history and influence of the danube delta lobes on the evolution of the ancient harbour of orgame dobrogea romania on the coast of northern dobrogea south of the danube delta the greek settlement of orgame was founded in the mid 7th c bc probably by milesian colonists the ancient city was located on the cape dolojman which today overlooks a large lagoon complex we undertook a chronostratigraphic study to i understand coastal changes around cape dolojman since ca 5000 years bp in connection with the construction of the danube delta lobes and ii identify potential sediment impacts related to human occupation of the site three cores were extracted from the lagoon area sedimentological and biological analyses were undertaken to reconstruct the evolution of the coastal palaeoenvironments the results show a closure of the marine bay around 3500 cal bp and its transformation into a lagoon environment the first major environmental change was due to the construction of the lobe st george i and the formation of the barrier lupilor around 2000 cal bp the formation of an intra lagoonal lobe the dunavatz led to the gradual transformation of the lagoon into a fluvial dominated system paradoxically lagoon waters today still wash the ancient greek harbour environment which has not been totally infilled by alluvial sediments to understand this paradox in a context of coastal progradation we compared and contrasted the geomorphological data with the nearby city of istros histria which was already landlocked at this time the location of these two greek colonies relative to the coastal sediment cell and barriers partly explains their contrasting palaeoenvironmental evolution until 2650 cal bp the increase in charcoal and organic matter in sedimentary archives is interpreted as an anthropogenic signal for a more extensive use of the vegetation cover following the foundation of the city of orgame e g for domestic use and funeral rites

seismic evidence for overpressured subducted oceanic crust and megathrust fault sealing water and hydrous minerals play a key role in geodynamic processes at subduction zones however there are few seismological constraints on the presence of water within the subducting plate audet et al model converted teleseismic waves to constrain the seismological properties of subducted oceanic crust from the cascadia continental margin to its intersection with the forearc mantle their observations suggest that water is pervasively present in fluid form at high pore pressures indicating that the megathrust is a low permeability boundary these results may hold important implications for our understanding of seismogenesis subduction zone structure and the mechanism of episodic tremor and slip this study models converted teleseismic waves to constrain the seismological properties of subducted oceanic crust from the cascadia continental margin to its intersection with the forearc mantle the observations suggest that water is pervasively present in fluid form at high pore pressures indicating that the megathrust is a low permeability boundary these results may hold important implications for our understanding of seismogenesis subduction zone structure and the mechanism of episodic tremor and slip water and hydrous minerals play a key part in geodynamic processes at subduction zones1 2 3 by weakening the plate boundary aiding slip and permitting subduction and indeed plate tectonics to occur4 the seismological signature of water within the forearc mantle wedge is evident in anomalies with low seismic shear velocity marking serpentinization5 6 7 however seismological observations bearing on the presence of water within the subducting plate itself are less well documented here we use converted teleseismic waves to obtain observations of anomalously high poisson s ratios within the subducted oceanic crust from the cascadia continental margin to its intersection with forearc mantle on the basis of pressure temperature and compositional considerations the elevated poisson s ratios indicate that water is pervasively present in fluid form at pore pressures near lithostatic values combined with observations of a strong negative velocity contrast at the top of the oceanic crust our results imply that the megathrust is a low permeability boundary the transition from a low to high permeability plate interface downdip into the mantle wedge is explained by hydrofracturing of the seal by volume changes across the interface caused by the onset of crustal eclogitization and mantle serpentinization these results may have important implications for our understanding of seismogenesis subduction zone structure and the mechanism of episodic tremor and slip

worldwide initiation of holocene marine deltas by deceleration of sea level rise radiocarbon dated deltaic sequences of holocene age from different parts of the world began to accumulate within a restricted time range from about 8500 to 6500 years ago evaluation of major delta processes indicates that deceleration in sea level rise was the key factor in holocene delta formation within many deltas there is as much as a 2000 year age range between basal deposits in seaward and landward cores this age difference records the progressive landward migration of near mean sea level depositional environments during the lower to mid holocene establishment of a chronostratigraphic framework for holocene delta development provides a fundamental global baseline for distinguishing sea level change from vertical land motion by tectonism and isostasy and for evaluating rates of future marine incursion into low lying deltas

role of fault gouge dilatancy on aseismic deformation transients 1 in the vicinity of episodic aseismic transients in several subduction zones the presence of interstitial fluids and near lithostatic pore pressure has been proposed to interpret seismic observations of high p to s wave speed ratio and high poisson s ratio under such conditions fault stabilization by dilatancy induced suction during increased shear strain rates becomes very efficient we analyze the frictional and hydraulic conditions for spontaneous transients on a fluid infiltrated fault including dilatancy and pore compaction in the framework of rate and state friction with a membrane diffusion approximation in both a simplified spectral model and a 2 d cascadia like subduction fault model the fault response is mainly controlled by three nondimensional parameters 1 w h the along dip width of the high pore pressure velocity weakening fault relative to a characteristic nucleation size 2 a drainage parameter u the relative time scales for fluid diffusion and friction evolution and 3 a dilatancy parameter e the relative contributions to stress drop from dilatancy and friction evolution the incorporation of dilatancy enables aseismic transients at much larger values of w h than is possible under conditions of constant pore pressure an analytic estimate of the maximum slip velocity as a function of w h e and u is derived and agrees reasonably well with the simulation results the dependence of the properties of modeled transients on the drainage parameter u is similar to that on the dilatancy parameter e for u e less than 1 maximum velocity decreases while recurrence period remains relatively constant for u e greater than 1 maximum velocity approaches the steady state velocity and recurrence period approaches the period at neutral stability in the subduction fault model using gabbro gouge friction properties the slip per episode and the recurrence period increase with w h generally following the trend defined without dilatancy the maximum velocity with dilatancy can be several orders of magnitude smaller than that without in particular for larger values of e and values of w h near the no dilatancy stability limit

mechanism of deep low frequency earthquakes further evidence that deep non volcanic tremor is generated by shear slip on the plate interface 1 we study the mechanism of low frequency earthquakes lfes in the nankai trough in western shikoku japan precise locations have previously suggested that they represent shear slip on the plate boundary in this paper we examine the mechanism of these events due to the low signal to noise ratio we analyze stacked lfe waveforms and compare them with the waveforms of nearby earthquakes of known mechanism within the subducting philippine sea plate analysis of both the focal mechanism using p wave first motions and the moment tensor using s waveforms indicates that lfes represent shear slip on a low angle thrust fault dipping to the northwest namely the plate interface together with reports that deep tremor consists of a swarm of lfes our results suggest that deep tremor is generated directly by shear slip on the plate interface and as such represents a seismic signature of the accompanying slow slip events

yangtze delta eastern china 1 geometry and subsidence of holocene depocenter abstract stratigraphic analysis of 59 borings serves to define the subsurface configuration of late quaternary deposits of the outer yangtze delta including both subaerial lower plain and its contiguous submerged sector isopachous maps of the holocene sediment section reveal a linear thickened trend parallel to the lower yangtze estuary chongming island which extends seaward southeast to the mid shelf maps depicting depths of the holocene to late pleistocene contact also highlight this thickened northwest to southeast trend and a deep downward bowing depression formed by the sedimentary sequence seaward of the yangtze mouth radiocarbon dated facies in the cores serve to calculate long term averaged subsidence rates for the holocene section 0 1 to 3 0 mm year on land and 1 6 to 4 4 mm year at sea this preliminary information is vital for planning coastal protection erosion salt water intrusion in this densely populated low lying region vulnerable to marine inundation

land subsidence in the nile delta inferences from radar interferometry the nile delta formed by progression of a complex system of deltaic fans throughout the pleistocene with the modern delta being formed from sediments supplied by at least ten distinct distributaries throughout the holocene with an average elevation of approximately 1 m above sea level within 30 km of the coast and a predicted rise in sea level of 1 8 5 9 mm yr the subsidence of the northern delta has become a topic of major concern to the egyptian population and government the nile delta is home to more than 50 million people and the major agricultural production area for egypt we evaluated the modern rates of subsidence of sections of the northeastern nile delta a total length of 110 km up to 50 km from the coastline using persist ent scatterer radar interferometry techniques applied to 14 ers 1 and ers 2 scenes the area covered includes the present active depocenter of the damietta promontory and the nearby mendesian depocenter that was active up to recent times to 2500 years ago the highest subsidence rates 8 mm yr twice average holocene rates do not correlate with the distribution of the thickest holocene sediments but rather with the distribution of the youngest depositional centers major deposition occurred between 3500 yr bp and present at the terminus of the damietta branch the adjacent slightly older 8000 2500 yr bp mendesian branch depositional center is subsiding at slower rates of 2 6 mm yr results are interpreted to indicate that 1 modern subsidence in the delta is heavily influenced by compaction of the most recent sediments and 2 highly threatened areas are at the terminus of the damietta and possibly the rosetta branches where active deposition is occurring

