seismic tomography a window into deep earth abstract the goal of this paper is to provide an overview of the current state of the art in seismic tomography and trace its origins from pioneering work in the early 1970s to its present status as the pre eminent tool for imaging the earth s interior at a variety of scales due to length limitations we cannot hope to cover every aspect of this diverse topic or include mathematical derivations of the underlying principles rather we will provide a largely descriptive coverage of the methodology that is targeted at readers not intimately familiar with the topic the relative merits of local versus global parameterization ray tracing versus wavefront tracking backprojection versus gradient based inversion and synthetic testing versus model covariance are explored a variety of key application areas are also discussed including body wave traveltime tomography surface wave tomography attenuation tomography and ambient noise tomography established and emerging trends many of which are driven by the ongoing rapid increases in available computing power will also be examined including finite frequency tomography full waveform tomography and joint tomography using multiple datasets several practical applications of seismic tomography including body wave traveltime attenuation and surface waveform are presented in order to reinforce prior discussion of theory

improving global shear wave traveltime tomography usingthree dimensional ray tracing and iterative inversion a fully non linear approach to global tomography using s wave arrival times has been implemented using 3 d ray tracing with an iterative linearized inversion scheme the starting model for the 3 d inversion was the long wavelength saw12d model derived from inversion of global waveforms the traveltime tomography leads to the introduction of smaller scale structure and a final model in which small scale detail exists and can be resolved with a smooth interconnection through long wavelength structure the two point ray tracing was implemented using a pseudo bending approach for a full spherical 3 d model of the mantle generally the ray paths in the full 3 d model and 1 d reference model are quite close but the inclusion of a more accurate treatment of the rays improves the resolution of wave speed gradients and the positioning of heterogeneity particularly near strong variations in wave speed for example in subduction zones a further advantage of the use of 3 d ray tracing is that it is possible to undertake resolution tests with fewer approximations with the aid of the non linear inversion a number of global s models have been constructed using different assumptions about the character of the model for example solutions can be produced that are designed to introduce minimum differences from a 1 d reference model a variance reduction of 48 per cent was achieved in the inversions with considerable benefit from the inclusion of iterative inversion with 3 d ray tracing and the improved quality of the data set used in this study resolution in the lower part of the mantle has been improved by supplementing the s arrival time data with sks times for the distance range from 84 to 118 the new global s models retain the general features of models derived by one pass linearized inversion with 1 d ray tracing but provide more focused images with a higher perturbation level for the same damping parameters the new models are able to provide a good definition of features revealed by regional tomography using arrival time and waveform data for example the complex slab morphology beneath the tonga and kermadec regions and the sharp boundary between slow and fast uppermost mantle regions beneath western and eastern europe

ray tracing directly in a 3 d ellipsoidal earth model for multiphase global arrivals seismic ray tracing methods are widely used in seismology with most such algorithms being executed in cartesian or spherical coordinate systems however the actual earth is not a perfect sphere but rather an ellipsoid meaning that results calculated in spherical coordinates may be different from the actual situation the general approach is to first calculate traveltimes in a spherical earth model then apply ellipsoidal time corrections to obtain more accurate traveltime data alternatively one may directly conduct the ray tracing in the ellipsoidal earth model without any time corrections in this paper we extend the functional of the multistage irregular shortest path method previously formulated for a spherical earth model to an ellipsoidal earth model in order to trace multiphase global seismic arrivals the results of two models indicate that the proposed algorithm has high computational accuracy which can be further tuned by decreasing the secondary node spacing comparison tests indicate that the traveltime differences between the ellipsoidal and spherical coordinate ray tracing methods cannot be ignored for direct p and s arrivals reflected pcp and scs arrivals and reflected and converted pcs and scp arrivals the traveltime differences te ts computed by the ellipsoidal and spherical ray tracing methods have different distribution patterns being dependent on the source locations however in general these traveltime differences te ts have relatively large negative values near the polar region and positive values near the equatorial region except for sources located near the polar region for ellipsoidal time correction in a specific case the maximum differences between the traveltimes computed by the ellipsoidal coordinate ray tracing method and the ak135 traveltime table after application of ellipsoidal time corrections are less than 0 1 s meanwhile the maximum differences between the traveltimes predicted by the ellipsoidal coordinate ray tracing method and by the spherical coordinate ray tracing method after application of ellipsoidal time corrections are only 0 075 s for the six stated phases these results indicating that ray tracing could be conducted directly in the ellipsoidal earth model

