contribution of peat compaction to relative sea level rise within holocene deltas 1 modern and forecasted flooding of deltas is accelerated by subsidence of holocene deposits subsidence caused by tectonics isostasy sediment compaction and anthropogenic processes combined with eustatic sea level rise results in drowning and increased flood risk within densely populated deltas many deltaic sedimentary successions include substantial amounts of peat which is highly compressible compared to clay silt and sand peat compaction therefore may contribute considerably to total delta subsidence existing studies are inadequate for quantifying peat compaction across deltas we present a numerical peat compaction model calibrated with an extensive field dataset the model quantifies spatial and temporal trends in peat compaction within fluvial dominated holocene flood basin sequences of different compositions subsidence due to peat compaction is highly variable in time and space with local rates of up to 15 mm yr depending on sedimentary sequence this is extremely important information for developing sound delta management strategies artificial groundwater table lowering may cause substantial additional subsidence subsidence due to peat compaction might even exceed estimates of relative sea level rise and thus may seriously increase the risk of delta drowning and human vulnerability to flooding

compression behaviour of minerogenic low energy intertidal sediments existing geotechnical approaches that describe volumetric changes in intertidal sediments in response to applied vertical effective stresses are limited by a lack of empirical research into their one dimensional compression behaviour in this paper we address this deficiency by presenting the results of an investigation into the compression behaviour of minerogenic low marsh and tidal flat sediments we have tested samples of these sediment types obtained from greatham creek cowpen marsh tees estuary uk analysis of physical properties and oedometer compression tests demonstrates that contrary to the implicit assumptions of existing models the surface sediments studied are overconsolidated structural variability between samples arises due to sedimentological factors notably variations in organic content we attribute overconsolidation to tidal exposure and falls in groundwater level that permit desiccation and cause capillary suction stresses greater rates of compression with respect to effective stress occur in sediments with higher initial voids ratios and more open unstable initial structures variability in structure decreases with application of higher effective stresses due to the destructuration of the sediments which also creates increased homogeneity of compression behaviour under higher effective stresses we subsequently develop a new conceptual framework to describe compression behaviour in minerogenic intertidal sediments that incorporates overconsolidation we advocate a statistical approach that accounts for structural variability and variations in compression behaviour at effective stresses less than and greater than the yield stress we argue that our conceptual framework is broadly applicable to minerogenic intertidal sediments at different locations and burial depths within holocene stratigraphic sequences providing site specific compression data are collected inter site transfer and application of measured material properties should not be undertaken due to local variations in compression behaviour resulting from varying ecological sedimentological geochemical climatic geomorphic and hydrographic conditions the individual characteristics of different field locations should be carefully considered before the suggested framework is routinely applied

a three dimensional surface velocity field for the mississippi delta implications for coastal restoration and flood potential accurate estimates of the current rate of subsidence in the mississippi delta southern united states provide a context for planning of wetland restoration and predictions of storm surge flooding we present a comprehensive three dimensional surface velocity field for the mississippi delta based on a network of 36 high precision continuous gps stations we show that while the majority of the delta is relatively stable the southern portion continues to experience high rates of subsidence 5 6 mm yr 1 our data are consistent with long term tide gauge records at grand isle louisiana and several stations in florida the current rate of relative sea level rise combined effect of land subsidence and sea level rise along parts of the coastal delta is 8 9 mm yr 1 most tide gauge stations have recorded sea level rise acceleration after a d 1970 these data have implications for land reclamation and wetland restoration in the region parts of the delta may not be viable in the long term

unprecedented erosion of the upper texas coast response to accelerated sea level rise and hurricane impacts the upper texas coast is an ideal location to examine coastal response to global change over geologic and historic time here we quantify the long term sequestration for sand eroded from an island into two main sinks offshore galveston island and san luis pass tidal delta in order to compare long term and short term erosion we determine the average storm related offshore sand fl ux for the middle part of the holocene ca 5240 5040 2 cal yr b p to present to be 4200 4400 670 m 3 yr with a decrease in the offshore sand fl ux to 920 970 270 m 3 yr during the latter part of the holocene ca 2730 2610 2 cal yr b p to present the tidal delta initially formed ca 2100 1 median cal yr b p when the rate of sealevel rise slowed from 2 0 mm yr to 0 60 mm yr we calculate the sand fl ux from galveston island into san luis pass from ca 2100 1 median cal yr b p to 200 yr ago to be 4700 m 3

mantle flow in subduction systems the subslab flow field and implications for mantle dynamics 1 the character of the mantle flow field in subduction zones remains poorly understood despite its importance for our understanding of subduction dynamics in particular little attention has been paid to mantle flow beneath subducting slabs in order to identify processes that make first order contributions to the global pattern of subslab mantle flow we have compiled shear wave splitting measurements from subduction zones worldwide from previously published studies and estimated average splitting parameters for the subslab region globally the subslab region is overwhelmingly dominated by trench parallel fast splitting directions we tested for relationships between splitting delay time a measure of the strength of anisotropy and parameters that are indicators of tectonic processes such as trench migration velocity convergence velocity and obliquity age of subducting lithosphere and slab dip curvature seismicity and thickness we used several different plate motion models to describe plate and trench motions and evaluated the differences among the models we find that only one parameter namely the trench migration velocity in a pacific hot spot reference frame appears to correlate well with the strength of the subslab splitting signal this finding supports a model in which the mantle beneath subducting slabs is dominated by three dimensional flow induced by trench migration we explore several implications of our model for various aspects of mantle dynamics including the choice of a suitable reference frame s for mantle flow the existence of a thin decoupling zone between slabs and the subslab mantle and consequences for mass transfer between the upper and lower mantle

small scale mantle convection produces stratigraphic sequences in sedimentary basins cyclic sedimentary deposits link stratigraphic sequences that are now geographically distant but were once part of the same depositional environment some of these sequences occur at periods of 2 to 20 million years and eustatic sea level variations or regional tectonic events are likely causes of their formation using numerical modeling we demonstrate that small scale mantle convection can also cause the development of stratigraphic sequences through recurrent local and regional vertical surface movements small scale convection driven stratigraphic sequences occur at periods of 2 to 20 million years and correlate only at distances up to a few hundred kilometers these results suggest that previous sequence stratigraphic analyses may contain erroneous conclusions regarding eustatic sea level variations

on mantle chemical and thermal heterogeneities and anisotropy as mapped by inversion of global surface wave data 1 we invert global observations of fundamental and higher order love and rayleigh surface wave dispersion data jointly at selected locations for 1 d radial profiles of earth s mantle composition thermal state and anisotropic structure using a stochastic sampling algorithm considering mantle compositions as equilibrium assemblages of basalt and harzburgite we employ a self consistent thermodynamic method to compute their phase equilibria and bulk physical properties p s wave velocity and density combining these with locally varying anisotropy profiles we determine anisotropic p and s wave velocities to calculate dispersion curves for comparison with observations models fitting data within uncertainties provide us with a range of profiles of composition temperature and anisotropy this methodology presents an important complement to conventional seismic tomography methods our results indicate radial and lateral gradients in basalt fraction with basalt depletion in the upper and enrichment of the upper part of the lower mantle in agreement with results from geodynamical calculations melting processes at mid ocean ridges and subduction of chemically stratified lithosphere compared with preliminary reference earth model prem and seismic tomography models our velocity models are generally faster in the upper transition zone tz and slower in the lower tz implying a steeper velocity gradient while less dense than prem density gradients in the tz are also steeper mantle geotherms are generally adiabatic in the tz whereas in the upper part of the lower mantle stronger lateral variations are observed the retrieved anisotropy structure agrees with previous studies indicating positive as well as laterally varying upper mantle anisotropy while there is little evidence for anisotropy in and below the tz

reservoir fluid substitution effects on seismic profile interpretation a physical modeling experiment p wave seismic surveys are performed on realistic physical models of a reservoir formed of interbedded sand and shale layers and filled with gas water and oil they show characteristic behaviour which can be used to distinguish between fluids with significant implications for the interpretation of time lapse experiments discontinuous reflections originate in gas filled reservoirs with widely varying amplitude compared to oil or water filled reservoirs anomalous changes in seismic amplitude difference attributes for reflections within the reservoir are seen for gas oil substitution oil water substitution results in only weak variations of reservoir elastic properties thus amplitude difference attributes may be unsuitable for monitoring changes in oil water saturation however direct differences between the time traces are strong on time lapse sections strong amplitude difference anomalies do not necessarily correspond to the region where the fluid variations occur this is significant for monitoring oil field development by water injection

three dimensional seismic geomorphology and analysis of the ordovician paleokarst drainage system in the central tabei uplift northern tarim basin western china high quality three dimensional seismic data acquired in the central tabei uplift tarim basin western china provide a rare opportunity to characterize in exceptional detail the three dimensional geomorphology of a deeply buried 5500 6500 m 18 045 21 325 ft ordovician unconformity and the related paleokarst drainage system an integrated approach was applied that emphasized integration of seismic data with available conventional core wireline logs and age equivalent outcrops the exceptional quality of the seismic data allowed a seismic detection limit of karstified features of less than 75 75 m 246 246 ft horizontally and 6 m 20 ft vertically interpreted geomorphologic and depositional elements include fluvial channels and canyons fluvial valleys sinkholes and tower karsts and hills the modern tower karst drainage system in guilin china is very similar to the mapped ordovician karst drainage system and is used as a modern analog the interaction between the surface karst drainage system and the shallow subsurface cave passage system is evidenced by the observation that surface canyons appear to initiate in areas associated with intense sinkhole development also surface river valleys tend to correspond to dip oriented surface depressions partly related to near surface cave collapse during burial into the deeper subsurface the combination of intrastratal collapse karstified strata and suprastratal collapse postkarst deposited strata created large damage zones hundreds of meters thick and kilometers wide coalesced collapsed paleocave systems can be interpreted from the unique circular pattern of faults observed in map view that are associated with seismic bright spots

