheets with the use of a climate model of intermediate complexity we demonstrate that with mwp 1a originating from the antarctic ice sheet consistent with recent sea level fingerprinting inferences the strength of north atlantic deep water nadw formation increases thereby warming the north atlantic region and providing an explanation for the onset of the bolling allerod warm interval the established mode of active nadw formation is then able to respond to subsequent freshwater forcing from the laurentide and fennoscandian ice sheets setting the stage for the younger dryas cold period the melting of continental ice sheets during the last deglaciation provided a freshwater source to the ocean that affected global sea level and the strength of the thermohaline circulation an exceptionally large melting event inferred from far field relative sea level records occurred

mud volcanoes the most important pathway for degassing deeply buried sediments abstract this paper discusses the nature of the phenomenon of mud volcanism with respect to degassing of deeply buried sediments mud volcanoes are defined as geological structures and their main elements are described based on the nature of activity mud volcanoes are grouped in to three main types and the relationship between each type and corresponding morphological expression is discussed the presented up to date data of the world geographical distribution of mud volcanoes show that they approximate to 1800 individuals a detail overview of geological environments in which they occur helps to deduce some necessary conditions for mud volcano formation the basic mechanisms of mud volcano formation are discussed specifically the fluid pressure hypothesis and some triggering events are identified the most common investigation approach and some criteria for recognizing of a submarine mud volcano on side scan sonar records and seismic sections are given mud volcanism in the mediterranean ridge an accretionary complex and black sea abyssal plane a back ark basin with tectonic regime of extension are described as case studies to show variety in morphology and common factors in development of mud volcanoes the manifestation of continuous gas migration through mud volcanoes is clarified and the attempt made to quantify the gas release shows that mud volcanoes are one of the significant natural sources of atmospheric methane emitting a total amount of about 10 3 to 12 6 tg annually

late brittle deformation in a caledonian ductile thrust wedge new evidence for gravitational collapse in the moine thrust sheet sutherland scotland abstract in the ductile regions of orogenic wedges late brittle structures formed at shallow crustal depths have received little attention however they are important as they of ten record the final stages in deformational history during uplift and erosion of the orogen in the moine rocks of sutherland late caledonian brittle folds and low angle faults post date ductile structures formed during wnw nw directed thrust movements earlier in the same orogenic event in the western moine nappe the late structures display geometries which indicate that they formed during regionally ese directed extensional movements down the dip of the pre existing regional foliation these late structures are correlated with similar wnw directed extensional low angle faults recognised in the moine thrust zone south of the assynt culmination both are thought to have formed in response to late caledonian gravity induced thinning of the moine thrust wedge and both pre date devonian extension associated with the formation of the west orkney basin along strike changes in the location and sense of extensional movements north and south of the assynt culmination are explained by changes in the pre existing structural geometry of the caledonian ductile thrust nappes within the moine hence earlier deformation patterns are thought to exert important controls over later events in an evolving orogenic wedge

structural interpretation of the eastern sulaiman foldbelt and foredeep pakistan the sulaiman foldbelt is an active tectonic feature on the northwestern margin of the indian plate seismic reflection data have been combined with surface geological mapping and drill hole data to interpret the structural style and tectonic shortening of the eastern sulaiman foldbelt and its adjacent foredeep the data show that the basement is more than 8 km deep near the deformation front and that it deepens towards the west the foredeep adjacent to the eastern sulaiman foldbelt is a broad synclinal structure with a steep western limb the more gentle eastern limb has monoclinal dips from near zero to 2 5 several salt cored anticlines are observed on the eastern part of the monocline but the salt structures are lacking in the western foredeep and in the frontal part of the sulaiman foldbelt the basal decollement under the sulaiman lobe lies either in ductile eocambrian salt or within a deep zone of other material that undergoes ductile behavior near the deformation front ramps from the basal detachment become flats in lower triassic and lower cretaceous shales a steep and highly elevated zone immediately to the west of the frontal folds is interpreted to be underlain by a passive roof duplex the culmination wall of this oblique duplex is separated from the overlying roof sequence by a passive roof thrust in lower cretaceous shales the roof thrust has a backthrust sense of movement relative to the forelandward propagating duplex and may extend obliquely 100 km into the interior of the foldbelt fault propagation and fault bend folds are present in the frontal portion of the eastern sulaiman foldbelt palinspastic restoration of a balanced cross section shows 108 km of shortening in the eastern sulaiman foldbelt east of the kingri strike slip fault the presence of more than 11 km of pre neogene strata on top of basement suggests that the mesozoic rifted margin of the indian subcontinent may lie beneath the sulaiman foldbelt this interpretation is also favored by the presence of ophiolites and flysch deposits overthrusted on late cretaceous shelf strata

sea level at the last glacial maximum evidence from northwestern australia to constrain ice volumes for oxygen isotope stage 2 new sea level information from the bonaparte gulf in northwestern australia is used to constrain the magnitude and rates of change of ice volumes during the last glacial maximum lgm the region is tectonically stable and far from the former ice covered regions the glacio hydro isostatic adjustment of the coast is therefore relatively small and the corrections for this evect are not sensitive to details of the rebound model microfossil analysis and ams radiocarbon dating of 11 gravity cores taken across the shelf and bonaparte gulf demonstrate that 1 the lgm sea levels were locally at 125 4 m 2 the lgm terminated abruptly at 19 000 cal yr bp with a rapid rise in sea level of about 15 m over the next 500 years and 3 the onset of the minimum sea levels occurred before 22 000 cal yr bp when corrected for the glacio hydro isostatic evects the increase of lgm ice volumes over the present day ice volume is 52 5 106 km3 the termination of the lgm is marked by a rapid ice discharge of 5 2 106 km3 2001 elsevier science b v all rights reserved

