a teleseismic analysis of the new brunswick earthquake of january 9 1982 the analysis of the new brunswick earthquake of january 9 1982 has important implications for the evaluation of seismic hazards in eastern north america although moderate in size mb 5 7 it was well recorded teleseismically source characteristics of this earthquake have been determined from analysis of data that were digitally recorded by the global digital seismograph network from broadband displacement and velocity records of p waves we have obtained a dynamic description of the rupture process as well as conventional static properties of the source the depth of the hypocenter is estimated to be 9 km from depth phases the focal mechanism determined from the broadband data corresponds to predominantly thrust faulting from the variation in the waveforms the direction of slip is inferred to be updip on a west dipping nne striking fault plane the steep dip of the inferred fault plane suggests that the earthquake occurred on a preexisting fault that was at one time a normal fault from an inversion of bodywave pulse durations the estimated rupture length is 5 5 km average properties of the rupture process were examined by a moment tensor analysis of long period p and sh body waves the long period moment of this earthquake was 5 3 1024 dyne cm the static and dynamic stress drops are 41 and 65 bars respectively similar to those of many earthquakes with similar moment in regions that are more seismically active the joint epicenter determination algorithm was used to locate relative to the mainshock the three teleseismically recorded aftershocks that occurred through march 31 1982 the relocated hypocenters of the aftershocks are significantly different from each other and from that of the mainshock they provide additional support for the source dimensions inferred from the waveform analysis

active and passive microwave signatures of antarctic firn by means of field measurements and satellite data the angular dependence and polarization behaviour of back scattering and emission of polar firn at 5 2 ghz and 10 3 ghz were measured during an oversnow traverse in dronning maud land antarctica the signatures emphasize the importance of snow stratification in the interpretation of microwave remote sensing measurements highest backscattering coefficients and little angular variations were observed for refrozen firn near the coast in permanently dry snow areas with high accumulation rates and homogeneous snow morphology showed low backscattering coefficients and high emissivities pronounced layering and related density variations in low accumulation zones resulted in increased polarization differences of brightness temperatures and increased like polarized backscattering coefficients this behaviour is confirmed by the analysis of c band scatterometer measurements of the active microwave instrument aboard the european space agency s ers 1

chemical weathering indices applied to weathering profiles developed on heterogeneous felsic metamorphic parent rocks abstract chemical weathering indices are commonly used for characterizing weathering profiles by incorporating bulk major element oxide chemistry into a single metric for each sample generally on homogeneous parent rocks weathering indices change systematically with depth however the weathering of heterogeneous metamorphic rocks confounds the relationship between weathering index and depth in this paper we evaluate previously defined chemical weathering indices for their suitability in characterizing weathering profiles developed on felsic heterogeneous metasedimentary bedrock from coweeta hydrologic laboratory north carolina usa among the weathering indices evaluated here the weathering index of parker wip is the most appropriate for application to weathering profiles on heterogeneous and homogeneous parent rock because the wip includes only the highly mobile alkali and alkaline earth elements in its formulation it yields values that differ greatly from those of the parent rock in addition the wip allows for aluminum mobility unlike other weathering indices these characteristics combine to make the weathering index of parker the most applicable index for studying the weathering of heterogeneous metasedimentary rocks however the wip should be applied judiciously as alkali and alkaline earth metals may be readily depleted during weathering in addition to reflecting weathering the chemical index of alteration cia chemical index of weathering ciw plagioclase index of alteration pia and vogt s residual index v may be sensitive to subtle geochemical changes such as hydrothermal alteration along a fault and or alteration at the water table weathering indices that include iron in their calculations were not included in this study because they do not distinguish between ferric and ferrous iron the oxidation state and distribution of iron in a weathering profile is influenced by the proportion of oxidation states in the pre weathered metamorphic rock and interaction with groundwater during weathering

a model for altimeter returns from penetrable geophysical media the radar altimeter is a well understood instrument for monitoring the world s oceans there has been a recent effort to extend altimeter techniques to the study of the world s ice sheets to this end several authors have developed average altimeter waveform models that incorporate pulse penetration effects to varying degrees in this paper the authors extend these models to more adequately account for the effects of surface roughness and subsurface inhomogeneities on the average scattered waveform this leads to a waveform model that is useful in analyzing altimeter returns obtained over a wider range of geophysical media such as snow ice and foliage which are characterized by strong subsurface inhomogeneities representative results of applying this extended model to airborne altimeter measurements made over various regions of the greenland ice sheet in september 1991 are provided

growth of the greenland ice sheet a performance assessment of altimeter retracking algorithms the authors compare the performance of different altimeter retracking algorithms for measuring ice sheet elevations and growth rates the results show that the threshold esa and s v retracking algorithms produce growth rates that are 30 55 smaller than those produced by the nasa algorithm based upon a comparison of crossover point standard deviations the analysis indicates that the surface elevation estimates produced by these algorithms are more repeatable than the nasa surface elevations an analysis of the nasa algorithm shows that a mixing of its 5 and 9 parameter functional fits on the crossover point altimeter waveforms occurs in over 70 of the crossover data the mixing of the functional fits is shown to reduce the repeatability of the nasa elevations and this may be responsible for the larger estimates of ice sheet growth produced by the nasa retracking algorithm the extremely close agreement between the standard deviations and the growth rate estimates from the threshold esa and s v retracking algorithms lead the authors to conclude that 0 10 m yr is a more accurate estimate of the growth of the greenland ice sheet from 1978 1987 south of 72 spl deg n

growth of greenland ice sheet measurement measurements of ice sheet elevation change by satellite altimetry show that the greenland surface elevation south of 72 degrees north latitude is increasing the vertical velocity of the surface is 0 20 0 06 meters per year from measured changes in surface elevations at 5906 intersections between geosat paths in 1985 and seasat in 1978 and 0 28 0 02 meters per year from 256 694 intersections of geosat paths during a 548 day period of 1985 to 1986

intraplate extensional tectonics of the eastern basin range inferences on structural style from seismic reflection data regional tectonics and thermal mechanical models of brittle ductile deformation the general lack of a correlation between earthquakes and surface faulting in the interior of the western u s cordillera has motivated our efforts to evaluate the geometry structural style and mechanism of normal faulting characteristic of this region of intraplate extension to address the problem we have interpreted over 1500 km of seismic reflection data and constructed detailed cross sections of the upper crust rheological models of the continental crust were calculated to examine the possibility of shallow quasi plastic flow and its influence on faulting in the eastern basin range the western colorado plateau and the middle rocky mountains our data and interpretations have revealed the following styles of cenozoic deformation 1 steep to low angle dip normal faulting along the wasatch fault 2 low angle dip and listric normal faulting possibly associated with movement on preexisting thrusts 3 the occurrence of asymmetric mostly eastward tilted tertiary basins that are bounded by low to moderate dipping planar and listric faults and 4 at least three vertically stacked en echelon low angle reflections in the mid to upper crust that dip gently westward from 3 km beneath the wasatch plateau to over 15 km at the utah nevada border these reflections are interpreted as normal detachment faults the structural style of the pervasive low to moderate angle dipping faults cannot be easily reconciled with classic brittle failure theory but the interpreted termination of normal faults at or above the deeper low angle reflections suggests the presence of shallow zones of ductile deformation that may have accommodated slip an important observation based on interpretations of seismic reflection profiles is that normal fault zones dip more gently in the subsurface than their associated scarps in unconsolidated surficial deposits segment boundaries of the wasatch fault zone apparently coincide with the positions of east trending displacement transfer structures in thrust sheets and the position of the precambrian uinta aulacogen suggesting that preexisting crustal structure partly controls the geometry of extension to examine the influence of ductile deformation quasi plastic flow was modeled for appropriate geotherms of the basin range and colorado plateau crusts these models provide constraints on the depth to the frictional quasi plastic transition that occurs as shallow as 8 km in the eastern basin range this depth also corresponds to the approximate depth above which most accurately determined earthquake foci for small earthquakes m 5 5 appear to nucleate at 10 15 km in or near the brittle ductile transition the rheological modeling suggests that a thermally deforming continental lithosphere plays an important role in the evolution of this extending intraplate region large scale low angle reflections may represent decollements and normal faults at the top of upper crustal zones of reduced shearing strength and higher ductility

particle size related mineral magnetic source sediment linkages in the rhode river catchment maryland usa characterization of both the source materials and the bottom sediments of an estuary by magnetic characters on a particle size basis allows the source of the bottom sediments to be determined and indicates a shift in sediment sources corresponding to changing land use patterns the major source of the sediments in the lower part of cores from the middle of the estuary is eroding shorelines soil derived particulates from the uplands dominate the upper part of the cores this change in source occurred in the early part of the 19th century the magnetic character of the most recent sediments suggests a progressive depletion through time of the upland soils in the finest fractions

