petrogenesis and tectonic setting of late precambrian ensimatic volcanic rocks central eastern desert of egypt abstract early stages in the geologic evolution of the central eastern desert of egypt ced reflect an intense episode of ensimatic volcanic activity similar to modern magmatism of the ocean floors and island arcs this paper reports results from studies of the petrology and petrogenesis and interprets the significance of these late precambrian volcanic rocks a three fold stratigraphy is preserved in the basement of the ced a basal section of oceanic crust includes ultramafics gabbros and pillowed basalts these older metavolcanics omv are conformably succeeded by dominantly volcanogenic metasediments which are in turn succeeded by a dominantly andesitic calc alkaline sequence of younger metavolcanics ymv the omv and ymv are largely restricted to the ced in egypt but analogous terranes are found in northern arabia 40 400 ppm and ni 30 260 ppm they are poor in k 2 o 0 05 0 92 rb 0 3 5 0 ppm and ba 11 89 ppm on ti zr cr v ni p discriminant diagrams the omv plot in the field of modern abyssal tholeiites high k rb 450 1800 and light ree depletions support this inference although k ba 25 45 is lower than modern mid ocean ridge basalts morb the sum of omv geochemical characteristics requires that these magmas were derived by the fractional fusion of the mantle it is suggested that the omv were generated by 20 25 fractional melting of previously depleted mantle at depths of less than 60 km relatively little fractionation accompanied ascent to the surface where the omv were erupted in a primitive crustal environment either a small oceanic rift or a back arc basin metamorphism of the ymv resulted in little elemental redistribution these andesites have sub alkaline clinopyroxenes and major element geochemical characteristics indistinguishable from modern calc alkaline andesites ymv andesites in the central and western ced have k rb 400 600 k ba 20 40 and are light ree enriched and heavy ree depleted high concentrations of cr 50 150 ppm and ni 20 100 ppm and low initial 87 sr 86 sr ratios 0 7028 0 7030 indicate that these magmas were generated by melting in the mantle modelling studies and consideration of experimental data indicate that these andesites were formed by 2 10 fractional fusion of hydrous undepleted garnet therzolite at depths of 65 km or more in the mantle the data show that an intense episode of instability convection and widespread melting occurred in the mantle beneath afro arabia at the end of the precambrian

precambrian alluvial fan and braidplain sedimentation patterns example from the mesoproterozoic rjukan rift basin southern norway abstract an integrated approach of facies analysis geochemistry and paleohydrology provides new insight into the sedimentology and paleogeography of alluvial sediments in the precambrian here alluvial fan and braidplain sedimentation patterns are documented in a mesoproterozoic rift basin called known as the rjukan rift basin in southern norway the studied formation heddersvatnet formation consists of volcanoclastic breccias and conglomerates cross bedded sandstones with associated mudstones and subaerial basaltic lava beds deposited in a rift basin during the syn rifting phase based on genetically related major lithofacies associations and individual minor lithofacies the sedimentation is characterized by colluvial and screen apron deposits subaerial debris flows hyperconcentrated or sheet flood deposits in the proximal part representing waning flood cycles the distal part contains shallow water traction current deposits and associated subaerial continental flood basalts that flowed down the rift valleys the synsedimentary intra rift faulting formed seasonal or climatically controlled intrafan ponded lake with playa lake type cycles and shrinkage cracks the geochemical composition of the of the studied sandstones and mudstones suggests a passive rifted continental margin with minor to moderate chemical weathering possible in a semi arid arid paleoclimate clastic petrofacies of the sandstones indicate a locally uplifted and syn rift paleotectonic setting during the main sedimentation stage passing toward a post rifting stage of the depositional basin small scale structures within the sedimentary basin affected the depositional patterns of the heddersvatnet formation by creating local sites of uplift and erosion controlling the sediment transport and defining the accommodation space for deposition the sedimentation of the heddersvatnet formation reflects a tectonic base level fall which resulted in an accumulation of thick alluvial fan or braidplain sediments near uplifted flank s of the sedimentary basin this was combined with intensive erosion of the basement in the pre vegetation landscape which resulted in changes in the hydraulic geometry of flow and sediment discharge of stream channels the following criteria observed from the heddersvatnet formation are suggestive of an ancient alluvial fan and associated braidplain sedimentation 1 deposition close to the source area 2 slightly divergent paleoflows 3 high energy flows with waning flood cycles 4 abundance of poorly sorted and laterally extensive subaerial debris flows and related streamflows possible sheetfloods hyperconcentrated flows and their associations 5 great distribution of grain size and lithofacies changes in proximal vs distal parts 6 limited suite of sedimentary structures cross stratification ripple marks and desiccanation cracks 7 fault bounded basin graben with hanging wall close to uplifted flank s 8 paleoslope estimation indicating at least moderate paleotopographic highs 9 colluvial and scree apron breccias 10 lack of any typical braided stream channel fill conglomerates and floodplains and 11 channelized sediment bodies lacking extensive lateral continuity

petrological geochemical and statistical analysis of eocene oligocene sandstones of the western thrace basin greece and bulgaria abstract the rhodopian orogen developed since the late cretaceous early eocene during accretionary processes following the closure of the vardar ocean basin a branch of neotethys through a multidisciplinary approach including sandstone petrology and geochemistry of the clastic and volcanoclastic sediments we reconstruct the unroofing history of the rhodopian orogen and characterize the formation and the evolution of the western portions of the thrace basin in greece and bulgaria between the late eocene and oligocene detrital modes of 127 sandstone samples provide evidence of three distinctive petrofacies quartzolithic quartzofeldspathic and volcanoclastic the petrographic composition gives evidence of contributions from three key source areas corresponding to the three main tectonic units the circum rhodope belt the variegated complex ultramafic complex and the gneiss migmatite complex the three petrofacies reflect multiple provenance from different tectonic settings as they evolve from quartzolithic to quartzofeldspathic to volcanoclastic corresponding to collisional orogen crustal block uplift and volcanic arc settings respectively geochemical data on major elements and trace elements are used to discuss the efficacy of tectonic setting discrimination diagrams and compare them to the dickinson model as well as to distinguish and characterize i petrographically homogeneous gneiss supplied subbasins and ii volcanic contributions to sandstone composition multivariate statistical techniques are used to unravel the complex web of factors controlling sediment composition biplot analysis highlights the influence of two independent processes 1 mixing between carbonate and silicate phases and 2 evolution from mafic to felsic source rocks the latter indicates progressively increasing supply rates from deeper crustal levels the compositional evolution of the sandstone suites of thrace basin in ne greece and se bulgaria is strictly related to various geodynamic stages of the rhodope region provenance analysis of thrace sandstones provide an example of the changing nature of orogenic belt sand associate basins through time and may contribute to the general understanding of similar geodynamic settings

channel and floodplain response to recent abrupt climate change the tyne basin northern england this paper examines the timing nature and magnitude of river response in upland piedmont and lowland reaches of the tyne basin northern england to high frequency 20 30 year changes in climate and flood regime since 1700 ad over this period fluvial activity has been characterized by alternating phases of river bed incision and stability coinciding with non random decadal scale fluctuations in flood frequency and hydroclimate that appear to be linked to changes in large scale upper atmospheric circulation patterns episodes of widespread channel bed incision 1760 1799 1875 1894 1955 1969 result from a higher frequency of large floods 20 year return period and cool wet climate under meridional circulation regimes phases of more moderate floods 5 20 year return period corresponding to zonal circulation types 1820 1874 1920 1954 are characterized by enhanced lateral reworking and sediment transfer in upper reaches of the catchment and channel narrowing and infilling downstream rates of fluvial activity are reduced in intermediate periods 1800 1819 1895 1919 with no dominant circulation regime associated with lower flood frequency and magnitude the results of this study provide a valuable guide for forecasting probable drainage basin and channel response to future climate change

river behaviour and holocene alluviation the river severn at welshpool mid wales u k a combination of archaeological evidence 14c dates terrace mapping heavy metal analysis grain size analysis and historical maps is used in a detailed analysis of the alluvial history of the river severn floodplain around welshpool in mid wales u k welshpool gravels underlie a higher terrace surface up to 6 7 m above the present channel they form a sequence of gravels at least 30 m in thickness the upper surface is characterized by a series of braided palaeochannel patterns these sediments were probably deposited at the end of the last glaciation as outwash and are contemporaneous with other high gravelly terrace deposits found in the severn and other mid wales basins overlying the welshpool gravels on the contemporary floodplain are a variable thickness of finer sediments the leighton silts morphological mapping and dating of two cut offs to 2850 60 a bp and 1190 70 a bp indicates that a channel pattern similar to the present planform had formed by the mid to late holocene from this period floodplain development has been dominated by a single thread meandering channel with fine vertical sedimentation and limited lateral gravel accretion abandonment of extended lengths of channel formed by an avulsion mechanism is apparent a combination of historical map data 14c dates and the analysis for heavy metals in fine sediments which were washed into the river system during mining indicates that there has been at least 4 m of sedimentation since the early 17th century but only in a central belt of varying width metal rich waste identified in the fine sediments of this zone of trehelig silts indicates those areas which were most heavily sedimented during the peak of metalliferous mining in the 18th and 19th centuries although the near channel margins appear to be superficially similar to the older floodplain the spatial and vertical pattern of historic sedimentation is complex and is not reflected in marked elevation differences the division of sedimentation periods into these three broad time spans late quaternary terraces late holocene alluviation and avulsion and the historical metal mining period shows that an apparently simple planar floodplain is in reality underlain by complex sedimentation units floodplain construction has involved the development of inset units in cut offs and adjacent to migrating channels as well as the expected contrasts between in channel and overbank environments this has implications both for alluvial sedimentation modelling and for the identification of high pollution zones on the floodplain these cannot be predicted on the basis of simple in channel and overbank environments given the historically complex evolution