on recent seismic tomography for the western united states 1 in recent years a number of relatively high resolution seismic tomography models for the uppermost mantle underneath the western united states have been published and vigorous debate has ensued about their tectonic interpretation i present a straightforward yet quantitative comparison between models in order to help establish a framework for geodynamic interpretation and to help judge the role of tomographic theory vs data selection mapped s and p wave anomalies are found to be remarkably consistent between models which implies that seismologists are beginning to narrow down the structure underneath active continental margins to scales of 200 km large discrepancies between published anomaly amplitudes exist however and the models on the high end of the spectrum raise questions as to how they are to be interpreted in terms of temperature composition and melting

a low seismic wavespeed anomaly beneath northwestern india a seismic signature of the deccan plume abstract seismic tomography of the indian region using p wave arrival times reveals an approximately cylindrical region of lowered seismic velocities in the upper mantle to the north of the gulf of cambay and the present exposure of the deccan flood basalts this anomaly with low velocities interrupts the characteristically high seismic velocities in the lithosphere beneath peninsular india and extends from shallow depth down to a more extensive low velocity zone beneath 200 km the centre of the low velocity anomaly lies just below the earliest alkaline magmatism which has been directly associated with the deccan plume in the northern portion of the cambay graben these magmatic events precede the main deccan flood eruptions by at least 3 myr the lowered seismic wavespeeds link into the ancient narmada lineament and to some extent to the south but here unfortunately the tomographic image runs out of resolution synthetic tests indicate that such a zone of lowered wavespeeds can be recovered with some loss of amplitude towards the south the association of the current seismic anomaly with the deccan traps is intriguing since the cambay graben remains a place of raised heat flow one explanation would be that the seismic anomaly represents the signature of the initial conduit through which plume material forced its way through the lithosphere beneath the cambay rift the zone of lowered seismic velocities beneath the indian lithosphere might then represent the remains of the initial plume head which would need to have moved with india over the 65 myr since the deccan eruptions

an interdisciplinary approach to evaluation of potential instability in alluvial channels abstract a modular procedure to assess the magnitude distribution and potential for channel instabilities at a large number of sites has been designed and implemented the procedure based on diagnostic interdisciplinary criteria of alluvial channel morphology and associated riparian vegetation is presented the modules include 1 initial site evaluations 2 gis based data input and management 3 ranking of relative channel stability 4 identification of spatial trends 5 ranking of socio economic impacts and identification of most critical sites and 6 collection of additional field data for more detailed evaluation of the magnitude and type of future instabilities and the effects of proposed mitigation measures the procedure using site evaluation forms as the fundamental means of data collection takes a trained person 1 to 1 5 hours to complete site evaluation forms can be altered according to the specific environment being studied and the objectives of the study an objective ranking scheme based on physical attributes extracted from the gis data base permits the identification of the most unstable channel sites and thereby focuses attention on potentially critical sites if a significant concern about a bridge or adjacent lands arises or if mitigation measures are considered various methods to estimate future channel changes are proposed these include 1 numerical alluvial channel modeling 2 empirical models of channel evolution 3 regime equations and 4 empirical relations based on process dominance in different fluvial environments the methods require differing amounts of additional field data and provide results of varying detail and accuracy the decision on which method to use must be based on the objectives and resources of the agency involved in the evaluation study

sharpening the tomographic image of the subducting slab below sumatra the andaman islands and burma summary taking advantage of the increased ray coverage due to seismicity following the 2004 december and 2005 march great earthquakes an improved iterative regional global tomographic method was applied to the sumatra andaman and adjacent regions to better constrain the 3 d mantle velocity heterogeneity in the region velocity and hypocentral parameters were iteratively perturbed to sharpen the image of the subducted slab several iterations were performed and the effects of source mislocation were considered in the iterative process an issue usually neglected in global tomography we find that source relocation between iterations increases the amplitudes of slab anomalies and sharpens the definition of slab geometry beyond what can be achieved by a fixed source iterative inversion alone in addition extensive restoration tests of synthetic data were conducted that emphasize enhancements obtained by our iterative process these tests show significant increases in amplitude and decreased smearing of synthetic slab features thus when applied to the real data similar enhancements are inferred in the resulting model which better illustrates the complex slab geometry in the upper mantle and transition zone regions along the sumatra andaman and burma subduction zones

