abyssal serpentinites as gigantic factories of marine salts and oil abstract serpentinites occur worldwide in various geological settings such as in magma starved oceanic basins abyssal serpentinites are long term storage for chlorine and carbon the latter forming dominantly reduced and subordinately oxidized compounds hence serpentinites salts and reduced carbon phases coexist in an abyssal association although huge reservoirs of salts and reduced carbonaceous matter in abyssal serpentinites are thought to be lacking this may be more a reflection of intrinsic limits in research methods than an indication of their absence on the other hand shallow seated hydrocarbon rich mud volcanoes and diapirs consisting of salts hydrocarbons oils and gases and clayey muds including mudded serpentines can provide evidence for such an oceanic association here we search for scientific data in support of the oceanic association and hence we propose a reappraisal of exploitable worldwide salt hydrocarbon reservoirs even gigantic in size abyssal serpentinites are well known source rocks of abiotic gaseous hydrocarbons via fischer tropsch type reaction ftt whereas macromolecular carbonaceous matter mostly bitumen found in serpentinites is postulated to be biogenic this inference is based mainly on three assumptions i ftt in nature does not yield oils ii hydrocarbons derive essentially from the thermal alteration of microbial molecules iii the presence of biomarkers traditionally considered evidence of the biological origin of oils nevertheless some lines of strong evidence disprove these accepted conventions i lab experiments demonstrated that ftt can synthesize significant quantities of liquid hydrocarbons oils under conditions compatible with the deeper and more reduced level of serpentinite hosted hydrothermal systems ii macromolecules generally thought to derive from microbial activity can be abiotically generated as documented in extraterrestrial bodies iii biomarkers are evidence for the proliferation of microbial communities which subsist on serpentinization and ftt products thus they are biological pollutants moreover seawater driven serpentinization consumes water producing huge amounts 11 kg halite m 3 of peridotite of salts that can be stored in the deeper zone of abyssal type hydrothermal systems thus the origin of shallow sited salt deposits even gigantic in size can be related to either the advective upwelling of hot hydrothermal brines due to the dehydration of abyssal serpentinites or to the passive upwelling of buoyant saline geobodies piercement structures are indeed seismically imaged in several localities such as south atlantic the gulf of mexico the serpentinite belt extending from cuba to hispaniola the north sea trench and the zagros orogenic belt similar lines of evidence at the microscopic scale have been found in some hyblean serpentinite xenoliths south eastern sicily being representative of the unmetamorfosed in situ relic of the palaeo tethys ocean upon which sicily and its off shore areas lie in spite of the accepted stereotype of hydrocarbons as fossil fuels and hence finite resources reduced carbon compounds abiotically produced in abyssal serpentinites may be copious protracted over time and thus renewable

higher himalaya in the bhagirathi section nw himalaya india its structures backthrusts and extrusion mechanism by both channel flow and critical taper mechanisms the higher himalayan crystalline hhc in the bhagirathi river section india on fieldwork reveals two extensional ductile top to n ne shear sub zones the south tibetan detachment system and the basal detachment besides a preceding top to s sw ductile shear a top to n ne brittle shear was identified as backthrusts from the hhc except its northern portion that occur repeatedly adjacent to numerous top to s sw brittle shears as fore thrusts the northern portion of the hhc the gangotri granite exhibits infrequent total six extensional and compressional brittle shear senses the backthrusts could be due to a low friction between the lower boundary of the hhc i e the main central thrust zone and the partially molten hot rock materials of the hhc subduction of the eurasian plate towards s sw below the indian plate more extensively in the garhwal sector could be the second possible reason presence of two ductile extensional shear sub zones may indicate channel flow or several exhumation mechanisms of the hhc in a shifting mode similar to mukherjee et al in int j earth sci 101 253 272 2012 the top to s sw extensional brittle shear exclusively within the upper northern portion of the hhc and a top to s sw brittle shear within the remainder of it is a possible indicator of critical taper deformation mechanism thus this work provides the field evidences of possibly both channel flow and critical taper conditions from a higher himalayan section besides that by larson et al geol soc am bull 122 1116 1134 2010

estimation of offsets in gps time series and application to the detection of earthquake deformation in the far field extracting geophysical signals from global positioning system gps coordinate time series is a well established practice that has led to great insights into how the earth deforms often small discontinuities are found in such time series and are traceable to either broad scale deformation i e earthquakes or discontinuities due to equipment changes and or failures estimating these offsets accurately enables the identification of coseismic deformation estimates in the former case and the removal of unwanted signals in the latter case which then allows tectonic rates to be estimated more accurately we develop a method to estimate accurately discontinuities in time series of gps positions at specified epochs based on a so called offset series the offset series are obtained by varying the amount of gps data before and after an event while estimating the offset two methods a mean and a weighted mean method are then investigated to produce the estimated discontinuity from the offset series the mean method estimates coseismic offsets without making assumptions about geophysical processes that may be present in the data i e tectonic rate seasonal variations whereas the weighted mean method includes estimating coseismic offsets with a model of these processes we investigate which approach is the most appropriate given certain lengths of available data and noise within the time series themselves for the sumatra andaman event with 4 5 yr of pre event data we show that between 2 and 3 yr of post event data are required to produce accurate offset estimates with the weighted mean method with less data the mean method should be used but the uncertainties of the estimated discontinuity are larger

high resolution p cable 3d seismic imaging of gas chimney structures in gas hydrated sediments of an arctic sediment drift the newly developed p cable 3d seismic system allows for high resolution seismic imaging to characterize upper geosphere geological features focusing on geofluid expressions gas chimneys shallow gas and gas hydrate reservoirs seismic imaging of a geofluid system of an arctic sediment drift at the vestnesa ridge offshore western svalbard provides significantly improved details of internal chimney structures from the seafloor to not vert similar500 m bsf below seafloor the chimneys connect to pockmarks at the seafloor and indicate focused fluid flow through gas hydrated sediments the pockmarks are not buried and align at the ridge crest pointing to recent topography controlled fluid discharge chimneys are fuelled by sources beneath the base of gas hydrate stability zone ghsz that is evident at not vert similar160 170 m bsf as indicated by a bottom simulating reflector bsr conduit centres that are not vertically straight but shift laterally by up to 200 m as well as discontinuous internal chimney reflections indicate heterogeneous hydraulic fracturing of the sediments episodically active pressure driven focused fluid flow could explain the hydro fracturing processes that control the plumbing system and lead to extensive pockmark formation at crest of the vestnesa ridge high amplitude anomalies in the upper 50 m of the chimney structures suggest formations of near surface gas hydrates and or authigenic carbonate precipitation acoustic anomalies expressed as high amplitudes and amplitude blanking are irregularly distributed throughout the deeper parts of the chimneys and provide evidence for the variability of hydrate and or carbonate formation in space and time

salt tectonics in the atlantic margin of morocco the offshore basins of morocco s atlantic margin represent the westernmost exploration frontier area in north africa figure 1 whereas the presence of an active petroleum system is very well established onshore e g essaouira basin only promising oil shows and one minor oil accumulation have been found to date offshore e g tarfaya basin however all previous exploration effort concentrated only on the shelfal region and therefore it should not be very surprising that several blocks were licensed in the last few years covering large offshore acreage in water depths to almost 3000 m figure 1 as the reconnaissance licenses for these permits are in the process of being converted to exploration licenses a shift from regional scale 2 d seismic reflection data acquisition to prospect scale 2 d and even 3 d is under way figure 1 index map of the atlantic margin of morocco showing location of a regional cross section figure 2 and simplified salt tectonics map figure 3 an active petroleum system is not proven in the deepwater region although a broad world class salt basin stretches along the coastline creating spectacular structural traps the first deepwater well might be spudded as early as next year to test one of these salt related structures a potential target zone within the deepwater salt basin is at the westernmost leading edge of the salt deformational front where a very well developed toe thrust zone formed during the mid tertiary the salt tectonics of offshore morocco may provide some very specific analogs for exploration efforts in other salt basins of the world perhaps the easiest way to understand the scale of the salt basin offshore morocco is to compile regional seismic transects figure 2 shows a line drawing of a regional composite seismic profile across the ras tafelney and safi haute mer permits figure 1 note that the atlantic passive margin of

mud volcanism in the gulf of cadiz results from the ttr 10 cruise a new deep water mud volcano field between 2000 and 3500 m water depth was discovered in the deep south portuguese margin as well as several new mud volcanoes in the south spanish and western moroccan margins of the gulf of cadiz during the ttr 10 training through research unesco ioc cruise in july august 2000 this work followed the discovery of a large mud volcano field in the gulf of cadiz first investigated during the ttr 9 cruise gardner 2001 geophys res lett 28 339 342 kenyon et al 2000 ioc technical series no 56 the discoveries were made based on a seamap side scan sonar mosaic and multibeam bathymetry seabeam collected in the area by the naval research laboratory nrl washington dc usa in 1992 kindly released for this purpose single channel seismics long range side scan sonar okean tv controlled grab hull mounted 3 5 khz profiler and coring were used to investigate several seafloor features observed on the side scan sonar imagery in the south iberia spanish and moroccan margins of the gulf of cadiz which were confirmed to be mud volcanoes the typical structures related to fluid venting in the gulf of cadiz are essentially represented by conical mud volcanoes with diameters ranging from several tens of meters to 4 km and heights that can reach 200 m some of these structures appear to be aligned along major conjugate ne sw and nw se trending faults that can be identified on the side scan sonar imagery the new field discovered in the south portuguese margin is the deepest in the gulf of cadiz area and includes three new mud volcanoes bonjardim olenin and carlos ribeiro which seem to be quite active with near surface gas hydrate occurrence and a high saturation in h2s and hydrocarbon gases mainly methane in the mud breccia and overlying pelagic sediments gas hydrates were recovered from the bonjardim mud volcano an intensely gassified mud breccia with one fragment of semi consolidated claystone with a thin bituminous veneer at the surface was recovered from the carlos ribeiro mud volcano the fauna recovered consists mainly of pogonophoran worms belonging to several species and undetermined species of foraminifera three new mud volcanoes were also discovered in the nw moroccan margin rabat student and jesus baraza these show a richer fauna that includes several species of molluscs polychaetes pogonophoran worms crustaceans echinoderms and some fragments of dead coral madrepora and lophelia carbonate crusts were recovered from the student mud volcano the ginsburg mud volcano discovered during the previous ttr 9 cruise was revisited and gas hydrates recovered once again a new mud volcano was also discovered in the spanish margin tasyo where evidence was found of coral build ups on the hard substratum of the mud volcanic edifice