seismoacoustic coupled signals from earthquakes in central italy epicentral and secondary sources of infrasound in this study we analyze infrasound signals from three earthquakes in central italy the m w 6 0 amatrice m w 5 9 visso and m w 6 5 norcia earthquakes generated significant epicentral ground motions that couple to the atmosphere and produce infrasonic waves epicentral seismic and infrasonic signals are detected at i26de however a third type of signal which arrives after the seismic wave train and before the epicentral infrasound signal is also detected this peculiar signal propagates across the array at acoustic wave speeds but the celerity associated with it is 3 times the speed of sound atmosphere independent backprojections and full 3 d ray tracing using atmospheric conditions of the european centre for medium range weather forecasts are used to demonstrate that this apparently fast arriving infrasound signal originates from ground motions more than 400 km away from the epicenter the location of the secondary infrasound patch coincides with the closest bounce point to i26de as depicted by ray tracing backprojections

preservation potential for late quaternary river alluvium valley sequences of late quaternary alluvial units reflect alluvial preservation as well as alluvial production factors effects of lateral channel migration incision aggradation and channel stability on preservation potential are explored and then considered in the light of 14 available data sets cartographically dated and model data based on lateral channel migration well mapped and dated late quaternary valley unit surveys and composite age frequency plots for dated alluvial units and flood sediments despite much expectable variation between sites and the complex effects of river activity combinations a common characteristic of the data sets examined is the significance of preservation factors lateral migration tends to eliminate older units as it creates new alluvial deposits whereas incision may lead to the preferential preservation of older units beyond the incision slot aggradational environments are likely to preserve more complete records although simultaneous lateral migration may eliminate possibly repeatedly the upper parts of alluvial units the common pattern of inset and incised streams within pleistocene and early holocene fills or bedrock gives finite extent to later units within narrowing valleys so that development of new valley floor units is necessarily at the expense of reprocessing earlier ones floods associated with both slack water deposits and berms are also responsible for the removal of accessible earlier materials thus limiting the preserved record of earlier events in light of these censoring effects of river activities the sequence of preserved late quaternary units within uk sequences is reconsidered it is concluded that preservation potential factors have led to spatial and temporal bias in the alluvial record and that both here and elsewhere preservation potential needs to be considered systematically alongside variable sedimentation resulting from allogenic environmental factors when interpreting the alluvial archive copyright 2003 john wiley sons ltd journal of quaternary science

river channel adjustment to meander cutoffs on the river bollin and river dane northwest england morphological adjustment of a channel after cutoff should be expected but rarely has the mode and timescale of adjustment in natural channels been measured four natural cutoffs which have occurred since 1980 on two rivers in northwest england have been monitored from pre cutoff stage two of the cutoffs were neck cutoffs of large loops two were chute cutoffs in which significant bend curvature remained all the cutoffs were the terminal result of progressive bank erosion and or scour of the floodplain rather than overflow and all the cutoffs took place in peak flow events though two of these were of relatively low magnitude high frequency rapid widening and sedimentation took place within the straight channels produced by neck cutoffs immediately after breaching adjustment was mainly by formation of multiple riffles and bars producing a variable morphology in the first 2 4 years subsequently the morphology became more regular and in one case had stabilised within about eight years progressive steepening and acceleration of bank erosion appears to have been propagated upstream in one case but in the other cases erosion was very localised rates of vertical accretion at the entrances to the old channel were much higher than most quoted in the literature rates of change in all morphological sedimentary and biotic components exhibit an exponential decline with time but with slightly differing timescales on these active gravel bed streams major adjustment within the new channels may be completed within 6 12 years though lakes persist in the abandoned channels for much longer

fluvial development and the sediment regime of the lower calder ribble catchment northwest england in the lower reaches of the calder lancashire tributary of the ribble catchment northwest england five river terraces set into the surrounding glacial terrain have been mapped and their underlying sediments radiocarbon dated the earliest terrace t1 reflects sandur style deposition during deglaciation and it aggraded in a reach cut into glacial diamict and glaciolacustrine muds incision below t1 spanned the start of the holocene driven by a combination of reduced sediment supply under a stabilising landscape and lower base levels t2 had aggraded and was being abandoned by 4000 bc its formation latterly involving a period of comparative stability in terms of channel migration perhaps a function of extensive forest cover and sea levels reaching above present day levels the last 3000 years were marked by substantial changes in the sedimentary regime with increased and varying sediment supply driving cycles of cut and fill and greater lateral channel migration these changes coincided with the first widespread and substantial reductions in forest cover and a progression towards an agricultural landscape between the aggradation of terraces t3 and t4 there was a substantial increase in sediment supply which is broadly in keeping with the erosion history in the surrounding uplands this sediment slug appears to have induced a switch from highly sinuous meandering to lower sinuosity channels characterised by lateral scroll style migration late holocene vegetation changes particularly woodland removal driven by anthropogenic land pressure appear to have rendered the floodplain prone to channel migration and the landscape more susceptible to erosion

evidence of flandrian valley alluviation in staindale north york moors the dovedale griff has incised into valley fill deposits in staindale to expose sub fossil wood at the base of a meander cut bank the wood includes oak quercus sp driftwood and apparently in situ stumps of willow salix sp and alder alnus sp an alder stump is dated at 6270 radiocarbon years bp fluvial gravels approximately 1 5 m thick have accumulated above the wood which has been exposed by renewed incision

infrasonic forerunners exceptionally fast acoustic phases 1 a vapor cloud explosion occurred at an oil depot near buncefield in the uk in 2005 three infrasound arrays in the netherlands detected various stratospheric phases some of these phases appeared with celerities i e horizontal propagation velocity in the conventional range of 0 28 to 0 31 km s exceptionally fast arrivals infrasonic forerunners were identified with celerities of 0 31 to 0 36 km s these phases could be explained by head wave like propagation in a high velocity acoustic channel between 40 and 50 km height where stratospheric zonal winds reached values of 120 m s the manifestation of infrasonic forerunners is validated by modeling with raytracing through actual atmospheric models and determining the celerity apparent velocity and back azimuth one phase occurred with a celerity of 0 25 km s hence we propose a new celerity range for fast stratospheric phases of 0 31 to 0 36 km s and to lower the limit of the conventional range to 0 25 km s

reappraisal of strain estimations and measurement methods in the hammamat group sediments comparison of primary and secondary grain fabrics with new data from wadi zeidun and wadi arak basins ced egypt abstract in this study pebble and sand grain shape and orientation data from undeformed and deformed conglomerates and sandstones in the egyptian central eastern desert ced wadi zeidun and wadi arak basins were collected with the aim of providing more accurate tectonic strain estimations for deformed hammamat sediments by comparing their primary and secondary sedimentary fabrics common assumptions about primary pebble fabrics and pebble deformation behaviour in previous strain studies of the region are shown to be invalid this raises doubts about the accuracy of earlier reported strain estimates for the hammamat that were based on such assumptions for low strains in the hammamat sediments the best strain measurement method is normalized fry nfry analysis of sand grain centre to centre distance data an alternative is conventional fry analysis of pebble ellipse centre to centre distance data provided that large numbers of pebbles 300 are used and the pebbles form closely packed aggregates with high degrees of anticlustering this study also provides systematic guidelines for pebble axial length and orientation measurements in the field the progressive changes in the mechanical behaviour of pebbles with increasing bulk strain are discussed

composition of modern deep sea sands from arc related basins summary petrographic and chemical examination of modern deep sea sands shows a clear distinction between active and passive plate tectonic settings among active settings sands from forearc basins of island arcs and basins from strike slip continental margins can be distinguished but those from other arc related settings overlap considerably in composition in particular sands from continental margin subduction zones and those from the backarc of island arcs appear to be indistinguishable chemically arc related sands are very close in composition to ancient greywacke sandstones for instance sodium almost always exceeds potassium thus it is not necessary for sodium to be added to sands diagenetically to make greywackes as has been suggested the influence of tectonics on the composition of sandstones has long been a central feature of sandstone petrology the geosynclinal model of global tectonics stimulated much thought on this subject probably the best known ideas are those of krynine e g 1942 subsequently such research declined but the plate model for global tectonics has produced a new wave of interest e g crook 1974 schwab 1975 potter 1978 dickinson suczek 1979 much of this work has relied on data from ancient sediments where diagenetic changes and difficulty in de ciphering the tectonic setting limit the useful ness of the conclusions much more work is needed on recent sediments to establish a base line against which ancient sediments can be compared we have previously reported valloni maynard 1981 the results of our work on the petrography of a set of recent deep sea sands from piston cores in this paper we shall com pare this petrographic information with bulk chemistry and attempt to relate these to tecto nics in arc related settings

the chronology and stratigraphy of the alluvial terraces of the river dane valley cheshire n w england three groups of alluvial terraces together with the modern floodplain mark the postglacial development of the middle part of the dane valley cheshire these are a high terrace group of late pleistocene age a middle terrace group of late pleistocene to early holocene age a low terrace of mid late holocene age and a modern post ca 1840 ad floodplain a chronology of erosion deposition and landform development since mid holocene times is established in this paper on the basis of terrace morphology stratigraphy sedimentology soil analysis magnetic mineral analysis and four radiocarbon dates after dissection of the middle terrace during the early to mid holocene a long period of lateral activity by the river was followed by a major aggradation phase which formed the low terrace surface this was followed by dissection during the last ca 300 years and the development of the modern floodplain since ca 1840 ad various explanations for the changes during the holocene are considered the low terrace aggradation appears to be related to a major phase of mediaeval soil erosion

