kinematic evolution of the junction of the san andreas garlock and big pine faults california if the san andreas fault with about 300 km of right slip the carlock fault with about 60 km of left slip and the big pine fault with about 15 km of left slip are considered to have been contemporaneously active a space problem at their high angle junctions becomes apparent large crustal masses converge in the area of the junctions as a result of the simultaneous large displacements on the faults we present here a model in which an early straight north northwest trending san andreas deforms to its present bent configuration in response to a westward displacement of crust north of the garlock fault during this deformation the crust north of the garlock in the vicinity of the junction undergoes north south shortening while the fault junction migrates along the trace of the san andreas fault to the southeast relative to its original position as a result of this migration the mojave area is displaced to the east relative to the original junction position we suggest a similar history in mirror image for the big pine fault and the areas of crust adjacent to it

asphalt volcanoes as a potential source of methane to late pleistocene coastal waters natural petroleum seepage emits large volumes of oil and methane to the oceans every year accompanied by the formation of asphalt volcanoes on the sea floor the discovery of seven asphalt volcanoes off the coast of southern california may help to explain high methane emissions recorded during the late pleistocene

the hellenic subduction beneath the peloponnesus first results of a microearthquake study abstract a preliminary examination of the 1070 earthquake locations determined from 6 weeks of recording in 1986 by 46 stations show that the seismicity is spread over a wide area of the peloponnesus and the western hellenic arc and throughout the whole crust no clear individual faults can be identified from the seismicity but clusters of activity are observed in some places seismicity is concentrated above 40 km and deeper earthquakes were not numerous only 28 of the 466 events with uncertainties in depth less than 5 km occurred deeper than 40 km seismicity deeper than 30 km defines a flat zone at a depth between 40 km and 70 km starting from the trench to about 200 km towards the northeast further northeast the dip of the seismic zone abruptly changes to 45 fault plane solutions for the deeper events generally indicate t axes plunging northeast within the subducted slab therefore we interpret the seismicity deeper than 30 km as due to the superposition of two different causes 1 the steep zone is due to the subduction of the african litospheric plate beneath the aegean and 2 the shallow flat zone located between the trench and the argolide is partly due to the loading of the overriding aegean plate which is deforming above the african plate

geophysical characterisation of active thermogenic oil seeps in the salt province of the lower congo basin part i detailed study of one oil seeping site abstract we report the geophysical characterisation of natural oil seep sites through a combination of sea surface evidence of oil leakage from spatial imagery with a large collection of seafloor and subsurface geophysical data this paper provides a detailed characterisation of one selected active seep site and identifies possible specific feature of oil seep sites the oil seep is a complex shaped feature on the seafloor consisting of a cluster of heterometric pockmarks inside a main depression area and peripheral metre scale seafloor mounds a strong deformation related to salt tectonics controls the location of the seafloor source by fracturing the overburden the associated thermal anomaly induces a vertical modification position of the base of the gas hydrate stability zone bghsz that is used as a fluid migration route towards the crest of the diapir the combination of local depressions and seafloor amplitude anomalies linked with vertical high amplitude pipes rooted on the bghsz suggests a focused fluid flow towards the seafloor in peripheral areas the seafloor mounds are linked by shallow faults to buried high amplitude patches on sub bottom profiler sections the combination of restricted size seafloor mounds with a progressive deepening of the high amplitude from the seafloor suggests a substantial decrease of the hydrocarbon flow towards peripheral areas the proximity of actively oil supplying seafloor depressions and seafloor mounds shows that the hydrocarbon flow rapidly decreases laterally the thermogenic seep site is affected by two consistent and sub parallel reflections with negative polarity the first is interpreted as the methane related bghsz the second could correspond to the base of a thermogenic bghsz produced by a mixture of heavier gas the seafloor roughness and double bsr appear to be specific features of oil seep sites the geophysical features revealed at a localised study area will be extrapolated towards a larger province for relevance validation

seismicity normal faulting and the geomorphological development of the gulf of corinth greece the corinth earthquakes of february and march 1981 three major destructive earthquakes of m s 6 7 6 4 6 4 occurred in the eastern part of the gulf of corinth in february and march 1981 associated normal faulting was observed on both the north and the south sides of the gulf examination of teleseismic local seismic surface faulting and geomorpbological data suggests that the first and second of these shocks activated major north dipping normal faults these faults control the topography and bathymetry and are related to the recent uplift and subsidence of the coastline it is probable that the first earthquake occurred on a faultwhich outcrops underwater and the second on a fault which is visible on land it appears that the third shock activated an antithetic normal fault dipping southwards on the north side of the gulf and that the overall structure of the gulf of corinth graben is asymmetric the northern antithetic fault clearly demonstrates the geomorphological changes associated with developing young normal faulting in addition we suggest that observations of recent coastline movement provide a powerful tool for identifying major active fault systems and predicting their historical role in the paleogeography of an area

the rudbār mw 7 3 earthquake of 1990 june 20 seismotectonics coseismic and geomorphic displacements and historic earthquakes of the western high alborz iran summary the rudb r earthquake of 1990 june 20 the first large magnitude earthquake with 80 km left lateral strike slip motion in the western high alborz fold thrust mountain belt was one of the largest and most destructive earthquakes to have occurred in iran during the instrumental period we bring together new and existing data on macroseismic effects the rupture characteristics of the mainshock field data and the distribution of aftershocks to provide a better description of the earthquake source its surface ruptures and active tectonic characteristics of the western high alborz the rudb r earthquake is one of three large magnitude events to have occurred in this part of the alborz during recorded history the damage distribution of the 1485 august 15 upper polrud earthquake suggests the east west kelishom left lateral fault which is situated east of the rudb r earthquake fault as a possible source the 1608 april 20 alamutrud earthquake may have occurred on the alamutrud fault farther east analysis of satellite imagery suggests that total left lateral displacements on the rudb r fault are a maximum of 1 km apparent left lateral river displacements of 200 m on the kashach l fault and up to 1 5 km of the kelishom fault which are situated at the eastern end of the rudb r earthquake fault also appear to indicate rather small cumulative displacements given the relatively small displacements the presently active left lateral strike slip faults of the western high alborz fold thrust belt may be younger than onset of deformation within the alborz mountains as a whole

evidence for pre folding vein development in the oligo miocene asmari formation in the central zagros fold belt iran in order to understand the interplay between vein development and folding in the carbonates of the oligo miocene asmari formation one of the main hydrocarbon reservoir rocks in iran several anticlines have been investigated in the central part of the zagros folded belt combining observations of relative chronology between veins based on calcite filling phases and crosscutting abutting relationships as well as aerial satellite image interpretation on several anticlines allowed proposing a tectonic model highlighting the widespread development of veins and other extensional micro meso structures in the central zagros folded belt our data suggest that most of the veins affecting the asmari formation predated the main miocene pliocene folding episode an early regional vein set striking n50 marked the onset of collisional stress build up in the region then n150 and n20 trending vein sets were initiated in response to local extension caused by large scale flexure drape folds above n s and n140 basement faults reactivated under the regional ne compression at the onset and during miocene pliocene folding of the sedimentary cover the early formed veins were reactivated reopened and or sheared while duplexes low angle reverse faults and thrusts formed beyond regional implications this study puts emphasis on the need of carefully considering regional local vein development predating folding as well as influence of underlying basement faults in models of folded fractured reservoirs in fold thrust belts

the deep crustal structure of the mojave desert california from cocorp seismic reflection data cocorp seismic reflection profiling in the western and northern mojave desert of southern california has revealed the presence of numerous major low angle reflecting horizons within the crust these complex though laterally continuous horizons are interpreted to represent major southwesterly dipping crustal fault zones and as such they place important constraints on the tectonic evolution of the region the upper most horizon is interpreted to be the rand thrust which where exposed places precambrian and late cretaceous crystalline rocks over possibly younger pelona rand orocopia schist this reflecting horizon extends for 25 km southwest of the rand mountains where it appears to be truncated at a depth of about 7 4 km by another horizon which may be a later low angle normal fault the other reflecting horizons are not traceable to the surface and so greater ambiguity remains in their interpretation the most prominent of these horizons occurs at midcrustal depths 15 6 km exhibits a ramp and flat geometry and extends over the northern area of the mojave survey into the basin and range province a lower horizon at depths of 20 30 km in the northern part of the survey area is antiformal and appears to terminate above a flat and relatively continuous moho depth horizon the crustmantle transition appears to be represented by a continuous series of reflections which occur at about 10 s 33 km in the north of the survey and at about 8 9 s 26 29 km in the south these reflections are offset in the vicinity of the town of mojave the deep intracrustal fault zones inferred from the cocorp survey may represent 1 the deep crustal continuation of the system of mesozoic thrusts which crops out in southern nevada and southeastern california 2 late cretaceous to early cenozoic northeast vergent thrusts related to the uplift of the pelona orocopia rand schist or 3 low angle normal faults related to early miocene northeast southwest directed crustal extension the cocorp survey also traversed the major strike slip faults that bound the mojave block the san andreas fault zone appears to truncate reflectors at depths of 6 8 and 20 km within the mojave basement suggesting that it is a major vertical feature which extends to at least 20 km depth conversely the garlock fault does not offset an underlying reflecting horizon which occurs at 9 km depth and therefore appears to be a relatively shallow crustal feature