transgressive depositional systems of the mississippi delta plain a model for barrier shoreline and shelf sand development abstract depositional sequences generated in the mississippi river delta plain consist of a regressive and a transgressive component the transgressive component has been considerably less studied but accounts for the majority of the surface area on the lower mississippi river delta plain and up to 50 percent of the total sequence thickness in shallow water deltas the development and preservation of transgressive depositional systems in abandoned delta complexes follows the process of transgressive submergence in which the horizontal component of reworking occurs during shoreface retreat combined with a vertical component of submergence acting to preserve the sequence the evolution of transgressive depositional systems in each of the abandoned holocene mississippi river delta complex s can be summarized in a three stage model beginning with stage 1 an erosional headland and flanking barriers in this stage regressive sand deposits contained within abandoned deltaic headlands are reworked by the eroding shoreface and dispersed longshore into contiguous flanking barriers enclosing restricted interdistributary bays submergence of the delta plain during relative sea level rise generates an intradeltaic lagoon separating the former stage 1 sand body from the shoreline forming stage 2 a transgressive barrier island arc the landward migrating barrier island arc is unable to keep pace with relative sea level rise and the retreating mainland shoreline resulting in submergence and the formation of stage 3 an inner shelf shoal following submergence the former barrier island arc sand body continues to be reworked into a marine sand body on the inner continental shelf during stage 3 this sequence of coastal evolution provides direct evidence of barrier island formation with each stage producing a distinctive stratigraphic signature the current sea level rise models of shoreface retreat and in place drowning developed for the u s atlantic continental shelf do not adequately explain either the morphology or the stratigraphy of transgressive mississippi river delta sand bodies current models of mississippi deltaic stratigraphy emphasize the deep water artificially maintained balize delta which differs considerably from the shallow water shelf phase delta complexes that are the primary depositional constituents of he holocene mississippi river delta plain

ring shear studies of till deformation coulomb plastic behavior and distributed strain in glacier beds a ring shear device was used to study the factors that control the ultimate steady strength of till at high shear strains tests at a steady strain rate and at different stresses normal to the shearing direction yielded ultimate friction angles of 26 3 and 18 6 for tills containing 4 and 30 clay sized particles respectively other tests at steady normal stresses and variable shear strain rates indicated a tendency for both tills to weaken slightly with increasing strain rate this weakening may be due to small increases in till porosity these results provide no evidence of viscous behavior and suggest that a coulomb plastic idealization is reasonable for till deformation however viscous behavior has often been suggested on the basis of distributed shear strain observed in subglacial till we hypothesize that deformation may become distributed in till that is deformed cyclically in response to fluctuations in basal water pressure during a deformation event transient dilation ofdiscrete shear zones should cause a reduction in internal pore water pressure that should strengthen these zones relative to the surrounding till a process called dilatant hardening consequent changes in shear zone position when integrated over time may yield the observed distributed strain

delta progradation and chenier formation in the huanghe yellow river delta china abstract to clarify holocene development of the huanghe yellow river delta and the relationship between delta progradation and chenier formation detailed sediment analyses and high resolution radiocarbon dating were done on borehole samples taken from two sites on the present huanghe h9601 latitude 37 40 5 n and longitude 118 28 7 e with an altitude of 5 5 m and h9602 lat 37 47 8 n and long 118 54 3 e 4 8 m downcore changes of sediment facies and accumulation rate show that delta progradation occurred at least twice during ca 2 6 1 2 c 14 yrbp and 1855 present at the two borehole sites these phases of progradation correlate with superlobes 6 and 7 and superlobe 10 respectively of ten superlobes composing the holocene huanghe delta shown by c xue historical changes in the yellow river delta china marine geology 113 321 329 1993 the boundary of these sediments at h9602 is sharp and erosional and correlates with cheniers located between borehole sites on the delta plain the diastem period between these phases of progradation almost coincides with the periods when the river mouth of the huanghe was located in the northwestern part of the bohai sea during 1048 1128 ad superlobe 8 and the jiangsu region facing the yellow sea during 1128 1855 superlobe 9 this suggests that chenier formation and delta progradation are linked and controlled by sediment supply and river course shifts of the lower reaches of the huanghe

the seismic facies of a tidally influenced holocene delta boundary bay fraser river delta b c abstract the tidally influenced fraser river delta in southwestern british columbia is actively prograding into the strait of georgia to investigate the geometry stratigraphy and structure of the post glacial fraser river delta sediments a high resolution shallow seismic reflection survey was carried out during the summer of 1987 in the boundary bay region of the delta twenty kilometers of optimum offset seismic reflection data were collected these high resolution seismic profiles were shot with 3 m spacing between geophones and a two way travel time of 200 ms four seismic facies were identified representing foreset topset slope failure and distributary channel deposits the foreset seismic facies has reflections that dip at angles of 1 to 7 towards boundary bay along strike the reflections have horizontal or mounded patterns horizontal continuous reflections typify the topset seismic facies the slope failure facies is located within the foreset seismic facies and consists of upper convex reflections and broken internal reflections the distributary channel seismic facies is characterized by concave downward reflections and is incised into the top of the foreset facies

time dependent inversion of three component continuous gps for steady and transient sources in northern cascadia 1 an approach to invert gps time series to estimate crustal block rotations fault locking and strain rates while simultaneously solving for transient slow slip events is described and applied to the northern cascadia subduction zone the method can use continuous or survey mode gps time series or both i invert 5 6 years of 3 component continuous gps time series at 53 sites from cascadia to estimate simultaneously the block motions and strains locking on the subduction zone and source parameters of the four most recent slow slip events over the time period and section of the cascadia margin sampled the strain released in slow slip was 7 to 10 of the accumulated subduction strain but at the base of and immediately downdip of the locked zone beneath the olympic peninsula

archaeology to refine holocene subsidence rates along the nile delta margin egypt archaeological material and sites in the northern nile delta record rates of land subsidence that are higher than those derived from radiocarbon dated subsurface sediments reassessment of subsidence rate calculations reveals that previous subsidence measurements of 1 5 mm yr for the delta are minimum rates because sediment reworking can result in radiocarbon dated core ages that are older than the ages of final burial integration of archaeological and geologic subsurface data is essential for accurate age determinations differentiation of sub sidence from sea level rise and more precise calculation of vertical earth movement application herein of archaeological data to geological problems helps to refine subsidence rate measurements between the flexure zone landward margin of the holocene nile delta depocenter and the coast

yangtze delta eastern china 2 late quaternary subsidence and deformation abstract late quaternary deposits examined on high resolution seismic profiles provide evidence of recent subsidence of the outer yangtze delta in the east china sea deformed late pleistocene strata and mud diapirs tilted bedding and gas deformed structures in holocene sequences record remobilization of underconsolidated sediment within and adjacent to the yangtze depocenter deformation types and their specific position relative to the depocenter record displacement of sediment as a result of quaternary overburden and probable compaction and deep seated tectonic motion the configuration of depositional sequences demonstrates that subsidence in the outer yangtze delta has continued from the late pleistocene to the present

modelling of short interval silent slip events in deeper subduction interfaces considering the frictional properties at the unstable stable transition regime summary recent high resolution observations of crustal movements have revealed silent slip events sses with propagation velocities of around 10 15 km d 1 and with intervals of 3 14 months along the deeper parts of the cascadia and nankai subduction zones this study develops 2 d and 3 d models of these short interval sses considering the frictional behaviour that was confirmed experimentally by shimamoto for the unstable stable transition regime to represent this frictional behaviour a small cut off velocity to an evolution effect is introduced in a rate and state dependent friction law when the cut off velocity to the evolution effect is significantly smaller than that to a direct effect steady state friction exhibits velocity weakening at low slip velocities and velocity strengthening at high slip velocities at the deeper cascadia and nankai subduction interfaces the pore pressure is inferred to be high because of the dehydration of materials in the descending plate under conditions where the pore fluid pressure is nearly equal to the lithostatic pressure and the critical weakening displacement is very small short interval sses with propagation velocities and slip velocities of 4 8 km d 1 and 2 4 10 7 m s 1 respectively can be reproduced the propagation velocity of short interval sses is in proportion to the slip velocity the results also show that during the nucleation process of large earthquakes the occurrence of short interval sses becomes irregular because of the accelerated slips that occur at the bottom of the seismogenic zone our results suggest that monitoring of short interval sses might be useful for forecasting the main earthquakes

