an integrated hypothesis for regional patterns of shoreline change along the northern north carolina outer banks usa combining analyses of plan view shoreline change and shoreline curvature with existing nearshore geologic and bathymetric data and the results of a recent theoretical large scale shoreline evolution model that couples geologic framework to alongshore sediment transport we propose an integrated explanation for persistent patterns of shoreline change observed on the northern outer banks of north carolina usa concentrated sources of coarse grained sediment derived from relict fluvial stratigraphy or densely grouped relict inlet channels excavated from the shoreface may both enable persistence of nearshore bathymetric anomolies and control multi km scale undulations in shoreline curvature which in turn affect gradients in wave driven alongshore sediment transport that drive long term shoreline change

high angle wave instability and emergent shoreline shapes 2 wave climate analysis and comparisons to nature 1 recent research has revealed that the plan view evolution of a coast due to gradients in alongshore sediment transport is highly dependant upon the angles at which waves approach the shore giving rise to an instability in shoreline shape that can generate different types of naturally occurring coastal landforms including capes flying spits and alongshore sand waves this instability merely requires that alongshore sediment flux is maximized for a given deepwater wave angle a maximum that occurs between 35 and 50 for several common alongshore sediment transport formulae here we introduce metrics that sum over records of wave data to quantify the long term stability of wave climates and to investigate how wave climates change along a coast for long point a flying spit on the north shore of lake erie canada wave climate metrics suggest that unstable waves have shaped the spit and furthermore that smaller scale alongshore sand waves occur along the spit at the same locations where the wave climate becomes unstable a shoreline aligned along the trend of the carolina capes united states would be dominated by high angle waves numerical simulations driven by a comparable wave climate develop a similarly shaped cuspate coast local wave climates along these simulated capes and the carolina capes show similar trends shoreline reorientation and shadowing from neighboring capes causes most of the coast to experience locally stable wave climates despite regional instability

modeling large scale shoreline change caused by complex bathymetry in low angle wave climates abstract coastlines where waves consistently approach at highly oblique angles experience anti diffusional behavior causing perturbations to grow seaward and form sand waves capes and spits coasts where waves approach at low offshore angles experience the opposite perturbations diffuse and the coastline remains or becomes smooth in this paper by coupling a 2 d large scale coastline evolution model to a spectral wave model we show that anti diffusional behavior is also possible in low angle wave climates if the nearshore wave field is altered by complex bathymetry in model simulations low angle waves refract over local shoals creating a convergence in alongshore sediment flux behind the shoals that coalesces into small minor capes depending on wave height and period shoreline features take 80 400 years to reach an equilibrium cross shore relief of 1 1 5 km over an alongshore distance of 20 km the modeled equilibrium time scale is consistent with analytically determined characteristic shoreline diffusion time scales and the modeled cross shore relief and aspect ratio are similar to observed minor capes along the u s atlantic coast where offshore bathymetric anomalies have previously been linked to shoreline change patterns better understanding of the links among nearshore bathymetry wave transformation and alongshore sediment transport is critical to understanding shoreline change patterns at the local level and how they fit into broader regional scale behavior

regional seismic stratigraphy and controls on the quaternary evolution of the cape hatteras region of the atlantic passive margin usa abstract seismic and core data combined with amino acid racemization and strontium isotope age data enable the definition of the quaternary stratigraphic framework and recognition of geologic controls on the development of the modern coastal system of north carolina u s a seven regionally continuous high amplitude reflections are defined which bound six seismic stratigraphic units consisting of multiple regionally discontinuous depositional sequences and parasequence sets and enable an understanding of the evolution of this margin data reveal the progressive eastward progradation and aggradation of the quaternary shelf the early pleistocene inner shelf occurs at a depth of ca 20 40 m beneath the western part of the modern estuarine system pamlico sound a mid to outer shelf lowstand terrace also early pleistocene with shelf sand ridge deposits comprising parasequence sets within a transgressive systems tract occurs at a deeper level ca 45 70 m beneath the modern barrier island system the outer banks and northern pamlico sound seismic and foraminiferal paleoenvironmental data from cores indicate the occurrence of lowstand strandplain shoreline deposits on the early to middle pleistocene shelf middle to late pleistocene deposits occur above a prominent unconformity and marine flooding surface that truncates underlying units and contain numerous filled fluvial valleys that are incised into the early and middle pleistocene deposits the stratigraphic framework suggests margin progradation and aggradation modified by an increase in the magnitude of sea level fluctuations during the middle to late pleistocene expressed as falling stage lowstand transgressive and highstand systems tracts thick stratigraphic sequences occur within the middle pleistocene section suggesting the occurrence of high capacity fluvial point sources debouching into the area from the west and north furthermore the antecedent topography plays a significant role in the evolution of the geomorphology and stratigraphy of this marginal system

formation of coastline features by large scale instabilities induced by high angle waves along shore sediment transport that is driven by waves is generally assumed to smooth a coastline this assumption is valid for small angles between the wave crest lines and the shore as has been demonstrated in shoreline models but when the angle between the waves and the shoreline is sufficiently large small perturbations to a straight shoreline will grow here we use a numerical model to investigate the implications of this instability mechanism for large scale morphology over long timescales our simulations show growth of coastline perturbations that interact with each other to produce large scale features that resemble various kinds of natural landforms including the capes and cuspate forelands observed along the carolina coast of southeastern north america wind and wave data from this area support our hypothesis that such an instability mechanism could be responsible for the formation of shoreline features at spatial scales up to hundreds of kilometres and temporal scales up to millennia

large scale dynamics of sandy coastlines diffusivity and instability 1 the dynamics of small amplitude perturbations of an otherwise rectilinear coastline due to the wave driven alongshore sediment transport is examined at large time and length scales years and kilometers a linear stability analysis is performed by using an extended one line shoreline model with two main improvements 1 the curvature of the coastline features is accounted for and 2 the coastline features are assumed to extend offshore as a bathymetric perturbation up to a finite distance for high incidence angles instability is found in accordance with ashton et al 2001 however it is seen that instability is inhibited by high waves with long periods and gently sloping shorefaces so that in this case the coastline may be stable for any angle similarly there is no instability if the bathymetric perturbation is confined very close to the coast it is found that the traditional linearized one line model larson et al 1987 tends to overpredict the coastline diffusivity the overprediction is small for the conditions leading to a stable coastline and for moderate incidence angles but can be very dramatic for the conditions favoring instability an interesting finding is that high angle waves instability has a dominant wavelength at the linear regime which is in the order of 4 15 km one to two orders of magnitude larger than the length scale of surf zone rhythmic features intriguingly this is roughly the same range of the wavelength of some observed shoreline sand waves and in particular those observed along the dutch coast a model application to this coast is presented

non hydrostatic numerical modelling of nearshore wave transformation over shore oblique sandbars abstract observations from high resolution bathymetric surveys on the coast of north carolina indicate areas with shore parallel depth contours and other areas with shore oblique sandbars these shore oblique bars are large scale morphological features that extend up to 1000 m from shore and previous studies have shown that they are spatially correlated with higher shoreline change rates and induce erosional hotspots to investigate the influence the oblique sandbar morphology has on nearshore wave transformation and energy distribution a non hydrostatic wave model is used with the bathymetry corresponding to two areas with shore parallel depth contours and two areas with shore oblique sandbars the model is applied with a horizontal resolution of 5 m and a boundary condition representative of the directional spectrum of a typical southeast swell event an idealized approach with relatively short alongshore model domains and cyclic lateral boundary conditions is adopted due to limited availability of high resolution bathymetry however this approach elucidates the influence of shore oblique sandbars on the nearshore hydrodynamics the numerical results show that higher alongshore variability in depth due to the shore oblique bars drive large alongshore changes in cross shore wave energy flux and cause spatial variability in dissipation in the nearshore region the simulations indicate that alongshore variations in wave energy caused by the shore oblique bars results in a 50 75 reduction in wave setup and a 25 40 decrease in alongshore velocity averaged across the surf zone for the conditions investigated the results suggest that wave driven hydrodynamics can influence nearshore sediment dynamics to create erosional zones compared to areas with shore parallel bathymetric contours since the morphology of shore oblique sandbars are an important control on wave energy that impacts the beach

stress adjustment revealed by seismicity and earthquake focal mechanisms in northeast china before and after the 2011 tohoku oki earthquake abstract in order to understand the influence of the march 11 2011 m w 9 0 tohoku oki earthquake on regional scale seismicity we study the seismicity rate and focal mechanism solutions fmss of earthquakes in northeast china nec before and after the megathrust event broadband seismic waveforms from 270 permanent and temporary stations are used to invert for the moment tensors of 69 earthquakes between 2009 and 2013 in the nec our results show that there are distinct changes in seismicity rate on major nec faults before and after the 2011 tohoku oki event although the seismic moment rate of the whole region remains roughly constant in comparison to a wide distribution of earthquakes before the tohoku oki event fmss of crustal earthquakes in the nec after the megathrust event can be categorized into two groups strike slip events with e w compression and normal faulting events with n s extension stress field inversions before and after the tohoku oki event suggest that the variations in seismicity and fmss are due to a minor adjustment of regional stress state imposed by the megathrust event which is further confirmed by static coulomb stress change calculations mantle depth seismicity is also influenced by the megathrust event possibly via a down dip transfer of compressional stress along the subducting plate as manifested by the absence of moderate sized mantle depth earthquakes m w 4 5 between may 2011 and april 2013 and the occurrence of deep focus events with p axes along the dip direction of the subducting pacific plate in e w vertical cross sectional view and in wnw ese direction in map view