emplacement of a passive margin evaporitic allochthon in the betic cordillera of spain the triassic section of the external domain of the betic cordillera is rootless and thus allochthonous the frontal accretionary wedge of the guadalquivir allochthon consists dominantly of triassic evaporites and red beds forming a melange with upper cretaceous paleogene deep water sedimentary rocks throughout the unit jurassic rocks are absent it is here proposed that the widespread triassic evaporites of the guadalquivir allochthon were originally emplaced as gravitational allochthonous masses in a passive margin setting much like the widespread allochthonous salt of the texas louisiana gulf of mexico thus on the betic passive margin allochthonous evaporites were first emplaced during the late cretaceous paleogene later during neogene time these evaporites were overthrusted as an accretionary wedge to form the guadalquivir allochthon a schematic reconstructed position of the guadalquivir allochthon places the original passive margin allochthon in its continental slope setting

the geometry and kinematics of the main boundary thrust and related neotectonics in the darjiling himalayan fold and thrust belt west bengal india abstract the main boundary thrust mbt is well exposed in a section of the tista river valley in the darjiling himalayan fold and thrust belt the fault trace trends e w across the n s flowing tista and thrusts gondwana permian age sandstones over lower siwalik miocene age sandstones the mbt has been folded into a fault propagation synform antiform pair by tectonic activity along a younger south kalijhora thrust skt in its footwall that transports lower siwalik rocks over middle siwalik sandstones the skt cuts through the fault propagation structure preserving the mbt fault propagation fold pair in its hanging wall the motion along the skt rotated the bedding and the limbs of the folded mbt in its hanging wall footwall imbrication in front of the skt further rotated the folded mbt footwall imbrication continued to about 30 km south of the study area in the middle siwalik and younger section the region has been subsequently reactivated as evident from uplifted gravel beds and strath terraces along the folded trace of the mbt fault zone and also in the footwall of the skt the reactivation resulted in the formation of connective splays off the existing faults probably forming horses of a connecting splay duplex in the sub surface within the siwalik section the motion along these splays passively folded overlying beds and formed uplifted gravel beds and strath terraces along the local drainage the rotations resulting from footwall imbrication and reactivated splays probably caused the southern limb of the fault propagation synform to become overturned the duplexing also raised the river bed and arrested the flow of the river tista causing the river to pond and deposit its load resulting in the formation of a bar upstream of the mbt trace the tectonic reactivation of the area points to taper building activities in a subcritical wedge probably in response to monsoon induced excessive erosion in the middle of the darjiling sikkim tibet himalayan thrust wedge

mud volcanoes revealed and sampled on the western moroccan continental margin we surveyed and sampled two active and 3 inactive mud volcanoes on the atlantic continental margin of morocco the active mud volcanoes named yuma and ginsburg are each about 4 km in diameter rise between 150 250 meters above the seafloor and are the first active methane related mud volcanoes to be identified in this region the inactive volcanoes range in diameter from 1 3 km with relief between 50 and 80 meters gravity cores from the crest of the active mud volcanoes yielded methane hydrates and mud breccia deposits chemosynthetic communities of pogonophora worms and the bivalve solemya were found on the surface of the active mud volcanoes sediment cores from the inactive volcanoes contained hemipelagic sediments rich in foraminifera and ahermatypic coral debris overlying mud breccia

structure of mud volcano systems and pockmarks in the region of the ceuta contourite depositional system western alboran sea abstract new high resolution seismic and swath bathymetry data reveal the detailed structure of nine mud volcanoes and two large fields of pockmarks at water depths of 400 1100 m in the western alboran sea these features are related to episodes of focused fluid flow through pliocene quaternary contourite deposits of the ceuta drift we describe nine mud volcano systems composed of two key structural elements i extrusive edifices comprising cones bicones and low dip mudflows interfingering with adjacent drift sediments and ii intrusive feeder complexes comprising pipes and unstratified downward tapering cones underlying the extrusive edifices the mud volcano systems are grouped into four types i complex edifices ii stacked single edifices iii single edifices fed by buried bicones and iv single edifices all except the last record episodic extrusive activity since the pliocene the timing of which is constrained by correlation between the main mud extrusion episodes and dated unconformities within the ceuta drift complex mud volcanoes composed of twin to multiple seabed cones are the longest lived systems with at least six extrusive episodes since the mid pliocene most of the mud volcanoes appear to have been reactivated in the mid pleistocene 0 9 ma mpr discontinuity and all at mis12 0 4 ma while the onset of focused fluid flow was triggered by mid pliocene tectonically driven diapirism of lower miocene shales that form the rooting zone of the mud volcanoes we suggest that some of the pleistocene phases of mud extrusion might be related to erosion of the contourite drift during major sea level falls in addition to vertical focused fluid flow we propose that leakages from the mud volcano feeder complexes into high permeability contourite sediments may cause lateral fluid migration and form gas accumulations lateral fluid flow in the near surface sediments could be responsible of forming subsurface reservoirs and consequently random pockmarks by fluidification and or liquefaction of the non consolidated shallow sediments stacked buried paleo pockmarks indicate that this mechanism has been persistent along recent times at least after the mid pleistocene

higher himalayan shear zone sutlej section structural geology and extrusion mechanism by various combinations of simple shear pure shear and channel flow in shifting modes the higher himalayan shear zone hhsz in the sutlej section reveals 1 top to sw ductile shearing 2 top to ne ductile shearing in the upper and the lower strands of the south tibetan detachment system stdsu stdsl and 3 top to sw brittle shearing corroborated by trapezoid shaped minerals in micro scale in the proposed extrusion model of the hhsz the e1 phase during 25 19 ma is marked by simple shearing of the upper sub channel defined by the upper strand of the main central thrust mctu and the top of stdsu as the lower and the upper boundaries respectively subsequently the e2a pulse during 15 14 ma was characterized by simple shear pure shear and channel flow of the entire hhsz finally the e2b pulse during 14 12 ma observed simple shearing and channel flow of the lower sub channel defined by the lower strand of the main central thrust mctl and the top of the stdsl as the lower and the upper boundaries respectively the model explains the constraints of thicknesses of the stdsu and the stdsl along with spatially variable extrusion rate and the inverted metamorphism of the hhsz the model predicts 1 shear strain after ductile extrusion to be maximum at the boundaries of the hhsz which crudely matches with the existing data the other speculations that cannot be checked are 2 uniform shear strain from the mctu to the top of the hhsz in the e1 phase 3 fastest rates of extrusion of the lower boundaries of the stdsu and the stdsl during the e2a and e2b pulses respectively and 4 variable thickness of the stdsl and rare absence of the stdsu non parabolic shear fabrics of the hhsz possibly indicate heterogeneous strain the top to sw brittle shearing around 12 ma augmented the ductile extruded rocks to arrive a shallower depth the brittle ductile extension leading to boudinage possibly did not enhance the extrusion

current shortening across the himalayas of nepal summary underthrusting of the indian lithosphere beneath the himalayas occurs during the quaternary period along a gently north dipping main basal detachment main himalayan thrust mht from which the southernmost emergent ramp main frontal thrust mft branches historical seismicity shows that slip on the mht is frequently accommodated through m 8 shallow earthquakes but shows a seismic gap in western nepal this absence of major historical earthquakes in western nepal can be explained either by an aseismic slip on the mht or a longlived elastic strain accumulation to test these hypotheses the present day displacement field has been measured for a gps network formed of 35 sites the updated solution presented in this paper combines data from 1995 1997 1998 and 2000 measurements the lack of deformation less than 3 10 8 yr 1 through the outer belt does not fit with a regional aseismic slip along the southern part of mht a less than 3 mm yr 1 aseismic slip could nonetheless affect restricted areas of the outer belt in contrast a strain accumulation of more than 30 10 8 yr 1 is measured south of the higher himalayas in a zone where an intense microseismicity reflects a stress build up it is presumably generated by locking of the aseismic creep that occurs along the mht beneath the higher himalayas and tibet the displacement field is simulated by a dual dislocation model that takes into account the pattern of microseismicity and particularly a segmentation between central and western nepal the best fit between the measured and simulated displacement fields is obtained with 19 mm yr 1 thrust and 0 1 mm yr 1 dextral strike slip components along a 117 ne dislocation locked to a depth of 20 21 km beneath western nepal and 19 20 mm yr 1 thrust and 0 2 mm yr 1 dextral strike slip components along a 108 ne dislocation locked to a depth of 17 21 km beneath central nepal the width of the locked zone between the main frontal thrust and the creeping zone is of the same order but rather greater in western nepal than in central nepal therefore it is expected that m 8 earthquakes could occur in western nepal

seafloor instabilities and sediment deformation processes the need for integrated multi disciplinary investigations abstract in this paper we present the current practice of investigations of seafloor instabilities and deformation processes based on extensive research conducted over the last years which sets the scene for future research activities in this field the mapping of the continental margins and coastal areas with ever increasing resolution systematically reveals evidence of instabilities and deformation processes both active and palaeo features in order to properly assess the hazards and risks related to these features an integrated and multi disciplinary approach is essential but challenging such an approach consists of combining field data geophysics geology sedimentology geochemistry and geotechnical data with numerical simulations constrained by results from laboratory data as such it is of paramount importance to build a common knowledge base and understanding that unify these disciplines into more complete and conceptual models constrained by all the data we review the status of this integrated approach adapted to palaeo landslides e g storegga ana vesteralen and recent deformations finneidfjord nice gulf of guinea allowing to identify gaps in our knowledge at these sites by reviewing these case studies one can conclude that each case remains highly site specific in which both the regional and local geological tectonic settings have a distinct effect of the type of instability or deformation taking place or that can take place our knowledge on the actual triggers remains poorly constrained and there is even ambiguity for historic landslides e g finneidfjord also our knowledge of the preconditioning factors is incomplete there is a general lack of geotechnical data both in situ and from laboratory and therefore modelling the dynamics e g rheology of the instabilities relies on a number of assumptions rather than facts in addition excess pore pressure and its evolution is one of the key parameters driving instabilities despite this fact in situ excess pore pressure is rarely measured or monitored much work remains to be done to relate and integrate geotechnical data with geophysics e g through inversion and rock physical models in order to obtain additional quantitative information from the sub surface but also with respect to partial saturation free gas hydrate and pore pressure behaviour or lithologies it is of critical importance to be able to identify the different processes which can lead to hazardous situations which include establishing recurrence intervals timing and frequencies through event recognition and age control and magnitudes so that proper mitigation measures can be developed in this perspective the smaller scale instabilities deserve much attention as there are many instances where such features had far reaching consequences for society e g nice finneidfjord in that perspective human interferences e g exploitation drilling blasting loading must be one of the factors that should be taken into consideration

