earthquake swarms precursory to moderate to great earthquakes in the northeast india region abstract the northeast india region has seen ten m 7 1 2 earthquakes since 1897 including two great earthquakes of m 8 7 in 1897 and 1950 the last m 7 1 2 earthquake occurred on august 17 1952 with the exception of three earthquakes others are found to be associated with periods of background normal seismicity precursory swarms quiescence and mainshocks and the associated foreshocks and aftershocks the dataset has been critically examined for completeness considering the current capabilities for defining locations and also considering other parameters regression equations relating the mainshock magnitude mm the average magnitude of the largest two events in the swarm mp and the time interval mp between the beginning of the swarm and the mainshock have been developed these are mm 1 37mp 1 41 and mm 3log10tp 3 27 it is important to recognize precursory swarms and quiescence in real time indeed we believe we have recognized one such sequence in the vicinity of the arakan yoma fold belt on the basis of mp and tp values the lateral extent of swarm activity and the fact that no event of m 6 has occurred since 1975 in the preparation zone defined by the 1963 1965 swarm we estimate that an m 8 earthquake could occur at any time in the area bounded by 21 and 25 1 2 n and 93 and 96 e the focal depth of this impending earthquake is estimated to be 100 40 km in view of the focal depths of the other events in the swarm

earthquake prediction in northeast india a review a multidimensional geophysical approach is made to study earthquake precursors in northeast india resistivity gravity and seismological precursor anomalies for the two recent damaging earthquakes one on december 30 1984 magnitude 5 8 and the other on august 6 1988 magnitude 7 5 are very encouraging to intensify these studies in the region improved methods of magnetic and geohydrological precursor studies are suggested

suspended sediment transport in the deepwater navigation channel yangtze river estuary china in the dry season 2009 1 observations over spring and neap tidal cycles 1 the in situ data in the deepwater navigation channel dnc yangtze river estuary yre china in the dry season 2009 shows spring tides associated with greater maximum velocities more mixing less stratification and diffused fluid mud whereas neap tides are associated with smaller maximum velocities greater stratification inhibited mixing and stratified fluid muds the balance of salt flux indicates the seaward salt transport is dominated by fluvial flows and the landward salt transport is generated by compensation flows during spring tides but shear effects during neap tidal cycles the balance of suspended sediment flux illustrates the offshore sediment transport is dominated by fluvial flows as well but the onshore transport is induced by tidal pumping effects on spring tides and shear effects on neaps the suspended sediment transport is strongly affected by the salinity distribution and salinity gradient induced stratification in the dnc the spring neap asymmetry is generated by the estuarine gravitational circulation during low flow conditions while the flood ebb asymmetric stratification within a tidal cycle is due to the semidiurnal tidally movement of the salt front

sediment trapping in the changjiang estuary observations in the north passage over a spring neap tidal cycle abstract water current salinity and suspended sediment concentration ssc were measured at three anchored boat sites along the north passage np of the changjiang estuary over a spring neap tidal cycle in order to study sediment trapping and siltation in the estuary pronounced stratification was observed during the late flood tide and the following early ebb tide along with an advancing and retreating salt wedge whereas strong vertical mixing occurred during the late ebb when the effect of the salt wedge faded therefore the ssc in the flood ebb tidal cycle tended to be asymmetric in the upper reach of the np the seaward advective near bed sediment transport dominated the total near bed sediment transport whereas in the middle reach of the np the landward tidal pumping component dominated accordingly a notable convergent near bed residual sediment transport was generated near the middle reach because the convergence of residual sediment transport in the region of a salt wedge is generally recognized as sediment trapping convergent near bed residual sediment transport is the cause of the high sedimentation rate in the np

sediment pumping by tidal asymmetry in a partially mixed estuary 1 observations collected at two laterally adjacent locations are used to examine the processes driving sediment transport in the partially mixed york river estuary estimates of sediment flux are decomposed into advective and pumping components to evaluate the importance of tidal asymmetries in turbulent mixing at the instrumented location in the estuarine channel a strong asymmetry in internal mixing due to tidal straining is documented with higher values of eddy viscosity occurring during the less stratified flood tide as a result of this asymmetry more sediment is resuspended during the flood phase of the tide resulting in up estuary pumping of sediment despite a net down estuary advective flux at the instrumented location on the adjacent shoal where no pronounced tidal asymmetry in internal mixing was found both the pumping flux and advective flux were directed down estuary the down estuary pumping of sediment on the shoal appears to be driven by asymmetries in bed stress the impact of tidal asymmetries in bed stress at the channel location was negated because the amount of sediment available for resuspension was limited as a result the pumping flux was dominated by the overlying asymmetries in internal mixing the asymmetries in stratification appear to exert an important control on the vertical distribution of sediment by both impacting the eddy diffusivity as well as the fall velocity during the more turbulent flood tide the fall velocities are smaller suggesting the kolmogorov microscale is setting the upper bound on floc diameter

seismotectonics in northeast india a stress analysis of focal mechanism solutions of earthquakes and its kinematic implications summary in northeast india three major plates interact along two convergent boundaries the himalayas and the indo burma ranges which meet at the assam syntaxis to clarify this tectonic interaction and the underlying dynamics we determine the regional seismotectonic stress from the stress inversion of 285 double couple focal mechanism solutions of earthquakes with an average magnitude of 5 we then compare the reconstructed stress regimes with the available information about geodetically determined relative displacements north south compression in a direction consistent with india eurasia convergence prevails in the whole area from the eastern himalayas to the bengal basin through the shillong mikir massif and the upper assam valley e w extension in tibet is related to this n s india eurasia convergence not only does the major n s compression affect the outer segments of the indo burma ranges it also extends into the descending slab of indian lithosphere below these ranges although stresses at depth are controlled by bending of the slab beneath the burmese arc the existence of widespread n s compression in the bengal basin far away from the himalayan front is compatible with the previously proposed convergence between a shillong mikir assam valley block and the indian craton e w compression inside this block supports the hypothesis of a component of eastward extrusion stress inversion of focal mechanism solutions in the indo burma ranges reveals a complex stress pattern the burmese arc and its underlying lithosphere experience nearly arcperpendicular extension with ese wnw trends in the northernmost ne trending segment and ene wsw trends in the main n s arc segment such extensional stress documented from many arcs is likely a response to pull from and bending of the subducting plate at the same time the indo burma ranges are under compression as a result of oblique convergence between the sunda and indian plates the maximum compressive stress rotates from ne sw across the inner and northern arc to e w near the bengal basin this rotation is consistent with the deformation partitioning reflected in the rotation of relative displacement vectors from a ssw directed sunda burma motion to a wsw directed burma india motion as a consequence of this partitioning the major belt parallel fault zones show a variety of movements across the main n s arc segment from right lateral slip in the inner ranges to oblique reverse dextral slip in the outer ranges and pure thrusting in the westernmost foreland belt