quantifying holocene lithospheric subsidence rates underneath the mississippi delta abstract the pattern of holocene relative sea level rsl change on the us gulf coast has been a long standing subject of debate featuring opposing scenarios of continuous submergence versus one or more holocene rsl highstands the significance of this debate is that the relative role of eustasy glacial isostatic adjustment gia and lithospheric flexural subsidence associated with mississippi delta sediment loading remains unresolved here we present a new rsl record from the louisiana chenier plain 100 km west of the mississippi delta margin based on ams 14 c dated marsh basal peat this enables us to provide for the first time constraints on holocene lithospheric subsidence rates underneath one of the world s major deltas our new record conclusively shows that no middle holocene rsl highstands occurred on the central us gulf coast rather it exhibits a pattern of progressive rsl rise comparable to that from the mississippi delta suggesting that long wavelength gia is a dominant deformational process driving lithospheric subsidence in the entire region by means of forebulge collapse nevertheless a 0 15 0 07 mm yr differential rate of subsidence between the chenier plain and key portions of the mississippi delta including the new orleans metropolitan area exists this shows that while the sediment loading effect is real it is about an order of magnitude smaller than recent studies have postulated

anthropogenic and geologic influences on subsidence in the vicinity of new orleans louisiana new measurements of ongoing subsidence of land proximal to the city of new orleans louisiana and including areas around the communities of norco and lutcher upriver along the mississippi are reported the rates of vertical motion are derived from interferometric synthetic aperture radar insar applied to uninhabited aerial vehicle synthetic aperture radar uavsar data acquired on 16 june 2009 and 2 july 2012 the subsidence trends are similar to those reported for 2002 2004 in parts of new orleans where observations overlap in particular in michoud the 9th ward and chalmette but are measured at much higher spatial resolution 6 m the spatial associations of cumulative surface movements suggest that the most likely drivers of subsidence are groundwater withdrawal and surficial drainage dewatering activities high subsidence rates are observed localized around some major industrial facilities and can affect nearby flood control infrastructure substantial subsidence is observed to occur rapidly from shallow compaction in highly localized areas which is why it could be missed in subsidence surveys relying on point measurements at limited locations

geodynamics layer cake or plum pudding whether convection in the earth s mantle extends through its entire depth or if the mantle is layered has long been debated recent research suggests that spatially and temporally intermittent or partial layering is the most likely solution

low seismic resolution cannot explain s p decorrelation in the lower mantle 1 inverted models of the deep mantle show a decorrelation between maps of shear vs and compressional vp wave velocities an anti correlation between the bulk sound velocity v and vs and a much larger variability of vs with respect to vp expressed by large values of the ratio of their relative lateral variations we carried out synthetic tests to verify if these features could be artifacts explained by limits in tomographic resolution synthetic data are calculated for an input model and linearly inverted as in tomography to find an output model comparing the values of the aforementioned parameters for two different chemically homogeneous input models with the associated reconstructed output ones we found that artifacts caused by realistic data noise and the nonuniform distribution of seismic sources and stations over the globe are not sufficient to introduce the features previously described we confirm that compositional effects are required to explain them

recovery estimates for the rio cruces after the may 1960 chilean earthquake abstract the may 22nd 1960 chilean earthquake was the largest earthquake on record with a magnitude 9 5 the event caused extensive subsidence and uplift over wide areas at least 130 000 km 2 with uplift on the offshore south american plate margin and downwarping in the coastal and landward areas which ranged in magnitude from 1 2 m the subsidence deepened coastal rivers creating extensive shallow banks now wetlands in many rivers including the rio cruces the amount of subsidence was well documented with field measurements recorded soon after the event this study using sediment accumulation histories predicts the recovery time of the rio cruces to pre 1960 conditions an important factor for assessing the fidelity of seismic recorders in the geological record sediment cores n 139 from the subtidal areas of the rio cruces were lithologically logged and selectively analyzed using high resolution particle size distribution psd plots microfossil analysis thecamoebians and 210 pb 137 cs dating documenting the post 1960 thickness of sediment the analysis differentiated four main facies which include 1 floodplain soil horizon 2 tsunami or flood unit 3 post earthquake adjustment and 4 river sedimentation the post 1960 river sediment is clearly demarcated in the cores by highly peaked psds 4 5 phi abundant thecamoebian tests and high diversities compared to the underlying facies species compositions are typical of lacustrine or slow moving river systems cucurbitella tricuspis difflugia oblonga centropyxis constricta centropyxis aculeata lagenodifflugia vas and difflugia protaeiformis based on this core data the shallow banks along the rio cruces will likely shoal in less than 100 yrs

a physical modeling study of seismic features of karst cave reservoirs in the tarim basin china abstracton seismic migration sections anomalous bright spots called the string of beads response sbr are common features of carbonate karst reservoirs at the seismic scale in the tarim basin china to understand the sbr features of different karst caves which is an important issue for local exploration we conducted a physical modeling experiment within the physical model we included various single caves with different scales velocities shapes and fluids as well as multiple caves in different spatial distributions sbrs of all caves were extracted and summarized from the migration sections first we investigated effects of the cave scale velocity spatial distribution shape and fluids on sbrs the relative amplitude of sbrs increased with the cave width ranging from 25 to 400 m and decreased with the cave velocity the sbr split into two new sbrs when the cave height was larger than 100 m spatially distributed multiple caves resulted in some special sbrs such as long sbrs inclined sbrs

how stable is the mississippi delta large deltas are commonly believed to exhibit rapid rates of tectonic subsidence largely due to sediment loading of the lithosphere as a result deltaic plains are prone to accelerated relative sea level rise coastal erosion and wetland loss hurricane katrina s devastation testifies to the severe threat that these processes pose to the mississippi delta but the relative role of tectonics versus other mechanisms causing land subsidence remains elusive relative sea level records derived from basal peat have the potential to quantify differential crustal movements over holocene time scales with exceptionally high accuracy and precision here we present new sea level index points from two study areas in the southwestern mississippi delta that essentially coincide with a recently published detailed relative sea level record from the eastern part of the delta our results show that differential vertical movements among the three study areas have been only 0 1 mm yr 1 w e compare our evidence with a recent sea level compilation from the caribbean to a large extent based on data from areas that are tectonically stable our sea level index points nearly coincide with the caribbean data showing surprising tectonic stability for considerable sections of the mississippi delta however the well documented high subsidence rates in and near the birdfoot of the mississippi delta indicate that different conditions prevail there the rapid wetland loss in coastal louisiana is likely due to a considerable extent to the compaction of holocene strata

mathematical modeling of autocompaction of a holocene transgressive valley fill deposit wolfe glade delaware six thousand years of sediment accumulation and autocompaction in a transgressive valley fill deposit are simulated numerically rates of accumulation of freshwater organic rich mud subtidal mud and organic rich mud of the modern salt marsh are specified by using existing sedimentologic paleontologic and geochronologic data processes of pore water explusion and autocompaction are determined from finite strain consolidation theory model parameters for subtidal mud facies are determined from laboratory consolidation tests model parameters for organic rich deposits are determined by sampling equivalent modern sedimentary environments and by model calibration model calibration involves 1 reproducing the present distribution of void ratios measured in a 7 6 m vibracore 2 correctly calculating the preserved thickness of lithologic units and 3 determining a history of elevation changes of the sediment surface that is consistent with the delaware sea level curve and the known sequence of paleoenvironments of wolfe glade delaware the results indicate that preserved horizons in the 10 m holocene section of wolfe glade have been lowered a maximum of 2 3 m the rate of lowering due to autocompaction alone has been one half to one third of the rate of sea level rise during most of the past 6000 yr numerical experiments suggest that organic rich freshwater wetland deposits are primarily responsible for the extensive autocompaction at wolfe glade our approach may be used to correct holocene coastal stratigraphic data for autocompaction but careful model calibration based in part on the stratigraphy will usually be required

controls on natural levee development in the columbia river british columbia canada natural levees of the columbia river near golden british columbia were investigated to identify the mechanisms that control levee development and morphology topographic profiles of 12 levee pairs were surveyed and measurements of water surface elevation flow velocity flow direction and turbidity were obtained during an average magnitude flood 1ae2 years recurrence interval sedimentation rates and grain size distributions were measured from sediment traps placed along levee to floodbasin transects results show that water and sediment exchange between the channel and floodbasin was mainly by advection during flooding local floodbasins behave more as efficient water pathways than water storage features resulting in down valley floodbasin flows capable of limiting basinward growth of levees levee shape results primarily from two independent factors 1 maximum channel water stage which limits levee height and 2 floodbasin hydraulics which control width in the columbia river the competence of floodbasin flows results in relatively narrow and steep levees natural levees grow under two general conditions of deposition as governed by flood stage elevation relative to levee crest elevation front loading and back loading during large floods when crests are inundated front loading preferentially aggrades the proximal portions of levees with sediment directly from the channel thus increasing levee slope during average or below average floods when many levee crests are not overtopped back loading preferentially aggrades the distal levee areas and floodbasin floor reducing levee slope in the study area a balance between front and back loading sustains these narrow and steep levee shapes for long periods reflecting an equilibrium between hydraulic regime floodplain morphology and deposition