post 12 m y rotation of southwest washington paleomagnetic field directions from the basalt of pack sack lookout are compared to those from the pomona member of the saddle mountains basalt of the columbia river basalt group the pomona crops out over a wide region on the columbia plateau east of the cascade range and the basalt of pack sack lookout crops out well to the west of the cascades about 30 to 60 km east of the washington coast our paleomagnetic results support existing geologic and geochemical evidence that both these units are part of a single 12 m y old flow that erupted in western idaho and flowed to the washington coast the magnetic data further indicate that southwest washington has undergone clockwise rotation with respect to the columbia plateau and stable north america the data suggest that both a large scale regional rotation of 16 and locally complex small scale rotations exist the two being present to different degrees in the eastern and western regions of southwest washington the cascade range appears to coincide with the tectonic boundary separating rotated and unrotated regions of washington state rotation of southwest washington appears to have been associated with the rotation of large pieces of western oregon and southern washington possibly as a result of either a ridge push force from the basin and range province or shear along the pacific north america plate boundary

fluid pressure induced seismicity at regional scales the role of high fluid pressure as a seismogenic agent has been the subject of intense study hubert and rubey 1959 hanshaw and bredehoeft 1968 healy and rubey 1968 simpson 1976 walder and nur 1984 sibson 1990 of particular interest is the so called fault valve mechanism sibson 1976 sibson 1990 a hypothesis whereby fluid pressure rises as a result of tectonic compression and pore volume reduction until crustal failure occurs triggering seismic activity and upward fluid discharge sealing and healing of the rock matrix richter and simmons 1977 sprunt and nur 1979 angevine et al 1982 following coseismic stress drop facilitates reaccumulation of fluid pressure initiating another loading cycle the fault valve mechanism is entertained as a plausible explanation for present day seismic activity in the western transverse ranges of california we provide a quantitative test of the fault valve hypothesis that uses geologic data and rates of active tectonics for a cross section through an active fold and thrust belt on the flank of a developing mountain range rates of fluid pressure buildup and average recurrence times of large earthquakes in the fold and thrust belt are estimated to be on the order of 104pa yrand hundreds of years respectively

the 1978 earthquake sequence near thessaloniki northern greece summary this paper presents a detailed study of teleseismically and locally recorded foreshocks and aftershocks of the 1978 thessaloniki earthquake sequence and discusses the relations between the locations and mechanisms of these shocks and the three dimensional geometry of faulting in the source region sixteen teleseismically recorded events were relocated using a relative relocation method and positioned geographically using the accurate locally determined location of the largest aftershock all these shocks had depths shallower than 15 km the spatial distribution of the foreshocks showed that the activity was initiated at the central part of the epicentral region progressed westwards and for about 20 days clustered in the region of the imminent mainshock no teleseismically recorded foreshock was located west of the mainshock location in less than 1 hr after the mainshock large aftershocks occurred west of it and in later stages spanned the entire western part of the epicentral region no teleseismically recorded aftershocks were located east of the mainshock locally recorded aftershocks were accurately located and provided a more detailed picture of the seismic deformation they occurred at depths between 3 and 12 km and in three distinct clusters separated by well defined gaps the largest foreshock on may 23 had a moment of 5 6 1024dyne cm and a mean displacement of 31cm the mainshock on june 20 had a moment of 5 2 1025dyne cm a strain drop of 4 0 10 5 static stress drop of 12 bar and a mean displacement of 64 cm these values are for one of the two possible interpretations of the aftershock distribution which suggests that the largest earthquakes of the sequence occurred on two different but adjacent fault segments the first event 1 on may 23 occurred along the central fault segment and was followed 28 days later by the second event 2 on june 20 along a western fault segment finally 61 days later another smaller earthquake event 3 occurred along another fault east of event 1

the structural evolution of active fault and fold systems in central otago new zealand evidence revealed by drainage patterns abstract central otago in new zealand is an area of active continental shortening in which a peneplain surface cut into schist has been deformed by folds which are developed above buried reverse faults we use the drainage patterns in this region to demonstrate various processes in fold and fault growth and interaction that would be difficult to identify by other means in particular we show 1 how simple asymmetric folds can develop into box folds 2 how apparently continuous ridges were formed by the coalescing of quite separate propagating fold and fault segments 3 evidence for the relative ages or relative uplift rates of adjacent structures and 4 evidence for the propagation direction of folds or faults as they grow the few quantitative estimates we obtain for fault propagation rates suggest an increase in length of 10 50 m per earthquake on faults about 20 km long these estimates are very uncertain but are similar in magnitude to an estimate made in nevada for a normal fault of similar size and are also similar to predicted estimates from theoretical growth models they raise the question of whether fault growth earthquake recurrence rates and climate change can interact to produce semi regular discrete features in an active landscape

map restoration of folded and faulted late cenozoic strata across the oak ridge fault onshore and offshore ventura basin california the ventura basin lies within the east west trending active fold and thrust belt of the western transverse ranges california this basin has been the site of significant earthquakes on structures within it and bordering it the purpose of our study is to identify the main structures in the basin and its borders and to quantify their rate of deformation our study includes the onshore and offshore ventura basin the arcuate basin bounding oak ridge reverse fault and the oxnard shelf to the south shortening fault slip and crustal block motions were studied using a three dimensional map restoration technique structure contour maps on the 6 ma surface and other horizons were digitized and restored to the initial horizontal state by unfolding them using the computer program unfold and then fitting the unfolded surfaces across faults comparing the restored and present configuration allows us to estimate total net finite displacements relative to a fixed horizontal reference line average post 5 ma shortening rates estimated from our restoration are slower than both post 1 ma rates and present rates determined by global positioning systems most shortening due to folding in the onshore basin is post 1 ma although slip on the oak ridge fault has occurred both before and after 1 ma displacement due to faulting and folding includes left lateral strike slip motion on the northeast southwest coastal segment of the oak ridge fault and associated clockwise rotation of the adjacent ventura basin the oxnard shelf is bordered to the south by mountains and islands that have been previously interpreted as folds above thrust fault ramps this onshore offshore block moves as one continuous thrust sheet similarly beyond the well studied onshore fault a kinematically continuous offshore oak ridge mid channel left oblique fault system is interpreted to continue at least an additional 100 km westward beneath the santa barbara channel

drivers of holocene palsa distribution in north america abstract palsas and peat plateaus are climatically sensitive landforms in permafrost peatlands climate envelope models have previously related palsa peat plateau distributions in europe to modern climate but similar bioclimatic modelling has not been attempted for north america recent climate change has rendered many palsas peat plateaus in this region and their valuable carbon stores vulnerable we fitted a binary logistic regression model to predict palsa peat plateau presence for north america by relating the distribution of 352 extant landforms to gridded modern climate data our model accurately classified 85 3 of grid cells that contain observed palsas peat plateaus and 77 1 of grid cells without observed palsas peat plateaus the model indicates that modern north american palsas peat plateaus are supported by cold dry climates with large seasonal temperature ranges and mild growing seasons we used palaeoclimate simulations from a general circulation model to simulate holocene distributions of palsas peat plateaus at 500 year intervals we constrained these outputs with timings of peat initiation deglaciation and postglacial drainage across the continent our palaeoclimate simulations indicate that this climate envelope remained stationary in western north america throughout the holocene but further east it migrated northwards during 11 5 6 0 ka bp however palsa extents in eastern north america were restricted from following this moving climate envelope by late deglaciation drainage and peat initiation we validated our holocene simulations against available palaeoecological records and whilst they agree that permafrost peatlands aggraded earliest in western north america our simulations contest previous suggestions that late permafrost aggradation in central canada was climatically driven

holocene changes in seasonal precipitation highlighted by fire incidence in eastern canada postglacial fire history has been reconstructed for eastern canada from charcoal influx anomalies from 30 sites taken from a lacustrine charcoal database the reconstruction exhibits coherent patterns of fire occurrence in space and time the early holocene is characterised by high fire incidence there is a major change to much lower occurrence slightly after 8 ka bp a return to more fire appears after 3 ka bp this sequence does not fit with the hydro climatic reconstruction deduced from lake level reconstructions for northeastern north america which indicates a dry early and mid holocene and a wet late holocene fire occurrence however closely matches summer relative humidity inferred from 18o the differences between fire frequency and lake level history are due to changes in the seasonality of precipitation and drought frequency lake levels are essentially controlled by winter precipitation while summer precipitation controls fire occurrence the early holocene before 8 7 5 ka bp experienced dry summers due to higher solar radiation and dry adiabatic winds from the residual laurentide ice sheet the middle holocene was dominated by wet summers due to stability of the atlantic air mass over eastern canada after 2 5 ka bp summers became drier albeit not as fire conducive as during the early holocene late holocene summers conducive to fire are explained by more frequent incursions of dry cool pacific or cold arctic air masses over eastern canada