lightning in the anvils of supercell thunderstorms abstractthis study uses data from the oklahoma lightning mapping array ok lma the national lightning detection network and the norman oklahoma koun prototype weather surveillance radar 1988 doppler wsr 88d radar to examine the evolution and structure of lightning in the anvils of supercell storms as they relate to storm dynamics and microphysics several supercell storms within the domain of the ok lma were examined to determine whether they had lightning in the anvil region and if so the time and location of the initiation of the anvil flashes were determined every warm season supercell storm had some flashes that were initiated in or near the stronger reflectivities of the parent storm and propagated 40 70 km downstream to penetrate well into the anvil some supercell storms also had flashes that were initiated within the anvil itself 40 100 km beyond the closest 30 dbz contour of the storm these flashes were typically initiated in one of three locations 1 coincident with a local reflec

a model of channel response in disturbed alluvial channels dredging and straightening of alluvial channels between 1959 and 1978 in west tennessee caused a series of morphologic changes along modified reaches and tributary streams degradation occurred for 10 to 15 years at sites upstream of the area of maximum disturbance and lowered bed levels by as much as 6 1 m following degradation reaches upstream of the area of maximum disturbance experienced a secondary aggradation phase in response to excessive incision and gradient reduction aggradation downstream of the area of maximum disturbance reached 0 12 m per year with the greatest rates occurring near the stream mouths the adjustment of channel geometry and phases of channel evolution are characterized by six process oriented stages of morphologic development premodified constructed degradation threshold aggradation and restabilization down cutting and toe removal during the degradation stage causes bank failure by mass wasting when the critical height and angle of the bank material is exceeded threshold stage channel widening continues through the aggradation stage as the slough line develops as an initial site of lower bank stability the bank profile develops three dynamic elements 1 vertical face 70 to 90 2 upper bank 25 to 50 and 3 slough line 20 to 25 alternate channel bars form during the restabilization stage and represent incipient meandering of the channel

upper mantle structure beneath the siberian craton and surrounding areas based on regional tomographic inversion of p and pp travel times abstract we present a model of 3d seismic anomalies in the upper mantle beneath a part of northern asia that includes the siberian craton the west siberian plate the mountains framing siberia altai sayan and baikal and mongolia we used the differential travel times of pp and p phases to investigate the deep seismic structure beneath a large part of the siberian region where neither stations nor earthquake distributions are sufficient to apply other body wave tomographic schemes to show the reliability of the results based on inversion if the pp p residuals we performed various tests including 1 tests with odd even data 2 synthetic tests with checkerboard and realistic patterns and 3 inversions in other areas with clear structures furthermore for the southern part of the study area we present another model based on the inverse tomographic scheme its which uses travel times recorded by worldwide stations from events located in the study area in the overlapping areas these two independent models are generally consistent the main model of this study is obtained by merging the results of the pp p and its schemes this model shows a clear differentiation between the high velocity siberian craton and low velocity structures beneath the mountains framing siberia the area of cenozoic magmatism in western sayan is clearly associated with a low velocity anomaly at a depth of 600 700 km this low velocity pattern is located beneath the cratonic area while at shallower depths it seems to flow around the bottom of the thick craton lithosphere to the sw margin of the craton

seismic evidence for a chemical heterogeneity in the midmantle a strong and slightly dipping seismic reflector beneath the mariana subduction zone 1 a clear later phase 80 s after the direct p wave is observed in most of individual seismograms recorded by a short period seismometer network in japan j array from a cluster of deep earthquakes that occurred at the northern mariana subduction zone this phase 1 shows a p wave particle motion 2 arrives later from earthquakes with shallower focal depths 3 has a steeper incident angle than that of p wave and 4 shows a deviation of a few degrees in the arrival azimuth from that of p wave we interpret it as an s to p converted wave which takes off downward from the source and is reflected at a velocity discontinuity reflector below the earthquakes travel time inversion shows that the seismic reflector dips southwest by 20 at 24 25 n 144 75 e and at a depth of 1115 km with a lateral extension at least 100 100 km the location corresponds to the lower edge of a high velocity anomaly in global tomographic models amplitude and waveform analyses suggest a decrease of s wave velocity by 2 6 and an increase of density by 2 9 within the reflector there is almost no difference in p wave velocity 1 between the reflector and the surrounding mantle the estimated thickness of the reflector is 12 km these observations indicate that the observed seismic structure is more likely to be a chemical reservoir rather than a purely thermal anomaly the seismic reflector might be a piece of subducted oceanic crust as suggested by a previous study it also could be related to the break down of the d phase of dense hydrous magnesium silicates at midmantle pressure condition reported by recent mineral physics studies both scenarios imply that mechanical chemical segregation might occur within the subducted slab at midmantle condition