magnitude and timing of peat to coal compaction the peat to coal transition is commonly assumed to be accompanied by compaction that decreases the thickness of the organic deposit to values of 10 or less of the original peat thickness decompaction modeling using such values for coal seams in contact with penecontemporaneous channel sandstones leads to impossible depositional geometries for the sandstones which have a final thickness that is 90 of their original thickness similarly decompaction modeling of the fragments of organic material within channel lags using the assumed large peat compaction value results in the destruction of the associated sedimentary structures such as trough cross beds dinosaur tracks in the roofs of coal mines show a shallow depth of penetration and a preservation of foot morphology that is not possible unless the peat the animals walked upon was very firm these data confirm the macroscopic observations from coal balls that the compaction associated with the peat to coal transformation is minimal equally important the data also show that most of the compaction occurs essentially at the surface and not at the depths where coalification takes place

abnormal transmission attenuation and its impact on seismic fracture prediction a physical modeling study fracture induced anisotropy can lead to observable azimuthal variations of seismic attributes that then can be used for characterizing a fracture system unfortunately abnormal transmission losses along raypaths also can result in similar azimuthal variations leading to uncertainty in such fracture determination using a physical model containing gas filled fractures we investigate the impact of abnormal transmission loss on fracture detection from ultrasonic data in a laboratory setting recorded reflection amplitudes and traveltimes are used to study ultrasonic responses to the presence of the gas filled fractures and to understand observed azimuthal attribute anomalies experimental results from this study highlight the pitfalls in using azimuthal attribute variations as indicators of the presence of fractures when abnormal transmission attenuation is significant

accelerated river avulsion frequency on lowland deltas due to sea level rise sea level rise subsidence and reduced fluvial sediment supply are causing river deltas to drown worldwide affecting ecosystems and billions of people abrupt changes in river course called avulsions naturally nourish sinking land with sediment however they also create catastrophic flood hazards existing observations and models conflict on whether the occurrence of avulsions will change due to relative sea level rise hampering the ability to forecast delta response to global climate change here we combined theory numerical modeling and field observations to develop a mechanistic framework to predict avulsion frequency on deltas with multiple self formed lobes that scale with backwater hydrodynamics results show that avulsion frequency is controlled by the competition between relative sea level rise and sediment supply that drives lobe progradation we find that most large deltas are experiencing sufficiently low progradation rates such that relative sea level rise enhances aggradation rates accelerating avulsion frequency and associated hazards compared to preindustrial conditions some deltas may face even greater risk if relative sea level rise significantly outpaces sediment supply then avulsion frequency is maximized delta plains drown and avulsion locations shift inland posing new hazards to upstream communities results indicate that managed deltas can support more frequent engineered avulsions to recover sinking land however there is a threshold beyond which coastal land will be lost and mitigation efforts should shift upstream

the potential for sea level rise induced barrier island loss insights from the chandeleur islands louisiana usa abstract as sea level rises and hurricanes become more intense barrier islands around the world become increasingly vulnerable to conversion from self sustaining migrating landforms to submerging or subaqueous sand bodies to explore the mechanism by which such state changes occur and to assess the factors leading to island disintegration we develop a suite of numerical simulations for the chandeleur islands in louisiana u s a which appear to be on the verge of this transition our results suggest that the chandeleurs are likely poised to change state leading to their demise within decades depending on future storm history contributing factors include high rates of relative sea level rise limited sediment supply muddy substrate current island position relative to former mississippi river distributary channels and the effects of changes in island morphology on sediment transport pathways although deltaic barrier islands are most sensitive to disintegration because of their muddy substrate the importance of relative sea level rise rate in determining the timing of threshold crossing suggests that the conceptual models for deltaic barrier island formation and disintegration may apply more broadly in the future

triggering mechanism and reactivation probability of loess mudstone landslides induced by rainfall infiltration a case study in qinghai province northwestern china rainfall especially rainstorm is a major factor in inducing loess mudstone landslides and plays an essential role in landslide reactivation the aim of the paper is to study the triggering mechanism and reactivation probability of a loess mudstone landslide induced by rainfall infiltration in qinghai province northwestern china according to the numerical model of elastic plastic mechanics the triggering mechanism of loess mudstone landslides was revealed then the reactivation probability of the potential landslide was evaluated by the combination of the limit equilibrium and monte carlo methods for one thing the relationship between water content and shear strength of media was analyzed based on the mechanical test of materials for another the effects of rainfall conditions were analyzed on the distribution of water content in the aerated zone with the two dimensional coupling model of unsaturated saturated seepage the results show that the shear strength of media is very sensitive to water content because of water rock interaction including hydration and dissolution besides the water content significantly increases at the interface between the loess and mudstone after the rainstorm occurring owing to the permeability heterogeneous of media and topographic feature which leads to the strength deterioration although the whole landslide is stable in the rainstorm conditions its middle part can be reactivated along the original sliding zone with high probability by a geomechanical model of sliding tension therefore the landslide reactivation is controlled by the water sensitivity of media the permeability heterogeneous of media the topographic feature and the original sliding zone especially the original sliding zone this research provides a valuable reference for the occurrence and reactivation of similar landslides

calibrated density profiles of caribbean mangrove peat sequences from computed tomography for assessment of peat preservation compaction and impacts on sea level reconstructions oceanic mangroves accumulate peat with sea level rise without terrestrial sediment inputs but fossil peat s elevation as a tide range limited sea level indicator is assumed to be affected by compaction despite assumption of decomposition compression and dewatering pure rhizophora mangle peat appears coarse water saturated and loose even at depth calibrated peat densities from computed tomography ct and petrologic analysis allow quantitative assessment of compaction in continuous peats from florida 6 m thick belize 12 m thick and panama 3 5 m thick pure peat exhibits voids at all depths and 80 water contents ct density does not increase with depth bulk densities are low minimally variable and trend free higher ct density intervals coincide with compositional changes sediment coral ct of peat buried under sediment shows a shift to higher densities ct of air dried continuous peat shows uncompressed fine and coarse roots and voids with negative densities indicative of air in place of interstitial water peat s high water content and hydraulic conductivity prevent dewatering and compaction hypothetically maintaining original sea level indicative elevations at intermediate depths non compacted sediment free offshore peats can provide a continuous proxy for reconstructing the record of sea level rise at any site if depositional disturbance and geochemical and biotic processes affecting 14 c ages are also assessed

geotechnical and landslide aspects in weathered granitoid rock masses serre massif southern calabria italy abstract the weathering processes produce important chemical and physical transformations in rock masses producing a decay of their strength and then stability in this study different methodologies were employed to define the physical mechanical properties and the minero petrographical changes at each grade of weathering useful to determine a geological model of the weathered granitoids involved in mass movements the paper focuses on a multidisciplinary research on the weathering profiles of the paleozoic granitoid rocks surrounding the village of fabrizia located in the serre massif southern calabria italy fabrizia lies on an old erosion surface composed of basement rocks made up of weathered granitoids belonging to the serre massif granitoid complex and overlain by thin eluvial colluvial deposits the tectonic uplift of the area combined with mediterranean climatic conditions both active at least since the quaternary are the main causes of the deep weathering of the plutonic rocks the weathered profiles of the granitoid complex have been studied through field observations borehole explorations with geotechnical tests and seismic surveys coupled to minero petrographical analysis and laboratory tests weathered profiles are mainly composed by rock masses varying from completely weathered and residual soil classes v vi to moderately weathered rocks class iii characterized by a progressive increase of geotechnical properties e g seismic wave velocity rock quality designation internal friction angle uniaxial compressive strength with a decrease of weathering the weathered rocks display a wide variety of mass movement landslide types are rockfalls for the fresher rocks class iii translational slides occur between different weathering degrees classes iv and v and rotational slides dominate at the top of the slopes and generally involve the weathering grades from class iv to classes v vi the shallow horizons are composed of thin eluvial colluvial deposits and more weathered granitoids classes v vi that may generate dangerous debris flows or debris avalanches during intense and prolonged rainfall the landslide surface is usually at a depth lower than 2 m in the debris flow type while deeper landslides depth 2 m are rotational and translational types with sliding surfaces occurring mainly in the transition between the classes iv and v the field survey coupled to geotechnical geophysical and minero petrographical data allowed the recognition of the different weathered horizons and relative geotechnical properties useful to the reconstruction of the reliable geological model the model represents an important support for the study of the landslide processes and for a sustainable management of the territory the used approach provided results to set a general reference framework for establishing more precise correlations between mass movement phenomena and weathering processes