modelling ground to air coupling for the shallow ml 4 3 folkestone united kingdom earthquake of 28 april 2007 abstract an earthquake that occurred with a local magnitude of 4 3 and at a depth of 3 km beneath the coastal town of folkestone united kingdom generated atmospheric acoustic waves in the 2 5 hz bandwidth infrasound these were recorded at the flers microbarometer array in france at a range of 284 km earthquake generated infrasound is often associated with large earthquakes close to large mountain ranges the shaking of prominent topographic points act as infrasound sources coupling seismic energy into the atmosphere in this example there is little prominent topography in the source region apart from the coastal cliffs which have an average height of 75 m we explore the possibility that the seismic to infrasound coupling occurs at the cliffs by modelling a 23 km length of coast as a series of 305 pistons independently generating acoustic waves synthetic seismograms modelling the motion of the cliffs are constrained using recordings from a three component accelerometer located 4 km from the epicenter meteorological data combined with array processing of the microbarometer records suggest that the acoustic energy propagated to flers within the troposphere the synthetic microbarograms show close agreement with the observations the modelled arrival time is 5 sec earlier than that observed and the peak to peak amplitude and signal duration are within a factor of 2 of those recorded this study shows that moderately sized shallow seismic disturbances can generate observable infrasound if the topographic conditions close to the epicenter are favorable

sandstone provenance of north western sectors of the intracontinental cenozoic qaidam basin western china tectonic vs climatic control abstract sandstone samples from all cenozoic formations of the nonmarine internally drained qaidam basin have been collected for provenance analysis to monitor possible changes in sandstone composition driven either by tectonics or climate provided an appropriate hinterland biotite contents may be a reasonable indicator for aridity moderately sorted sandstones with subangular to subrounded grains from the northwestern part of the qaidam basin are immature indicated by a high proportion of feldspars and lithic fragments nevertheless they have relatively high quartz contents of 29 65 averaging between 40 and 45 the average framework compositions of the formations show only a slight variation over time limited to the oldest and youngest cenozoic formations contents of white mica and biotite are significantly higher in upper portions of the section white mica contents increases from 1 0 to 3 7 and biotite from 0 1 to 1 6 respectively this change can be explained by increasing aridity during neogene and surface uplift of altyn mountains and qimantagh which led to higher relief when plotted on basic variation diagrams total quartz feldspar lithic fragments there is a slight shift from continental block field to orogenic field which might reflect the motion of the altyn tagh fault since oligocene times although climate changed during the cenozoic from arid over semiarid back to arid we could not find any distinct changes in the framework mineral compositions over time that could be related to climatic events few selected mudstones from eocene to lower miocene formations have been geochemically analysed by icp ms all samples display uniform high enrichment in light rees in chondrite normalized diagrams with one exception the ree concentrations are decreasing in a stepwise manner although insignificantly from formation to formation with time due to a diluting effect by carbonate

a method to estimate hydraulic conductivity from bulk geochemical compositions a new method has been developed to estimate the hydraulic conductivity in unconsolidated aquifers the method uses bulk geochemical compositions correlated with hydraulic conductivities measured by pumping tests the concept is based on a general rule that hydraulic conductivity is principally controlled by grain size distribution and particle shape both of which relate to mineralogical composition using a minlith algorithm normative mineralogical compositions can be derived from bulk geochemical compositions economically and expediently and then correlated to the hydraulic conductivity determined by pumping tests in the field in this study 202 sediment samples from nine unconsolidated aquifers were analyzed by x ray fluorescence although hydraulic conductivity does not show a definite relationship with geochemical compositions it does demonstrate a linear logarithmic equation to the content of normative earthy minerals however linear regressed equations should not be applied to aquifers composed of medium to coarse sand and gravel sizes due to interference from lithic fragments in addition this equation tends to overestimate hydraulic conductivity possibly because the effect of compaction is ignored in this study

dating of post glacial landforms in the central howgills little is known of holocene landform development in upland britain this paper describes a site at middle langdale in the howgill fells of cumbria where large but now stabilized and inactive gullies cut through periglacial material at the base of the gullies large debris cones have buried earlier alluvial sediments on the valley floor on these sediments and buried by the debris cones is a well developed organic soil from which two 14c dates have been obtained in an attempt to estimate the age range of the soil these dates range from 2580 55 years bp for the fine particulate fraction from the base of the organic horizon to 940 95 years bp for fossil rootlets from the uppermost organic layer immediately below the overlying debris cones the pollen evidence suggests that the valley floor site was initially dominated by alder carr and later by a juncus marsh with birch alder and hazel nearby the pollen from the surrounding upland area suggests woodland on the valley sides dominated by oak and elm that was later replaced by a more open environment rich in heath species and in which disturbed ground species were present the magnetic evidence indicates a stable local environment during soil formation but shows a sudden inwash of unweathered debris at the top of the buried soil the evidence suggests that the valley floor was geomorphologically stable throughout the period of soil formation although there was a local change in valley floor vegetation and a reduction of woodland cover on the valley sides at sometime during the period the evidence then points to major geomorphological changes a wave of soil erosion gully development and debris cone deposition perhaps following the scandinavian introduction of sheep farming in the tenth century a d

a repeating secondary source of infrasound from the wells nevada earthquake sequence 1 the wells nevada earthquake of february 21 2008 generated a complex seismo acoustic wavefield epicentral infrasound was recorded at 5 seismo acoustic arrays in nevada utah and wyoming in addition to epicentral infrasound the earthquake triggered a secondary source of infrasound at the bgu array in utah which was also triggered by subsequent aftershocks by applying simple constraints on the propagation of seismic and infrasound waves we show that the secondary source is an isolated peak floating island that appears to efficiently generate infrasound through the interaction with seismic surface waves this hypothesized source location is broadly consistent with crosswind directions extracted from the ground to space g2s atmospheric model for the appropriate time and source receiver locations although modeling the propagation of infrasound predicts this source location to be within the so called zone of silence in contrast to epicentral infrasound secondary infrasound associated with the wells nevada earthquake sequence appears to be local to each array i e not observed at multiple arrays secondary infrasonic arrivals observed at bgu are much higher in amplitude than epicentral arrivals highlighting the importance of being able to clearly identify and separate epicentral and secondary arrivals for infrasonic event discrimination

two orogenies in the meatiq area of the central eastern desert egypt abstract the pan african basement exposed in the meatiq area west of quseir egypt consists of an infracrustal basement overthrusted by a supracrustal cover the infracrustal rocks were developed as a result of an old orogeny referred to as the meatiqian orogeny where granite gneiss migmatitic gneisses and migmatized amphibolites were formed the granite gneiss represents a deformed granite pluton emplaced at 626 2 ma whereas the migmatitic gneisses and amphibolites are of mixed igneous and sedimentary parentage in view of the data so far available the nature of the meatiqian orogeny could not be deciphered in spite of the young isotopic ages it is suggested that at least the metasedimentary gneisses represent older rocks in the stratigraphic sequence of the infracrustal basement the supracrustal cover represents a part of an extensive ophiolitic melange obducted onto the infracrustal basement during the next orogeny abu ziran orogeny which culminated at 613 2 ma an active continental margin type regime can adequately explain the evolution of such a supracrustal cover during obduction the ophiolitic melange and the upper 2 km thick part of the infracrustal basement were intensely deformed and metamorphosed under pt conditions of the greenschist epidote amphibolite facies the deformed infracrustal basement was converted into mylonitic blastomylonitic rocks and schists composing five thrust sheets and subsequently intruded by synkinematic granitoid sheets later both the infracrustal basement and the overlying supracrustal cover were isostatically uplifted subjected to complex shallow folding giving rise to the major meatiq domal structure and were intruded by a postkinematic adamellite pluton at 579 6 ma

river response to rapid holocene environmental change evidence and explanation in british catchments macklin m g jones a f lewin j 2010 river response to rapid holocene environmental change evidence and explanation in british catchments quaternary science reviews 29 13 14 1555 1576 sponsorship welsh assembly government and the higher education funding council for wales for funding this study through its support of the centre for catchment and coastal research at aberystwyth university