quantitative measure of the variation in fault rheology due to fluid rock interactions we analyze friction data from two published suites of laboratory tests on granite in order to explore and quantify the effects of temperature t and pore water pressure pp on the sliding behavior of faults rate stepping sliding tests were performed on laboratory faults in granite containing gouge granite powder both dry at 23 to 845 c lockner et al 1986 and wet pp 100 mpa at 23 to 600 c blanpied et al 1991 1995 imposed slip velocities v ranged from 0 01 to 5 5 m s and effective normal stresses were near 400 mpa for dried granite at all temperatures and wet granite below 300 c the coefficient of friction shows low sensitivity to v t and pp for wet granite above 350 drops rapidly with increasing t and shows a strong positive rate dependence and protracted strength transients following steps in v presumably reflecting the activity of a water aided deformation process by inverting strength data from velocity stepping tests we determined values for parameters in three formulations of a rate and state dependent constitutive law one or two state variables were used to represent slip history effects each velocity step yielded an independent set of values for the nominal friction level five constitutive parameters transient parameters a b1 and b2 and characteristic displacements dc1 and dc2 and the velocity dependence of steady state friction ss ln v a b1 b2 below 250 data from dry and most wet tests are adequately modeled by using the slip law ruina 1983 and one state variable a 0 003 to 0 018 b 0 001 to 0 018 dc 1 to 20 m dried tests above 250 can also be fitted with one state variable in contrast wet tests above 350 require higher direct rate dependence a 0 03 to 0 12 plus a second state variable with large negative amplitude b2 0 03 to 0 14 and large characteristic displacement dc2 300 to 4000 m thus the parameters a b1 and b2 for wet granite show a pronounced change in their temperature dependence in the range 270 to 350 c which may reflect a change in underlying deformation mechanism we quantify the trends in parameter values from 25 to 600 c by piecewise linear regressions which provide a straightforward means to incorporate the full constitutive response of granite into numerical models of fault slip the modeling results suggest that the succeptibility for unstable stick slip sliding is maximized between 90 and 360 c in agreement with laboratory observations and consistent with the depth range of earthquakes on mature faults in the continental crust

a new interpolation method to measure delta evolution and sediment flux application to the late holocene coastal plain of the argens river in the western mediterranean abstract rapid environmental changes along the mediterranean coasts influenced the sedimentary dynamics shoreline position and human settlements in deltaic areas over the last millennia an innovative and multiproxy approach using geostatistical modelling was developed to estimate geomorphic evolution and sediment fluxes in deltaic areas while palaeoecological conditions and environmental changes were assessed from geochemistry and cluster analyses of molluscan fauna this method was applied to the coastal plain of the argens river in southern france depositional environments of prodelta delta front river channel floodplain marsh and abandoned channel were identified from the study of facies associations the late holocene sediment flux in the argens river bayhead delta ranged from 15 800 2300 to 52 000 8500 m3 yr 1 the highest rate of sediment deposition between 2500 and 2000 cal yr bp was associated with increased river flooding in southeastern france a general decrease in subaqueous sediment flux over the past 2500 years was primarily controlled by a decrease in accommodation space and delta slope from 500 to 0 cal yr bp a sharp increase in subaerial sediment flux probably due to hydroclimatic change was contemporaneous with a period of high flood frequency during the little ice age a southward shift of the north atlantic westerlies combined with either a negative phase of the east atlantic west russian pattern or a negative phase of the east atlantic pattern coupled to a northward migration of the intertropical convergence zone could have led to increased fluvial activity in the lower argens valley during the late holocene

a slow thrust slip event following the two 1996 hyuganada earthquakes beneath the bungo channel southwest japan we report a slow thrust slip event that occurred beneath the bungo channel region southwestern japan on oct and dec 1996 two hyuganada earthquakes both mw 6 7 followed by afterslips occurred in addition a crustal movement characterized by an extremely slow rise was observed around the bungo channel about 200 km north from the epicenters and continued for about 300 days long assuming a slow slip on the plate boundary we estimate its duration and surface displacements from gps time series data by curve fitting and then determine the fault slip distribution we found that a slow slip without any earthquakes continued for nearly one year and released the seismic moment comparable to that of the hyuganada earthquakes occurrence of the slow thrust slip event suggests that this kind of event may be a characteristic mode of stress release at a transition region of interplate coupling

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

deltas radiocarbon dating and measurements of sediment storage and subsidence in holocene marine deltaic sequences there is no simple relationship between radiocarbon age and depth of sampling the nile and ganges brahmaputra deltas show remarkably similar radiocarbon age depth relationships 1 most radiocarbon dates by conventional and accelerator mass spectrometric ams analyses are older some by 4000 yr than reasonably expected 2 dates are commonly inverted i e older upcore and 3 sample dates at delta surfaces commonly exceed 2000 yr b p these anomalous age depth phenomena are in part a response to reservoir effects introduction of old carbon and emphasized herein influence of sediment storage and remobilization that prevail in fluvial and delta plains in fluvial systems sediment generally is not transported in a single episode from its original source area to the sea rather material transported from upland reaches and river valley to coast is subject to a repeated series of depositional burial and erosional events induced by episodic flooding overbank sedimentation and channel migration because sediment is likely to be temporarily stored in the delta plain it is difficult to determine the time of a sediment9s final deposition and burial at a delta site a successful strategy requires use of several independent dating methods including ams analyses of in situ basal peats and fossils and where possible archaeological evaluation of associated artifacts that are in place accurate dates are needed for reliable measurement of rates of delta plain aggradation and land subsidence information to help implement effective coastal protection measures

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

eastern mississippi delta late wisconsin unconformity overlying transgressive facies sea level and subsidence abstract analysis of 92 engineering core logs located in the balize sector of the eastern mississippi delta focuses on the late wisconsin unconformity and lithofacies of strata lying immediately below and above this stratigraphic horizon this major sequence boundary is a key feature used to correlate strata across shelf and slope to the basin observations emphasize lithofacies distributions of the latest pleistocene sediments underlying the unconformity the late pleistocene to early holocene transgressive facies and the immediately overlying deltaic deposits maps and a cross section compiled with this information highlight the critical relation between lithofacies distributions and late wisconsin sea level oscillations core analysis reveals that the transgressive facies comprises distinct environments of deposition offshore to onshore findings identify criteria to determine the approximate position of the shoreline at the late wisconsin maximum sea level lowstand and at the extent of early holocene maximum marine inundation in the balize complex mapping of lithologies along the late wisconsin unconformity serves to improve correlation of sediment facies with changes in acoustic response along high resolution seismic profiles an estimate of long term averaged land subsidence suggests lowering of at least 1 mm year near the shelfedge during the past 18 000 years this mapping also refines sea level response models for the mississippi delta including criteria to locate key paleogeographic features such as shelfedges and maximum flooding surfaces in other recent marine deltas and in older stacked deltaic sequences

late quaternary deltaic lowstand wedges on the rhone continental shelf france abstract shallow seismic profiles on the rhone continental shelf have shown the existence of stacked progradational lowstand wedges on the outer shelf accumulated during late quaternary glacioeustatic lowstands the wedges are bounded by sharp to erosional sequence boundaries and onlap onto the middle shelf the thickness of individual wedges attains 50 meters at the shelf edge where they are sheared by slumping the wedges exhibit well developed progradational clinoforms episodically interrupted by internal unconformities on which there is a downward shift of the succeeding clinoforms these represent small scale in the order of a few meters falls in sea level during the quaternary eustatic cycles the durations of the stable highstand conditions appear to have been too brief to permit the regressive highstand tract to prograde to the outer shelf therefore the shelf edge builds up entirely with lowstand wedges

punctuated eustatic sea level rise in the early mid holocene whether eustatic sea level rise through the holocene has been punctuated or continuous has remained controversial for almost two decades resolving this debate has implications for predicting future responses of remaining ice sheets to climate change and also for understanding the drivers of human settlement and dispersal patterns through prehistory here we present a sea level curve for the past 8900 yr from singapore a tectonically stable location remote from ice loading effects we also present critical and unique sedimentation rate organic 13c and foraminiferal 13c proxy records of sea level change derived from a shallow marine sediment core from the same area over the same time interval the sea level curve corroborated by the independent proxy records suggests rapid rise at a rate of 1 8 m 100 yr until 8100 cal calibrated yr b p a near cessation in the rate of sea level rise between 7800 and 7400 cal yr b p followed by a renewed rise of 4 5 m that was complete by 6500 cal yr b p we suggest that this period of relatively stable sea level during the early to mid holocene enabled modern deltas to advance providing a highly productive environment for the establishment of coastal sedentary agriculture periods of rapid sea level rise before and after may have catalyzed significant postglacial episodes of human dispersal in coastal regions

reef drowning during the last deglaciation evidence for catastrophic sea level rise and ice sheet collapse elevations and ages of drowned acropora palmata reefs from the caribbean atlantic region document three catastrophic metre scale sea level rise events during the last deglaciation these catastrophic rises were synchronous with 1 collapse of the laurentide and antarctic ice sheets 2 dramatic reorganization of ocean atmosphere circulation and 3 releases of huge volumes of subglacial and proglacial meltwater this correlation suggests that release of stored meltwater periodically destabilized ice sheets causing them to collapse and send huge fleets of icebergs into the atlantic massive inputs of ice not only produced catastrophic sea level rise drowning reefs and destabilizing other ice sheets but also rapidly reduced the elevation of the laurentide ice sheet flipping atmospheric circulation patterns and forcing warm equatorial waters into the frigid north atlantic such dramatic evidence of catastrophic climate and sea level change during deglaciation has potentially disastrous implications for the future especially as the stability of remaining ice sheets such as in west antarctica is in question

