delineation of fracture anisotropy signatures in wudayhi field by azimuthal seismic data wudayhi field in the eastern province of saudi arabia figure 1a is an anticlinal structure in the paleozoic cenozoic rocks it is 30 km in length and 10 km in width and trends ene the wudayhi anticline is one in a group of forced folds related to draping of the sedimentary cover over basement block faults in the eastern margin of arabia the anticline is asymmetric with southern vergence and gentle dip angles that rarely exceed several degrees

classification of sea floor features associated with methane seeps along the gulf of cadiz continental margin abstract based on recently gathered swath bathymetry high to ultra high resolution seismic and underwater camera data along with dredging and coring samples this paper examines the relationship between sea floor features and the nature of hydrocarbon enriched fluid and gas leaks from degassing of deeply buried sediments along the continental margin of the gulf of cadiz eastern central atlantic a classification into three main groups is proposed on the basis of the morphology and nature of deposits 1 mud volcanoes 2 methane derived authigenic carbonates mdac mounds and 3 crater like pockmarks mud volcanoes are topographically cone shaped sea floor edifices built up from catastrophic mud and fluid degassing intercalated with periods of inactivity so far more than 25 mud volcanoes have been discovered in the gulf of cadiz named in memory of deceased colleagues e g ginsburg and baraza or researchers birth places e g faro cibeles almazan san petersburgh yuma rabat bonjardim coruna gades these structures range from 800 to 2500 m in diameter and tower 150 300 m above the seabed the volcanoes consistently feature a well defined outer ring or circular terrace and an inner dome all mud volcanoes are built up of episodes of mud breccia flows intercalated with deep current deposits with evident indications of gas saturation degassing structures a strong h2s smell and chemosynthetic fauna such as pogonophora sp tube worms and calyptogena sp commonly observed carbonate crusts and slabs overlying some mud volcanoes are thought to have been formed by slow diffuse venting during periods of inactivity or slower rates of fluid venting following the ejection of mud a fermentation process the result of microbial mediated oxidation of hydrocarbon enriched fluids seems to play an important role in the growth of large deep water carbonate mounds and chimneys during periods of low methane seep fluid pressure more than 400 crater like pockmarks a common sea floor feature in the tasyo field have been observed their seabed diameter ranges from 500 to 3000 m with steep slopes ranging from 12 to 35 according to their internal structure pockmarks can be grouped into 1 pockmarks with low central mounds and 2 crater like pockmarks apparently collapse structures lacking central mounds with a flat to slightly undulating sea bottom surrounded by steep slopes up to 25

glacial geomorphic features in the northern barents sea direct evidence for grounded ice and implications for the pattern of deglaciation and late glacial sedimentation

hydrocarbon sources of cold seeps off the vesteralen coast northern norway abstract we investigated active methane seeps in a water depth of 200 m in the hola area off the coast of vesteralen northern norway to assess 1 hydrocarbon sources 2 migration pathways and 3 the influence of hydrocarbon seepage on sediment pore water and water column chemistry the seepage area is characterised by the presence of gas flares in the water column as revealed by hydro acoustic surveys and elevated methane concentrations of up to 42 nm ca 5 m above the seafloor pore water analyses of three gravity cores from the seepage area show varying depths of the sulphate methane transition zone smtz between 80 cm and 250 cm indicating spatially heterogeneous methane ascent the isotopic composition of methane 13 c from 40 to 63 and 2 h from 191 to 225 and 13 c depth profiles of methane and dissolved inorganic carbon show that the hydrocarbons are predominantly of thermogenic origin consistent with 13 c values of c 2 to c 4 hydrocarbons isotope data also indicate considerable biodegradation of propane seismic profiles from the study area reveal major faults and steeply dipping unconformities between the basement and overlying mesozoic sedimentary rocks we propose that these act as migration pathways for the hydrocarbons from late jurassic to early cretaceous source rocks

inferred gas hydrates and clay diapirs near the storegga slide on the southern edge of the voring plateau offshore norway this paper presents a new data set including single channel airgun seismic lines okean long range side scan sonar data and gravity cores acquired on the edge of the voring plateau and in the region of the storrega slide the data acquisition was part of the 8th training through research ttr 8 expedition with r v professor logachev the acoustic profiles clearly show two laterally separated zones characterised by the presence of bottom simulating reflectors bsrs at about 350 ms twt subbottom depth the lower bsr zone is located on the slope of the voring plateau in the immediate vicinity of the northern headwall of the storegga slide and in some places below the slide deposits this zone runs parallel to the general trend of the continental slope the spatial distribution of the upper bsr zone located upslope in an area where diapir like structures are found does not demonstrate any topographic control interpretation of high backscatter patches on the okean sonographs associates the observed structures with fluid escape features on the seabed most of them are pockmarks but in a few places diapirs are cropping out and form dome like elevations after analysing the behaviour of the bsr sometimes crosscutting and its acoustic characteristics reversed polarity and after applying seismic inversion processing to estimate the acoustic velocity change across the bsr this reflector is interpreted to represent the base of the local gas hydrate stability field ghsf this information was used to derive the regional geothermal gradient spatial variations of the inferred geothermal field appeared to be negligible the observation of two separated bsr zones suggests different environmental controls for the growth of the hydrates enhanced reflectors observed in the intermediate zone can be explained by the presence of strata bound free gas accumulations and migration combined with overlying permeability barriers therefore a model for gas hydrate formation in relation to directional fluid migration processes fluid escape features and the presence of diapiric structures is proposed in this paper our model is supported by sedimentological analyses of seafloor samples which demonstrate the presence of stiff clays with evidence of gas migration and by paleontological studies of the cores retrieved from the pockmarks the presence of a bsr in the sedimentary section within the slide scar area implies the repositioning of hydrates to newly established equilibrium conditions after the slide event this observation allows us to simply estimate an upper limit of the fluid migration velocity in the order of several cm year finally the effect of hydrate dissociation on slope instability is considered assuming that the in situ decomposition of hydrates due to instantaneous depressurisation is slow enough to permit the excess volume of released gas and water to be re distributed through the whole sedimentary section above the paleo bsr with consuming heat and increasing pore pressure dissociation tends to shift the pt conditions back to equilibrium values it appears that the dissociation of hydrates due to sliding would cause only 0 2 increase of the pore pressure which would hardly contribute to further slope instability

p wave anisotropy from azimuthal avo and velocity estimates using 3d seismic data from saudi arabia a horizontal well is most productive in tight reservoirs when it intersects a large number of vertical fractures yet strata near the borehole remain mechanically stable azimuthal velocity analysis and p wave amplitude versus offset avo using 3d wide azimuth prestack surface seismic data provide a remote yet detailed way to map a fracture pattern away from well control we estimate fracture direction and relative fracture intensity from such data at two gas fields in saudi arabia our results show a small azimuthal variation in p wave velocity maximum 5 and a larger variation in azimuthal avo at the reservoir larger than 100 computed fracture attributes for field 1 show a consistent east west fracture direction however in field 2 fracture azimuth is variable but generally east west and north south with the strongly anisotropic north south orientation correlating with faults and areas of large structural curvature in the reservoir in both fields azimuthal avo analysis shows a more consisten

a case study of a mesospheric bore event observed with an all sky airglow imager at tirunelveli 8 7 n 1 a prominent front separating bright and dark regions of all sky airglow images was recorded on the night of 22 23 march 2007 at the low latitude indian station tirunelveli 8 7 n 77 8 e and is attributed to a mesospheric bore with the help of complementary wind information from the colocated mf radar and temperature and density data from the saber instrument onboard timed mission the parameters of the bore are calculated and discussed because the observed wind at the emission altitude was orthogonal to the direction of bore propagation doppler ducting was not likely to support the bore the analysis that makes use of the square of buoyancy frequency profiles reveals a thermal duct that would provide favorable conditions for the propagation of the bore this is the first report of a mesospheric bore event from the indian sector

large pockmarks gas charged sediments and possible clay diapirs in the skagerrak abstract extensive patches of shallow gas charged sediments have previously been documented in the eastern skagerrak the strait between norway and denmark recently obtained high resolution side scan sonar and sub bottom profiler data presented here document several surface and sub surface features at the border and inside zones of such gas charged shallow sediments four examples are presented and discussed 1 a low profile 3 m deep pockmark and gas charged sediments 2 a low profile 6 m deep pockmark associated with a rugged sub surface reflector 3 large up to 24 m deep and 500 m wide pockmarks and 4 patches of exposed material from the rugged sub surface reflector from similarities with previously described features and also with features found in the kattegat further south it is concluded that the pockmarks are formed by gas eruption and seepage and that the rugged sub surface reflector could possibly represent the upper surface of a diapirically deformed unit of gas charged plastic clays

shallow bedrock geology of the olga basin area northwestern barents sea 1 the east west trending olga basin has possibly the largest post jurassic sedimentary rock thickness in the northwestern barents sea the thickness of these mainly shallow marine deposits exceeds 750 m in the study area and increases eastward the olga basin is characterized by relatively undisturbed layers which except for local areas rarely dip more than 3 degrees the storbanken area is heavily penetrated by normal faults which probably are related to the late cretaceous uplift in the region differential uplift along the flanks of the olga basin during the oxfordian hauterivian led to deposition of onlapping units in the central parts whereas erosion and limited deposition prevailed on the topographic highs the overlying barremian sequence is more uniform and is t least 350 m thick in the hammerfest basin in the southern barents sea corresponding barremian deposits are found the post jurassic strata contain sandstones of three different kinds subarkose sublitharenite litharenite and lithic arkose the barremian subarkoses sublitharenites have relatively high porosities and may be potential reservoir rocks the organic geochemistry analyses show somewhat higher hydrogen index values than those found in the corresponding sedimentary strata on spitsbergen however the strata are slightly less mature than the corresponding strata on spitsbergen