depth determination for shallow teleseismic earthquakes methods and results the depths of moderate sized shallow earthquakes can be routinely determined to an accuracy of several kilometers using teleseismic data alone making it possible to determine the vertical positions of earthquakes within the lithosphere this capability provides a valuable tool for plate tectonic studies since earthquake depths can be used to constrain lithospheric thermal and mechanical structure at plate boundaries and in intraplate regions two basic techniques are used for depth analyses surface wave spectra can be used to determine focal depths as mode excitation reflects the behavior of the eigenfunctions with depth the primary limitation on such studies stems from lateral heterogeneity of velocity structure the waveforms of body waves are also diagnostic of focal depth which controls the time separation between the direct arrival and near source surface reflections these studies can be limited by a partial trade off between depth and source time function duration the reliability of the body wave modeling approach now in general use is shown by excellent agreement between depths determined by different investigators using different algorithms the depth determination is robust to typical uncertainties in focal mechanism and near source structure the trade off with source time function duration generally does not produce major difficulties for small events ms 6 5 for larger events the trade off can be resolved using a approach in which for a given depth the time function yielding the best fit to a suite of seismograms is found by deconvolution deconvolution at a series of depths yields a misfit function whose minimum indicates the focal depth tests with synthetic data show that the deconvolution process yields reliable depth estimates even given uncertainties in focal mechanism and near source structure it successfully handles multiple sources moderate sized finite sources and horizontally propagating ruptures good results are obtained for vertically propagating ruptures until the fault area becomes so large that waveforms differ significantly from the point source approximation a number of important tectonic results have emerged from studies using these depth determination methods the maximum depth of oceanic intraplate seismicity increases with lithospheric age and is approximately bounded by the 750 c isotherm this depth roughly equals the flexural thickness of the lithosphere but is much less than the depth to the low velocity zone indicated by surface wave dispersion the maximum depth of continental intraplate seismicity is also temperature limited but by a lower temperature these observations are consistent with the rapid weakening of the appropriate rocks with depth predicted by standard temperature dependent rheologies the maximum depth of oceanic transform seismicity corresponds to an isotherm of about 400 c this temperature is lower than would be predicted from the intraplate results and may indicate that transforms are either hotter or weaker than expected the depths of ridge crest earthquakes large enough for teleseismic analysis are extremely shallow 0 8 km the depth distribution of seismicity in continental normal faulting regions provides constraints on the nature of the extension process at subduction zones precise depth determinations can resolve the upper and lower flexural regions in the bending downgoing plate precisely locate the plate interface and map the vertical extent and position of faulting in large earthquakes

environmental magnetic studies on some quaternary sediments of varied depositional settings in the indian sub continent abstract the efficacy and limitations of routine environmental magnetic approaches to characterize and compare the quaternary sediments of varied depositional settings fluvial fluvio lacustrine and marine from the indian sub continent are discussed the various studied profiles fall under tropical wet and dry subtropical humid cold arid and alpine climatic zones at altitudes varying from 2000 m below sea level to 4500 msl the magnetic mineral assemblages are characterized by magnetic susceptibility high field hysteresis parameters and their ratios and bivariate plots besides applying the conventional models we produced new and multi parametric environmental magnetic models for finer discrimination of the mineral magnetic assemblages mma amongst these deposits in similar hinterland setup and climate zones independent mma characteristics are shown by the late quaternary frontal himalayan basins the ganga basin the intermontane pinjor dun and the folded siwalik sequence such variations are attributed to diverse energy conditions due to varied basin morphology climate and the source to sink proximity contrasting channel to overbank mma relations are discernible during the glacial and interglacial periods within the ganga basin the siwalik sediments are notably restricted to antiferromagnetic region of the bivariate plots indicating formation and stability of iron oxides under warm humid to arid conditions the post siwalik intermontane sediments show steep gradients in mma domain within a short distance from proximal to distal fan regime in the tropical peninsular region the source to sink relation is marked by the deccan trap province source and bengal submarine fan sink at least since the last glacial maxima lgm in the middle fan region the mmas for the lacustrine and fluvio lacustrine deposits in the himalayan foothills as well as the higher himalaya indicate detrital variations governed by the fluvial dynamics in the region this demands a more detail catchment to sink studies in each basin and to explore the climatic tele connections amongst the varied altitudinal regions overall this study indicates a strong detrital control on mma governed by the energy conditions of the transporting media that in turn is controlled by catchment morphology regional tectonics and climatic fluctuations in the absence of suitable unmixing models the new bivariate and diamond plots attempted here are helpful in describing the detrital modes within the basin and its comparison to other basins

a very broad band inversion method for the recovery of earthquake source parameters abstract waveform studies of the earthquake source have traditionally been performed in narrow bands of the seismic spectrum waveform matching of p and sh waves emphasizes frequencies near and above the corner frequency normal mode and surface wave analyses on the other hand are performed on data which contain information only below the corner frequency a new method is presented which formally includes the result of a long period centroid moment tensor analysis in an inversion of broad band body wave phases a parametrized source model is used which allows for the recovery of a detailed source time function as well as the direction and magnitude of rupture propagation the technical details and the performance of the method are demonstrated in an analysis of the october 28 1983 borah peak idaho earthquake in particular it is shown how the combination of the long period and broad band data sets in the inversion improves the resolution of both the focal mechanism and the scalar moment the very broad band method is applied in an analysis of the september 19 1985 michoacan m w 8 0 earthquake two concentrations of moment release are identified in the source time function separated by 25 30 s in time the spatial distribution of moment is well explained both by a model of unilateral rupture towards the east with a propagation velocity of 2 4 km s 1 and by two point sources separated by 95 km it is shown that the p wave data are largely insensitive to the scalar moment and that source time functions obtained without consideration of the total moment release exaggerate the heterogeneity of slip on the fault plane source time functions which do contain the total moment show that a large fraction of the moment was released smoothly over the whole duration 80 s of the event the results suggest that the fault plane was characterized by two regions of high stress drop but that a large portion of slip occurred on surrounding weak portions of the plane

growth of greenland ice sheet interpretation an observed 0 23 m year thickening of the greenland ice sheet indicates a 25 to 45 excess ice accumulation over the amount required to balance the outward ice flow the implied global sea level depletion is 0 2 to 0 4 mm year depending on whether the thickening is only recent 5 to 10 years or longer term 100 years if there is a similar imbalance in the northern 60 of the ice sheet area the depletion is 0 35 to 0 7 mm year increasing ice thickness suggests that the precipitation is higher than the long term average higher precipitation may be a characteristic of warmer climates in polar regions

geometry of cenozoic extensional faulting dixie valley nevada precise definition of geometric relationships between individual basins and ranges may help to reveal the mechanical processes of basin and range cenozoic extensional faulting at depth previous studies have attempted to identify simple horsts and grabens tilted crustal blocks with planar faulting or tilted crustal blocks with listric faulting in the shallow crust normal faults defining these crustal blocks may root 1 individually in the ductile lower crust 2 in regional or local low angle detachment faults or 3 in igneous intrusions or decoupling surfaces produced by the intrusions the present study in dixie valley west central nevada makes use of a seismic reflection survey gravity models seismograms from earthquakes occurring on december 16 1954 and geometrical block models these data show a structurally asymmetric basin bounded by a single zone of faulting on the northwest and by a downbowed and step faulted floor to the southeast the northwest bounding fault is moderately dipping 50 and planar to a depth of 3 km the southeast boundary is step faulted and altogether the faults indicate an extension of 20 across the valley at the rate of 0 38 mm y for the last 8 my synthetic earthquake seismograms confirm a focal depth of 15 km and fault dip of 62 for the fairview peak earthquake and suggest that the focal depth of the dixie valley earthquake was also 15 km instead of the previously reported 40 km local microearthquakes cluster around 10 15 km the geometrical block models indicate that crustal horst graben faulting and planar high angle normal faults rooted in a low angle detachment surface do not readily account for development of the subsidiary step faults found in dixie valley extension of the crust by intrusion may develop high angle faults and with further intrusion may develop the subsidiary faults and produce a complex sagged asymmetric graben like dixie valley

higher erosion rates in the himalaya geochemical constraints on riverine fluxes the modern erosion rate of continental scale mountains is difficult to estimate and is usually based on measurement of the suspended load flux of rivers combined with assumptions about river bedload transport and sedimentation in flood plains these two parameters are very difficult to measure directly in continental scale basins in this paper we examine the chemical composition of the suspended load bedload and dissolved load of the ganga and brahmaputra rivers and compare them with the average composition of himalayan source rocks a mass balance equation of erosion fluxes shows that a si rich component is needed in addition to suspended and dissolved load fluxes to account for the composition of the source rock it corresponds to bedload sediment and flood plain deposits which are enriched in quartz by mineral sorting during transport the combined budget of si al and fe in the river system allows us to estimate this si rich flux by this method the total himalayan erosion is estimated to be twice the measured flux of suspended load the comparison between the brahmaputra and the ganga shows that the eastern himalaya has a higher erosion rate 2 9 mm yr than the western himalaya 2 1 mm yr this is likely the result of the higher runoff in the brahmaputra basin the intensity of the monsoon acts as a first order control of the erosion rate in the range