foraminifera as indicators of methane rich environments a study of modern methane seeps in santa barbara channel california methane hydrates have been implicated as a possible forcing mechanism for rapid climate change during the late quaternary via the release of methane from marine reservoirs carbon isotopic excursions of foraminifera observed in high resolution sediment records from santa barbara basin odp site 893 have been interpreted as evidence of episodes of methane release during the late quaternary however the potential relationship between methane in the modern environment and its effect on the stable isotopic composition of benthic and planktonic foraminifera is not well understood short cores taken inside a 500 m diameter pockmark with active methane seeps in santa barbara channel ca usa yield information on the effect of high concentrations of environmental methane on foraminiferal assemblages and their stable isotopic composition these seeps reside at 120 m water depth in the eastern portion of the channel associated with faults and fractures in the miocene monterey formation planktonic foraminiferal assemblages and radiocarbon ages show that surface sediments are of late glacial age 25 300 calendar years this finding suggests an absence of holocene and deglacial sedimentation in the seep area likely due the formation of the pockmarks and subsequent winnowing or lack of sedimentation benthic foraminiferal assemblages are marked by high abundance of bolivina tumida a species previously observed during interstadial episodes and the early holocene in santa barbara basin interpreted to include episodes of high methane flux from the basin while oxygen isotopic values of both benthic and planktonic foraminifera appear normal for cool glacial conditions negative carbon isotopic values are seen in benthic foraminifera primarily in the near surface intervals in one interval 1 2 cm below surface both benthic and planktonic species record highly negative carbon isotopic values implying that isotopically light methane influenced the entire water column this spike is of similar or larger magnitude than several earlier observed spikes in the late quaternary record from odp site 893 single specimen isotopic analyses give an indication of the total range of carbon isotopic values recorded 0 01 to 25 23 for benthics 0 07 to 22 22 for planktonics in the spike interval since modern methane seeps are commonly associated with authigenic carbonate precipitation scanning electron microscopy was used to assess the possibility that post depositional alteration may have affected the isotopic composition of the test these experiments indicate that authigenic carbonate is absent and therefore unable to account for the highly negative carbon isotopic signatures these data improve our understanding of methane associated environments by showing that foraminiferal isotopic composition and assemblages may be used to discern the flux of methane from the oceanic reservoir in the geologic record

plate tectonics and orogenic research after 25 years a tethyan perspective abstract orogeny the process by which the earth s prominent mountain ranges are constructed has been a central topic of interest in the earth sciences since at least the end of the 18th century the recognition that strains and displacements of very considerable magnitude occur along all of the three dimensions within an orogenic belt during its evolution has grown gradually during the last two centuries emphasis on primary vertical movements dominated the ideas on the nature of orogeny during the first half of the 19th century whereas compression and consequent uplift across mountain belts were believed to be the main cause for their origin during the subsequent one hundred years or so that were spent under the dominance of the fixist contraction theory mobilist tectonicians realised that continental drift in places also required motion along the trend of orogenic belts but this view did not gain general acceptance recognition of significant strike slip motion parallel or subparallel with mountain ranges evolved independently and mostly within the fixist camp by the 1960 s presence of important motions both along and across mountain belts had become common knowledge but no theoretical basis existed to account for them all

structural transect of the western transverse ranges california implications for lithospheric kinematics and seismic risk evaluation a retrodeformable cross section that integrates surface and subsurface data across the western transverse ranges california illustrates an actively developing fold and thrust belt that began forming at 2 3 ma high level thrusts are interpreted to root in a mid crustal detachment at 12 15 km depth which coincides with the maximum depth of earthquakes the cross section documents 53 km of convergence above the mid crustal detachment dividing this by the time since onset of deformation yields convergence rates of 17 6 26 5 mm yr the high density lithospheric anomaly beneath the transverse ranges is related to subduction of lower crust and lithosphere below the mid crustal detachment to balance the shallow crustal shortening thrust ramps coincide with zones of high seismicity in the transverse ranges this suggests that ramp regions have the highest potential for compressive earthquake events e g the recent whittier narrows earthquake of october 1 1987 m sub l 5 9 occurred along the eastern part of a ramp zone

coastal tectonics on the eastern margin of the pacific rim late quaternary sea level history and uplift rates channel islands national park california usa abstract the pacific rim is a region where tectonic processes play a significant role in coastal landscape evolution coastal california on the eastern margin of the pacific rim is very active tectonically and geomorphic expressions of this include uplifted marine terraces there have been however conflicting estimates of the rate of late quaternary uplift of marine terraces in coastal california particularly for the northern channel islands in the present study the terraces on san miguel island and santa rosa island were mapped and new age estimates were generated using uranium series dating of fossil corals and amino acid geochronology of fossil mollusks results indicate that the 2nd terrace on both islands is 120 ka and the 1st terrace on santa rosa island is 80 ka these ages correspond to two global high sea stands of the last interglacial complex marine isotope stages mis 5 5 and 5 1 respectively the age estimates indicate that san miguel island and santa rosa island have been tectonically uplifted at rates of 0 12 0 20 m ka in the late quaternary similar to uplift rates inferred from previous studies on neighboring santa cruz island the newly estimated uplift rates for the northern channel islands are however an order of magnitude lower than a recent study that generated uplift rates from an offshore terrace dating to the last glacial period the differences between the estimated uplift rates in the present study and the offshore study are explained by the magnitude of glacial isostatic adjustment gia effects that were not known at the time of the earlier study set in the larger context of northeastern pacific rim tectonics channel islands uplift rates are higher than those coastal localities on the margin of the east pacific rise spreading center but slightly lower than those of most localities adjacent to the cascadia subduction zone the uplift rates reported here for the northern channel islands are similar to those reported for most other localities where strike slip tectonics are dominant but lower than localities where restraining bends such as the big bend of the san andreas fault result in crustal shortening

geophysical characterisation of active thermogenic oil seeps in the salt province of the lower congo basin part ii a regional validation abstract the lower congo basin is known to discharge a substantial volume of oil towards the sea surface from more than one hundred seafloor seep sites distributed throughout the deep province of the lower congo basin a large geochemical coring survey confirmed the presence of oil on the seabed the combination with the seismic data considerably improved the identification of the origin of the oil slicks on the seabed multiple specific geophysical characteristics of thermogenic hydrocarbon seep sites were highlighted in a previous detailed analysis of seismic datasets this study aims to test the characteristics previously identified at regional scale the active discharge zone is limited to the distal province of the basin it is characterised by strong compression shortening due to the sliding of the post salt super sequence resulting in numerous salt diapirs that control the location of seafloor oil seep sites the paper describes the bathymetric reflectivity amplitude and sub bottom profiler characteristics of a group of thermogenic seep sites they correspond essentially to submarine mounds or pockmarks of complex and irregular shape surrounded by hummocky mounds active oil pockmarks are systematically associated with positive amplitude anomalies on the seabed and are linked to vertical high amplitude columns rooted in the seismic reflector and associated with the base of the gas hydrate stability zone the sub bottom profiler data shows that the hummocky mounds are connected by a network of faults to high amplitude bodies buried under a consistent sediment thickness based on the definition of specific geophysical features seafloor mounds complex shape and irregular pockmarks positive anomalies of seafloor amplitude high amplitude vertical pipes we identified a series of potential oil seep sites at basin scale the mounds are particularly recognizable using the seismic curvature attribute we have identified 2946 individual hummocks that are grouped in 50 zones with a density of 35 240 per km2 they are believed to be associated with asphalt storage on the seafloor and related to the biodegradation of heavy oils during hydrocarbon dysmigration through the sedimentary pile unusual double bsrs occur over the study area these are also a specific feature of thermogenic seep sites barely half of the potential sites identified on the seismic datasets are associated with recurrent oil slicks at the sea surface the proportion of remaining anomalies may be associated with inactive seep sites over the period of satellite based monitoring or gas dominated seep sites

temporal and spatial aspects of peatland initiation following deglaciation in north america abstract a set of simple ecological models accounts well for the cumulative initiation of peatlands throughout north america in relation to glacial retreat the most parsimonious form incorporates first a delay term to account for the lag during which newly deglaciated land became suitable for peatland initiation and second an intrinsic rate of initiation related to the probability of migration and establishment of plant propagules from elsewhere the goodness of fit of the models based on 1680 basal peat dates throughout the continent allows projection of past trends into the future factors contributing to the lag of about 4000 years between deglaciation and peatland initiation are suggested and data on colonization of deglaciated land by beavers known to initiate peatlands are presented the rate of peatland initiation peaked between 7000 and 8000 years ago but remains appreciable today a marked depression of peatland initiation 8360 8040 bp interrupted the peak rate the time of the interruption matches the 8200 bp cold dry event recorded in greenland ice cores and suggests that this event caused a substantial continent wide depression of an important ecosystem function i e carbon sequestration from the atmosphere by peat deposition spontaneous initiation of new peatlands is projected to continue for millennia to come

geomorphic criteria to determine direction of lateral propagation of reverse faulting and folding fault related folds develop above active faults and as these faults propagate laterally so do the folds they produce geomorphic criteria useful in evaluating rates and direction of lateral propagation of active folds in the direction of propagation are 1 decrease in drainage density and degree of dissection 2 decrease in elevation of wind gaps 3 decrease in relief of the topographic profile along the crest 4 development of characteristic drainage patterns 5 deformation of progressively younger deposits or landforms and 6 decrease in rotation and inclination of forelimb all these criteria are consistent with lateral propagation but do not prove it the presence of more than one wind or water gap formed by the same stream however is strong evidence of lateral propagation rates of lateral propagation of folding may be several times the rate of uplift and fault slip lateral propagation of anticlinal folds allows for a new explanation of how drainage may develop across active fold belts development of drainage across an active fold belt is probably a function of relatively long structurally controlled drainage diversion parallel to fold axes and development of relatively short antecedent stream reaches around the nose plunge panel of a fold water and or wind gaps form as uplift drainage diversion and stream capture associated with fold growth continue