driving mechanisms of coastal change peat compaction and the destruction of late holocene coastal wetlands abstract this paper examines the role of peat compaction as a driving mechanism behind the widespread inundation of a late holocene coastal wetland in southeast england uk detailed stratigraphic and dating evidence lithology grain size foraminifera pollen and radiocarbon dates from a sample site in romney marsh documents the gradual inundation of a coastal wetland after 1263 1085 cal yr bp c 700 850 ad and the establishment of a saltmarsh shortly thereafter there was a rapid increase in water depth that was associated with the deposition of nearly 4 m of laminated intertidal mudflat and tidal channel sediments prior to site reclamation from the sea by ad 1460 grain size data and statistical analysis of sand and mud laminae thicknesses suggest the laminated sediments accumulated rapidly c 0 2 m per year as heterolithic tidal rhythmites rapid compaction of the thick peat bed that underlies the study site provided the accommodation space for their deposition this process began with the gradual tidal inundation of the site but accelerated following the widening of a breach in a coastal barrier in the 13th century compaction lowered the peat surface by at least 3 m and was associated with widespread landscape change the study demonstrates the powerful influence that compaction had on the evolution of the late holocene landscape at this site and we believe at many other coastal lowlands in northwest europe this process is likely to have been a key driving mechanism behind rapid late holocene coastal change far exceeding the longer term effects of either eustatic change or crustal uplift subsidence

stratigraphic record of holocene coseismic subsidence padang west sumatra 1 stratigraphic evidence is found for two coseismic subsidence events that underlie a floodplain 20 km south of padang west sumatra along the mentawai segment 0 5 s 0 3 s of the sunda subduction zone each earthquake is marked by a sharp soil mud contact that represents a sudden change from mangrove to tidal flat the earthquakes occurred about 4000 and 3000 cal years b p based on radiocarbon ages of detrital plant fragments and seeds the absence of younger paleoseismic evidence suggests that late holocene relative sea level fall left the floodplain too high for an earthquake to lower it into the intertidal zone our results point to a brief few thousand year window of preservation of subsidence events in tidal wetland stratigraphic sequences a result that is generally applicable to other emergent coastlines of west sumatra

quantitative evidence that compaction of holocene sediments drives the present land subsidence of the po delta italy 1 deltas are highly dynamic coastal systems that over the last few decades have generally experienced a substantial area loss caused by trapping of river sediments in upland drainage basins as well as land subsidence due to natural and anthropogenic causes a major example is the po delta in the mediterranean in northeastern italy this area has experienced as much as 3 m of land subsidence from the 1930s to the 1970s primarily because of the extraction of gas bearing waters however present subsidence rates are largely unknown and the ground settlement is supposedly controlled by natural long term deep processes we have combined radar interferometric point target analysis ipta with previous geomorphological investigations on aerial satellite images and seismic surveys and geochronological data from core samples and geomechanical in situ tests to assess the current sinking of the delta and to understand the processes controlling the vertical movement the high density of the measurable point targets more than 15 000 allows characterization of the spatial variation in the vertical land motions vlm ranging from 1 to 15 mm yr we find that subsidence rates are significantly correlated with the age of highly compressible holocene deposits that compose the shallowest 30 40 m of the sedimentary sequence a typical log type consolidation equation applicable at the scale of the entire delta has been obtained we conclude that the consolidation of late holocene sediments is the major cause of the present land subsidence in the po river delta this finding has significant impact on the understanding of many other modern deltas that were formed in the lower holocene epoch

a revised chronology for mississippi river subdeltas radiocarbon measurements by accelerator mass spectrometry relating to three of the four late holocene mississippi river subdeltas yielded consistent results and were found to differ by up to 2000 carbon 14 years from previously inferred ages these geological dataare in agreement with archaeological carbon 14 data and stratigraphic ages based on ceramic seriation and were used to develop a revised chronologic framework which has implications for prehistoric human settlement patterns coastal evolution and wetland loss and sequence stratigraphic interpretations

post glacial sediment load and subsidence in coastal louisiana 1 sea level rise in the gulf of mexico has occurred at a rate of 1 8 2 2 mm yr during the 20th century or nearly the same as observed globally due to combined steric and water mass changes tide gauges in coastal louisiana however record a substantially larger rate of rise and while a number of causal mechanisms may be responsible their specific contribution is poorly understood using a realistic viscoelastic earth model detailed geologic parameters for south louisiana and new gps data we demonstrate that holocene sedimentary loading in the gulf and mississippi river delta is capable of contributing to 1 8 mm yr of subsidence over areas of 30 0 75 103 km2

estimating shallow subsidence in microtidal salt marshes of the southeastern united states kaye and barghoorn revisited abstract simultaneous measurements of vertical accretion and change in surface elevation relative to a shallow 3 5 m subsurface datum were made in selected coastal salt marshes of louisiana florida and north carolina to quantitatively test kaye and barghoorn s contention that vertical accretion is not a good surrogate for surface elevation change because of autocompaction of the substrate rates of subsidence of the upper 3 5 m of marsh substrate were calculated for each marsh as the difference between vertical accretion and elevation change measured with feldspar marker horizons and a sedimentation erosion table surface elevation change was significantly lower than vertical accretion at each site after 2 years indicating a significant amount of shallow subsidence had occurred ranging from 0 45 to 4 90 cm the highest rate of shallow subsidence occurred in the mississippi delta results confirm kaye and barghoorn s contention that vertical accretion is not generally a good surrogate for elevation change because of processes occurring in the upper few meters of the substrate including not only compaction but also apparently shrink swell from water storage and or plant production decomposition at some sites indeed surface elevation change was completely decoupled from vertical accretion at the florida site the assumption of a 1 1 relationship between vertical accretion and surface elevation change is too simplistic a generalization of the complex interactions between accretionary and substrate processes consequently the potential for coastal marsh submergence should be expressed as an elevation deficit based on direct measures of surface elevation change rather than accretion deficits these findings also indicate the need for greater understanding of the influence of subsurface and small scale hydrologic processes on marsh surface elevation

interpretative lessons from three dimensional modeling three dimensional 3 d seismic modeling has been accomplished by describing geologic surfaces with triangular plates and then computing the seismic response by kirchhoff wave theory the resulting time sections illustrate many interesting 3 d phenomena which are useful in interpreting geologic structures three dimensional resolution studies relate the concept of fresnel zone reflection to seismic resolution if high resolution is desired both horizontally and vertically then not only is a dense field survey required but also a detailed amplitude study the dense seismic coverage is required to map the focal line of concave boundary edges which are difficult to delineate with conventional seismic data additional studies on complex models such as grabens and 3 d permeability traps associate interpretational pitfalls to a wandering specular reflection path that is side swipe in each geologic model maximum resolution is obtained on a principal plane line dip line if a seismic dip line is not

how much subsidence is enough to change the morphology of river deltas understanding the effect of subsidence on fluviodeltaic morphology is important not only to maintain sustainable coastal cities and habitats but also to interpret the information contained in the stratigraphic record while tectonic steering in alluvial environments has been investigated similar studies in fluviodeltaic environments are limited to physical experiments and field observations we perform numerical experiments with a parcel based cellular model to analyze the deltaic surface and subsurface responses to regional subsidence we quantify model results using robust metrics and show that while sediment partitioning and shoreline pattern vary gradually with increasing subsidence rate channel mobility and stratigraphic connectivity of channel deposits show a threshold transition conditions for this transition are captured with a dimensionless filling index defined as the ratio between the rates of accommodation creation and sediment supply a channel locking mechanism activates when exceeds 0 6 and is responsible for the threshold transition

normal mode and free air gravity constraints on lateral variations in velocity and density of earth s mantle with the use of a large collection of free oscillation data and additional constraints imposed by the free air gravity anomaly lateral variations in shear velocity compressional velocity and density within the mantle dynamic topography on the free surface and topography on the 660 km discontinuity and the core mantle boundary were determined the velocity models are consistent with existing models based on travel time and waveform inversions in the lowermost mantle near the core mantle boundary denser than average material is found beneath regions of upwellings centered on the pacific ocean and africa that are characterized by slow shear velocities these anomalies suggest the existence of compositional heterogeneity near the core mantle boundary

delamination in collisional orogens thermomechanical modeling 1 modes of mantle delamination in collision zones are discussed in the light of 2d numerical modeling freely evolving thermomechanical models take into account phase changes in the mantle and melting in the crust distinct modes are identified in which orogens undergo mantle delamination concurrently or after collision delamination propagates along the moho of the subducted plate together with the retreating trench provided that slab pull is sufficient and that the meta stability of the crust lithospheric mantle interface is overcome topography is an instantaneous response to delamination and migrates with the focused and localized separation between crust and lithospheric mantle delamination front early exhumation of high pressure rocks is followed by exhumation of high temperature partially molten rocks convective stabilization of delamination outlasts slab break offs and impedes renewed build up of mechanically strong lithospheric mantle by static cooling parameter studies investigate the sensitivity of delamination to the age of the subducted oceanic plate the collision rate the mantle rheology and explore the effects of melting and sedimentation mantle flow patterns that form around delamination and subduction are sensitive to and often limited by the semi permeable 670 km spinel perovskite transition demonstrating that phase changes are essential factors delamination may account for the formation of complex boundary zones between continents such as between africa and europe in the mediterranean where transient compression and extension the lack of mantle lithosphere and the exhumation of high grade metamorphic core complexes are features also obtained in our modeling results