the terminology of structures in thrust belts abstract a review of structures and geometric relationships recognized in thrust belts is presented a thrust is defined as any contractional fault a corollary being that thrusts must cut up section in their transport direction flats are those portions of a thrust surface which were parallel to an arbitrary datum surface at the time of displacement and ramps are those portions of thrusts which cut across datum surfaces ramps are classified on the basis of their orientation relative to the thrust transport direction and whether they are cut offs in the hangingwall or footwall of the thrust lateral variations in the form of staircase trajectories are joined by oblique or lateral ramps which have a component of strike slip movement an array of thrusts which diverge in their transport direction may form by either of two propagation models these are termed piggy back propagation which is foreland directed and overstep propagation which is opposed to the thrust transport direction an array of thrust surfaces is termed an imbricate stack and should these surfaces anastamose upwards a duplex will result the fault bounded blocks are termed horses a duplex is bounded by a higher roof thrust and a lower floor thrust the intersection of any two thrust planes is termed a branch line thrusts can be classified on the basis of their relationship to asymmetric fold limbs which they cut a further classification arises from whether a particular thrust lies in the hangingwall or footwall of another one the movement of thrust sheets over corrugated surfaces or the local development of thrust structures beneath will fold higher thrust sheets these folds are termed culminations and their limbs are termed culmination walls accommodation of this folding may require movement on surfaces within the hangingwall of the active thrust these accommodation surfaces are termed hangingwall detachments and they need not root down into the active thrust this category of detachment includes dip slip hangingwall drop faults which are developed by differential uplift of duplex roofs and out of the syncline thrusts which develop from overtightened fold hinges back thrusts as well as forming as hangingwall detachments may also form due to layer parallel shortening above a sticking thrust or by rotation of the hangingwall above a ramp

residual and postliquefaction strength of a liquefiable sand abstractseismic design of geotechnical structures often requires estimates of how shearing resistance of liquefiable soil is reduced to its minimum value residual strength sr as pore pressures build up and is subsequently regained as pore pressures dissipate it was envisioned that the shear strength of liquefying sands could be measured in flight in a seismic geotechnical centrifuge model by pulling thin coupons plates horizontally through the sand models before during and after shaking to simulate the large strains and strain rates associated with liquefaction flow failures this paper presents the results of seismic centrifuge tests that were used to make such measurements companion ring shear rs tests also are described although centrifuge and rs residual strengths were generally similar and increased with relative density the centrifuge sr and sr vo sr divided by preshaking effective vertical stress increased significantly with small changes in relative density while the rs test sr a

glacial interglacial wetland biomass burning and geologic methane emissions constrained by dual stable isotopic ch4 ice core records atmospheric methane ch4 records reconstructed from polar ice cores represent an integrated view on processes predominantly taking place in the terrestrial biogeosphere here we present dual stable isotopic methane records 13ch4 and d ch4 from four antarctic ice cores which provide improved constraints on past changes in natural methane sources our isotope data show that tropical wetlands and seasonally inundated floodplains are most likely the controlling sources of atmospheric methane variations for the current and two older interglacials and their preceding glacial maxima the changes in these sources are steered by variations in temperature precipitation and the water table as modulated by insolation local sea level and monsoon intensity based on our d ch4 constraint it seems that geologic emissions of methane may play a steady but only minor role in atmospheric ch4 changes and that the glacial budget is not dominated by these sources superimposed on the glacial interglacial variations is a marked difference in both isotope records with systematically higher values during the last 25 000 y compared with older time periods this shift cannot be explained by climatic changes rather our isotopic methane budget points to a marked increase in fire activity possibly caused by biome changes and accumulation of fuel related to the late pleistocene megafauna extinction which took place in the course of the last glacial

influence of heterogeneous lithostructural layering on orogenic deformation in the variscan front zone eastern belgium the ramp flat thrust model and other classical models based on rocky ountains or appalachians structures allow a better understanding of ault and fold interaction in a sequence dominated by competent rocks n which in most cases thrusts propagate forward in sequence this attern however fails to explain the deformation history of rock uccessions with low proportions of competent rocks in such ithologies out of sequence faults are more common features the ariscan front zone in eastern belgium serves as a case study for this on classical deformation model cross sections are well constrained by urface data covering a large area the devono carboniferous sequence esting unconformably on caledonian basement has shortened drastically nd the tectonic history can best be explained by a composite structural odel continuous and discontinuous deformations took place in uccessive steps a lame anticline developed first it evolved ubsequently into either break thrust or translated fault propagation olds out of sequence thrusting by the theux tunnel fault formed the esdre nappe the latter is the northern part of the ardenne allochthon he main discrepancies with the ramp flat thrust model are emphasized articularly the vesdre nappe which is the highest thrust sheet is ot the youngest event of deformation common elements of the variscan ront zone between northern france and western germany are discussed he theux tunnel fault has the same kinematics significance as the idi aachen fault the footwall of the vesdre nappe is the eastward rolongation of the brabant foreland the complex structure of the theux indow reflects imbrications under the allochthon and can be compared ith other wedges and thrust sheets c 1999 elsevier science b v all ights reserved