seabed morphology and hydrocarbon seepage in the gulf of cadiz mud volcano area acoustic imagery multibeam and ultra high resolution seismic data abstract extensive mud volcanism mud diapirism and carbonate chimneys related to hydrocarbon rich fluid venting are observed throughout the spanish portuguese margin of the gulf of cadiz all the mud volcanoes and diapirs addressed in this paper lie in the region of olistostrome accretionary complex units which were emplaced in the late miocene in response to nw directed convergence between the african and eurasian plates the study area was investigated by multibeam echo sounder high and ultra high resolution seismic profiling dredging and coring the structures observed on multibeam bathymetry at water depths between 500 and 1300 m are dominated by elongate mud ridges mud cones mud volcanoes and crater like collapse structures ranging in relief from 50 to 300 m and size from 0 8 to 2 km in diameter the main morphotectonic features named the guadalquivir diapiric ridge gdr and the cadiz diapiric ridge cdr are longitudinally shaped diapirs which trend ne sw and consist of lower middle miocene plastic marly clays the gdr field and the tasyo field which consist of mud volcanoes and extensive fluid venting related to diapiric ridge development are described in this paper the gdr field is characterised by numerous single sub circular mud volcanoes and mud cones the single mud volcanoes are cone shaped features with relatively gentle slopes of 3 6 consisting of several generations of mud breccia deposition with indications of gas saturation degassing structures and the presence of h2s the mud cones have asymmetric profiles with steep slopes of up to 25 and contain large surficial deposits of hydrocarbon derived carbonate chimneys and slabs the tasyo field is characterised by an extensive concentration of small sub circular depressions oval and multi cone mud volcanoes and large sediment slides mud volcanoes in this area are characterised by moderate slopes 8 12 have bathymetric relief ranging from 100 to 190 m and consist of sulphide rich mud breccia calcite chimneys carbonate crusts and chemosynthetic fauna pogonophora tube worms we propose that all these hydrocarbon seepage structures are related to lateral compressional stress generated at the front of the olistostromic accretionary wedge this stress results in the uplifting and squeezing plastic marly clay deposits additionally the compressional stress at the toe of the olistostrome forms overpressurised compartments which provide avenues for hydrocarbon enriched fluids to migrate

structure and evolution of the olistostrome complex of the gibraltar arc in the gulf of cadiz eastern central atlantic evidence from two long seismic cross sections reflection profiles characterize the structure and the upper mesozoic to cenozoic deposits of the gulf of ca diz region two long ene wsw multichannel seismic lines ca 400 500 km long are analyzed to study the evolution of the area from the continental shelf to the horseshoe and seine abyssal plains the huge allochthonous deposits emplaced in this region the socalled olistostrome of the gulf of cadiz are described in terms of three different domains on the basis of the seismic architecture the main tectonic features and the nature of the basement oceanic or continental the eastern domain extends along the continental shelf and upper and middle slope and corresponds to the offshore extension of the betic rifean external front it is characterized by salt and shale nappes later affected by extensional collapses the central domain develops along the lower slope between the betic rifean front and the abyssal plains and is characterized by a change in dip of the allochthonous basal surface and the basement the allochthonous masses were emplaced by a combined gravitational and tectonic mechanism the northern boundary of this domain is marked by the occurrence of an outstanding wnw ese trending thrust fault with a strike slip component termed here as the gorringe horseshoe fault the westernmost domain corresponds to the abyssal plains where the distal emplacement of the allochthonous body takes place it is characterized by thrust faults affecting both the sedimentary cover and the oceanic basement the allochthonous masses show a less chaotic character and the thickness decreases notably these domains represent different evolutionary steps in the mechanisms of emplacement of the allochthonous units the eastern domain of the allochthonous units was emplaced as part of the pre messinian orogenic wedge related to the collision that gave rise to the betic rifean belt whereas the allochthonous wedge of the central and western domains were emplaced later as a consequence of the ne sw late miocene compression that continues in present times

higher himalayan shear zone zanskar indian himalaya microstructural studies and extrusion mechanism by a combination of simple shear and channel flow thin section studies of the zanskar shear zone zsz rocks reveal a top to sw and subsequent primary and secondary top to ne ductile shearing brittle ductile and brittle extensions top to sw brittle shear steep normal faulting and fracturing in the proposed two phase model of ductile extrusion of the higher himalayan shear zone hhsz a top to sw simple shearing during 22 18 ma was followed by a combination of top to sw simple shear and channel flow at 18 16 ma the second phase simulates a thin zsz characterized by a top to ne shearing the channel flow component ceased around 16 ma the extruding hhsz entered the brittle regime but the top to sw shearing continued until perturbed by faults and fractures variation in the extrusion parameters led to variable thickness of the zsz shear strain after the extrusion is presumably maximum at the boundaries of the hhsz and falls towards the base of the zsz which crudely matches with the existing data the other predictions 1 spatially uniform shear strain after the first stage 2 fastest extrusion rate at the base of the zsz and 3 a lack of continuation of the zsz along the himalayan trend are not possible to validate due to paucity of suitable data non parabolic shear fabrics of the zsz indicate their heterogeneous deformation

crustal deformation and strain analysis in nepal from gps time series measurement and modeling by arma method high precision global positioning system gps measurements from 2002 to 2017 in nepal has been analyzed and modeled with autoregressive moving average arma method the measured velocities of the gps sites in itrf 2014 indicate 6 12 mm year n s convergence inside the nepal between india and tibet this convergence occurs in the southern and western border of nepal but it is negligible to the eastern border of nepal arma modeled result of india fixed velocities is able to successfully model within 0 5 mm year the current measured velocities in nepal synthetic or modeled velocities using arma method and measured velocity have difference 2 mm year at some sites this indicates the possibility of very small level of a ductile deformation in the present best fit arma model the modeled velocities 8 10 mm year convergence taken up from northern to southern boundaries of nepal indicates slip along active main himalayan thrust mht which is the cause of change in tectonic strain and may be able to trigger earthquakes inside the country dislocation modeling of active mht is also carried out in the study using gps vertical displacement the geometric model of the mht is characterized by a rectangular plane with dip angle of 9 5 and the reverse kinematics with a slip of 19 mm year the thrust is located at a depth of 20 km in addition the regional deformation of the nepal has been checked by baseline measurement and coordinate stability of gps sites for the different zones the baseline divergence and convergence of nearest gps sites have been tested using triangular sites the summary of regional deformation implies n s convergence only and rules out any type of e w convergence finally the investigation of observed and modeled strain confirms that there is no significant strain accumulation due to localized regional deformation or earthquakes specific to the active dislocations and faults this suggests that the convergence from northern to southern boundaries of nepal is associated with the slip along the mht only

spatially variable extension in southern tibet based on gps measurements 1 we use global positioning system gps data and kinematic block models to study the present day deformation of southern tibet gps data from 33 sites in southern tibet and nepal surveyed between 1991 and 2000 reveal 13 2 mm yr of n110 e extension between lhasa and shiquanhe 80 e 91 e of which 9 7 3 0 mm yr represents permanent extension of the tibetan crust the remaining 3 mm yr results from elastic deformation from the locked curving main himalayan thrust fault this extension is spatially nonuniform one half to two thirds of the permanent extension is concentrated across the yadong gulu rift with an opening rate of 6 5 1 5 mm yr most of the remainder occurs on or near the thakkola graben with little extension across the rifts between them differential velocities of sites north and south of the yarlung zangbo suture in western tibet imply that the suture or an adjacent structure may be active as a strike slip fault a numerical model suggests that right lateral strike slip on the yarlung zangbo suture may extend from the karakorum fault zone in the west at least to the yadong gulu rift in the east with 3 mm yr slip rate accommodating part of the eastward extrusion of tibet the convergence directions inferred from gps are consistent with slip vectors of earthquakes however the rate of slip of india beneath tibet along the himalaya is lower than those previously estimated we estimate a slip rate of 12 4 0 4 mm yr between longitudes 83 e and 88 e and 17 1 and 19 1 mm yr in the western and eastern himalaya respectively the variable slip rate correlates with the variable extension rate in southern tibet and we suggest that it results from variation in the deformation rate of the overriding tibetan crust we infer that the slower convergence rate in the central himalaya is significant

shallow gas transport and reservoirs in the vicinity of deeply rooted mud volcanoes in the central black sea abstract the principal objective of this paper is to understand the gas migration process and the structures of mud volcanoes in the central black sea multichannel seismic lines were acquired across 6 mud volcanoes in the central black sea msu yuzhmorgeologiya malyshev kornev goncharov and vassoevitch based on a high resolution seismic processing we analyzed acoustic anomalies and studied near surface sediment structures of these mud volcanoes four types of pathways for gas and fluid migration and three types of gas reservoirs were recognized a regional bottom simulating reflection bsr seems to be absent in most parts of the study area however a clear bsr was observed in one of the seismic profiles the free gas migrating upwards along these pathways were sealed by gas hydrates or fine grained sediments in the gas hydrate stability zone four seismic units were separated according to a suggested age model and identified seismic facies combining with the possible sedimentary processes of the central black sea we try to reveal the active mechanism of these mud volcanoes these mud volcanoes reveal two to three major active stages these active stages might be related to distinct sea level falls which seem to be one of the main trigger factors of the mud volcano eruptions in the central black sea a structural model for the msu mud volcano was presented with respect to mechanisms of gas migration and the origin of the gas