anomalous behaviour of precursor resistivity in shillong area ne india summary daily measurement of apparent resistivity from 1984 may to 1985 october in shillong plateau india has been carried out for an earthquake precursor study the resistivity changes which occur 7 to 10 days before earthquakes do not necessarily satisfy the dilatancy hypothesis which of late has been subjected to criticisms of not being a generalized phenomenological explanation of precursor resistivity variation prior to earthquakes resistivity may increase or decrease or may not even show any change depending on the orientation of measuring electrodes the elastic nature of the geological formation where observations are made and the direction of tectonic stress

particle trapping in estuarine tidal flows particle trapping in estuarine turbidity maxima etm is caused primarily by convergent mean and or tidal fluxes of sediment the result is an approximately bell shaped along channel distribution of vertically integrated tidal cycle mean suspended sediment concentration observations from the columbia river estuary suggest that 1 strong two layer or internal along channel residual and overtide flows are generated by time varying stratification and 2 correlations between the near bed velocity and the suspended sediment fields at these frequencies are important in landward transport of sediment a new spatially and temporally integrated form of the sediment conservation equation has been derived to analyze this trapping process time changes in tidally averaged sediment concentration between two estuarine cross sections can be shown to be related to the divergence of the seaward river flow transport the divergence of velocity shear sediment stratification correlations for the mean flow and each tidal constituent and net erosion or deposition at the bed vertically integrated variables other than seaward river transport are absent from this integrated balance analysis of sediment fluxes using this balance supports the idea that internal residual and overtide circulations are primarily responsible for the landward sediment transport on the seaward side of etm found near the upstream limits of salinity intrusion the balance also shows that attempts to represent fluxes causing trapping of sediment in an etm as a product of a time mean vertically integrated along channel gradient and a diffusivity inevitably lead to the appearance of countergradient transport and thus a negative diffusivity on the seaward side of the etm this result occurs because the trapping process is inherently nonlinear and at least two dimensional and because a one dimensional representation is physically unrealistic

bedforms and bed material transport pathways in the changjiang yangtze estuary abstract bed features were mapped using a thermal depth recorder and a side scan sonar in the changjiang yangtze estuary and flows were observed and bed surface materials were sampled to investigate bed material transport pathways distinct scales and dimensions of dunes were observed in terms of the classification scheme of ashley ashley g m 1990 classification of large scale sub aqueous bedforms a new look at an old problem journal of sedimentary research 61 160 172 forming a dune set in the flood season large dunes occurred predominately in the surveyed area of the estuarine zone and two dimensional dunes predominated in the dry season while three dimensional dunes prevailed in the flood season sharp lee sides of dunes have low angles indicating a significant suspended load transport for the bedform migration and the majority of them face down estuary reflecting the controlling process by the ebb current the bed material migrations in terms of relative maximum gross transport show a satisfactory agreement with the sonar mapping in the dry season the relative maximum gross transport as an independent estimator of migration direction can be used to effectively determine the bed material transport directions in the changjiang estuary

the formation of estuarine turbidity maxima due to density effects in the salt wedge a hydrodynamic process study abstract by means of a numerical model of an idealized flat bottom estuary the paper studies the hydrodynamic control of the turbidity zone by the combined effect of the salt wedge and tidal movements the model is of two dimensional x z finite difference type with high resolution in time and space it computes momentum surface elevation salinity suspended particulate matter spm turbulent kinetic energy and dissipation rate as prognostic state variables at the seaward boundary a tidal forcing is applied at the landward boundary a weir is situated where a constant freshwater discharge is prescribed the initial spm concentration is horizontally homogeneous after simulating a few tidal periods the model results exhibit the evolution of a stable spm peak the estuarine turbidity maximum or etm at the tip of the salt wedge an inspection of the tidal mean velocity profiles around the etm shows that this trapping of spm is due to a residual near bottom upstream current in the region of the salt

analysis of coal banding texture and implications for megascopic image analysis abstract window filtering methods were modified to analyse megascopic textural information acquired from banded bituminous coal seams in the field although banding texture directly influences the physical properties of coal methods for its characterisation and analysis are poorly developed banding texture was obtained manually from the coal face and core at a minimum resolution of 1 mm window filtering was used to determine the optimum resolution 30 50 mm required for accurate discrimination of coal lithotypes by either manual or image analysis methods methods used to automate this procedure and their problems are discussed

process based morphodynamic modeling of the yangtze estuary at a decadal timescale controls on estuarine evolution and future trends abstract understanding the decadal morphodynamic evolution of estuaries and deltas and their controls is of vital importance regarding management for estuarine function and sustainable development this work addresses this issue by applying a process based model system delft3d to hindcast and then forecast the morphodynamic evolution of the yangtze estuary at a decadal timescale forced by the river and tides the model considers sand mud mixture and the variations of river water discharge and sediment discharge the morphodynamic model is validated against three periods i e an accretion period 1958 1978 an erosion period 1986 1997 and a recent accretion period with human activities 2002 2010 model results show good performance with respect to spatial erosion and deposition patterns sediment volume changes and hypsometry curves the model reveals quite different behaviors for mud transport between the dry and wet seasons which is subject to the prescription of river boundary conditions and bed composition we define six scenarios to project evolution to the year 2030 under decreased river inputs and increased relative sea level the simulations reveal that overwhelming amount of erosion will likely occur in the inner and mouth bar area of the estuary particularly the mouth zone will shift from net deposition before 2010 to net erosion by 2030 mainly because of decreasing sediment supply changes in water discharge have minor effects on the projected trend net erosion will be considerable when the sediment supply is extremely low 100 mt yr 1 due to the abundance of erodible modern sediment in the yangtze estuary erosion within the mouth bar area may be unexpected including the deepening of the tidal inlet at east chongming mudflat and the formation of a flood channel on the seaward side of jiuduansha shoal overall the model results provide valuable information for sustainable delta management under changing conditions for both the yangtze system and other similar estuaries and deltas with diminishing sediment supplies