uplift of immersed tunnel in liquefiable seabed under wave and current propagation abstract in ocean environments wave usually propagates in association with a current the paper presents a cyclic characterization framework for elastoplastic consolidating behavior of liquefiable seabed around the immersed tunnel under combined wave and current loading based on the biot dynamic consolidation theory special attention is placed on modeling the nonlinear wave current interaction the cyclic plasticity behavior of marine deposits and the soil structure contact effect the paper extends an existing masing model to large strain regime in the order of 10 2 in the framework of cyclic plasticity for capturing the liquefaction induced nonlinear behavior of marine deposits then the proposed cyclic plasticity model is implanted into an explicit time matching finite difference analysis platform permitting a comprehensive simulation of the intensive response of the immersed tunnel in the seabed experiencing the excess pore pressure accumulation and residual liquefaction retrospective simulation of a well documented centrifuge test by the proposed framework indicates satisfactory agreement validating the reliability for capturing the excess pore pressure accumulation and residual liquefaction during wave propagation finally the influences of current on the wave induced liquefaction in the vicinity of an immersed tunnel are investigated by a numerical example the results indicate that the ocean current significantly changes the original characteristics of wave induced liquefaction as well as the induced uplift of the immersed tunnel especially with consideration of the cyclic plasticity behavior of marine deposits the mechanisms of seabed liquefaction and the induced uplift of the immersed tunnel under wave and current actions are also interpreted

strains and folds within thrust sheets an analysis of the heilam sheet northwest scotland abstract the changes of shape and orientation of fossil worm burrows have been used to carry out a detailed strain analysis of the heilam thrust sheet in the moine thrust zone northwest scotland the strains have been factorised into components of layer parallel shear 1 layer normal shear 2 and layer parallel shortening or elongation variations in the 1 shear are largely lithologically controlled some strain is due to flexural processes as the thrusts and overlying beds change dip over thrust ramps or are tightened by later deformation while there may also be a component of drag which increases towards the overlying thrust this predating the shear due to flexure a contoured map of the values suggests that major folds within the thrust sheet developed as a result of stick or drag on the floor thrust prior to ramp climb this led to differential movement in the transport direction causing layer parallel shortening accompanied or followed by buckling of the layers a map showing layer normal shear strains 2 suggests that the heilam sheet forms a major surge zone the central part having moved further wnw than the northern and southern parts this has led to components of lateral shear along parts of the sheet especially in the north producing curvature of the imbricate faults

distinguishing thrust sequences in gravity driven fold and thrust belts abstract piggyback or foreland propagating thrust sequences where younger thrusts develop in the footwalls of existing thrusts are generally assumed to be the typical order of thrust development in most orogenic settings however overstep or break back sequences where later thrusts develop above and in the hangingwalls of earlier thrusts may potentially form during cessation of movement in gravity driven mass transport deposits mtds in this study we provide a detailed outcrop based analysis of such an overstep thrust sequence developed in an mtd in the southern dead sea basin evidence that may be used to discriminate overstep thrusting from piggyback thrust sequences within the gravity driven fold and thrust belt includes upright folds and forethrusts that are cut by younger overlying thrusts backthrusts form ideal markers that are also clearly offset and cut by overlying younger forethrusts portions of the basal detachment to the thrust system are folded and locally imbricated in footwall synclines below forethrust ramps and these geometries also support an overstep sequence however new short cut basal detachments develop below these synclines indicating that movement continued on the basal detachment rather than it being abandoned as in classic overstep sequences further evidence for synchronous thrusting where movement on more than one thrust occurs at the same time is provided by displacement patterns on sequences of thrust ramp imbricates that systematically increases downslope towards the toe of the mtd older thrusts that initiate downslope in the broadly overstep sequence continue to move and therefore accrue greater displacements during synchronous thrusting our study provides a template to help distinguish different thrust sequences in both orogenic settings and gravity driven surficial systems with displacement patterns potentially being imaged in seismic sections across offshore mtds

lateral ramps and thrust terminations an example from the moine thrust zone nw scotland detailed remapping within the assynt culmination in nw scotland shows that the ben more thrust joins the glencoul thrust along a lateral branch line positioned in loch glencoul this branch line marks the northern lateral termination of the glencoul thrust the thrust on the northern shore of loch glencoul the famous view is thus the ben more thrust the ben more thrust sheet is therefore much larger than previously thought the lateral terminations of the ben more thrust to the north and the south are of two distinct types this reinterpretation negates the existence of surge zones in assynt

simplified procedure for estimating earthquake induced deviatoric slope displacements a simplified semiempirical predictive relationship for estimating permanent displacements due to earthquake induced deviatoric deformations is presented it utilizes a nonlinear fully coupled stick slip sliding block model to capture the dynamic performance of an earth dam natural slope compacted earth fill or municipal solid waste landfill the primary source of uncertainty in assessing the likely performance of an earth waste system during an earthquake is the input ground motion hence a comprehensive database containing 688 recorded ground motions is used to compute seismic displacements a seismic displacement model is developed that captures the primary influence of the system s yield coefficient ky its initial fundamental period ts and the ground motion s spectral acceleration at a degraded period equal to 1 5 ts the model separates the probability of zero displacement i e 1 cm occurring from the distribution of nonzero displacement so that very low values of calculated

geological constraints structural evolution and deep geology of the northwest scottish caledonides the front of the caledonian orogenic belt in nw scotland is marked by a zone of foreland thrusting which contains imbricates of lewisian basement proterozoic cover and cambrian shelf sediments faults within this moine thrust belt in most localities propagated in a foreland directed sequence therefore the earliest of these thrusts was the moine thrust which carried a basement assemblage of moine and lewisian rocks over the cambrian shelf the development of large duplex and imbricate structures in the footwall postadted movement on this thrust hence a restoration of these imbricates provides a minimum estimate of the eastern extent of the cambrian shelf no synsedimentary or prethrust extensional features are recognised within the cambrian succession which displays a remarkable stratigraphic and thickness consistency this implies a corresponding consistency in crustal structure beneath these cover rocks immediately prior to caledonian thrusting a balanced cross section constructed across the northern part of the moine thrust belt has given a restored width for the cambrian shelf of 54 km geophysical data suggest that the present foreland crustal thickness is 28 km if this is taken to be the crustal thickness beneath the cambrian shelf during caledonian thrusting a minimum cross sectional area of 1512 km of lewisian rocks must remain beneath the present outcrop of the moine thrust sheet this foreland basement wedge may have been imbricated subsequent to the development of the cambrian imbricates caledonian structures within the moine thrust sheet are interpreted as forming an imbricate stack with the moine thrust acting as a floor thrust the ductile imbricate thrusts possibly roofed into the naver slide late open folds which warp foliation slides and metamorphic isograds within the moine sheet may represent culminations in the foreland lewisian imbricates beneath the moine thrust these postulated culminations may have been sufficient to initiate gravity driven structures this may explain late movements on high level faults within the moine thrust belt