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

earthquake nucleation on rate and state faults aging and slip laws we compare 2 d quasi static earthquake nucleation on rate and state faults under both aging and slip versions of the state evolution law for both versions mature nucleation zones exhibit 2 primary regimes of growth well above and slightly above steady state corresponding respectively to larger and smaller fault weakening rates well above steady state aging law nucleation takes the form of accelerating slip on a patch of fixed length this length is proportional to b 1 and independent of a where a and b are the constitutive parameters relating changes in slip speed and state to frictional strength under the slip law the nucleation zone is smaller and continually shrinks as slip accelerates the nucleation zone is guaranteed to remain well above steady state only for values of a b that are low by laboratory standards near steady state for both laws the nucleation zone expands the propagating front remains well above steady state giving rise to a simple expression for its effective fracture energy g c this fracture energy controls the propagation style for the aging law g c increases approximately as the square of the logarithm of the velocity jump this causes the nucleation zone to undergo quasi static crack like expansion to a size asymptotically proportional to b b a 2 for the slip law g c increases only as the logarithm of the velocity jump and crack like expansion is not an option instead the nucleation zone grows as an accelerating unidirectional slip pulse under both laws the nucleation front propagates at a velocity larger than the slip speed by roughly b divided by the logarithm of the velocity jump where is the effective elastic shear modulus for this prediction to be consistent with observed propagation speeds of slow slip events in subduction zones appears to require effective normal stresses as low as 1 mpa

low sediment accumulation rates and erosion on the middle and outer nile delta shelf off egypt abstract the nile delta and its contiguous continental margin seaward of egypt form the major sediment repository on the north african margin together they constitute an integral depositional system man has increasingly modified the delta since pre dynastic time but most extensively this century by the emplacement of two dams across the nile at aswan in upper egypt sediment once transported by the nile river to the coast is now almost cut off and it is postulated that changes induced by man are likely to impact on sedimentation in distal sectors beyond the coast and inner continental shelf continued anthropogenic modification of the delta is expected to result in the increased erosion of the surficial sediment cover of the middle and outer nile delta shelf eddy flow patterns mapped by others show the interrelation of bottom currents on the mid and inner shelf thus in designing engineering projects on the nile delta and sinai margin it would be useful to monitor depositional changes seaward of the inner shelf

song hong red river delta evolution related to millennium scale holocene sea level changes abstract the song hong red river delta occurs on the northwest coast of the south china sea its evolution in response to holocene sea level changes was clarified on the basis of sedimentary facies and 14 radiocarbon dates from the 40 m long duy tien core from the delta plain and using previously reported geological geomorphological and archaeological data the delta prograded into the drowned valley as a result of early holocene inundation from 9 to 6 cal kyr bp as sea level rise decelerated the sea level highstand at 2 3 m from 6 to 4 cal kyr bp allowed widespread mangrove development on the delta plain and the formation of marine notches in the ha long bay and ninh binh areas during sea level lowering after 4 cal kyr bp the former delta plain emerged as a marine terrace and the delta changed into the present tide and wave influenced delta with accompanying beach ridges delta morphology depositional pattern and sedimentary facies are closely related to holocene sea level changes in particular falling sea level at 4 cal kyr bp had a major impact on the evolution of the song hong delta and is considered to be linked to climate changes

young danube delta documents stable black sea level since the middle holocene morphodynamic paleogeographic and archaeological implications new radiocarbon and optical dates show that the holocene danube delta started to build out of a black sea embayment 5200 yr ago delta lobe development phases differ by as much as 5 k y from previously proposed ages the new chronology allows for a better understanding of the danube delta paleogeography includ ing the demise of istria the main ancient greek roman city in the region prior reconstructions of sea level in the black sea inferred fluctuations to 15 m in range however stratigraphy of beach ridg es in the delta shows that the relative black sea level for the past 5 k y was stable in the danube delta region within 2 m and 1 5 of the current level hydroisostatic effects related to a proposed catastrophic reconnection of the black sea to the world ocean in the early holocene may have been responsible for the sea level reaching the highstand earlier than estimated by models the new sea level data suggest that submergence at several ancient settle ments around the black sea may be better explained by local fac tors such as subsidence rather than by basin wide sea level fluctuations

radiocarbon anomalies suggest late onset of agricultural intensification in the catchment of the southern part of the yangtze delta china abstract previously underused information from radiocarbon dates in well characterised sedimentary sequences in the southern yangtze delta china is here utilised in reconstruction of patterns of ancient erosion the southern yangtze delta was an important focus of food production in the early neolithic anomalous radiocarbon dates in holocene sediments from the southern part of the delta are unevenly distributed through time two clusters of dates in sediments ca 9000 7000 cal bp and ca 3000 1000 cal bp most likely indicate two periods of intensive erosion and redeposition of organic materials the older of the two clusters may have been associated with a marked episode of marine transgression whereas the younger cluster could reflect increasing levels of human disruption of soils and sediments in the catchment a relatively late increase in anthropogenic soil erosion supports recent archaeological evidence that following its early neolithic origins agricultural expansion and intensification occurred later on the southern yangtze delta than previously thought

high pore fluid pressure may cause silent slip in the nankai trough silent slip events have been detected at several subduction zones but the cause of these events is unknown using seismic imaging we detected a cause of the tokai silent slip which occurred at a presumed fault zone of a great earthquake the seismic image that we obtained shows a zone of high pore fluid pressure in the subducted oceanic crust located down dip of a subducted ridge we propose that these structures effectively extend a region of conditionally stable slips and consequently generate the silent slip

natural and anthropogenic influences on depositional architecture of the ural delta kazakhstan northern caspian sea during the past 70 years abstract this paper focuses on the ural delta in the northern zone of the caspian sea an area with particular characteristics where intense influence from anthropogenic and natural factors exists which acts on the fragile delta system we built a database to integrate the data from the published sources bathymetric survey and recent images in the geographical information system gis environment the results were linked to the caspian sea level csl curve which had many variations changing the ural delta system s dynamics and in its architecture in addition the anthropogenic changes contribute to shaping the actual ural delta architecture through the link between the results and csl we reconstructed an evolution model for the ural delta system for the last century and identified three different architectures for the ural delta determined by the energy that acted on the system in the last century and by the anthropogenic changes this work identifies six different delta phases which are shaped by csl changes during the last 70 years and by anthropogenic changes the delta phases recognized are i a lobate delta phase shaped during high csl before 1935 ii natural elongate delta 1935 1950 formed during rapid csl fall iii anthropogenic elongate delta 1950 1966 formed during rapid csl fall and after the ural caspian sea canal construction which modified the sedimentary deposition on the delta iv anthropogenic elongate delta 1966 1982 shaped during low csl phase v anthropogenic elongate delta 1982 1996 formed during a rapid csl rise phase and vi anthropogenic elongate delta 1996 2009 shaped during high csl that represent the last phase and actual ural delta architecture

evolution of the intra coastal tidal range in the rhine meuse delta and flevo lagoon 5700 3000 yrs cal b c abstract the evolution of the coastal and intra coastal tidal range in the western netherlands during the period 5700 3000 yrs cal b c 6875 4400 yrs b p is considered by comparing one coastal mean high water curve and two local mean high water curves mhw with respect to three alternative relative mean sea level msl curves 1 the existing 1982 msl curve for the western and northern netherlands 2 a msl curve based on the oldest part of the 1982 msl curve and the youngest part of a recently published msl curve based on data from the east central coastal plain and 3 a hypothetical msl curve for the east central coastal area assuming crustal subsidence of 0 10 m 1000 yr relative to the 1982 msl curve with regard to coastal tidal range the first and third msl curve yield a similar result a minor increase in coastal tidal range between 5200 yrs cal b c 6200 yrs b p and 4200 yrs cal b c 5350 yrs b p the second msl curve gives an increase in coastal tidal range from an assumed value of 2 m by 5200 yrs cal b c 6200 yrs b p to ca 3 m by 4100 yrs cal b c 5300 yrs b p conflicting with existing model results intra coastal tidal damping was a widespread phenomenon and played an important role in the evolution of the coastal plain for the first and second msl curves tidal attenuation in the rhine meuse delta and the east central coastal sector begins around 5250 yrs cal b c 6275 yrs b p with the third msl curve the reduction of the tidal range starts is 500 years later the first and third msl curves result in complete tidal damping in the rhine meuse delta and the east central coastal area with the second msl curve the tidal range in the rhine meuse delta remains ca 1 3 m whereas in the east central area tidal reduction is complete in spite of these different results it is clear that the period 5300 4300 yrs cal b c ca 6375 5400 yrs b p was very important for the subsequent evolution of the west netherlands coastal plain given that a the relative msl rise slowed down from about 0 8 m 100 yr to 0 23 m 100 yr b the coastal tidal range increased possibly by as much as 1 m resulting in higher sediment input into the intra coastal area while c further landward transportation of sediment was hampered due to intra coastal tidal damping which reduced rates of local mhw rise tidal current velocities and accommodation space