clockwise rotation of the brahmaputra valley relative to india tectonic convergence in the eastern himalaya naga hills and shillong plateau gps data reveal that the brahmaputra valley has broken from the indian plate and rotates clockwise relative to india about a point a few hundred kilometers west of the shillong plateau the gps velocity vectors define two distinct blocks separated by the kopili fault upon which 2 3 mm yr of dextral slip is observed the shillong block between longitudes 89 and 93 e rotating clockwise at 1 15 myr and the assam block from 93 5 e to 97 e rotating at 1 13 myr these two blocks are more than 120 km wide in a north south sense but they extend locally a similar distance beneath the himalaya and tibet a result of these rotations is that convergence across the himalaya east of sikkim decreases in velocity eastward from 18 to 12 mm yr and convergence between the shillong plateau and bangladesh across the dauki fault increases from 3 mm yr in the west to 8 mm yr in the east this fast convergence rate is inconsistent with inferred geological uplift rates on the plateau if a 45 n dip is assumed for the dauki fault unless clockwise rotation of the shillong block has increased substantially in the past 4 8 myr such acceleration is consistent with the reported recent slowing in the convergence rate across the bhutan himalaya the current slip potential near bhutan based on present day convergence rates and assuming no great earthquake since 1713 a d is now 5 4 m similar to the slip reported from alluvial terraces that offsets across the main himalayan thrust and sufficient to sustain a mw 8 0 earthquake in this area

impact of skeletal dissolution and secondary aragonite on trace element and isotopic climate proxies in porites corals restricted zones of recent dissolution and secondary aragonite infilling were identified in a coral core collected in 1986 from a living massive porites colony from the central great barrier reef australia secondary aragonite needles 20 m long cover skeletal surfaces deposited from 1972 to late 1974 and increase bulk density by 10 dissolution is observed above this zone whereas older skeleton is pristine we investigate the impact of both types of early marine diagenesis on skeletal geochemistry and coral paleoclimate reconstructions by comparison with similar records from eight contemporary porites colonies collected at nearby reefs secondary aragonite overgrowth causes anomalies in skeletal density mg ca sr ca u ca o and c the secondary aragonite is consistently associated with a cool temperature anomaly for each of the sea surface temperature sst proxies o sst 1 6 c sr ca sst 1 7 c mg ca sst 1 9 c u ca sst 2 8 c dissolution through incongruent leaching also causes cool sst artifacts but only for trace element ratios mg ca sst 1 2 c sr ca sst 1 2 c u ca sst 2 1 c the sequence of preference with respect to dissolution of coral skeleton in seawater is mg ca sr u rigorous screening of coral material for paleoclimate reconstructions is therefore necessary to detect both dissolution and the presence of secondary minerals the excellent agreement between apparent sst anomalies generated by different modes of diagenesis means that replication of tracers within a single coral cannot be used to validate climate proxy interpretations poor replication of records between different coral colonies however provides a strong indication of nonclimatic artifacts such as dissolution and secondary aragonite copyright 2007 by the american geophysical union

submersible study of mud volcanoes seaward of the barbados accretionary wedge sedimentology structure and rheology abstract in 1992 the nautile went to a mud volcano field located east of the barbados accretionary wedge near 13 50n using nannofossil analysis on cores we determined the sedimentation rate and provided a new estimation of the age of the mud volcanoes 750 000 years for the oldest one six structures have been explored with the submersible nautile and manifestations of fluid venting chimneys carbonate cementation and chemosynthetic communities were observed on all sedimentological analysis identifies two sources of diapiric mud most mud volcanoes expel mud containing late miocene to quaternary faunae that have the same composition as sediments drilled above the barbados wedge decollement one volcano also contains older oligocene taxa with a mud composition corresponding to the sedimentary sequence below the decollement we use diving observations to map the fine scale morphology the distribution of chemosynthetic fauna and define two end member types of structures mud pies flat topped mud volcanoes and conical mounds mud pies atalante and cyclops are characterised by the presence of a lake of highporosity mud 70 to 75 in their central parts chemosynthetic benthic communities calyptogena colonies and sponge bushes are concentrated in the outer parts contrasting morphologies of the two mud pies indicate different stages of activity cyclops is growing whereas atalante is collapsing expulsion of water and methane occurs mostly through the mud lake and may be stronger during the collapse phase on conical mounds there are no mud lakes fluid venting concentrates near the summit and occurs through carbonate cemented chimneys which form within the sediment viscosity measurements have been carried out on mud samples from the two mud pies and one conical mound all mud samples have a plastic fluid behaviour the plastic threshold decreases with porosity and thixotropy is observed for a porosity of more than 70 an analogue experiment shows that for this thixotropic mud shearing in the feeding conduit liquefies the mud which then spreads to form a mud pie conical mounds form when the mud remains plastic we show that the dissociation of methane hydrate is the cause of the high porosity in mud pies and confirm that these structures are a consequence of large scale dissociation of methane hydrate at the base of its stability field dissociation of hydrates before and during ascent is only slightly contributing to the pore fluid in conical mounds but solid hydrates still present in the mud may contribute to its buoyancy

large scale slope failure involving triassic and middle miocene salt and shale in the gulf of cadiz atlantic iberian margin sheets of salt and ductile shale advancing beyond the thrust front of the gibraltar arc iberian moroccan atlantic continen tal margin triggered downslope movements of huge allochth onous masses these allochthons represent the cadiz nappe which detached from the gibraltar arc along low angle normal faults and migrated downslope from the iberian and moroccan continental margins towards the atlantic ocean extensional tectonics initiated upslope salt withdrawal and downslope diapirism during large scale westward mass wasting from the shelf and upper slope low angle salt and shale detachments bound by lateral ramps link extensional structures in the shelf to folding thrusting and sheets of salt and shale in the gulf of cadiz from backstripping analyses carried out on the depo centres of the growth fault related basins on the shelf we infer two episodes of rapid subsidence related to extensional collapses these were from late tortonian to late messinian 200 400 m myr 1 and from early pliocene to late pliocene 100 150 m myr 1 the extensional events that induced salt movements also affected basement deformation and were probably associated with the westward advance of frontal thrusts of the gibraltar arc as a result of the convergence between africa and eurasia the complexities of salt and or shale tectonics in the gulf of cadiz result from a combination of the deformations seen at convergent and passive continental margins

tectonics and mud volcano development in the gulf of cadiz many structures associated with fluid escape including mud volcanoes mud carbonate mounds pockmarks and slides have been identified and characterized in the gulf of cadiz most of the mud volcanoes following ne sw and nw se main trends are found at 350 2000 m depth in the eastern domain of the gulf of cadiz which corresponds to the betic rifean margin scattered mud volcanoes have also been recognized on the lower slope at 2300 3900 m depth the major tectonic structures are thrust faults extensional faults strikeslip faults and diapirs all these tectonic structures have provided escape pathways for overpressured material and fluids or have favoured upward fluid movement along the sedimentary column and eventually the build up of mud volcanoes in this work we present images of the mud volcano plumbing systems and the relationship between regional tectonics and mud volcano development seismic profiles acquired during the tasyo 2000 and mvseis ttr 15 cruises are used to image and interpret the link between the mud volcano edifices and the subsurface tectonic structures

significance of mud volcanism 1 mud volcanism and diapirism have puzzled geoscientists for 2 centuries they have been described onshore and offshore in many places on earth and although they occur in various tectonic settings the majority of the features known to date are located in compressional tectonic scenarios this paper summarizes the main thrusts in mud volcano research as well as the various regions in which mud volcanism has been described mud volcanoes show variable geometry up to tens of kilometers in diameter and several hundred meters in height and a great diversity regarding the origin of the fluid and solid phases gas predominantly methane water and mud may be mobilized at subbottom depth of only a few meters but in places can originate from several kilometers depth with minor crustal or mantle input the possible contribution of mud extrusion to global budgets both from quiescent fluid emission and from the extrusive processes themselves is important in regions where mud volcanoes are abundant such as the collision zones between africa and eurasia fluid flux through mud extrusion exceeds the compaction driven pore fluid expulsion of the accretionary wedge also quiescent degassing of mud volcanoes may contribute significantly to volatile budgets and hence to greenhouse climate

seismotectonic perspectives on the himalayan arc and contiguous areas inferences from past and recent earthquakes abstract spread over countries including pakistan india nepal bhutan and china the himalayan mountain chain the most spectacular result of the indo eurasian plate collision is a locus of destructive earthquakes past earthquakes from this region have impacted vast swathes of frontal himalaya and stretches of alluvial plains south of the range front risk from future earthquakes has increased considering the burgeoning population and an ever expanding built environment in the region while considerable ambiguities exist on the locations ruptures and sizes of the earthquakes during the first half of the last millennium 1255 1344 and 1505 ce those during the latter half 1803 and 1833 ce are quite well documented all reported from the central himalayan segment comprising eastern nepal kumaun and garhwal while dormancy prevailed in the central segment in the intervening period the himalayan arc elsewhere witnessed three large great earthquakes in the last century namely 1905 kangra mw 7 8 1934 bihar nepal mw 8 2 and 1950 upper assam mw 8 6 the last one being the largest intra continental earthquake in the recorded history the april 25 gorkha nepal earthquake mw 7 8 located in the central seismic gap terminated the period of low level seismic productivity that followed the 1950 event the himalayan arc and its contiguous regions are now being investigated using various tools including paleoseismology quite understandably the interpretations and tectonic models do not always converge given the diverse quality and type of data the data from variously sized modern day earthquakes sourced in the diverse structural settings of the himalaya provide better constraints on the source properties of the himalayan earthquakes the source complexity and diversity is a striking point of interest for the post 1950 events and at least some of them seem to deviate from the generally accepted model of great ruptures on a shallow dipping detachment a prime example of such anomalies is the 2005 kashmir earthquake mw 7 6 sourced on an out of sequence thrust the sources of the 1991 uttarkashi mw 6 8 1999 chamoli mw 6 6 and the 2015 gorkha nepal mw 7 8 earthquakes all in the central himalayan segment are attributed to the ramp flat on the down dip part of the main himalayan thrust mht in contrast the 2011 sikkim mw 6 9 and the 2016 imphal mw 6 7 earthquakes are intraplate events sourced within the subducting slab source models of modern day earthquakes 1991 2016 discussed in this paper bring out this plurality of mechanisms expected of a complex subduction cum collisional boundary this review presents the status of current seismotectonic understanding of the himalaya from the analyses of significant earthquakes from the past as well as recent events with a focus on the central himalayan segment