patterns of carbonate authigenesis at the kouilou pockmarks on the congo deep sea fan abstract different types of seep carbonates were recovered from the kouilou pockmarks on the congo deep sea fan in approximately 3100 m water depth the carbonate aggregates are represented by pyritiferous nodules crusts and slabs tubes and filled molds the latter are interpreted to represent casts of former burrows of bivalves and holothurians the nodules consisting of high mg calcite apparently formed deeper within the sediments than the predominantly aragonitic crusts and slabs nodule formation was caused by anaerobic oxidation of methane dominantly involving archaea of the phylogenetic anme 1 group whereas aragonitic crusts resulted from the activity of archaea of the anme 2 cluster evidence for this correlation is based on the distribution of specific biomarkers in the two types of carbonate aggregates showing higher hydroxyarchaeol to archaeol ratios in the crusts as opposed to nodules formation of crusts closer to the seafloor than nodules is indicated by higher carbonate contents of crusts probably reflecting higher porosities of the host sediment during carbonate formation this finding is supported by lower 18 o values of crusts agreeing with precipitation from pore waters similar in composition to seawater the aragonitic mineralogy of the crusts is also in accord with precipitation from sulfate rich pore waters similar to seawater moreover the interpretation regarding the relative depth of formation of crusts and nodules agrees with the commonly observed pattern that anme 1 archaea tend to occur deeper in the sediment than members of the anme 2 group methane represents the predominant carbon source of all carbonates 13 c values as low as 58 9 v pdb and the encrusted archaeal biomarkers 13 c values as low as 140 v pdb oxygen isotope values of some nodular carbonates ranging from 3 9 to 5 1 v pdb are too high for precipitation in equilibrium with seawater probably reflecting the destabilization of gas hydrates which are particularly abundant at the kouilou pockmarks

active faults and paleoseismicity in fennoscandia especially sweden primary structures and secondary effects abstract fennoscandia today a region of low to moderately low seismicity was at the time of deglaciation with rates of uplift on the order of tens of centimetres per year a region of very high seismicity and active tectonics this is evident both from primary fault structures and from secondary sedimentary and hard rock effects in the region around the epicentral areas the map of active faults in fennoscandia includes numerous structures previously not recognised despite this the recording of active faults and paleoseismic events is still in its initial phase much more data will surely accumulate in the near future

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

lake sediment evidence of paleoseismicity timing and spatial occurrence of late and postglacial earthquakes in finland abstract sediment profiles in six lake basins located near the late and postglacial fault surface ruptures in northern finland were investigated for turbidites and soft sediment deformation structures that could reveal information on the timing and spatial occurrence of paleoearthquakes in the area we used geophysical sub bottom profiling and lithological logging of sediment cores combined with radiocarbon and paleomagnetic dating in three lakes immeljarvi aakenus and laukkujarvi sediment records provided evidence of postglacial earthquakes or landslides whereas in three others lakes pyhajarvi kallojarvi and syvajarvi no disturbance structures were observed in their sequences that cover roughly the holocene period combined with previous data on paleoseismicity in finland the results enhance the non stationary hypothesis of seismicity throughout the late weichselian and the holocene with three general maxima that cluster around the deglaciation 12 0 10 0 kyr bp the mid holocene 5 0 7 0 kyr bp and the late holocene 1 5 3 0 kyr bp a strong asymmetry of the offset profiles of the finnish postglacial fault complexes indicate that the general rupture propagation was from sw to ne the present data also indicates that the oldest and highest magnitude events mw 7 or higher generally took place in the sw sector of the finnish pgf complexes during or soon after the retreat of the continental ice sheet the ruptures then propagated towards the ne sector of pgf complexes in a cascading fashion and were generally characterized by lower magnitude events mw 6 during the holocene

tree ring correlation between prehistoric landslides and abrupt tectonic events in seattle washington radiocarbon ages of submerged trees on landslide deposits in lake washington seattle indicate that the most recent slides in three separate areas may have occurred simultaneously about 1000 years ago tree ring crossdating shows that seven bark bearing trees from one of these recent slides and a tree 23 kilometers to the northwest in a probable tsunami deposit on the shore of puget sound died in the same season of the same year the close coincidence among the most recent lake landslides a probable tsunami abrupt subsidence and other possible seismic events gives evidence for a strong prehistoric earthquake in the seattle region

geochemical signatures of intense episodic anaerobic oxidation of methane in near surface sediments of a recently discovered cold seep kveithola trough nw barents sea abstract at cold seep environments the detection of large 34s enrichments within bulk sulphide minerals has been frequently used as a proxy to infer the vertical migrations of the sulphate methane transition zone smtz processes related to the oxidative part of the sulphur cycle can alter the original stable sulphur isotope composition 34s of the solid sulphur phases in particular at the sediment water interface identification of paleo and present positions of methane fronts in the sedimentary records requires the use of multiple geochemical proxies authigenic enrichment of mo has been demonstrated to represent a valid and durable tracer of the past smtz depth fluctuations and of the intensities of the related methane seepages this study is based on two closely spaced short cores collected from the main drift of the kveithola trough a glacially carved depression located in northwestern barents sea active fluid seepage has been recently reported in this area and a gas flare was specifically observed in proximity of the sampling sites where the cores object of our study were retrieved in order to collect evidences of the possible occurrence of anaerobic oxidation of methane aom at the sediment water interface of the investigated area and infer the entity of the associated methane flux we combined the analyses of reduced sulphur species 34s total organic carbon and redox sensitive elements the negative 34s values within the extracted solid sulphur phases up to 49 1 for pyritic sulphur show that organoclastic sulphate reduction osr coupled with disproportionation of sulphur intermediates are the only active processes in the near surface sediments however moderate to strong enrichments of mo detected in the relatively organic carbon poor intervals of both cores and the lack of concurrent enrichments of co cu ni v and zn usually associated to osr dominated environment suggested that the sulphidic conditions favouring the mo enrichments were produced by aom therefore we infer that high methane flux events characterized the drift area of the kveithola occasionally moving upward the smtz and thus inducing intense aom in proximity of the sediment water interface of this part of the trough our results confirmed the validity of sedimentary mo as an indicator of the occurrence and intensity of past methane seepages

insar data as a field guide for mapping minor earthquake surface ruptures ground displacements along the paganica fault during the 6 april 2009 l aquila earthquake 1 on 6 april 2009 a moderate earthquake mw 6 3 ml 5 8 struck the abruzzo region in central italy causing more than 300 fatalities and heavy damage to l aquila and surrounding villages coseismic surface effects have been thoroughly documented by timely field surveys as well as by remote sensing analyses of satellite images the outstanding quality of geological seismological geodetic and interferometric synthetic aperture radar insar information arguably represents the best ever data set made available immediately after a moderate seismic event based on this data set we aim at testing the capability of coupled geological and insar data to map surface faulting patterns associated with moderate earthquakes coseismic ground ruptures have been mapped at a scale of 1 500 in the whole epicentral area traces of surface ruptures have been inferred from linear phase discontinuities identified in the interferogram a very good agreement between the two methods resulted in the characterization of the main surface rupture along the paganica fault the same approach applied to ground ruptures hypothesized along other capable fault segments provided more questionable results thus the combined field and insar approach appeared useful for detecting continuous surface ruptures exceeding 1 km in length and showing displacements greater than a few centimeters these are the typical faulting parameters for moderate earthquakes 6 0 mw 6 5 in central apennines for continuous ground cracks shorter than a few hundred meters and or that show displacements smaller than 1 2 cm the described approach may be less helpful most probably due to the limited resolution of the data

a multidiagnostic investigation of the mesospheric bore phenomenon 1 imaging measurements of a bright wave event in the nighttime mesosphere were made on 14 november 1999 at two sites separated by over 500 km in the southwestern united states the event was characterized by a sharp onset of a series of extensive wavefronts that propagated across the entire sky the waves were easily visible to the naked eye and the entire event was observed for at least 5 hours the event was observed using three wide angle imaging systems located at the boston university field station at mcdonald observatory mdo fort davis texas and the starfire optical range sor albuquerque new mexico the spaced imaging measurements provided a unique opportunity to estimate the physical extent and time history of the disturbance simultaneous radar neutral wind measurements in the 82 to 98 km altitude region were also made at the sor which indicated that a strong vertical wind shear of 19 5 ms 1km 1 occurred between 80 and 95 km just prior to the appearance of the disturbance simultaneous lidar temperature and density measurements made at fort collins colorado 1100 km north of mdo show the presence of a large 50 k temperature inversion layer at the time of the wave event the observations indicated that the event was most probably due to an undular mesospheric bore a relatively uncommon disturbance which has only recently been reported taylor et al 1995a evidence is also shown to suggest that a large east west tropospheric frontal system lying over the northern united states was the origin of the disturbance