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

analysis and retracking of continental ice sheet radar altimeter waveforms the seasat i radar altimeter data set acquired over both the antarctic and greenland continental ice sheets is analyzed to obtain corrected ranges to the ice surface the radar altimeter functional response over the continental ice sheets is considerably more complex than over the oceans causal factors identified in this complicated response include sloping surfaces undulating ice surfaces with characteristic wavelengths on the same spatial scale as the altimeter beam limited footprint off track reflections and dynamic lag of the altimeter tracking circuit retracking methods using the altimeter return pulse waveforms give range corrections that are typically several meters the entire set of seasat i altimetry over the continental ice sheets is being retracked by fitting a multi parameter function to each waveform many waveforms have double ramps indicating near normal reflections from two distinct portions of the ice surface within the altimeter beam two independent range measurements differing by less than 25 m are obtained from retracking the double ramp waveforms

grain size characteristics and provenance determination of sediment and dissolved load of alaknanda river garhwal himalaya india alaknanda river is a major tributary of river ganga in its upper catchment area the significant feature of the river is its high rates of sediment erosion and chemical denudation the alaknanda river catchment area has many major hydroelectric power projects and is always in the news because of environmental concerns in the present study both suspended and bank sediment characteristics of the river were evaluated for grain size and composition the results show that suspended and bank sediment sizes vary from 8 79 to 56 34 m and 23 73 to 563 24 m respectively suspended sediments are mostly finer to symmetrically skewed whereas the tributaries are found to be negatively skewed in case of bank sediments grains are moderately sorted and mesokurtic the provenance determination using rare earth elements and major oxide composition in suspended and bank sediments shows the higher himalayas as the dominant supplier of sediments along with the sediments the source reservoir of dissolved load was determined using the water composition and an often used forward model the results of forward model show silicate and carbonate weathering processes as a major contributor of dissolved load using this multi approach of dealing with sediment and water geochemical nature of water and sediments of the alaknanda river has been better understood from the present study

intraplate earthquakes and the state of stress in oceanic lithosphere abstract the sources of stress responsible for oceanic intraplate earthquakes and their usefulness for inferring the tectonic stress field are investigated through a synthesis of the source mechanisms of 58 of the largest such events determined by inversion of long period p and sh waveforms further constraints are provided by the global distribution of oceanic intraplate seismicity and a calculation of the seismic moment release per unit volume of seismogenic lithosphere as a function of lithosphere age although frequently associated with relict tectonic features large oceanic intraplate earthquakes are generally reliable indicators of the state of stress in the source region most oceanic intraplate seismicity occurs in young lithosphere

a waveform model for surface and volume scattering from ice and snow a method for combining surface and volume scattering effects to model the radar altimeter power waveforms recorded over continental ice and snow such as that present on greenland and antarctica is discussed the surface model that is used is a variant of the well known impulse response based method that is capable of modeling the returns for an altimeter having a general configuration of altitude antenna beamwidth transmitted pulsewidth and pointing angle the newly formulated volume model is also an impulse response based method that differs from previously introduced versions in that it can also be applied to a general altimeter configuration the two models are added together assuming completely incoherent scattering an example of fitting this combined model to altimeter data is given to illustrate the importance of accounting for the volume scattering present in ice snow data an optimization method can then be used to achieve a least squares fit to actual altimeter data providing an estimate of the parameters for that area on the ice shelf

greenland ice sheet surface properties and ice dynamics from ers 1 sar imagery c band synthetic aperture radar sar imagery from the european space agency s ers 1 satellite reveals the basic zonation of the surface of the greenland ice sheet the zones have backscatter signatures related to the structure of the snowpack which varies with the balance of accumulation and melt at various elevations the boundaries of zones can be accurately located with the use of this high resolution imagery the images also reveal a large flow feature in northeast greenland that is similar to ice streams in antarctica and may play a major role in the discharge of ice from the ice sheet

chemical weathering rates in the alaknanda bhagirathi river basins in himalayas india abstract the alaknanda and bhagirathi rivers flow through the higher and lesser himalayas and confluence at devprayag which represents the origin of the ganga or ganges river in the present study a vast number of temporal and spatial samples of the river waters were collected and analyzed for major cations and anions in addition more recent and time series water flow data have been obtained and based on these inputs a more refined dissolved flux rates have been estimated the alaknanda and bhagirathi rivers show significant variations in chemical compositions during different seasons carbonate rock weathering is responsible for more than 70 of the chemical compositions in the river waters the chemical weathering rates show seasonal variations and are much higher during non monsoon season the dissolved flux of alaknanda river is much higher 1 80 106 tons yr 1 as compared to the bhagirathi river 0 34 106 tons yr 1 the chemical weathering rates in the basin vary between 85 and 155 tons km 2 yr 1 which is significantly higher compared to the global average of 24 tons km 2 yr 1

is chemical index of alteration cia a reliable proxy for chemical weathering in global drainage basins the chemical weathering of silicate rocks in continents as an important sink of atmospheric co2 is of great significance for global environmental change rivers play a key role in earth surface processes and are regarded as the most important carrier of terrigenous materials into the sea the chemical index of alteration cia has been widely used as a proxy for chemical weathering in sediment source area in this paper the cia values of suspended particulate matters from 44 rivers worldwide are recalculated the cia values vary significantly with the highest average value occurring in african rivers and the lowest in north american rivers the correlation analyses suggest that on a global scale the cia is sensitive to land surface temperature latitude at river mouth and soil depth in the drainage basins but poorly correlated with drainage area precipitation average elevation and runoff however the cia of the rivers draining east china are closely related to temperature precipita tion latitude and runoff primarily reflecting the dominant control of monsoon climate on chemical weathering in the catchments it is therefore unrealistic to find a simple law of regulating chemical weathering in continents the cia actually reflects the integrated weathering history in the drainage basins and therefore caution should be taken while using it as a direct and quantitative proxy for evaluating the intensity of instantaneous chemical weathering in continents

preliminary determination of focal mechanisms from the inversion of spectral amplitudes of mantle waves abstract we present a method for the preliminary determination of focal mechanisms pdfm based on the inversion of deviatoric moment tensor components from depleted datasets of mantle wave spectral amplitudes the latter are found to be largely insensitive to errors in epicentral estimates which can hamper the inversion of the full complex spectrum under real time operational conditions robust solutions can be obtained from rayleigh wave spectra at as few as three stations and from a combination of rayleigh and love waves at only two stations provided they sample 60 in azimuth the systematic application of this method to a dataset of 43 large earthquakes during 1996 1999 yielded mechanisms rotated an average of only 17 from the published harvard cmt a figure comparing favorably with the case of other catalogues such as the usgs moment tensor solutions

evaluation of sediment provenance using magnetic mineral inclusions in clastic silicates comparison with heavy mineral analysis magnetic fe oxide inclusions within framework clastic grains in sediments provide an indication of the provenance of the enclosing host silicate particles magnetic mineral inclusion characterisation is performed using a variety of magnetic properties that are related to magnetic mineral abundance magnetic grain size domain state oxidation state and magnetic grain interaction the magnetic methodology extends that based on a conventional set of environmental magnetic measurements using a variety of recent sediments transported from known rock sources within the uk and eire it is demonstrated using discriminant function analysis that the magnetic properties of the fe oxide inclusions provide a clear distinction of primary provenance this is both at the large scale in terms of various gneiss schist and granite sources and also at a smaller scale when considering subdivisions of these sources using case studies from the marine upper jurassic piper formation and non marine triassic sediments otter bank sandstone and foula sandstone formations it is shown that provenance differences clearly expressed by the results of heavy mineral analysis are also sensitively displayed by the magnetic mineral inclusion data the provenance classification is based around use of hierarchical cluster analysis and multidimensional scaling simple statistical tools are developed to determine a least noisy subset of magnetic parameters which are most suitable for stratigraphic provenance discrimination the triassic case study has indicated the magnetic mineral inclusion technique is most sensitive when using the sediment fractions larger than 150 m

geochemistry of large river suspended sediments silicate weathering or recycling tracer this study focuses on the major and trace element composition of suspended sediments transported by the world s largest rivers its main purpose is to answer the following question is the degree of weathering of modern river borne particles consistent with the estimated river dissolved loads derived from silicate weathering in agreement with the well known mobility of elements during weathering of continental rocks we confirm that river sediments are systematically depleted in na k ba with respect to the upper continental crust for each of these mobile elements a systematics of weathering indexes of river borne solids is attempted a global consistency is found between all these indexes important variations in weathering intensities exist a clear dependence of weathering intensities with climate is observed for the rivers draining mostly lowlands however no global correlation exists between weathering intensities and climatic or relief parameters because the trend observed for lowlands is obscured by rivers draining orogenic zones an inverse correlation between weathering intensities and suspended sediment concentrations is observed showing that the regions having the highest rates of physical denudation produce the least weathered sediments finally chemical and physical weathering are compared through the use of a simple steady state model we show that the weathering intensities of large river suspended sediments can only be reconciled with the silicate derived dissolved load of rivers by admitting that most of the continental rocks submitted to weathering in large river basins have already suffered previous weathering cycles a simple graphical method is proposed for calculating the proportion of sedimentary recycling in large river basins finally even if orogenic zones produce weakly weathered sediments we emphasize the fact that silicate chemical weathering rates and hence co2 consumption rates by silicate weathering are greatly enhanced in mountains simply because the sediment yields in orogenic drainage basins are higher hence the parameters that control chemical weathering rates would be those that control physical denudation rates