characterisation of soils by mineral magnetic measurements processes of iron mineral authigenesis diagenesis and dissolution in interaction with primary inputs of iron minerals act to produce vertical differentiation of soil magnetic properties thus magnetic iron oxides in common with other iron forms may both respond to and reflect soil forming processes investigation of the degree of detectable and persistent magnetic differentiation within different soil materials can provide insights into the nature and direction of distinct sets of soil processes evidence of clear association between magnetic variation and discrete types of soil environment also has applied significance in several areas of environmental study for example the observed magnetic variation can be used to discriminate between individual soils and soil horizons for the purposes of soil surveying sediment tagging and tracing and empirical modelling of source sediment linkages this paper reports the use of mineral magnetic techniques to characterise the iron oxide assemblages within soils of varying type and provenance the effect of different pedogenic regimes have been investigated through measurement of a range of magnetic parameters including magnetic susceptibility frequency dependent susceptibility and anhysteretic and saturation remanences contrary to current pedological thought but in accord with other magnetically based studies e g mullins the presence of magnetite maghemite typically of superparamagnetic single domain grain size within soils has been found to be an extremely widespread phenomenon its contemporary neoformation within the soil environment is inferred however the input of artificially generated ferrimagnetic material is indicated for one of the magnetically enhanced soils examined here and the possibility of extraneous sources of magnetite in topsoils should be considered before pedogenic processes of magnetic enhancement are inferred from the data presented discrimination of industrially derived magnetic particles appears possible on the basis of their very low levels of frequency dependent susceptibility fd low anhysteretic remanence arm and dissociation from the finer clay sized not the formation but the active dissolution of ferrimagnetic minerals is indicated for soils affected by the processes of gleying and podsolisation eluvial horizons of podsolised profiles demonstrate almost total loss of detectable magnetic content variations in the form of the iron reprecipitated in the underlying illuvial layers may reflect differences in the pedological characteristics of these horizons within gleyed waterlogged soils processes of magnetite dissolution appear to be grain size specific preferential reduction of those grains of ultrafine superparamagnetic and fine single domain magnetic grain size is indicated where soil forms a major contributor to catchment sediment loads this has significance in the area of source sediment modelling soil derived from permanently wet or highly leached catchment areas is unlikely to contribute to peaks in the magnetic content of deposited sediments further only those erosional processes that operate at a faster rate than those of magnetic depletion will have the capacity to produce peaks in sediment ferrimagnetic concentrations such as have been observed within the historical magnetic record

holocene alluvial fan and terrace formation in the bowland fells northwest england in the bowland fells lancashire northwest england in the headwater valleys of the hodder river system is a suite of holocene fluvial landforms debris cones and alluvial fans at tributary junctions and river terraces along the main valleys post date late pleistocene forms and pre date the modern valley floor alluvial forms eight 14c dates from wood samples incorporated within the terrace and fan deposits have allowed two main phases of holocene erosion to be identified with debris cone fan deposition taking place after c 5400 bp but before c 1900 bp and again at c 900 bp some of the fans and cones are complex with deposits attributable to both phases others are simple and attributable only to the later phase in the headwaters an upper terrace at c 5400 bp pre dates the cones and a lower terrace is contemporaneous with the first debris cone phase lower downvalley the youngest of three terraces date from c 5000 bp or earlier indicating that the sequence is less complex downstream

the quaternary of the british isles factors forcing environmental change this paper considers the processes that have controlled cool temperate latitude terrestrial environments over the last ca 3 ma with particular reference to the british isles a scheme is proposed that is based on the processes that act on the land over any given period of time and are the product of climate modulated by rock type the resisting agent and relief determined by tectonics and antecedent relief forming factors climate is generalised in terms of the range and rates of climate change determined by orbital forcing during precession cycles climate change was small and insolation levels were forced by chemically and biologically driven processes the period of obliquity cycles is characterised by patterns of climate change in which physical processes became effective and high magnitude fluvial and slope processes were reinforced by periglaciation and glaciation in susceptible regions eccentricity cycles include climate extremes of longer duration and glaciation and periglaciation were the major contributors to landscape change sediment transfer and sediment mixing these climate forced processes produce distinctive landform sediment and soil assemblages characteristic of particular episodes of quaternary time the lags between the successive systems are identified copyright 2010 john wiley sons ltd

prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations abstract the exposed crust consists mainly of plagioclase 35 quartz 20 k feldspar 11 volcanic glass 12 biotite 8 and muscovite 5 quartz is a resistate thus feldspars and glass represent approximately 75 percent of the labile minerals the weathering characteristics of these constituents are summarized in the context of thermodynamic mass balance and kinetic considerations experimentally determined release rate constants were used to predict the proportions of ca na and k released by feldspars of plutonic rocks granites to gabbros to weathering solutions the chemical weathering trends of the weathered residues calculated from the kinetic data conform closely to the initial trends observed in some recent weathering profiles demonstrating the accuracy of the predictions since the weathering of feldspars is controlled by processes that should not change through geological time the relative release rates of ca na and k from the feldspars of granitic rocks can be calculated for future and past episodes of continental weathering experimentally determined release rate constants are not available for a wide range of volcanic glass compositions but the limited data indicate that compositional trends are predictable in weathering profiles developed on volcanic rocks the kinetic data available for rhyolitic glasses accurately predict the initial weathering trends observed in a recent rhyolite weathering profile

modal and geochemical compositions of the lower silurian clastic rocks in north qilian nw china implications for provenance chemical weathering and tectonic setting abstract the north qilian orogenic belt records the transition from ordovician marine back arc basin to early devonian terrestrial molasse basin as the central qilian block was sutured to the north china craton the detrital framework and geochemical composition of lower silurian sedimentary rocks within the north qilian belt record the provenance tectonic setting and a variety of sedimentary processes that operated during transport from source to sink the petrological and geochemical characteristics of sandstones siltstones and shales in the western segment of the north qilian belt indicate a generally low degree of chemical weathering of source area s and limited sorting prior to deposition these characteristics suggest an active tectonic setting in contrast samples studied from the eastern part of the north qilian belt indicate low to moderate chemical weathering and low to moderate hydraulic sorting such characteristics imply a more stable tectonic setting geochemical data including eu eu ti nb th sc and co th ratios suggest contrasting source regions for the western and eastern segments of the north qilian belt sources in the west included basement rocks of the central qilian block and the north china craton in addition western sources may have included mafic rocks located within the north qilian arc in contrast data derived from eastern samples suggest a felsic provenance that probably formed part of the basement complex in the central qilian block and the north china craton overall detrital and geochemical data combined with the regional geology suggest a foreland basin setting that formed during collision of the central qilian block with the north china craton

geology geochemistry and tectonic setting of archaean greywackes from karnataka nucleus india more than 80 of the area covered by the chitradurga and shimoga schist belts 3 0 2 6 ga of karnataka nucleus india is made up of greywackes feldspathic lithic and quartzose greywackes are deposited respectively along the western northern and the eastern margin of the chitradurga schist belt greywackes of the shimoga schist belt show a large compositional scatter between feldspathic and lithic types compositional differences indicate variable provenance for the different localities tonalite trondhjemite gneisses ttg mafic ultramafic schists basic intermediate acid volcanic rocks sedimentary rocks like banded iron formation quartzites and cherts and k granites in minor quantity were exposed in the source area volcanic debris was also contributed from contemporaneous volcanism in the basin greywackes in this region are invariably interbedded with fine grained biotite rich phyllites and schists marked compositional differences are observed between the greywackes and the interbedded phyllites the greywackes have k2o na2o 1 whereas phyllites show large variation in k2o na2o ratios ranging from 1 5 to 15 0 high cr ni content of the greywackes and phyllites of the chitradurga belt are indicative of an important contribution from ultramafic rocks light ree enrichment and negative eu anomalies are particularly pronounced in the mudpacks of the greywackes represented by phyllite the ree and other chemical data such as la th ti zr and k2 mgo ratios indicate that these greywackes were supplied from a juvenile continental nucleus and were laid down on a simatic and converging active continental margin an archaean miniplate model with low angle subduction and sedimentary basins of moderate size is proposed to explain the geochemical and tectonic features of the schist belts

holocene debris cone evolution in glen etive western grampian highlands scotland stratigraphic investigations radiocarbon dating of buried soils and pollen analyses were employed to reconstruct the history of development of a fluvially reworked debris cone in glen etive paraglacial aggradation of debris flow deposits resulted in cone formation between c 10000 yr b p and c 4000 yr b p until supplies of sediment from upslope were effectively exhausted and debris flow activity ceased there ensued a prolonged period of stability and soil development on the cone surface this ended sometime after c 550 yr b p when human interference including burning resulted in destruction of the natural vegetation cover and triggered fluvial incision and the development of an alluvial fan of reworked sediment that buried the lower part of the debris cone the wider implications of these findings are discussed

major element geochemistry of purple soils rocks in the red sichuan basin china implications of their diagenesis and pedogenesis major element compositions and chemical weathering features of the purple soils and their corresponding rocks in the red sichuan basin china were studied in this paper to infer the diagenetic features of the purple rocks and the pedogenetic features of the purple soils the results showed that all of the rock and soil samples except those from yibin have strongly similar major element compositions and the distribution patterns of their major element compositions are similar to those of the upper continental crust chemical index of alteration chemical index of weathering and na2o k2o indicate that the purple soils and rocks have similar chemical weathering intensities whereas the al2o3 cao na2o k2o a cn k relationship suggests that chemical weathering was strong during diagenesis of the purple rocks but weak during pedogenesis of the purple soils variations in major element compositions of the purplish rock samples except that from yibin do not primarily reflect differences in compositions of the sediment source sediment recycling and potassium metasomatism and therefore the effects of chemical weathering on the major element compositions were mainly dependent on climate condition and the residence time of material exposed to chemical weathering chemical weathering of the purple rocks reached only moderate degrees under the general influence of warm and humid climate during jurassic and cretaceous warmer and more humid climate conditions partly resulted in stronger chemical weathering of rocks in the southern region of the basin than in the central and western region whereas shorter residence time of material in upslope position partly resulted in weaker chemical weathering of rocks in the eastern region than in the central and western region the same climate and stable tectonic setting led to comparable chemical weathering intensities of rocks in the ziliujing and jiaguan formations gradually colder and dryer climate from early jurassic to middle jurassic then to late jurassic and shorter residence time in tectonically active setting of middle jurassic and late late jurassic resulted in the following order of chemical weathering intensity of the purple jurassic rocks ziliujing formation shaximiao formation suining formation penglaizhen formation