rapid strand plain accretion in the northeastern nile delta in the 9th century a d and the demise of the port of pelusium an unusually large 1 km 3 and rapid influx of nile river sediment in the early 800s a d resulted in accretion of an extensive strand plain 6 to 15 m thick 35 km long and as much as 12 km wide on the subsiding northeastern nile delta margin egypt this event is related to blockage of the pelusiac branch and breaking through of a new distributary to the west of present day port said probably representing initiation of the damietta branch the sand is of analytically identical age throughout the area and was deposited within less than 60 yr as indicated by 14 c and amino acid racemization analyses of donax shells from a series of cores radiocarbon dates in combination with historical accounts by al jakubi who found the strand plain already in existence when he visited the area in the late 800s place this event in the early 800s nilometer flood records suggest that the sequence of great floods of 813 816 and 820 may have been the triggering events this sudden displacement of sand caused pelusium then the principal port and fortified city of the northeastern nile delta located at the mouth of the pelusiac branch to be cut off from both the nile and the mediterranean and led to its decline and eventual abandonment by the 12th century when the crusaders arrived

holocene floodplain lake sediments in the amazon 14c dating and palaeoecological use abstract the holocene biostratigraphic record of amazon lowland rain forests is fragmentary and is based on restricted number of cores the majority representing sedimentation in a floodplain environment these biostratigraphic data have often been interpreted as demonstrating climatic oscillation between wetter and drier conditions and the subsequent vegetation changes here we survey and 14c date a further six western amazon floodplain lakes and examine their fluvially controlled sedimentation processes the lakes which are of the cutoff type are located along the rivers manu tambopata and amazon solimoes in the peruvian amazon lowlands all the lakes cored are under the influence of current overbank sedimentation of the parent suspension rich whitewater rivers and receive an annual fill of allochthonous inorganic suspension during the flood most of the cores collected were rich in minerogenic sediments gyttja clay loss on ignition we think that the observed bias towards older 14c ages documented in the gyttja clays is caused by the high proportion of old fine particulate organic matter being recirculated and resedimented within the suspension load the strong fluvial control of lake sedimentation and the unreliability of the 14c dates from the amazon suspension rich floodplains call for caution in palaeoecological interpretation furthermore owing to the low number of within lake replicate cores in the amazon holocene stratigraphy analyses we consider the postulated holocene climatic oscillation schemes to be tentative only

recent subsidence and northeast tilting of the nile delta egypt abstract sediment borings collected in the nile delta of egypt many of them radiocarbon dated indicate that the entire northern sector of this major depositional center in the eastern mediterranean is presently subsiding mapping of the base of the holocene deltaic facies which is dated at about 8000 6500 yrs b p reveals that differential lowering of the northern delta plain is preferentially accentuated toward the northeast long term subsidence rates at or near the coast averaged for the mid to upper holocene range from about 0 1 to 0 25 cm yr between alexandria and the north central delta margin rates increase markedly eastward to a maximum of about 0 5 cm yr in the port said manzala lagoon region and this rapid lowering explains the presence of thick marine delta lobe sequences of holocene age in cores in the northeastern delta in contrast only reworked remnants of holocene marine delta lobe deposits of the earlier river nile branches which once flowed to the north and northwest are preserved seaward of the present north delta coast subsidence has induced marked environmental changes particularly with respect to coastal erosion and salt water incursion the asymmetric pattern of saline ground water here attributed in part to the northeast tilt of the delta plain has serious implications for agricultural development in this intensely cultivated region

abrupt changes in north american climate during early holocene times recent studies of the greenland ice cores have offered many insights into holocene climatic dynamics at decadal to century timescales1 2 3 despite the abundance of continental records of holocene climate few have sufficient chronological control and sampling resolution to compare with the greenland findings4 butannually laminated sediments varves from lakes can provide high resolution continental palaeoclimate data with secure chronologies here we present analyses of varved sediments from deep lake in minnesota usa trends in the stable oxygen isotope composition of the sedimentary carbonate indicate a pronounced climate cooling from 8 9 to 8 3 kyr before present probably characterized by increased outbreaks of polar air decreased precipitation temperatures and a higher fraction of the annual precipitation falling as snow the abrupt onset of this climate reversal over several decades was probably caused by a reorganization of atmospheric circulation and cooling of the arctic airmass in summer that resulted from the final collapse of the laurentide ice near hudson bay and the discharge of icebergs from the quebec and keewatin centres into the tyrell sea the timing and duration of this climate reversal suggest that it is distinct from the prominent widespread cold snap that occurred 8 200 years ago in greenland and other regions1 5 6 no shifts in the oxygen isotope composition of sediment carbonate occurred at 8 2 kyr before present at deep lake but varve thickness increased dramatically probably as a result of increased deposition of aeolian dust taken together our data suggest that two separate regional scale climate reversals occurred between 9 000 and 8 000 years ago and that they were driven by different mechanisms

temperature and air pollution affected tree ring δ13c and water use efficiency of pine and oak trees under rising co2 in a humid temperate forest abstract to better predict forest productivity under rising atmospheric co 2 concentration co 2 it is critical to understand how intrinsic water use efficiency wue i and its relationship with tree growth are affected by the concomitant changes in environmental conditions such as precipitation temperature and air pollution that either enhance or undermine any potential co 2 fertilization effect we investigated changes in 13 c and wue i in annual rings and basal area increment bai of pinus densiflora from 1968 to 2007 and quercus variabilis from 1970 to 2007 trees in relation to precipitation temperature and air pollution in a humid temperate forest the wue i of p densiflora increased by 39 9 whereas that of q variabilis did not change over time in the study period the wue i was not affected by precipitation for both species but increased p p densiflora and with so 2 emissions for both species multiple regression models suggested that the effect of co 2 on tree growth was much higher than temperature however for the period 1998 to 2007 when so 2 emissions data were available so 2 emission was the driver of changes in bai and wue i and temperature effects became stronger than co 2 overall bai and wue i were positively p p densiflora but not for q variabilis we conclude that temperature and air pollution rather than precipitation were key determinants of wue i at the study site and that the two species had contrasting responses to environmental changes

episodic slow slip events and rate and state friction 1 there are several ways of generating episodic slow slip events in models of rate and state friction here i explore the possibility that they arise on velocity weakening faults whose length is tuned in some sense unlike spring block sliders which have a unique critical stiffness for instability elastically deformable faults have multiple length scales stiffnesses relevant to nucleation slow slip events occur when the fault is large enough to initiate an event but too small for that event to reach dynamic instability the available window of lengths depends upon the effective fracture energy of the growing nucleation zone for the aging evolution law this fracture energy increases rapidly with slip speed and the range of permissible lengths increases nearly as b b a where a and b are the coefficients of the velocity and state dependence of the frictional strength this range becomes very large for faults that are near velocity neutral a b however existing lab data firmly favor the slip law as a predictor of nucleation style and for this law the effective fracture energy increases much less rapidly with slip speed the range of fault lengths capable of hosting slow slip events in this case seems too small to explain why they are common to so many subduction zones slow slip can be stabilized over an exceedingly large range of fault lengths if the fracture energy increases with slip speed much more rapidly than for the aging law an appealing mechanism is inelastic dilation of the fault zone coupled with pore pressure reduction and diffusive recovery

examining the chronology of transgressions since the late pleistocene in the fujian coast southeastern china abstract the chronological framework of late pleistocene and holocene transgressional strata along the fujian coasts in southeastern china were examined using new 14c dates osl ages and diatom data from cores drilled in longhai this location was chosen because previous studies in the region have interpreted the occurrence of mis3 mis2 and holocene transgressions our study and a critical review of previous studies show that 14c dates of bulk samples from coastal areas tend to be erroneously older than the depositional age due to enhanced input of old carbon via erosion of mesozoic basement rocks from mountainous inlands also osl dates of deltaic and fluvial sediments either vary widely due to unsuitable luminescence properties of quartz grains or tend to be older than true depositional ages due to partial bleaching as such the previously considered late pleistocene transgression may have occurred in the holocene overall the early holocene transgression is well documented along fujian coast revealing largely consistent early holocene sea level histories from northern and southern sectors of fujian coast however late pleistocene transgressions are not well preserved along fujian coasts likely due to pervasive erosion our examination of the chronology of transgression in fujian coast suggests cautions for 14c dating of bulk samples and for osl dating of sediments in fluvial deltaic settings and emphasizes the importance of establishing a reliable chronological framework for understanding relative sea level history in this region and in similar settings elsewhere