current subsidence rates due to compaction of holocene sediments in southern louisiana 1 relative contributions of geologic and anthropogenic processes to subsidence of southern louisiana are vigorously debated of these shallow sediment compaction is often considered dominant although this has never been directly observed or effectively demonstrated quantitative understanding of subsidence is important for predicting relative sea level rise storm surge flooding due to hurricanes and for successful wetland restoration despite many shallow borings few appropriate stratigraphic and geotechnical data are available for site specific calculations we overcome this by determining present compaction rates from monte carlo simulations of the incremental sedimentation and compaction of stratigraphies typical of the holocene of southern louisiana this approach generates distributions of present compaction rates that are not expected to exceed 5 mm yr but may locally locations with present subsidence rates greater than the predicted maximum probable shallow compaction rates are likely influenced by additional processes

compaction of holocene strata and the implications for relative sealevel change on the east coast of england the contribution of compaction of holocene strata to sea level rise shoreline erosion and wetland loss is difficult to decipher because of a lack of long term empirical data we analyzed more than 360 radiocarbon dated index points to constrain relative sea levels along the east coast of england during the holocene and to provide estimates of sediment compaction the isostatic effect of glacial rebound explains regional scale differences in relative sea levels northeast england the most northern study area reveals a middle to late holocene highstand 1 m above present ca 3 4 kyr b p whereas the tees estuary humber estuary lincolnshire marshes fenlands and north norfolk each reveal sea level histories of an upward trend during the holocene within each area sediment compaction explains the variation in elevation between sealevel reconstructions derived from index points taken from basal peat and those from peat intercalated within thick sequences of holocene sediments we find average compaction rates of 0 4 0 3 mm yr 1 with higher values for the large estuaries rates of late holocene relative sea level changes calculated from basal peats range from 0 2 0 1 mm yr 1 i e sea level fall in northeast england to 0 8 0 1 mm yr 1 in north norfolk inclusion of intercalated index points overestimates late holocene rates by 0 1 0 4 mm yr 1 because of the effects of sediment compaction

the impact of reservoir scale on amplitude variation with offset to investigate the vertical and horizontal impact of reservoir scale on the amplitudeversus offset characteristics we conduct seismic numerical simulations on models containing spatially confined lithologic units with different scales we find that the reservoir scale has a nonlinear effect on the amplitude versus offset intercepts and gradients as the reservoir width increases amplitude versus offset intercept and gradient both first increase then decrease and finally remain stable the amplitudeversus offset intercept is maximum when the reservoir width is 80 larger than the fresnel zone radius whereas the amplitude versus offset gradient peaks at 1 5 times the fresnel zone radius both amplitude versus offset intercept and gradient are approximately proportional to the reservoir width prior to reaching their maxima when the lateral extent of the reservoir is more than three times the fresnel zone radius the amplitude versus offset attributes are constant modelling the reservoir thickness shows that intercept and gradient behave in a manner similar to that of tuning of thin beds both the amplitude versus offset intercept and gradient first increase and then decrease with the thickness peaking at the tuning thickness the thickness contribution to amplitude versus offset variations is negligible when the thickness is larger than 1 6 times of the tuning thickness considering the magnitude of the changes in amplitude versus offset intercept and gradient caused by reservoir scale the width causes a maximum 433 intercept increase and a 344 gradient increase whereas the thickness causes a maximum 100 intercept increase and a 73 gradient increase cross plotting the amplitude versus offset intercept and gradient shows the reservoir scale change gives rise to an anti clockwise spiraling effect in conclusion the lateral and vertical extents of the reservoir both play an important role in amplitude variation with offset our analysis shows that the lateral reservoir extent has a larger impact on the amplitude variation with offset than the vertical tuning effect

seismological evidence for thermo chemical heterogeneity in earth s continental mantle abstract earth s thermo chemical structure exerts a fundamental control on mantle convection plate tectonics and surface volcanism there are indications that mantle convection occurs as an intermittent stage process between layered and whole mantle convection in interaction with a compositional stratification at 660 km depth however the presence and possible role of any compositional layering in the mantle remains to be ascertained and understood by interfacing inversion of a novel global seismic data set with petrologic phase equilibrium calculations we show that a compositional boundary is not required to explain short and long period seismic data sensitive to the upper mantle and transition zone beneath stable continental regions yet radial enrichment in basaltic material reproduces part of the complexity present in the data recorded near subduction zones and volcanically active regions our findings further indicate that 1 cratonic regions are characterized by low mantle potential temperatures and significant lateral variability in mantle composition and 2 chemical equilibration seems more difficult to achieve beneath stable cratonic regions these findings suggest that the lithologic integrity of the subducted basalt and harzburgite may be better preserved for geologically significant times underneath cratonic regions

seismic characterization of a carbonate reservoir in tarim basin abstractseismic characterization of carbonate reservoirs is a challenging task for geophysicists because of their special depositional environment and complex interior structures we developed a case study of the seismic characterization of a karstified carbonate reservoir in the tarim basin western china the characterization procedure is sequential and includes fault and fracture detection seismic facies classification seismic impedance inversion and lithofacies classification we presented a dip steered coherence algorithm for detecting faults and karst fractures in the carbonate reservoir incorporating the dip information improves the performance and robustness we applied normalized seismic segments rather than the amplitude values as the input to seismic facies classification so as to reduce the impact of strong amplitudes such as karst fractures and to enable the analysis of weak amplitudes in the background strata for the impedance inversion we adopted a fourier integral method for fas

shallow landslides in deeply weathered slates of the sierra de collcerola catalonian coastal range spain abstract stability conditions in an area located nw of barcelona spain are discussed here several mass movements were observed mainly affecting weathered paleozoic slates many of these failures involved slopes cut along recent infrastructures debris flows wedge and plane failures generally surficial occurred more frequently after a detailed geological and geomorphologic survey geomechanic characterization was carried out according to rmr and smr classifications this rating gave a prediction of slope behaviour in fairly good agreement with the real observed one stability numerical analysis was carried out for the main cut slopes based upon the limit equilibrium method first of all the deterministic factor of safety was computed using the mean values of parameters after that a simulation technique based upon the monte carlo method was applied in order to obtain factor of safety distributions the probability of failure was estimated as p f finally results from deterministic and probabilistic approaches were compared the effectiveness of different possible remedial measures was highlighted by means of a sensitivity analysis which showed that the more important parameters in the study area are the geometrical ones height slope and failure plane angles the final technical solutions adopted are briefly outlined

physical modeling of overburden effects reservoir properties can be inferred from the amount of anisotropy estimated from seismic data unfortunately irregularities in the formations above the reservoir unit can mask or overprint the true seismic anisotropy of the reservoir unit this overburden effect subjects the measured reservoir seismic anisotropy to a high degree of uncertainty we investigate this overburden effect on p waves with a three layer ultrasonic laboratory scale model whose middle layer contains localized gas filled vertical fractures we analyze the reflection amplitudes and traveltimes of a p wave reflection event from below the overburden to understand the overburden effect on anisotropy analysis and imaging our study shows that steps must be taken to reduce the p wave overburden effect when significant irregularities occur in the formations above the reservoir unit

basaltic accumulation instability and chaotic plate motion in the earliest mantle inferred from numerical experiments 1 a series of self consistent numerical models of mantle convection with magmatism and moving plates are presented to clarify the dynamics of the strongly heated mantle of the earliest earth broad hot accumulations of subducted basaltic crusts develop on the core mantle boundary and remain there for geologic time only when the internal heating rate is below a threshold above the threshold the basaltic accumulations become unstable instead the thermal buoyancy induced by the strong internal heating repeatedly causes a massive upwelling or burst of hot materials from deep mantle the mantle burst induces vigorous magmatic activity on the surface the magmatic activity in turn damages the lithosphere and disintegrates it into smaller fragments in contrast to the well ordered plate motion observed below the threshold the lithospheric fragments chaotically move and new subduction zones sporadically develop the mantle burst and chaotic motion of lithospheric fragments effectively stir the mantle and the mantle remains chemically rather homogeneous in spite of the chemical differentiation due to the vigorous magmatism the earth s mantle convection has probably changed its regime from one dominated by frequent mantle bursts and chaotic motion of lithospheric fragments to one dominated by stable basaltic accumulations and well ordered plate motion as the internal heat source decays the suggested regime transition fits in with the earth s tectonic evolution inferred from geologic observations of the continents of various ages

evidence of regional subsidence and associated interior wetland loss induced by hydrocarbon production gulf coast region usa analysis of remote images elevation surveys stratigraphic cross sections and hydrocarbon production data demonstrates that extensive areas of wetland loss in the northern gulf coast region of the united states were associated with large volume fluid production from mature petroleum fields interior wetland losses at many sites in coastal louisiana and texas are attributed largely to accelerated land subsidence and fault reactivation induced by decreased reservoir pressures as a result of rapid or prolonged extraction of gas oil and associated brines evidence that moderately deep hydrocarbon production has induced land surface subsidence and reactivated faults that intersect the surface include 1 close temporal and spatial correlation of fluid production with surficial changes including rapid subsidence of wetland sediments near producing fields 2 measurable offsets of shallow strata across the zones of wetland loss 3 large reductions in subsurface pressures where subsidence rates are high 4 coincidence of orientation and direction of displacement between surface fault traces and faults that bound the reservoirs and 5 accelerated subsidence rates near producing fields compared to subsidence rates in surrounding areas or compared to geological rates of subsidence based on historical trends subsidence rates in the gulf coast region near producing fields most likely will decrease in the future because most petroleum fields are nearly depleted alternatively continued extraction of conventional energy resources as well as potential production of alternative energy resources geopressured geothermal fluids in the gulf coast region could increase subsidence and land losses and also contribute to inundation of areas of higher elevation