effects of permafrost aggradation on peat properties as determined from a pan arctic synthesis of plant macrofossils permafrost dynamics play an important role in high latitude peatland carbon balance and are key to understanding the future response of soil carbon stocks permafrost aggradation can control the magnitude of the carbon feedback in peatlands through effects on peat properties we compiled peatland plant macrofossil records for the northern permafrost zone 515 cores from 280 sites and classified samples by vegetation type and environmental class fen bog tundra and boreal permafrost and thawed permafrost we examined differences in peat properties bulk density carbon c nitrogen n and organic matter content and c n ratio and c accumulation rates among vegetation types and environmental classes consequences of permafrost aggradation differed between boreal and tundra biomes including differences in vegetation composition c n ratios and n content the vegetation composition of tundra permafrost peatlands was similar to permafrost free fens while boreal permafrost peatlands more closely resembled permafrost free bogs nitrogen content in boreal permafrost and thawed permafrost peatlands was significantly lower than in permafrost free bogs despite similar vegetation types 0 9 versus 1 5 n median long term c accumulation rates were higher in fens 23g c m 2 yr 1 than in permafrost free bogs 18g c m 2 yr 1 and were lowest in boreal permafrost peatlands 14g c m 2 yr 1 the plant macrofossil record demonstrated transitions from fens to bogs to permafrost peatlands bogs to fens permafrost aggradation within fens and permafrost thaw and reaggradation using data synthesis we have identified predominant peatland successional pathways changes in vegetation type peat properties and c accumulation rates associated with permafrost aggradation

lithalsa distribution morphology and landscape associations in the great slave lowland northwest territories canada abstract lithalsas are permafrost mounds formed by ice segregation in mineral rich soil that occur within the zone of discontinuous permafrost nearly 1800 lithalsas were mapped using archival aerial photographs within the great slave lowland northwest territories canada these are up to 8 m high and several hundred meters in length and width one lithalsa examined by electrical resistivity and boreholes rises 4 to 6 m above an adjacent peatland shows clear evidence of ice segregation at depth and ground heave of between 2 5 and 4 0 m and is estimated to have formed within the past 700 years regionally lithalsas are typically located adjacent to ponds and streams with mature forms vegetated by deciduous birch forest or mixed birch and spruce forest with a herb shrub understory and include circular crescentic and linear forms they are abundant within the lowland region which contains widespread glaciolacustrine lacustrine and alluvial fine grained sediments the lithalsas are most common within the first few tens of meters above the present level of great slave lake indicating that many are late holocene and some less than 1000 years in age a comparison with lithalsas in contemporary environments reveals that comparatively warm but extensive discontinuous permafrost fine grained sediments alluvial lacustrine marine or glaciomarine and available groundwater supply provide the climatic and hydro geological parameters for the development of lithalsas in permafrost terrain the identification of lithalsas in this region is important given their sensitivity to climate change and potential hazards to northern infrastructure upon thawing

soil organic carbon pools in the northern circumpolar permafrost region of all soils in the northern permafrost region is approximately 18 782 10 3 km 2 o r approximately 16 of the global soil area in the northern permafrost region organic soils peatlands and cryoturbated permafrost affected mineral soils have the highest mean soil organic carbon contents 32 2 69 6 kg m 2 here we report a new estimate of the carbon pools in soils of the northern permafrost region including deeper layers and pools not accounted for in previous analyses carbon pools were estimated to be 191 29 pg for the 0 30 cm depth 495 80 pg for the 0 100 cm depth and 1024 00 pg for the 0 300 cm depth our estimate for the first meter of soil alone is about double that reported for this region in previous analyses carbon pools in layers deeper than 300 cm were estimated to be 407 pg in yedoma deposits and 241 pg in deltaic deposits in total the northern permafrost region contains approximately 1672 pg of organic carbon of which approximately 1466 pg or 88 occurs in perennially frozen soils and deposits this 1672 pg of organic carbon would account for approximately 50 of the estimated global belowground organic carbon pool

spatial and temporal variation in late cenozoic back arc volcanic rocks aegean sea region abstract the aegean sea and adjacent areas comprise thinned continental crust forming an extensional back arc basin behind the south aegean arc in this back arc region are many small volcanic centres with a wide range of volcanic products this late miocene to quaternary volcanism is volumetrically minor in contrast to the voluminous igneous activity of the south aegean arc the age and major and trace element geochemistry of these back arc volcanic rocks are reviewed from the literature where necessary new geochemical analysis have been made five magma types are recognised continental alkaline basalts sodic basalts with incompatible element enrichment and nb depletion trachytes shoshonites and calc alkaline andesites all but the continental alkaline basalts appear geochemically related to subduction processes there is a regular distribution of rock types in time and space the subduction related rocks occur in a broad arc between the modern south aegean arc and the early to middle miocene volcanicity of the central aegean region sodic basalts occur in the most inboard regions and are later than the trachytes shoshonites and calc alkaline magmas occur in the most outboard regions this back arc volcanism occurs only in areas of abundant shallow seismicity however areas of extension and seismicity in the northeast aegean distant from the subducting slab lack volcanoes with the exception of the continental alkaline basalts the magmas are derived only from mantle influenced by the aseismic part of the hellenic subduction slab between 200 and 400 km depth back arc extension associated with rotation of the aegean microplate and strike slip motion on the north anatolian fault system has created a fault system allowing these magmas to reach the surface analogous processes may be common in the final stages of closure of ancient orogens

palaeoecology of a palsa and a filled thermokarst pond in a permafrost peatland subarctic quebec canada radiocarbon dating and macrofossil data from a palsa and a filled thermokarst pond within a subarctic permafrost peatland were used to reconstruct their evolution and to distinguish between allogenic and autogenic processes that had been involved in their development peat began to accumulate in the peatland basin shortly after 6000 cal bp the initial stage was a shallow bay or a salty marsh followed by a wet marsh triggered by a relatively rapid drop in sea level related to a rapid isostatic uplift of land by 5640 cal bp the site had transformed into a rich fen a high rate of peat accumulation led to the establishment of a short lived intermediate fen by 4610 cal bp and to a poor fen from 4200 cal bp until 1760 cal bp low water tables associated with decreased precipitation occurred between 5170 and 4610 cal bp and 3100 and 1760 cal bp between 1760 and the little ice age there was ombrotrophication of the site largely as a result of a thick peat accumulation during this period autogenic processes had controlled the general hydrosere while allogenic processes mainly precipitation had influenced species composition permafrost established during the little ice age leading to palsa formation and it has been melting in response to recent climate warming and precipitation increases macrofossil results from the filled thermokarst pond show that plant succession used the followed hydrosere calliergon giganteum and sphagnum riparium when the pond s depth was at a maximum s riparium and c giganteum when the pond was partly filled in and s lindbergii and s riparium since the pond has been completely filled in

mid holocene climates of the americas a dynamical response to changed seasonality simulations of the climatic response to mid holocene 6 ka bp orbital forcing with two coupled ocean atmosphere models foam and csm show enhancement of monsoonal precipitation in parts of the american southwest central america and northernmost south america during northern hemisphere summer the enhanced onshore flow that brings precipitation into central america is caused by a northward displacement of the inter tropical convergence zone driven by cooling of the equatorial and warming of the northern subtropical and mid latitude ocean ocean feedbacks also enhance precipitation over the american southwest although the increase in monsoon precipitation there is largely driven by increases in land surface temperature the northward shift in the equatorial precipitation band that causes enhanced precipitation in central america and the american southwest has a negative feedback effect on monsoonal precipitation in northern south america the simulations demonstrate that mid holocene aridity in the mid continent of north america is dynamically linked to the orbitally induced enhancement of the summer monsoon in the american southwest with a spatial structure wet in the southwest and dry in the mid continent similar to that found in strong monsoon years today changes in winter precipitation along the west coast of north america in central america and along the gulf coast caused by southward displacement of the westerly storm tracks indicate that changes in the northern hemisphere winter monsoon also play a role in regional climate changes during the mid holocene although the simulations with foam and csm differ in detail the general mechanisms and patterns are common to both the model results thus provide a coherent dynamical explanation for regional patterns of increased or decreased aridity shown by vegetation lake status and aeolian data from the americas

long term stability of permafrost in subarctic peat plateaus west central canada long term vegetation succession and permafrost dynamics in subarctic peat plateaus of west central canada have been studied through detailed plant macrofossil analysis and extensive ams radiocarbon dating of two peat profiles peatland inception at these sites occurred around 5800 5100 yr bp 6600 5900 cal bp as a result of paludification of upland forests at the northern peat plateau site located in the continuous permafrost zone palaeobotanical evidence suggests that permafrost was already present under the forested upland prior to peatland development paludification was initiated by permafrost collapse but re aggradation of permafrost occurred soon after peatland inception at the southern site located in the discontinuous permafrost zone the aggradation of permafrost occurred soon after peatland inception in the peat plateaus permafrost conditions have remained very stable until present sphagnum fuscum dominated stages have alternated with more xerophytic communities characterized by erica

space geodesy constrains ice age terminal deglaciation the global ice 6g_c vm5a model a new model of the last deglaciation event of the late quaternary ice age is here described and denoted as ice 6g c vm5a it differs from previously published models in this sequence in that it has been explicitly refined by applying all of the available global positioning system gps measurements of vertical motion of the crust that may be brought to bear to constrain the thickness of local ice cover as well as the timing of its removal additional space geodetic constraints have also been applied to specify the reference frame within which the gps data are described the focus of the paper is upon the three main regions of last glacial maximum ice cover namely north america northwestern europe eurasia and antarctica although greenland and the british isles will also be included if peripherally in the discussion in each of the three major regions the model predictions of the time rate of change of the gravitational field are also compared to that being measured by the gravity recovery and climate experiment satellites as an independent means of verifying the improvement of the model achieved by applying the gps constraints several aspects of the global characteristics of this new model are also discussed including the nature of relative sea level history predictions at far field locations in particular the caribbean island of barbados from which especially high quality records of postglacial sea level change are available but which records were not employed in the development of the model although ice 6g c vm5a is a significant improvement insofar as the most recently available gps observations are concerned comparison of model predictions with such far field relative sea level histories enables us to identify a series of additional improvements that should follow from a further stage of model iteration