reworking and discontinuities in holocene sedimentation in the nile delta documentation from amino acid racemization and stable isotopes in mollusk shells abstract the late holocene sedimentary history of the northwestern edge of the nile delta is reconstructed from amino acid racemization radiocarbon and stable isotope analysis of a series of bivalve shells from a core taken at the edge of lake maryut near alexandria amino acid racemization confirmed by radiocarbon and stable isotope analysis indicates that in many parts of the core mixed age mollusk assemblages are present dating of the time of sediment accumulation at various levels in the core is therefore based on the age of the youngest shells which are identified by amino acid racemization analysis lowest d l values ams radiocarbon analysis is used to determine the ages of the shells except for the most recent sediments last 100 yr for which aspartic acid racemization provides more precise ages amino acid racemization analysis of 59 shells from 21 levels in the 4 8 m holocene sequence in the core enabled identification of a large hiatus holocene sedimentation started at ca 2400 bc apparently corresponding to a westward shift of the course of the canopic nile distributary which lies to the east deposition continued at a rate of 1 4 mm per year ceasing at ca 550 bc at which time the canopic nile shifted eastward again and subsequently became defunct a marine connection during this period is indicated by stable isotope values of shells sediment accumulation began again only at the end of the 19th century when a series of irrigation canals was connected to the lake maryut basin stable isotope values indicate a strong freshwater influence deposition has continued to the present at a very high rate 19 mm per year due to supply of sediments by agricultural activity the relative ease with which racemization analyses can be carried out permits detailed analysis of core chronostratigraphy leading to more accurate reconstruction of core chronology hiatuses can be pinpointed and documented and age mixtures can be identified with appropriate individual shells being selected for ams radiocarbon analysis aspartic acid racemization analysis permits dating of samples from the last several hundred years a period for which radiocarbon analyses provide poor precision

aseismic slip transients emerge spontaneously in three dimensional rate and state modeling of subduction earthquake sequences 1 to investigate the possible physical mechanisms of recently observed aseismic slip events in the cascadia japan and mexico subduction zones we apply a dieterich ruina rate and state friction law to a three dimensional model of a shallow subduction fault that is loaded by imposed steady plate slip rate far downdip along the thrust interface friction properties are temperature and hence depth dependent such that sliding is stable at depths below about 30 km the system is perturbed into a significantly nonuniform slip mode along strike by introducing small along strike variations in the constitutive parameters a and a b in addition to large heterogeneous earthquake slip at seismogenic depths and associated postseismic transients we found that slip events which have clearly aseismic slip rates emerge spontaneously around the downdip end of the seismogenic zone both transients which start well after a seismic event and those which are triggered by other transients are observed from the simulations the slip velocity depth range and sometimes along strike migration speed of simulated transients are similar to the observations from natural subduction zones unstable stable transitional friction properties near the downdip end of the seismogenic zone are suggested to be an ingredient allowing such transients simulated transients can weaken the locking intensity of the updip seismogenic zone while enhancing that of the transition zone spatial temporal correlation of aseismic transients and nearby seismicity in the guerrero mexico area suggests that transients may signal a period of increased probability for nucleating their high frequency counterparts as damaging subduction thrust events

effects of frictional heating on the thermal hydrologic and mechanical response of a fault the mechanical response of a fault zone during an earthquake may be controlled by the diffusion of excess heat and fluid pressures generated by frictional heating in this study we formulate a fault model which incorporates the effects of frictional heating on the thermal hydrologic and mechanical response of a small patch of the failure surface this model is used to examine the parameters that control the fault response and to determine their critical range of values where thermal pressurization is significant the problem has two time scales a characteristic slip duration and a characteristic time for thermal pressurization the slip duration is set by the fault geometry the characteristic time for thermal pressurization is set by the slip rate the friction coefficient and the thermal and hydraulic characteristics of the medium the response of the fault depends on the relative magnitude of these two times results suggest that the fault width and hydraulic characteristics of the fault zone and adjacent medium are the primary parameters controlling the mechanical response for earthquakes occurring across zones of low porous medium compressibility 10 9 pa 1 and permeability 10 18 m2 the characteristic time for thermal pressurization is small in this case frictional heating can cause fluid pressures to approach lithostatic values the shear strength to approach zero and the temperature rise to stabilize at a maximum value dependent on the pore dilatational and transport properties of the porous medium whether the patch acts as a barrier to slip or exhibits substantial strain weakening is dependent on the shear strain across the fault moderate slip events where shear strains exceed two cause substantial strain weakening and consequently large stress drops accelerations and displacements thus it is possible for the patch to act as a barrier for small earthquakes but not for large ones both the dynamic stress drop and total displacement decrease for zones with larger compressibility permeability or width if the compressibility or permeability exceeds 10 8 pa 1 or 10 14 m2 or the shear strain is less than one then the effects of frictional heating may be negligible and the fault will exhibit no strain weakening characteristics consequently the patch acts as barrier that halts or resists further fault motion extrapolation of these results suggests that spatial variations in fault width and hydraulic characteristics will cause a heterogeneous stress drop and fault slip over the failure surface explaining many of the features of active faulting e g barriers nonuniform slip rupture stoppage random ground accelerations strong motions and frequency magnitude relations

exchanges of sediment between the flood plain and channel of the amazon river in brazil sediment transport through the brazilian sector of the amazon river valley a distance of 2010 km involves exchanges between the channel and the flood plain that in each direction exceed the annual flux of sediment out of the river at obidos 1200 mt yr 1 the exchanges occur through bank erosion bar deposition settling from diffuse overbank flow and sedimentation in flood plain channels we estimated the magnitude of these exchanges for each of 10 reaches of the valley and combined them with calculations of sediment transport into and out of the reaches based on sediment sampling and flow records to define a sediment budget for each reach residuals in the sediment budget of a reach include errors of estimation and erosion or deposition within the channel the annual supply of sediment entering the channel from bank erosion was estimated to average 1570 mt yr 1 1 3 the obidos flux and the amount transferred from channel transport to the bars 380 mt yr 1 and the flood plain 460 mt yr 1 in channelized flow 1230 mt yr 1 in diffuse overbank flow totaled 2070 mt yr 1 1 7 the obidos flux thus deposition on the bars and flood plain exceeded bank erosion by 500 mt yr 1 over a 10 16 yr period sampling and calculation of sediment loads in the channel indicate a net accumulation in the valley floor of approximately 200 mt yr 1 over 16 yr crudely validating the process based calculations of the sediment budget which in turn illuminate the physical controls on each exchange process another 300 400 mt yr 1 are deposited in a delta plain downstream of obidos the components of the sediment budget reflect hydrologic characteristics of the valley floor and geomorphic characteristics of the channel and flood plain which in turn are influenced by tectonic features of the amazon structural trough

relation of sequence stratigraphy to modern sedimentary environments one method of testing the concept of sequence stratigraphy is to compare it to quaternary sediments in which chronology stratigraphic relations and facies geometry are more clearly understood than in older rocks rapid deposition rates during quaternary glacial eustatic cycles in large deltaic depocenters generate sequences comparable to those in the ancient stratigraphic record in the northern gulf of mexico the late wisconsinan holocene mississippi river has deposited a type 1 sequence that includes lowstand transgressive and high stand systems tracts characteristics of modern mississippi river sedimentary environments support the methodology used in sequence analysis but the short time taken for sequence generation here raises important questions about sequence time scales correlation and driving mechanisms

dating modern deltas progress problems and prognostics 1 abstract radiocarbon dating is the method most frequently used to date holocene deltaic sequences but less than one quarter of 14c dates are within 500 years of predicted age such dates tend to be unreliable in other words often too old and commonly inverted upsection and core sample dates obtained near deltaic plain surfaces may be as old as mid to late holocene stratigraphic irregularities result primarily from downslope reworking of upland alluvial sediment with displacement of old carbon in the sediment that accumulates in lower valleys and deltaic plains use of dates that are too old results in inaccurately calculated rates most often too low of relative sea level rise and or land subsidence more reliable timing of deltaic sediment requires a multiple method dating approach including where possible identification of associated archaeological material developing an accurate dating strategy is a critical step for implementing reliable coastal protection measures needed for the rapi