hangingwall strain a function of duplex shape and footwall topography abstract the concept of piggy back thrust tectonics implies that foreland is progressively accreted onto a developing thrust sheet during duplex formation lateral shape changes in duplexes in the hangingwall of a thrust and corrugations in the footwall will fold higher thrust sheets to give culminations and depressions balancing of parts of high level thrust sheets with lower sheets and foreland requires a sequence of extensional and compressional strains orientated normal to the thrust transport direction culmination walls will be sites of strike parallel extension subsequent adjacent culminations will compress early culmination walls which will result in a sequence of irrotational strains examples of this geometry are given from the moine thrust zone of northwest scotland the model allows a re examination of strains and hangingwall evolution in some thrust sheets in the helvetic and external zones of the alps

balanced cross sections and their implications for the deep structure of the northwest alps discussion abstract field evidence around the southwestern termination of the mont blanc basement massif casts doubt on butler s interpretation of the massif as a relatively thin thrust sheet extending over the imbricated dauphind cover a thick skinned model of basement faulting analogous to laramide faulting in the western u s a seems more appropriate for the area

the thrust structures of southern assynt moine thrust zone the moine thrust zone of southern assynt forms part of the northwest margin of the caledonide belt and has aroused controversy concerning amounts and timing of thrust displacement and sequence of thrust development recent mapping shows it to have been a foreland propagating thrust sequence the uppermost ductile moine thrust formed first followed by sequences of imbricates a major thrust the ben more thrust and then several lower duplex zones this sequence is clear from new observations that many of the earlier thrusts were folded and or breached during the development of the underlying structures a displacement of over 54 km has been estimated for the zone as a whole an alkaline igneous complex including the large borrolan syenite was intruded during the development of the thrust zone and much of it was carried some 30 km to the west northwest onto the foreland late extensional structures in southern assynt are an integral part of the caledonide thrust sequence and probably developed from the collapse of the thrust wedge as it climbed from stronger basement rocks on to a weaker cover sequence on the foreland

the nature of roof thrusts in the moine thrust belt nw scotland implications for the structural evolution of thrust belts buried thrust systems commonly analysed in terms of duplex structures are often interpreted as forming in a particular sequence this model considers that only one thrust is active at a time and the resulting structural geometry is well ordered however a reappraisal of structural geometries from the moine thrust belt in nw scotland has shown that many apparent duplex structures are more complex although the upper roof thrust of some duplexes may be folded and bulged by underlying imbricate slices in accordance with simple duplex models the footwall to these roof thrusts cut up and down stratigraphic section in conflict with the simple duplex models examples include the glencoul thrust with its underlying imbricate system and the foinaven duplex simultaneous slip on an array of imbricate thrusts can bulge duplex roofs relationships classically used to infer piggy back sequences of thrust propagation however activity on more hinterland ward imbricate thrusts can cause the roof onto which they branch to truncate more foreland ward structures in this fashion the duplex roof can cut up and down stratigraphic section mimicking an extensional fault by varying thrust activity in three dimensions within an imbricate system local parts of roof thrusts can generate domains of overstep behaviour that have only local significance existing interpretations of overstep relationships in the moine thrust belt as representing late orogenic low angle extensional faults may need revision the new interpretations of deformation activity where displacements in thrust arrays happen synchronously rather than sequentially are consistent with emergent thrust and fold belts with analogue experiments and with mechanical models of orogenic wedges

the distribution of methane in the upper waters of the southern california bight profiles of dissolved methane in the upper 300 m of a 190 000 km2 area of southern californian waters were determined during november 1989 and march 1990 methane in near surface waters ranged from 1 to 1416 nmol l 1 the lowest concentrations were at depths 200 m the highest levels were found along the coast especially in the region extending from point conception to santa barbara vertical profiles of methane are characterized by maxima in supersaturation within a narrow density band located within the pycnocline this layer is continuous over a large geographic area offshore stations exhibiting elevated levels of methane are spatially coincident with mesoscale eddies of the california current system interpretation of hydrographic and chemical data suggests that ch4 rich waters are upwelled from relatively shallow areas that are characterized by numerous hydrocarbon seeps the data are consistent with a nearshore source of methane presumably submarine seeps subsurface maxima in offshore waters are likely maintained by lateral transport of allochthonous ch4 along density surfaces from coastal waters and autochthonous microbial production