seismic evidence for a mantle plume oceanwards of the kamchatka aleutian trench junction summary a non linear iterative p wave traveltime tomography has revealed a mantle plume originating at a depth of nearly 1000 km rising across the 600 km discontinuity and deflecting subhorizontally in the uppermost mantle presumably by shear flow due to the overlying moving plate data from the geophysical survey of russia 1955 1997 were inverted jointly with the catalogues of international seismological centre and usgs national earthquake information centre 1964 1998 the result shows a 300 500 kmwide cylindrical low velocity anomaly yx2 per cent that extends from a depth of greater than 900 km to shallower than 200 km the anomaly is almost vertical at depths up to y400 km and rises obliquely to the north up to y200 km under the ocean floor near the northern end of emperor seamounts above y300 km depth a subsidiary anomaly extends subhorizontally to the nw in fair agreement with the direction of movement of the pacific plate the overlying seafloor is characterized by anomalously high heat flow which may be attributed to the thermal effect of the mantle plume

density and bulk sound velocity jumps across the 660 km seismic discontinuity abstract molecular dynamics md simulation with realistic and accurate potential models previously obtained for mg2sio4 polymorphs mgo periclase and mgsio3 polymorphs is used to predict the density and bulk sound velocity jumps in the phase transformation from mg2sio4 spinel to mgsio3 perovskite plus mgo periclase at high temperature and high pressure conditions corresponding to the 660 km seismic discontinuity in the mantle the simulated density and bulk sound velocity jumps are then compared with seismological models reported for the 660 km discontinuity the md simulation for a pyrolite composition 60 vol spinel is found to be compatible with a recent model sf99 shearer and flanagan science 285 1999 1545 within nearly 1 limit for both density and bulk sound velocity jumps the md simulated bulk sound velocity jump for a piclogite composition 40 vol spinel is also consistent with sf99 within 1 while the md density jump for the piclogite lies outside the sf99 data our md computed density and bulk sound velocity jumps either for the pyrolite or the piclogite composition differ substantially from the values by the prem or the ak135 model

joint seismic tomography for bulk sound and shear wave speed in the earth s mantle high quality p and s travel times are now available from careful reprocessing of data reported to international agencies a restricted data set has been extracted for which comparable ray coverage is achieved for p and s and used for a joint inversion to produce a three dimensional model for shear and bulk sound velocities represented in terms of 2 2 cells and 18 layers in depth through the mantle about 106 times for each of p and s are combined to produce 312 549 summary rays for each wave type linearizing about the ak135 reference model 583 200 coupled tomographic equations are solved using an iterative partitioned scheme clear high resolution images are obtained for both bulk sound speed and shear wavespeed the bulk and shear moduli have differing sensitivity to temperature and mineral composition and so the images of the two velocity distributions help to constrain the nature of the processes which produce the variations different heterogeneity regimes can be recognised in the upper mantle the transition zone most of the lower mantle and the lowermost mantle in the upper mantle many features can be explained by thermal effects but in some orogenic zones e g western north america the opposite sense of the bulk sound and shear wave speed variation requires compositional effects or volatiles to outweigh any thermal effects in the lower mantle pronounced narrow structures which may represent remnant subduction are most marked in shear the level of large scale variations in bulk sound speed compared to shear diminishes with depth in the lower mantle reaching a minimum near 2000 km below this depth the variability of both wave speeds increases near the core mantle boundary the variations of the two wave speeds show little concordance suggesting the presence of widespread chemical heterogeneity