damped regional scale stress inversions methodology and examples for southern california and the coalinga aftershock sequence 1 we present a new focal mechanism stress inversion technique to produce regional scale models of stress orientation containing the minimum complexity necessary to fit the data current practice is to divide a region into small subareas and to independently fit a stress tensor to the focal mechanisms of each subarea this procedure may lead to apparent spatial variability that is actually an artifact of overfitting noisy data or nonuniquely fitting data that does not completely constrain the stress tensor to remove these artifacts while retaining any stress variations that are strongly required by the data we devise a damped inversion method to simultaneously invert for stress in all subareas while minimizing the difference in stress between adjacent subareas this method is conceptually similar to other geophysical inverse techniques that incorporate damping such as seismic tomography in checkerboard tests the damped inversion removes the stress rotation artifacts exhibited by an undamped inversion while resolving sharper true stress rotations than a simple smoothed model or a moving window inversion we show an example of a spatially damped stress field for southern california the methodology can also be used to study temporal stress changes and an example for the coalinga california aftershock sequence is shown we recommend use of the damped inversion technique for any study examining spatial or temporal variations in the stress field

seismic imaging crustal stress and gps data analyses implications for the generation of the 2008 wenchuan earthquake m7 9 china abstract seismic imaging together with global positioning system gps and crustal stress data analyses show that the mw7 9 2008 wenchuan earthquake occurred within a distinct area of high crustal stress 17 5 mpa and high poisson s ratio 7 10 anomalies centered on the longmen shan shan means mountain in chinese tectonic fault belt low p wave and s wave velocities in the southwest sw segment contrast with high velocity anomalies in the central portion cp and northeast ne segment within the uppermost 15 km depths along the tectonic fault belt though a presumably ductile zone with low velocity anomalies separates the cp and ne segment the rupture initiated near the southwestern end of the cp at a zone of high poisson s ratio which extends down into the lower crust these low velocity and high anomalies immediately below the source hypocenter together with the high crustal stress indicate the presence of high pressure fluids from the lower crust which might have reduced the mechanical strength of the fractured rock matrix and triggered the earthquake our study suggests that the structural heterogeneity and high crustal stress played an important role in the nucleation of the wenchuan earthquake and its rupture process

stress tensor changes related to fluid injection at the geysers geothermal field california 1 studying variations of the stress field in reservoirs caused by massive fluid injection is important toward an improved understanding of geomechanical processes involved we report on spatio temporal variations of the local stress tensor orientation at the geysers geothermal field california we apply two stress inversion methods with detailed uncertainty assessments using a selection of events recorded between 2007 and 2012 our results clearly indicate variations in the orientation of the principal stress axes for the reservoir as a whole showing a normal faulting regime at the reservoir depth between 2 and 3 7 km bounded by a strike slip regime above and below analyzing the temporal evolution of the stress tensor orientation for a prominent seismicity cluster we observe a clear correlation of changes in orientation for 1 3 with the highest injection rates these results suggest that temporal changes in the stress tensor orientation could contribute to characterize reservoirs during stimulation

high angle wave instability and emergent shoreline shapes 1 modeling of sand waves flying spits and capes 1 contrary to traditional findings the deepwater angle of wave approach strongly affects plan view coastal evolution giving rise to an antidiffusional high wave angle instability for sufficiently oblique deepwater waves with angles between wave crests and the shoreline trend larger than the value that maximizes alongshore sediment transport 45 a one contour line numerical model shows that a predominance of high angle waves can cause a shoreline to self organize into regular quasiperiodic shapes similar to those found along many natural coasts at scales ranging from kilometers to hundreds of kilometers the numerical model has been updated from a previous version to include a formulation for the widening of an overly thin barrier by the process of barrier overwash which is assumed to maintain a minimum barrier width systematic analysis shows that the wave climate determines the form of coastal response for nearly symmetric wave climates small net alongshore sediment transport cuspate coasts develop that exhibit increasing relative cross shore amplitude and pointier tips as the proportion of high angle waves is increased for asymmetrical wave climates shoreline features migrate in the downdrift direction either as subtle alongshore sand waves or as offshore extending flying spits depending on the proportion of high angle waves numerical analyses further show that the rate that the alongshore scale of model features increases through merging follows a diffusional temporal scale over several orders of magnitude a rate that is insensitive to the proportion of high angle waves the proportion of high angle waves determines the offshore versus alongshore aspect ratio of self organized shoreline undulations

late neogene and quaternary evolution of the northern albemarle embayment mid atlantic continental margin usa seismic surveys in the eastern albemarle sound adjacent tributaries and the inner continental shelf define the regional geologic framework and provide insight into the sedimentary evolution of the northern north carolina coastal system lithoand chronostratigraphic data are derived from eight drill sites on the outer banks barrier islands and the mobil 1 well in eastern albemarle sound within the study area parallel bedded gently dipping miocene beds occur at 95 to n160 m below sea level m bsl and are overlain by a southward thickening pliocene unit characterized by steeply inclined southward prograding beds the lower pliocene unit consists of three seismic sequences the 55 60 m thick quaternary section unconformably overlies the pliocene unit and consists of 18 seismic sequences exhibiting numerous incised channel fill facies shallow stratigraphy b40 m bsl is dominated by complex fill patterns within the incised paleo roanoke river valley radiocarbon and amino acid racemization aar ages indicate that the valley fill is latest pleistocene to holocene in age at least six distinct valley fill units are identified in the seismic data cores in the valley fill contain a 3 6 m thick basal fluvial channel deposit that is overlain by a 15 m thick unit of interlaminated muds and sands of brackish water origin that exhibit increasing marine influence upwards organic materials within the interlaminated deposits have ages of 13 11 cal ka the interlaminated deposits within the valley are overlain by several units that comprise shallow marine sediments bay mouth and shoreface environments that consist of silty fine to medium grained sands containing open neritic foraminifera suggesting that this area lacked a fronting barrier island system and was an open embayment from 10 ka to 4 5 ka seismic data show that initial infilling of the paleo roanoke river valley occurred from the north and west during the late pleistocene and early holocene later infilling

influence of the pre existing xiaoyudong salient in surface rupture distribution of the mw 7 9 wenchuan earthquake china abstract field investigations show that the wenchuan earthquake on the 12th of may 2008 ruptured two nw dipping imbricate reverse faults along the longmen shan fault zone the length of the beichuan yingxiu fault reaches nearly 240 km southeast of this fault a smaller displacement occurred along the guanxian jiangyou fault which has a length of about 70 km a nw striking left lateral reverse fault the xiaoyudong fault was clearly observed between these two main surface ruptures this co seismic surface rupture pattern is one of the most complicated patterns of recent great earthquakes in order to clarify how rupture progressed northward during the wenchuan earthquake we conducted a detailed investigation including rupture tracing displacement measurement fault kinematic estimation and stress analysis of the xiaoyudong area our results show that the xiaoyudong fault is not a simple tear fault in contrast it is an independent active fault located on the northern boundary of the xiaoyudong salient the xiaoyudong salient is an independent topographic highland occupying a surface area of approximately 100 km2 from a stratigraphic point of view this highland is a little older than the adjacent area the s shape stream north of the xiaoyudong salient indicates that the xiaoyudong fault is still active the xiaoyudong salient plays an important role in controlling fault propagation and stress delivery when the wenchuan earthquake occurred in the south of the xiaoyudong salient this salient partially impeded the northward propagating rupture and dispersed it into two branches to the north the rupture distribution north of xiaoyudong would be significantly different without this salient the existence of the xiaoyudong salient and the rupture pattern of the wenchuan earthquake also prove that the multi segment rupturing model is a better approximation than a single segment model for estimating the maximum magnitude of the paleo earthquake of the longmen shan fault zone

reconstructing and understanding the impacts of storms and surges southern north sea coastal barriers are ubiquitous globally and provide a vital protective role to valuable landforms habitats and communities located to landward they are however vulnerable to extreme water levels and storm wave impacts a detailed record of sub annual to annual decadal and centennial rates of shoreline retreat in frontages characterised by both high 3 m and low 1 m dunes is established for a barrier island on the uk east coast for four storms 2006 2013 we match still water levels and peak significant wave heights against shoreline change at high levels of spatial densification the results suggest that at least in the short term shoreline retreat of typically 5 8 m is primarily driven by individual events separated by varying periods of barrier stasis over decadal timescales significant inter decadal changes can be seen in both barrier onshore retreat rates and in barrier extension rates alongshore whilst the alongshore variability in barrier migration seen in the short term remains at the decadal scale shoreline change at the centennial stage shows little alongshore variability between a region of barrier retreat at 1 15 m a 1 and one of barrier extension a data mining approach synchronising all the variables that drive shoreline change still water level timing of high spring tides and peak significant wave heights is an essential requirement for validating models that predict future shoreline responses under changing sea level and storminess

a review on active tectonics and deep crustal processes of the western sichuan region eastern margin of the tibetan plateau abstract one of remarkable geological and geomorphological features in continental china is the presence of a north south trending tectonic zone which separates the seismically active tibetan plateau to the west from the tectonically stable south china and ordos blocks to the east the zone also owns a name of north south seismic belt as a large number of great historical earthquakes occur on it the most recent one the 2008 wenchuan earthquake attests its recent tectonic activity in this review i take the western sichuan region as an example to probe the structural styles and kinematic pattern as well as deep geological process associated with tectonic deformation of the north south trending zone through integrated studies on active faults gps crustal deformation and geophysical structure we show that deformation in the western sichuan is governed by interactions among three crustal blocks songpan chuandian and south china of distinctive rheological properties under the tectonic framework that eastward growth of the soft eastern tibet is blocked by the hard lithosphere of the south china block the left lateral xianshuihe fault continues to the north south trending fault system without crustal shortening to form a bounding fault to limit the northern extend of the magnificent clockwise rotation of crustal material around the eastern himalaya syntax upper crust of the three blocks is dominated by brittle deformation whereas the ductile flow of lower crust would drag the brittle upper crustal blocks to move with respect to each other the relative motions among the brittle upper crustal blocks cause strain accumulations among their bounding faults to generate large earthquakes deformation of the western sichuan region can thus be described in terms of combined model of rigid block movement and continuous deformation we suggest this combined model can be applied to entire continental china