geological controls on fluid flow and gas hydrate pingo development on the barents sea margin vista a basic research program in collaboration between the norwegian academy of science and letters and equinor

diverse fracture properties and their impact on performance in conventional and tight gas reservoirs saudi arabia the unayzah south haradh case study the upper permian carboniferous unayzah formation in south haradh saudi arabia includes two major mechanical and petrophysical layers that are separated by shale rich zones open tectonic fracture clusters are rare and not essential for fluid flow in the unayzah a zone which has high porosity and permeability however such fracture clusters are essential to and impact the production performance in the unayzah b c tight gas reservoir the occurrence of the tectonic fractures in the unayzah formation is linked to the rock mechanical properties which vary with porosity shale volume cement type and texture the b c unit is more fractured than the a unit but its layers vary in the degree of fracturing the variation in fracture development within the b c unit results in differences in fracture enhanced permeability based on production profiles where flow is restricted to preferentially fractured mechanical layers that lack effective vertical fluid communication with other layers we identify two tectonic fracture systems an older subordinate fully mineralized system and a younger primary mostly open system early extensional fractures including joints and faults developed parallel to the basement faults during the opening of the neotethys these are fully mineralized and have little or no function as fluid conduits the younger system includes open fracture clusters that are predominantly parallel or nearly parallel to the regional east northeast west southwest maximum horizontal stress of the zagros that has been active since the late cretaceous and is independent of local structures therefore these fractures are controlled by remote stresses instead of the basement rooted forced folds and faults in this article we demonstrate that in the unayzah b c natural fractures are essential to permeability and in some areas to porosity and thence to reservoir performance the results of this study are being implemented in well placement and completion design to optimize the intersection of open fracture clusters with positive preliminary results

the structure and formation of diapirs in the yinggehai song hong basin south china sea abstract the occurrence of shale diapirs in the yinggehai song hong ygh sh basin is well documented as is their association with big petroleum fields in order to better understand how and why the diapirs form we performed a detailed geophysical analysis using a new regional compilation of high resolution two and three dimensional seismic reflection data as well as drilling data that cover the diapirs in ygh sh basin as many as 18 diapirs were identified and are arranged in six n s striking vertical en echelon zones on seismic reflection sections gas chimney structures diapiric faults and palaeo craters are genetically linked with the process of diapirism here we use geophysical and geological observations to propose a three stage model for diapirism initiation emplacement and collapse during these three stages different diapiric structure styles are formed which we describe in detail these include buried diapirs piercing diapirs and collapsed diapirs we link the diapirism to activity on the offshore continuation of the red river fault as shown on our high resolution seismic reflection data which is also related to a high paleogeothermal gradient caused by crustal thinning we also recognize the role of loading by the very large volume of sediment eroded from the edges of the tibetan plateau and delivered by the red river to the basin

paleoseismology the application of multiple parameters in four case studies in sweden abstract many different primary and secondary effects of an earthquake can be used in order to reconstruct and determine a paleoseismic event in this case we advocate the application of multiple criteria four case studies in sweden are examined two late glacial and two late holocene events special accounts are given of bedrock fracturing away from the primary fault liquefaction with multiple phases and structureless sand layers tsunami distribution of seabed turbidites dating by varves methane venting tectonics and magnetic grain rotation the multitude of observational data related to all four cases are combined into simple tables where the environmental and spatial effects can be explicitly assessed in terms of documentation intensity and magnitude

paleoearthquake deformations recorded by magnetic variables abstract faults and related deformational structures give evidence of earthquakes in the past the ground shaking at high magnitude seismic events usually generates liquefaction the higher seismic magnitude the larger area of liquefaction we can now demonstrate that it is possible to discriminate between plastic and liquefied deformations with magnetic methods besides it is possible to record internal crypto deformations not visibly observed this offers new means of recording past earthquakes fine particles carrying the magnetic remanence are shown to move rotate and re align with respect to the prevailing geomagnetic field direction or in response to the applied shaking forces we call this seismomagnetization this implies that paleoseismics may generate excursion like paleomagnetic signals despite the absence of visible deformation structures

geological and oceanographic controls on seabed fluid escape structures in the northern zhongjiannan basin south china sea abstract mega pockmarks which can reach a few kilometers in width and a few hundred meters in depth and associated fluid escape features in the northern zhongjiannan basin south china sea have received much attention in the recent years due to their large variety of morphologies and sizes in this work an integrated interpretation of detailed multibeam bathymetry conventional multi channel seismic reflection and seismic oceanography sections covering the northern zhongjiannan basin south china sea are used to image the seafloor morphology the subsurface geology and the water column in order to better understand the geological and oceanographic controls on the formation and evolution of the widespread fluid escape features in this region regional uplift and volcanism took place in this area near the palaeogene neogene boundary and during the neogene quaternary post rift thermal subsidence period differential subsidence and diapirism deformed the overlying kilometer scale successions mainly after the miocene focused flow of fluids originated at depth occurred along gas pipes polygonal faults tapered reflectors and faults into the shallow sediments resulting in intense fluid blowouts and complex fluid escape structures on the seafloor our results show that elongated pockmarks pockmark gullies and gullies in the northern slope are generally controlled by underlying buried channels and gullies however pockmark gullies and gullies in the southern slope are controlled by gravity sliding slumping along with crescent pockmarks developing parallel to water depth contours to varying degrees intense fluid escape activities associated with mud diapirism and gas escape in the study area resulted in mud extrusion and the formation of mud volcanoes complex seabed morphologies and irregular pockmarks mega pockmarks collapse structures and blind valleys have formed at the apexes of tectonic uplifts related to volcanism and above basement highs which suggests that these processes played a role in creating pathways for fluid escape bottom currents associated with the south china sea western boundary current imaged here for the first time with the seismic oceanographic method mainly flow to the south and erode the seafloor making pockmark walls and slopes of gullies and channels in the north steeper than those in the south some fluid escape structures such as the mega pockmarks and pockmark gullies are buried by sediment transported by the bottom currents turbidity currents flowing downslope along the long pockmark gullies also erode the seafloor and make the nw slopes of the mud volcanoes less steep than those in the se eddies imaged by the seismic sections may also play a role in transporting sediment to the deep sea in this area some of the reported fluid escape structures are still active as indicated by the fluid pathways that reach the seafloor and plumes in the water column imaged by the seismic sections

concurrent oh imager and sodium temperature wind lidar observation of a mesopause region undular bore event over fort collins platteville colorado 1 we reported the observation of a mesospheric front with the properties of an undular bore by an oh imager over the fort collins platteville area on 6 7 october 2002 unlike the earlier bore observations a na lidar capable of measuring mesopause region temperature zonal and meridional winds was in operation concurrently the lidar data confirm for the first time the existence of a collocated temperature inversion layer to serve as the ducting region for bore propagation as required by the simple theory proposed by dewan and picard 6 years ago in addition the lidar data in principle provide sufficient information for the determination of all parameters of the bore as suggested by the simple theory the parameters so determined are compared to two bores previously studied like the earlier cases the horizontal wavelength estimated from the theory is in good agreement with the observation the lifetime of this undular bore 120 min was considerably shorter than the other two continued lidar observation after the bore event reveals that the ducting region may be controlled by a long period wave most likely related to a semidiurnal tide and that atmospheric dynamic instability occurs simultaneously with the destruction of the wave train associated with the bore it is possible that this constitutes for the first time the observation of the transition from an undular to a turbulent or foaming internal bore predicted by the theory

an unusual mesospheric bore event observed at high latitudes over antarctica 1 all sky ccd observations of short period mesospheric gravity waves have been made from halley station antarctica 76 s 27 w on 27 may 2001 an unusual wave event exhibiting several features characteristic of a bore was observed in the oh na and o2 nightglow emissions mesospheric bores are rare wave events that have previously been observed at mid and low latitudes this event was particular interesting as 1 it initially appeared as a single high contrast linear front accompanied by a sharp enhancement in intensity in all three emissions 2 a number of trailing wave crests were observed to form with a measured growth rate of 6 6 waves hr and 3 the wave pattern exhibited unusual dynamics with significant variability in the observed phase speed and a reduction in the horizontal wavelength by 50 over a 1 hr period the location of halley and the observed propagation suggests a ducted wave consistent with current bore models

all sky imaging observations of mesospheric fronts in oi 557 7 nm and broadband oh airglow emissions analysis of frontal structure atmospheric background conditions and potential sourcing mechanisms 1 all sky imaging observations of distinct large horizontal transient mesospheric structures with a spatial scale of 100 km detected in images of broadband oh and oi 557 7 nm airglow emissions were made over clemson south carolina on the night of 14 15 october 2001 we designate these structures as mesospheric fronts and present a detailed summary of this night series of observations paying particular attention to the details of the different frontal structures the wave like activity seen throughout the night and the background atmospheric conditions these data are compared to other observations of similar mesospheric fronts found in the literature and we seek to understand them in relation to mesospheric bores ducted gravity waves mesospheric wall events and nonlinear gravity wave interactions we find that the observed frontal characteristics and the atmospheric background structure exhibit a close resemblance to previous observations of mesospheric bores owing to this similarity and supported by gravity wave ray tracing experiments we propose a sequence of events that generated the mesospheric fronts observed in the airglow emission furthermore we note this similarity in atmospheric structure suggests a potential means of predicting the occurrence of such mesospheric phenomena