seismotectonics of the nepal himalaya from a local seismic network the national seismological network of nepal consists of 17 short period seismic stations operated since 1994 it provides an exceptional view of the microseismic activity over nearly one third of the himalayan arc including the only segment between longitudes 78 e and 85 e that has not produced any m 8 earthquakes over the last century it shows a belt of seismicity that follows approximately the front of the higher himalaya with most of the seismic moment being released at depths between 10 and 20 km this belt of seismicity is interpreted to reflect interseismic stress accumulation in the upper crust associated with creep in the lower crust beneath the higher himalaya the seismic activity is more intense around 82 e in far western nepal and around 87 e in eastern nepal western nepal between 82 5 and 85 e is characterized by a particularly low level of seismic activity we propose that these lateral variations are related to segmentation of the main himalayan thrust fault the major junctions between the different segments would thus lie at about 87 e and 82 e with possibly an intermediate one at about 85 e these junctions seem to coincide with some of the active normal faults in southern tibet lateral variation of seismic activity is also found to correlate with lateral variations of geological structures suggesting that segmentation is a long lived feature we infer four 250 400 km long segments that could produce earthquakes comparable to the m 8 4 bihar nepal earthquake that struck eastern nepal in 1934 assuming the model of the characteristic earthquake the recurrence interval between two such earthquakes on a given segment is between 130 and 260 years

stress triggering in thrust and subduction earthquakes and stress interaction between the southern san andreas and nearby thrust and strike slip faults 1 we argue that key features of thrust earthquake triggering inhibition and clustering can be explained by coulomb stress changes which we illustrate by a suite of representative models and by detailed examples whereas slip on surface cutting thrust faults drops the stress in most of the adjacent crust slip on blind thrust faults increases the stress on some nearby zones particularly above the source fault blind thrusts can thus trigger slip on secondary faults at shallow depth and typically produce broadly distributed aftershocks short thrust ruptures are particularly efficient at triggering earthquakes of similar size on adjacent thrust faults we calculate that during a progressive thrust sequence in central california the 1983 mw 6 7 coalinga earthquake brought the subsequent 1983 mw 6 0 nunez and 1985 mw 6 0 kettleman hills ruptures 10 bars and 1 bar closer to coulomb failure the idealized stress change calculations also reconcile the distribution of seismicity accompanying large subduction events in agreement with findings of prior investigations subduction zone ruptures are calculated to promote normal faulting events in the outer rise and to promote thrust faulting events on the periphery of the seismic rupture and its downdip extension these features are evident in aftershocks of the 1957 mw 9 1 aleutian and other large subduction earthquakes we further examine stress changes on the rupture surface imparted by the 1960 mw 9 5 and 1995 mw 8 1 chile earthquakes for which detailed slip models are available calculated coulomb stress increases of 2 20 bars correspond closely to sites of aftershocks and postseismic slip whereas aftershocks are absent where the stress drops by more than 10 bars we also argue that slip on major strike slip systems modulates the stress acting on nearby thrust and strike slip faults we calculate that the 1857 mw 7 9 fort tejon earthquake on the san andreas fault and subsequent interseismic slip brought the coalinga fault 1 bar closer to failure but inhibited failure elsewhere on the coast ranges thrust faults the 1857 earthquake also promoted failure on the white wolf reverse fault by 8 bars which ruptured in the 1952 mw 7 3 kern county shock but inhibited slip on the left lateral garlock fault which has not ruptured since 1857 we thus contend that stress transfer exerts a control on the seismicity of thrust faults across a broad spectrum of spatial and temporal scales

linked halokinesis and mud volcanism at the mercator mud volcano gulf of cadiz mud volcanoes are seafloor expressions of focused fluid flow that are common in compressional tectonic settings new high resolution 3 d seismic data from the mercator mud volcano mmv and an adjacent buried mud volcano bmv image the internal structure of the top 800 m of sediment at both mud volcanoes revealing that both are linked and have been active episodically the total volumes of extruded mud range between 0 15 and 0 35 km3 and 0 02 0 05 km3 for the mmv and the bmv respectively the pore water composition of surface sediment samples suggests that halokinesis has played an important role in the evolution of the mud volcanoes we propose that erosion of the top of the vernadsky ridge that underlies the mud volcanoes activated salt movement triggering deep migration of fluids dissolution of salt and sediment liquefaction and mobilization since the end of the pliocene since beginning of mud volcanism in this area the mud volcanoes erupted four times while there was only one reactivation of salt tectonics this implies that there are other mechanisms that trigger mud eruptions the stratigraphic relationship of mudflows from the mmv and bmv indicates that the bmv was triggered by the mmv eruptions this may either be caused by loading induced hydrofracturing within the bmv or due to a common feeder system for both mud volcanoes this study shows that the mud volcanoes in the el arraiche mud volcano field are long lived features that erupt with intervals of several tens of thousands of years

geophysical evidence of gas hydrates in shallow submarine mud volcanoes on the moroccan margin 1 gas hydrates inside mud volcanoes have been observed in several locations but are generally found at water depths of 1000 m and deeper we present the first observation of the base of a gas hydrate stability zone within a shallow mud volcano in the el arraiche mud volcano field on the moroccan atlantic margin the mud volcano base is located at about 475 m and is over 125 m high on high resolution seismics we observed an anomalous but coherent reflection under the slopes of the mud volcano the event was interpreted as the base of a gas hydrate stability zone because of its inverse polarity and its morphology far from the crater the event is nearly parallel to the seafloor closer toward the crater the event shallows inside the mud volcano crater no event is observed a stability model using thermogenic gas compositions is applied to local p t conditions indicating that thermogenic gas hydrates can be stable at this depth the high modeled heat flow in the crater of the mud volcano indicates a focused flow of warm fluids below the slopes of the mud volcano the inferred heat flow is also elevated but less high in areas of thermogenic gas production gas hydrates can occur at shallow water depths even in areas with high heat flow this also suggests that dewatering of the accretionary wedge complex is mainly focused along fault surfaces and through seafloor structures such as mud volcanoes

implications of channel flow analogue models for extrusion of the higher himalayan shear zone with special reference to the out of sequence thrusting the higher himalayan shear zone hhsz contains a ductile top to n ne shear zone the south tibetan detachment system lower stdsl and an out of sequence thrust oost as well as a top to n ne normal shear at its northern boundary and ubiquitously distributed compressional top to s sw shear throughout the shear zone the oost that was active between 22 ma and the holocene varies in thickness from 50 m to 6 km and in throw from 1 4 to 20 km channel flow analogue models of this structural geology were performed in this work a newtonian viscous polymer pdms was pushed through a horizontal channel leading to an inclined channel with parallel and upward diverging boundaries analogous to the hhsz and allowed to extrude to the free surface a top to n ne shear zone equivalent to the stdsu developed spontaneously this also indirectly connotes an independent flow confined to the southern part of the hhsz gave rise to the stdsl the pdms originally inside the horizontal channel extruded at a faster rate through the upper part of the inclined channel the lower boundary of this faster pdms defined the oost the model oost originated at the corner and reached the vent at positions similar to the natural prototype some time after the channel flow began the genesis of the oost seems to be unrelated to any rheologic contrast or climatic effects profound variations in the flow parameters along the hhsz and the extrusive force probably resulted in variations in the timing location thickness and slip parameters of the oost variation in pressure gradient within the model horizontal channel however could not be matched with the natural prototype channel flow alone presumably did not result in southward propagation of deformation in the himalaya

himalayan seismic hazard the devastating earthquake in bhuj on 26 january 2001 highlighted the high earthquake risk in the indian region of gujarat in their perspective bilham et al warn that major earthquakes may be expected in another part of india the himalayan arc an analysis of historic earthquakes suggests that several major earthquakes are overdue in this region but that recent low activity has focused attention away from the himalayan arc projections from earlier earthquakes suggest that just one of the possibly overdue himalayan earthquakes may lead to 200 000 predictable fatalities

millenary mw 9 0 earthquakes required by geodetic strain in the himalaya the himalayan arc produced the largest known continental earthquake the m w 8 7 assam earthquake of 1950 but how frequently and where else in the himalaya such large magnitude earthquakes occur is not known paleoseismic evidence for coseismic ruptures at the front of the himalaya with 15 to 30 m of slip suggests even larger events in medieval times but this inference is debated here we estimate the frequency and magnitude of the largest earthquake in the himalaya needed so that the moment released by seismicity balances the deficit of moment derived from measurements of geodetic strain assuming one third of the moment buildup is released aseismically and the earthquakes roughly follow a gutenberg richter distribution we find that m w 9 0 events are needed with a confidence level of at least 60 and must return approximately once per 800 years on average

satellite interferometric observations of displacements associated with seasonal groundwater in the los angeles basin 1 the newport inglewood fault zone nifz displays interferometric synthetic aperture radar sar phase features along most of its length having amplitudes of up to 60 mm however interpretation in terms of right lateral shallow slip along the fault fails to match the range of geologic estimates of slip recently bawden et al 2001 proposed that these phase features as well as a broader deformation pattern in the los angeles basin are due to vertical motion related to annual variations in the elevation of the water table we confirm this hypothesis through the analysis of a longer span of data consisting of 26 sar images collected by the ers 1 and ers 2 spacecraft between june 1992 and june 2000 moreover we use continuous gps measurements from 1995 to the present to establish the amplitude and phase of the vertical deformation the los angeles basin becomes most inflated one quarter of the way through the year which is consistent with water table measurements as well as with the end of the rainy season when the aquifer should be at a maximum the spatial pattern of the amplitude of the annual signal derived from continuous gps measurements is consistent with the shape of the interferometric fringes gps sites both near the nifz and in a 20 by 40 km zone within the basin also show significant n s annual variations that may be related to the differential expansion across the fault since these horizontal signals have peak to trough amplitudes of 6 mm they mask the smaller tectonic signals and need to be taken into account when interpreting gps time series of site position moreover since the groundwater signal appears to have a long term vertical trend which varies in sign depending on location it will be difficult to distinguish interseismic tectonic slip along the nifz and within the affected areas in the basin