sorted bed forms as self organized patterns 1 model development 1 here we present a modified version of the exploratory numerical model originally presented by murray and thieler 2004 and use it to further investigate the development of sorted bed forms on the inner continental shelf the new version of the model is based on widely accepted parameterizations for hydrodynamics and sediment transport that are more detailed and empirically tested than the parameterizations used in the original model the shallow water wave equations are replaced by the general equations and changes in water depth related to morphological development are accounted for this model reproduces the main results of the previous one supporting the hypothesis that sorted bed forms are a self organized pattern and develop as a result of a coupling between bed composition and sediment flux the sensitivity of the model predictions evaluated in terms of the geometry of the sorted bed forms and their growth rate with respect to external forcing variables and internal model parameterizations shows increasing decreasing sorted bed form spacing height with increasing wave height and period the opposite occurs for increasing water depths more complicated behavior is observed when the ratio fine to coarse sediment diameter or the percentage of fine and coarse material is varied the shape of the suspended sediment and current profiles and the formulation used to predict the geometry of wave generated ripples can significantly affect or even inhibit growth rates of sorted bed forms results from a sensitivity analysis show that there are deficiencies in the description of small scale processes that limit the ability to quantitatively predict sorted bed form evolution highlighting gaps in our knowledge of sediment transport over mixed grain beds that need to be filled

geological characteristics and spatial distribution of paleo inlet channels beneath the outer banks barrier islands north carolina usa abstract nearly 200 km of high resolution ground penetrating radar gpr data were acquired along the outer banks barrier island system of north carolina usa gpr data combined with lithofacies and biofacies data reveal multiple depositional facies including inlet channel flood tide delta overwash peat and inner shelf previously undocumented paleo inlet channels constitute a significant portion of the shallow geologic framework between oregon inlet and cape hatteras gpr data reveal the complex stratigraphy associated with multiple sequences of cut and fill within inlet channels two types of paleochannels non migrating and migrating were classified based on geometry and fill patterns sediments and foraminifera collected from vibracores were correlated to gpr data to define the regional shallow stratigraphic framework channel fill facies are characterized by clinoform packages sometimes bounded by erosional surfaces indicating variable sediment transport directions from the ocean and sound sides channels are incised into older flood tide delta deposits corresponding to older inlet activity when barriers existed further seaward flood tide delta deposits are capped with marsh peat and overwash units migrating inlet facies occur under the widest portions of the island whereas narrow portions of the island are underlain by the non migrating inlet facies or flood tide delta overwash facies this geologic geomorphic relationship is attributed to the successional stage of island evolution during transgression and sediment transport processes associated with the different inlet types the radar facies lithofacies and biofacies provide a comprehensive dataset that will permit more precise identification of barrier island facies in the geologic record

influence of fluvial processes on the quaternary geologic framework of the continental shelf north carolina usa abstract digital single channel high resolution seismic reflection profiles were acquired from the insular continental shelf of north carolina usa along a data grid extending from oregon inlet northward 48 km to duck north carolina and from the nearshore zone seaward approximately 28 km total surveyed area 1334 km 2 these data were processed and interpreted to delineate principal reflecting horizons and develop a three dimensional seismic stratigraphic framework for the continental shelf that was compared to stratigraphic data from the shoreward back barrier estuarine and barrier island system six principal reflecting horizons designated r 0 through r 5 were present within the upper 60 m of the shelf stratigraphic succession three dimensional mapping of reflector r 1 demonstrated its origin from fluvial incision of the continental shelf during an episode or episodes of lowered sea level fluvial processes during development of reflector r 1 were responsible for extensive reworking and re deposition of sediment throughout most of the northern half of the study area five seismic stratigraphic units designated s 1 through s 5 were tentatively correlated with depositional sequences previously identified from the north carolina back barrier estuarine and barrier island system these five stratigraphic units span the quaternary period s 1 early holocene s 2 51 78 ka s 3 330 530 ka s 4 1 1 1 8 ma s 5 earliest pleistocene unit s 1 is composed of fine grained fluvial estuarine sediment that back filled incised streams during early holocene sea level rise the four other stratigraphic units s 2 s 5 display tabular depositional geometries low total relief and thicken toward the east southeast as their basal reflectors dip gently between 0 41 m km 1 0 02 and 0 54 m km 1 0 03 knowledge of the three dimensional subsurface stratigraphic architecture of the continental shelf enhances understanding of the development of shelf depositional successions and provides a framework for development of better quaternary sea level data especially offshore north carolina where such data are sparse

decoupling processes and scales of shoreline morphodynamics abstract behavior of coastal systems on time scales ranging from single storm events to years and decades is controlled by both small scale sediment transport processes and large scale geologic oceanographic and morphologic processes improved understanding of coastal behavior at multiple time scales is required for refining models that predict potential erosion hazards and for coastal management planning and decision making here we investigate the primary controls on shoreline response along a geologically variable barrier island on time scales resolving extreme storms and decadal variations over a period of nearly one century an empirical orthogonal function analysis is applied to a time series of shoreline positions at fire island ny to identify patterns of shoreline variance along the length of the island we establish that there are separable patterns of shoreline behavior that represent response to oceanographic forcing as well as patterns that are not explained by this forcing the dominant shoreline behavior occurs over large length scales in the form of alternating episodes of shoreline retreat and advance presumably in response to storms cycles two secondary responses include long term response that is correlated to known geologic variations of the island and the other reflects geomorphic patterns with medium length scale our study also includes the response to hurricane sandy and a period of post storm recovery it was expected that the impacts from hurricane sandy would disrupt long term trends and spatial patterns we found that the response to sandy at fire island is not notable or distinguishable from several other large storms of the prior decade

the influence of shelf indenting canyons and infralittoral prograding wedges on coastal morphology the carchuna system in southern spain abstract submarine canyons and progradational sedimentary bodies are common features of continental margins worldwide few studies have analyzed the relationship between the coastal morphology and the morphology and sedimentary characteristics of the adjacent shelf in wave dominated coasts or the potential role played by shelf indenting canyons as inducers of sediment deposition in shallow waters this work presents a study that correlates the coastal morphology with the characteristics of the adjacent offshore shallow shelf in an area with a complex inner bathymetry the carchuna system spain the study area is characterized by large scale non rhythmic cuspate features in the coastline whereas the inner bathymetry exhibits a shallow water infralittoral prograding wedge ipw and a shelf indenting canyon that has tributaries located a short distance from the coastline using detailed bathymetric measurements observational data and wave propagation modeling the influence of the different bathymetric elements was quantified and a mechanism proposed for the generation of the carchuna ipw the wave propagation results show that the canyon is the main source of the alongshore modulation of nearshore waves and that it plays a major role in the generation of the large scale cuspate features in the shoreline additionally these results suggest that the long term coastal erosion associated with extreme storms yielded sufficient sediment which when subsequently transported eastward the dominant littoral drift direction formed the ipw once formed the ipw modified the wave propagation patterns and contributed to the development and reinforcement of the shoreline features

advancement in source estimation techniques using broadband regional seismograms one important constraint on source retrieval from regional seismograms comes from the amplitude difference between various phases such as pnl surface wave sv sh because the misfit errors used in some waveform inversions are normalized by the data and synthetics the amplitude information in the data has not been fully utilized in this article we modify the cut and paste source estimation technique zhao and helmberger 1994 by removing this type of normalization it is shown that the modified method increases the stability and resolution of inversion when multiple stations at different distance ranges are used a distance scaling factor is introduced to compensate for the amplitude decay with distance by applying the technique to the terrascope data we have determined source mechanisms and depths of 335 southern californian events with m l 3 5 the amplitude decays with distance are r 1 13 for pnl r 0 55 for love waves and r 0 74 for rayleigh waves in contrast to generally shallow source depths reported by the southern california short period network the depth distribution from waveform inversion shows a strong peak around 12 km with few earthquakes occurring above 5 km and below 20 km