a tsunami about 1000 years ago in puget sound washington water surged from puget sound sometime between 1000 and 1100 years ago overrunning tidal marshes and mantling them with centimeters of sand one overrun site is 10 kilometers northwest of downtown seattle another is on whidbey island some 30 kilometers farther north neither site has been widely mantled with sand at any other time in the past 2000 years deposition of the sand coincided to the year or less with abrupt probably tectonic subsidence at the seattle site and with landsliding into nearby lake washington these findings show that a tsunami was generated in puget sound and they tend to confirm that a large shallow earthquake occurred in the seattle area about 1000 years ago

intraplate seismicity in northern central europe is induced by the last glaciation there is growing evidence that climate induced melting of large ice sheets has been able to trigger fault reactivation and earthquakes around the migrating ice limit even today the stress due to glacial isostatic adjustment can continue to induce seismicity within the once glaciated region northern central europe lies outside the former ice margin and is regarded as a low seismicity area however several historic earthquakes with intensities of up to vii occurred in this region during the past 1200 years here we show with numerical simulations that the seismicity can potentially be explained by the decay of the scandinavian ice sheet after the weichselian glaciation combination of historic earthquake epicenters with fault maps relates historic seismicity to major reverse faults of late cretaceous age mesozoic normal faults remained inactive in historic times we suggest that many faults in northern central europe are active during postglacial times this is a novelty that sheds new light on the distribution of postglacial faulting and seismicity in addition we present the first consistent model that can explain both the occurrence of deglaciation seismicity and the historic earthquakes in northern central europe

mesospheric bores the 1993 airborne lidar and observations of hawaiian airglow airborne noctilucent cloud campaigns a spectacular gravity wave event was observed from haleakala on a four color allsky imager as well as in oh meinel band intensity and temperature on october 10 1993 during the airborne lidar and observations of hawaiian airglow aloha 93 campaign taylor et al 1995 the event consisted of a sharp frontal passage in airglow brightness propagating at 76 m s across the field of view and accompanied by small scale waves behind the front the purpose of this paper is to propose an explanation for the frontal passage in terms of an internal mesospheric undular bore although there have been a number of observations of internal bores in the troposphere and in the ocean we believe this is the first reported observation of such a bore in the mesosphere a simple two layer model constructed by analogy with the theory of bores in river channels explains the observations quantitatively several predictions are advanced which could serve to test the model

paleoearthquakes in the puget sound region recorded in sediments from lake washington u s a holocene sediments in lake washington contain a series of turbidites that were episodically deposited throughout the lake the magnetic signatures of these terrigenous layers are temporally and areally correlatable large earthquakes appear to have triggered slumping on the steep basin walls and landslides in the drainage area resulting in turbidite deposition one prominent turbidite appears to have been deposited about 1100 years ago as the result of a large earthquake downcore susceptibility patterns suggest that near simultaneous slumping occurred in at least three separate locations two of which now contain submerged forests several other large earthquakes may have occurred in the last 3000 years

tidal perturbations and variability in the mesopause region over fort collins co 41n 105w continuous multi day temperature and wind lidar observations 1 an unusually long data set was acquired at the sodium lidar facility at colorado state university 41n 105w between sep 18 and oct 01 2003 including a 9 day continuous observation this time is long enough to average out the perturbations of gravity waves and short period planetary waves as such it can be used to define tidal period perturbations in temperature and horizontal wind assuming the sodium mixing ratio is a constant of motion the observed tidal period oscillation in sodium density follows that of vertical wind thus the data set defines tidal period perturbations of temperature and wind vector the observed amplitudes and phases were compared to global scale wave model predictions both gswm00 and gswm02 we found excellent agreement in diurnal phases and reasonable agreement in semidiurnal phases however gswm02 overestimates diurnal amplitudes and both model versions underestimate observed semidiurnal amplitudes since the data period is long enough for the study of planetary waves and of tidal variability we perform spectral analysis of the data revealing a strong quasi 3 day wave in meridional wind a 14 hour perturbation in zonal wind and both 14 hour and 10 hour periods in meridional wind likely the result of nonlinear interactions the observed semidiurnal amplitudes are much larger than the corresponding diurnal amplitudes above 85 km and over a few days the diurnal and semidiurnal amplitudes vary by factors of 2 3 causes for the observed tidal variability in terms of planetary wave modulation and tide gravity wave interaction are explored qualitatively

neotectonic faulting in northern norway the stuoragurra and nordmannvikdalen postglacial faults abstract a systematic compilation and characterisation of many reports of neotectonic crustal deformation in norway both on local and regional scales has identified two neotectonic faults in northern norway the stuoragurra fault is a large reverse fault in finnmark county the nordmannvikdalen fault is a much smaller normal fault in troms county the stuoragurra postglacial fault can be followed in several discontinuous sections for 80 km in a ne sw direction the fault has up to 10 m of displacement during 1998 two trenches were made across the fault the hanging wall was seen to be thrust upwards over the footwall with 7 m vertical displacement evident from displaced glacial contacts the fault did not penetrate the overlying glacial materials but rather folded them forming a blind thrust large liquefaction and other deformation structures were found in the glaciofluvial sediments in both trenches veins of angular and subangular pebbles from the local bedrock penetrate more than 10 m laterally from the thrust plane and into the sediments in the footwall it is thought that these veins were injected during the fault activity the major deformation of the sediments has a decollement plane that continues laterally in the e b horizon contact of the modern soil on top of the footwall this may indicate that an initial pedogenesis had taken place before the fault activity occurred however no macro plant fossils to support this were found in the possible buried soil deformational structures seen in the trench can be explained as a result of one major fault event the nordmannvikdalen postglacial fault is a nw se trending normal fault dipping to the ne the fault offsets till on the nw slope of nordmannvikdalen the escarpment varies in height from 0 5 to 1 5 m with a trench often present between the hanging wall and the footwall the fault locally splits into two subparallel branches however this is probably only in the glacial overburden ground penetrating radar gpr profiles show two prominent bedrock reflectors dipping approximately 40 to the ne an upward extrapolation of the northernmost reflector through the overburden coincides with the position of the surface scarp the bedrock is well exposed along a streamed parallel to the gpr profiles bedding and foliation cannot be responsible for the reflectors visible in the gpr profiles gravitational forces have been ruled out as the origin of the fault although both faults probably formed shortly after weichselian deglaciation there is evidence that isostatic uplift was not the only force acting quaternary tilting of fennoscandia due to ridge push or mantle convection may also play a role in neotectonic activity in norway

giant irregular pockmark craters in the palaeogene of the outer moray firth basin uk north sea a cluster of irregular pockmark craters of palaeogene age in block 15 18 in the outer moray firth uk north sea have been mapped on 3d seismic data with well control the craters range from 0 5 to 4 km in diameter between 50 and 200 m in depth and have been buried by tertiary subsidence and sedimentation to present day depths of between 1000 and 1400 m sub sea they are circular to elliptical in plan view and are located in a delta front and upper pro deltaic slope position on the dornoch delta the structures are confined to the top of the lower eocene balder formation and regional mapping across the moray firth basin shows they are restricted to an area of ca 15 15 km2 well data show that the craters are sand filled and have excavated an argillaceous and tuffaceous unit the crater filling sands are sealed by overlying mudstone units planar wing like features emanate from the margins of the craters well control indicates that these seismically identified wings consist of sandstone suggesting that the craters have been modified by an episode of sand remobilisation and injection the proposed mechanism for the formation of these structures is large scale fluid eruption probably shallow gas at the early eocene seafloor these craters are significantly larger in size than those typically observed on contemporary sea floors we argue that the gas is more likely to have been sourced from deeper jurassic or carboniferous sediments within the witch ground graben than from shallow biogenic origins these structures rank in scale alongside the largest known pockmarks and demonstrate that natural fluid and hydrocarbon seeps have a long ancestry in this basin

repeated fluid expulsion through sub seabed chimneys offshore norway in response to glacial cycles abstract focused fluid flow through sub seabed sediments is a common phenomenon on continental margins worldwide however the governing controls and timing of this fluid release have been difficult to understand in particular for fluid flow features buried beneath sub surface sediments a link between fluid flow activity ensuing pockmark formation and the last glacial maximum has been hypothesized on the formerly glaciated norwegian margin new high resolution p cable 3d seismic data from the nyegga area on the mid norwegian margin reveal at least two more periods of fluid expulsion from sub seabed sediments the 3d seismic data show depositional patterns within chimney features expressed as truncations of seismic horizons against the flanks of the chimneys the truncations are interpreted by analogy with present day observations as evidence for buried carbonate mounds and or sediment wash out during formation of pockmarks in the past the truncations are hence an indicator and a chronological marker for fluid expulsion in the past the classification of chimneys results in three major groups 1 chimneys that have been formed and consecutively reactivated one or two times during the last 200 kyr and that have a fluid flow expression at the present seafloor 2 chimneys that are approx 125 160 ka bp old without any associated fluid flow expression at the present day seafloor 3 chimneys with no stratigraphical evidence for reactivation formed after the last glacial maximum 18 25 ka bp the observations suggest that each activity period was likely related to the last stages of maximum glaciations in the region the emplacement of thick sequences of glacigenic debris flow deposits during these maximum stages most likely caused rapid increase in overpressure and subsequently the formation of focused fluid flow features piercing through sediments of the naust formation at nyegga