environmental magnetic characterization of the alaknanda and ramganga river sediments ganga basin india abstract the ganga basin represents a network of complex river systems experiencing rapid changes due to natural and anthropogenic activities the alaknanda and ramganga rivers lying adjacent to each other in the nw himalayas represent two unique sub basins of river ganga having distinct physiography climate physical and chemical processes and land use patterns the present study employs mineral magnetic technique to unravel the controlling factors that influence alteration in sediment source composition and transport processes along the routing pathway the variations in magnetic mineralogy and concentrations provide a suite of information discriminating the sediment sources and transport mechanisms the results show dominant ferrimagnetic mineral assemblage in the alaknanda basin whereas an admixture of ferrimagnetic and antiferromagnetic minerals in the ramganga basin the high spatial variability in concentration of magnetic minerals in alaknanda basin indicates the role of felsic and mafic rocks weathering as well as anthropogenic contribution in sediment magnetism the tributaries flowing through peculiar lithology and anthropocentric polluted areas influence the magnetism of main river channels the loss of mafic weathering signatures in downstream sediment of the ramganga floodplains is due to reconstruction of man made dam at kalagarh which traps upstream sediment load the magnetically hard antiferromagnetic minerals in sediments of ramganga floodplain region compared to mountainous region indicate its possible source either from pollution due to extensive land use for industrial and agricultural practices or from more oxidative weathering under low sedimentation and low energy environment the findings signify new aspects of sediment sources accentuate anthropogenic perturbation and demonstrates the applicability of environmental magnetism for developing sediment dispersal mixing and pollution model for the larger ganga basin

sm nd age of the garhwal bhowali volcanics western himalayas vestiges of the late archaean rampur flood basalt province of the northern indian craton abstract whole rock sm nd isotope dating of the garhwal and bhowali mafic volcanics of the kumaun lesser himalayan sector yield an age of 2 51 0 08 ga and an initial nd 5 1 0 5 this age and initial nd are the same as that of the rampur mandi volcanics which occur to the west in the lesser himalayas in addition to confirming the widespread presence of the late archaean crustal elements in the himalayas these data constrain the age of the oldest rifting event and deposition of supracrustal sediments in the himalayas and set at rest the long standing controversy about the age and inter relationship of these mafic volcanics despite their present day disparate occurrence as a result of the post eruption deformation the area covered by these mafic volcanics is large enough to classify them as flood basalts the rampur flood basalt rfb province rift related volcanism of the same age is known from the contiguous aravalli region of the nw indian shield the orientation of the rifts in the two regions suggests the possibility of a mantle plume setting for the rfb

weathering and global denudation a negative correlation between sediment yield and weathering history as measured by the chemical alteration cia of the suspended sediment is observed for many of the world s major rivers and other regions of denudation the weathering history is a first order control on the sediment yield of such areas termed equilibrium denudation regions for other areas data scatter with either apparent increases or decreases of sediment yield for given cia values these areas are termed nonequilibrium denudation regions low sediment yields can be attributed to moderated erosion either natural or human induced and or the incorporation of unweathered glacial debris accelerated erosion resulting in high sediment yield is primarily human induced and results from cultivation and other land use each of these effects has a profound influence on global sediment discharge from the continents pre human suspended sediment discharge from the continents is estimated to be 12 6 times 10 15 g yr or about 0 6 the

the depth of penetration in antarctic firn at 10 ghz measurements taken by an x band pulse radar system in east antarctica in 1987 were analyzed to determine the depth of penetration of radar energy in polar firn a minimum estimate of the penetration depth at 10 ghz for the cold and dry polar plateau region is approximately 4 7 m spatial variations in the amount of signal penetration were observed and are related to latitude surface elevation and mean annual temperature the amount of signal penetration and its spatial variation are important factors that should be considered when processing datasets from microwave remote sensing systems that operate in the polar regions

temporal and spatial variations in water discharge and sediment load in the alaknanda and bhagirathi rivers in himalaya india abstract the alaknanda and bhagirathi rivers originate in the mountainous regions of the himalayas garhwal and result in high sediment yields causing flood hazards downstream of the ganga river and high sediment flux to the bay of bengal the rivers are perennial since runoff in these rivers is controlled by both precipitation and glacial melt in the present study three locations in the upper reaches of the ganga river were monitored for 1 yr daily observations of more than 1000 samples for suspended sediment concentrations in addition more than one hundred samples were collected from various locations of the alaknanda and bhagirathi rivers at different periods to observe spatial and temporal variations in river suspensions further multi annual data up to 40 yrs of water flow and sediment concentrations were used for inferring the variations in water flow and sediment loads on longer time scales in most previous studies of himalayan rivers there has been a general lack of long term water flow and sediment load data in the present study we carried out high frequency sampling considered long term discharge data and based on these information discussed the temporal and spatial variations in water discharge and sediment loads in the rivers in the himalayan region the results show that 75 of annual sediment loads are transported during the monsoon season june through september the annual physical weathering rates in the alaknanda and bhagirathi river basins at devprayag are estimated to be 863 tons km 2 yr 1 3 25 mm yr 1 and 907 tons km 2 yr 1 3 42 mm yr 1 respectively which are far in excess of the global average of 156 tons km 2 yr 1 0 58 mm yr 1

earthquake source mechanisms from body waveform inversion and intraplate tectonics in the northern indian ocean double couple point source parameters for 11 of the largest intraplate earthquakes in the northern indian ocean during the last 20 y were determined from a formal inversion of long period p and sh waveforms nine of the events have centroid depths at least 17 km below the seafloor well into the upper mantle two have centroid depths as great as 39 km using the source mechanisms of these earthquakes we distinguish two major intraplate tectonic provinces in the northern indian ocean to the west of the ninetyeast ridge in the southern bay of bengal intraplate earthquakes have thrust faulting mechanisms with p axes oriented n s the centroid depths of these earthquakes range from 27 to 39 km below the seafloor lithospheric shortening in this region is thus accomplished by thrust faulting in the strong core of the oceanic upper mantle while other geophysical evidence suggests that shallow sedimentary and crustal layers apparently deform predominantly by folding in the immediate vicinity of the ninetyeast ridge earthquakes display strike slip mechanisms with left lateral motion on planes parallel to the ridge this type of faulting occurs from at least 10 s to the northern end of the ninetyeast ridge near 10 n where the ridge meets the sunda arc seismic activity diminishes to the east of the ninetyeast ridge but is also characterized by strike slip faulting despite these variations in deformational style the inferred orientation of greatest compressive stress in the northern indian ocean displays a consistent long wavelength pattern over a large portion of the indian plate varying smoothly from nearly n s in the bay of bengal to nw se in the northeastern indian ocean this plate wide stress pattern and the high level of intraplate seismicity in the northern indian ocean are likely the results of substantial resistance along the himalayan continental collision zone to the continued northward motion of the western portion of the indian plate oceanic intraplate earthquakes in other regions where the level of deviatoric stress associated with the long wavelength part of the stress field is likely to be smaller need not be comparably reliable indicators of the plate wide stress field

variations in snowpack melt on the greenland ice sheet based on passive microwave measurements a simple microwave emission model is used to simulate 37 ghz brightness temperatures associated with snowpack melt conditions for locations across the greenland ice sheet the simulated values are utilized as threshold values and compared to daily gridded smmr and ssm i passive microwave data in order to reveal regions experiencing melt the spatial extent of the area classified as melting is examined on a daily monthly and seasonal may august basis for 1979 91 the typical seasonal cycle of melt coverage shows melt beginning in late april a rapid increase in the melting area from mid may to mid july a rapid decrease in melt extent from late july through mid august and cessation of melt in late september seasonal averages of the daily melt extents demonstrate an apparent increase in melt coverage over the 13 year period of approximately 3 8 annually significant at the 95 confidence interval this increase is dominated by statistically significant positive trends in melt coverage during july and august in the west and southwest of the ice sheet we find that a linear correlation between microwave derived melt extent and a surface measure of ablation rate is significant in june and july but not august so caution must be exercised in using the microwave derived melt extents in august nevertheless knowledge of the variability of snowpack melt on the greenland ice sheet as derived from microwave data should prove useful in detecting climate change in the arctic and examining the impact of climate change on the ice sheet

elevation change of the southern greenland ice sheet from 1978 to 1988 interpretation the spatial pattern of elevation change estimates derived from satellite radar altimeter data for the period from 1978 to 1988 for the southern greenland ice sheet is examined as reported previously the results from 12 ice cores widely distributed in the study area indicate that much of the spatial variability in the elevation change estimates can be explained by temporal variations in accumulation most notably the areas of largest thickening and thinning east and west of the ice divide around 66 n recently experienced substantial decadal fluctuations in accumulation sufficient to explain the observed elevation change rates that span the range of 24 cm yr 1 elevation change estimates in the nw of the study area around the 2000 m elevation contour were found to be inconsistent with both short and long term changes in accumulation fluctuations examination of stratigraphy in several shallow ice cores in the nw indicates that significant melting took place in 1977 and 1978 and this was followed by many years of very little melt activity this likely resulted in a significant downward bias in the 1978 1988 elevation change estimates in the nw comparison of measured surface velocities with those calculated assuming steady state balance show very good agreement overall but there are many instances in the southeast where the steady state velocities are significantly smaller than measured surface velocities we cannot rule out the possibility that increased ice flow in lower elevation outlet glaciers has migrated farther upstream thereby causing negative long term mass imbalance in southeast greenland