controls on coastal dune morphology shoreline erosion and barrier island response to extreme storms abstract the response of a barrier island to an extreme storm depends in part on the surge elevation relative to the height and extent of the foredunes which can exhibit considerable variability alongshore while it is recognized that alongshore variations in dune height and width direct barrier island response to storm surge the underlying causes of the alongshore variation remain poorly understood this study examines the alongshore variation in dune morphology along a 11 km stretch of santa rosa island in northwest florida and relates the variation in morphology to the response of the island during hurricane ivan and historic and storm related rates of shoreline erosion the morphology of the foredune and backbarrier dunes was characterized before and after hurricane ivan using empirical orthogonal function eof analysis and related through canonical correlation analysis cca the height and extent of the foredune and the presence and relative location of the backbarrier dunes varied alongshore at discrete length scales of 750 1450 and 4550 m that are statistically significant at the 95 confidence level cospectral analysis suggests that the variation in dune morphology is correlated with transverse ridges on the inner shelf the backbarrier cuspate headlands and the historical and storm related trends in shoreline change sections of the coast with little to no dune development before hurricane ivan were observed in the narrowest portions of the island between headlands west of the transverse ridges overwash penetration tended to be larger in these areas and island breaching was common leaving the surface close to the watertable and covered by a lag of shell and gravel in contrast large foredunes and the backbarrier dunes were observed at the widest sections of the island the cuspate headlands and at crest of the transverse ridges due to the large dunes and the presence of the backbarrier dunes these areas experienced less overwash penetration and most of the sediment from the beachface and dunes was deposited within the upper shoreface it is argued that this sediment is returned to the beachface through nearshore bar migration following the storm and that the areas with larger foredunes and backbarrier dunes have smaller rates of historical shoreline erosion compared to areas with smaller dunes and greater transfer of sediment to the washover terrace since the recovery of the dunes will vary depending on the availability of sediment from the washover and beachface it is further argued that the alongshore pattern of dune morphology and the response of the island to the next extreme storm is forced by the transverse ridges and island width through alongshore variations in storm surge and overwash gradients respectively these findings may be particularly important for coastal managers involved in the repair and rebuilding of coastal infrastructure that was damaged or destroyed during hurricane ivan

sedimentology and morphodynamics of a barrier island shoreface related to engineering concerns outer banks nc usa abstract forty nine vibracores were collected from a barrier island shoreface following 12 4 years of biweekly profile surveying the sedimentologic architecture of the shoreface was linked to time series elevation change and profile shape to determine relationships between morphodynamics facies development erosional processes profile closeout and cross shore transport the modern shoreface mass which erosionally overlies a tidal inlet associated complex attains a maximum thickness of 3 4 m below the beach to middle profile before pinching out seaward between 9 and 12 m depth concave erosional surfaces overlain by cross stratified fine to medium sand and gravel make up most of the lower half of the shoreface prism below the beach through middle profile reflecting longshore trough incision and subsequent current dominated aggradation at the landward margin gravel rich laminae record episodic seaward progradation of beach surfaces over coarse inner trough settings seaward a parallel laminated fine sand facies dominates the upper part of the prism recording intermittent shoal zone buildup including trough filling under high velocity plane bed conditions similarly a bioturbated parallel laminated fine to very fine sand facies makes up the entire prism below the outermost lower ramp sector again indicating buildup under high velocity conditions however accretion of the lower ramp results from major storms that cause trough scour along landward locations and simultaneous displacement of fine sand onto the lower ramp conversely lower ramp erosion typically occurs during less energetic conditions as sediment is slowly returned shoreward causing inner shoreface buildup close spacing of major storms during some years led to net progradation of the shoreface the upper and lower limits of surveyed elevation change ule and lle repeatedly develop similar limit profile shapes over shoreface accretion erosion cycles the ule reflects accretion maxima resulting from beach bar and lower ramp buildup the lle and lower sedimentologic limit lls along the inner 250 to 300 m of the active shoreface are a product of storm trough scour down to a maximum depth of 5 5 m below the lower ramp facies the lle and lls are primarily products of less energetic wave erosion down to 5 m shoreward and 9 m offshore depths the lle closely matches the lls documenting that 90 of the shoreface prism was reworked during the 12 4 year period whereas actual ages for erosional events indicate a potential of 2 to 4 years for complete reworking of the shoreface mass textural distribution indicates net long term transport direction and loci of deposition for different sized material the coarsest material is concentrated at landwardmost locations and well sorted fine to very fine sand at seaward locations medium sand to gravel tends to remain within the trough zone even during extreme storm events the ule and lle also represent the upper and lower limits for profile closure events a location of about 4 5 m depth at 300 to 350 m from shoreline marks the boundary between inner profile and lower ramp associated closure events the boundary between trough associated and lower ramp facies and the lower ramp morphologic break all of which correspond to the juncture between longshore current and shoaling wave dominated zones the lower ramp zone of closure is a zone of seaward decreasing storm transport in which fine to very fine sand is the typical bedload material

hardbottom morphology and relationship to the geologic framework mid atlantic continental shelf abstract high energy sediment starved continental shelves of the mid atlantic region have abundant hardbottoms that extend from the shoreface to the shelf edge because of the thin and irregularly distributed holocene sand sheet shelf morphology is determined mainly by outcropping tertiary and pleistocene stratigraphic units each unit and combination of units produces different hardbottom morphologies that depend upon the geometry and spatial relationships of the units lithology and patterns of stratification and subsequent weathering and erosion hardbottoms vary in surface relief from smooth flat surfaces to scarped surfaces with up to 10 m of relief the morphology ranges from sloping and stepped erosional ramps to vertical and undercut scarps with associated broad rubble ramps hardbottoms associated with each of the different gently dipping tertiary depositional sequences have distinctive morphologies hardbottoms developed on pleistocene units unconformably overlie the tertiary sequences as flat lying marine carbonates or cut into them as channel systems backfilled with fluvial and estuarine sediments initial dissection of hardbottoms produced highly convoluted surfaces that resulted from subaerial weathering stream erosion and karst formation during sea level lowstands during subsequent sea level highstands these rimary morphologies were greatly modified through the interaction of bioerosion and storms understanding continental shelf hardbottoms is critical for interpreting the sedimentology and stratigraphy of the atlantic coastal plain and for reconstructing paleoceanographic conditions for the following reasons 1 they are an extensive part of the stratigraphic record on shelves that are not actively subsiding and have small volumes of terrigenous input with low sediment accumulation rates 2 they are important stages in the formation of major stratigraphic unconformities condensed sections and sequence boundaries 3 they support diverse biological communities that produce primary carbonate sediments and are rapidly degraded and modified by bioerosion and physical processes supplying abundant new sediment to the continental shelf

spatial variation of the crustal stress field along the ryukyu taiwan luzon convergent boundary 1 we applied an improved stress inversion method to a comprehensive data set of earthquake focal mechanisms to depict the pattern of crustal stress along the western convergent boundary of the philippine sea plate our results indicate that the crustal stress along the ryukyu fore arc is segmented with boundaries at or near the places of seamount subduction including the tokara channel an extensional stress regime is observed along the entire ryukyu back arc implying that back arc rifting may have extended northward to kyushu a triangular area near the southernmost terminus of the ryukyu arc is characterized by a unique stress signature the eastern boundary of this ryukyu taiwan stress transition coincides with the 123 e meridian where the gagua ridge intercepts the ryukyu trench whereas its western boundary agrees remarkably well with the border between the postcollision and waning collision domains in northern taiwan the taiwan collision zone is dominated by compression that rotates locally according to the structural configuration of the lukang magnetization high lmh suggesting that the lmh may be critical in controlling the local stress distribution the stress signature of the luzon arc taiwan collision reaches as far south as 19 5 n the tectonic stress along the manila trench luzon fore arc is dominated by a complex regime of extension that cannot be explained by simple plate bending or in slab membrane stress since this extensional regime is observed only south of 22 n it probably marks the northern limit of the contemporary boundary between the subduction along the manila trench and the collision in taiwan

observations and 3d hydrodynamics based modeling of decadal scale shoreline change along the outer banks north carolina abstract long term decadal scale shoreline change is an important parameter for quantifying the stability of coastal systems the decadal scale coastal change is controlled by processes that occur on short time scales such as storms and long term processes such as prevailing waves the ability to predict decadal scale shoreline change is not well established and the fundamental physical processes controlling this change are not well understood here we investigate the processes that create large scale long term shoreline change along the outer banks of north carolina an uninterrupted 60 km stretch of coastline using both observations and a numerical modeling approach shoreline positions for a 24 yr period were derived from aerial photographs of the outer banks analysis of the shoreline position data showed that although variable the shoreline eroded an average of 1 5 m yr throughout this period the modeling approach uses a three dimensional hydrodynamics based numerical model coupled to a spectral wave model and simulates the full 24 yr time period on a spatial grid running on a short second scale time step to compute the sediment transport patterns the observations and the model results show similar magnitudes o 105 m3 yr and patterns of alongshore sediment fluxes both the observed and the modeled alongshore sediment transport rates have more rapid changes at the north of our section due to continuously curving coastline and possible effects of alongshore variations in shelf bathymetry the southern section with a relatively uniform orientation on the other hand has less rapid transport rate changes alongshore gradients of the modeled sediment fluxes are translated into shoreline change rates that have agreement in some locations but vary in others differences between observations and model results are potentially influenced by geologic framework processes not included in the model both the observations and the model results show higher rates of erosion 1 m yr averaged over the northern half of the section as compared to the southern half where the observed and modeled averaged net shoreline changes are smaller

coastline responses to changing storm patterns 1 researchers and coastal managers are pondering how accelerated sea level rise and possibly intensified storms will affect shorelines these issues are most often investigated in a cross shore profile framework fostering the implicit assumption that coastline responses will be approximately uniform in the alongshore direction however experiments with a recently developed numerical model of coastline change on a large spatial domain suggest that the shoreline responses to climate change could be highly variable as storm and wave climates change large scale coastline shapes are likely to shift causing areas of greatly accelerated coastal erosion to alternate with areas of considerable shoreline accretion on complex shaped coastlines including cuspate cape and spit coastlines the alongshore variation in shoreline retreat rates could be an order of magnitude higher than the baseline retreat rate expected from sea level rise alone