strong tremor near parkfield ca excited by the 2002 denali fault earthquake 1 we show clear evidence of non volcanic tremor triggered by 2002 mw7 8 denali fault earthquake near parkfield triggered tremor is identified as bursts of high frequency 2 8 hz non impulsive seismic energy whose envelope is coherent among many stations and has the same periodicity as the passing surface waves the tremor originates from at least three hypocenters near the san andreas fault with differing frictional regimes two in the creeping section and the other where the san andreas is transitional between creeping and locked all the sources originate below the seismogenic zone suggesting that transitional frictional properties are necessary conditions for tremor generation tremor is excited by the love waves when the san andreas is sheared in a right lateral sense encouraging slip and is absent when the san andreas is sheared in a left lateral sense consistent with a simple frictional response to the driving stress

sequence stratigraphy seismic profiles and cores of pleistocene deposits on the rhone continental shelf abstract high resolution seismic profiles on the rhone deltaic shelf has shown the existence of a complex of pleistocene superimposed prograding wedges interrupted by a major incised valley system cutting across the shelf the individual wedges are interpreted from internal geometry and coring data as prograding shoreface deposits accumulated during periods of relative sea level lowering punctuated by small scale relative sea level falls or forced regressions they are related to 5th order glacio eustatic cycles and are stacked to form a composite 4th order sequence radiocarbon dating tandetron ams of the upper wedge to 40 ka bp indicates a stratigraphic hiatus across the shelf corresponding to the glacial maximum lowstand at the end of the wurmian cycle isotopic stage 2 during which sea level had dropped to 120 m below present sea level seaward tilting of the wedge boundaries indicate that the shelf has been subjected to differential subsidence that provides the necessary accommodation space for deposits to accumulate on the mid outer shelf the seaward tilting results from a cumulative effect of sediment and hydrostatic loading tectonism is also expressed by a westward shore parallel tilting in the area east of the incised valleys the amount of tilting the stacking pattern of the wedges and the location of incised valleys are structurally controlled by the alpine orogen which dips westward under the rhone margin the tectonic component interacts with glacio eustatic sea level fluctuations and accounts for the partition of the shelf into two areas with specific features separated by the rhone incised valleys

variation in radiocarbon ages of soil organic matter fractions from late quaternary buried soils radiocarbon dating of three organic matter fractions total humic acid and residue isolated from late quaternary buried soils of the central great plains reveals that there often are considerable differences among but no consistent order to the ages of fractions for late holocene soils the residue fraction or the total fraction generally produces the oldest age for late pleistocene soils however no fraction was consistently the oldest the absence of a consistent sequence of fraction ages is attributed to postburial contamination of soils when bulk samples from the same soil were split and sent to two laboratories different radiocarbon ages were usually obtained the variability in radiocarbon ages of soil organic matter confirms that caution should be taken when using radiocarbon ages obtained from different laboratories to make regional stratigraphic correlations

seasonal interannual and mesoscale variability of the black sea upper layer circulation derived from altimeter data 1 topex poseidon and ers altimeter data comprising the period from may 1992 to may 1999 are assimilated into a shallow water model for providing a dynamically consistent interpretation of the sea surface height variations and estimation of the temporal and spatial characteristics of the upper layer circulation in the black sea these 7 year long observations offer a new capability for interpretation of major transient and quasi permanent features of the upper layer circulation the instantaneous flow fields involve a complex eddy dominated system with different types of structural organizations in which the eddies and the gyres of the interior cyclonic cell interact continuously among themselves and with meanders and filaments of the rim current the circulation possesses a distinct seasonal cycle whose major characteristic features repeat every year with some year to year variability an organized two gyre winter circulation system disintegrates gradually into a series of interconnecting eddies in the summer and autumn months which are also characterized by more pronounced and complex mesoscale activity in the peripheral flow system our analyses suggest a revised schematic circulation picture of the major quasi permanent and recurrent elements of the black sea

spontaneous and triggered aseismic deformation transients in a subduction fault model 1 aseismic deformation transients can emerge as a natural outcome of the rate and state friction processes revealed in laboratory fault sliding experiments when that constitutive formulation is applied to model subduction earthquake sequences transients can arise spontaneously for certain effective stress variations with depth we show that if interstitial fluids are present and pore pressure is near lithostatic around and downdip from the frictional stability transition transients with recurrence intervals of 1 year are predicted on the basis of laboratory friction parameters and their temperature hence depth variations the recurrence interval decreases with and reaches 14 months when is 2 3 mpa dimensional analysis and numerical studies show that the fault response primarily depends on a parameter w h here the high pore pressure zone extends distance w updip from the stability transition and h is the stable patch size for steady sliding evidence that such fluid conditions may actually be present is independently provided by the occurrence of nonvolcanic tremors as apparent responses to extremely small stress changes and by petrological constraints on expected regions of dehydration for the shallow dipping subduction zones where transients are observed transient sequences can also be triggered by a modest one time step like interseismic stress perturbation on the subduction fault due to nearby earthquakes or to pore pressure changes e g during episodes of metamorphic fluid release properties of triggered transients and future thrust earthquakes depend on the interseismic time when the perturbation is introduced its relative location along the subduction fault and its magnitude

elastodynamic analysis for slow tectonic loading with spontaneous rupture episodes on faults with rate and state dependent friction we present an efficient and rigorous numerical procedure for calculating the elastodynamic response of a fault subjected to slow tectonic loading processes of long duration within which there are episodes of rapid earthquake failure this is done for a general class of rate and state dependent friction laws with positive direct velocity effect the algorithm allows us to treat accurately within a single computational procedure loading intervals of thousands of years and to calculate for each earthquake episode initially aseismic accelerating slip prior to dynamic rupture the rupture propagation itself rapid post seismic deformation which follows and also ongoing creep slippage throughout the loading period in velocity strengthening fault regions the methodology is presented using the two dimensional 2 d antiplane spectral formulation and can be readily extended to the 2 d in plane and 3 d spectral formulations and with certain modifications to the space time boundary integral formulations as well as to their discretized development using finite difference or finite element methods the methodology can be used to address a number of important issues such as fault operation under low overall stress interaction of dynamic rupture propagation with pore pressure development patterns of rupture propagation in events nucleated naturally as a part of a sequence the earthquake nucleation process earthquake sequences on faults with heterogeneous frictional properties and or normal stress and others the procedure is illustrated for a 2 d crustal strike slip fault model with depth variable properties for lower values of the state evolution distance of the friction law small events appear the nucleation phases of the small and large events are very similar suggesting that the size of an event is determined by the conditions on the fault segments the event is propagating into rather than by the nucleation process itself we demonstrate the importance of incorporating slow tectonic loading with elastodynamics by evaluating two simplified approaches one with the slow tectonic loading but no wave effects and the other with all dynamic effects included but much higher loading rate

widespread triggering of nonvolcanic tremor in california we identified seven locations on or near the transform plate boundary in california where nonvolcanic tremor was triggered by the 2002 denali earthquake this result implies that the conditions essential for nonvolcanic tremor exist in a range of tectonic environments models explaining tremor typically require conditions endemic to subduction zones that is high temperatures and fluid pressures because previously tremor was nearly exclusively documented in subduction zones the absence of tremor in geothermal areas is inconsistent with such models additionally we found no correlation between creeping or locked faults and tremor contrary to predictions of frictional models of tremor

transient fault slip in guerrero southern mexico the guerrero region of southern mexico has ac cumulated more than 5 m of relative plate motion since the last major earthquake in early 1998 a continuous gps site in guerrero recorded a transient displacement modeling indicates that anomalous fault slip propagated from east to west along strike of the subduction megathrust campaign gps and leveling data corroborate the model the moment release was equivalent to an mw 6 5 earthquake no m 5 earthquakes accompanied the event indicating the frictional regime is velocity strengthening at the location of slip

improving methodology for high resolution reconstruction of sea level rise and neotectonics by paleoecological analysis and ams 14c dating of basal peats abstract sea level research in several submerging coastal regions has traditionally been based on 14 c dating of basal peats that overlie a compaction free substratum and can be related to paleo ground water levels provided that an unequivocal relationship between ground water level and sea level can be assumed this approach contains two sources of uncertainty 1 the paleoenvironmental interpretation of samples is usually based on inherently inaccurate macroscopic descriptions in the field and 2 14 c ages of bulk peat samples may be erroneous as a result of contamination due to the uncertainties in both the altitude and the age the two crucial sources of evidence necessary to arrive at accurate sea level curves sea level index points are therefore represented by considerable but typically not quantified error boxes accelerator mass spectrometry ams opens new perspectives for this type of sea level research as illustrated by a paleoecological and ams 14 c study of basal peats from a small study area in the rhine meuse delta the netherlands where previous conventional work revealed highly problematic results a detailed macrofossil analysis has two purposes 1 an inferred paleoecological succession indicates a relatively accurate level of paludification of the site and hence rise of the ground water level 2 suitable macrofossils from that specific level are then selected for ams 14 c dating in spite of very small sample sizes our results are consistent and indicate that this approach can constitute a step forward in high resolution reconstruction of sea level rise the new results further enable a revision of holocene ground water gradient lines for the rhine meuse delta a knickpoint in these gradient lines can be related to the effect of faulting this approach therefore also has considerable potential to unravel and quantify neotectonic activity in submerging coastal settings