on the limits of linear moment tensor inversion of teleseismic body wave spectra the limits of linear moment tensor inversions from long period teleseismic body waves are analysed in detail using inverse methods we focus our attention on single station and few stations methods information on the feasibility of full or deviatoric moment tensor determinations prior to inversion are deduced from the system conditioning the resolution and correlation of the momenttensor components are analysed using the resolution matrix conclusions on the importance and independence of the data are drawn from the information matrix the single station case and its implications are discussed in greater detail as well as possible constraints on the inversion

stress in the indo australian plate cloetingh s and wortel r 1986 stress in the ind austr ian plate in b johnson and a w bally editors intraplate deformation characteristics processes and causes tectonophysics 132 49 67 we modelled the state of stress in the indo australian plate in order to investigate quantitatively variations observed in tectonic style the numerical procedure incorporates the dependence of slab pull and ridge push on the age of the oceanic lithosphere estimates are presented for the average net resistive forces at the himalayan collision zone the suction force acting on the overriding indo australian plate segment at the tonga kermadec trench and the drag at the base of the lithosphere our modelhng shows a concen ation of compressive stresses of the order of 3 5 lcbar in the ninetyeast ridge area the effects of the compressive resistance associated with himalayan collision and subduction of young lithosphere off the northern part of the sunda arc are focused in this region the stress field as calculated gives a consistent explanation for the observed concentration of seismic activity stein and okal 1978 and significant deformation in the oceanic crust weissel et al 1980 mcadoo and sandwell 1985 in the area the calculated stress field in the area adjacent to the southeast and central india ridges is characterized by tension parallel to the spreading axis this explains the concentration of near ridge normal faulting seismicity with t axes subparaile1 to the spreading ridge in the indian ocean as recently observed by bergman et al 1984 and wiens and stein 1984 the regional stress field along the strike of the sunda arc varies from compression seaward of and parallel to the sumatra trench segment to tension perpendicular to the java flores segment this explains the selective occurrence of well developed grabens seaward off the java flores segment of the trench observed by hilde 1983 our modelling shows that the observed rotation of the stress field denham et al 1979 in the australian continent is mainly the consequence of its geographic position relative to the surrounding trench segments and the variations of the forces acting on the down going slab in each of these the state of compression in west and central australia is induced by the action of resistive forces at the himalayan and banda arc collision zones the joint occurrence of high levels of compression in the plate s interior and normal faulting seismicity in the near ridge areas is a transient feature unique to the present dynamic situation of the indo australian plate

two unique weathering regimes in the changjiang and huanghe drainage basins geochemical evidence from river sediments the present research reconstructs the histories of chemical weathering in the drainage basins of the changjiang and huanghe based on the chemical compositions of the river sediments the silicate weathering of the changjiang basin is strong and naand ca silicate minerals are considerably dissolved while other silicate minerals are less attacked in comparison the huanghe basin is characterized by very weak silicate weathering and the weathering degree corresponds well with that of the loess which is the predominant source of the huanghe sediment overall the changjiang and huanghe basins constitute a consistent weathering spectrum from the early to intermediate stage the similarity of chemical compositions between upper continental crust and the huanghe sediments as well as the low degree of chemical weathering in the huanghe basin imply that the river sediments can be considered to be the representative of ucc and are suitable for studying the evolution of continental crust our observations indicate that climate is the predominant factor controlling silicate weathering in both river basins while controls by source rocks and relief are subordinate highly erosive river basins such as the huanghe produce poorly weathered materials which casts doubt on the idea that strong physical weathering naturally contributes much to chemical weathering differences in silicate weathering processes between the changjiang and huanghe basins may provide more constraints in estimating atmospheric co2 budget in china d 2003 elsevier b v all rights reserved

modelling of depth phases and source processes of some central aleutian earthquakes abstract short period synthetic seismograms are computed to determine the relative amplitudes and arrival times of p pp pwp water surface reflection and sp phases except along nodal planes of upgoing p pwp is of greater amplitude than sp for central aleutian earthquakes pwp dominates over sp and pp at north american stations for thrust mechanisms and modelled crustal structures the pwp phase is clearly identified in three aleutian events and can be used to constrain focal depths complex fracturing processes are identified in two of the events in simple events smaller phases which are consistent from station to station can be identified as sub surface reflections and used for modelling the structure of the forearc

thermoelastic stress how important as a cause of earthquakes in young oceanic lithosphere we present a series of exploratory models which test the hypothesis that thermoelastic stress is a significant contributor to the state of stress in young oceanic lithosphere less than 35 m y in age in support of this hypothesis is the concentration of seismicity in lithosphere younger than 15 m y where cooling rates are relatively high most near ridge earthquakes have focal depths between the moho and the depth of the 800 c isotherm thrust and strike slip events dominate the shallowest seismicity while the focal mechanisms of the deeper events are generally characterized by normal faulting to assess the importance of thermal stress in the generation of near ridge earthquakes we model the lithosphere as an elastic half space in which the response to cooling is computed using the method of thermoelastic displacement potentials a key assumption in the models is that stress is relieved on time scales generally short compared with the age of the lithosphere a further assumption in some models is that material will not contribute thermal stress until it has cooled below an elastic blocking temperature normal faulting is predicted throughout the lithosphere in thermal stress models based on simple half space cooling models in which a cooled surface layer is incorporated to simulate the effect of hydrothermal circulation on shallow thermal structure predict stresses that can match the locations of both thrust and normal faulting earthquakes near mid ocean ridges the addition of a ridge push stress to the computed thermal stress enhances the likelihood of thrust faulting in the uppermost lithosphere at ages greater than about 15 m y but probably contributes little to the stress field at younger ages though these simple models are limited by several simplifying assumptions particularly in the immediate vicinity of the ridge axis they support the hypothesis that thermoelastic stress can play a major role in the tectonics of young oceanic lithosphere

distribution and sources of particulate organic matter in the water column and sediments of the fly river delta gulf of papua papua new guinea suspended particles from surface and bottom waters and surficial sediments from the seabed were collected throughout the fly river subaqueous delta region during the monsoon season in january 2003 because of the unusually low river discharge associated with a strong el nino water column salinities were relatively high 10 to 32 throughout most of the delta with brackish salinities 4 wt relatively high organic carbon nitrogen molar ratios oc n 20 mol mol and quite depleted stable isotopic compositions of organic carbon 13coc 27 in contrast surface sediments in the seabed displayed spatially uniform compositions that were characterized by markedly lower oc contents 1 1 0 8 wt lower oc n ratios 17 9 mol mol and relatively enriched 13coc compositions 25 5 1 1 the radioisotopic compositions of oc from a selected set of seabed samples 14coc of 408 82 indicate om in surface sediments is old 14c ages of 2800 to over 6000 years before present the ratios of organic carbon to mineral surface area exhibited by these sediments are within the typical mono layer equivalent ranges characteristic of shelf sediments and do not reflect the preferential removal of terrigenous om overall these compositions indicate that while water column pom appears to be derived mainly from terrigenous vascular plant debris and riverine estuarine phytoplankton the source of most of the sedimentary pom is aged soil oc ultimately derived from c3 vegetation we speculate that the concentrations and sources of suspended pom in the water column of the fly river delta region reflect the conditions of low river discharge low wave energy and neap tides encountered at the time of sampling in contrast pom compositions in surface sediments are consistent with the transport and deposition of old mineral bound oc most likely eroded from the upland regions of the fly river watershed which is characterized by steep slopes high precipitation and c3 tropical forests and grasslands

the ciw index a new chemical index of weathering abstract a new chemical index of weathering that can be applied to modern soils and precambrian paleosis is proposed ciw al2o3 the value of this index increases as the degree of weathering increases and the difference between ciw index values of the silicate parent rock and soil or sediment reflects the amount of weathering experienced by the weathered material

grain size characteristics of suspended sediment in the yellow river china abstract based on the data from the yellow river and its tributaries a systematic study has been made of the spatial and temporal variations in grain size feature of suspended sediment the grain size characteristics of suspended sediment in the yellow river basin are closely influenced by precipitation seasonal alternations of wind and water action and the nature of surface materials the lower the mean annual precipitation the stronger the wind action the coarser the surface loess materials the coarser is the suspended sediment in particular grain size characteristics of suspended sediment of the middle yellow river s tributaries are controlled by hyperconcentrated flows with suspended sediment concentrations of 300 000 400 000 mg l or more at a station the relationship between grain size and suspended sediment exhibits two peaks with percentages of the 0 05 mm suspended sediment occurring at both low and very high suspended sediment concentrations based on the data from all the tributaries of the middle yellow river an optimal grain size composition of suspended sediment has been identified that leads the annual suspended sediment concentration to the highest values the long term variation of grain size suspended sediment in the yellow river can be related to variations in precipitation and human activities the 30 year record from longmen station shows that during the 1960s the suspended sediment size increased but since the 1970s it has declined controlled by the influencing factors grain size of suspended sediment in the middle yellow river decreases from northwest to southeast