a sequential back arc and foreland basin thrust duplex model for the southern uplands of scotland thrust imbrication of ordovician and silurian submarine fan sequences overlapping pelagic deposits in the southern uplands has been interpreted in terms of an accretionary prism formed above a nw directed subduction zone structural features invoked to support accretion are not definitive and could be explained in terms of a thin skinned thrusting model new palaeocurrent and compositional evidence from llandeilo to mid llandovery age turbidites in the northern part of the southern uplands proves interdigitation of sediments with strongly contrasting petrography turbidites derived from the south contain significant quantities of fresh andesitic detritus whereas those from the north form more mature quartz rich formations this implies a back arc situation the turbidites being deposited in a basin with a relatively mature continental landmass to the north and a rifted continental fragment containing an active volcanic arc to the south oblique collision of the opposing continental margins of the iapetus ocean during the llandovery caused the cessation of subduction underthrusting of the southern margin initiated a se propagating thrust stack which deformed the back arc basin sequence and may eventually have ramped over the eroded and faulted remains of the volcanic arc a southward migrating foreland basin formed ahead of the rising thrust stack and is now represented by the late llandovery hawick group and wenlock sequences mid to end silurian sinistral strike slip resulted from oblique collision and produced a transpressional regime during which reactivation of deep seated structures allowed the intrusion of lamprophyre dykes and granites

mylonites lessons from eriboll eriboll has been an important area in understanding the geology and structure of the nw highlands of scotland it came to prominence during the highland controversy between nicol and murchison in the 1850s nicol recognized a major regional or grand dislocation the moine thrust zone at eriboll whereas murchison denied its existence an important element in the resolution of the controversy was the repeated observation of a distinctive schistose rock that often marked nicol s dislocation lapworth named it a mylonite and related its development to mechanical metamorphism resulting from tectonic milling movements along the dislocation peach horne and co workers whose contributions to early mylonite studies are often overlooked described the effects of increasing strain on mylonite development recorded the prominent lineation within mylonites and identified its kinematic significance via thrust geometries and a first use of shear sense indicators in this contribution those elements of the highland controversy that led to the identification of mylonites will be reviewed concentrating on the contributions of lapworth and of peach horne and co workers it will include an examination and discussion of the mylonites from lapworth s locality and of the mylonitized moine schists at eriboll it will conclude with comments on mylonite classification and nomenclature

anomalous sea floor backscatter patterns in methane venting areas dnepr paleo delta nw black sea the relation between acoustic sea floor backscatter and seep distribution is examined by integrating multibeam backscatter data and seep locations detected by single beam echosounder this study is further supported by side scan sonar recordings high resolution 5 khz seismic data pore water analysis grain size analysis and visual sea floor observations the datasets were acquired during the 2003 and 2004 expeditions of the ec funded crimea project in the dnepr paleo delta area northwestern black sea more than 600 active methane seeps were hydroacoustically detected within a small 3 96 km by 3 72 km area on the continental shelf of the dnepr paleo delta in water depths ranging from 72 m to 156 m multibeam and side scan sonar recordings show backscatter patterns that are clearly associated with seepage or with a present dune area seeps generally occur within medium to high backscatter areas which often coincide with pockmarks high resolution seismic data reveals the presence of an undulating gas front i e the top of the free gas in the subsurface which domes up towards and intersects the sea floor at locations where gas seeps and medium to high backscatter values are detected pore water analysis of 4 multi cores taken at different backscatter intensity sites shows a clear correlation between backscatter intensity and dissolved methane fluxes all analyzed chemical species indicate increasing anaerobic oxidation of methane aom from medium to high backscatter locations this is confirmed by visual sea floor observations showing bacterial mats and authigenic carbonates formed by aom grain size analysis of the 4 multi cores only reveals negligible variations between the different backscatter sites integration of all datasets leads to the conclusion that the observed backscatter patterns are the result of ongoing methane seepage and the precipitation of methane derived authigenic carbonates mdacs caused by aom the carbonate formation also appears to lead to a gradual self sealing of the seeps by cementing fluid pathways horizons followed by a relocation of the bubble releasing locations

the strain and textural history of thin skinned tectonic zones examples from the assynt region of the moine thrust zone nw scotland abstract the moine thrust zone at assynt is a classical example of a foreland propagating thin skinned thrust zone ideal for an examination of thrust related folds deformation textures and strains and complex incremental strain history divergent transport directions oblique trending folds duplex zones and extensional strains normal to the main transport direction may all be explained in terms of thrust propagation leading to the development of oblique to lateral ramps the majority of thrusts cut up section from basement to cover in the transport direction but there is also localised extensional flow and thinning of the thrust sheets in northern assynt the thrust zone involves a wide vertical zone of sinistral shear within which forethrusts backthrusts and associated folds and cleavages are oblique to the general transport direction it is suggested that north of this shear the thrusts moved further probably under a thicker cover while to the south movement was more intermittent probably under a thinner cover this variation is probably due to a change in thrust geometry in the moines east of the moine thrust zone causing a variation in gravitational potential along the length of the moine thrust

sphagnum peatland distribution in north america and eurasia during the past 21 000 years the distribution and abundance of sphagnum spores in north america and eurasia are mapped for the past 21 ka the present day distribution of abundant sphagnum spores corresponds closely to areas with peatland development with maximum sphagnum abundance between 630 and 1300 mm annual precipitation and between 2 and 6 c mean annual air temperature during the wisconsin glaciation there were apparently not large areas of peatland in north america except in alaska high sphagnum spore percentages were found in eastern north america during deglaciation major peatland development occurred in boreal north america after 9 ka and there was a southward movement of high sphagnum spore abundance after 5 ka in the western great lakes region major peatland development began after 9 ka in europe and asia on the basis of maps of the area supporting peatlands carbon accumulation in peatlands is estimated to be low prior to 11 ka increased slightly between 11 and 5 ka and greatly increased during the past 5 ka