geomorphic evidence for tear faults accommodating lateral propagation of an active fault bend fold wheeler ridge california abstract wheeler ridge is the topographic expression of an actively growing fault bend fold developed in the hanging walls of a system of mostly north vergent blind thrusts the eastern tip of the fold system has migrated laterally by approximately 3 km during the last 120 ka perpendicular to the regional shortening direction comparison of surface topography and structural cross sections indicates that eastern wheeler ridge comprises three fold segments whose topographic expression steps southward towards the eastern end of the structure lateral propagation of the fold is associated with numerous tear faults expressed as fault scarps that face towards the eastern end of the fold we suggest that these tear faults accommodate earthquake related processes that collectively build plunge of the fold and lateral propagation on blind thrusts we envisage that the fold will grow primarily by thrust faulting events with similar displacement s along strike that are terminated abruptly at tear faults build displacement over multiple earthquake cycles and then step eastward to form a new tear fault formation of especially large tear faults is inferred to be in response to an increase in rock strength governed by lithology the high fault displacement vs length d l for wheeler ridge may be related to high strain rates across a restraining bend in the nearby san andreas strike slip fault system

tectonic geomorphology of marine terraces santa barbara fold belt california uplifted marine terraces are common landforms in coastal regions where active tectonics are an important component of landscape evolution such as along the coastal stretches of southern california the pattern and elevation of shoreline angles on active folds provide information about rates of uplift and fold growth which is important for defining tectonic models a particularly impressive succession of marine terraces are developed across the santa barbara fold belt sbfb in southern california which comprises an east west linear zone of active folds and mostly blind faults on the coastal piedmont and in the santa barbara channel the fold belt is characterized by several flights of emergent late pleistocene marine terraces uplifted and preserved on the flanks of active anticlines at several locations along the fold belt the first emergent marine terrace is numerically dated by methods that include uranium series dating on terrace corals 14 c dating on terrace shells and detrital charcoal optically stimulated luminescence of marine terrace sands and oxygen isotopic signatures 18 o of mollusks individual marine terraces have as many as four ages using up to three different dating methods providing confidence in terrace chronology ages of higher terraces are estimated assuming a constant rate of uplift for a particular flight of the 31 terraces 22 formed during a time of falling sea level with 9 forming at or near marine oxygen isotope stage mis 3 or 5 highstands ages and rates of uplift of the first emergent terrace vary systematically from west younger and higher to east older and lower the first emergent marine terraces in the westernmost sbfb are approximately 45 ka mis 3 and the rate of local surface uplift is 2 m k y in the central part of the belt first emergent terraces date to 60 70 ka mis 5 and uplift rates decrease to 1 2 m k y first emergent marine terraces preserved in the easternmost fold belt range from 70 ka to 105 ka mis 5 with rates of local surface uplift of 0 5 m k y lower rates of uplift in the eastern end of the fold belt result from the mis 5 terrace being tilted down into the carpinteria syncline rates of vertical uplift in the western end of the fold belt are about six times higher than previously reported suggesting the seismic hazard is also greater

a data calibrated distribution of deglacial chronologies for the north american ice complex from glaciological modeling article i nfo past deglacial ice sheet reconstructions have generally relied upon discipline specific constraints with no at tention given to the determination of objective confidence intervals reconstructions based on geophysical inversion of relative sea level rsl data have the advantage of large sets of proxy data but lack ice mechanical constraints conversely reconstructions based on dynamical ice sheet models are glaciologically self consistent but depend on poorly constrained climate forcings and sub glacial processes as an example of a much better constrained methodology that computes explicit error bars we present a dis tribution of high resolution glaciologically self consistent deglacial histories for the north american ice com plex calibrated against a large set of rsl marine limit and geodetic data the history is derived from ensemble based analyses using the 3d mun glacial systems model and a high resolution ice margin chronol ogy derived from geological and geomorphological observations isostatic response is computed with the vm5a viscosity structure bayesian calibration of the model is carried out using markov chain monte carlo methods in combination with artificial neural networks trained to the model results the calibration provides a posterior distribution for model parameters and thereby modeled glacial histories given the observational data sets that takes data uncertainty into account final ensemble results also account for fits between com puted and observed strandlines and marine limits given the model including choice of calibration parameters input and constraint data sets and vm5a earth rhe ology we find the north american contribution to mwp1a was likely between 9 4 and 13 2 m eustatic over a 500 year interval this is more than half of the total 16 to 26 m meltwater pulse over 500 to 700 years with lower values being more probable indicated by the barbados coral record fairbanks 1989 peltier and fairbanks 2006 if one assumes a 5 meter living range for the acropora palmata coral 20 ka ice volume for north america was likely 70 1 2 0 m eustatic or about 60 of the total contribution to eustatic sea level change we suspect that the potentially most critical unquantified uncertainties in our analyses are those related to model structure especially climate forcing deglacial ice margin chronology and earth rheology

the relationship between strain rates crustal thickening palaeomagnetism finite strain and fault movements within a deforming zone the deformation of continental lithosphere generally does not occur on a single fault but is distributed over a zone up to a few hundred kilometers wide if the deformation rate is constant throughout the zone and if the velocity is continuous everywhere and does not change with time the deformation gradient tensor can be obtained analytically this tensor directly determines the amount of crustal thickening and is related in a complicated manner to the finite strain tensor the declination of remnant magnetization measured within the zone can also be rotated by the deformation because palaeomagnetic measurements are generally made on rigid blocks which have not been deformed there is no simple relationship between such rotations and the finite strain expressions for all these quantities are obtained in terms of the velocity gradients which are taken to be constant the history of western north america is used to illustrate the relationship between the present deformation by strike slip and thrust motions the rotations of the remnant magnetization vectors and the shape of accreted terranes at the surface distributed deformation is taken up by motion on faults which separate the zone into blocks the displacement rate on the faults their strike and the finite rotations of the blocks are all controlled by the velocity gradients analytic expressions relating these quantities are obtained a deforming zone containing normal faults which crosses central greece takes up both strike slip and extension and illustrates the relationship between the structures within and the motion across the zone a similar but more complicated zone in northeastern iran involves both strike slip and shortening

near surface permafrost aggradation in northern hemisphere peatlands shows regional and global trends during the past 6000 years the history of permafrost aggradation and thaw in northern peatlands can serve as an indicator of regional climatic history in regions where records are sparse we infer regional trends in the timing of permafrost aggradation and thaw in north american and eurasian peatland ecosystems based on plant macrofossils and peat properties using existing peat core records from more than 250 cores results indicate that permafrost was continuously present in peatlands during the last 6000 years in some present day continuous permafrost zones and formed after 6000 bp in peatlands in the isolated to discontinuous permafrost regions rates of permafrost aggradation in peatlands generally increased after 3000 bp and were greatest between 750 and 0 bp corresponding with neoglacial cooling and the little ice age lia respectively peak periods of permafrost thaw occurred after 250 bp when permafrost aggradation in peatlands reached its maximum extent and as temperatures began warming after the lia suggesting that p

structure and origin of holocene cold events abstract the present interglacial the holocene spans the period of the last 11 700 years it has sustained the growth and development of modern society the millennial scale decreasing solar insolation in the northern hemisphere summer lead to northern hemisphere cooling a southern shift of the intertropical convergence zone itcz and a weakening of the northern hemisphere summer monsoon systems on the multidecadal to multicentury scale periods of more stable and warmer climate were interrupted by several cold relapses at least in the northern hemisphere extra tropical area based on carefully selected 10 000 year long time series of temperature and humidity precipitation as well as reconstructions of glacier advances the spatiotemporal pattern of six cold relapses during the last 10 000 years was analysed and presented in form of a holocene climate atlas hoclat see http www oeschger unibe ch research projects holocene atlas a clear cyclicity was not found and the spatiotemporal variability of temperature and humidity precipitation during the six specific cold events 8200 6300 4700 2700 1550 and 550 years bp was very high different dynamical processes such as meltwater flux into the north atlantic low solar activity explosive volcanic eruptions and fluctuations of the thermohaline circulation likely played a major role in addition internal dynamics in the north atlantic and pacific area including their complex interaction were likely involved

the holocene evolution of permafrost near the tree line on the eastern coast of hudson bay northern quebec permafrost evolution in postglacial marine silts near the tree line was reconstructed using landform analysis 14c dating and palynostratigraphic analysis of peat sections in the forest tundra below the tree line four sites in peat plateaus have a stratigraphic sequence indicating an alluvial plain environment from 6000 to 4800 bp followed by a wetland supporting trees and shrubs with deep snow accumulation and without permafrost ground heave occurred between 1900 and 1200 bp as peat plateaus and palsas were formed in the shrub tundra above the tree line three permafrost sites with buried peat beds suggest that climatic conditions were cold enough for discontinuous permafrost in the surrounding landscape starting from land emergence about 5800 bp however fen expansion and sedge peat accumulation continued over unfrozen ground until 2300 1560 and 1400 bp at these dates the sites were buried with silt probably as a result of mass wasting on nearby permafrost mounds and then permafrost aggrad