geomorphology survive or subside deltas are among the most valuable coastal ecosystems but they are very dynamic and the factors that influence their health are complex the rate of compaction of underlying sediments might be a more significant factor than was thought

a new gis approach for reconstructing and mapping dynamic late holocene coastal plain palaeogeography the geomorphological development of holocene coastal plains around the world has been studied since the beginning of the twentieth century from various disciplines resulting in large amounts of data however the overwhelming quantities and heterogeneous nature of this data have caused the divided knowledge to remain inconsistent and fragmented to keep improving the understanding of coastal plain geomorphology and geology cataloguing of data and integration of knowledge are essential in this paper we present a gis that incorporates the accumulated data of the netherlands coastal plain and functions as a storage and integration tool for coastal plain mapped data the gis stores redigitised architectural elements beach barriers tidal channels intertidal flats supratidal flats and coastal fresh water peat from earlier mappings in separate map layers a coupled catalogue style database stores the dating information of these elements besides references to source studies and annotations regarding changed insights using scripts the system automatically establishes palaeogeographical maps for any chosen moment combining the above mapping and dating information in our approach we strip the information to architectural element level and we separate mapping from dating information serving the automatic generation of time slice maps it enables a workflow in which the maker can iteratively regenerate maps which speeds up fine tuning and thus the quality of palaeogeographical reconstruction the gis currently covers the late holocene coastal plain development of the netherlands this period witnessed widespread renewed flooding along the southern north sea coast coinciding with large scale reclamation and human occupation our gis method is generic and can be expanded and adapted to allow faster integrated processing of growing amounts of data for many coastal areas and other large urbanising lowlands around the world it allows maintaining actual data overview and facilitates new ways of analysis at national regional and local scales 2016 elsevier b v

tectonic control of subsidence and southward displacement of southeast louisiana with respect to stable north america 1 gps data collected between 1995 and 2006 suggest that southeast louisiana including new orleans and the larger mississippi delta are both subsiding vertically and moving southward with respect to stable north america both motions are likely related due to their common tectonic setting subsidence in the new orleans area occurs in part because it is located in the hanging wall of a large listric normal fault system that forms the northern boundary of a 7 10 km thick allochthon that is detached from stable north america southward motion of this allochthon relative to stable north america occurs at 2 2 0 6 mm yr the average subsidence rate for gps sites located on the allochthon is 5 2 0 9 mm yr relative to earth s center of mass or 7 mm yr relative to mean sea level motion of the allochthon is likely due to the gravity instability created by rapid holocene sediment deposition in the delta following continental glacial retreat and is facilitated at depth by weak salt horizons because new orleans and other communities of southeastern louisiana lie atop this active allochthon future motion of this body should be considered during rebuilding of the region following hurricanes katrina and rita

mississippi delta subsidence primarily caused by compaction of holocene strata coastal subsidence causes sea level rise shoreline erosion and wetland loss which poses a threat to coastal populations this is especially evident in the mississippi delta in the southern united states which was devastated by hurricane katrina in 2005 the loss of protective wetlands is considered a critical factor in the extensive flood damage the causes of subsidence in coastal louisiana attributed to factors as diverse as shallow compaction and deep crustal processes remain controversial current estimates of subsidence rates vary by several orders of magnitude here we use a series of radiocarbon dated sediment cores from the mississippi delta to analyse late holocene deposits and assess compaction rates we find that millennial scale compaction rates primarily associated with peat can reach 5mm per year values that exceed recent model predictions locally and on timescales of decades to centuries rates are likely to be 10 mm or more per year we conclude that compaction of holocene strata contributes significantly to the exceptionally high rates of relative sea level rise and coastal wetland loss in the mississippi delta and is likely to cause subsidence in other organic rich and often densely populated coastal plains

modern day tectonic subsidence in coastal louisiana subsidence is leading to the slow inundation of communities and wetlands of louisiana mississippi texas and alabama united states by the gulf of mexico the prevailing paradigm considers subsidence to be the result of young sediment compaction and or consolidation and human activities this paper describes the results of a test of this theory based on an examination of historic motions of benchmark in the michoud area of orleans parish louisiana this methodology allowed for an assessment of vertical change at different levels over time relative to a precise vertical datum north american vertical datum of 1988 navd88 data do not support the current theory on the origins of subsidence they demonstrate that tectonic causes dominate in the study area during 1969 1971 and 1971 1977 tectonism was responsible for 16 9 mm yr and 7 1 mm yr of subsidence respectively these contributions account for 73 and 50 of the total subsidence during these intervals the change in deep subsidence is attributed to renewed motion along a large normal fault michoud fault over the same time intervals intermediate depth subsidence due to compaction of pleistocene to middle miocene strata was constant 4 6 mm yr similarly subsidence due to shallow processes i e sediment compaction and groundwater offtake was 1 5 mm yr and 2 5 mm yr subsidence associated with petroleum extraction was not a factor due to the lack of local production

characterizing seismic bright spots in deeply buried ordovician paleokarst strata central tabei uplift tarim basin western china anomalous seismic amplitude bright spots are a common feature in deeply buried 5500 to 6500 m ordovician limestone strata in the central tabei uplift area of the tarim basin in northwest china those anomalies have proven to be useful indicators of reservoir quality the bright spots as seen on seismic data are tied to high gamma ray low velocity zones in wireline logs and correspond to clastic cave sediment fills in the host limestone in core synthetic seismic models confirm this relationship between seismic bright spots and cave sediment fills a seismic traveltime map of the top ordovician unconformity illustrates erosional topography and seismic geomorphologic patterns associated with the unconformity with numerous sinuous fluvial channels and canyons fluvial valleys sinkholes and tower karsts and hills a mature surface drainage system interacted with a near surface karst system and allowed terrigenous sediments to enter an underground cave system karst related bright spots probably correspo

development of texture and seismic anisotropy during the onset of subduction 1 how reliable are shear wave splitting measurements as a means of determining mantle flow direction this remains a topic of debate especially in the context of subduction the answer hinges on whether our current understanding of mineral physics provides enough to accurately translate between seismic observations and mantle deformation here we present an integrated model to simulate strain history dependent texture development and estimate resulting shear wave splitting in subduction environments we do this for a mantle flow model that in its geometry approximates the double sided molucca sea subduction system in eastern indonesia we test a single sided and a double sided subduction case results are compared to recent splitting measurements of this region by di leo et al 2012a the setting lends itself as a case study because it is fairly young and therefore early textures from the slab s descent from the near surface to the bottom of the mantle transition zone which we simulate in our models have not yet been overprinted by subsequent continuous steady state flow second it allows us to test the significance of the double sided geometry i e the need for a rear barrier to achieve trench parallel subslab mantle flow we demonstrate that although a barrier amplifies trench parallel subslab anisotropy due to mantle flow it is not necessary to produce trench parallel fast directions per se in a simple model of a type olivine lattice preferred orientation and one sided subduction trench parallel fast directions are produced by a combination of simple shear and extension through compression and pure shear in the subslab mantle

human induced discharge diversion in a tropical delta and its environmental implications the patia river colombia summary the patia river the number one in terms of sediment yield 1500 t km 2 yr 1 draining the western south america has the most extensive and well developed delta on the pacific coast measuring 1700 km 2 during the holocene nature forced the patia delta to the south however a major water diversion starting in 1972 diverted the patia flow to the sanguianga river the latter a small stream draining internal lakes from the pacific lowlands this human induced discharge diversion shifted the active delta plain back to the north and changed the northern estuarine system into an active delta plain overall major environmental consequences of this discharge diversion in terms of morphological changes along the delta coast and distributary channels are evidenced by 1 coastal retreat along the abandoned delta lobe 63 of the southern shoreline is retreating at maximum rates of 7 m yr 1 with a corresponding coastal land loss of 106 m yr 1 2 transgressive barrier islands with exposed peat soils in the surf zone 3 abandonment of former active distributaries in the southern delta plain with associated closing of inlets and formation of ebb tidal deltas 4 breaching events on barrier islands and 5 distributary channel accretion in the northern delta plain by morphological processes such as sedimentation also in crevasses overbank flow increasing width of levees interdistributary channel fill and colonization of pioneer mangrove the sanguianga mangrove national park smnp the largest mangrove reserve in colombia measuring 800 km 2 lies in this former estuary where major hydrologic and sedimentation changes are occurring observed environmental changes in the smnp include 1 seaward advance of the sub aqueous delta front at the sanquianga inlet evidenced by an increase in tidal flat area from 5 4 mm 2 in 1986 to 14 mm 2 in 2001 2 freshening conditions in the sanguianga distributary channel a hydrologic change that has shifted the upper estuarine region salinity 1 for the 1984 2006 yr period after the devastating tsunami of 1979 in the patia catchment erosion rates have been more pronounced during the 1970 1980 and 1990 2000 decades as a result of land degradation and deforestation preliminary results indicate that relative resent anthropogenic influences on the patia river drainage basin have altered the deltaic environment and beyond significantly