the development and application of a database of radiocarbon dated holocene fluvial deposits in great britain abstract this paper reports on the development of a british database of 14c dated holocene fluvial units over the last 15 years since its inception in 1989 the database has undergone substantial expansion refinement and improvement together with considerable methodological development so that today it serves as a powerful research tool for investigating the spatial and temporal dynamics of holocene river development and flooding in great britain the improved analytical method is here applied to the currently existing database by examining datasets of 14c dated fluvial units from river basins that lie within and beyond the limits of late devensian glaciation this analysis indicates how the contrasted conditions in these two types of river environment have to an extent led to divergent records of flooding in response to holocene climate and land use change however even in the contrasting sedimentary records of upland glaciated and lowland unglaciated river basins six corresponding episodes of increased flood frequency are identified at c 5730 c 3540 c 2730 c 2280 c 660 and c 570 cal bp these represent widespread common responses from british river systems to large scale changes in climate the method of database construction and analysis outlined and demonstrated in this paper could be readily adopted in other parts of the world to improve our understanding of holocene river behaviour at the continental and global scale

agro industrial alluvium in the swale catchment northern england as an event marker for the anthropocene foulds s a macklin m g brewer p a 2013 agro industrial alluvium in the swale catchment northern england as an event marker for the anthropocene the holocene 23 4 587 602

geochemistry of the floodplain sediments of the kaveri river southern india abstract the floodplain sediments of the kaveri river southern india derived from archean gneissic and charnockitic source regions show interbedding of silty 4 4 7 and sandy units 1 4 3 7 the geochemistry of silty beds is remarkably uniform at a given location and over a lateral distance of nearly 250 km the sandy beds have more variable chemical compositions yet are comparable to those of silty beds except for the diluting effect of quartz silty sediments retain the geochemical signature of prominently exposed source rocks for almost all elements and provide evidence of tectonic instability in the source region the floodplain sediments contain all size grades sand silt and clay which may have resulted in minimizing the biases imposed on suspended and bedload sediments due to sorting the low chemical index of alteration cia the dominance of unweathered primary minerals and the minor proportion of smectitic clay all suggest that the region has been subjected to little chemical weathering this is possible if the region has undergone recent uplift exposing fresh archean rock to surface denudation the formation of fertile farmland along the kaveri river course and its delta is related to these recent geological processes

compositions and sources of metasediments in the upper dharwar supergroup south india texturally mature quartz rich sandstones texturally mature mafic rich sandstones and texturally immature graywackes are abundant in the late archean chitradurga group of the dharwar craton in south india when compared to graywackes of paleozoic age from northeastern north america the chitradurga graywackes have slightly higher average concentrations of na and ferromagnesian elements indicating the existence of a more tonalitic and mafic rich provenance during the late archean in karnataka the regional tonalitic gneiss peninsular gneiss is the predominant source of these sediments although mafic ultramafic volcanic debris from unidentified sources is also important neither intermediate nor felsic volcanics nor an extensive metasedimentary terrane were prominent in the provenance although the composition of the craton was dominantly sialic the presence of abundant ferromagnesian debris in some of the texturally mature sandstones that probably formed in shallow water intracratonic or platform

infrasound associated with 2004 2005 large sumatra earthquakes and tsunami 1 large earthquakes that occurred in the sumatra region in 2004 and 2005 generated acoustic waves recorded by the diego garcia infrasound array the progressive multi channel correlation pmcc analysis is performed to detect the seismic and infrasound signals associated with these events the study is completed by an inverse location procedure that permitted reconstruction of the source location of the infrasonic waves the results show that ground motion near the epicenter and vibrations of nearby land masses efficiently produced infrasound the analysis also reveals unique evidence of long period pressure waves from the tsunami earthquake m9 0 of december 26 2004

geochemistry of fine grained clastic sediments in the archean abitibi greenstone belt canada implications for provenance and tectonic setting abstract archean sandstone and shale samples from turbiditic tf and alluvial facies af in the southern volcanic zone of the abitibi greenstone belt canada have been analyzed for major and trace elements the sandstones from tf are mainly greywackes whereas those from af are lithic arenite sio 2 ranges from 51 to 68 geochemically the clastic sediments cluster into mafic element mep and low mafic element lmep populations the mep sediments which include turbiditic facies sediment samples from the larder lake group in the kirkland lake area are characterized by elevated abundances of mgo 5 ni 200 ppm cr 400 ppm sc 22 ppm and feo 7 5 abundances lower contents of incompatible elements such as th u ta hf zr and total rees n ratios are 4 5 with eu eu 1 the lmep sediments which include samples from the beatty dome and three nations lake formations in timmins the kewagama group noranda area and timiskaming group in the kirkland lake area however show reverse abundance distributions the geochemical gaps shown by the major and trace elements define two populations of sediments suggesting contrasting provenances for them the mep sediments require a dominantly mafic and ultramafic 90 source with 10 felsic contribution whereas the lmep sediments require a mixture of felsic 75 and mafic 25 rocks this compositional distribution of the sediments is closely related to their tectonic environments the mep was formed in basins proximal to or within an active oceanic rift consequently having ultramafic and mafic rocks as the major source for the lmep calc alkaline volcanic sequences formed in an island arc like setting were the major source these two contrasting volcanic plutonic terranes were tectonically juxtaposed during late archean collisional tectonics

provenance tectonic setting and geochemistry of greywackes and siltstones of the late precambrian hammamat group egypt abstract greywackes and siltstones from the neoproterozoic hammamat group in the wadi hammamat and wadi bali areas eastern desert of egypt were analyzed for major and trace elements the sedimentary rocks are characterized by na 2 o k 2 o 1 a wide range of both al 2 o 3 na 2 o 2 5 7 and al 2 o 3 tio 2 13 33 plus a chemical index of alteration between 60 and 44 these data suggest that the hammamat sedimentary rocks are chemically immature and that there was minimal chemical weathering involved in their erosion and deposition the sedimentary units show two broad compositional groupings in the two studied areas the wadi bali sedimentary rocks are characterized by low mgo cr ni v ba nb y and zr and high na2o cao and sr relative to the wadi hammamat sedimentary rocks these geochemical differences suggest contrasting provenance for the sedimentary rocks in the two areas the wadi hammamat sedimentary rocks were derived from 30 mafic rocks 25 granodiorite 25 intermediate volcanics and 20 felsic volcanics whereas those of the wadi bali area were derived from a relatively homogeneous source of 90 intermediate volcanics and 10 felsic volcanics the wadi hammamat sedimentary rocks were deposited in an intra arc basin that developed as a result of the creation of considerable topographic and structural relief after development of a continental arc the source rocks were continental arc volcanics dokhan volcanics and the uplifted older oceanic tholeiites and island arc assemblages the wadi bali sedimentary rocks were formed by the same scenario as the wadi hammamat sedimentary rocks but the absence of rock fragments older than the dokhan volcanics indicates a closed intra arc basin where the dokhan volcanics were the main source of clasts

geodetic model of the 2016 central italy earthquake sequence inferred from insar and gps data we investigate a large geodetic data set of interferometric synthetic aperture radar insar and gps measurements to determine the source parameters for the three main shocks of the 2016 central italy earthquake sequence on 24 august and 26 and 30 october mw 6 1 5 9 and 6 5 respectively our preferred model is consistent with the activation of four main coseismic asperities belonging to the sw dipping normal fault system associated with the mount gorzano mount vettore mount bove alignment additional slip equivalent to a mw 6 1 6 2 earthquake on a secondary 1 ne dipping antithetic fault and or 2 on a wnw dipping low angle fault in the hanging wall of the main system is required to better reproduce the complex deformation pattern associated with the greatest seismic event the mw 6 5 earthquake the recognition of ancillary faults involved in the sequence suggests a complex interaction in the activated crustal volume between the main normal faults and the secondary structures and a partitioning of strain release

geochemical evolution of archean shales from south africa i the swaziland and pongola supergroups abstract the fig tree group and moodies group part of the swaziland supergroup are exposed in the barberton mountain land and are 3 3 3 5 ga old shales from the fig tree group are characterized by variable rare earth element ree patterns with lan ybn 5 5 1 8 95 confidence and eu eu 0 97 0 18 shales from the moodies group have more fractionated ree patterns lan ybn 8 7 2 0 and less variable eu anomalies eu eu 0 92 0 02 both groups are characterized by very high abundances of cr and ni modelling of those trace elements which are relatively unfractionated during sedimentary processes ree th sc is consistent with the derivation of these sedimentary rocks from a mixture of the archean bimodal igneous suite mafic volcanics tonalites trondhjemites felsic volcanics with the moodies group requiring a larger percentage of the felsic end member the data for shales from the swaziland supergroup support models suggesting that the archean exposed crust was of more mafic composition than the post archean upper crust and that intracrustal melting was relatively unimportant in differentiating the archean crust the pongola supergroup is younger than the swaziland supergroup but older than 2 9 ga shales and mudstones from the nsuze and mozaan groups show ree characteristics intermediate between the older shales of the swaziland supergroup and typical post archean shales one quartzite sample from the witwatersrand supergroup ca 2 6 ga has a ree pattern virtually parallel to average post archean shales but with much lower abundances the change from typical archean to post archean sedimentary trace element patterns has been documented in early proterozoic successions from canada and australia this change has been related to a short interval of intense growth and chemical differentiation of the continental crust during the late archean 2 7 2 5 ga in southern africa this change appears to have taken place much earlier 3 2 2 9 ga but can be related to similar processes thus the period of crustal evolution related to the archean proterozoic boundary while virtually episodic regionally occurred over a protracted period world wide during the period ca 3 2 2 5 ga