cyclonic spirals in tidally accelerating bottom boundary layers in the zhujiang pearl river estuary abstracta velocity spiral in the tidally accelerating bottom boundary layer bbl was defined as a directional shear of the prevailing flow with the elevation and the tidal phase however so far there is no information on the spiral for the oscillatory bbl flows or a valid explanation for its origin life history and persistence to investigate this rotating current in the tidally accelerating bbl flow the authors performed instrumented tripod observations in the tidally energetic zhujiang pearl river estuary the tidal bbl flows may fall into three distinct regimes i the quasi steady phase in the peak tide ii the accelerating decelerating phase at the slack tide and iii the transition between i and ii when a cyclonic spiral occurs only in the early late ebb the subcritical spiral defined by a froude number of the oscillatory bbl flow may be analytically examined by unsteady linearized turbulent bbl equations the spiral is formed under the momentum balance between local acceleration

a model of turbidity maximum maintenance in the irish sea a two dimensional model has been developed in order to improve understanding of the processes which interact to maintain the sediment concentrations at an isolated turbidity maximum in the irish sea throughout the year the model comprises two interchangeable populations of particles with different diameters one of fine cohesive material the other made up of flocs both populations are slow settling and subject to horizontal diffusion resuspension settling aggregation and disaggregation the equations used to describe the processes of aggregation and the break up of flocs in response to sediment concentration and turbulent shear have been developed by the tuning of the model to observations due to high turbulent shear at the turbidity maximum the particles are predominantly fine while the sediment in the surrounding water is made up of larger flocs diffusion of small particles out of the turbidity maximum balanced by the diffusion of aggregated material towards it provides a mechanism for its maintenance the modelled sediment concentrations at the turbidity maximum can be reproduced year on year with no loss due to diffusive processes this is achievable with a limited exhaustible source of material which is not replenished once resuspended through comparison with satellite imagery the correlation of the modelled sediment concentrations with observations is investigated both spatially and temporally the seasonal cycle is reproduced well by the model with winter and summer concentrations matching those observed spatially the model also performs well in both turbid regions and those where the surface sediment load is low

contrasts between estuarine and river systems in near bed turbulent flows in the zhujiang pearl river estuary china a bottom mounted instrumental tripod was deployed in the tidally energetic zhujiang pearl river estuary to examine the contrasting properties of the bottom boundary layer bbl flows between estuarine and tide affected river systems three aspects of the bbl flows were investigated to understand the mechanism of the turbulence responses to the large scale ambient forcing the flow structures profile anisotropy and spectra shearing strains and stresses and the balance of turbulent kinetic energy tke single log law profiles and turbulence anisotropy predominated in the two systems but the non log regime and stronger anisotropy occurred more frequently at the slack tide in the estuary the adv based turbulence intensities and shearing strains both exceeded their low frequency counterparts frictional velocities and mean shears derived from the logarithmic law on the contrary the adv based reynolds stresses were smaller than the log profile derived bottom stresses so the hypothesis of a constant stress layer cannot be well satisfied especially in the river the bandwidth of the inertial subrange in the river was of one decade larger than in the estuary the balance between shear production and viscous dissipation was better achieved in the straight river this first order balance was significantly broken in the estuary and in the meandering river by non shear production dissipation due to wave induced fluctuations or salinity sediment stratification all these disparities between two systems in turbulence properties are essentially controlled by the anisotropy induced by the large scale processes such as secondary currents density stratification in conclusion the acceleration of unsteady flows determines the profile structure of the bbl flow and turbulence anisotropy results in the invalidation of the phenomenological relations such as the constant stress hypothesis and the first order tke balance

sediment resuspension and implications for turbidity maximum in the changjiang estuary abstract a comparative study on the properties and transport of the cohesive sediments in the mouths of the changjiang estuary proves that the suspended sediment concentration ssc is principally enhanced by the resuspension of bottom sediment in the mouth bar reach coupled with the deformed tidal wave and strong tidal current salinity intrusion and vertical gravitational circulation lead to the trapping of the suspended sediment inflowed from the river and the sea the turbidity maximum tm is therefore delivered by the local resuspension of the accumulated materials and bed erosion the tm in the changjiang estuary is marked not only by its high ssc relative to the adjacent reaches but also by the high wash load content transport of sediment is very important settling velocity of suspended sediment is increased by flocculation the massive settling during weak current periods often gives rise to the formation of fluid mud the tm coincides locally with the mouth bars the transport of suspended sediment in the tm is analysed by using a splitting method it is concluded that the contributing factors consist of advective terms and tidal pumping advective transport is dominant in the north channel and tidal pumping predominate in the north branch and south passage and the north passage is in an intermediate situation