changes in greenland ice sheet elevation attributed primarily to snow accumulation variability the response of grounded ice sheets to a changing climate critically influences possible future changes in sea level recent satellite surveys over southern greenland show little overall elevation change at higher elevations but large spatial variability using satellite studies alone it is not possible to determine the geophysical processes responsible for the observed elevation changes and to decide if recent rates of change exceed the natural variability here we derive changes in ice sheet elevation in southern greenland for the years 1978 88 using a physically based model of firn densification and records of annual snow accumulation reconstructed from 12 ice cores at high elevation our patterns of accumulation driven elevation change agree closely with contemporaneous satellite measurements of ice sheet elevation change and we therefore attribute the changes observed in 1978 88 to variability in snow accumulation similar analyses of longer ice core records show that in this decade the greenland ice sheet exhibited typical variability at high elevations well within the long term natural variability our results indicate that a better understanding of ice sheet mass changes will require long term measurements of both surface elevation and snow accumulation

contribution of seismic tomography in moment tensor inversions using teleseismic surface wave spectra the knowledge of lateral heterogeneities is crucial for path corrections in moment tensor inversions using surface waves after some attempts to use regionalized earth models for very long period surface wave moment tensor inversions recent tomographic earth models offer the possibility to make short period path corrections and therefore retrieve more reliable moment tensors for teleseismic earthquakes first we try to evaluate the precision required for path corrections in comparison with source effects some selected earth models are tested to evaluate how their results compare to those using multiple frequency filtering techniques some real cases illustrate the sensitivity of moment tensor solutions to the different path corrections and it appears clearly that regionalized earth models and tomographic models deduced from long period data alone greater than 150 sec cannot lead to trustworthy broadband moment tensor inversions recent tomographic models using phase velocities at much shorter periods 40 to 200 sec offer a precision comparable to that of the multiple frequency filtering technique both methods lead to acceptable source mechanisms using a small number of stations in more than two cases out of three the use of recent global tomographic models based upon shorter period surface waves might thus be a useful alternative to heavy multiple frequency filtering techniques to automate source studies especially for rapid determinations using a small number of stations

channel evolution on the dammed elwha river washington usa abstract like many rivers in the western u s the elwha river washington has changed substantially over the past century in response to natural and human forcing the lower river is affected by two upstream dams that are slated for removal as part of a major river restoration effort in preparation for studying the effects of dam removal we present a comprehensive field and aerial photographic analysis of dam influence on an anabranching gravel bed river over the past century with the dams in place loss of the upstream sediment supply has caused spatial variations in the sedimentary and geomorphic character of the lower elwha river channel bed sediment is armored and better sorted than on the naturally evolving bed upstream of the dams on time scales of flood seasons the channel immediately below the lower dam is fairly stable but progresses toward greater mobility downstream such that the lowermost portion of the river responded to a recent 40 year flood with bank erosion and bed elevation changes on a scale approaching that of the natural channel above the dams in general channel mobility in the lowest 4 km of the elwha river has not decreased substantially with time enough fine sediment remains in the floodplain that given sufficient flood forcing the channel position sinuosity and braiding index change substantially the processes by which this river accesses new fine sediment below the dams rapid migration into noncohesive banks and avulsion of new channels allow it to compensate for loss of upstream sediment supply more readily than would a dammed river with cohesive banks or a more limited supply of alluvium the planned dam removal will provide a valuable opportunity to evaluate channel response to the future restoration of natural upstream sediment supply

geochemistry dissolved elemental flux rates and dissolution kinetics of lithologies of alaknanda and bhagirathi rivers in himalayas india alaknanda and bhagirathi ab river basins in the himalayan region in india expose lithologies comprising mainly of granites low high grade metamorphics shales and carbonates which in conjunction with the monsoon rains and glacial melt control water chemistry and dissolved elemental flux rates in the present study we monitored two locations a srinagar on the alaknanda river and b maneri on the bhagirathi river for daily variations in total suspended sediments major ions and dissolved silica over one complete year july 2004 june 2005 based on long term discharge data discharge weighted composition and dissolved elemental flux rates with respect to ca mg hco3 si of the river were estimated the information thus obtained has substantially added up to the existing chemical data of these rivers and has refined the flux rates our high frequency samples provide informations such as a water chemical compositions that show a large temporal and spatial variation and b carbonate lithology that controls water chemistry predominantly the dissolution kinetics of various lithologies namely leucogranite gneiss quartzite phyllite and shale of the ab river basins were studied through batch experiments at controlled temperature 25 and 5 c and ph 8 4 condition in laboratory these lithologies undergo slow rates of dissolution 10 13 to 10 15 mol m2 s while field weathering rates based on dissolved elemental flux rates in the ab rivers are much higher 10 8 to 10 9 mol m2 s extremely high physical weathering rates in ab rivers which enhance chemical weathering significantly mainly attribute this wide discrepancy in laboratory derived rates of representative basin rocks and dissolved elemental fluxes in the field however laboratory simulated experiments facilitate to quantify elemental release rates understand the kinetics of the dissolution reactions and compare their roles at individual level

predicting the terrestrial flux of sediment to the global ocean a planetary perspective a new model for predicting the long term flux of sediment from river basins to the coastal ocean is applied to a global data set of 340 river basins the model is based on relief basin area or averaged discharge and basin averaged temperature basinaveraged temperature is determined from basin location latitude longitude and the lapse rate across the basin relief hypsometric approximation the sediment flux model incorporates climate through basin temperature and hydrologic runoff solutions are provided for each of the major hemispheric climate regions polar temperate and tropic the model successfully predicts the pre anthropogenic flux of sediment to within the uncertainties associated with the global observations within a factor of two for 75 of rivers that range across five orders of magnitude in basin area and discharge most of the problem rivers are associated with low observational loads often smaller rivers where anthropogenic impacts are often magnified and temporal variability is high model predictions provide a baseline for researchers 1 to question the quality of observational data where available and disagreement is greatest 2 to examine a river basin for unusually large anthropogenic influences i e causes of erosion or causes of hinterland sediment retention and 3 to uncover secondary factors not addressed by our model lithology lakes the model provides a powerful tool to address the impact of paleo climate fluctuations warmer colder wetter drier on the impact of sediment flux to the coastal ocean d 2003 elsevier b v all rights reserved

stability of fault plane solutions for the major n italy seismic events in 2012 abstract we propose a critical analysis of the moment tensor solutions of the major seismic events that affected northern italy in 2012 inverting full waveforms at regional distance using the non linear method named inpar we investigate period dependent resolution that affects in particular the solutions of shallow events this is mainly due to the poor resolution of mzx and mzy components of the seismic tensor when inverting signals whose wavelengths significantly exceed the source depth as a consequence instability affects both source depth and fault plane solution retrieval and spurious large compensated linear vector dipole components arise the inversion performed at cutoff periods shorter than 20 s reveals in many cases different details of the rupture process which are supported by independent geodynamical arguments thus we conclude that inversion of full waveforms at cutoff period as short as possible should be preferred

variations in trace element including rare earth element concentrations with grain sizes in loess and their implications for tracing the provenance of eolian deposits the concentrations of rare earth elements rees and other 28 trace elements were determined in seven grain size fractions from four loess samples collected from the tibetan plateau the sichuan basin and the chinese loess plateau the results indicate that concentrations of rees except for heavy rare earth elements hrees are almost grain size independent however rees show clear fractionation with grain size middle rare earth element mree depletion increases with decreasing grain size whereas hree enrichment increases with decreasing grain size excluding rees and y most of the other trace element concentrations tend to increase with decreasing grain sizes the trace element geochemistry indicates that the potential sources of eolian deposits from the sichuan basin the chinese loess plateau and the tibetan plateau differ from one another this comparative study confirmed that the eolian materials from the asian continent are the source of the terrigenous component of the central north pacific sediments and the loess from the chinese loess plateau could represent the average composition of eolian dust from the asian continent in contrast the eolian deposits in the sichuan basin and in the tibetan plateau are mainly of local origin with short distance eolian transport

seasonal variability of grain size weathering intensity and provenance of channel sediments in the alaknanda river basin an upstream of river ganga india the ganga river in the indian sub continent is amongst the highest sediment transporting rivers to the world s oceans previous studies estimated that ganga river derives 65 of its sediment load from the higher himalayas the alaknanda river is a headwater stream of the ganga river and has a high sediment flux in the present study freshly deposited channel sediments were collected from the alaknanda river and its tributaries during the post monsoon pre monsoon and monsoon seasons and were analyzed for grain size distribution major oxides composition magnetic susceptibility and heavy mineral assemblages the results show that the channel sediments are mostly medium to coarse sand 56 4 930 m unimodal and symmetrical to fine skewed in distribution the presence of dams and reservoirs seemed to affect the natural grain size distribution in the alaknanda river the average value of the chemical index of alteration of 56 and weathering index of parker of 43 indicates intense physical weathering in the basin the magnetic susceptibility and heavy mineral assemblages showed the effect of local lithology in controlling sediment composition the principal component analysis on the major oxide composition of channel sediment shows that felsic mafic and carbonate weathering contribute to the high sediment load of the alaknanda river this study established that along with weathering of higher himalayan crystallines weathering of garhwal group enriched in magnesite dolomites and mafic intrusion is also a significant source of channel sediments in the upper ganga basin