dilatancy controlled spatiotemporal slip evolution of a sealed fault with spatial variations of the pore pressure summary a range of observations suggest the formation and maintenance of sealed and hence overpressured compartments in fluid infiltrated fault zones it is assumed that hydromechanical properties of regions with variable pore pressure states control the fault s stability and thus its characteristic response that is seismic or aseismic slip accumulation we investigate in a systematic parameter space study the effects of spatial variations in pore pressure on spatiotemporal slip evolution along a hydraulically isolated fault plane the 3 d continuum model is governed by rate and state friction and constitutive laws for porosity reduction we show that the model response is sensitive to the degree of overpressurization and the efficiency of dilatant hardening mechanisms low pore pressures and small dilatancy effects result in unstable response types whereas high pore pressures and large dilatant effects lead to stable and aseismic creep regions with an unstable response are shown to support most of the stresses accumulated during interseismic periods accelerated slip nucleates preferably in regions of low pore pressure statistical properties of model seismicity produce a wide range of event sizes for moderate and large earthquakes in the case where dilatant mechanisms are inefficient in case of efficient slip rate controlled porosity increase less instabilities grow into large earthquakes final slip maps demonstrate the applicability of the chosen method to model seismicity controlled by frictional and hydraulic processes on a planar fault plane the evolution of governing variables that depend on the pore pressure environment provide a conceptual basis for the interpretation of observed response characteristics

an inflection in the rate of early mid holocene eustatic sea level rise a new sea level curve from singapore this study presents a sea level curve from 9500 to 6500 cal bp for the farfield location of singapore on the sunda shelf in southeast asia the curve is based on more than 50 radiocarbon dates from elevations of 1 43 m to 15 09 m representing sea level index points in intertidal mangrove and shallow marine sediments deposited by sea level rise accompanying deglaciation the results indicate that mean sea level rose rapidly from around 17 m at 9500 cal bp to around 3 m by 8000 cal bp after this time the data suggest but do not unequivocally prove that the rate of sea rise slowed for a period of 300 500 years centred on 7700 cal bp shortly after the cessation of meltwater input to the oceans from the northern hemisphere renewed sea level rise amounting to 3 5 m began around 7400 cal bp and was complete by 7000 cal bp the existence of an inflection in the rate of sea level rise with a slow down centred on 7700 cal bp is broadly consistent with other available sea level curves over this interval and is supported by evidence of stable shorelines and delta initiation elsewhere at this time as well as evidence of comparatively rapid retreat of the west antarctic ice sheet beginning around 7500 cal bp stepped sea level rise occurring shortly after 7500 cal bp and also earlier during deglaciation may have served to focus significant post glacial episodes of human maritime coastal dispersal into comparatively narrow time intervals

evidence suggesting fluid flow beneath japan due to periodic seismic triggering from the 2004 sumatra andaman earthquake 1 we show that very large surface waves from the 2004 sumatra andaman earthquake m9 2 triggered deep low frequency dlf seismic tremors beneath japan over a 500 km wide region the triggered seismicity was periodically excited synchronized with the amplitudes and phases of the oscillatory surface waves incident on the region periodic excitation implies that the specific phase of the surface waves plays an important role for the triggering estimation of stress changes in the source regions showed that the volumetric dilatation larger than 10 8 was the predominant factor for triggering thereby strongly supporting the hypothesis that dlf events are caused by processes related to fluid flow

recent subsidence of the northern suez canal in contrast to a recent interpretation of delta coast stability1 we now show that the northeastern nile delta in egypt has been actively sinking relative to the sea during the recent holocene epoch the northern nile delta is only about 1 m above sea level making the northern suez canal and coastal cities of port said and port fuad combined population nearly 500 000 highly vulnerable subsidence and world sea level rises contribute to coastal erosion incursion of salt in the groundwater underlying the delta plain and silting problems in the canal entrances2 these processes must be considered when implementing protection measures for this area

neotectonic history of eastern maine evaluated from historic sea level data and 14c dates on salt marsh peats we constructed a local relative sea level curve for eastern maine from 14 c dates on salt marsh peats to evaluate potential holocene neotectonic activity this sea level chronology indicates that contrary to suggestions made previously low elevations of late glacial shoreline features in eastern maine are not related to neotectonic activity during the past 5 ka a comparison between seismicity and tide gauge records leads to the conclusion that there is no relation between seismic activity and contemporary subsidence of eastern coastal maine we propose that eastern maine has not been affected by anomalous subsidence during at least the past 5 ka

the modern po delta system lobe switching and asymmetric prodelta growth the modern po delta system comprising five main delta lobes has been investigated by integrating vhr seismic surveys recorded offshore from water depths as shallow as 5 m to the toe of the prodelta in about 30 m with accurate historical cartography extending back several centuries previous studies give sedimentological and geochronological information from precisely positioned sediment cores this combined historical and stratigraphic reconstruction of the modern po prodelta allows volumetric reconstructions indicating an average sediment load of 9 4 10 6 ty r 1 for po di pila and po di goro gnocca lobes this estimate is remarkably consistent with the total sediment load of 11 5 10 6 ty r 1 available for parts of the last century from a gauge station at the apex of the delta plain in pontelagoscuro these integrated stratigraphic studies allow to explain the key characters of the po delta system a the marked asymmetry of the whole delta prodelta system reflecting prevailing sediment dispersal to the south of each individual delta outlet b the shoreparallel overlapping of successive prodelta lobes fed by distinct river outlets of ever changing relative importance c the delta outlets being artificially forced in a fixed position so that natural avulsion is prevented and delta lobes undergo headland retreat leaving a marked erosion on the prodelta d the presence of prodelta lobes showing widespread bcut and fillq features ranging from 100 to 300 m and depths up to 4 5 m filled with massive silt to very fine sand offshore of short lived very active distributary channels e g po di tolle lobe and suggesting that in some particular interval short lived episodes of submarine erosion are induced by catastrophic increases in river discharge of natural origin or induced by human maintenance the seismic stratigraphy of the modern po delta documents that markedly distinct prodelta architectures form when a newly activated lobe is located updrift north in this case or downdrift south of the one that is retreating in the first case the abandoned lobe becomes sheltered by the new rapidly advancing one in the opposite case the retreating lobe is updrift and a substantial portion of the sediment is cannibalized and transported to the new lobe downdrift d 2005 elsevier b v all rights reserved

postglacial deltaic sediments southern fraser river delta british columbia the fraser river delta the largest delta on the west coast of canada has been built into the strait of georgia during the holocene drill hole and seismic reflection records reveal a succession of sedimentary units deposited during early holocene progradation of the delta these overlie an irregular surface developed on pleistocene drift mud and silt similar to sediments presently accumulating off the mouth of fraser river in the southern strait of georgia are conformably overlain by a thick unit of sandy foreset beds dipping gently to the south southwest into boundary bay and deposited in a foreslope environment the foreset unit is sharply overlain by a much thinner topset sequence comprising silt and sand deposited in intertidal fluvial channel and overbank environments and peat deposited in swamps and bogs fifteen accelerator mass spectrometry radiocarbon dates on shell and wood indicate that most of the deltaic sediments south of the main channel of fraser river were deposited between ca 7

subglacial till a physical framework for its properties and processes the continuum theory of mixtures provides a framework around which present knowledge of subglacial till can be organized the proposed framework is provisional in two senses the constitutive description of till will require improvement and not all potentially significant processes have been included till is treated as a three component mixture of water clasts coarse grained solids and fine grained matrix solids these components obey mass balance equations and their behavior is subject to constitutive relations that describe such processes as darcian water transport fine grained sediment transport consolidation shear deformation dilatancy and comminution five state variables uniquely determine the compressibility permeability shear strength and other physical properties numerical solutions of the state evolutions equations illustrate that the properties of till are highly responsive to changes in the subglacial environment

holocene variation of radiocarbon reservoir age offshore western taiwan derived from paired charcoals and mollusks abstract we use the carbon content of charcoals from coastal sediments to evaluate the magnitude of alteration and apply this as a screening criterion for radiocarbon dating charcoals with carbon yields

a silent slip event on the deeper cascadia subduction interface continuous global positioning system sites in southwestern british columbia canada and northwestern washington state usa have been moving landward as a result of the locked state of the cascadia subduction fault offshore in the summer of 1999 a cluster of seven sites briefly reversed their direction of motion no seismicity was associated with this event the sudden displacements are best explained by 2 centimeters of aseismic slip over a 50 kilometer by 300 kilometer area on the subduction interface downdip from the seismogenic zone a rupture equivalent to an earthquake of moment magnitude 6 7 this provides evidence that slip of the hotter plastic part of the subduction interface and hence stress loading of the megathrust earthquake zone can occur in discrete pulses