radon content of groundwater as an earthquake precursor evaluation of worldwide data and physical basis the properties of a worldwide data set of 91 radon 222 rn anomalies the frequency of occurrence the precursor time interval and the distribution of peak amplitudes are correlated with earthquake data such as the respective magnitude and epicentral distance these anomalies were reported as precursors to earthquakes in the united states ussr china japan and iceland although the data set is incomplete and limited by experimental deficiencies several consistent patterns emerge radon anomalies from different tectonic regions show similar patterns the radon anomalies occur at greater epicentral distances for earthquakes of the larger magnitude anomalies preceding large earthquakes m 6 are frequently observed at a distance of 100 to 500 km these distances are larger than several times the rupture dimensions of the future earthquakes the time from the onset of an anomaly to the time of the earthquake the precursor time increases with magnitude but decreases with distance between epicenter and radon station in addition radon anomalies are observed more frequently prior to large earthquakes than prior to small ones indicating that the preparation zone increases in size as magnitude increases the peak amplitude does not scale with magnitude but forms a consistent pattern with epicentral distance in that the larger the earthquake magnitude the farther away the largest amplitudes tend to occur the preparation zone of the earthquake where the anomalies occur forms an almost continuous annulus that expands with time away from the future rupture zone the outer radius of this annulus scales with the earthquake magnitude model calculations indicate that strain fields of at most 10 6 to 10 8 strain caused the radon anomalies if these strains are divided by the appropriate precursor time minimum strain rates from 10 7 day 1 to 10 10 day 1 are obtained such small strains and strain rates suggest that in most cases neither mechanical crack growth induced by dilatancy nor mechanical coupling between pore pressure and the rock matrix caused the anomalies large changes in the orientation of the local strain field however could occur and affect the local stress intensity factor since changes in the stress intensity factor can result in stress corrosion the occurrence of radon anomalies is attributed to slow crack growth controlled by stress corrosion in a rock matrix saturated by groundwater

a total load algorithm for sand transport by fast steady currents a simple algorithm for total load sand flux is proposed which is suitable for application to high energy environments where fast currents promote significant sand suspension the algorithm is a power relationship constrained by a threshold condition q k u1 u1t u1t nwhereqis total sand flux u1andu1tare mean current velocity and threshold current velocity 1 m above the bed respectively andkis an appropriate entrainment function the algorithm has been calibrated for sands mean grain diameter 190 930 m over a range of mean current velocities 0 2 1 5 ms 1 using the extensive experimental data set of guyet al 1966 prof papers u s geology survey 462 96 it is shown thatkandnare dependent on mean grain diameter they can be determined from appropriate calibration curves the exponentnvaries from 4 increasing with decreasing grain diameter as transport by suspension becomes increasingly important napproaches a minimum constant value for coarser sands as bed load transport becomes dominant there is evidence that the exponentndecreases with increasing current velocity in the case of fine sands moved by fast currents the entrainment functionkdecreases with decreasing grain diameter as bed roughness and entrainment efficiency decrease and approaches a minimum constant value for fine sands the algorithm reproduces flume sand transport rates more reliably than the previous formulations of gaddet al 1978 journal of sedimentary petrology 48 239 252 and hardisty 1983 journal of sedimentary petrology 53 1007 1010 which ignore suspension and use erroneous calibration coefficients

microseismicity and source mechanism study shillong plateau northeast india microearthquakes recorded by two surveys in the shillong plateau during december 1982 july 1983 and january february 1984 respectively have been analyzed for seismicity and tectonic study in the region of 1 000 events recorded during the surveys 180 events with reliable p and s readings which are observed within 50 km radius of the network are relocated by the homogeneous station method it is found that the events are mostly confined within a depth range of 10 to 35 km the seismicity in general may be correlated with the major geological structure lineaments in the area high rates of seismicity are observed in the shillong and tura areas on the other hand an aseismic zone is delineated to the east of shillong composite source mechanisms of two groups of microearthquakes show thrust fault mechanisms one group of microearthquakes 1982 to 1983 in the shillong area shows pure thrust faulting with a se nw compressive stress p axis whereas the other group of microearthquakes 1984 in the tura area shows thrust faulting with a strike slip component and a ene wsw compressive stress p axis the stress orientations are compatible with the known tectonics of the region collision of the indian plate with the eurasian plate at the himalaya and subduction of the indian plate beneath the burmese plate at the arakan yoma range

maceral controls on porosity characteristics of lithotypes of pennsylvanian high volatile bituminous coal example from the illinois basin abstract porosity characteristics of vitrain clarain durain and fusain lithotypes of the springfield coal member of the petersburg formation and the danville and hymera coal members of the dugger formation from the illinois basin were investigated with a special emphasis on the control of coal macerals on pore size distribution these pennsylvanian coals are of high volatile bituminous rank and have vitrinite reflectance ranging from 0 51 to 0 60 the lithotypes studied show decreasing values of brunauer emmett teller surface area and micro and mesopore volumes from vitrain through clarain and durain to fusain within the mesopore size range vitrain and clarain are dominated by pore size widths of 4 to 10 nm whereas durain and fusain have more volume for pores larger than 20 nm in contrast to mesopores micropore sizes are very similar for all lithotypes averaging 1 37 to 1 39 nm in addition to differences among lithotypes there are significant differences in pore characteristics among the three coals studied with largest surface areas and pore volumes documented for the hymera followed by the danville and the springfield a strong relationship exists between surface area mesoporosity and microporosity and maceral composition with vitrinite having a very strong positive correlation liptinite having a weak positive correlation and inertinite having a strong negative correlation negative correlations of total porosity with vitrinite and liptinite and positive correlations with inertinite suggest that among the maceral groups pores in inertinite contribute most to the total porosity the fourier transform infrared spectrometry technique demonstrates that fusains from the three coals studied have higher aromaticity and a higher degree of aromatic ring condensation and lower hydrocarbon potential than the other lithotypes whereas chemical differences between vitrain clarain and durain are less distinct in addition there is a relationship between aromaticity of the lithotypes and surface area and mesopore and micropore volumes

suspended sediment transport in the deepwater navigation channel yangtze river estuary china in the dry season 2009 2 numerical simulations 1 a three dimensional wave current sediment coupled numerical model with wetting and drying process is developed to understand hydrodynamics and sediment transport dynamics in the deepwater navigation channel dnc the north passage of the yangtze river estuary yre china the model results are in good agreement with observed data and statistics show good model skill scores and correlation coefficients the model well reproduces the spring neap variation between a well mixed estuary and a highly stratified estuary model results indicate that the estuarine gravitational circulation plays the most important role in the estuarine turbidity maximum etm formation in the dnc the upstream nonlocal sediment intrusion through the spillover mechanism is a major source of sediment trapping in the north passage after the morphological changes numerical studies are conducted to show scenarios in the yre under the effects of different forcings river discharges waves and winds between these study cases surface wave breaking relieves the sediment trapping and bottom wave current interaction aggravates the bed erosion and elevates the ssc in the etm the former and the latter have the least and largest influence on the suspended sediment transport in the dnc the wind effects have a greater influence on sediment trapping than the river discharges and the steady northwesterly wind condition favors the siltation in the dnc most the significance of density driven turbidity current is also assessed which can enhance the saline water intrusion and suppress the turbulent mixing in the bottom boundary layer