the relationship between tectonic uplift and chemical weathering rates in the washington cascades field measurements and model predictions tectonic uplift is one of the key factors controlling the supply of material to weathering environments at present however there is debate about whether tectonics or climate plays a larger role in controlling chemical weathering rates on a global scale over geologic time we measured riverine weathering fluxes from twelve catchments along the skykomish river in the washington cascades where long term exhumation rates have been constrained by u th he thermochronom etry to examine the effect of tectonic uplift on chemical weathering rates we show that in the western washington cascades dissolved si fluxes increase from approxi mately 1900 to 3000 mol ha 1 yr 1 from west to east across the range and are correlated with rock exhumation rates we use dissolved si flux data from these catchments depth to bedrock measurements and long term exhumation rates to test a steady state weathering model that describes the relative importance of reaction kinetics and rock supply on weathering rates characterization of study basins with respect to two key variables in this model weathering zone depth and exhumation rate allows us to examine the relative effects of climate and tectonics on chemical weathering by analyzing the ratio of the timescale of reaction kinetics and the residence time in the weathering zone evaluation of this model shows that chemical weathering rates in the cascades are controlled by the rate of rock erosion and factors that influence the depth of the active weathering zone however the model predicts that in tectonically inactive areas the supply of material limits the overall rate of chemical weathering while in active tectonic or erosional environments the rate of supply exceeds the ability of a system to weather that material resulting in a landscape in which weathering rates are expected to respond strongly to changes in climatic conditions

focal depths and moment tensor representations of shallow earthquakes associated with the great sumba earthquake focal depths in the range 8 to 24 km below the seafloor were determined for seven of the larger shocks associated with the great sumba earthquake of august 19 1977 depth control was achieved by modeling digitized long period p waves recorded by the world wide standard seismic network if the base of the rupture at the time of the mainshock were no greater than the depth of the deepest aftershock the stress drop would be nearly 500 bars amplitude and first motion data from the p waves were inverted for point source moment tensors the inversion of rayleigh and love wave spectra computed from digital seismograms recorded by the seismic research observatories sro and the abbreviated seismic research observatories asro broadened the source study to include earthquakes with moments as small as 1024 dyn cm too small for either traditional first motion solutions or p wave modeling the inversion procedure was applied to data in the passband from 30 to 120 s the propagation phase for the love and the rayleigh waves was calibrated with signals from two earthquakes for which the source phase was inferred from the p wave solutions agreement with the corresponding p wave solutions is nearly the same whether or not the smaller eigenvalues of the inner product matrix are retained in the inversions the double couple components generally account for more than two thirds of the total moment normal faulting along an east to northeasterly strike characterizes the mechanisms in the principal zone of aftershock activity strike slip mechanisms consistent with horizontal compression normal to the arc prevail in the delayed aftershock zone located 200 km northwest of the mainshock of the earthquakes subjected to this surface wave analysis the foreshock stood out as having felt a significantly higher apparent stress perhaps as much as one half an order of magnitude higher than the others these results suggest that accurate source parameters for moderate to small magnitude earthquakes can be determined from surface waves recorded by the sro and asro in particular the mechanisms of small magnitude foreshocks could be obtained in this way

temporal change in the extinction coefficient of snow on the greenland ice sheet from an analysis of seasat and geosat altimeter data the extinction coefficient of snow k sub e along the central portion of the greenland ice sheet is mapped using data from the seasat 1978 and geosat 1985 1989 altimeters the extinction coefficient is obtained by fitting altimeter waveforms with a surface volume scattering model the authors find that in the lower latitudes the seasat and geosat extinction coefficients are very nearly the same while in a specific higher latitude region of the ice sheet the seasat k sub e values exceed the geosat values by over 100 by analyzing 18 months of the geosat data the author quantified the variability inherent in the extinction coefficient measurements the results show that the observed temporal variation in the extinction coefficient from 1978 to 1985 is three times larger than the measured variability this indicates that the average grain size of the near surface snow in this region may have decreased during the time span between the two altimeter datasets the temporal change in extinction coefficient found in this study demonstrates the important contributions that time series analysis of satellite datasets can make to the study of the polar ice sheets in addition these results have important implications for the study of long term elevation change over the ice sheets using altimeter data the author s study demonstrates that significant biases could be introduced into ice sheet elevation change estimates because of temporal variations in the surface conditions of the ice sheet future investigations of ice sheet mass balance using altimetry data should be aware of this possibility

geochemical compositions and provenance discrimination of the central south yellow sea sediments geochemical compositions and sedimentation rates of surface and core sediments in the central south yellow sea were analyzed for the identification of sediment origins the sediment accumulation rates measured by 210 pb geochronology decrease significantly from the western part to the central area calcium carbonate total organic carbon and most elements are more enriched in the western muddy sediments than in the sandy eastern part overall geochemical compositions of the central south yellow sea sediments vary between those of chinese and korean river sediments supplied into the sea although caco3 content exhibits regional variations in the central south yellow sea the discrimination diagram of sc al vs cr th distinctly suggests that the muddy holocene sediments in the central western part are derived ultimately from chinese rivers especially the huanghe river whereas the eastern sandy sediments primarily came from the korean rivers during the postglacial transgression 2007 elsevier b v all rights reserved

geochemistry of mansar lake sediments jammu india implication for source area weathering provenance and tectonic setting abstract the sediment geochemistry including ree of surface and core samples from mansar lake along with mineralogical investigations have been carried out in order to understand the provenance source area weathering hydrolic sorting and tectonic setting of the basin the geochemical signatures preserved in these sediments have been exploited as proxies in order to delineate these different parameters the major element log values fe 2 o 3 k 2 o vs sio 2 al 2 o 3 and na 2 o k 2 o vs sio 2 al 2 o 3 demarcate a lithology remarkably similar to that exposed in the catchment area the chondrite normalized ree patterns of lake samples are similar to post archaean australian shale paas with lree enrichment a negative eu anomaly and almost flat hree pattern similar to a felsic and or cratonic sedimentary source however the la th sc plot of samples fall in a mixed sedimentary domain close to upper continental crust ucc and paas suggesting sedimentary source rocks for the mansar detritus it also indicates that these elements remained immobile during weathering and transportation the mineralogical characteristic rees and high field strength elements hfse together with the high percentage of metamorphic rock fragments in the siwalik sandstone support a metamorphic source for lower siwalik sediments a very weak positive correlation between zr and sio 2 poor negative correlation with al 2 o 3 negative correlation of la yb n and gd yb n ratios with sio 2 and positive correlation with al 2 o 3 suggest that zr does not dominantly control the ree distribution in mansar sediments the petrographic character and textural immaturity indicate a short distance transport for the detritus the distribution of elements in core samples reflect fractionation the higher zr th and zr yb ratios in coarse sediments and paas compared to finer grained detritus indicate sedimentary sorting plots of the geochemical data on tectonic discrimination diagrams suggest that the sediments derived from the lower siwalik were originated within a cratonic interior and later deposited along a passive margin basinal setting it therefore reveals lower siwalik depositional history

major and trace element geochemistry in upper ganga river in the himalayas india chemical weathering and resulting water compositions in the upper ganga river in the himalayas were studied for the first time temporal and spatial sampling for a 1 year period monthly intervals was carried out and analyzed for dissolved major elements trace elements rare earth elements ree and strontium isotopic compositions amounts of physical and chemical loads show large seasonal variations and the overall physical load dominates over chemical load by a factor of more than three the dominant physical weathering is also reflected in high quartz and illite mica contents in suspended sediments large seasonal variations also occur in major elemental concentrations the water type is categorized as hco3 so42 ca2 dominant which constitute 60 of the total water composition on an average only about 5 12 of hco3 is derived from silicate lithology indicating the predominance of carbonate lithology in water chemistry in the head waters of the ganga river more than 80 na and k are derived from silicate lithology the silicate lithology is responsible for the release of low sr with extremely radiogenic sr 87sr 86 sr 0 75 in bhagirathi at devprayag however there is evidence for other end member lithologies for sr other than carbonate and silicate lithology trace elements concentrations do not indicate any pollution although presence of arsenic could be a cause for concern high uranium mobilization from silicate rocks is also observed the ree is much less compared to other major world rivers such as the amazon perhaps because in the present study only samples filtered through 0 2 m were analysed negative eu anomalies in suspended sediments is due to the excess carbonate rock weathering in the source area