geochemistry of jurassic to earliest cretaceous deposits in the nagato basin sw japan implication of factor analysis to sorting effects and provenance signatures abstract one of the intractable problems in provenance analysis is the hydraulic sorting effect and resultant mineralogical heterogeneity in coarse and fine grained sediments which conceals provenance characteristics the present study uses factor analysis to address geochemical responses to the sorting effect and provenance of late mesozoic sediments in the nagato basin sw japan factor analysis has proven useful for comprehending geochemical gradients between coarse and fine grained sediments in the present example compositional differences are based on varying proportions of quartz plagioclase chrome spinel authigenic minerals and phyllosilicates the contrasting behaviors of these minerals during the depositional stage resulted in the systematic fractionation of sio2 al2o3 na2o k2o and cr ba sandstones and mudstones exhibit an array of compositions in sio2 al2o3 na2o k2o and sio2 al2o3 cr ba diagrams the ranges of which reflect compositional variations due to the sorting effect sediments of different provenance exhibit distinctive mineral arrays and can be discriminated simply by reading the gradients of the continua therefore this kind of data management concurrently quantifies the sorting effect and allows an estimation of the original source material the sio2 al2o3 na2o k2o diagram is particularly useful for scrutinizing igneous and mature continental provenances while the sio2 al2o3 cr ba diagram ascertains contributions from mafic sources this investigative approach delineates a systematic provenance transition within the nagato basin a serpentinite melange provenance in the early early jurassic a magmatic arc in the late early to middle middle jurassic and a continental interior in the latest jurassic to earliest cretaceous the provenance changed by the direct input of mature continental material into the nagato basin which resulted from dissection of the volcanic arc

infrasound from earthquakes 1 infrasonic signals have been observed from 31 earthquakes by arrays of microphones operated by the los alamos national laboratory between 1983 and 2003 the properties of the signals are presented signal amplitudes corrected for propagation and distance show a relation with seismic magnitude the variance in the relation is understood primarily in terms of the uncertainties or errors in the ground motion deduced from an independent data set and the stratospheric winds which strongly influence signal propagation signal durations can extend over many minutes a relation is found between signal duration and magnitude to understand this we propose a model in which regions distant from the epicenter are excited by seismic surface waves the surface motion of these regions in turn produces signals which precede or follow the signals from the epicenter analysis failed to detect signals from 56 earthquakes during the observation period predicted signal to noise ratios for these earthquakes indicated that the signals would have been too weak for detection

non synchronous response of adjacent floodplain systems to holocene environmental change abstract two adjacent upland floodplains are compared to establish the local response of floodplains to environmental change radiocarbon dating the analysis of sedimentary exposures terrace mapping aerial photography and archaeological evidence are used to examine late quaternary valley fill sediments on the afon tanat and the afon vymwy in the upper severn basin wales uk the alluvial stratigraphy of the two floodplain systems consists of late devensian last glacial fluvio glacial sediments at the valley margins deposited under a braided outwash river regime holocene age terraces with floodplain and palaeochannel deposits composed of gravels overlain by silty sands are inset into this older unit and were formed by meandering fluvial channel systems a combination of field and laboratory data demonstrates that from the mid late holocene the two floodplain systems had divergent development the afon vyrnwy has remained vertically stable for the last ca 4000 yrs whereas the adjacent afon tanat continued to be vertically and laterally active both floodplain systems have been affected by late quaternary climatic fluctuations and anthropogenic activity from the bronze age to the roman period but local geomorphic gradient controls combined with a possibly greater focus of anthropogenic activity in the tanat catchment may explain the differential evolution of the two systems the data demonstrate that multiple reach scale studies are essential for revealing significant stages in the chronology and historical development of fluvial systems

river sedimentation and fluvial response to holocene environmental change in the yorkshire ouse basin northern england holocene alluvial sediment sequences and floodplain geomorphological histories from three valley floor sequences in the yorkshire ouse basin have been determined using a variety of field evidence and laboratory methods geomorphological mapping sediment coring and trenching physical and chemical analysis of sedimentary units and 14c dating the application of multiple methods has revealed contrasting phases of river erosion alluviation and depositional styles during the late quaternary at each of the individual study reaches the gravel bedded river swale at catterick has been characterized by progressive valley floor incision during the late holocene with major phases of incision occurring during the cooler and wetter phase of the little ice age within the last c 245 years substantial thicknesses up to 2 m of overbank alluvium contaminated by metalliferous mining have been deposited across thefloodplain in contrast floodplain development in the lower reaches of the river swale at myton and t

terraced fills of pleistocene and holocene age in the rheidol valley wales the legacy of repeated pleistocene glaciations has endowed many welsh river valleys with locally thick successions of glacial and alluvial sediments investigations of a well preserved flight of terraced sediments with good exposures at capel bangor on the afon rheidol mid wales has allowed its quaternary valley fill stratigraphy to be examined in detail study has revealed five terraced fills consisting of seven distinct sedimentary units these range from late devensian ice contact and ice marginal deposits to holocene high sinuosity stream sediments with episodes of man induced accelerated deposition of fine grained alluvium and to aggradation and subsequent incision associated with historic metal mining examination of general sedimentary properties e g granulometry sedimentary structures terrace surface morphology show both differences in the pattern and controls of deposition and also progressive changes over late devensian and holocene times the sediments of the rheidol valley record the response and subsequent recovery of a drainage basin to glaciation and the increasing influence of man on sediment yields channel processes and sediment quality

sediment transfer and transformation of an alluvial valley floor the river south tyne northumbria u k the amounts of alluvial storage and the mechanisms responsible for the dispersal of sediment associated with historic metal mining are examined for a 115 year timespan on a 22 km reach of the river south tyne northern england analysis of lateral and vertical channel change over this period the extent of actively reworked gravels and identification of metals in alluvial units show five sedimentation zones separated by more stable reaches aggradation in the late nineteenth century was followed by a period of storage and local reworking and then incision some reaches show short term storage of sediment injected from tributaries which may be dispersed by floods there is some evidence of transfer of sediment bodies downvalley within sedimentation zones and of a sediment wave movement between zones in lower parts of the south tyne investigated present day incision the variation in the area of actively reworked gravel spreads and the widespread dispersal of fine grained toxic metal mining wastes all have practical implications the intricate response of the channel system to historic changes in sediment supply is not readily described by either a complex response model or a simple translatory wave

geochemistry of archean shales from the witwatersrand supergroup south africa source area weathering and provenance with a few exceptions shales from the archean witwatersrand supergroup 2800 ma in south africa are depleted in na ca lile ree and hfse compared to phanerozoic shales cr co and ni are enriched in all witwatersrand shales and fe and mg are high in shales from the west rand groups wrg and lower central rand group crg shales from the crg and uppermost wrg are enriched in na al lile ree hfse and transition metals relative to shales from the lower wrg chondrite normalized ree patterns for all witwatersrand shales are enriched in light ree and exhibit small to moderate negative eu anomalies a positive correlation of ree and al2o3 contents in the shales suggests that ree are contained principally in clay minerals relative to shales from the crg shales from the wrg exhibit depletions of na ca and sr a feature probably reflecting intense chemical weathering of their source rocks cia indices in witwatersrand shales are variable chiefly 70 98 even within the same shale unit such variations reflect chiefly variable climatic zones or rates of tectonic uplift in source areas with perhaps some contribution from provenance and element remobilization during metamorphism compared to present day upper continental crust all but the orange grove roodepoort and k8 shales appear to have been derived from continental sources depleted in lile ree and hfse and enriched in transition metals computer mixing models based on six relatively immobile elements th hf yb la sc co and four source rocks indicate that the relative proportions of granite basalt and komatiite increased with time in sediment source areas at the expense of tonalite the contributions of basalt and komatiite appear to reach a maximum during deposition of the booysens shale and granite during deposition of the k8 shales and possibly during deposition of the orange grove shales

infrasonic imaging of the kunlun mountains for the great 2001 china earthquake 1 on november 14 2001 a strong earthquake occurred on the high plateau of western china at a distance of 1800 km from the epicenter coherent infrasonic waves were detected for more than one hour using both an inverse location procedure and a complete simulation of the radiated pressure field distant source regions are accurately located the seismo acoustic coupling along a mountain belt is clearly demonstrated such an event offers an opportunity to validate velocity models in the atmosphere as well as to improve the understanding of the amplification of ground displacement caused by the topography

river entrenchment and terrace formation in the uk holocene abstract a meta analysis of a large database of 14c dated fluvial units is used to assess the chronology and controls of episodic holocene river entrenchment and terrace formation in the uk most holocene terraces are of a fill cut type developed in pleistocene sediments in places now reaching down to pre holocene bedrock holocene terraces are widespread in higher relief areas of the uk and peripheral higher energy rivers and include up to 7 levels in some valley floor reaches using 14c constrained data sub sets for incision episodes the onset vertical ranges formation times and rates of entrenchment are examined together with geographical distributions the height range of terrace separation is relatively small 0 5 3 5 m with a long term averaged incision rate over the late and mid holocene of 0 43 0 5 0 67 0 7 and 0 81 m ka in the tweed rheidol severn ouse and ribble catchments and a regional similarity in the scale of incision events the periods 4200 3700 3100 2900 2100 1900 1800 1500 cal bp and most notably the last 1000 years with prominent peaks at 900 800 and 700 600 cal bp were times of accelerated incision it appears likely that extreme flood events triggered the formation of incision slots rather than entrenchment being a direct response to glacio tectonic uplift or the result of incremental valley floor lowering by combined incision and lateral reworking river entrenchment has also been rapid in recent centuries reflecting the coupling of extreme events with anthropogenic effects on catchment hydrology incision results in changes of river channel flood power and overbank flood extent and improved data on the long term and large scale vertical tendency of uk rivers are needed for flood risk management purposes