seismic rays and traveltime tomography of strongly heterogeneous mantle structure application to the central mediterranean summary the structure of the earth s upper mantle near convergent plate margins such as along the nubia eurasia collision zone in the mediterranean involves strong seismic wave speed contrasts associated with subducting lithospheric slabs and opening backarc basins in this environment seismic wave propagation is strongly influenced by heterogeneity and requires appropriate modelling practice although accurate numerical methods are often used to model seismic traveltimes in the crust only approximate techniques have been used for the mantle on the assumption that speed contrasts are weaker we devise optimize and test a method aimed at recovering strongly heterogeneous mantle structures using a finite difference scheme to calculate first arrival traveltimes and trace seismic rays with high accuracy even in the presence of strong gradients we adapt this forward scheme successfully used in local scale tomography to spherical geometry through source specific earth flattening approximations and we split calculations in meshes with different step size to model optimally the crust with a 2 km step and the mantle 6 km step we then use an iterative non linear inversion approach starting from a simple 1 d prior model we test the ability of this procedure to reconstruct sample structures devised to be illustrative for the mediterranean region using synthetic data calculated on the real distribution of sources and stations reported by the bulletins of the international seismological centre isc besides regular checkerboard patterns we also reconstruct a more representative model different strategies are used and compared in linear and non linear inversion we find that a linear approach by which rays are only traced once in the background model may result in an illusory fit to data realistic upper mantle structures strongly deflect seismic rays and correct paths can only be found after a few iterations although linear inversion seems able to identify the main features quite well we verify how non linear inversion and 3 d ray tracing significantly improve the results especially when we attempt to reconstruct a realistic structure we also apply the finite difference non linear traveltime tomography to data from the isc to retrieve upper mantle structure in the central mediterranean we verify that the non linear inversion is able to reveal sharpened velocity contrasts and thinner bodies than linear inversion clear differentiation found in the nonlinear result between signatures of northern and southern dinarides showing lithosphere subducting only beneath the southern sector is more coherent with the regional geodynamic framework such improvements due to non linear mantle tomography may contribute to the general picture of slab detachment and small scale mantle convection in the mediterranean region and therefore significantly impact on geodynamic implications of resulting models

antenna structures and cloud to ground lightning location 1995 2015 spatial analyses of cloud to ground cg lightning occurrence due to a rapid expansion in the number of antenna towers across the united states are explored by gridding 20 years of national lightning detection network data at 500 m spatial resolution the 99 8 of grid cells with 100 cgs were within 1 km of an antenna tower registered with the federal communications commission tower height is positively correlated with cg occurrence towers taller than 400 m above ground level experience a median increase of 150 in cg lightning density compared to a region 2 km to 5 km away in the northern great plains the cumulative cg lightning density near the tower was around 138 117 higher than a region 2 to 5 km away in the september february march august months higher cg frequencies typically also occur in the first full year following new tower construction creating new lightning hot spots

bankfull width and morphological units in an alpine stream of the dolomites northern italy abstract this research examines variations in bankfull cross sections along a steep stream of the dolomites cordevole stream belluno northern italy field measurements were conducted to determine variations in the channel top width at bankfull stage in relation to the drainage area and to the length of the flow path after grouping the bed morphologies according to the montgomery and buffington montgomery d r buffington j m 1997 channel reach morphology in mountain drainage basins geol soc of am bull 109 5 596 611 classification we analyzed the increase in bankfull width for the dominant stream units cascades step pools isolated pools and colluvial reaches at the head of the basin we observed that the morphologies more related to the drainage area are colluvial reaches and pools the less adaptable are steps and cascades these differences likely result from the absence of lateral constriction in the colluvial reaches and pools whereas the presence of coarser sediments in the bed can affect the transverse adjustments in steps and reaches dominated by cascades linkages between cross section geometry and parameters related to flow i e drainage area and stream power have been analyzed together with the distribution of surface grain sizes and its coarsening pattern the existence of distinctive bankfull widths between different morphological units points out the degree of susceptibility to be modeled according to the channel slope reference diameter d90 and contributing area