source mechanisms of earthquakes near mid ocean ridges from body waveform inversion implications for the early evolution of oceanic lithosphere to investigate the early tectonic evolution of oceanic lithosphere we present a synthesis of the characteristics of near ridge earthquakes i e earthquakes which occur off the axis of major mid ocean spreading centers but in lithosphere less than 35 m y old near ridge seismicity for the past two decades has been rather evenly distributed along the major ridge systems with the exception of the central indian ocean and the eastern part of the cocos plate which have experienced a high rate of earthquake activity during that time for 32 near ridge earthquakes we determined the double couple orientation seismic moment centroid depth and source time function using a formal inversion technique based on matching synthetic and observed p and sh waveforms all types of faulting styles are observed seismogenic deformation in young oceanic lithosphere is concentrated in the first 15 m y and occurs almost entirely in the uppermost mantle from just below the moho to depths at which the temperature estimated from standard thermal models exceeds 800 c thrust faulting is not observed at depths greater than 10 km below the seafloor the deepest near ridge earthquakes are generally characterized by normal faulting focal mechanisms with the t axis oblique or perpendicular to the local spreading direction most of these earthquakes occur in the central indian ocean the transition from mechanisms characteristic of ridge axes to those characteristic of the near ridge environment occurs within the first few million years for lithosphere less than 35 m y old horizontal compressive stress associated with the cooling and subsidence of the lithosphere ridge push does not appear to be the dominant source of stress released in earthquakes this result may be used to place a lower bound of several hundred bars on the typical stress difference in young oceanic lithosphere this bound together with the observed depth of faulting implies that the strain rate associated with seismic deformation is locally at least 10 15 s 1 we propose that thermoelastic stresses associated with plate cooling play an important role in near ridge earthquakes this source of stress can account for the mechanisms and depths of many near ridge earthquakes and for the concentration of activity in very young lithosphere the comparative aseismicity of the oceanic crust may reflect the concentration of thermoelastic stress below the moho due to different material properties for the crust and upper mantle or the early release of thermoelastic stresses through hydrothermal circulation and cracking throughout the crust at or near the ridge axis the higher level of near ridge seismicity in the indian ocean may be the result of modification or enhancement of the more typical near ridge stress state by such local processes as the continental collision between india and asia or active secondary convection beneath the young lithosphere of the indian plate

empirical measurements of tectonic moment release in nuclear explosions from teleseismic surface waves and body waves summary a method of source parameter estimation based principally on observations of teleseismic long period surface waves is developed and applied to 71 underground nuclear explosions at the balapan shagan river test site in kazakhstan first we quantify the observed radiation patterns of love and rayleigh waves noting that such data place only three linear constraints on the five parameters of the standard point source model for each explosion the three constraints are the strengths of the isotropic sin2 and cos2q components of the observed pattern where is azimuth the five source parameters are the isotropic moment m the doublecouple moment adt and the strike dip and rake angles qs 6 a these last four parameters characterize the inferred faulting tectonic release surface waves which propagate from different seismic events in a geographically tight cluster to a distant station are similar in shape and for very shallow sources the propagation operator can be described by a single wave shape a differential propagation delay and a single amplitude factor containing the effects of attenuation scattering focusing and geometrical spreading the inverse problem is formulated which iteratively solves simultaneously for the path amplitude factors and the three radiation pattern parameters for all events using observed seismograms as the empirical wave shapes we fit 1110 relative measurements of rayleigh and love wave amplitudes to determine path amplitude factors to 29 globally distributed stations and radiationpattern parameters for the 71 explosions second we present a new method for interpreting such radiation patterns in previous studies two of the five source parameters have typically been fixed by making the very restricted assumption of pure dip slip faulting at 45 dip the assumption leads to estimates of strike that are mostly in the north west south east direction at balapan and to estimates of m that correlate very poorly with estimates based upon short period signals p lg however now that excellent yield estimates have become available we can avoid the assumption of pure dip slip faulting instead we can estimate mi from p and lg wave data thus adding a fourth constraint to help in interpreting the teleseismic surface wave amplitudes the outcome is a method for estimating the strike as of faulting associated with tectonic release for each explosion and for estimating the two combinations m sin 6 cos a and mo sin 26 sin a which respectively are the strike slip and dip slip components of the tectonic release the strike directions of inferred faulting at balapan are found to lie in the range 90 120 which conforms better with limited geological information on faulting in the region than does the trend that has long been inferred from assuming pure dip slip faulting we find that without additional information about individual explosions we are not able to provide a high precision isotropic moment or yield estimate from teleseismic surface waves

a diffuse plate boundary model for indian ocean tectonics it is suggested that motion along the virtually aseismic owen fracture zone is negligible so that arabia and india are contained within a single indo arabian plate divided from the australian plate by a diffuse boundary the boundary is a zone of concentrated seismicity and deformation commonly characterized as intraplate the rotation vector of australia relative to indo arabia is consistent with the seismologically observed 2 cm yr of left lateral strike slip along the ninetyeast ridge north south compression in the central indian ocean and the north south extension near chagos

new precipitation and accumulation maps for greenland annual total precipitation and the annual accumulation on the greenland ice sheet are evaluated and presented in two maps the maps are based on accumulation measurements of 25 1 pits and cores obtained from the upper accumulation zone and precipitation measurements made at 35 meteorological stations in the coastal region to construct the accumulation map the annual precipitation was split into solid and liquid precipitation components annual total precipitation exceeding 2500 mm w e occurs on the southeastern tip of greenland while the minimum precipitation is estimated to occur on the northeastern slope of the ice sheet the mean annual precipitation for all of greenland is 340 mm w e the largest annual accumulation of about 1500 mm w e is found on the glaciers in the southeastern corner of greenland while the smallest accumulation is found on the northeastern slope of the ice sheet west of danmarkshavn the mean accumulation on the greenland ice sheet is estimated at 310 mm w e the regional difference in accumulation is examined with respect to the 850 hpa m bar level circulation the present surface topography is found to play an important role in determining regional accumulation on the ice sheet

particle size characteristics of suspended sediment in hillslope runoff and stream flow this study examines the particle size characteristics of hillslope soils and fluvial suspended sediments in an agricultural catchment samples of surface runoff and stream flow were collected periodically and analysed for the size distributions of the effective undispersed sediment this sediment was subsequently dispersed and the ultimate size distributions determined the median effective particle size of stream suspended sediment was considerably coarser than the median ultimate particle size indicating that most of the load included a substantial proportion of aggregates moreover the proportion of fine material i e silt and clay increased and the proportion of sand sized material decreased with increasing discharge this decrease in sediment size with increased flow which is contrary to the traditional assumption of a positive discharge particle size relationship is thought to reflect i the influx of silt and clay predominantly the former originating on the catchment slopes and brought to the stream by overland flow along vehicle wheelings roads and tracks and ii erosion of fine material from the channel bed and banks during large storms however the proportion of sand sized sediment increased during the rising limb of the hydrograph as a result of the entrainment of coarser source material from the valley floor during overbank flooding the stream suspended sediment was finer than the catchment soils and considerably finer than material eroding from the catchment slopes during storms the degree of clay and silt enrichment in the suspended sediments was largely the result of preferential deposition of the coarser fraction during the transport and delivery of sediment from its source to basin outlet the data from this study confirm that a significant mode of sediment transport in fluvial systems is in the form of aggregates and that the dispersed sediment size distribution is inappropriate for determining the transportability of sediment by flow 1997 by john wiley sons ltd

chemical indices cia and wip as proxies for integrated chemical weathering in china inferences from analysis of fluvial sediments abstract rivers play a key role in earth surface processes by weathering and eroding the upper continental crust under variable climate regimes how to quantitatively determine the chemical weathering intensity in the drainage basins using geochemistry of fluvial sediments remains unclear the chemical index of alteration cia and the weathering index of parker wip have been used worldwide as proxies to evaluate the chemical weathering intensity in large watersheds and in specific weathering profiles in this study concentrations of major oxides in the suspended particulate matter spm and fine grained floodplain sediments from 13 major rivers in china from north to south were analysed and compiled for the estimation of chemical weathering in china the gradual increase in cia and decrease in wip values with decreasing latitude of the catchments suggest enhanced weathering intensity in these river basins a combined monsoon climate effect of temperature runoff and precipitation primarily controls the chemical weathering in china the provenance rock types and relief play minor roles in weathering whereas an active tectonic setting and typhoon events play key roles in the weathering process in taiwan the cia values of the finer spm samples within a given river are overall greater than those in the corresponding coarser floodplain sediments underscoring the effect of sediment grain size on cia values the irregular seasonal variation of the cia within a specific river further confirms the notion that the cia does not reflect the instantaneous chemical weathering on continents although it is impossible to build a general model for regulating the chemical weathering of continents this study reveals that the integrated chemical weathering intensity in large latitudinal watersheds can with careful application be quantitatively estimated using the proper geochemical proxies of river sediments

pre and post monsoon variations in the magnetic susceptibilities of soils of mumbai metropolitan region implications to surface redistribution of urban soils loaded with anthropogenic particulates mumbai metropolitan region mmr in india represents one of the most industrialized and thickly populated areas of the monsoon dominated asian region we present here pre and post monsoon magnetic susceptibility variations in the top soils representing sampling domains of industrial heavy traffic and forested areas within mmr the rock magnetic studies including isothermal and anhysteric remanent magnetization and hysteresis loop analysis infer predominant pseudo single domain to multi domain grains in an overall ferrimagnetic dominant mineralogy of the soils the susceptibility temperature variations from 190 to 700 c infer maghemite fe2o3 as the chief mineral component of pedogenic origin and the pure magnetite fe3o4 is of anthropogenic nature spatial distribution of ferrimagnetic concentration is in agreement with polluting sources the post monsoon redistribution pattern is greatly controlled by the surface runoff and topographic conditions the study demonstrates that in a ferrimagnetically reach substrate like mmr the spatial distribution patterns derived from routine concentration and grain size dependent rock magnetic parameters integrated with topographic and seasonal attributes yield significant information on the style and surface re distribution of anthropogenically loaded soils and sediments to identify its seasonal dumping alternatively knowing the source of signal the magnetic susceptibility can be further used as a robust parameter to produce detailed maps to monitor the pollutions in urban areas