estimating bottom stress in tidal boundary layer from acoustic doppler velocimeter data bed stresses in the bottom boundary layer of the york river estuary virginia were estimated from three dimensional near bottom velocities measured by acoustic doppler velocimeters advs and also by a profiling array of electromagnetic current meters by assuming the measurements were made in a constant stress layer four methods of stress estimation were evaluated using advs direct covariance cov measurement turbulent kinetic energy inertial dissipation utilizing the kolmogorov spectrum and log profile the four methods yielded similar estimates of frictional velocity u based on adv output from both 14 cm and 44 cm above bed all eight estimates of average u were consistent with the overall mean of 1 10 cm s to within the 95 confidence interval for individual burst estimates the cov method worked slightly better nearer the bed possibly because of the sensitivity of cov to the upper limit of the constant stress layer the inertial dissipation method performed marginally well at 14 cm above bed likely because of sediment induced stratification and insufficient separation of turbulent production and dissipation scales the log profile method was the most variable and appeared most sensitive to stratification and to the thickness of the constant stress layer the turbulent kinetic energy method was the most consistent at both heights and appears most promising for further development results encourage future use of the adv in estuarine environments but also favor the simultaneous use of several methods to estimate bottom stress

background seismicity rates and precursory seismic quiescence imperial valley california the problem of recognizing precursory seismicity rate changes consists of two steps first a background or normal rate must be determined and second anomalous rates must be recognized in this paper we address the first of these steps determining a background seismicity rate two problems must be dealt with if a meaningful background rate is to be determined first dependent events must be recognized and removed from consideration and second detection or reporting changes must be accounted for a number of techniques are available for recognizing dependent events we used the one developed by mcnally 1976 in this work the technique we used for recgonizing detection and reporting changes was developed by habermann 1983 we demonstrate these techniques on seismicity from the imperial valley region of california after a reasonable background rate is determined we examine seismicity rates in this region prior to the imperial valley earthquake of 15 october 1979 the source area of the earthquake shows a possible precursory quiescence which started during july 1979 the time of this rate decrease is close to the time of a change in the seismic instrumentation in the imperial valley which makes it difficult to determine whether the decrease is real or related to detection several other seismicity rate changes observed in the imperial valley appear to be related to changes in the operation of the network there these include quiescent periods which occur only if magnitude cutoffs are applied to the data and periods of low reporting of events with m 2 5 these observations suggest that magnitudes were not reported for some events during several time periods all of these observations indicate that determination of detection histories is crucial for meaningful seismicity studies

long term morphodynamic evolution and the equilibrium mechanism of a flood channel in the yangtze estuary china the stability of flood channels has attracted considerable attention because of their complicated interactions with the prevailing hydrodynamics and importance in ship navigation this research examines long term morphodynamic evolution in the yangtze estuary from 1861 to 2002 and the equilibrium mechanism of the xinqiao channel in the yangtze estuary by digitizing 15 selected maritime charts and calculating the volume of the channel although the total period of channel development is much longer than the historical data used in this paper three stages are identified during the study period the first embryonic stage 66 years the second formation stage 33 years and the third equilibrium stage 45 years variations in coastline location channel volume and hydrodynamics in the channel during the three stages indicate that the channel equilibrium was reached and maintained when the channel direction was aligned with the direction of offshore tidal wave propagation variations in river and sediment discharges affect erosion and deposition in the channel and thus channel geometry however future reduction in sediment supply by 10 33 due to the ongoing river engineering projects would increase the volume of the xinqiao channel only by 1 3 it seems unlikely that the above change in sediment discharge will disrupt the equilibrium of the xinqiao channel

field studies of estuarine turbidity under different freshwater flow conditions kaipara river new zealand abstract we present a first interpretation of three days of measurements made in 2013 from the tidal reaches of the kaipara river new zealand under both low and high freshwater inputs and a neap tidal cycle during the first day we occupied two stations that were approximately 6 km apart in a tidal reach that runs for 25 km from the river mouth to the upstream limit of tidal influence during the second day longitudinal surveys were conducted over a distance of 6 km centred on the upstream station the data reveal a turbidity maximum in the form of a high concentration plug of suspended mud that was advected downstream on the ebbing tide past the upper hb measurement station and which exchanged sediment with the seabed by settling at low slack water and by resuspension in the early flooding tide the data suggest that fine sediment is transported landwards and trapped in the upper part of the tidal reach under these low flow conditions on the third day of measurements we repeated the experiments of the first day but later in the year for a much higher freshwater flow this interpretation of our data set highlights the potential contribution of a range of processes to the generation of the observed suspended sediment signals including resuspension of local bed sediment advection by the tidal current settling of suspended sediment over a long timescale compared to the advection timescale advection of longitudinal gradients in suspended sediment and suppression of vertical mixing by density stratification of the water column the level of temporal and spatial detail afforded by these measurements allows a much clearer understanding of the timing and importance of vertical stratification on the transport of suspended particulate matter than is generally possible using fixed point sensors

automated petrographic characterization of coal lithotypes abstract although petrographic analysis of the lithotypes present in coal samples has been successfully used in the correlation of coal seams the study of the environments of coal seam deposition and the evaluation of the mining and cleaning properties of numerous coal seams coal lithotype analysis is not routinely performed in north america at this time because it is very time consuming and requires the services of a highly skilled petrographer the objective of this study was to evaluate the capability of one of the newly improved image analysis microscope systems to characterize coal lithotypes and perform automated lithotype analyses on polished block samples of coal the results of this study show that each of the lithotypes examined vitrain clarain fusain and durain yield a characteristic reflectance histogram and that analysis of reflectance histograms taken from a transverse perpendicular to bedding down a polished block sample yield results on the kinds and thicknesses of the lithotypes present that are in good agreement with the results obtained by manual methods