fluid venting in the eastern aleutian subduction zone fluid venting has been observed along 800 km of the alaska convergent margin the fluid venting sites are located near the deformation front are controlled by subsurface structures and exhibit the characteristics of cold seeps seen in other convergent margins the more important characteristics include 1 methane plumes in the lower water column with maxima above the seafloor which are traceable to the initial deformation ridges 2 prolific colonies of vent biota aligned and distributed in patches controlled by fault scarps over steepened folds or outcrops of bedding planes 3 calcium carbonate and barite precipitates at the surface and subsurface of vents and 4 carbon isotope evidence from tissue and skeletal hard parts of biota as well as from carbonate precipitates that vents expel either methane or sulfide dominated fluids a biogeochemical approach toward estimating fluid flow rates from individual vents based on oxygen flux measurements and vent fluid analysis indicates a mean value of 5 5 0 7 l m 2 d 1 for tectonics induced water flow wallmann et al 1997b a geophysical estimate of dewatering from the same area von huene et al 1997 based on sediment porosity reduction shows a fluid loss of 0 02 l m 2 d 1 for a 5 5 km wide converged segment near the deformation front our video guided surveys have documented vent biota across a minimum of 0 1 of the area of the convergent segment off kodiak island hence an average rate of 0 006 l m 2 d 1 is estimated from the biogeochemical approach the two estimates for tectonics induced water flow from the accretionary prism are in surprisingly good agreement

lake sediments as natural seismographs earthquake related deformations seismites in central canadian lakes abstract central canada experiences numerous intraplate earthquakes but their recurrence and source areas remain obscure due to shortness of the instrumental and historic records unconsolidated fine grained sediments in lake basins are natural seismographs with the potential to record ancient earthquakes during the last 10 000 years since the retreat of the laurentide ice sheet many lake basins are cut into bedrock and are structurally controlled by the same precambrian basement structures shear zones terrane boundaries and other lineaments implicated as the source of ongoing mid plate earthquake activity a regional seismic sub bottom profiling of lakes gull muskoka joseph rousseau ontario wanapitei fairbanks vermilion nipissing georgian bay mazinaw simcoe timiskaming kipawa parry sound and lake of bays encompassing a total of more than 2000 kilometres of high resolution track line data supplemented by multibeam and sidescan sonar survey records show a consistent sub bottom stratigraphy of relatively thick lowermost lateglacial facies composed of interbedded semi transparent mass flow facies debrites slumps and rhythmically laminated silty clays mass flows together with cratered kettled lake floors and associated deformations reflect a dynamic ice contact glaciolacustrine environment exceptionally thick mass flow successions in lake timiskaming along the floor of the timiskaming graben within the seismically active western quebec seismic zone wqsz point to a higher frequency of earthquakes and slope failure during deglaciation and rapid glacio isostatic rebound though faulting continues into the postglacial lateglacial faulting diapiric deformation and slumping of coeval lateglacial sediments is observed in parry sound lake muskoka and lake joseph which are all located above prominent precambrian terrane boundaries lateglacial sediments are sharply overlain by relatively thin rhythmically laminated and often semi transparent postglacial silty clay laminations postglacial neotectonic activity is recorded by co seismic water escape structures faults slumps and debris flows in lake simcoe above a terrane boundary and especially within lakes timiskaming and kipawa recording ongoing deformation within the wqsz high resolution seismo stratigraphic data presented here support the model that ongoing mid plate earthquake activity is a consequence of brittle deformation of the upper crust of the north american plate such activity appears to have been greatest during deglaciation but continues today

methane cold seeps as biological oases in the high arctic deep sea cold seeps can support unique faunal communities via chemosynthetic interactions fueled by seabed emissions of hydrocarbons additionally cold seeps can enhance habitat complexity at the deep seafloor through the accretion of methane derived authigenic carbonates mdac we examined infaunal and megafaunal community structure at high arctic cold seeps through analyses of benthic samples and seafloor photographs from pockmarks exhibiting highly elevated methane concentrations in sediments and the water column at vestnesa ridge vr svalbard 79 n infaunal biomass and abundance were five times higher species richness was 2 5 times higher and diversity was 1 5 times higher at methane rich vestnesa compared to a nearby control region seabed photos reveal different faunal associations inside at the edge and outside vestnesa pockmarks brittle stars were the most common megafauna occurring on the soft bottom plains outside pockmarks microbial mats chemosymbiotic siboglinid worms and carbonate outcrops were prominent features inside the pockmarks and high trophic level predators aggregated around these features our faunal data visual observations and measurements of sediment characteristics indicate that methane is a key environmental driver of the biological system at vr we suggest that chemoautotrophic production enhances infaunal diversity abundance and biomass at the seep while mdac create a heterogeneous deep sea habitat leading to aggregation of heterotrophic conventional megafauna through this combination of rich infaunal and megafaunal associations the cold seeps of vr are benthic oases compared to the surrounding high arctic deep sea

methane and nitrous oxide distributions across the north american arctic ocean during summer 2015 we collected arctic ocean water column samples for methane ch4 and nitrous oxide n2o analysis on three separate cruises in the summer and fall of 2015 covering a 10 000 km transect from the bering sea to baffin bay this provided a three dimensional view of ch4 and n2o distributions across contrasting hydrographic environments from the oligotrophic waters of the deep canada basin and baffin bay to the productive shelves of the bering and chukchi seas percent saturation relative to atmospheric equilibrium ranged from 30 800 for ch4 and 75 145 for n2o with the highest concentrations of both gases occurring in the northern chukchi sea nitrogen cycling in the shelf sediments of the bering and chukchi seas likely constituted the major source of n2o to the water column and the resulting high n2o concentrations were transported across the arctic ocean in eastward flowing water masses methane concentrations were more spatially heterogeneous reflecting a variety of localized inputs including likely sources from sedimentary methanogenesis and sea ice processes unlike n2o ch4 was rapidly consumed through microbial oxidation in the water column as shown by the 13c enrichment of ch4 with decreasing concentrations for both ch4 and n2o sea air fluxes were close to neutral indicating that our sampling region was neither a major source nor sink of these gases our results provide insight into the factors controlling the distribution of ch4 and n2o in the north american arctic ocean and an important baseline data set against which future changes can be assessed

methane hydrate in crystalline bedrock and explosive methane venting tectonics abstract methane hydrate clathrate ice does not only form in shelf environments but may also accumulate in voids and fractures in continental crystalline rocks this has turned out to be the case in formerly glaciated areas where the waxing and waning of thick ice caps following the quaternary alterations between ice ages and interglacial implied very large changes both in temperature and pressure in the bedrock below the swedish situation is highlighted seepage of methane gas from the crystalline bedrock is recorded methane accumulated as ice in fractures and voids in the rock in postglacial time such accumulations vented explosively generating methane venting tectonics this occurred both spontaneously as a function of changes in temperature and load pressure and partly as violent deformational events as a function of earthquake events whilst most venting events refer to the time of deglaciation three major deformational events occurred shortly after the uplift induced land emergence in late holocene time a possible analogous event in association with the 1988 saguenay earthquake in canada is revisited

intense earthquakes and seismotectonics as a function of glacial isostasy abstract old shields and plate interiors have often been assumed to exhibit a high crustal stability during the last decade or two we have learnt more and more about the fragility not to say untenability of this concept however high magnitude earthquakes and large scale fault movements have been recorded where they were not supposed to be able to occur within formerly glaciated areas like northern europe scotland and northern north america a rapidly increasing number of field observations indicates that the glacial isostatic readjustment process was linked to intense seismotectonic activity we will here investigate the fennoscandian situation and propose a novel causation model for the high deglaciation seismicity in comparison with the present day situation

locating distributed faulting contributions from insar imaging to probabilistic fault displacement hazard analysis pfdha abstract prediction of location and amount of slip for distributed faulting associated to strong earthquakes is a recently explored issue with major implications in terms of hazard assessment currently the best practice involves the applications of probabilistic fault displacement hazard analysis pfdha whose results fit sufficiently well real data in the near range of the primary fault but show considerable inaccuracies in the far range we believe that this inaccuracy descends from the biased earthquake databases used for regression analysis whose data relative to old earthquakes were largely collected only by field surveys focused close to the primary fault i e near range remotely sensed data i e interferometric radar imaging insar offer the opportunity to precisely measure the surface deformation induced by strong earthquakes and thus to explore its possible relation with distributed faulting we analyze the l aquila earthquake case study 29th april 2009 mw 6 3 and explore the correlation between location and slip on distributed faulting and insar derived deformation field we find a significant correlation between occurrence of distributed faulting and profile curvature of the dislocation field in spite of the distance from the primary fault moreover distributed faults tend to occur within the area deformed by the earthquake as imaged by insar data and whose extent is directly proportional to the earthquake magnitude mw according to a dataset of 30 recent earthquakes we then propose that these observations have to be incorporated into the present pfdha practice as limit boundaries to possible scenarios of probabilistic analysis and that an integrated use of field based and remotely data collection have to be implemented following strong earthquakes