avo as a fluid indicator a physical modeling study information on time lapse changes in seismic amplitude variation with offset avo from a reservoir can be used to optimize production we designed a scaled physical model experiment to study the avo response of mixtures of brine oil and carbon dioxide at pressures of 0 1 03 and 2 07 mpa the small changes in density and velocity for each fluid because of increasing pressure were not detectable and were assumed to lie within the error of the experiment however avo analysis was able to detect changes in the elastic properties between fluids that contained oil and those that did not when the avo response was plotted in the avo intercept gradient domain fluids containing oil were clearly separated from fluids not containing oil this was observed in the avo response from both the top and base of the fluids in the physical model we then compared the measured avo response with the theoretical avo response given by the zoeppritz equations the measured and theoretical avo intercept responses for the t

geological impacts on coastal wetland landscapes some general effects of sediment autocompaction in the holocene of northwest europe a simulation model is described providing general insights into autocompaction effects in stratigraphic sequences formed on coastal mudflats and marshes over uneven basements lithological units and buried landscapes are progressively displaced and distorted the synthetic sequences resembling bedding geometries described from the northwest european holocene autocompaction also promotes local deposition rates that may greatly exceed the rates at which accommodation space is created transgressive silts are associated with especially large deposition rates because of the high compressibility of underlying peats the experimental relationships between apparent rates of sea level rise and bed thickness resemble empirical trends for the holocene the latter are however reinforced by an intrinsic lithology related effect not included in the model

degradation of the plaquemines sub delta and relative sea level in eastern mississippi deltaic coast during late holocene abstract the stratigraphic architecture of plaquemines sub delta lobe is identified from sedimentary cores and sub bottom seismic data collected at lower breton sound louisiana usa four lithofacies were identified in cores from bottom to top 1 organic poor mud 2 organic poor silty sand 3 massive mud 4 organic rich peat and root rich soft mud overall the lithofacies displays a typical progradational deltaic deposit at bottom with upward coarsening feature and then an upward fining deposit overlying on top stratigraphic position of the organic rich peat facies indicates that it is formed after the fluvial sediment source moves away from this region and it is recognized as a termination of progradation of the plaquemines sub delta dated peat samples show that sub delta progradation stops between 876 and 1384 yr ad during which a 20 70 cm relative sea level rise is detected the geological framework reported in this study provides critical information for future modeling on river diversions the stratigraphic architecture underlying lower breton sound implicates that top three facies of root rich soft mud organic rich peat and massive mud are likely to be eroded away before the development of new crevasse splay or sub delta when sediment diversion is in operation the deeper organic poor silty sand lithofacies however can serve as a firm foundation to build new land

space geodesy subsidence and flooding in new orleans a subsidence map of the city offers insight into the failure of the levees during hurricane katrina

deformation and mantle flow beneath the sangihe subduction zone from seismic anisotropy abstract subduction of oceanic lithosphere is the most direct feedback between the earth s surface and deep interior however the detail of its interaction with the broader convecting mantle is still unclear mantle flow around subduction zones can be constrained using seismic anisotropy but despite many such studies a simple global picture is lacking the sangihe subduction zone where the molucca sea microplate is subducting westward beneath the eurasian plate is part of the tectonically complex sulawesi philippine region and an ideal natural laboratory to study complex subduction processes we investigate the anisotropic structure of the sangihe subduction zone with shear wave splitting measurements of local s and sks phases at two stations mni in sulawesi dav in the philippines as well as downgoing s phases at five stations at teleseismic distances combining different phases allows a better vertical resolution of anisotropic fabrics than is possible with a single phase the broad depth distribution of local events 60 630 km allows us to observe a change in splitting behaviour at 380 km depth above fast directions are trench parallel and delay times t are 0 34 0 53 s with no increase with depth we suggest this anisotropy is caused by aligned cracks possibly melt filled beneath the volcanic arc and fossil anisotropy in the overriding plate below 380 km is predominantly trench normal and t are slightly higher 0 53 0 65 s as no correlation is observed with inferred distance travelled inside the slab we attribute this anisotropy to shear layers atop the slab which are coherent from 200 to 400 km depth and perhaps extend into the transition zone sks and source side measurements show larger t 1 53 and 1 33 s respectively and trench parallel since these phases predominantly sample sub slab mantle we consider along strike lateral flow associated with the double sided subduction of the molucca sea microplate to be the most likely explanation we thus infer three dominant regions of anisotropy at the sangihe subduction zone one within the overriding lithosphere one along the slab wedge interface and one below the subducting molucca sea slab the mantle wedge above 200 km depth and the slab itself do not seem to contribute notably to the measured anisotropy this study demonstrates the insight seismic anisotropy can provide into mantle dynamics even in tectonically complex subduction systems

a review of sediment diversion in the mississippi river deltaic plain abstract one of the proposed methods for restoring the disappearing mississippi delta is sediment diversion which uses channels and structures to divert water and sediment from the mississippi and atchafalaya rivers into adjacent basins this study presents a comprehensive review of geological and physical aspects of sediment dynamics in the mississippi river deltaic plain mrdp with special reference to diversion studies over the past two decades we synthesize these studies present the current understanding of sediment diversions in the context of sediment dynamics identify multiple key knowledge gaps and make recommendations for future studies to maximize net land building in the mrdp management strategies should be focused on a enhancing river sediment delivery both mud and sand b increasing sediment retention in receiving basins and c minimizing erosion in bays and estuaries compared with extensive studies of land building there have been relatively fewer studies of erosional processes a heterogeneous coastal geological framework cohesive sediment erodibility and subsidence together play complicated yet critical roles in future sediment dynamics in bays and estuaries of the mrdp sediment retention rates are highly sensitive to spatial and temporal scales types of sediments and delivery season sediment diversions to seaward receiving basins provide more surge protection but tend to have lower sediment retention due to active coastal processes structures and devices that improve sediment retention trap sediments dissipate waves and build living shorelines should be explored and cost to benefit analysis is needed long term planning should consider more landward diversions strategic community relocation and nonlinear response of the complex sedimentary system of the mrdp

decoding the origins of vertical land motions observed today at coasts in recent decades geodetic techniques have allowed detecting vertical land motions and sea level changes of a few millimetres per year based on measurements taken at the coast tide gauges on board of satellite platforms satellite altimetry or both global navigation satellite system here contemporary vertical land motions are analysed from january 1993 to july 2013 at 849 globally distributed coastal sites the vertical displacement of the coastal platform due to surface mass changes is modelled using elastic and viscoelastic green s functions special attention is paid to the effects of glacial isostatic adjustment induced by past and present day ice melting various rheological and loading parameters are explored to provide a set of scenarios that could explain the coastal observations of vertical land motions globally in well instrumented regions predicted vertical land motions explain more than 80 per cent of the variance observed at scales larger than a few hundred kilometres residual vertical land motions show a strong local variability especially in the vicinity of plate boundaries due to the earthquake cycle significant residual signals are also observed at scales of a few hundred kilometres over nine well instrumented regions forming observation windows on unmodelled geophysical processes this study highlights the potential of our multitechnique database to detect geodynamical processes driven by anthropogenic influence surface mass changes surface loading and glacial isostatic adjustment and tectonic activity including the earthquake cycle sediment and volcanic loading as well as regional tectonic constraints future improvements should be aimed at densifying the instrumental network and at investigating more thoroughly the uncertainties associated with glacial isostatic adjustment models

factors controlling peat compaction in alluvial floodplains a case study in the cold temperate cumberland marshes canada abstract subsidence due to peat compaction may have important implications in alluvial floodplains because it leads to wetland loss land inundation and damage to buildings and infrastructure furthermore it potentially influences spatial and temporal river sedimentation patterns and hence the evolution of alluvial floodplains as the vast majority of peatlands occur in cold temperate regions alluvial plains situated in such areas are most susceptible to these implications to determine which locations within alluvial floodplains are most vulnerable to high amounts of compaction induced subsidence it is necessary to quantify compaction and to identify which factors influence the amount and rate of peat compaction for this we carried out field work in the cumberland marshes east central saskatchewan canada guided by the following two questions 1 how much peat compaction has occurred over the past decades to centuries and 2 which factors control the amount and rate of peat compaction at the same timescale to address these questions we used methods involving construction of stratigraphic cross sections organic matter content and bulk density measurements and radiocarbon dating a new sampling device was devised to sample uncompacted peat in the field results show that peat layers have compacted up to 43 within a few centuries with compaction rates of up to 6 08 mm yr the dominant factors influencing peat compaction are 1 organic matter content 2 stress imposed on a peat layer and to a lesser extent 3 plant species composition in an alluvial setting crevasse splays and natural levees are sites that are most susceptible to high amounts of peat compaction at short timescales 100 102 years sheet like splay deposits initially compact underlying peat uniformly whereas differential compaction commonly occurs beneath natural levees due to lateral variations in sediment thickness subsidence due to peat compaction creates additional accommodation space and hence locally enhances floodplain sedimentation rates