active tectonics of the alpine himalayan belt between western turkey and pakistan summary over 80 new fault plane solutions combined with satellite imagery as well as both modern and historical observations of earthquake faulting are used to investigate the active tectonics of the middle east between western turkey and pakistan the deformation of the western part of this region is dominated by the movement of continental material laterally away from the lake van region in eastern turkey this movement helps to avoid crustal thickening in the van region and allows some of the shortening between arabia and eurasia to be taken up by the thrusting of continental material over oceanic type basement in the southern caspian mediterranean makran and black sea thus central turkey bounded by the north and east anatolian strike slip faults is moving west from the van region and overrides the eastern mediterranean at two intermediate depth seismic zones one extending between antalya bay and southern cyprus and the other further west in the hellenic trench the motion of northern iran eastwards from the van region is achieved mainly by a conjugate system of strike slip faults and leads to the low angle thrusting of iran over the southern caspian sea the seismicity of the caucasus shows predominantly shortening perpendicular to the regional strike but there is also some minor elongation along the strike of the belt as the causcasus overrides the caspian and black seas the deformation of the eastern part of this region is dominated by the shortening of iran against the stable borders of turkmenistan and afghanistan the north east direction of compression seen in zagros is also seen in north east iran and the kopet dag where the shortening is taken up by a combination of strike slip and thrust faulting large structural as well as palaeomagnetic rotations are likely to have occurred in ne iran as a result of this style of deformation north south strike slip faults in southern iran allow some movement of material away from the collision zone in ne iran towards the makran subduction zone where genuinely intermediate depth seismicity is seen within this broad deforming belt large areas such as central turkey nw iran azerbaijan central iran and the southern caspian appear to be almost aseismic and therefore to behave as relatively rigid blocks surrounded by active belts 200 300 km wide the motion of these blocks can usefully be described by poles of rotation the poles presented in this paper predict motions consistent with those observed and also predict the opening of the gulf of iskenderun ne of cyprus the change within the zagros mountains from strike slip faulting in the nw to intense thrusting in the se and the relatively feeble seismicity in se iran baluchistan this description also explains why the north south structures along the iran afghanistan border do not cut the east west ranges of the makran within the active belts surrounding the relatively aseismic blocks a continuum approach is needed for a description of the deformation even though motions at the surface may be concentrated on faults the evolution of fault systems within the active zones is controlled by geometric constraints such as the requirement that simultaneously active faults do not in general intersect many of the active processes discussed in this paper particularly large scale rotations and lateral movement along the regional strike are likely to have caused substantial complexities in older mountain belts and should be accounted for in any reconstructions of them

glacial lake mcconnell paleogeography age duration and associated river deltas mackenzie river basin western canada abstract glacial lake mcconnell lasted from 11 8 to 8 3 ka bp while occupying parts of the great bear great slave and athabasca lake basin the retreating laurentide ice front formed the eastern margin whereas low rolling hills formed the north west and south shorelines three major deltas were deposited at the mouths of the laird peace and athabasca rivers the total extent of all phases of the lake was 240 000 km 2 while the largest extent was 210 000 km 2 at 10 5 ka bp downwarping of the basin by glacial ice was the main cause of the lake whereas sediment blockage between jean marie river and fort simpson was secondary initially glacial lake mcconnell occupied the northwestern corner smith arm of the great bear lake basin and discharged through the hare indian river outlet by 11 5 ka bp the enlarged water body flowed out the great bear river but only for a short period of time the mackenzie river formed the third outlet near jean marie river at 11 ka bp and flow in the great bear river ceased until 9 ka bp at 9 9 ka bp glacial lake mcconnell was impacted by a major flood from glacial lake agassiz with a peak discharge of 2 7 10 6 m 3 sec flood water discharged from glacial lake mcconnell peaking at 0 35 0 57 10 6 m 3 sec and receding flow continued for 30 months the massive influx of floodwater into glacial lake mcconnell caused an abrupt increase of discharge which enlarged the outlet channel to between 6 and 13 km wide between fort simpson and jean marie river at 8 3 ka bp isostatic rebound ended the 3500 year old extensive lake by dividing it into the great slave lake and lake athabasca

deformation in the santa barbara channel from gps measurements 1987 1991 geodesy is one of the few techniques that can be used to estimate strain rates across the submerged structures in the santa barbara channel by resolving relative surface velocities the global positioning system gps can be used to infer crustal deformation rates independent of geologic models gps measurements from the period 1987 1991 have been used to derive velocities for a 8 station network bounding the channel these estimates are based on 10 gps experiments each of several days in length over this 4 5 year period precision of individual determinations of intersite vectors range from 3 to 7 mm for the horizontal components and average 20 mm in the vertical the gps data indicate high rates of shortening in the eastern channel 6 1 mm yr at n16 3e and low rates of deformation in the western channel comparisons with previous geodetic studies suggest that deformation in the region has not been uniform over the last 100 years

quaternary tectonics of the argolikos gulf and adjacent basins greece a single channel seismic reflection survey of the argolikos gulf and idhra channel casts light on the tectonic history of this extensional basin of which the current subsidence phase is less than 0 5 ma old although the gulf has very low seismicity holocene subsidence on the western boundary faults increases southward from 50 to 100 cm ka 1 the eastern margin of the gulf is offset eastward twice for these offsets we postulate two left lateral strike slip faults accommodating a southward increase in the extension rate these features can be traced on land where at least one of them shows evidence of left lateral movement the idhra channel has a different tectonic pattern of e w trending extensional troughs separated by basement ridges the latter diverge westward and continue into the southern argolid as mesozoic limestone ridges separated by ophiolite floored tectonic valleys the causes of this discordant pattern remain obscure

listric thrusts in the western transverse ranges california some of the main faults accommodating current shortening in the western transverse ranges are probably listric because 1 they are associated with progressive tilting and 2 they may be preexisting normal faults that accommodated miocene extension these faults have been reactivated in the pliocene quaternary transpressive regime we propose a listric thrust model where slip is proportional to backlimb dip this model requires relatively little fault slip to account for progressive tilting and for wide in the dip direction and gently dipping backlimbs in contrast widely applied fault bend fold and fault propagation fold models relate fault slip to limb width alone and typically predict more shortening by the blind thrusts that can be accounted for by folding in the cover above them we trace the southernmost structural high in the transverse ranges from the santa monica mountains through the southern santa barbara channel the north dipping backlimb of this anticline is 20 30 km wide and 220 km long its presence suggests a very large north dipping thrust that could generate very large earthquakes the slip rate for this fault however is substantially lower for a listric thrust model than for a single step ramp flat model

spatial modelling of palsa mires in relation to climate in northern europe palsa mires are mire complexes that occur in the northern hemisphere representing one of the most marginal permafrost features at the outer limit of the permafrost zone a climate based spatial model is presented for the distribution of palsa mires in northern europe the model is based on an extensive spatial data of palsa mires and climatological variables from 1913 grid cells in an area of c 240 000 km2 generalized linear modelling glm with curvilinear and interaction terms is used to derive the palsa mire climate relationships the nal model correctly classi ed 77 6 per cent of the palsa mire presence squares the results indicate a positive association of the distribution of palsa mires with increasing frost number and continentality whereas precipitation and temperature showed a negative correlation with the distribution of palsa mires additionally interaction of thawing degree days and summer time precipitation showed a negative association climatologically the optimum areas of palsa mires occur in areas of low precipitation 450 mm and a mean annual temperature between 3 c and 5 c potential reasons for the performance of the model and the sensitivity of palsa mires to climate change are discussed the application of a gis based generalized linear modelling as used here provides a versatile method to study the distribution of different geomorphological phenomena across climatological gradients copyright 2004 john wiley sons ltd

modeling of neogene crustal block rotation case study of southeastern california numerical modeling using a two dimensional distinct element method dem was performed to give an additional understanding of the mechanism of crustal block rotation in a highly active portion of the pacific north america transform plate boundary paleomagnetic and structural investigations have shown that large 30 50 horizontal rotations of crustal blocks occurred in the eastern transverse zone and the northeast mojave block southeastern california since the end of early miocene the main aspect of the modeling was to investigate whether an anisotropic horizontal stress state can be responsible for the rotation of crustal blocks with a length of 100 km or not the simulations were performed using different stress boundary conditions and different parameters of the fault strength applying an assumed ratio of 2 for the horizontal stress components as boundary condition block rotations in the order of 40 only occur if 1 the major horizontal stress sh is oriented n20 e with a maximal deviation of 15 to the east or west and 2 the fault strength described by the friction coefficient is smaller than 0 12 or 14 only of the value 0 85 for intact rocks byerlee s law for a weakening model of the fault strength an initial friction coefficient of 0 85 allows also rotations of about 40 if the friction coefficient decreases rapidly due to an increasing shear displacement to a basic friction coefficient of 0 12 or smaller for the same amount of rotation 40 a decreasing stress ratio requires a lowering of the friction coefficient used whereas an increase of the ratio allows a higher friction coefficient the simulation also show that the modeling with elastic blocks can adequately describe the observed main features of the crustal deformation especially the cumulative slip values discrepancies in the observations and modeling results for the western parts of the mojave desert are the result of a neglect of the three dimensional deformation in our two dimensional modeling

regional stratigraphic architecture and reservoir types of the oligo miocene deposits in the dezful embayment asmari and pabdeh formations sw iran

glacial lake agassiz a 5000 yr history of change and its relationship to the δ18o record of greenland lake agassiz was the largest lake in north america during the last period of deglaciation the lake extended over a total of 1 5 10 6 km 2 before it drained at ca 7 7 14 c ka 8 4 cal calendar ka new computer reconstructions controlled by beaches isostatic rebound data the margin of the laurentide ice sheet outlet elevations and a digital elevation model dem of modern topographic data show how variable the size and depth of this lake were during its 4000 14 c yr 5000 cal yr history abrupt reductions in lake level ranging from 8 to 110 m occurred on at least 18 occasions when new outlets were opened reducing the extent of the lake and sending large outbursts of water to the oceans three of the largest outbursts correlate closely in time with the start of large 18 o excursions in the isotopic records of the greenland ice cap suggesting that those freshwaters may have had an impact on thermohaline circulation and in turn on climate