pore pressure and dissipated energy in earthquakes field verification the possibility of a correlation between dynamic pore pressure increase p and dissipated energy density d in soils subjected to earthquake shaking has been the subject of speculation for nearly 20 years while cyclic loading tests have tended to confirm the d p hypothesis in the laboratory no field confirmation has been given in this paper compelling evidence is presented to support the d p model from two real earthquakes downhole acceleration records from two earthquakes are analyzed to obtain approximate histories of shear stress shear strain and dissipated energy over a range of depths the measured data were obtained from the lotung downhole array in taiwan and from the sunamachi downhole array near tokyo both of these arrays also contain pore pressure measurement devices and records of pore pressure increase during the earthquakes are available time histories of measured pore pressure will be directly compared with calculated values based on the d p hypothesis the results of this study suggest dissipated energy density may be remarkably well correlated with pore pressure increase in field situations

spatial and temporal constraints on sources of seismic anisotropy evidence from the scottish highlands 1 routine sks splitting analyses of seismic anisotropy usually suffer from limitations in station density that hinder attempts to place spatial constraints on anisotropic fabrics data from a 20 km station spacing network in scotland show that splitting parameters vary considerably t 0 45 1 5 s 49 128 over short 10 20 km length scales improved spatial constraints then lead to tighter temporal constraints on the anisotropic sources asthenospheric fabrics due to tertiary rifting and present day plate motions do not strongly influence our results that instead correlate with lithospheric scale trends inferred from surface geology splitting observations track scotland s tectonic history from the precambrian emplacement of crustal basement and through the activation of large scale faulting and thrusting during the caledonian orogeny the shallow lithosphere beneath scotland has preserved a fossil anisotropic signature up to hundreds of millions of years after it was formed

the thrust and shear zones of the moine thrust zone and the nw scottish caledonides the caledonian thrust belts of nw scotland exhibit many features typical of foreland fold and thrust belts the major structures propagated westwards towards the foreland the thin carapace of cambro ordovician sediments being accreted in imbricate and duplex zones beneath the major thrust sheets on a broad scale the rules of thrust geometry are obeyed but many local anomalies are found particularly in the assynt region in assynt several large fault bounded gravity spreading structures surge zones have been identified extensional faults have been traced into strike slip and then contractional faults there are zones of extensional and contractional imbricate faults and extensional and contractional ductile flow similar structures have been found along the length of the moine thrust belt suggesting that gravity spreading was an important mechanism during the later stages of movement within the main caledonian fold belt there are several major tectonic slides which are recognized by a local increase in intensity of deformation the majority are nw verging and were originally gently dipping in the highlands se of the great glen there are early major se verging recumbent folds associated with considerable crustal thickening reflected in high pressure 12kbar metamorphism many of the major slides may have formed by spreading away from this thickened crust the caledonian deformation and metamorphism occurred later in the moines and moine thrust zone than in the dalradian and grampian moines to the se of the great glen this may reflect different levels of deformation alternatively it may argue for a large strike slip displacement on the great glen fault juxtaposing crustal blocks which had experienced different ages of caledonian deformation and metamorphism the late movement on the moine thrust involved spreading from an area of thickened caledonian crust formed either by the stair step trajectory of the basal thrust to the moines and or by thickening due to intrusion of large masses of late caledonian granites

tectonic stratigraphy and structural continuity of the northernmost moine thrust zone and moine nappe scottish caledonides the moine thrust zone and overlying moine nappe represent classic ground in scottish geology in which neoproterozoic moine metasedimentary rocks were translated towards the wnw over the laurentian foreland comprising lewisian basement gneisses and a cambrian cover succession during caledonian orogenesis at c 430 ma systematic mapping of both the moine nappe and underlying moine thrust zone in the loch hope to whiten head region of sutherland extends the tectonic stratigraphy developed in other parts of the thrust zone to the little studied north coast section an apparent continuum of deformation is recognized from the moine nappe down into the underlying thrust zone with a consistent gently ese dipping foliation associated with down dip mineral and extension lineations the polyphase fold history present within the moine nappe and the thrust zone results from progressive deformation during thrusting thrust related fold axes and bedding cleavage intersections are typically subparallel to the transport direction in high strain zones whereas gently north or south plunging attitudes are common in lower strain portions of the thrust zone thrusts are commonly deformed by folds developed within their footwalls consistent with a foreland propagating sequence of deformation the newly defined lochan riabhach thrust is interpreted as an out of sequence structure that sliced at low angles across the thrust zone and toward the wnw after initial thrust stacking comparison with the downfaulted segment of the moine nappe and thrust zone exposed on the foreland at faraid head demonstrates cross strike continuity of the thrust sheet template and structural history for at least 15 km to the nw

pore pressure generation of silty sands due to induced cyclic shear strains it is well established that the main mechanism for the occurrence of liquefaction under seismic loading conditions is the generation of excess pore water pressure most previous research efforts have focused on clean sands yet sand deposits with fines are more commonly found in nature previous laboratory liquefaction studies on the effect of fines on liquefaction susceptibility have not yet reached a consensus this research presents an investigation on the effect of fines content on excess pore water pressure generation in sands and silty sands multiple series of strain controlled cyclic direct simple shear tests were performed to directly measure the excess pore water pressure generation of sands and silty sands at different strain levels the soil specimens were tested under three different categories 1 at a constant relative density 2 at a constant sand skeleton void ratio and 3 at a constant overall void ratio the findings from this study were used to develop insight into the behavior of silty sands under undrained cyclic loading conditions in general beneficial effects of the fines were observed in the form of a decrease in excess pore water pressure and an increase in the threshold strain however pore water pressure appears to increase when enough fines are present to create a sand skeleton void ratio greater than the maximum void ratio of the clean sand