stratigraphy and paleoceanography of a topography controlled contourite drift in the pen duick area southern gulf of cadiz abstract the northern part of the gulf of cadiz has and still is receiving a lot of attention from the scientific community due to among others the recent iodp expedition 339 in contrast its southern part or the moroccan margin has received far less attention although mud volcanoes diapiric ridges and cold water corals are present in this region the el arraiche mud volcano field is characterized by a compressive regime creating several ridges and assisting the migration of hydrocarbon fluids towards the seabed surface this study presents seismic and multibeam evidence for the existence of a contourite drift at water depths between 550 and 650 m along the southwestern flank of the pen duick escarpment and gemini mud volcano within the el arraiche mud volcano field from the onset of the quaternary when the escarpment started to lift and the local mud volcanism initiated contouritic deposition was initiated as well at the foot of both topographic obstacles initially fairly low velocity bottom currents gave rise to sheeted drift deposits affected by the uplift of the escarpment or mud extrusion from the middle pleistocene onwards separated mounded drift deposits were formed due to intensified bottom currents an antarctic intermediate water origin is inferred as driving mechanism for the drift development although glacial conditions are not yet well constrained the influence of mediterranean outflow water mow cannot be substantiated here moreover the changes recorded within this contourite drift differ from the mow dominated contourite depositional system in the northern gulf of cadiz as drift deposits only occur as early as the base of the quaternary compared to the early pliocene for the north and mounded drift deposits only occur from the middle pleistocene onwards compared to the early pleistocene cold water coral mounds have been observed within and on top of the sedimentary sequence at the foot of the pen duick escarpment this implies that environmental conditions in which cold water corals thrive were not necessarily restricted to the top of the pen duick escarpment

implications of passive salt diapir kinematics for reservoir segmentation by radial and concentric faults abstract reservoirs associated with salt diapirs that are circular or elliptical in plan view can be segmented by radial faults concentric faults both or neither explanations for this variation are offered based on integration of fault kinematics published studies and seismic examples strata around diapirs can be divided into three structural domains with characteristic fault styles 1 roof zone between the present day depositional surface and crest of a buried inactive diapir this zone is characterised by doming radial faults and occasionally conic graben doming is usually caused by differential compaction and increases with depth 2 a steeply dipping sheath of strata surrounds the diapir out to a distance of less than one diapir radius recording near surface diapir growth in poorly lithified sediments these contain early gravity slumps and late concentric extensional faults regional layer bound polygonal fault systems form radial faults within approximately one diapir radius the only significant radial faulting mechanism below the roof zone 3 diapir root zone of strata whose structural architecture records the diapirs initiating mechanism typically rim synclines or graben that detach on the salt source layer concentric faults at radial distances of a kilometre or more have been found only in root zone rim synclines and sheared sheath strata these models and observations can assist seismic interpretation and structural model building in areas of poor geophysical imaging for instance below overhanging salt

isotopic evidence 87sr 86sr δ7li for alteration of the oceanic crust at deep rooted mud volcanoes in the gulf of cadiz ne atlantic ocean the chemical and isotopic composition of pore fluids is presented for five deep rooted mud volcanoes aligned on a transect across the gulf of cadiz continental margin at water depths between 350 and 3860 m generally decreasing interstitial li concentrations and sr 87 sr 86 ratios with increasing distance from shore are attributed to systematically changing fluid sources across the continental margin although highest li concentrations at the near shore mud volcanoes coincide with high salinities derived from dissolution of halite and late stage evaporites clayey terrigenous sediments are identified as the ultimate li source to all pore fluids investigated light delta li 7 values partly close to those of hydrothermal vent fluids delta li 7 11 9 parts per thousand indicate that li has been mobilized during high temperature fluid sediment or fluid rock interactions in the deep sub surface intense leaching of terrigenous clay has led to radiogenic sr 87 sr 86 ratios similar to 0 7106 in pore fluids of the near shore mud volcanoes in contrast non radiogenic sr 87 sr 86 ratios similar to 0 7075 at the distal locations are attributed to admixing of a basement derived fluid component carrying an isotopic signature from interaction with the basaltic crust this inference is substantiated by temperature constraints from li isotope equilibrium calculations suggesting exchange processes at particularly high temperatures 200 degrees c for the least radiogenic pore fluids of the most distal location advective pore fluids in the off shore reaches of the gulf of cadiz are influenced by successive exchange processes with both oceanic crust and terrigenous fine grained sediments resulting in a chemical and isotopic signature similar to that of fluids in near shore ridge flank hydrothermal systems this suggests that deep rooted mud volcanoes in the gulf of cadiz represent a fluid pathway intermediate between mid ocean ridge hydrothermal vent and shallow marginal cold seep due to the thicker sediment coverage and slower fluid advection rates the overall geochemical signature is shifted towards the sediment diagenetic signal compared to ridge flank hydrothermal environments c 2009 elsevier ltd all rights reserved

sources of mud volcano fluids in the gulf of cadiz indications for hydrothermal imprint mud volcanism in the gulf of cadiz occurs over a large area extending from the shelf to more than 3500 m water depth and is triggered by compressional stress along the european african plate boundary affecting a deeply faulted sedimentary sequence of locally more than 5 km thickness the investigation of six active sites shows that mud volcano mv fluids on average are highly enriched in ch4 li b and sr and depleted in mg k and br the purity of the fluids is largely controlled by the intensity of upward directed flow flow rates could be constrained by numerical modelling and vary between 0 05 and 15 cm yr 1 application of d 18o systematics identifies clay mineral dehydration most likely within mesozoic and tertiary shales and marls as the major source of fluids hence cl and na in the pore fluids are mostly depleted below seawater values following a general trend of dilution however deviations from this trend occur and are likely caused by the dissolution of halite in evaporitic deposits other secondary processes overprinting the original fluid composition may occur along the flow path such as dissolution of anhydrite or gypsum and or the formation of calcite and dolomite different sources of fluids are also indicated by variations in 87sr 86sr which range from 0 7086 to 0 7099 at the different sites dehydration may be induced primarily by overburden and tectonic compression however very high concentrations of li and b specifically at captain arutyunov mv camv indicate additional leaching at temperatures above 150 c which could be explained by the injection of hot fluids along deep penetrating major e w strike slip fault systems this hypothesis is supported by the occurrence of generally thermogenic but significantly ch4 enriched light volatile hydrocarbon gases at camv which cannot be explained by shallow microbial methanogenesis li and li b ratios from different types of hot and cold vents are used to infer that high temperature signals seem to be preserved at various cold vent locations and indicate a closer coupling of both systems in continental margin environments than outlined in previous studies

the el arraiche mud volcano field at the moroccan atlantic slope gulf of cadiz the el arraiche field is a new mud volcano field discovered near the moroccan shelf edge in the gulf of cadiz that consists of 8 mud volcanoes in water depths from 200 to 700 m the largest mud volcano in the field al idrissi mud volcano is 255 m high and 5 4 km wide the cluster was discovered during a survey with the rv belgica and studied further during leg 2 of the ttr 12 survey onboard the r v prof logachev the 2002 surveys yielded detailed multibeam bathymetry over a 700 km 2 study area dense grids of high resolution seismic data deep tow sub bottom profiles sidescan sonar mosaics over the major structures selected video imagery lines video guided grab samples dredge samples gravity cores and box cores were collected for groundtruthing purposes eight mud volcanoes in water depths from 200 to 700 m cluster around two sub parallel anticlines and associated active extensional faults rock clasts and regional seismic data locate the el arraiche field over a late miocene pliocene extensional basin the onset of mud volcanic activity is estimated at about 2 4 ma and probably roots in the cretaceous miocene accretionary wedge stacked outflows are visible up to a depth of about 500 m below the sea floor the occurrence of long lived mud volcanoes bear witness to continued overpressure generation at depth either by in situ oil and gas generation or by focussed flow and accumulation in the area geochemical analyses of pore water from cores demonstrate the presence of thermogenic hydrocarbon processes the activity of the mud volcanoes is indicated by the thickness of hemi pelagic sediments covering extruded mud breccia the

forecasting the evolution of seismicity in southern california animations built on earthquake stress transfer 1 we develop a forecast model to reproduce the distribution of main shocks aftershocks and surrounding seismicity observed during 1986 2003 in a 300 310 km area centered on the 1992 m 7 3 landers earthquake to parse the catalog into frames with equal numbers of aftershocks we animate seismicity in log time increments that lengthen after each main shock this reveals aftershock zone migration expansion and densification we implement a rate state algorithm that incorporates the static stress transferred by each m 6 shock and then evolves coulomb stress changes amplify the background seismicity so small stress changes produce large changes in seismicity rate in areas of high background seismicity similarly seismicity rate declines in the stress shadows are evident only in areas with previously high seismicity rates thus a key constituent of the model is the background seismicity rate which we smooth from 1981 to 1986 seismicity the mean correlation coefficient between observed and predicted m 1 4 shocks the minimum magnitude of completeness is 0 52 for 1986 2003 and 0 63 for 1992 2003 a control standard aftershock model yields 0 54 and 0 52 for the same periods four m 6 0 shocks struck during the test period three are located at sites where the expected seismicity rate falls above the 92 percentile and one is located above the 75 percentile the model thus reproduces much but certainly not all of the observed spatial and temporal seismicity from which we infer that the decaying effect of stress transferred by successive main shocks influences seismicity for decades finally we offer a m 5 earthquake forecast for 2005 2015 assigning probabilities to 324 10 10 km cells

origin of light volatile hydrocarbon gases in mud volcano fluids gulf of cadiz evidence for multiple sources and transport mechanisms in active sedimentary wedges widespread mud volcanism across the thick 7000 between sites mixing of shallow biogenic and deep thermogenic gases cannot account for the observed compositions which instead result mainly from extensive migration of thermogenic gases in the deeply buried sediments possibly associated with biodegradation of c2 homologues and secondary methane production at captain arutyunov and carlos ribeiro mvs at the deep water bonjardim olenin and carlos ribeiro mvs generation of c2 enriched gases is probably promoted by high heat flux anomalies which have been measured in the western area of the wedge at porto mv gases are highly enriched in ch4 having delta c 13 ch4 similar to 50 parts per thousand as at most sites but markedly lower delta h 2 ch4 values 250 parts per thousand suggesting that it is not generated by thermal cracking of n alkanes but rather that it has a deep archaeal origin the presence of petroleum type hydrocarbons is consistent with a thermogenic origin and at sites where ch4 is predominant support the suggestion that gases have experienced extensive transport during which they mobilized oil from sediments similar to 2 4 km deep these fluids then migrate into shallower thermally immature muds driving their mobilization and extrusion at the seafloor at porto mv the limited presence of petroleum in mud breccia sediments further supports the hypothesis of a predominantly deep microbial origin of ch4 c 2009 elsevier b v all rights reserved