widespread global peatland establishment and persistence over the last 130 000 y glacial interglacial variations in co2 and methane in polar ice cores have been attributed in part to changes in global wetland extent but the wetland distribution before the last glacial maximum lgm 21 ka to 18 ka remains virtually unknown we present a study of global peatland extent and carbon c stocks through the last glacial cycle 130 ka to present using a newly compiled database of 1 063 detailed stratigraphic records of peat deposits buried by mineral sediments as well as a global peatland model quantitative agreement between modeling and observations shows extensive peat accumulation before the lgm in northern latitudes 40 n particularly during warmer periods including the last interglacial 130 ka to 116 ka mis 5e and the interstadial 57 ka to 29 ka mis 3 during cooling periods of glacial advance and permafrost formation the burial of northern peatlands by glaciers and mineral sediments decreased active peatland extent thickness and modeled c stocks by 70 to 90 from warmer times tropical peatland extent and c stocks show little temporal variation throughout the study period while the increased burial of northern peats was correlated with cooling periods the burial of tropical peat was predominately driven by changes in sea level and regional hydrology peat burial by mineral sediments represents a mechanism for long term terrestrial c storage in the earth system these results show that northern peatlands accumulate significant c stocks during warmer times indicating their potential for c sequestration during the warming anthropocene

gas hydrate and mud volcanoes on the southwest african continental margin off south africa widespread occurrence of bottom simulating reflectors bsrs has been detected in multichannel seismic profiles on the upper continental slope in the southern periphery of the orange river delta probably indicating the presence of large quantities of gas hydrate in this area this report is the first to show the presence of bsrs on seismic records on the southwest african continental margin south of the walvis ridge another remarkable feature in the area is the occurrence of a large number of mud volcanoes the distribution of the bsrs and the location of the mud volcanoes are controlled by the locations of active faults the gas hydrate in this region may consist of a mixture of microbial and thermogenic gas whereas much of the gas flowing through the mud volcanoes probably originated from deep seated aptian source shales

the neotectonics of the aegean an alternative view minor reverse faults in widely dispersed neogene outcrops in the central aegean have led several people to suggest that the regional extension which started in the lower pliocene or earlier was interrupted by short periods of compression the durations of these postulated compressional episodes are short compared to the time scale on which convective forces acting on the base of the lithosphere can change thus possible mechanisms for driving such motions are limited in this paper we offer alternative explanations for these observations and in particular show that these apparently compressional episodes are probably not regional in extent and may not be truly compressional in origin in some places they are more likely to be a consequence of the considerable rotation that is found in extensional terranes the plio quaternary paleogeography of the central aegean is satisfactorily explained by uplift in the footwall blocks of normal faults and does not require regional compression studies of the faulting associated with recent large earthquakes suggest that the sort of microtectonic analysis which is typically carried out on small faults in surficial sediments is more likely to reflect the internal deformation of blocks bounded by major fault structures than be a reliable indicator of regional stress patterns

climate and ground temperature relations at sites across the continuous and discontinuous permafrost zones northern canada1 21this article is one of a series of papers published in this cjes special issue on the theme of fundamental and applied research on permafrost in canada 2earth science sector ess contribution 20110128 climate ground temperature relations are examined under a range of conditions for 10 sites across northern canada the sites are located between 60 n and 83 n and at elevations of 40 to 1840 m ab

microseismicity and focal mechanisms at the western termination of the north anatolian fault and their implications for continental tectonics summary for seven weeks a temporary network of 68 seismological stations was operated in central greece in the region of thessaly and evia located at the western termination of the north anatolian fault system we recorded 510 earthquakes and computed 80 focal mechanisms seismic activity is associated with the ne sw dextral north aegean fault or with very young e w striking normal faults that are located around the gulf of volos and the gulf of lamia the important nw se striking faults bounding the pilion or the basins of larissa and karditsa are not seismically active suggesting that it is easier to break continental crust creating new faults perpendicular to the principal stresses than to reactivate faults that strike obliquely to the principal stress axes

atmospheric nitrous oxide during the last 140 000 years article i nfo reconstructions of past atmospheric concentrations of greenhouse gases provide unique insight into the biogeochemical cycles and the past radiative forcing in the earth s climate system we present new measurements of atmospheric nitrous oxide along the ice cores of the north greenland ice core project and talos dome sites using records of several other ice cores we are now able to establish the first complete composite nitrous oxide record reaching back to the beginning of the previous interglacial about 140 000 yr ago on the basis of such composite ice core records we further calculate the radiative forcing of the three most important greenhouse gases carbon dioxide methane and nitrous oxide during more than a full glacial interglacial cycle nitrous oxide varies in line with climate reaching very low concentrations of about 200 parts per billion by volume during marine isotope stages 4 and 2 and showing substantial responses to millennial time scale climate variations during the last glacial a large part of these millennial time scale variations can be explained by parallel changes in the sources of methane and nitrous oxide however as revealed by high resolution measurements covering the dansgaard oeschger events 17 to 15 the evolution of these two greenhouse gases may be decoupled on the centennial time scale carbon dioxide and methane concentrations do not reach interglacial levels in the course of millennial time scale climate variations during the last glacial in contrast nitrous oxide often reaches interglacial concentrations in response to both glacial terminations and dansgaard oeschger events this indicates from a biogeochemical point of view similar drivers in both temporal cases while carbon dioxide and methane concentrations are more strongly controlled by climate changes in high latitudes nitrous oxide emissions changes may mainly stem from the ocean and or from soils located at low latitudes accordingly we speculate that high latitudes could play the leading role to trigger glacial terminations

active tectonics at wheeler ridge southern san joaquin valley california wheeler ridge is an east west trending anticline that is actively deforming on the upper plate of the pleito wheeler ridge thrust fault system holocene and late pleistocene deformation is demonstrated at the eastern end of the anticline where salt creek crosses the anticlinal axis uplift tilting and faulting associated with the eastward growth of the anticline are documented by geomorphic surfaces that are higher and older to the west faulting and associated folding is propagating eastward as indicated by increases in both the degree of surface dissection and the degree of soil development from east to west distinct topographic areas having distinct degrees of surface dissection bounded by tear faults suggest that faulting and folding have propagated eastward in discrete segments numerical dates indicate 1 the anticline is propagating eastward at a rate of about 30 mm yr about 10 times the rate of uplift 2 folding was initiated about 400 ka 3 a prominent wind gap was formed during q3 time about 60 ka when an antecedent stream was defeated forcing the stream east around the nose of the fold today drainage through the ridge is by way of two antecedent streams water gaps east of the wind gap and 4 the rate of uplift at the easternmost and youngest past 1 k y part of the fold is at least 3 mm yr investigations of the tectonic geomorphology of wheeler ridge support the hypothesis that climatic perturbations are primarily responsible for producing geomorphic surfaces such as alluvial fan segments and river terraces tectonic perturbations deform the surfaces

holocene vegetational and climatic changes in the forest zone of western siberia according to pollen records from the extrazonal palsa bog bugristoye pollen stratigraphy of an extrazonal palsa bog in the middle taiga of the west siberian plain is dated by radiocarbon at five levels local pollen assemblage zones lpaz are the basis for palaeogeographical reconstructions tundra steppe plant communities with shrub birch betula nana dominated in the latest pleistocene warming after 10 000 14c yr bp caused the local thawing of permafrost forming shallow lakes larixand then picea spread along river valleys and depressions steppe plant communities existed on the dry interfluves further climatic warming and drying caused picea to retreat and betula forest steppe dominated 9500 8900 yr bp dense pinus sylvestris and pinus sibirica forests then spread over the whole area and steppe communities decreased about 8300 yr bp the holocene climatic optimum 6000 5000 yr bp was characterized by warm and wet conditions and abies was widespread cooling then caused retreat of abiesforests to the south and the expansion of pinus sibirica forests on clay soils

a possible dependence of tectonic strength on the age of the crust in asia in asia the intensity and style of active tectonics appears to depend on the age of the last orogenic activity the shields have remained essentially undeformed during the india eurasian collision but paleozoic and mesozoic orogenic belts apparently have been reactivated by this collision with a suggestion of greater reactivation and more diffuse deformation of the younger belts if the greater observed heat flow in regions of more recent orogenic activity reflects at least in part a greater heat flow from the mantle beneath the younger belts then the temperatures in the mantle beneath the younger belts should be higher than beneath older belts and shields because of the strong dependence on temperature of the creep strength of minerals particularly of olivine the crust and mantle beneath the hotter younger belts should be much weaker than those beneath older belts this difference in temperature and consequent difference in strength may be the cause of the greater reactivation of younger belts

large scale quaternary detachments in ventura basin southern california the ventura basin is an east north east trending trough in the california transverse ranges which records major quaternary detachment faulting at three levels the earliest thrusting occurred along weak siltstone interbeds in a sequence dominated by competent basin plain turbidite sandstone because sedimentation continued during thrusting the age rate and direction of thrusting can be worked out faulting began 1 3 m y ago and ceased 0 65 m y ago with a maximum slip rate of 2 8 mm yr to the southeast the fault set moved up a 45 ramp and ended as a blind thrust the ramp had topographic expression on the seafloor diverting turbidites around the ramp and preserving ash beds along with other hemipelagic sediments on its crest following the end of deposition 0 2 m y ago the competent basin plain turbidites underwent flexural slip folding over an incompetent miocene sequence dominated by shale underlying competent paleogene strata were not folded the south flank of the ventura avenue anticline tilted at 3 4 rad yr the anticlinal crest rose at a rate of 15 16 mm yr decelerating to 4 3 5 2 mm yr and the anticline and an adjacent syncline shortened at a rate of 20 mm yr the high rate of folding in the ventura avenue oil field resulted in overpressured sandstone reservoirs and oil water interfaces which have not had time to reach gravity equilibrium the red mountain san cayetano and santa susana faults mark the surface expression of a seismically active midcrustal detachment which produced convergence across the ventura basin at rates as high as 23 mm yr total convergence across the eastern san cayetano fault near fillmore is 11 600 2000 m in the last million years