the tectonic history of kohistan and its implications for himalayan structure the tectonic history of kohistan northern pakistan involves two collisional events cleavage and folding developed at 90 100 ma along the northern suture between the kohistan island arc and the asian plate at the same time there was major folding and shearing of the lower part of the kohistan arc approximately 100 km south of the suture this deformation was followed by ocean subduction south of the kohistan arc generating the kohistan calc alkaline batholith with subsequent ocean closure during the eocene and obduction of the kohistan arc together with the adjacent part of the asian plate over the indian continental crust the construction of balanced cross sections through the imbricated upper part of the indian continental crust in the footwall to this southern suture indicates a minimum displacement of 470 km requiring the western himalayan hinterland to be underlain by a large wedge of indian middle to lower crust there is some shortening of the overriding kohistan and asian plates by thrusts and shear zones but it is insufficient to satisfy the palaeomagnetic data there must be major crustal shortening involving thrusts in the hindu kush and pamirs north of kohistan the post eocene thrust direction which for most of pakistan is towards 160 is almost perpendicular to that immediately to the east in the himalayan belt generating complex refolded thrust patterns in the hazara syntaxis and large scale folding and rapid uplift with associated brittle faulting and seismic activity adjacent to the nanga parbat syntaxis these different thrust trends indicate that major thrust movement as well as the folds and deformation fabrics cannot always be related to plate movement vectors but are modified by or develop from complex rotations during place collision or from the gravitational spreading of a thickened crust a regional approach is required to recognize and correctly attribute the various components in thrust displacements

a structural interpretation of a section of the gavarnie nappe and its implications for pyrenean geology abstract the gavarnie nappe is a feature of the tertiary pyrenean orogen and is shown to consist of at least two thrust sheets of palaeozoic rocks which are overlain by a southward dipping sequence of cretaceous and eocene sediments showing folded thrust structures the gavarnie nappe covers a basement and mesozoic cover rock sequence which is exposed in the tectonic windows of la larri and the troumouse cirque here previously unrecognized thrusts involving basement were responsible for folding the overlying gavarnie nappe these basement involved thrusts climb up section westwards giving a westward lowering of the gavarnie thrust along strike the structural evolution of the gavarnie nappe in a region extending from heas in france to the valle de pineta in spain can be explained in terms of a piggy back thrusting sequence on a regional scale thrust tectonic models may be used to explain the double vergence of the pyrenean chain where early southward directed thrusting was responsible for structures in the south pyrenean zone a later northward directed back thrusting event or rotation of southward directed thrust sheets by the stacking of lower thrust horses can explain the steepness of structures in the axial zone and the northward verging north pyrenean thrust zone both models suggest that prior to the pyrenean orogeny some of the hercynian structures in the axial zone were flatter lying and have been rotated to their present steepness during the pyrenean orogeny

late quaternary crustal shortening rate across the shinjo basin northeast japan 1 the active fault and fold belt in the eastern shinjo basin has contributed to late quaternary crustal shortening of the northeastern japan arc the geometries of several deformed strata and geomorphic surfaces recorded different rates of cumulative shortening fluvial terraces as old as 290 ka were dated by 14c and fission track dating and tephrochronology we used published seismic profiles to constrain the deep structure of the belt vertical offsets of different terrace surfaces show that the slip rate of the chojahara fault in the innermost basin has increased through time on the basis of its seismic profile this fault was interpreted to dip at a high angle the funagata anticline between the chojahara fault and the ou ranges was probably caused by a low angle blind thrust at about a 2 km depth the different geometries between the basin sediments and fluvial terraces caused by the blind thrust indicate downward propagation of the thrust through time synchronous development of the chojahara fault increased slip rate and the blind thrust beneath the funagata anticline downward propagation suggests that these faults form a piggyback fault system connecting to the deep part of the basin bounding kyodanbara fault estimated crustal shortening rates are averaged to be 0 65 1 05 and 0 79 1 42 m kyr over the last 200 260 and 12 28 ka respectively accounting for about 0 7 1 6 of the convergence between the pacific and eurasian plates estimated strain rates are 0 07 0 11 and 0 08 0 14 ppm yr for the last 200 260 and 12 28 ka respectively

geometric and kinematic evolution of basement cored structures intraplate orogenesis within the yanshan orogen northern china abstract detailed surface mapping lithology facies analysis drillcore data and aeromagnetic interpretation reveal the geometries of the basement involved structures of laowopu nantan liudaohe xinglong and malanyu to have been generated by folding and thrusting the resulting basement cored anticlines are asymmetric with a shallowly dipping top and backlimb and a steep to overturned forelimb and or frontal fault linked with a gently dipping synclinal limb both the fold axes and frontal faults trend roughly east west suggesting north south shortening north to northeast trending faults behave as tear lateral or oblique ramp structures and formed coevally with their frontal faults their trends may have been inherited from proterozoic synsedimentary faults and archaean basement ductile shear zones foliations and mafic dikes thin skinned thrusts and their three dimensional geometry are locally controlled by detachment within mechanically incompetent layers four types of interrelationships between the thick and thin skinned structures occur including 1 lateral changes along the length of a fault 2 displacement transfer between thick and thin skinned structures 3 buttressing of thin skinned thrusts against the basement involved structures and 4 generation of an out of the syncline thrust under thick skinned shortening most of the deformation within the study area involved brittle behaviour but ductile shear zones developed where fluid access was possible both the basement involved structures and the thin skinned structures formed in the early mesozoic as constrained by cross cutting relationships isotopic ages of igneous rock and syntectonic basins the model of geometric and kinematic evolution of the basement involved structures and their relationship with the thin skinned structures defined in this paper provides an alternative to the current metamorphic core complex model used for the yanshan intraplate orogen