fluvial responses to land use changes and climatic variations within the drury creek watershed southern illinois abstract fluvial responses to climatic variation and anglo american settlement were documented for the drury creek watershed southern illinois by examining stratigraphic geomorphic climatic and historical data regional analyses of long term precipitation records document a period of decreasing mean annual precipitation from 1904 to about 1945 and an increasing trend in annual precipitation from 1952 to the present the period between 1945 and 1951 experienced a large number of intense storms that resulted in high annual precipitation totals statistical relationships illustrate that changes in precipitation totals are transferred to the hydrologic system as fluctuations in stream discharge historical records of southern illinois show that a maximum period of settlement and deforestation occurred between the 1860s and 1920s this era ended in the 1940s when large tracts of land were revegetated in an attempt to curtail erosion which had caused extensive upland degradation in response to hillslope erosion at least two meters of fine grained sediments were deposited on valley floors average sedimentation rates determined using decdrochronologic techniques are estimated to be 2 11 cm yr for the period between 1890 and 1988 rates that are 1 to 2 orders of magnitude greater than pre settlement values calculated for other areas of the midwest however botanical data suggest that aggradation was episodic possibly occurring during three periods characterized by greater annual precipitation since the 1940s sedimentation rates have declined reduced rates of sedimentation are related to an episode of channel entrenchment that reduced overbank flooding entrenchment coincided with a period of 1 reduced sediment yields associated with watershed revegetation and the introduction of soil conservation practices and 2 intense storm activity that resulted in long periods of high discharge as a result of channel incision and hillslope erosion newly exposed bedrock in upstream areas currently provides a source of gravel load to the channels the distribution of coarse bedload material along tributary streams combined with downstream decreases in width depth ratios and tractive force estimates suggest that channels in the drury creek watershed are slowly adjusting their configuration to transport coarse bedload material the fluvial response to the increased influx of coarse sediment began more than 45 years ago and continues today

critical evaluation of six tectonic setting discrimination diagrams using geochemical data of neogene sediments from known tectonic settings abstract an attempt is made to evaluate 6 tectonic setting discrimination diagrams 1 discriminant function and 5 bivariate diagrams frequently used by many researchers for this purpose an extensive database was established for major element geochemistry derived from miocene to recent sand and sandstone medium to fine grained samples collected from a variety of tectonic settings including 1 passive margin pm setting 2 active continental margin acm setting and 3 oceanic island arc oia setting our results suggest that the discrimination fields proposed to infer tectonic settings for six commonly used discrimination diagrams do not work properly for the analyzed miocene to recent sediments the success for these diagrams varies from 0 to about 62 we therefore recommend that these diagrams be used with prudence

evidence for both crustal and mantle earthquakes in the subducting juan de fuca plate 1 we investigate the relationship between high precision hypocentres in the subducting juan de fuca plate beneath southwest british columbia and the velocity structure from receiver function analysis and reflection seismic data 108 earthquakes at depths of 40 to 65 km were relocated using a double difference algorithm to obtain precise earthquake locations correlation of the relocated seismicity with structural information shows a concentration of earthquakes near the top of the subducting oceanic crust and a deeper layer of seismicity in the uppermost mantle of the subducting juan de fuca plate the strong correlation of the seismicity with the structure of the subducting plate suggests that seismic failure is caused by changes in mechanical strength within the plate supporting the hypotheses that phase transformations and thermal petrological conditions play an important role in the seismogenesis of double seismic zones index terms 7209 seismology earthquake dynamics and mechanics 7218 seismology lithosphere and upper mantle 7230 seismology seismicity and seismotectonics 7220 seismology oceanic crust citation cassidy j f and f waldhauser evidence for both crustal and mantle earthquakes in the subducting juan de fuca plate geophys res lett 30 2 1095 doi 10 1029 2002gl015511 2003

the spatial distribution of heavy metal contaminated sediment across terraced floodplains abstract deposits of fine alluvial sediment contaminated by heavy metals derived from mining provide an opportunity to reconstruct the alluvial histories of mineralised catchments field data were collected to identify the spatial distribution of heavy metal contamination in surficial floodplain sediments and establish the relationships between terrace height terrace age and metal concentrations floodplain terrace morphology was mapped and terrace heights were measured for three separate study reaches in the upper sevem basin mid wales concentrations of pb ba and zn were determined in 97 samples taken from fine overbank units capping these terrace surfaces between the three study reaches element concentrations showed wide ranges pb 11 964ppm ba 141 1118 ppm zn 73 1134 ppm they also exhibited significant spatial variation across the floodplain at each study reach e g at llandinam pb 36 964ppm ba 141 1118 ppm and zn 173 1134 ppm peak metal concentrations at morfodion pb 399 ppm ba 474 ppm and welsh pool pb 149 ppm ba 558 ppm were found on terrace surfaces 1 5 2 5m and 2 0 3 0 m above present river level respectively lower concentrations reflect natural background levels of contaminants higher terraces and post mining reworking of spoil heaps and floodplains lower terraces in general the spatial distribution of floodplain contaminants is more significantly correlated with terrace height than with terrace age different flooding mechanisms and styles of channel instability in relation to the timing and mode of sedimentation have resulted in different patterns of floodplain contamination focused deposition particularly in palaeochannels is also an important mechanism for creating strongly contaminated sites within the floodplain environment

a quantitative soil stratigraphic approach to the correlation and dating of post glacial river terraces in glen feshie western cairngorms little is known about holocene river terrace development in upland scottish valleys interpretation of many of the terrace sequences previously suggested to have been formed by meltwaters either from the last scottish ice sheet or the loch lomond advance has generally been based on morphological data in this paper an alternative approach to the traditional height based method of terrace correlation and dating is presented using data from glen feshie western cairngorms terrace fragments are numerically classified and objectively grouped using quantitative soil stratigraphic data principal components analysis is used to both quantify pedological data and separate temporal trends in the data from variance due to local site factors the scores on the temporal component are used to derive soil stratigraphic units developed on the surficial sediments of the glen feshie terraces by grouping soil sites using a hierarchical clustering technique this provides evidence for at least five soil stratigraphic units developed on the fluvial surfaces various methods of absolute dating control permits association of these surfaces with five phases of terrace development these are placed tentatively at 13 000 10 000 3600 1000 and 80 radiocarbon years b p suggesting at least three phases of valley floor incision in glen feshie during the late holocene

infrasound radiated during the montana earthquake of 1959 august 18 summary seismic waves caused by earthquakes radiate infrasound into the atmosphere as they proceed over the earth s surface several instances of such sound waves radiated locally by seismic waves passing through the washington d c area have been observed at the infrasonic station there a notable instance was the great montana earthquake of 1959 august 18 measurements of the radiated infrasound gave data on the seismic waves including their travel times local speeds directions of travel amplitudes and waveforms

hydrous minerals on mars as seen by the crism and omega imaging spectrometers updated global view 1 the surface of mars has preserved the record of early environments in which its basaltic crust was altered by liquid water these aqueous environments have survived in the form of hydrological morphologies and alteration minerals including clays and hydrated salts because these minerals probe on earth aqueous environments compatible with biotic activity understanding their formation processes on mars is of great exobiological relevance and also offers insight into earth s now erased ancient water environments using remote sensing we conducted a large scale investigation of the distribution composition age and geomorphic settings of hydrous minerals on mars providing a sharpened global view of the early aqueous environments and their evolution with time aqueous alteration seems to have produced clays on a planetary scale but these are found to be restricted to the oldest observable terrains on mars 4 gyr however very diverse aqueous environments have also been found which suggest widespread complex aqueous settings from the surface to kilometric depths and spanning over 1 gyr by building a robust statistical sample of detections the global trends inferred here attempt to provide a broad view of our current understanding of hydrous minerals on mars and provide context for more localized in depth analyses collectively these trends suggest that at least transient conditions have existed on mars which may have been favorable for pre biotic to biotic activity

a holocene alluvial sequence in the lower tyne valley northern britain a record of river response to environmental change palaeoenvironmental investigations have been made of late quaternary sediments infilling the lower tyne valley at scotswood newcastle upon tyne 18 km upstream from the mouth of the river attention has focused on the holocene alluvial sedimentary sequence using sedimentological geochemical and palynological analyses holocene valley floor development from c 7500 bp has been largely dominated by a tendency towards river aggradation with some limited lateral and vertical reworking of sediments four alluvial fills have been identified and dated to 1 c 7500 4800 bp 2 from c 2590 bp up to the early first millennium ad and possibly as late as medieval times 3 between the medieval period and the early seventeenth century and 4 between the seventeenth and nineteenth centuries episodes of incision are dated to c 4800 2590 bp and to the period following the early seventeenth century marked variations in the rates and nature of sedimentation and erosion appear to coincide with rising post glacial