prehistoric rock avalanches in the olympic mountains washington rock avalanches blocked streams in the olympic mountains southwest of puget sound during the past few thousand years limiting radiocarbon ages indicated that three or four of six avalanches occurred from 1000 to 1300 years ago or shortly thereafter most of the dates were from the outer preserved rings of trees drowned behind avalanche dams these three or four avalanches may be coeval not only with one another but also with abrupt tectonic deformation in western washington no rock avalanches in the olympic mountains are known to have resulted from storms or earthquakes during the past century the avalanches strengthen the case that a large prehistoric earthquake occurred in the puget sound region

abrupt uplift within the past 1700 years at southern puget sound washington shorelines rose as much as 7 meters along southern puget sound and hood canal between 500 and 1700 years ago evidence for this uplift consists of elevated wave cut shore platforms near seattle and emerged peat covered tidal flats as much as 60 kilometers to the southwest the uplift was too rapid for waves to leave intermediate shorelines on even the best preserved platform the tidal flats also emerged abruptly they changed into freshwater swamps and meadows without first becoming tidal marshes where uplift was greatest it adjoined an inferred fault that crosses puget sound at seattle and it probably accompanied reverse slip on that fault 1000 to 1100 years ago the uplift and probable fault slip show that the crust of the north america plate contains potential sources of damaging earthquakes in the puget sound region

liquefaction and varve deformation as evidence of paleoseismic events and tsunamis the autumn 10 430 bp case in sweden coastal seismic events generate instantaneous changes in relative sea level i e land level vs sea level tsunamis may cause disastrous damage to coasts and coastal habitation liquefaction and deformations of annually varved sediments provide information on paleoseismic events the evidence for a major earthquake and associated tsunami waves in sweden are explored thanks to the varve chronology liquefaction structures and varve deformations caused by this event can be dated at the autumn 10 430 varve years bp the magnitude is estimated at 8 or more on the richter scale the tsunami washed the previously blocked outlet of the baltic free of icebergs and pack ice so that marine water could suddenly invade the entire baltic forming the yoldia sea

a new technology for the characterization of microfractured reservoirs test case unayzah reservoir wudayhi field saudi arabia this article presents a test case of a new technology using artificially enhanced anisotropy of magnetic susceptibility referred to here as eams for the characterization of microfractured reservoirs these are reservoirs in which microfractures are essential to porosity and or permeability a conventional geological characterization is costly time consuming and difficult to quantify in terms of assessing fracture impact on porosity and permeability therefore an efficient and effective method is required to characterize these microfractures and to determine their contribution to porosity and permeability the eams technology which we developed and tested allows rapid analysis that bridges reservoir geology and engineering using petrography the margin of error to detect microfractures that impact porosity and or permeability is 43 however it requires three times the sampling rate of the new eams technology the lower part of the unayzah reservoir unayzah b c in the wudayhi field saudi arabia where fractures were studied and microfractures are known to impact reservoir performance is used to develop and verify the eams technology the results show that eams derived microfracture fabric strikes east northeast west southwest consistent with that obtained by geological means the effective porosity profile obtained from eams tests is similar to that of the conventionally acquired porosity open microfractures in tested samples increase mean values of reservoir effective porosity by 36 50 in unayzah b c the occurrence of connected microfractures is estimated to cause an increase in average permeability of 75 in unayzah b c this is in agreement with the fact that wells in microfractured unayzah b c have 4 5 14 times the productivity of wells as nonfractured sections of this reservoir a maximum permeability trend of northeast southwest permeability anisotropy is detected the implementation of the eams technology in other fields with microfractured reservoirs will directly impact operational and simulation effort

deglacial paleoseismicity in sweden the 9663 bp iggesund event abstract the iggeesund event is an example of the high seismicity which occurred in fennoscandia during deglaciation as a function of the high rate of glacial isostatic uplift this event is dated to varve 9663 bp the iggesund hudiksvall area is represented by intensive postglacial fracturing of the bedrock recorded over an area of at least 50 50 km the most remarkable locality is the boda cave system a hill fractured into a field of large detached blocks with a cave system of more than 2 km length in the varve year 9663 bp an extensive turbidite was spread over an area of 210 80 km liquefaction structures are recorded over an area of 80 30 km and can be assigned to the same varve year structures and deposits of a tsunami are recorded over 80 50 km

varves in lake sediments a review abstract downcore counting of laminations in varved sediments offers a direct and incremental dating technique for high resolution climatic and environmental archives with at least annual and sometimes even seasonal resolution the pioneering definition of varves by de geer 1912 had been restricted to rhythmically deposited proglacial clays one century later the meaning of varve has been expanded to include all annually deposited laminae in terrestrial and marine settings under favourable basin configurations and environmental conditions limnic varves are formed due to seasonality of depositional processes from the lake s water column and or transport from the catchment area subsequent to deposition of topmost laminae the physical preservation of the accumulating varved sequence requires the sustained absence of sediment mixing for example via wave action or macrobenthic bioturbation individual sub laminae in varved lake sediments typically express contrasting colours always differ in terms of their organic chemical and or mineralogical compositions and often also differ with regard to grain size various predominating climatic and depositional conditions may result in clastic biogenic or endogenic incl evaporitic varved sediments and their mixtures to reliably establish a varve chronology the annual character of laminations needs to be determined and verified in a multidisciplinary fashion sources and influences of possible errors in varve chronologies are best determined and constrained by repeated varve counts and by including radioisotopes and correlation with historically documented events a well established varve chronology greatly enhances the scientific value of laminated limnic archives by securely anchoring the wealth of multi proxy palaeoenvironmental information in the form of time series for multidisciplinary investigations applications of varved records are discussed with special reference to advances since the 1980s these span fields like calibrating radiometric dating methods reconstructing past changes of the earth s magnetic field or detecting fluctuations in solar forcing once a varve chronology is established it can be applied to precisely date events like volcanic ash layers earthquakes or human impact as well as short and long term climate temperature precipitation wind hydroclimatic conditions or flooding and environmental changes eutrophication pollution due to their exceptional high temporal resolution and in combination with their robust and accurate internal time scale in calendar years annually laminated sediments can be regarded as one of the most precious environmental archives on the continents these records are necessary to extend temporally limited instrumental records back in time as such they have societal relevance with regard to risk assessments related to natural hazards arising from e g flooding or volcanic eruptions

late pleistocene holocene strain release by normal faulting along the main boundary thrust at logar in the northwestern kumaon sub himalaya india abstract a prominent nw se trending linear fault the logar fault which vertically displaced the quaternary alluvial fan logar fan was delineated previously at logar village in northwestern kumaon sub himalaya based on the surface expression of the discontinuous scarp and its expression on the satellite data the fault has been further extended on either sides to a total length of 9 5 km which in part lies in the older himalayan mega thrust zone of weakness the main boundary thrust mbt the distinctive south side up scarp maintains linearity throughout its length cut across the logar mega fan and thus form as a normal fault within the compressive regime logar normal fault has truncated and uplifted a remnant of the logar fan by 15 m since its deposition 20ka based on the osl dates of the fan sediments a trench excavation survey across the logar fault scarp for paleoseismic investigation was carried out at bairasari village variable height of the fault scarp along its strike suggests multiple faulting events that occurred along the same fault yielded a cumulative vertical height from 15 38 m the osl ages from the footwall show multilevel surfaces deposited between 20 and 8 7ka however in the hanging wall the base of the vertically stacked deposits show an age 20ka the osl age in the bottom unit of the trench in the hanging wall suggest commencement of post faulting deposition of the units after 20ka in the footwall younger ages of 11 and 8 7ka probably represent the youngest dated activity of the fault the ages obtained across the fault shows that the 20ka deposits are displaced the nature of faulting of logar fan suggest its genetic link with seismic activity in this region the geomorphic expression of the logar fault along the himalayan mega thrust suggest subsequent tectonic activity along the mbt the active logar normal fault identified north of the himalayan frontal thrust hft indicates that elastic strain released within the hanging wall is not limited to the front but it is dispersed above the decollement over a broad area

mesospheric bore evolution and instability dynamics observed in pmc turbo imaging and rayleigh lidar profiling over northeastern canada on 13 july 2018 two successive mesospheric bores were observed over northeastern canada on 13 july 2018 in high resolution imaging and rayleigh lidar profiling of polar mesospheric clouds pmcs performed aboard the pmc turbo long duration balloon experiment four wide field of view cameras spanning an area of 75 150 km at pmc altitudes captured the two evolutions occurring over 2 hr and resolved bore and associated instability features as small as 100 m the rayleigh lidar provided pmc backscatter profiling that revealed vertical displacements evolving brightness distributions evidence of instability character and depths and insights into bore formation ducting and dissipation both bores exhibited variable structure along their phases suggesting variable gravity wave gw source and bore propagation conditions both bores also exhibited small scale instability dynamics at their leading and trailing edges those at the leading edges comprised apparent kelvin helmholtz instabilities that were advected downward and rearward beneath the bore descending phases extending into an apparently intensified shear layer instabilities at the trailing edges exhibited alignments approximately orthogonal to the bore phases that resembled those seen to accompany gw breaking or intrusions arising in high resolution modeling of gw instability dynamics collectively pmc turbo bore imaging and lidar profiling enabled enhanced definition of bore dynamics relative to what has been possible by previous ground based observations and a potential to guide new three dimensional modeling of bore dynamics the observed bore evolutions suggest potentially important roles for bores in the deposition of energy and momentum transported into the mesosphere and to higher altitudes by high frequency gws achieving large amplitudes