lateral variations and linkages in thrust geometry the traligill transverse zone assynt culmination moine thrust belt nw scotland abrupt lateral changes in thrust geometry occur in many fold and thrust belts along so called transverse zones commonly related to pre existing basement faults however the causative structures are usually concealed we analyse here the traligill transverse zone in the assynt culmination of the caledonian moine thrust belt nw scotland this transverse zone trends sub parallel to the wnw transport direction and is associated with en echelon faults cutting thrusts discontinuity of thrust architecture and oblique fold and thrust structures thick thrust sheets north of the transverse zone contain thick basement slices thrust sheets to the south are thin and involve a thin bedded sequence the traligill transverse zone developed above the loch assynt fault a basement cross fault and reactivated proterozoic ductile shearzone piercing point analysis shows that the cross fault was active both before and after thrusting thrusting thus affected strata that were already disrupted by steep faults the amplitude of the disturbance in fold and thrust architecture along the traligill transverse zone is much greater than the vertical displacement along the fault this is attributed to localised transpressional thrust stacking other basement cross faults and their relationship with lateral variations within the moine thrust belt and in other thrust belts are discussed

discussion on a reassessment of the proposed lairg impact structure and its potential implications for the deep structure of northern scotland journal of the geological society london 176 817 829 the interpretation of the stac fada member of the stoer group of nw scotland as a proximal ejecta blanket of late mesoproterozoic age amor et al 2008 has led to the search for the impact crater from which it originated one prominent suggestion has been that this crater lies buried beneath east central sutherland broadly centred on the village of lairg fig 1 simms 2015 simms ernstson 2019 develop this suggestion by interpreting the well known negative anomaly that dominates the bouguer gravity map of northern scotland to represent the roots of this crater however they qualify their interpretation noting that the geology at the stac fada outcrops implies a more distant crater location and go on to propose hitherto unreported crustal shortening structures to explain this discrepancy in doing so they challenge current understanding of structural evolution in the moine thrust belt and for crustal structure in nw scotland the purpose of this discussion is to demonstrate not only that the simms ernstson 2019 proposals are incompatible with the known structural geology of northern scotland but that the geology of the moine thrust belt renders the lairg site to be one of the very few places that can be regarded as a highly unlikely source for the stac fada impact rocks internal earth processes rather than extra terrestrial interventions should be sought as explanations for the lairg gravity low a more general aim is to show through this discussion that making small changes to tectonic models commonly carries unintended consequences for geological interpretations that can go unrecognized if only illustrated on unscaled sketches fig 1 simplified geological map of northern scotland with locations discussed in the text together with the location of the contested lairg impact crater x y is the location of the section line for figure 2a as recognized

gaia s breath global methane exhalations abstract methane ch 4 is the most abundant organic compound in the earth s atmosphere where it acts as a greenhouse gas and thus has implications for global climate change the current atmospheric ch 4 budget however does not take into account geologically sourced ch 4 seepage geological sources of ch 4 include natural macro and micro seeps mud volcanoes and other miscellaneous sources such as gas hydrates magmatic volcanoes geothermal regions and mid ocean ridges macro seeps contribute 25 tg teragrams ch 4 yr to the atmosphere whereas micro seepage contributes perhaps 7 tg ch 4 yr mud volcanoes emit 5 tg ch 4 yr and miscellaneous sources emit 8 tg ch 4 yr to the atmosphere thus the total contribution to the atmosphere from geological sources is estimated to be 45 tg ch 4 yr which is significant to the atmospheric organic carbon cycle and should be included in any global inventory of atmospheric ch 4 we argue that the atmospheric ch 4 global inventory of the interplanetary panel on climate change must be adjusted in order to incorporate geologically sourced ch 4 from naturally occurring seepage

quantification of methane emission from bacterial mat sites at quepos slide offshore costa rica seafloor methane emission from the quepos slide on the submarine segment of the costa rica fore arc margin was estimated by extrapolating flux measurements from individual seeps to the total area covered by bacterial mats this approach is based on the combination of detailed mapping to determine the abundance of seeps and the application of a numerical model to estimate the amount of benthic methane fluxes model results suggest that the majority of the studied seeps transport rather limited amount of methane on average 177 mol cm 2 a 1 into the water column due to moderate upward advection allowing for intense anaerobic oxidation of methane aom on average 53 of the methane flux is consumed depth integrated aom rates 56 1 538 mol ch4 cm 2 a 1 are comparable with values reported from other active seep sites the overall amount of dissolved methane released into the water column from the entire area covered by bacterial mats on the quepos slide is estimated to be about 0 28 106 mol a 1 this conservative estimate which relies on rather accurate determinations of seafloor methane fluxes emphasizes the potential importance of submarine slides as sites of natural methane seepage however at present the global extent of methane seepage from submarine slides is largely unknown

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

thrust sequences and the significance of low angle out of sequence faults in the northernmost moine nappe and moine thrust zone nw scotland in common with most thrust belts the moine thrust zone scotland preserves a foreland propagating sequence of thrusting however significant examples of local to regional overstep sequences are also recognized and their interpretation remains controversial remapping of the northernmost moine thrust zone has defined a thick belt of mylonites in the centre of which lies the ductile wnw directed moine thrust the base of the mylonite belt however is marked by a regionally significant low angle west directed brittle fault here termed the lochan riabhach thrust that truncates thrust related structures in its footwall comparison of the tectonic stratigraphy of the mylonite belt with that preserved in a downfaulted outlier to the west at durness indicates that the lochan riabhach thrust cuts down section in its footwall and therefore appears to be extensional locally it is unequivocally breached by underlying imbricate thrusts we prefer to interpret the lochan riabhach thrust as an extensional fault that formed during a hiatus in thrust stacking we relate this faulting episode to the changes in the stability of the evolving orogenic wedge and reiterate that such extensional faults may be common although possibly unrecognized features in many other thrust belts