holocene sea level database from the atlantic coast of europe abstract high quality relative sea level rsl data reveal spatial and temporal variations in crustal movements during the holocene which are used for many applications ranging from calibrating models of earth rheology and ice sheet reconstructions to the development of coastal lowlands and human occupation here we present a holocene rsl database for the atlantic coast of europe ace and estimate rates of rsl change from the ace database using a spatio temporal empirical hierarchical model the database contains 214 index points which locate the rsl position in space and time and 126 limiting dates which constrain rsl to above or below a certain elevation at a specific point in time the temporal distribution extends from present to 11 5 ka with only 42 index points older than 7 ka the spatial distribution spans 1700 km from french flanders france to algarve portugal with more than half of the index points concentrated along the french coast the ace database shows rsl was below present during the holocene rates of rsl change were highest during the early holocene ranging between 6 8 0 5 mm yr 1 in middle portugal and 6 3 0 8 mm yr 1 in southern france from 10 to 7 ka mid to late holocene rates decreased over time with rates ranging between 0 9 0 4 mm yr 1 in middle france and 0 1 0 5 mm yr 1 in middle portugal from 4 ka to present comparison of the rsl data to output from a glacial isostatic adjustment model suggests that deglaciation of the british irish and fennoscandian ice sheets dominates the large scale variability captured by the ace database which reflects a decreasing influence of the collapsing british irish and fennoscandian peripheral forebulge that migrated from the northeast to the northwest after 4 ka

studying heterogeneity and anisotropy via numerical and physical modeling palaeozoic carbonate rocks are widely distributed in china the storage spaces of these carbonate reservoirs are mainly secondary and include dissolution caves holes and fractures the original porosity is less than 1 in most formations hydrocarbon distribution is controlled by the systems of fractures and caves which have a quasi layered shape the reservoir media are heterogeneous caves and holes and have varying degrees of anisotropy degree fractures so it is important to evaluate the heterogeneity and to check the accuracy of anisotropy inversion

delta changes in the pearl river estuary and its response to human activities 1954 2008 abstract this paper is concerned with delta evolution in response to human activities in the pearl river estuary utilizing more than 50 years data bathymetric data together with simulation fluvial discharge data the net accretion rate in the lingdingyang subaqueous delta decreased from 16 6 mm y over the period 1955 1964 to 1 6 mm y for the period 1998 2008 because there was a dramatic downward trend in the sediment load in particular the closure of the longtan dam ltd in 2006 resulted in the sediment load entering the pearl river falling from 75 mt y annual average 1954 2006 to 25 2 mt y a decrease of 67 another reason may be sand mining in the lingdingyang estuary based on the linear relationship between sediment load and accumulation rate an annual average sediment load of 21 7 mt y carried into the lingdingyang estuary is the critical threshold value that separates delta progradation from recession however the outer subaqueous delta in the modaomen estuary underwent deposition in the same period because there is no obvious change in sediment load into the area during 1954 2008 in the coming decades ongoing human interferences will reduce the fluvial sediment load entering the sea which probably will result in a phase of general delta recession replacing delta progradation

subducting slabs stagnant in the mantle transition zone the p wave velocity structure beneath the western pacific is found from the international seismological center first arrival data special attention was paid to the deep structure beneath the wadati benioff zone we discretized the whole mantle into blocks with finer blocks in the region of interest to obtain the velocities of all the blocks this way of discretization minimizes a problem with tomographic studies of regional scale difficulty in making corrections for the effects outside the region of interest our solution is iterative with the alternate step of the relocation of earthquakes using the whole mantle model of inoue et al 1990 as a starting model a first order smoothness constraint was imposed to suppress the possible fluctuation of the solution around the initial model the essential result depends little on whether the reference spherical model is smooth or discontinuous near 400 and 670 km depths we examined the resolution by calculating the resolving kernels for selected blocks and by reconstructing the checkerboard test patterns of velocity perturbation and the test structures of subducting lithosphere the resolution is depth dependent but in general good enough to see the slab configuration beneath the southern kurile japan izu bonin arcs and the java arc it is relatively poor beneath the northern kurile and mariana arcs the seismic image of subducting slab beneath the southern kurile to bonin arcs bends to subhorizontal near the leading edge of the wadati benioff zone and extends continentward over a distance of more than 1000 km the subhorizontal portion of the slab connects a high velocity blob to the bottom that reaches a depth of at least 800 km across the 670 km discontinuity under the japan arc although the image of the java slab directly penetrates the 670 km discontinuity it then bends to a shallow dip with a considerable spread reaching a depth of about 1200 km these results suggest that descending slabs of lithosphere in the western pacific tend to be stagnant in the transition zone under a subtle control of the 670 km discontinuity although stagnant slab materials eventually descend into the lower mantle they no longer maintain their original configuration below the 670 km discontinuity

origin and architecture of fractured cavernous carbonate reservoirs and their influences on seismic amplitudes ordovician carbonate is important for petroleum exploration and production in the tarim basin the matrix porosity of the carbonate reservoirs is usually less than 2 because of their age old sedimentary history and depth deeper than 5500 m the storage spaces are secondary dissolution pores and fractures which are dominated by visible dissolution caves holes and fractures zhou et al 2006 the reservoirs are therefore called fractured cavernous reservoirs good quality reservoir usually appears as a strong reflection called bead like reflection or br on poststack seismic sections and the corresponding reservoir is called a fracture cave body fcb which is the main drilling target of current e p in tarim basin the fcbs are unevenly distributed in carbonate strata and the storage spaces inside an fcb are also unevenly distributed therefore the reservoirs have both macroscopic and microscopic heterogeneities which bring great challenges to petroleum exploration

constraints on regional drivers of relative sea level change around cordova alaska abstract new records of paleoenvironmental change from two lakes near cordova south central alaska combined with analysis of previously reported sediment sequences from the adjacent copper river delta provide quantitative constraints on a range of earth system processes through their expression in relative sea level change basal sediment ages from upper whitshed lake indicate ice free conditions by at least 14 140 15 040 cal yr bp while upper and lower whitshed lakes provide only upper limits to relative sea level change interbedded layers of freshwater peat and intertidal silt extending more than 11 m below present sea level in copper river delta indicate net submergence over the last 6000 years and multiple earthquake deformation cycles in contrast lower whitshed lake situated just above present high tide level records only one episode of marine sedimentation commencing ad 1120 1500 that we interpret as the result of isostatic subsidence due to little ice age mass accumulation of the chugach mountain glaciers lower whitshed lake also records isostatic uplift at the end of the little ice age before the end of marine sedimentation caused by 1 5 m coseismic uplift in the great alaska earthquake of ad 1964 we successfully explain the records of relative sea level change from both copper river delta and the whitshed lakes by integrating the effects of eustatic sea level rise glacial isostasy earthquake deformation cycles sediment loading sediment compaction and late holocene changes in glacier mass into a single model this approach provides initial quantitative constraints on the individual contributions of these processes taking reasonable estimates of eustasy post last glacial maximum and neoglacial glacial isostatic adjustment and a simple earthquake deformation cycle we demonstrate that sediment loading and sediment compaction are both contributors to relative sea level rise at copper river delta together producing subsidence averaging approximately 1 2 mm yr 1 over the mid to late holocene further isolation basin studies have the potential to greatly improve our understanding of the individual contributions of these processes in this highly dynamic region

holocene sea level database for the atlantic coast of the united states we have constructed a database of holocene relative sea level rsl observations for the atlantic coast of the united states the database contains 492 index points which locate the position of rsl in time and space and 344 limiting dates which constrain the minimum or maximum limit of former sea level the majority of the index points in the database are from 6 ka bp to present with only 7 older than 6 ka bp spatially index points are distributed between maine and south carolina but there is an absence of data from georgia and the atlantic coast of florida the database is sub divided into 16 regions based on the distance from the former laurentide ice sheet and are classified depending upon their susceptibility to compaction the index points and limiting data demonstrate that rsl did not exceed present 0 m during the holocene except potentially in regions 1 and 2 eastern maine and southern maine rates of rsl change were highest during the early holocene and have decreased over time due to the diminishing response of the earth s mantle to glacial isostatic adjustment and reduction of ice equivalent meltwater input along the atlantic coast of the united states the linear rate of rsl rise prior to 4 ka bp ranged from 0 5 to 4 5 mm a 1 compared to 0 6 1 8 mm a 1 from 4 ka bp to ad 1900 the database suggests minimal 0 3 mm yr changes in these rates of rsl rise during the late holocene deglaciation of the laurentide ice sheet caused the spatial variability captured by the database the maximum rate of late holocene and ongoing rsl rise occurred in mid atlantic regions new jersey and inner delaware because of collapse of the peripheral forebulge

global climate changes recorded in coastal wetland sediments empirical observations linked to theoretical predictions 1 whether coastal areas are experiencing and responding to an accelerated rate of global sea level rise gslr is critically important for the 2 billion people living near earth s oceans accretion rates from a suite of physiographically diverse coastal wetlands surrounding long island ny accelerated during the 20th century at 2 3 0 2 10 2 mm yr 2 which is comparable to reported rates of gslr acceleration and global temperature changes wetlands varied in tidal range salinity and geomorphic setting and were located in embayments with limited human impacts in a region with limited and constant rates of subsidence from geochronologies with temporal resolutions of 2 5 yr we constructed new composite histories of sediment accretion and mineral deposition wetland dynamics are consistent with predictions from sedimentology and a numerical model of ecogeomorphic response suggesting that these systems and likely others worldwide are responding to accelerated gslr and related climatic changes

improving the resolution of impedance inversion in karst systems by incorporating diffraction information a case study of tarim basin chinaimpedance inversion with diffraction