orogenic evolution of the hellenides new aspects this progress report is based on investigations of the tectonometamorphic development of crystalline complexes and is restricted to a few key problems of the hellenides these results reveal the mechanisms of intracratonic tectonics remobilization of continental crust and intracrustal detachment throughout the evolution of the hellenides

timing of the last glacial maximum from observed sea level minima during the last glacial maximum ice sheets covered large areas in northern latitudes and global temperatures were significantly lower than today but few direct estimates exist of the volume of the ice sheets or the timing and rates of change during their advance and retreat here we analyze four distinct sediment facies in the shallow tectonically stable bonaparte gulf australia each of which is characteristic of a distinct range in sea level to estimate the maximum volume of land based ice during the last glaciation and the timing of the initial melting phase we use faunal assemblages and preservation status of the sediments to distinguish open marine shallow marine marginal marine and brackish conditions and estimate the timing and the mass of the ice sheets using radiocarbon dating and glacio hydroisostatic modelling our results indicate that from at least 22 000 to 19 000 calendar years before present land based ice volume was at its maximum exceeding today s grounded ice sheets by 52 5 x 10 exp 6 cu km a rapid decrease in ice volume by about 10 percent within a few hundred years terminated the last glacial maximum at 19 000 250 years

synthesis of studies of palsa formation underlining the importance of local environmental and physical characteristics this review presents a synthesis of four decades of palsa studies based on field experiments and observations mainly in fennoscandia as well as laboratory measurements palsas are peat covered mounds with a permanently frozen core in finnish lapland they range from 0 5 to 7 m in height and from 2 to 150 m in diameter these small landforms are characteristic of the southern margin of the discontinuous permafrost zone palsa formation requires certain environmental conditions long lasting air temperature below 0 c thin snow cover and low summer precipitation the development and persistence of their frozen core is sensitive to the physical properties of peat the thermal conductivity of wet and frozen peat is high and it decreases significantly as the peat dries and thaws this affects the development of the active layer and makes its response to climate change complex the insulating properties of dry peat during hot and dry summers moderate the thawing of the active layer on palsas in contrast humid and wet weather during the summer causes deep thawing and may destroy the frozen core of palsas ice layers in palsas have previously been interpreted as ice segregation features but because peat is not frost susceptible the ice layers are now reinterpreted as resulting from ice growth at the base of a frozen core that is effectively floating in a mire

fault related fold growth and isostatic subsidence california channel islands in the northern channel islands of california preservation of paleo shoreline features both as uplifted landforms onshore and subsided depositional features offshore has allowed precise measurement of late quaternary fold growth relative to sea level and has helped to disentangle the relative contributions of tectonic forcing and isostatic response we precisely measured several hundred points on uplifted pleistocene coastal terraces of santa cruz and anacapa islands the elevations of which document anticlinal growth of the islands since at least 400 ka we also interpreted a dense grid of seismic reflection profiles that image a complex of eustatic lowstand deltas that record regional subsidence surrounding the uplifting structure we combined onshore uplift with offshore subsidence measurements to produce a quantitative mass balance of structural growth since 400 ka the data outlined above were then used to test the hypothesis that subsidence around the northern channel islands represents the flexural isostatic response to tectonic loading of the islands calculations of cumulative uplifted mass and cumulative subsided mass across the structure closely match the values predicted for density driven isostatic compensation and local flexural support although the wavelength of flexure predicted for the study area suggests that an additional component of flexural support may extend distally 10s of kilometers into the surrounding offshore basins in the northern channel islands isostatic subsidence is explicitly manifested because erosional mass removal is small because the crust here is relatively thin and weak and most importantly because sea level provides an absolute datum against which to measure vertical deformation an explicit treatment of the interplay between crustal thickening erosional denudation surface uplift and isostatic response helps to illustrate the conditions under which isostatic subsidence may or may not be a significant process where surface denudation rates approach the rate of rock uplift for example isostatic subsidence will approach zero in contrast failure to recognize isostatic subsidence in earthquake hazard studies can lead to order of magnitude errors in slip rate and hazard estimates

tectonic geomorphology and hydrocarbon induced topography of the mid channel anticline santa barbara basin california the geomorphology of the western sector of the mid channel anticline mca santa barbara southern california suggests the actively growing fold is laterally propagating to the west the presence of fold scarps and cross faults that segment the structure suggests that buried faults that are producing the folding are present at shallow depths the summit area of the anticline at the last glacial maximum 22 to 19 ka was probably a small late pleistocene island evidence for presence of the island includes what appears to be terrestrial erosion and is supported by assumption of sea level change and rates of uplift and subsidence pockmarks and domes ranging in diameter from 10 to 100 m and several meters deep are present along the crest and flanks of the mca these features appear to be the result of hydrocarbon emission their formation has significantly modified the surface features producing simple to complex erosional and or constructional topography a large pockmark near the anticline crest dated by two calibrated ams radiocarbon dates of 25 3 and 36 9 ka continues to emit hydrocarbon gases we term the topography produced by hydrocarbon emission as hydrocarbon induced topography hit 2007 elsevier b v all rights reserved

slip distribution aftershocks and co seismic fault of some large persian earthquakes this investigation concentrates on slip distribution aftershocks mainshock location and related co seismic faults for seven continental large earthquakes in the persian plateau most of the earthquakes m s 5 7 7 7 1981 2005 with both measurable surface slip along a mature rupture and a precisely aftershock surveying with a local seismological network in iran are evaluated in most of the case studies we observe an acceptable correlation between maximum surface slip along the fault trace and the asperity an area which is recognized as an obvious gap or an area with lack of aftershocks on a fault plane on the other hand we conclude that the aftershocks which are associated with immeasurable or smaller surface slips mainly concentrate at the outside of the asperities also the mainshocks in most of the earthquakes are in neighboring with the big asperities and segment the co seismic faults we could see a gradual increase in the co seismic slip when the magnitude of the earthquake increases but examples with defuse aftershocks and with no specific pattern are also found

active faulting and growth folding in the eastern santa barbara channel california we develop new methods to identify blind thrust fault systems determine fault slip rates and estimate potential earthquake magnitudes and recurrence intervals in active fold and thrust belts these methods are applied to compressive folds along the offshore oak ridge and blue bottle trends which overlie active blind thrust faults in the eastern santa barbara channel these folds and their causative faults are interpreted using fault bend fold theory and are represented in balanced models and cross sections that integrate surface and subsurface data the structures are mapped using a new technique of axial surface mapping in seismic reflection grids which defines three dimensional structural geometries and shows changes in slip and subsurface fault geometry along strike analysis of syntectonic growth sediments yields pliocene and quaternary fault slip rates of 1 3 mm yr on a deep thrust 16 km and 1 3 mm yr on shallower faults 2 5 km the combined 2 6 mm yr slip rate represents only part of the 6 mm yr of shortening measured by geodesy across the channel and estimated from relative pacific north american plate motions across the transverse ranges additional shortening is probably accommodated on other active thrusts in the western transverse ranges and in the northern channel along the santa barbara coast deformed seafloor sediments and a swarm of axial surface seismicity along the fold trends indicate that the underlying thrusts are active and may pose significant earthquake hazards to coastal southern california unsegmented fault surfaces are used through empirical relationships between fault surface area and rupture magnitude to estimate the sizes of potential earthquakes this analysis suggests that a ramp in the channel islands fault beneath the offshore oak ridge trend is capable of rupturing in a m s 7 2 earthquake earthquakes of this magnitude may release 2 m of slip which when combined with the estimated slip rate 1 3 mm yr yields an earthquake recurrence interval of 1500 yr for this channel islands fault ramp

subsurface gas offshore of northern california and its link to submarine geomorphology abstract the northern california continental margin contains evidence of abundant subsurface gas and numerous seafloor features that suggest a causative link between gas expulsion and geomorphology analyses of seismic reflection sidescan sonar and high resolution multibeam bathymetric data show that the occurrence of subbottom gas and the migration processes beneath the shelf differ from those beneath the slope subsurface gas inferred from enhanced reflectors and other geophysical indicators is spatially variable and related more to total depth and stratigraphy than to underlying structure with the exception of one band of gas that follows the regional structural trend shallow depressions on the seafloor pockmarks are used to infer expulsion sites the largest zone of acoustically impenetrable subsurface gas occurs between water depths of 100 m and 300 m where expulsion features are rare the upper slope water depths 400 600 m has a high concentration of pockmarks diameter 10 20 m in contrast to a near absence of pockmarks at water depths shallower than 400 m of nearly 4000 pockmarks observed on sidescan sonar records more than 95 are located in water depths deeper than 400 m bottom simulating reflectors bsrs on some seismic reflection profiles indicate the possible presence of gas hydrate we find that gas and pore fluid migration in the offshore eel river basin is 1 correlated to surface morphology 2 a contributor to seabed roughness 3 a significant mode of sediment redistribution on the upper slope and 4 potentially a factor in large slope failures