sediment trapping of turbidity maxima in the changjiang estuary abstract sediment trapping in the turbidity maxima tm is highly variable in different estuaries or at different times in the same estuary how related processes influence the tm behavior and its structure has not yet been completely clear here we present moored and shipboard observations in the 2008 flood and dry seasons in the lower reaches of the changjiang estuary where the deepwater navigation channel was still under construction the excavation of the pristine mouth bar has caused the saline wedge to move upstream resulting in new tm zones the magnitude and extent of the tm are strongly seasonal under the influence of distinct sediment processes the tm appears as a high concentration undercurrent in the flood season whereas they occur as a low concentration sediment cloud over the water column in the dry season the hyperpycnal flow can be formed by flocculation settling and the sediment cloud can be caused primarily by resuspension the sediment trapping in the tm occurs more often during accelerating and decelerating ebb tides when the bed stress is small but the flow is highly accelerating and decelerating sediment resuspension and deposition at these tidal reversals can be induced by the growing and decaying flow spirals respectively therefore the diversity of the tm may be associated with density stratification accelerating flows flocculation or generally the interaction between stratified flows and cohesive sediments

is shillong region northeast india undergoing a dilatancy stage precursory to a large earthquake abstract gupta h k and singh v p 1982 is shillong region northeast india undergoing a dilatancy stage precursory to a large earthquake in a l hales and z suzuki editors earthquake prediction tectonophysics 85 31 33

crustal p wave velocity and velocity ratio study in northeast india by a microearthquake survey the upper crustal 20 km p wave velocity beneath the shillong plateau and nowgong area has been studied by the time distance plot method thep arrival data of the shallow 20 km microearthquakes from three temporary networks are used and the average velocity is found to be 5 55 km s the velocity ratio v p v s for the upper crust 0 20 km as well as for the lower crust 21 40 km are determined by the wadati plot method and station by station method the average value obtained by the two methods is compatible thev p v s ranges between 1 74 to 1 76 a generalized seismic velocity model of the area is suggested by this study which has been very useful for microearthquake location

maceral distributions in illinois coals and their paleoenvironmental implications abstract for purposes of assessing the maceral distribution of illinois u s a coals analyses were assembled for 326 face channel and drill core samples from 24 coal members of the pennsylvanian system the inertinite content of coals from the missourian and virgilian series averages 16 1 mineral free compared to 9 4 for older coals from the desmoinesian and older series this indicates there was generally a higher state of oxidation in the peat that formed the younger coals this state probably resulted from greater exposure of these peats to weathering as the climate became drier and the water table lower than was the case for the older coals although oxidation during allochthonous deposition of inertinite components is a genetic factor that needs further study to confirm the importance of the climate regional variation of the vitrinite inertinite ratio v i on a mineral and micrinite free basis was observed in the springfield no 5 and herrin no 6 coal members to be related to the geographical position of paleochannel river deposits known to have been contemporaneous with the peats that formed these two coal strata the v i ratio is highest generally 12 27 in samples from areas adjacent to the channels and lower 5 11 some 10 20 km away we interpret the v i ratio to be an inverse index of the degree of oxidation to which the original peat was exposed high v i ratio coal located near the channels probably formed under more anoxic conditions than did the lower v i ratio coal some distance away from the channels the low v i ratio coal probably formed in areas of the peat swamp where the watertable was generally lower than the channel areas

regional study of the anomalous change in apparent resistivity before the tangshan earthquake m 7 8 1976 in china electrical resistivity measurements have been conducted as a possible means for obtaining precursory earthquake information before five great earthquakes m 7 h 25 km in china the apparent resistivity a showed systematic variations within a region 200 km from the epicenters in particular 9 stations in the tangshan tianjin beijing region prior to the tangshan earthquake m 7 8 h 11 km 27 july 1976 showed a consistent decrease of apparent resistivity around the epicenter with a maximum resistivity change of 6 and a period of variation of 2 3 years simultaneous water table observations in this region showed a declining water table and ground surface observations indicated a slight 5 mm uplift in the epicenter region relative to its surroundings

estuarine and sediment dynamics in a microtidal tropical estuary of high fluvial discharge magdalena river colombia south america abstract relation among estuarine processes mixing mechanisms and turbidity maximum zone tmz formation was evaluated in a microtidal tropical estuary of high fluvial discharge magdalena river northwestern south america particularly assessing the effects of vertical stratification over mixing estuarine circulation and suspended sediment transport processes measurements of salinity temperature density currents and suspended sediment concentration ssc were performed at the magdalena river mouth during high and low streamflows to distinguish among two contrasting seasonal conditions flow conditions wind patterns wave energy salinity temperature density and location of the freshwater saltwater interface fsi exhibited a sharp seasonal variability the river mouth and delta front were stratified regardless of the hydrologic season whereas the riverine section was stratified during the low streamflow season reflecting the balance between fluvial advection and vertical stratification reduction of the vertical mixing led to a more clearly defined and extended stratification bottom friction is the main mixing mechanism but as stratification is strengthened along the river mouth the vertical mixing weakens promoting the developing of tmz ssc 4500 mg l 1 our results indicate that tmz developing is caused by the convergence of stratified layers near the nodal point and the weakening of bottom turbulence by stratification although the tmz exhibited a strong seasonal variation in its magnitude and extent it usually formed in the convergence front demarcated by saltwater intrusion streamflow is the major influence on the tmz formation since it allows the development of stratified conditions which weaken turbulent mixing and thus promotes particulate matter settling the magdalena river estuary can be classified as turbid 4000 mg l 1 10 000 mg l 1 these values are of the same order as the ssc reported for the yangtze and yellow estuaries classified as having the largest ssc values of the world