characterization of a double mesospheric bore over europe observations of a pair of mesospheric bore disturbances that propagated through the nighttime mesosphere over europe are presented the observations were made at the padua observatory asiago 45 9 n 11 5 e by the boston university all sky imager on 11 march 2013 the bores appeared over the north west horizon approximately 30 minutes apart and propagated towards the south east using additional satellite and radar data we present evidence indicating the bores originated in the mesosphere from a single larger scale mesospheric disturbance propagating through the mesopause region furthermore the large scale mesospheric disturbance appeared to be associated with an intense weather disturbance that moved southeastwards over the united kingdom and western europe during 10 and 11 march

submarine holocene sedimentary disturbances in the olkiluoto area of the gulf of bothnia baltic sea a case of postglacial palaeoseismicity abstract high resolution echo soundings were used to study the fault activity in the olkiluoto area of the gulf of bothnia southwestern finland echo sounding profiles in holocene submarine sediments show normal faults structures related to gas or groundwater seepage submarine slides and slumps and debris flow type structures the faults and other disturbance structures occur along two bedrock lineaments all faults occur at the same stratigraphical level whose age is estimated at 10 700 calendar years bp 9500 radiocarbon years bp it is suggested that their movement has been triggered by palaeoseismic event s when the late weichselian ice sheet was retreating from the site and bedrock stresses were released through lineaments and fracture zones these are the first observations of postglacial fault movements in quaternary sediments from southern finland but the timing of these movements is contemporaneous with the incidence of postglacial bedrock faulting 9000 10 000 radiocarbon years bp in northern fennoscandia the origin of the gas groundwater seepages remains unclear their reflections in the echo sounding profiles imply that part of the gas is derived from the organic bearing litorina and recent gyttja clays however at least some part of the gas is derived from the bedrock deep gas

atmospheric methane from organic carbon mobilization in sedimentary basins the sleeping giant abstract the mass of organic carbon in sedimentary basins amounts to a staggering 1016 t dwarfing the mass contained in coal oil gas and all living systems by ten thousand fold the evolution of this giant mass during subsidence and uplift via chemical physical and biological processes not only controls fossil energy resource occurrence worldwide but also has the capacity for driving global climate only a tiny change in the degree of leakage particularly if focused through the hydrate cycle can result in globally significant greenhouse gas emissions to date neither climate models nor atmospheric co2 budget estimates have quantitatively included methane from thermal or microbial cracking of sedimentary organic matter deep in sedimentary basins recent estimates of average low latitude eocene surface temperatures beyond 30 c require extreme levels of atmospheric co2 methane degassing from sedimentary basins may be a mechanism to explain increases of atmospheric co2 to values as much as 20 times higher than pre industrial values increased natural gas emission could have been set in motion either by global tectonic processes such as pulses of activity in the global alpine fold belt leading to increased basin subsidence and maturation rates in the prolific jurassic and cretaceous organic rich sediments or by increased magmatic activity such as observed in the northern atlantic around the paleocene eocene boundary increased natural gas emission would have led to global warming that was accentuated by long lasting positive feedback effects through temperature transfer from the surface into sedimentary basins massive gas hydrate dissociation may have been an additional positive feedback factor during hyperthermals superimposed on long term warming such as the paleocene eocene thermal maximum petm as geologic sources may have contributed over one third of global atmospheric methane in pre industrial time variability in methane flux from sedimentary basins may have driven global climate not only at time scales of millions of years but also over geologically short periods of time earth system models linking atmospheric ocean and earth surface processes at different timescales with the sedimentary organic carbon cycle are the tools that need to be developed in order to investigate the role of methane from sedimentary basins in earth s climate

new insights on speleoseismology the geothermal gradient and heat flow values in caves for the study of active faults abstract normally in paleoseismology the study of the tectonic slip rate is performed in trenches on the fault scarp or by the estimation of fault movements from the geomorphic features in this work we have carried out a paleoseismic analysis of the benis fault located in southeast spain combined with a geothermal analysis inside a deep cave related to the fault 350 m thus we have estimated the last earthquake magnitude and time of occurrence from evidence of ceiling collapse and displaced carbonate blocks inside a cave which is developed across the fault the magnitude was obtained from the application of the empirical relationship of the fault parameters and coseismic vertical displacement yielding a value ranging between m 5 9 and m 6 5 moreover we dated this paleoearthquake by the paleontological record of a lynx pardinus spelaea with an age of 65 18 ka bp additionally we have measured the thermal profile of the benis cave 350 m of depth from single rock point temperature measurements during 2 years the temperature profile shows three different parts inside the cave the shallow heterogeneous thermal zone till 50 m depth the homogeneous thermal zone 150 m till with constant temperature and the hetero thermal deep zone deeper than 150 m and till the deepest zone 350 m furthermore we have estimated the vertical geothermal gradient 1 85 c 100 m for the deepest zone 150 290 m the temperature increases with depth showing a reverse thermal profile in comparison with normal gradients in deep caves finally we have calculated the heat flux of 0 46 mwm 2

neotectonics and paleoseismicity within the stockholm intracratonal region in sweden abstract a number of sites with fresh faults and fractures have been mapped in detail their postglacial and sometimes late glacial age is confirmed they form simple and similar patterns consistent with stress release due to a combination of acting forces they are associated with the peak rate of glacial isostasy and increased strain rates by two orders of magnitude they often cut straight across bedrock hills between so called weak zones the fault throws correspond to approximately magnitude 7 on the richter scale sedimentary and morphological data confirm the seismo tectonic origin newly discovered large scale network of crossing faults is found to have changed the course of the stockholm esker in a way that reveals at least two major seismo tectonic events this is consistent with paleoseismic events of magnitude 7 or more

a large methane plume east of bear island barents sea implications for the marine methane cycle a pockmark field extending over 35 km2 at 74 54 n 27 3 e described by solheim and elverhoi 1993 was re surveyed and found to be covered with more than 30 steep sided craters between 300 and 700 m in diameter and up to 28 m deep the craters are thought to have been formed by an explosive gas eruption anomalously high concentrations of methane in the shelf waters around the craters suggest that a strong methane source near this area is still active today methane enrichment more than 10 km away from the crater field indicates the large dimensions of a plume and the amount of gas released from sources below the seafloor of the barents sea shelf from the characteristic vertical decrease of methane towards the sea surface it is concluded that biota are extensively using this energy pool and reducing the methane concentration within the water column by about 98 between 300 m depth and the sea surface degassing to the atmosphere is minimal based on the shape of the methane concentration gradient nevertheless the net flux of methane from this area of the barents sea is about 2 9 104 g ch4 km 2 yr 1 and thus in the upper range of the presently estimated global marine methane release this flux is a minimum estimate and is likely to increase seasonally when rough weather leads to more effective vertical mixing during autumn and winter the amount of methane consumed in the water column however is about 50 times greater and hence should significantly contribute to the marine carbon inventory

imaging magnetospheric boundaries at ionospheric heights 1 an all sky imager asi records atmospheric emissions from zenith to low on the horizon at all azimuths a region typically spanning millions of square kilometers each pixel with its unique elevation azimuth and emission height can be mapped along b field lines to the equatorial plane of the magnetosphere auroral and subauroral structures and boundaries seen in emission within the ionosphere thermosphere i t system can thus be related to source regions for a midlatitude site this i t to inner magnetosphere connection typically falls within the l 2 5 earth radii domain in this study we present the first case of a stable auroral red sar arc observed from three widely spaced asi sites europe north america new zealand sar arcs are produced during the main and recovery phases of a geomagnetic storm with emission driven by heat conduction from a very specific location in the magnetosphere the l value where the plasmapause and the inner edge of the ring current overlap using three site observations we show that this boundary can be followed for 24 consecutive hours simultaneous observations made by three satellites in the defense meteorological satellite program dmsp show that the lowest latitude peak in electron temperature can be used to map the same boundary a key structure of the inner magnetosphere that cannot be observed continuously from sensors orbiting within the magnetosphere is made continuously visible to ground based optical systems via effects caused by the drainage of small amounts of ring current energy into the i t system

gas hydrate stability zone modelling in areas of salt tectonics and pockmarks of the barents sea suggests an active hydrocarbon venting system the barents sea seabed exhibits an area of major glacial erosion exposing parts of the old hydrocarbon basins in this region we modelled the gas hydrate stability field in a 3d perspective including the effects of higher order hydrocarbon gases we used 3d seismic data to analyse the linkage between fluid flow expressions and hydrate occurrences above old sedimentary basin systems and vertical faults pockmarks showed a relation to fault systems where some of them are directly connected to hydrocarbon bearing sedimentary formations the influence of bottom water temperature pore water salinity and geothermal gradient variation on gas hydrate stability zone ghsz thickness is critically analysed in relation to both geological formations and salt tectonics our analysis suggests a highly variable ghsz in the barents sea region controlled by local variations in the parameters of stability conditions recovery of gas hydrate sample from the region and presence of gas enhanced reflections below estimated bsr depths may indicate a prevalent gas hydrate stable condition

evolution of a mesospheric bore in a duct observed by ground based double layer imagers and satellite observations over the tibetan plateau region