earthquake focal mechanisms in yunnan and their inference on the regional stress field using the broadband records from a regional permanent network we determined the focal mechanisms of 174 small and moderate earthquakes 3 4 m w 6 0 from january 2008 to march 2011 in yunnan china by fitting the three component waveforms of p and s waves results show that the earthquakes predominantly have strike slip mechanisms with occasional normal and very few thrust faulting events most earthquakes occur in the upper crust above 16 km depth we then derive the regional distribution of the stress field through a damped linear inversion using the focal mechanisms obtained in this study and augmented by the solutions in the global centroid moment tensor gcmt catalog and in xu et al 2010 inversion results suggest that the entire region is predominantly under a strike slip faulting regime orientations of both maximum and minimum principle axes exhibit a clockwise rotational pattern the axes of maximum compression are oriented roughly north south with a gradual change across the region from trending northwest southeast in the south china block to trending northeast southwest in the indo china block this pattern is consistent with the surface horizontal velocity derived from geodetic observations localized normal faulting stress regions are observed in the tengchong volcanic zone and in the qiao jia segment of the xianshuihe xiaojiang fault zone online material tables of earthquake catalogs and figures describing stress inversion tests

segmentation of the longmen mountains thrust belt western sichuan foreland basin sw china abstract many complex structures have developed in the longmen mountains thrust belt sw china over the course of polyphase tectonic movements in the region based on field investigations and interpretations of seismic sections we divided the belt into the following three segments and two transfer zones from northeast to southwest the northern segment anxian transfer zone ta central segment guanxian transfer zone tg and southern segment the northern segment located north of anxian county consists of the jiaoziding nappe comprising a triassic jurassic fold belt and a plastically deformed silurian belt the northern segment can be further divided into four sub segments the guangyuan chaotianyi sub segment n1 baitianba guangyuan sub segment n2 wenxingchang baitianba sub segment n3 and wuzhong mountain tangwangzhai nappe sub segment n4 the anxian transfer zone ta located between yuanmenba town and hanwangchang town consists of numerous thrust faults and strike slip faults at shallow levels with duplexes and detachment structures at deeper levels the central segment which consists of the jiudingshan nappe and numerous klippes and thrust faults is located between hanwangchang town and guanxian county this segment can be divided into two sub segments the mianzhu mianyang sub segment c1 and the dayuanbao sub segment c2 the guanxian transfer zone which is characterized by numerous thrust faults strike slip faults and duplexes is located between guanxian county and huaiyuan county the southern segment which consists of the baoxing nappe and contains arcuate thrust faults is located south of huaiyuan county the southern segment is divided into three sub segments the huaiyuan xinchang sub segment s1 xinchang lushan sub segment s2 and southern arcuate sub segment s3

process signatures in regional patterns of shoreline change on annual to decadal time scales gradients in wave driven alongshore sediment transport influence the morphologies of sediment covered coastlines on a range of spatial and temporal scales affecting accretion and erosion patterns relevant to human development recent theoretical findings predict that a correlation between shoreline change and shoreline curvature results from patterns of alongshore sediment flux the sign positive or negative of that correlation depends on whether high or low angle waves dominated the wave climate using lidar surveys of the northern north carolina coast from 1996 2005 to document shoreline change and quantify alongshore patterns of erosion and deposition we isolate these signals diagnostic of alongshore transport processes our analyses show a persistent significant negative correlation between shoreline position change and shoreline curvature consistent with a low angle dominated incident wave climate over the last decade at large spatial scales convex seaward promontories have eroded landward while concave seaward bays have aggraded seaward resulting in an apparent diffusion of alongshore morphological features

beware of slowly slipping faults the fault zone that hosted the devastating wenchuan earthquake in 2008 had been assigned a moderate to low seismic hazard rating because it slips slowly in hindsight it seems that this type of fault is not necessarily innocuous

reversing storm hotspots on sandy beaches spatial and temporal characteristics coastal erosion hotspots are defined as sections of coast that exhibit significantly higher rates of erosion than adjacent areas this paper describes the spatial and temporal characteristics of a recently identified type of coastal erosion hotspot which forms in response to storms on uninterrupted sandy coasts largely free from human intervention these are referred to here as reversing storm hotspots because the erosion is reversed by accretion of a similar magnitude to the storm induced erosion the accretion occurs within a few days or weeks of fair weather after the storm reversing storm hotspots observed here on two us east coast beaches have a longshore length averaging 3 86 km a cross shore excursion magnitude of erosion or accretion averaging 15 4 m and a time scale of days to weeks associated with individual storm events these spatial and temporal scales clearly distinguish reversing storm hotspots from previously described forms of longshore variability in erosion including those attributed to several types of shoreline undulations and hotspots associated with long term shoreline change

late cenozoic evolution of the eastern margin of the tibetan plateau inferences from 40ar 39ar and u th he thermochronology high topography in central asia is perhaps the most fundamental expression of the cenozoic indo asian collision yet an understanding of the timing and rates of development of the tibetan plateau remains elusive here we investigate the cenozoic thermal histories of rocks along the eastern margin of the plateau adjacent to the sichuan basin in an effort to determine when the steep topographic escarpment that characterizes this margin developed temperature time paths inferred from 40 ar 39 ar thermochronology of biotite multiple diffusion domain modeling of alkali feldspar 40 ar release spectra and u th he thermochronology of zircon and apatite imply that rocks at the present day topographic front of the plateau underwent slow cooling 30 50 c m y coincident with exhumation from inferred depths of 8 10 km at denudation rates of 1 2 mm yr samples from the interior of the plateau continued to cool relatively slowly during the same time period 3 c m y suggesting limited exhumation 1 2 km however these samples record a slight increase in cooling rate from 1 to 3 c m y at some time during the middle tertiary the tectonic significance of this change remains uncertain regardless late cenozoic denudation in this region appears to have been markedly heterogeneous with the highest rates of exhumation focused at the topographic front of the plateau margin we infer that the onset of rapid cooling at the plateau margin reflects the erosional response to the development of regionally significant topographic gradients between the plateau and the stable sichuan basin and thus marks the onset of deformation related to the development of the tibetan plateau in this region the present margin of the plateau adjacent to and north of the sichuan basin is apparently no older than the late miocene or early pliocene 5 12 ma

modern sedimentation on the shoreface and inner continental shelf at wrightsville beach north carolina u s a abstract the geologic framework and surficial morphology of the shoreface and inner continental shelf off the wrightsville beach north carolina barrier island were mapped using high resolution sidescan sonar bathymetric and seismic reflection surveying techniques a suite of over 200 diver vibracores and extensive seafloor observations by divers the inner shelf is a sediment starved active surface of marine erosion modern sediments where present form a patchy veneer over tertiary and quaternary units the lithology of the underlying units exerts a primary control on the distribution texture and composition of surficial sediments as well as inner shelf bathymetry the shoreface is dominated by a linear cross shore morphology of rippled scour depressions rsds extending from just seaward of the surf zone onto the inner shelf on the upper shoreface the rsds are incised up to 1 m below surrounding areas of fine sand and have an asymmetric cross section that is steeper sided to the north on the inner shelf the rsds have a similar but more subdued cross sectional profile the depressions are floored primarily by shell hash and quartz gravel vibracore data show a thick up to 1 5 m sequence of rsd sediments that unconformably overlies ancient coastal lithosomes in this sediment starved inner shelf setting rippled scour depressions probably form initially on preexisting coarse sediment substrates such as modern lag deposits of paleofluvial channel lithosomes or ancient tidal inlet thalwegs interannual observations of seafloor morphologic change and the longer term record contained in vibracores suggest that the present seafloor morphology is either relatively stable or represents a recurring preferential morphologic state to which the seafloor returns after storm induced perturbations the apparent stability is interpreted to be the result of interactions at several scales that contribute to a repeating self reinforcing pattern of forcing and sedimentary response which ultimately causes the rsds to be maintained as sediment starved bedforms responding to both along shore and across shore flows sediment accumulation from over 30 years of extensive beach nourishment at wrightsville beach appears to have exceeded the local shoreface accommodation space resulting in the leaking of beach and shoreface sediment to the inner shelf a macroscopically identifiable beach nourishment sediment on the shoreface and inner shelf was used to identify the decadal scale pattern of sediment dispersal the nourishment sediment is present in a seaward thinning wedge that extends from the beach over a kilometer onto the inner shelf to waters depths of 14 m this wedge is best developed offshore of the shoreline segment that has received the greatest volume of beach nourishment

longmen shan fold thrust belt and its relation to the western sichuan basin in central china new insights from hydrocarbon exploration the longmen shan fold thrust belt is one of the key regions of demonstrable mesozoic cenozoic tectonic evolution in china and the sichuan basin was the first natural gas producing area in china in this article the structural features of the longmen shan belt are presented using both seismic profiles and field data the complex structures of the northeast trending longmen shan fold thrust belt and its foreland in the western sichuan basin are formed by southeast directed thrusting several eastward verging rootless thrust sheets and imbricates of cambrian triassic rocks have been recognized in the northern longmen shan belt evidence suggests that the northern longmen shan belt experienced at least two major periods of deformation in the late triassic and cenozoic however the southern longmen shan belt is represented by the basement involved thrust structures and klippen and its major periods of deformation were in the latest cretaceous early cenozoic sedimentary features in the western sichuan basin reflect a two phase flexural loading history and illustrate that the late triassic foreland basin extends along the foredeep of the entire length of the longmen shan belt but the uppermost cretaceous paleogene rejuvenated foreland basin is restricted in the southern part of the western sichuan basin structural geometries suggest that prospective traps are mainly developed in the frontal zone of the longmen shan fold thrust belt and in the southern part of the western sichuan basin one of the major contributions of this article is finding preexisting paleozoic rift basins under the cenozoic thin skinned thrust belts which represent a new potential hydrocarbon play