observation of the sediment trapping during flood season in the deep water navigational channel of the changjiang estuary china abstract after the construction of the deep water navigational channel dnc in the north passage of the changjiang estuary siltation in the channel became severe during the flood season in the navigation channel to investigate the causes field observations of tidal current salinity and suspended sediment concentration ssc were conducted by 16 anchored boats in the navigation channel of north passage during spring tide in the flood season the across channel differences of salinity ssc and near bottom residual sediment transport at the high siltation area of the dnc were observed and analyzed the results show that the near bottom ssc presented a south to north decreasing trend during the flood tide at the lower reach of the north passage during the ebb tide a suspended sediment cloud of extremely high concentration was detected within the channel the observed longitudinal sediment trapping was not only shown as the turbidity maximum tm trapped within the moving salinity front but also as the longitudinal convergence of the residual sediment transport at the middle reach the mechanism for the longitudinal sediment trapping was due to the tidal asymmetry in mixing the observed lateral sediment trapping was prominent at the most severe siltation area of the dnc in the section 2 the lateral sediment trapping at the across channel section 2 was not only shown as the lateral transport of the sediments from the channel flanks during the flood slack but also as the lateral convergence of the residual sediment transport during the entire spring tidal cycle the mechanism for the lateral sediment trapping was dominated by the advective transport the lateral impact on the channel sediment trapping was not negligible in view of the depth mean lateral tidal straining on the water stratification the observed convergences of both the longitudinal and the lateral residual sediment transports were responsible for the severe channel siltation in the north passage

floc properties in the turbidity maximum of a mesotidal estuary during neap and spring tidal conditions in order to improve the understanding of how fine cohesive matter behaves during different tidal conditions within an estuary turbidity maxima high quality in situ data is of a prime requirement as part of the european commission cosinus project a series of measurements were carried out in the upper reaches of the tamar estuary to investigate how flocculated mud properties vary within the turbidity maximum zone floc populations were sampled at regular intervals using the optical inssev instrument the floc data was supplemented by simultaneous time series of near bed profiles of turbulent shear stress and suspended particulate matter the proportion of macroflocs 160 m changed significantly across the turbidity maximum before the passage of the turbidity maximum the total floc mass tended to be equally divided between the macroflocs and microflocs on neaps whilst on springs the macroflocs contributed 60 70 at spring tides a peak near bed spm concentration of 6 g l 1 was measured in the turbidity maximum this was over an order of magnitude higher than observed at neaps the turbulence measurements showed significant drag reduction at spm concentration gradients above 3 6 kg m 4 within the turbidity maximum the macrofloc proportion rose rapidly until they contributed at least 75 of the floc dry mass during neap conditions and at spring tides this reached in excess of 90 96 an abundance of fast settling macroflocs from spring tides accounted for a time series average of 83 of the mass settling flux where as during neap tides the macroflocs contributed 15 less to the settling flux rate this was partly due to a time series averaged macrofloc settling velocity of 3 9 mm s 1 from the spring tidal data 2 1 mm s 1 higher than for neap tide conditions during the turbidity maximum passage at springs macroflocs reached 2 2 mm in diameter these flocs had settling velocities of up to 16 6 mm s 1 but effective densities were less than 50 kg m 3 which means they would be prone to break up when settling to a region of high shear at the opposite and of the scale low turbidity and quiescent slack water conditions severely restricted floc production

movable bed roughness in unsteady oscillatory flow a model to predict the roughness in unsteady oscillatory flows over movable noncohesive beds is presented the roughness over movable beds is shown to be a function of the boundary shear stress rather than a fixed geometrical scale as is the case for fully rough turbulent boundary shear flows over immobile beds the model partitions the roughness into two distinct contributions these two contributions are due to the form drag around individual bed forms and to the near bed sediment transport the form drag over the bed forms is treated explicitly as a function of the boundary geometry and shear stress the ripples are predicted as a function of the local skin friction and a semiempirical expression is derived using standard law of the wall arguments which gives the ripple or form roughness as a function of the boundary geometry the ripple roughness is found to be proportional to the product of the ripple steepness and height favorable comparison of the form drag model with the results of bagnold s 1946 fixed ripple study is found the value of z0 associated with intense sediment transport in oscillatory flow over a flat bed is determined from carstens et al s 1969 experiments this value is found to be 7 or 8 grain diameters an expression is derived for the roughness associated with the maximum thickness of a near bottom sediment transporting layer consistent with owen s 1964 roughness hypothesis for saltation of uniform grains in air at large values of the boundary shear stress relative to the critical value for initial sediment motion the derived expression is similar to the results of smith and mclean s 1977 unidirectional flow approach modified for oscillatory flow the total roughness model is found to compare favorably with carstens et al s 1969 data in contrast to smith and mclean s 1977 steady flow findings the results here show that when ripples are present they account for a significant portion of the boundary roughness

sediment trapping turbidity maxima and bathymetric stability in macrotidal estuaries 1 this paper examines how fine marine sediments are trapped in macrotidal estuaries and what processes coexist to maintain bathymetric stability an analytical emulator is constructed integrating explicit formulations for tidal and residual current structures together with sediment erosion suspension and deposition the emulator estimates suspended concentrations and net sediment fluxes and indicates the nature of their functional dependencies and corresponding sensitivities to tidal elevation amplitude or tidal current channel depth d bed friction coefficient f sediment size specifically settling velocity ws and river flow velocity ur associated scaling analyses reveal the relative impacts of terms representing tidal nonlinearities gravitational circulation and delayed settling using the emulator to determine conditions consistent with zero net flux of sediments or bathymetric stability we deduce ws f overall finer sediments are imported and coarser ones are exported with more imports extending to a coarser fraction on spring tides than on neaps the emulator indicates that the spring neap shifting of this coarse fine boundary corresponds to particle diameters between 30 and 50 m this constitutes selective sorting maintaining a widely distributed source of continuously resuspended material in a size range commonly observed by illustrating the acute sensitivity of sediment fluxes to the bed friction coefficient we anticipate feedback adjustments between suspended and surficial sediments factors governing the generation location and characteristics of turbidity maxima are indicated including dependence on d a direct link is shown between parameters that control sediment flux at a specific cross section and net upstream tidal energy dissipation