sedimentation and inversion history of three molasse basins of the western central eastern desert of egypt implications for the tectonic significance of hammamat basins abstract the initiation deformation and tectonic significance of the zeidun and arak basins in the central eastern desert ced of egypt are the topics of this study the basins probably formed in a n s regional extensional regime with basin subsidence structurally controlled by marginal normal faults in these basins red grey and green coloured conglomerates litharenites and mudstones accumulated in an alluvial fan braided stream environment a two stage basin subsidence history included early modest basin relief during arak sedimentation followed by rapid increase in basin margins during zeidun deposition forced folding in the basin sediments may have occurred during the basin sedimentation stage or in the earliest stages of deformation a regional subhorizontal foliation with nw se stretching lineation is found in the arak and meesar basins and is correlated with foliations farther north in the wadi hammamat el qash and um esh um seleimat basins two substages of post foliation are identified based on different orientations of regional 1 nne to ne oriented in the early substage and e to ene oriented in the second substage early substage basin and basement structures are e to ene oriented steep reverse faults that are inverted normal faults and n s dextral strike slip shears basin and basement structures of the later substage are folds and ne and nw trending conjugate strike slip faults the post foliation deformation has reversed the normal displacements on basin marginal faults this is an example of basin inversion tectonic settings for the study area basins are discussed the role of the regional subhorizontal foliation and ced major extension ductile shear zones the edsz forming a carapace over the meatiq complex and the snsz along the northern boundary of the hafafit complex in the ductile thinning of the neoproterozoic crust is also considered in the light of recent tectonic extension models that explore the possibility of lithospheric delamination

late holocene channel changes of the middle trent channel response to a thousand year flood record this paper presents recent work on the floodplain sedimentology of the middle trent using data from gravel pits archaeological sites and documentary sources the middle trent has been unusually active during the holocene in comparison with other large lowland rivers in the british isles the holocene floodplain fill is dominated by sands and gravels with abundant structural evidence of changes in channel pattern and channel type a thousand year record of channel change has been reconstructed from palaeochannels and gravel units with radiocarbon dating of brushwood palaeomagnetic dating of fine channel fills dendrochronological dating of timber structures and dating via archaeological typologies the trent also has a reasonably well recorded flood history at least since the 11th century ad a comparison of the flood record and channel change indicates that the same degree of morphological and sedimentary response is not necessarily associated with floods of similar magnitudes i e there is no constant relationship between event magnitude and landform change instead the response seems dependent on the existing state of the channel and medium term trajectory of channel change there is evidence at both the hemington and colwick reaches of a cycle of channel change involving a change in channel typology and dating evidence that this may have migrated downstream the results of this work provide a medium term perspective on channel change which may be more appropriate for large british rivers than short term monitoring for both model validation and planning purposes

effective timescales of coupling within fluvial systems this paper presents a review of the coupling concept in fluvial geomorphology based mainly on previously published work coupling mechanisms link the components of the fluvial system controlling sediment transport down the system and the propagation of the effects of base level change up the system they can be viewed at several scales at the local scale involving within hillslope coupling hillslope to channel coupling and within channels tributary junction and reach to reach coupling at larger scales coupling can be considered as zonal coupling between major zones of the system or as regional coupling relating to complete drainage basins these trends are illustrated particularly by the examples of hillslope to channel coupling in the howgill fells northwest england badland systems in southeast spain alluvial fans in spain usa and uae and base level induced dissection of neogene sedimentary basins in southeast spain as the spatial scales increase so do the timescales involved effective temporal scales relate to magnitude and frequency characteristics recovery time and propagation time the relative importance changing with the spatial scale for downsystem coupling at the local scale the first two are important with propagation time increasing in importance in larger systems especially in those involving upsystem coupling related to base level change the effective timescales range from the individual event with a return period of decades through decadal to century timescales for downsystem coupling to tens to hundreds of thousands of years for the basinwide response to base level change the effective timescales influence the relative importance of factors controlling landform development

geochemistry and provenance of sediments from the pongola supergroup south africa evidence for a 3 0 ga old continental craton abstract the 3 0 ga pongola supergroup of south africa is one of the oldest well preserved supracrustal successions the sequence is divided into the nsuze chiefly volcanics quartzites and pelites and the overlying mozaan groups chiefly quartzites and pelites relative to north american shale composite nasc most pongola pelites have similar la yb and eu eu ratios and large ion lithophile elements lile high field strength elements hfse ree v and sc contents ni 30 300 ppm and cr 100 800 ppm contents are greater than those of nasc while cr ni ratios are generally higher than shales and pelites of all ages these trends may reflect residual cr enrichment during intense chemical weathering of komatiitic source rocks local populations of nsuze pelites based on major and trace element data may result from source heterogeneities and or contemporaneous volcanic input into the sedimentary basin pongola quartzite compositions and detrital modes are similar to those of sandstones from phanerozoic passive margin and basement uplift tectonic settings ree lile and hfse contents in pelites suggest that pongola source rocks were remarkably similar in composition to average phanerozoic upper continental crust trace element geographic and isotopic constraints favor 3 2 to 3 0 ga hood granites as a major source for pongola detritus moderate contributions from mafic sources are also required whereas relatively minor contributions from tonalite and komatiite are allowed these results indicate the existence of a chemically evolved felsic craton in southern africa by 3 0 ga this craton appears to have been more evolved than sources for either older moodies 3 3 ga or most of the younger witwatersrand sediments 2 8 2 7 ga pelites from the kaapvaal craton record at least two mafic to felsic source area compositional cycles in pelites deposited from the mid to late archean additional cycles may be masked by a depositional or erosional hiatus between the moodies and pongola sequences these sedimentary patterns suggest that crustal development in southern africa was episodic in nature during the early precambrian

multistation infrasonic observations of the chilean earthquake of 2005 june 13 summary on 2005 june 13 a major earthquake m7 8 occurred in the tarapaca region north chile within the region of high mountains at large distances from the epicentre this event produced coherent infrasonic waves detected by three infrasound stations that are part of the international monitoring system the observed azimuth variations and the long signal durations suggest that wide regions in the andes mountains radiated infrasonic waves from these observations the main sources regions are reconstructed such an event recorded by multiple stations offers an unique opportunity to evaluate the relative contributions of the different source mechanisms involved in large earthquakes as well as to improve our understanding of the amplification of ground displacement caused by the topography with a review of infrasound signals from past earthquakes extended empirical scaling relations are derived we show that beyond the seismic magnitude both seismic source and topographic features also play a predominant role in the generation of infrasound

holocene alluviation in southeast england and some implications for palaeohydrological studies implicit in models of palaeohydrological reconstruction is the assumption that a close relationship exists between climate hydrological regime and fluvial systems unfortunately there can be a number of complicating factors involved some of which are becoming increasingly well known research into holocene alluviation in southeast england has demonstrated some associated difficulties which range from the problem of relating anthropogenically modified drainage networks to an understanding of contemporary rates of floodplain development to the impact of prehistoric societies on valley sedimentation a theoretical model is presented whereby varying geomorphic domains contributing to floodplain and valley fill construction can be recognized it is suggested that attempts to apply this framework to palaeohydrological studies may assist in the realization of a more accurate reconstruction in which former hydrological responses are integrated within a broader palaeoenvironmental context

shrimp u pb dating of detrital zircons from the hammamat group at gebel umm tawat north eastern desert egypt

evanescent wave coupling in a geophysical system airborne acoustic signals from the mw 8 1 macquarie ridge earthquake atmospheric low frequency sound i e infrasound from underwater events has not been considered thus far due to the high impedance contrast of the water air interface making it almost fully reflective here we report for the first time on atmospheric infrasound from a large underwater earthquake mw 8 1 near the macquarie ridge which was recorded at 1325 km from the epicenter seismic waves coupled to hydroacoustic waves at the ocean floor after which the energy entered the sound fixing and ranging channel and was detected on a hydrophone array the energy was diffracted by a seamount and an oceanic ridge which acted as a secondary source into the water column followed by coupling into the atmosphere the latter results from evanescent wave coupling and the attendant anomalous transparency of the sea surface for very low frequency acoustic waves

tectonic evolution of the basement complex in the central eastern desert of egypt the egyptian basement rocks are gathered into three major rock groups viz meatiq group oldest abu ziran group and hammamat group youngest the last two groups belong to the pan african orogenic cycle the meatiq group is an old crystalline basement cropping out in gneiss domes the abu ziran group comprises the geosynclinal association which is formed of a lower ophiolite unit overlain by metasediments volcanoclastics and locally intermediate volcanics having clear island arc characters the hammamat group comprises molasse type clastics and penecontemporaneous dokhan volcanics of andesite to rhyolite composition syn to late tectonic calc alkaline granites are the plutonic equivalents of the dokhan volcanics

an analysis of ground shaking and transmission loss from infrasound generated by the 2011 tohoku earthquake 1 the 2011 mw9 0 tohoku earthquake generated infrasound that was recorded by nine infrasonic arrays most arrays recorded a back azimuth variation with time due to the expanse of the source region we use ray tracing to predict group velocities and back azimuth wind corrections a japan accelerometer network recorded ground shaking in unprecedented spatial resolution we back projected infrasound from arrays is44 kamchatka and is30 tokyo to the source region and compare these results with acceleration data is44 illuminates the complex geometry of land areas that experienced shaking is30 illuminates two volcanoes and a flat area around the city of sendai where the maximum accelerations occurred the arrays and epicentral region define three source receiver profiles the observed broadband energy transmission loss tl follows an exponential decay law the best fitting model which has parameters that are interpreted to include the effects of geometric spreading scattering and the maximum ratio of the effective sound speed in the stratosphere to that at the ground accounts for stratospheric wind speed yields a 65 variance reduction relative to predictions from a traditional tl relationship this model is a simplified version of the model of le pichon et al 2012 which yields an 83 variance reduction for a single frequency implying that fine scale atmospheric structure is required to explain the tl for stratospheric upwind propagation our results show that infrasonic arrays are sensitive to ground acceleration in the source region of megathrust earthquakes the tl results may improve infrasonic amplitude scaling laws for explosive yield