coseismic reverse and oblique slip surface faulting generated by the 2008 mw 7 9 wenchuan earthquake china the mw 7 9 wenchuan china earthquake ruptured two large thrust faults along the long menshan thrust belt at the eastern margin of the tibetan plateau this earthquake generated a 240 km long surface rupture zone along the beichuan fault and an additional 72 km long surface rupture zone along the pengguan fault maximum vertical and horizontal offsets of 6 5 m and 4 9 m respectively were measured along the beichuan fault a maximum vertical offset of 3 5 m was measured along the pengguan fault coseismic surface ruptures integrated with aftershocks and industry seismic profiles show that two imbricate structures have ruptured simultaneously resulting in the largest continental thrust event ever documented large oblique thrusting observed during this earthquake indicates that crustal shortening is an important process responsible for the high topography in the region as everywhere along the edge of tibetan plateau

active faulting and block movement associated with large earthquakes in the min shan and longmen mountains northeastern tibetan plateau the min shan and central and southern parts of the longmen mountains form the middle segment of the north trending earthquake zone at the eastern edge of the tibetan plateau the min shan mountains are a cenozoic to quaternary uplift zone that has undergone south directed block movements to produce the 1933 diexi earthquake m 7 5 on the min jiang fault and the 1976 songpan earthquake swarm m 7 2 6 7 7 2 on the huya fault the min jiang fault on the western boundary of the uplift zone is dominated by reverse movement with a right lateral component the huya fault on the eastern margin of the min shan uplift zone is also dominated by reverse movement but is associated with a left lateral component

geologic control in the nearshore shore oblique sandbars and shoreline erosional hotspots mid atlantic bight usa abstract beach and nearshore morphology defined primarily by slope and sandbar development is very dynamic and is largely controlled by waves currents and regional sediment characteristics results presented here challenge this long established concept and suggest that underlying framework geology may also exert a first order control on nearshore morphology by influencing the stability and or persistent re establishment of large scale sandbar morphology and position as well as surface sediment characteristics repeated sub bottom chirp and swath bathymetry surveys of the nearshore 2 10 m depths covering over 56 km of the north carolina outer banks and southeastern virginia indicate the following 1 development of shore oblique sandbars adjacent to large gravel outcrops that are surface exposures of the underlying geologic strata 2 identical re development or sustained maintenance of large scale sandbar morphology and position before and after very energetic conditions 3 vertical and horizontal heterogeneity of lithology and grain size and a minimum volume of sand ranging from 0 to 1 5 m thick and 4 close spatial alignment between the location of outcrops shore oblique bars and shoreline erosional hotspots a hypothesis is proposed from these findings that links framework geology to bar morphodynamics and sorted bedforms and ultimately erosional hotspots sediment transport and shoreline evolution models based solely on waves and currents and an assumption of unlimited and uniform sediment may be inadequate in similar heterogeneous sand limited regions

calculating shoreline erosion potential using nearshore stratigraphy and sediment volume outer banks north carolina 1 despite the acknowledged influence of coastal geological framework on the behavior of beaches and barrier islands and a wealth of geological and bathymetric observations from the inner shelf quantitatively connecting those observations to shoreline behavior has been difficult nearshore geologic and morphologic variability described by recent research is not well represented by conventional geologic parameters such as mean grain size and shoreface slope used in most shoreline change models we propose that total nearshore sediment volume as calculated to a continuous seismic reflection surface provides a flexible and robust metric for use in the prediction of shoreline change this method of determining the volume of sediment in the nearshore accounts for three dimensional sandbar morphologies and heterogeneous seafloor sediments the decadal scale shoreline change rate for northeastern north carolina is significantly correlated to the volume of sediment in the nearshore when a geologically defined base is used in volume determinations suggesting that the shallow stratigraphic framework of transgressive coasts is an important influence on decadal shoreline behavior nearshore sediment volume was overestimated when an arbitrary depth constant baseline was used and was not correlated to decadal shoreline change this implies that a volume metric which accounts for both framework geology and variable seafloor morphology better represents the geologic character of the shoreface and may help to improve existing models of shoreline change an empirical model of regional shoreline erosion potential demonstrates the importance of incorporating nearshore sediment volume shallow framework geology and surface morphology when predicting seasonal to decadal shoreline evolution

influence of inherited geologic framework on barrier shoreface morphology and dynamics abstract passive margin coastlines with limited sand supplies such as much of the u s atlantic margin are significantly influenced by the geologic framework of older stratigraphic units that occur beneath and seaward of the shoreface many u s east coast barrier islands are perched barriers in which the underlying pre modern sediments determine the morphology of the shoreface and strongly influence modern beach dynamics and composition perched barriers consist of varible layers of beach sand on top of older eroding stratigraphic units with highly variable compositions and geometries along many parts of the coastal system stratigraphically controlled bathymetric features on the inner shelf modify waves and currents and thereby effect patterns of sediment erosion transport and deposition on the adjacent shoreface it is essential to understand this geologic framework before attempting to model the large scale behavior of these types of coastal systems in north carolina most shoreline features are controlled by the pre holocene stratigraphic framework of the shoreface the beaches are perched on top of pre existing pleistocene tertiary and cretaceous sediments the surficial geology of the coastal zone is subdivided into two distinct provinces resulting in different stratigraphic controls of the shoreface north of cape lookout the geological framework consists of a quaternary sequence that fills a regional depositional basin called the albemarle embayment the coastal zone south of cape lookout is dominated by tertiary and cretaceous units that crop out across the coastal plain and continental shelf with very thin quaternary units only locally preserved superimposed upon this regional stratigraphy is an ancient drainage system resulting in a series of fluvial valleys filled with younger coastal sediments separated by large interfluve areas of older stratigraphic units this results in a coastal system in which the shoreface is either nonheadland or headland dominated respectively headland dominated shorefaces are further divided into subaerial and submarine categories nonheadland dominated shorefaces are further divided into those influenced primarily by transgressive or regressive processes or channel dominated depositional processes i e inlet migration or stream valley fill examples of each of these six types of shorefaces are presented to demonstrate the control that the geologic framework exhibits on shoreface morphologies and processes

source estimation from broadband regional seismograms recently developed source inversion techniques do not take full advantage of the broadband nature of regional seismograms the reason is that green s functions generated from flat layered models are not correct for the complicated propagational phenomena associated with realistic crustal structure the inversion is usually performed by removing short periods and inverting only selected portions of the records in this article we introduce a source estimation technique that allows for better use of the entire broadband record when only imperfect green s function are available the procedure desensitizes the timing between the principal crustal arrivals by fitting portions of the green s functions independently the preferred source is the orientation that minimizes the average l1 and l2 norms in term of the four parameters m 0 strike dip and rake the l2 error emphasizes the longer period surface waves while the l1 error weights the shorter period body waves we obtain estimates of duration by modeling long period and broadband signals the depth determination can be obtained directly from the surface reflected phases sp mp or ss ms or by cycling through the depth dependent green s functions in addition to the source parameters we obtain t phase alignments shifts that can be used as green s function corrections for relocating other events or as a guide to deriving new crustal models

sorted bed forms as self organized patterns 2 complex forcing scenarios 1 we employ a numerical model to study the development of sorted bed forms under a variety of hydrodynamic and sedimentary conditions results indicate that increased variability in wave height decreases the growth rate of the features and can potentially give rise to complicated a priori unpredictable behavior this happens because the system responds to a change in wave characteristics by attempting to self organize into a patterned seabed of different geometry and spacing the new wavelength might not have enough time to emerge before a new change in wave characteristics occurs leading to less regular seabed configurations the new seabed configuration is also highly dependent on the preexisting morphology which further limits the possibility of predicting future behavior for the same reasons variability in the mean current magnitude and direction slows down the growth of features and causes patterns to develop that differ from classical sorted bed forms spatial variability in grain size distribution and different types of net sediment aggradation degradation can also result in the development of sorted bed forms characterized by a less regular shape numerical simulations qualitatively agree with observed geometry spacing and height of sorted bed forms also in agreement with observations is that at shallower depths sorted bed forms are more likely to be affected by changes in the forcing conditions which might also explain why in shallow waters sorted bed forms are described as ephemeral features finally simulations indicate that the different sorted bed form shapes and patterns observed in the field might not necessarily be related to diverse physical mechanisms instead variations in sorted bed form characteristics may result from variations in local hydrodynamic and or sedimentary conditions

complex surface rupturing and related formation mechanisms in the xiaoyudong area for the 2008 mw 7 9 wenchuan earthquake china the large oblique reverse slip shock of the 2008 mw 7 9 wenchuan earthquake china produced one of the longest and most complicated surface ruptures ever known the complexity is particularly evident in the xiaoyudong area where three special phenomena occurred the 7 km long xiaoyudong rupture perpendicular to the beichuan yingxiu fault the occurrence of two parallel faults rupturing simultaneously and apparent discontinuity of the beichuan yingxiu rupture this paper systematically documents these co seismic rupture phenomena for the xiaoyudong area the discussion and results are based on field investigations and analyses of faulting mechanisms and prevalent stress conditions the results show that the beichuan yingxiu fault formed a 3 5 km wide restraining stepover at the xiaoyudong area the xiaoyudong fault is not a tear fault suggested by previous researches but a frontal reverse fault induced by the oblique compression at this stepover it well accommodates the deformation gap of the beichuan yingxiu fault in the xiaoyudong area further stress along the peng guan fault plane doubles due to a change in dip angle of the beichuan yingxiu fault across the xiaoyudong restraining stepover this resulted in two faults rupturing the ground s surface simultaneously to the north of the xiaoyudong area these results are helpful in deepening our understanding of the dynamic processes that produced surface ruptures during the wenchuan earthquake furthermore the results suggest more attention be focused on the influence of dextral slip component the change of the control fault s attitude and property differences in rocks on either side of faults when discussing the formation mechanism of surface ruptures