fluid evolution and authigenic mineral paragenesis related to salt diapirism the mercator mud volcano in the gulf of cadiz the formation of mud volcanoes in the gulf of cadiz is closely linked to diapirism in the deep subsurface the mercator mud volcano mmv is a rare example where diapiric emplacement in addition to being key for upward fluid migration is also an important zone for fluid and mineral diagenesis the most intriguing findings in the near surface muds of the mmv are extremely high salinities of up to 5 2 m of nacl from diapiric and evaporitic halite dissolution and the occurrence of authigenic gypsum and anhydrite crystals both of which have not been observed to date in the gulf of cadiz employing a thermodynamic model we elucidate how the interplay of temperature pulses strong salinity gradients and fluid flow dynamically drive mineral dissolution and re formation the strong increase in salinity in the pore fluids has important implications for thermodynamic equilibria by significantly lowering the activity of water thereby raising the gypsum anhydrite transition zone from 1 km to about 400 m sediment depth at the mmv this transition is further shifted to immediately below the seafloor during intervals of active mud and fluid expulsion when the mv surface temperature is heated up to at least 30 c as a consequence precipitation of authigenic gypsum near the sediment surface 1 2 mbsf has been linked to the dissolution of evaporites below the mmv more precisely the mechanisms generating supersaturation in the ascending gypsum saturated mmv fluids are 1 the slow and constant cooling of these fluids along the geothermal gradient during their ascent leading to formation of ubiquitous micro crystals and 2 the more rapid cooling after a heat pulse or transport from greater and warmer depth during an active mud volcano phase leading to the precipitation of cm scale gypsum crystals or even fist size concretions the mmv fluids approaching the salt diapir from farther below have experienced a genesis similar to those of other mud volcanoes in the gulf of cadiz located above deep rooted faults these processes include clay mineral dewatering thermogenic degradation of organic matter and deep high temperature leaching of terrigenous sediments or continental crust

fluvial incision and tectonic uplift across the himalayas of central nepal the pattern of fluvial incision across the himalayas of central nepal is estimated from the distribution of holocene and pleistocene terraces and from the geometry of modern channels along major rivers draining across the range the terraces provide good constraints on incision rates across the himalayan frontal folds sub himalaya or siwaliks hills where rivers are forced to cut down into rising anticlines and have abandoned numerous strath terraces farther north and upstream in the lesser himalaya prominent fill terraces were deposited probably during the late pleistocene and were subsequently incised the amount of bedrock incision beneath the fill deposits is generally small suggesting a slow rate of fluvial incision in the lesser himalaya the terrace record is lost in the high range where the rivers are cutting steep gorges to complement the terrace study fluvial incision was also estimated from the modern channel geometries using an estimate of the shear stress exerted by the flowing water at the bottom of the channel as a proxy for river incision rate this approach allows quantification of the effect of variations in channel slope width and discharge on the incision rate of a river the determination of incision rates requires an additional lithological calibration the two approaches are shown to yield consistent results when applied to the same reach or if incision profiles along nearby parallel reaches are compared in the sub himalaya river incision is rapid with values up to 10 15 mm yr it does not exceed a few millimeters per year in the lesser himalaya and rises abruptly at the front of the high range to reach values of 4 8 mm yr within a 50 km wide zone that coincides with the position of the highest himalayan peaks sediment yield derived from the measurement of suspended load in himalayan rivers suggests that fluvial incision drives hillslope denudation of the landscape at the scale of the whole range the observed pattern of erosion is found to closely mimic uplift as predicted by a mechanical model taking into account erosion and slip along the flat ramp flat geometry of the main himalayan thrust fault the morphology of the range reflects a dynamic equilibrium between present day tectonics and surface processes the sharp relief together with the high uplift rates in the higher himalaya reflects thrusting over the midcrustal ramp rather than the isostatic response to reincision of the tibetan plateau driven by late cenozoic climate change or late miocene reactivation of the main central thrust

contemporary deformation and seismicity analysis in southwest japan during 2010 2018 based on gnss measurements a significant amount of work has been conducted in the japanese islands on high precision positioning surveying natural disaster mitigation reference frame and datum definitions however there is substantial scope for exploring the current seismotectonic activity of japan which would provide further awareness of disaster management the short recurrence time of great inter plate earthquakes and well recorded geodetic observations provide one of the best examples to analyze the combination of contemporary deformation and seismic intensity in southwest sw japan in the current study we analyzed three districts of sw japan which include mainly kyushu district and parts of chugoku and shikoku districts we predicted global navigation satellite system gnss measurements based on amurian fixed reference frame aref velocities with the help of singular spectrum analysis ssa method and examined the regional deformation from april 01 2010 to december 31 2018 in addition we analyzed the earthquakes clustered calculated by the nearest neighborhood distance method which showed prominently bimodal seismicity of sw japan and revealed the existence of two statistically distinct earthquake populations the events inside a cluster were normally close to their nearest neighbors whereas events from distinct clusters were comparatively aloof from each other finally the paper provides the spatial strain and rotational rate variation for selected seismotectonic districts that are in relatively good agreement with the seismic deformation inferred from earthquake focal mechanisms we believe that our integrated approaches would provide a better insight into the active deformation of sw japan

seafloor expression of sediment extrusion and intrusion at the el arraiche mud volcano field gulf of cadiz 1 the el arraiche mud volcano field consists of eight mud volcanoes up to 255 m high and 5 4 km wide located in the moroccan margin of the gulf of cadiz at water depths between 700 and 200 m available data include detailed swath bathymetry over the entire area dense grids of high resolution seismic data very high resolution deep tow subbottom profiles side scan sonar mosaics over the major structures selected underwater video lines and sediment samples the main morphological aspects of the mud volcanoes are from the margin toward the center a subsidence rim or moat the mud volcano slope in some cases a deep crater and a recent central mud dome at the top the slope is characterized by radial outward sediment flow deposits or by a concentric pattern of terraces and steps the sediment flow deposits can be divided into elongate outflows that accumulate at the base of the slope and short bulky outflow deposits that freeze on the steep slope the crater hosts extruded sediment ranging from fluidized sand to mud breccia with centimeter to meter sized rock clasts issued from several vents within the crater the concentric slope terraces and the central mud dome are interpreted to result from several phases of uplift caused by sediment intrusion or shallow diapirism the mud volcano growth is thus interpreted to result from a combination of extrusive and intrusive processes

salt tectonics and mud volcanism in the latakia and cyprus basins eastern mediterranean salt tectonics and mud volcanism in the latakia and cyprus basin eastern mediterranean is investigated by means of swath sounding reflection seismics and side scan data as well as by camera and video sledge observations both basins are located east of cyprus and are associated with the collision front between the african and anatolian plate the pliocene quaternary sediment succession is underlain by up to 1 km thick messinian evaporites both thick skinned plate tectonic and thin skinned salt tectonic control fluid dynamics and associated mud volcanism in the latakia and cyprus basin as well as at the troodos latacia culmination which separates both basins an end member model is proposed which explains the presence of elongated topographic highs and trenches along the troodos larnaca culmination and south of it by gravity gliding of the messinian evaporites and associated fluid migration thin skinned extension in the troodos larnaca culmination and boudinage respectively facilitate fluid flow through and out of the evaporites the fluid or mud flow dissolutes the salt layer and creates elongated trenches mud intrudes into the pliocene quaternary sediments above the trenches consequently the overburden is thickened and forms morphological ridges south of the culmination the evaporites and overburden are folded due to thin skinned shortening of the evaporites in one instance fluid extrusion out of the evaporites is inferred from seismic data interpretation the outflow caused a volume reduction and collapse of the evaporites mud volcanoes and fold anticlines align above deep rooted transpressional fault systems which are associated with the african anatolian collision zone the faults may act as conduits for rising fluids in the western part of the survey area where the cyprus arc strikes almost west east and the collision occurred more frontal and stress was highest mud volcanoes emerged further to the east where the cyprus arc runs sw ne and sinistral strike slip has been proposed fold anticlines evolved particular mud volcanoes and folds emerged prior to the deposition of the messinian evaporites the undisturbed upper pleistocene sequences as well as the absence of significant mud outflow on the seafloor strongly suggest that the main fluid dynamic ceased

emplacement of giant mud volcanoes in the south caspian basin 3d seismic reflection imaging of their root zones exceptional quality 3d data for the largest mud volcano yet described provide the first detailed imaging of the plumbing architecture that connects a major volcanic edifice to its source layer at depth the volcano is in the south caspian basin and consists of an extruded submarine mud bicone 10 km wide and 1 4 km thick overlying an oval caldera 1 2 1 6 km in width and 0 5 km in depth the caldera narrows downwards into a zone of collapsed country rock forming a downward tapering cone 1 km in height the vertex of which is located close to the top of the mud source layer the imaged structural elements lead to an evolutionary model a narrow steep fluidization pipe fed the oldest pioneer cone we propose that numerous additional fluidization pipes injected the country rock forming a densely intruded cylindrical zone similar to gryphon swarms observed at outcrop onshore wall rock erosion and compaction of the intruded zone led to collapse of the downward tapering cone that linked upwards into ring faults that define the caldera margins later mud flowage focused on the conical sheared margins volumetric contraction of the extruded volcanic cone led to an unusual concentric system of minor outward facing normal faults this model has many similarities to syntheses of igneous maar diatreme caldera systems for which it may be analogous