a suspended sediment front in the severn estuary a zone of marked local gradient in the regional suspended solids field has been located along the axis of the severn estuary this front occupies virtually the same position on ebb and flood and on spring and neap tides although the amplitude of the gradient fluctuates thermohaline fronts have been described in coastal waters1 2 suspended sediment fronts associated with the discharge of major rivers into the sea are common3 5 whilst fronts caused by convergence of secondary circulations within estuaries have also been reported6 7 the previous work describes features with significant differences in the salinity or temperature fields in which any suspended sediment contrasts present are incidental and do not of themselves produce large horizontal density variations in contrast in the severn strong thermo haline gradients in the vicinity of the suspended solids front have not been detected the mechanisms for the formation and maintenance of the front are not yet known

an integrated optic and acoustic ioa approach for measuring suspended sediment concentration in highly turbid environments abstracts accurate measurement of suspended sediment concentration ssc in highly turbid environments has been a problem due to optical or acoustic signal saturation and attenuation the saturation returns a limited measurement range and the attenuation raises an ambiguity problem that a low optical or acoustic output could mean a low or a high ssc in this study an integrated optic and acoustic ioa approach is proposed to i overcome the ambiguity problem ii increase the measurement range to high ssc values and iii obtain high resolution ssc profiles the ioa approach is a combination of argus suspension meter asm optical backscatter sensor obs and acoustic doppler velocimeter adv in this approach the asm derived ssc is preferred because of its lowest relative error followed by obs and adv the asm can produce high resolution 1 cm interval ssc profiles when it is not saturated usually ssc

the influence of human activities on morphodynamics and alteration of sediment source and sink in the changjiang estuary abstract several works have discussed the morphological evolution in the changjiang estuary cje in recent years the erosion of its subaqueous delta in recent decades has been ascribed to a decline in fluvial sediment input however the interaction between the reduction of riverine sediment load and human activities in the estuary that could have caused morphological change has not been considered in this work we provide evidence on the morphological evolution around the delta front zone since 1986 and use a numerical model to explore the correlation between the change in hydrodynamics and the evolution pattern bathymetric data analysis suggests a decrease of net accretion rate from 16 7 mm year 1986 1997 to 9 1 mm year 1997 2010 in the study area spatially the tidal flats accreted whereas the subaqueous delta switched from deposition between 1986 and 1997 to erosion between 1997 and 2010 we used two indicators tidal energy dissipation and erosion rate to quantify the change in hydrodynamics and found that the erosion of the subaqueous delta in recent decades can readily be explained by the alteration of the hydrodynamics the newly built navigation training works in the north passage had a significant effect on the estuarine hydrodynamics resulting in a local morphological adjustment this erosion generated a new source of sediments to maintain the high suspended sediment concentration and tidal flat progradation the erosion of the subaqueous delta may continue and gradually slow down until the altered hydrodynamics and morphology reach an equilibrium state in the future

observations of distribution and flocculation of suspended particulate matter in the minjiang river estuary china abstract in this study we described the distribution pattern of suspended particulate matter spm and its influencing factors in the waters around the minjiang river estuary further we investigated the flocculation process of spm and its underlying mechanism in the study area the objectives were achieved using water temperature salinity turbidity fluorescence and particle size distribution of spm data measured in august 2009 as influenced by dilution from the minjiang river water the water column structure was significantly stratified in the estuary with an obvious thermocline and halocline the turbidity was relatively low in the surface water ssc 15 mg l fluorescence was high up to 10 l l in the surface water which was markedly lower and more uniform in the lower water layer the total volume concentration and particle size of the spm in the upper water layer were significantly higher than those of the lower water layer the in situ particle size frequency distribution of spm markedly changed in the different water layers whereas the dispersed particles were fine with little difference in frequency distribution the mean effective density of spm was generally 3 in the surface and benthic water and the values were slightly higher in the benthic water layer than in the surface water layer with a significant increase in the middle water layer the significant differences between the distribution trends of the total volume concentration and water turbidity were controlled by the size distribution of spm the concentration distribution of spm was mainly influenced by source re suspension and thermocline among other factors flocs widely occurred in the study area and the flocculation mechanism of spm varied in the different water layers in the upper water layer intense biological activity promoted the formation of stable macroflocs in the benthic water layer the biological activity was limited the flocculation of sediment particles was mainly caused by physico chemical attraction of inorganic particles and the hydrodynamic conditions and high settling velocity were also unfavourable to the formation of macroflocs

tripod measured residual currents and sediment flux impacts on the silting of the deepwater navigation channel in the changjiang estuary four bottom mounted instrument equipped tripods were deployed at two sections spanning the region characterized by severe sedimentation rates in the deepwater navigation channel dnc along the north passage of changjiang estuary in order to observe currents near bed suspended sediment and salinity seaward residual currents predominated in the up estuary section in contrast a classical two layered estuarine circulation pattern occurred in the down estuary section flow moved seaward in the upper layer and a heavier inflow driven by the salinity gradient moved landward in the lower layer the near bed residual currents in the up estuary section and the down estuary section acted in opposing directions which implies that the region is a convergence zone of near bed residual currents that trap sediment at the bottom the maximum salinity gradient at the maximum flood current indicates the presence of a strong front that induces sediment trapping and associated near bottom convergence of sediment which explains the high sedimentation rates in this section of the estuary

macroturbulence generated by dunes fraser river canada abstract a selectable frequency acoustic profiler and electromagnetic current meter were deployed in the lower fraser river canada to examine large turbulent structures features were generated on the lower stoss sides of dunes and appeared at the surface tens of metres downstream as strong upwellings boils they were identified with acoustic clouds in the acoustic profile event recurrence periods measured from acoustic time series and from ejection events identified in the current meter record had similar two component frequency distributions but the acoustic values lacked the highest frequencies a comparison of measured periods with predictions from the strouhal law indicate that both dune amplitude and the internal boundary layer developed over the dunes are significant length scales associated with the generation of the macroturbulence our data give no support to the notion that boils develop from microturbulent bursts