an improved method for determining the regional stress tensor using earthquake focal mechanism data application to the san fernando earthquake sequence the orientations of fault planes and slip directions indicated by a population of earthquake focal mechanisms can be used to determine best fit regional principal stress directions and r 2 1 3 1 a measure of relative stress magnitudes under the assumption of uniform stress in the source region this analysis allows for the possibility that failure occurs on preexisting zones of weakness of any orientation in the inversion we perform a grid search of stress models to find the one which requires the smallest total rotation of all the fault planes that is needed to match the observed and predicted slip directions the method allows for errors in orientations of both the fault planes and slip directions we have an objective means for identifying the more likely of the two possible fault planes from each focal mechanism relative to a given stress model thus we do not face the problem of ambiguity of nodal planes which plagues other analyses of this kind by using a grid search of stress models rather than a linearization scheme we are able to perform a realistic error analysis and thus establish confidence limits for the preferred regional stresses the method can be used to investigate possible stress inhomogeneities during earthquake sequences by analyzing subsets of the data population the technique has been applied to 76 events from the san fernando earthquake sequence for which we have found best fit stresses plunge and azimuth 1 7 187 2 27 281 3 62 84 and r 0 65 the average misfit between this stress model and all the data is about 8 and all but eight of the aftershocks have misfits of less than 20 these values are considerably less than the uncertainty of the focal mechanism determinations therefore significant stress inhomogeneities are not required by the data our analysis does not support the suggestion of a change in stresses during the aftershock sequence as proposed by others on the basis of an apparent change in focal mechanisms

linking framework geology and nearshore morphology correlation of paleo channels with shore oblique sandbars and gravel outcrops abstract this work describes a newly discovered spatial correlation between paleo channels and nearshore morphology along the barrier islands of northeastern north carolina and southeastern virginia u s mid atlantic coast these nearshore morphological features include regions of shore oblique sandbars and coincident gravel outcrops that previously have been linked to erosional hotspots at the shoreline these new findings have direct bearing on both nearshore morphodynamics and shoreline management paleo channels were identified in the chirp seismic record and compared to shore oblique sandbar locations discerned from bathymetric data and corroborated by gravel outcrops depicted in the side scan record both graphical correlation and statistical cross correlation analyses revealed a significant spatial relationship between these features with higher statistical correlation for channels 500 m wide seismic records also indicate that the gravel outcrops seen on the updrift flanks of the shore oblique bars are surface expressions of the underlying geology we hypothesize that these outcrops are composed of relict channel fill sediments that interact with the hydrodynamic regime to produce sorted bedforms the bathymetric anomalies then serve to alter incident wave energy and affect shoreline behavior the spatial and temporal stability of these features over several years and through a variety of wave conditions suggests some degree of underlying geologic control while the mechanisms responsible for this relationship remain speculative these results may bridge the gap between studies focusing on framework geology and its influence on shoreline change and those that investigate bar morphodynamics and the initiation of sorted bedforms

crustal thicknesses and poisson s ratios in the eastern tibetan plateau and their tectonic implications 1 crustal thicknesses and poisson s ratios in the eastern tibetan plateau were estimated using the h k stacking method on teleseismic receiver functions the data came mainly from the regional seismic networks in 2006 2008 results show that the crust thickens from east to west with a thickness difference of 30 km a sharp change of crustal thickness from 41 5 to 52 5 km is observed across the longmen shan crustal thickness predictions based on the airy type isostasy are consistent with the estimations from h k stacking implying that the topography is approximately compensated the study area can be divided into three parts according to the poisson s ratios 1 the northern songpan garze terrane and the western qinling orogenic belt with low ratios 0 26 2 the southern songpan garze terrane the sanjiang fold system and the sichuan basin with high to intermediate ratios 0 27 0 30 and 3 the southwestern yangtze platform with low to intermediate ratios 0 27 joint interpretation of the low average vp values from deep seismic sounding profiles and the low vp vs ratios from receiver function analysis favors the presence of felsic crust rather than significant volumes of partial melts in the northern songpan garze terrane and the western qinling orogenic belt the junction of the longmen shan fault zone the xianshuihe fault zone and the anninghe fault zone has an ultrahigh poisson s ratio 0 30 which could be considered as an evidence of local partial melt we propose that the eastward movement of upper and middle crustal material in the southern songpan garze terrane is obstructed by the more rigid sichuan basin resulting in strain accumulation along the longmen shan fault zone

on the evolution of seismogenic faults in the longmen shan eastern tibet abstract a fundamental debate exists regarding the geometry and depth extent of seismogenic faults in eastern tibet along the longmen shan geologic and seismic reflection data reveal a belt of low to moderate angle thrust faults some of which may have been activated in devastating earthquakes in 2008 mw 7 9 wenchuan and 2013 mw 6 6 lushan however geologic and geodetic constraints on these ruptures suggest rupture along relatively high angle listric reverse faults here we use a combination of focal mechanisms determined from 276 aftershocks ms 4 0 with well determined waveforms and aftershock distributions from the 2008 event to determine subsurface fault geometry our results imply that seismogenic slip occurred along relatively high angle structures that cross cut low angle imbricate faults imaged in reflection seismic data thus we suggest that current geometric models of seismogenic faults may not fully represent the distribution of subsurface seismic hazard along the heavily populated sichuan basin

cumulative versus transient shoreline change dependencies on temporal and spatial scale using shoreline change measurements of two oceanside reaches of the north carolina outer banks usa we explore an existing premise that shoreline change on a sandy coast is a self affine signal wherein patterns of change are scale invariant wavelet analysis confirms that the mean variance spectral power of shoreline change can be approximated by a power law at alongshore scales from tens of meters up to 4 8 km however the possibility of a power law relationship does not necessarily reveal a unifying scale free dominant process and deviations from power law scaling at scales of kilometers to tens of kilometers may suggest further insights into shoreline change processes specifically the maximum of the variance in shoreline change and the scale at which that maximum occurs both increase when shoreline change is measured over longer time scales this suggests a temporal control on the magnitude of change possible at a given spatial scale and by extension that aggregation of shoreline change over time is an important component of large scale shifts in shoreline position we also find a consistent difference in variance magnitude between the two survey reaches at large spatial scales which may be related to differences in oceanographic forcing conditions or may involve hydrodynamic interactions with nearshore geologic bathymetric structures overall the findings suggest that shoreline change at small spatial scales less than kilometers does not represent a peak in the shoreline change signal and that change at larger spatial scales dominates the signal emphasizing the need for studies that target long term large scale shoreline change

structural control of rupturing of the mw7 9 2008 wenchuan earthquake china abstract analyses of global seismic waveform data for the 2008 devastating wenchuan earthquake have indicated where the rupture started and how it expanded here we reveal that the rupture process of this earthquake was strongly controlled by structural heterogeneities of the upper crust we made a tomographic inversion of 200 000 local travel time data according to which the rupture was confined in a presumably brittle layer of high p and s wave velocity anomalies within the upper 15 km depths the rupture propagated northeastward through the southwest sw segment of the fault and then jumped to the northeast ne segment with little slip at the intervening presumably ductile zone characterized by low p and s velocities with high poisson s ratio the rupture initiated near the southwestern end of the sw segment within a body of high poisson s ratio which extends down into the lower crust suggesting upward migration of deep seated aqueous fluid to trigger the earthquake by reducing the mechanical strength of the brittle layer

nearshore shore oblique bars gravel outcrops and their correlation to shoreline change abstract this study demonstrates the physical concurrence of shore oblique bars and gravel outcrops in the surf zone along the northern outer banks of north carolina these subaqueous features are spatially correlated with shoreline change at a range of temporal and spatial scales previous studies have noted the existence of beach surf zone interactions but in general relationships between nearshore geological features and coastal change are poorly understood these new findings should be considered when exploring coastal zone dynamics and developing predictive engineering models the surf zone and nearshore region of the outer banks is predominantly planar and sandy but there are several discrete regions with shore oblique bars and interspersed gravel outcrops these bar fields have relief up to 3 m are several kilometers wide and were relatively stationary over a 1 5 year survey period however the shoreward component of the bar field does exhibit change during this time frame all gravel outcrops observed in the study region a 40 km longshore length were located adjacent to a shore oblique bar in a trough that had width and length similar to that of the associated bar seismic surveys show that the outcrops are part of a gravel stratum underlying the active surface sand layer cross correlation analyses demonstrate high correlation of monthly and multi decadal shoreline change rates with the adjacent surf zone bathymetry and sediment distribution regionally areas with shore oblique bars and gravel outcrops are correlated with on shore areas of high short term shoreline variability and high long term shoreline change rates the major peaks in long term shoreline erosion are onshore of shore oblique bars but not all areas with high rates of long term shoreline change are associated with shore oblique bars and troughs