seasonal and long term vertical deformation in the nepal himalaya constrained by gps and grace measurements 1 we analyze continuous gps measurements in nepal southern side of the himalaya and compare gps results with grace observations in this area we find both gps and grace show significant seasonal variations further comparison indicates that the observed seasonal gps height variation and grace derived seasonal vertical displacement due to the changing hydrologic load exhibit very consistent results for both amplitude and phase for continuous gps stations whose observation time span are longer than 3 years the average wrms reduction is 45 when we subtract grace derived vertical displacements from gps observed time series the comparison for annual amplitudes between gps observed and grace derived seasonal displacements also shows consistent correlation the good seasonal correlation between gps and grace is due to the improved gps processing strategies and also because of the strong seasonal hydrological variations in nepal besides the seasonal signal grace also indicates a long term mass loss in the himalaya region assuming no gia effect this mass loss therefore will lead to crustal uplift since the earth behaves as an elastic body we model this effect and remove it from gps observed vertical rates with a 2d dislocation model most gps vertical rates especially in the central part of nepal can be interpreted by interseismic strain from the main himalayan thrust and several exceptions may indicate the complexity of vertical motion in this region and some potential local effects

origin of salt giants in abyssal serpentinite systems worldwide marine salt deposits ranging over the entire geological record are generally considered climate related evaporites derived from the precipitation of salts mainly chlorides and sulfates from saturated solutions driven by solar evaporation of seawater this explanation may be realistic for a salt thickness 100 m being therefore inadequate for thicker 1 km deposits moreover sub seafloor salt deposits in deep marine basins are difficult to reconcile with a surface evaporation model marine geology reports on abyssal serpentinite systems provide an alternative explanation for some salt deposits seawater driven serpentinization consumes water and increases the salinity of the associated aqueous brines brines can be trapped in fractures and cavities in serpentinites and the surrounding country rocks successive thermal dehydration of buried serpentinites can mobilize and accumulate the brines forming highly saline hydrothermal solutions these can migrate upwards and erupt onto the seafloor as saline geysers which may form salt saturated water pools as are currently observed in numerous deeps in the red sea and elsewhere the drainage of deep seated saline brines to seafloor may be a long lasting effective process mainly occurring in areas characterized by strong tectonic stresses and or igneous intrusions alternatively brines could be slowly expelled from fractured serpentinites by buoyancy gradients and hence separated salts brines could intrude vertically into surrounding rocks forming salt diapirs serpentinization is an ubiquitous exothermic long lasting process which can modify large volumes of oceanic lithosphere over geological times therefore buried salt deposits in many areas of the world can be reasonably related to serpentinites

quaternary stratigraphic stacking patterns on the continental shelves of the southern iberian peninsula their relationship with global climate and palaeoceanographic changes abstract a quaternary stratigraphic stacking pattern on the continental shelves of the southern iberian peninsula has been determined by analysing and comparing a dense network of low medium high and very high resolution mono channel and multi channel reflection seismic lines and well log data four major low resolution depositional sequences related to a 3rd order cycle at 1 4 1 6 ma have been recognised in the pliocene quaternary sedimentary record m p1 p2 p3 q i and q ii they are separated by four discontinuities corresponding to the most drastic changes in climate and palaeoceanography affecting the atlantic and mediterranean linkage and especially to the most prominent sea level falls in the messinian m at 5 5 ma in the lower pliocene at 4 2 ma in the upper pliocene at 2 4 ma and in the mid pleistocene at 900 920 ka mpr these major sequences were built up by asymmetrical sea level cycles the regressive and lowstand system tracts are the best developed deposits controlling the main progradation of the shelf basinwards as well the quaternary shelf stratigraphy can be divided into asymmetric 3rd order sequences of 800 ka q i and q ii and into 4th order asymmetric sequences of approximately 400 ka q1 q4 200 ka a h and 100 ka on low medium and high resolution seismics the overall architectural stacking of the shelf shows a change after the mpr discontinuity characterised by well differentiated sequences of shelf break wedges with progradational sigmoid configurations assumed to be related to approximately 100 ka sea level cycles this change in the configuration of the shelf wedges during the quaternary is attributed to the onset of the 100 ka eccentricity orbital cycles which abruptly increased the amplitude of sea level variations 100 120 m during the last 900 920 ka

the betic orogen and the iberian african boundary in the gulf of cadiz geological evolution central north atlantic abstract the study of the gulf of cadiz on the basis of multichannel seismic profiles and wells illustrates the stratigraphy and tectonics the evolution of the southern iberian margins was more complex than in most north atlantic margins since it entailed several phases of rifting convergence and strike slip motions three main tectonic provinces surround the internal zones of the gibraltar arc orogenic belt these include in the iberian margin of the gulf of cadiz the flysch units of the campo de gibraltar complex the betic external zones and the neogene basins of the guadalquivir valley fault bounded blocks of flysch and subbetic units crops out over large areas of the southeastern iberian shelf the basement of the northwestern area in contrast is represented by the paleozoic rocks of the hercynian massif of iberia half graben structures determined the main structural trends of the margin during the mesozoic which were affected by inversion structures during the neogene compressional stages the mesozoic and lower cenozoic units are best observed in wells and seismic profiles from the northern area these units are either obscure below a thick olistostrome deposit or are absent in most of the rest of the gulf of cadiz seven lithoseismic units from triassic to upper oligocene and another seven neogene and quaternary units are identified based on the relationship to the depositional sequence and the emplacement of the olistostrome the first tectonic phase was characterized by a passive margin which was controlled by the development of half graben extensional structures and carbonate platforms this evolution comprises the mesozoic and early cenozoic ocean spreading in the north atlantic induced extensional tectonics which deformed the cretaceous syn tectonic post aptian deposits increased amounts of terrigenous materials were supplied to the margin from aptian to albian times controlling depositional patterns while terrigenous siliciclastic facies replaced the jurassic carbonate platforms from middle eocene to early miocene the margin was influenced by the relative motions of iberia and africa and the development of the alpine orogeny the iberian african boundary in the gulf of cadiz experienced transpression and the mesozoic basins probably underwent subduction the emplacement of an olistostrome took place in the gulf of cadiz towards the central atlantic basin plains during the tortonian the end of the olistostrome emplacement during the late miocene coincides with accelerated tectonic subsidence while thick progradational and aggradational depositional sequences were developed the occurrence of closely juxtaposed regions of compression and extension during the miocene may reflect the westwards progression of the gibraltar arc mountain front over a subducting thinned tethys crust when the motion between iberian and africa was n s to nnw sse oriented the migration of the arcuate mountain front into the eastern gulf of cadiz is attributed to a mechanism of collision induced delamination of the mantle lithosphere in contrast to the betic rif belts however there is no geophysical evidence to postulate that continental collision took place in the gulf of cadiz during the cenozoic

constraints on himalayan deformation inferred from vertical velocity fields in nepal and tibet spirit leveling data from the nepal himalaya between 1977 and 1990 indicate localized uplift at 2 3 mm yr in the lesser himalaya with spatial wavelengths of 25 35 km and at 4 6 mm yr in the greater himalaya with a wavelength of 40 km leveling data with significantly sparser spatial sampling in southern tibet between 1959 and 1981 suggest that the himalayan divide may be rising at a rate of 7 5 5 6 mm yr relative to central tibet we use two dimensional dislocation modeling methods to examine a number of structural models that yield vertical velocity fields similar to those observed although these models are structurally nonunique dislocation models that satisfy the data require aseismic slip rates of 2 7 mm yr on shallow dipping faults beneath the lesser himalaya and rates of 9 18 mm yr on deep thrust faults dipping at 25 n near the greater himalaya unfortunately the leveling data cannot constrain long wavelength uplift 100 km across the himalaya and unequivocal estimates of aseismic slip in central nepal are therefore not possible in turn the poor spatial density of leveling data in southern tibet may inadequately sample the processes responsible for the uplift of the greater himalaya despite these shortcomings in the leveling data the pattern of uplift is consistent with a crustal scale ramp near the greater himalaya linking shallow northward dipping thrust planes 3 6 beneath the lesser himalaya and southern tibet aseismic slip on the potential rupture surface of future great earthquakes beneath the nepal himalaya south of this ramp appears not to exceed 30 of the total convergence rate between india and southern tibet resulting in an accumulating slip deficit of 13 8 mm yr

structural insights from geodetic global positioning system measurements in the darjiling sikkim himalaya abstract deformation in active convergent wedges like the himalaya occurs over different time and space scales requiring integrated datasets for holistic insights into wedge scale deformation a new long time series 1998 2009 of geodetic static global positioning system gps dataset suggests that active deformation in the darjiling sikkim himalaya dsh is not confined to the himalayan front as previously believed instead the 9 mm yr n s active convergence here is divided almost equally within the lesser himalayan duplex lhd and the higher himalaya due to aseismic reverse slip of 18 mm yr on the himalayan decollement main himalayan thrust mht dipping 6 006 and locked at 16 km depth slip transfer along the mht causes minor to moderate earthquakes at the brittle ductile transition in the dsh measured east velocities show no systematic variation indicating that strike slip seismicity though dominant in the region does not alleviate the decollement mht seismic hazard continued slip along the mht therefore will cause a great decollement earthquake in the region also gps velocities vary in the eastern and western dsh suggesting segmentation of the himalayan arc along a transverse fault over geological to decadal time scales our integrated approach can provide better insight into active deformation in convergent wedges worldwide

authigenic barite records of methane seepage at the carlos ribeiro mud volcano gulf of cadiz submarine mud volcanoes mvs are dynamic features that episodically expel gas charged fluids and mud onto the seafloor transferring various chemical constituents into the overlying water column the temporal variability in mv activity is however poorly understood so their importance as a source of methane ch4 and higher hydrocarbons for the oceanic carbon budget although thought to be significant cannot be properly constrained in this study the history of fluid and gas seepage at the carlos ribeiro mv gulf of cadiz is assessed via geochemical analyses and transport reaction modelling of pore fluids and barium ba rich layers ba fronts in sediment cores recovered along a transect from the eye to the periphery of the mv x ray fluorescence data reveal that ba fronts are absent at the eye while a single front with up to 1740 ppm ba is present at the margin of the summit three ba fronts occur at 45 85 and 130 cm depth within a mudflow to the southeast of the crater spectrometric analyses indicate that barite is the ba rich mineral in these layers upward advecting pore fluids are enriched in barium but depleted in calcium ca2 relative to seawater modelling of the ba2 and ca2 pore fluid profiles indicates that the positions of the ba fronts reflect both the present day hydrodynamic conditions as well as higher fluxes of methane in the past fluid advection appears to have decreased since 340 cal yr before present but degassing of the mudflow is ongoing and is potentially an important source of ch4