paleoseismicity and geodynamics in sweden abstract paleoseismicity denotes past pre instrumental earthquakes as recorded by bedrock structures morphological features and sedimentological criteria glacial varves eskers and deltas are excellent records of paleoseismic events data from sweden are presented faults fractures and various types of sedimentary disturbances of late pleistocene and holocene age frequently occur it is concluded that the seismic activity was very intensive in connection with the peak rates of glacial isostatic uplift and that this was a natural effect of the geodynamic processes operating

gas induced erosion features in the north sea pockmarks are prominent features on the seafloor at two main regions of the north sea the south fladen area and the norwegian trench the pockmarks vary in size from 5 m across to about 150 m and in depth from 1 m to about 20 m some of the features consist of several very small unit pockmarks these are probably gas induced erosion features and found only in soft finegrained marine and glaciomarine sediments they are probably caused by shallow or deep seated gas or fluid release through the seabed whereby the finest particles are thrown into suspension and redistributed by nearbottom currents on the north sea plateau a small pockmarked area has recently been found a close relationship exists here between mobile gas in the upper sediments faulting in the soft sediments and the morphology of the seabed other morphological features in the north sea such as coast parallel depressions and elongated depressions or terraces are also interpreted here as gas induced erosion products this applies yet again to the mottled seabed features which appear as patches of high reflectivity on side scan sonar records from the north sea plateau they correspond to shallow seabed depressions on the deep towed boomer records judging from reported observations from several shallow seas world wide volatile transport through the seabed is probably quite common and several morphological features are undoubtably induced by this process several erosion features of similar origin are probably common also in deep ocean basins

an interpretation and catalogue of paleoseismicity in sweden abstract paleoseismic data provide a long term record of seismic activity to predict hazards for periods longer than one to a few centuries in sweden the analysis reveals there was a drastic change in dominant seismic mode from a high to super high deglacial mode to a low to moderately low mode in present and late holocene time paleoseismic criteria and characteristics include numerous different sources of information viz primary faults bedrock deformation sedimentary deformation rock and sediment slides liquefaction sorting by shaking tsunamis differing geomorphic expressions disordering and ordering of magnetic particles by applying multiple criteria it was possible to identify 44 paleoseismic events including 23 events of estimated m 6 7 12 events of m 7 8 and 6 events of m 8 varve dating often allows a precision as to a single year in one case even to the season of a year the key for paleoseismic reconstruction and testing is the application of multiple criteria

on the origin of mesospheric bores abstract a dramatic front of airglow radiance and wave structure reported by taylor et al 1995 was attributed in a previous paper of ours dewan and picard 1998 to a manifestation of an internal undular bore in the mesosphere in the current paper we address the question of what physical process could be responsible for generating such a bore at that altitude while it is relatively easy to find sources of internal tropospheric bores including the dramatic morning glory the same cannot be said for mesospheric bores it will be argued here that a likely candidate for the generator of such bores is the interaction of gravity waves with the mean flow at a critical layer this interaction could take place within an already existing inversion layer the latter playing the role of the channel in which the bore propagates as huang et al 1998 have shown a similar wave critical level interaction may be responsible for the inversion layer in question hence we are proposing that the physical process producing the channel is the same as the one responsible for subsequently generating the bore

varves and mass movement deposits record distinctly different sedimentation dynamics since the late glacial lake szurpily northeastern poland the sedimentological and geochemical characteristics of sediments from lake szurpily northeastern poland can be used as a record of mass movement and climate dynamics since the allerod late glacial sediments suggest enhanced runoff conditions in the catchment after the retreat of the scandinavian ice sheet while holocene varved sediments are interrupted by mass movement deposits mmds we identified 85 thin 1 m thick mmd type 2 consists of auto and allochthonous material and represents multistage processes including erosion and deformation of underlying varved sediments rapid deposition of clastic material and redeposition of previously eroded varved sediments seismic activity or permafrost degradation was responsible for the deposition of mmd type 2 furthermore varve thickness variability suggests gleissberg and suess solar cycles before 850 bc when human impact was limited additionally 22 and 11 yr sunspot cycles are recognized in light dark laminae thickness ratios and reflect influences of solar irradiance on lacustrine productivity

characterization of microbial activity in pockmark fields of the sw barents sea abstract multibeam bathymetry revealed the occurrence of numerous craterlike depressions so called pockmarks on the sea floor of the hammerfest basin and the loppa high south western barents sea to investigate whether these pockmarks are related to ongoing gas seepage microbial processes associated with methane metabolism were analyzed using geochemical biogeochemical and microbiological techniques gravity cores were collected along transects crossing individual pockmarks allowing a direct comparison between different locations inside assumed activity center on the rim and outside of a pockmark reference sites concentrations of hydrocarbons in the sediment particularly methane were measured as headspace free gas and in the occluded and adsorbed gas fraction down to a depth of 2 6 m below sea floor mbsf sulfate reduction rates were quantified by radiotracer incubations concentrations of dissolved sulfate in the porewater were determined as well neither the sulfate profiles nor the gas measurements show any evidence of microbial activity or active fluid venting methane concentrations and sulfate reduction rates were extremely low or even below the detection limit the results show that the observed sediment structures are most likely paleo pockmarks their formation probably occurred during the last deglaciation

abiotic methane seepage in the ronda peridotite massif southern spain abstract abiotic methane in serpentinized peridotites msp has implications for energy resource exploration planetary geology subsurface microbiology and astrobiology once considered a rare occurrence on earth reports of msp are increasing for numerous localities worldwide in low temperature land based springs and seeps we report the discovery of six methane rich water springs and two ponds with active gas bubbling in the ronda peridotite massif in southern spain water is hyperalkaline with typical hydrochemical features of active serpentinization ph 10 7 to 11 7 t 17 1 to 21 5 c ca oh facies dissolved ch4 concentrations range from 0 1 to 3 2 mg l the methane stable c and h isotope ratios in the natural spring and bubbling sites 13cch4 12 3 to 37 vpdb 2hch4 280 to 333 vsmow indicate a predominant abiotic origin in contrast springs with manmade water systems i e pipes or fountains appear to have mixed biotic abiotic origin 13cch4 44 to 69 2hch4 180 to 319 radiocarbon 14c analyses show that methane c in a natural spring is older than ca 50 000 y bp whereas dissolved inorganic carbon dic analysed in all springs has an apparent 14c age ranging from modern to 2334 y bp therefore most if not all of the ch4 is allochthonous i e not generated from the carbon in the hyperalkaline water methane is also released as bubbles in natural ponds and as diffuse seepages 101 102 mg ch4 m 2d 1 from the ground up to several tens of metres from the seeps and springs albeit with no overt visual evidence these data suggest that the gas follows independent migration pathways potentially along faults or fracture systems physically isolated from the hyperalkaline springs methane does not seem to be genetically related to the hyperalkaline water which may only act as a carrier of the gas gas bearing springs vents and invisible microseepage in land based peridotites are more common than previously thought in addition to other geological sources msp is potentially a natural source of methane for the troposphere and requires more worldwide flux measurements

in absurdum long term predictions and nuclear waste handling abstract careful use of scientific knowledge allows predictions into the future when the time units for our predictions increases to hundreds of thousands of years we have extended our abilities in absurdum this is true for long term safety statements regarding the handling of our high level nuclear waste the fennoscandian shield has been claimed to offer exceptionally stable bedrock conditions over immense time periods we only need to go back to the last deglacial phase some 10 000 years ago to have a totally different situation from that of today at that time sweden was characterized by exceptionally high seismic activity both in amplitude and frequency these conditions like a number of related phenomena will be repeated at future ice ages in such an environment there can be no safe repository in the bedrock in the absence of true long term safety we can only recommend the utilization of the dry rock deposit drd method where the waste is stored in the bedrock under dry conditions under constant control and monitoring accessible for maintenance and possible future methods of rendering the waste harmless and even removal

regulation of ice stream flow through subglacial formation of gas hydrates localized subglacial zones of high traction help to regulate ice sheet flow geophysical data from a palaeo ice stream suggest that methane gas accumulation and hydrate formation beneath ice sheets can produce such high traction sticky spots

massive blow out craters formed by hydrate controlled methane expulsion from the arctic seafloor widespread methane release from thawing arctic gas hydrates is a major concern yet the processes sources and fluxes involved remain unconstrained we present geophysical data documenting a cluster of kilometer wide craters and mounds from the barents sea floor associated with large scale methane expulsion combined with ice sheet gas hydrate modeling our results indicate that during glaciation natural gas migrated from underlying hydrocarbon reservoirs and was sequestered extensively as subglacial gas hydrates upon ice sheet retreat methane from this hydrate reservoir concentrated in massive mounds before being abruptly released to form craters we propose that these processes were likely widespread across past glaciated petroleum provinces and that they also provide an analog for the potential future destabilization of subglacial gas hydrate reservoirs beneath contemporary ice sheets

the baltic ice lake yoldia sea transition abstract the baltic ice lake the yoldia sea the ancylus lake and the littorina sea are the four classical stages in the postglacial evolution of the baltic basin the picture is complicated by what concerns the details of each of these stages between the baltic ice lake and the yoldia sea it is necessary to introduce a separate lake stage an entirely lacustrine phase of 300 years right after the drainage of the baltic ice lake and before the ingression of salt water that by definition signifies the onset of the yoldia sea during this lake stage a fully lacustrine ancylusfauna lived along the coasts of the islands of gotland and oland for historical reasons and mistakes we term this new stage the yoldia lake stage thus avoiding too much reorganization