subsurface structure and spatial segmentation of the longmen shan fault zone at the eastern margin of tibetan plateau evidence from focal mechanism solutions and stress field inversion abstract as the eastern margin of the tibetan plateau the longmen shan fault zone lmsfz is characterized by a complex structural style and strong seismicity such as the 2008 wenchuan ms8 0 and 2013 lushan ms7 0 earthquakes in order to better understand the subsurface geometry of the lmsfz we inverted 391 focal mechanism solutions fms of earthquakes m 3 5 that occurred between 2009 and 2016 in the longmen shan region using seismic waveforms subsequently we calculated the stress field based on the fmss the results show that the lmsfz is dominated by a thrust faulting stress regime with subhorizontal nw se trending maximum principal stress 1 and subvertical minimum principal stress 3 indicating a lateral compression due to the southeastward movement of the bayan har block changes in fault dips at 10 km depth are inferred as the result of a shallow level detachment layer which may also promote shortening of the upper crust and uplift of the longmen shan based on differences in subsurface fault geometry stress field and geomorphological evidence we divide the lmsfz into two segments by beichuan county the southwestern segment has a listric fault geometry while the northeastern segment is dominated by subvertical transpressional strike slip faults according to the fmss results we suggest that the lixian fault is a tear fault accommodating different thrusting rates in the eastern margin of the bayan har block the normal faulting earthquakes in the lixian area are caused by local extension resulting from the sinistral shear movement of lixian fault in a strike slip faulting stress regime it is suggested that under the continuous southeastward movement of the bayan har block and the obstruction of the rigid sichuan basin stress is accumulating along the southwestern segment of the lmsfz to which accordingly a high seismic hazard is ascribed and which should be carefully monitored

upper carboniferous fine grained turbiditic sandstones from southwest england a model for growth in an ancient delta fed subsea fan abstract the upper carboniferous crackington and bude formations of southwest england comprise laminated black mudstones gray siltstones thin medium and thick bedded sandstones and contorted silty sandstones the thick bedded sandstones only occur in the bude formation which overlies the crackington the sandstones were deposited predominantly by turbidity currents in a relatively shallow basin they are unusual for two reasons 1 sediment coarser than fine sand is entirely absent 2 unlike many previously described ancient subsea fan deposits organized bundles of sandstones displaying asymmetric upward thickening or upward thinning sequences are no more common than symmetric sequences and both types of organized bundles are much less common than disorganized nonsequential bundle particularly in the bude formation sediment was supplied directly from a delta to the north by resedimentation of delta front sands and slumping of upper pro delta muds and silts to form a lower pro delta turbidite fan fan growth is not readily explained by current models for single sourced tripartite subsea fans displaying radial growth it developed instead a bipartite growth pattern which was strongly influenced in its upper part by external variables including grain size distributary channel switching and other deltaic processes active tectonism within the basin and possibly sea level fluctuations the fan grew by down slope construction of independent levee channel complexes each of which headed in the upper pro delta and even possibly the delta front slumping and mobilization of argillaceous facies resulted in the random occurrence of contorted beds in all parts of the fan regionally extensive mudstones known as key shales within the fan deposits probably reflect large scal upslope delta lobe abandonment the crati and ebro fans of the mediterranean sea would appear to be good modern analogs for the crackington bude fan system

field evidence of rupture of the qingchuan fault during the 2008 mw7 9 wenchuan earthquake northeastern segment of the longmen shan thrust belt china abstract although many studies of the 2008 mw 7 9 wenchuan earthquake have described the ground deformation features rupture mechanism and structural features of the seismogenic fault zone associated with this event debate remains concerning the total length of the co seismic surface rupture zone and whether the earthquake ruptured the qingchuan fault in the northeastern segment of the longmen shan thrust belt lstb china in this paper we present new field evidence that the qingchuan fault was ruptured by the 2008 wenchuan earthquake and that the total length of the co seismic surface rupture zone is up to 285 300 km field investigations reveal that the earthquake produced a 60 km long surface rupture zone along the pre existing qingchuan fault with the offset being mainly right lateral strike slip and a distinct component of vertical slip co seismic surface ruptures are characterized by faults and extensional cracks field measurements indicate co seismic right lateral strike slip displacements along the qingchuan fault of 0 3 0 6 m and vertical offsets of 0 2 0 5 m which differs to the displacements observed along the central and southwestern segments of the wenchuan surface rupture zone in the displacement amount and sense the change in slip sense from thrust dominated slip in the central and southwestern segments of the lstb to right lateral strike slip dominated displacement along the qingchuan fault northeastern segment of the lstb reflects a change in the orientation of compressive stress along the lstb associated with eastward extrusion of the tibetan plateau as it accommodates the ongoing penetration of the indian plate into the eurasian plate

oblique high angle listric reverse faulting and associated development of strain the wenchuan earthquake of may 12 2008 sichuan china the 2008 wenchuan earthquake occurred on imbricate oblique steeply dipping slowly slipping listric reverse faults measurements of coseismic slip the distribution of aftershocks and fault plane solution of the mainshock all confirm this style of deformation and indicate cascading earthquake rupture of multiple segments each with coseismic slip occurring in the shallow crust above a depth range of 10 to 12 km interactions among three geological units eastern tibet the longmen shan and the sichuan basin caused slow strain accumulation in the longmen shan so that measurable preearthquake slip was minor coseismic deformation however took place mostly within the interseismically locked longmen shan fault zone the earthquake may have initiated from slip on a fault plane dipping 30 40 northwest in a depth range from 15 to 20 km and triggered oblique slip on the high angle faults at depths shallower than 15 km to form the great wenchuan earthquake

micropaleontologic record of late pliocene and quaternary paleoenvironments in the northern albemarle embayment north carolina u s a abstract micropaleontological data provide a strong actualistic basis for detailed interpretations of quaternary paleoenvironmental change the 90 m thick quaternary record of the albemarle embayment in the mid atlantic coastal plain of the usa provides an excellent opportunity to use such an approach in a region where the details of quaternary environmental change are poorly known the foraminiferal record in nine cores from the northern outer banks east of albemarle sound north carolina indicates the deposition of subhorizontal mostly open marine early to late pleistocene units unconformably upon a basement of late pliocene reduced oxygen fine grained shelf basin deposits pollen data record several warm cool fluctuations within the early to mid pleistocene deposits diatom data indicate that some fresh and brackish water units occur within the generally open marine pleistocene succession a channel cut by the paleo roanoke river during the last glacial sea level lowstand occurs in the northern part of the study area pollen indicates that the basal fluvial valley fill accumulated in cooler than modern climate conditions in the latest pleistocene overlying silts and muds accumulated under cool climatic estuarine conditions according to diatom and pollen data radiocarbon ages from the estuarine deposits indicate that the bulk of these sediments accumulated during the latest pleistocene the estuarine channel fill deposits are overlain by holocene open marine sands deposited as the rising sea transgressed into the estuary approximately 8 5 to 9 0 kyr bp within the barrier island drill cores of this study fully marine sedimentation occurred throughout the holocene however immediately west of the present barrier island mid to late holocene estuarine deposits underlie the modern albemarle sound the islands that currently form a continuous barrier across the mouth of albemarle sound have a complex history of holocene construction and destruction and large portions of them may be less than 3 kyr old the barrier island sands overlie open marine sands of colington shoal in the north and to the south overlie fluvial and marine sand filling paleo roanoke tributary valleys the pleistocene sediments underlying the northern outer banks study area are mainly of open inner to mid shelf origin if as is likely sea level continues to rise a return to such environmental conditions is likely in the near future

how does underlying geology affect coastline change an initial modeling investigation 1 conceptual geologic framework models predict that areas of the coast underlain by a weak or very fine grained lithology retreat landward faster than adjacent more resistant or coarser grained segments these apparently commonsense predictions seem inconsistent with observations that sandy coastlines underlain by heterogeneous lithology remain fairly smooth we have developed a numerical model to explore the interaction between shoreface lithology effects and alongshore transport processes on scales greater than years and kilometers shoreline indentations or sections of the coast that are slightly landward of adjacent sections tend to form in the model where the shoreface weathers more rapidly or is composed of finer grained material however alongshore transport tends to fill in these indentations slowing the weathering rates there while increasing them in adjacent areas where mobile sediment is preferentially removed over the long term this leads to an alongshore uniform retreat rate subtle shoreline undulations reflecting the heterogeneous geologic framework exist in the model but their amplitude reaches a steady state rather than increasing with time compositional heterogeneities determine the morphology of the coast while weathering rate heterogeneities control the thickness of sediment on the shoreface thus indentations can form in sections composed of harder less erodible rocks if they are finer grained

geomechanical model of the marmara sea region ii 3 d contemporary background stress field summary we present the contemporary 3 d background stress field of the marmara sea region derived from a geomechanical model the background stress field i e the component of the absolute stress state that is time independent over the seismic cycle primarily depends on the distribution of density and elastic parameters on the acting far field stresses from plate boundary forces and on fault geometries we take these into account to predict the 3 d background stress field including its spatial variations technically our model concept involves the definition of an appropriate initial stress state accounting for the gravitational reference stress state of the crust which is then changed by plate tectonics until the 3 d background stress field has evolved the modelled stress field agrees well with observations from earthquake focal mechanism solutions and their formal stress inversion with orientation of maximum horizontal stress and with the distribution of seismicity in the marmara sea in particular in the vicinity of fault bends the stress field deviates considerably from the regional nw se oriented maximum horizontal stress and exhibits variability of the stress regime our model results are consistent not only with dynamic observations but also with kinematic ones various kinematic observations are understandable from the stress field we show that a stress regime that indicates normal faulting in the basins is nonetheless reconcilable with almost pure strike slip motion on the main marmara fault the distribution of seismicity in the marmara sea can be explained in first order by the distribution of critical differential stress which is closely related to local fault geometries we refer the wide absence of seismicity between the bend of the main marmara fault near istanbul and the central basin to the relatively plane fault geometry of that segment normal stress on the main marmara fault is highly variable along strike which makes segment wise rupture more likely than a rupture of the seismic gap at once comparably low normal stress on the prince s islands segment indicates a shorter interevent time for this fault segment than for the central segment of the main marmara fault