channel adjustment of an unstable coarse grained stream opposing trends of boundary and critical shear stress and the applicability of extremal hypotheses channel adjustments in the north fork toutle river and the toutle river main stem were initiated by deposition of a 2 5 km3 debris avalanche and associated lahars that accompanied the catastrophic eruption of mount st helens washington on 18 may 1980 channel widening was the dominant process in combination adjustments caused average boundary shear stress to decrease non linearly with time and critical shear stress to increase non linearly with time at the discharge that is equalled or exceeded 1 per cent of the time these trends converged by 1991 1992 so that excess shear stress approached minimum values extremal hypotheses such as minimization of unit stream power and minimization of the rate of energy dissipation minimum stream power are shown to be applicable to dynamic adjustments of the toutle river system maximization of the darcy weisbach friction factor did not occur but increases in relative bed roughness caused by the concomitant reduction in hydraulic depths and bed material coarsening were documented predictions of stable channel geometries using the minimum stream power approach were unsuccessful when compared to the 1991 1992 geometries and bed material characteristics measured in the field it is concluded that the predictions are not applicable because the study reaches are not truly stable and cannot become so until a new floodplain has been formed by renewed channel incision retreat of stream side hummocks and establishment of riparian vegetation to limit the destabilizing effects of large floods further prediction of energy slope and consequently stream power by the sediment transport equations is inaccurate because of the inability of the equations to account for significant contributions of finer grained sand and gravel bank materials relative to the coarsened channel bed from bank retreat and from upstream terrace erosion

recent channel adjustments in alluvial rivers of tuscany central italy drastic channel adjustments have affected the main alluvial rivers of tuscany central italy during the 20th century bed level adjustments were identified both by comparing available topographic longitudinal profiles of different years and through field observations changes in channel width were investigated by comparing available aerial photographs 1954 and 1993 98 bed incision represents the dominant type of vertical adjustment and is generalized along all the fluvial systems investigated the arno river system is the most affected by bed level lowering up to 9 m whereas lower incision generally less than 2 m is observed along the rivers of the southern part of the region human disturbances appear to be the dominant factors of adjustments the main phase of vertical change occurred during the period 1945 80 in concomitance with the phase of maximum sediment mining activity at the regional scale the second dominant type of adjustment that involved most of the rivers in the region consists of a narrowing of the active channel based on measurements of channel width conducted on aerial photographs 38 of the reaches analysed experienced a narrowing greater than 50 of the initial channel width the largest values of channel narrowing were observed along initially braided or sinuous with alternate bars morphologies in the southern portion of the region a regional scheme of channel adjustments is derived based on initial channel morphology and on the amounts of incision and narrowing different styles of channel adjustments are described rivers that were originally sinuous with alternate bars to braided generally became adjusted by a moderate incision and a moderate to intense narrowing in contrast sinuous meandering channels mainly adjusted vertically with a minor amount of narrowing copyright 2003 john wiley sons ltd

application of a three dimensional ray tracing technique to global p pp and pdiff traveltime tomography summary a 3 d ray path tracing algorithm was successfully applied to global p wave traveltime tomography the inversion was conducted iteratively using the resultant p wave velocity model as the initial model for the subsequent iteration the lsqr method was adopted to solve a large and sparse system of equations this iteratively linearized inversion with 3 d ray tracing increased wave speed anomalies located heterogeneities better and reduced smearing as compared to those derived from a conventional one step inversion using 1 d ray tracing although the general pattern of velocity anomalies was similar a major difference was found in the lowermost mantle where the departure of a ray path from the great circle path tends to be in general greatest in particular a pronounced high velocity anomaly develops beneath the indian ocean a feature not obvious in the result of 1 d inversion the final p wave velocity model was obtained by including reported pp and pdiff traveltime data the addition of the pp data sharpened the images and enhanced velocity anomalies in the upper mantle especially at latitudes above 45 of the northern hemisphere the addition of the pdiff data sharpened and amplified velocity anomalies in the lowermost mantle in general

type specific reference conditions of fluvial landscapes a search in the past by 3d reconstruction abstract river floodplain restoration programs are often based on type specific reference conditions of the respective river section most large rivers in the industrialized world are heavily degraded and lack near natural reference sites for that reason historical analyses of the pre channelization state have been used to define adequate restoration targets at the austrian danube section in the alluvial zone national park downstream from vienna this study compares new reference data derived from 3d reconstructions in the form of digital terrain models from two historical danube river landscapes the machland floodplain in 1812 and the former floodplain in vienna in 1849 the focus is on the original hydrological surface and subsurface connectivity of the river floodplain systems related to different flow situations here we use water cover shorelines depth of the groundwater table and inundation depth as surrogates for measuring connectivity the results show that the two study sites naturally constituted extreme formations of the austrian anabranching danube sections the machland section was one of the narrowest floodplains but highly dynamic and the vienna lobau section was one of the broadest whereby only the central part close to the main channel originally showed high morphological turnover the analyses of hydrological surface connectivity relative to total floodplain extension reveal significant differences due to their basic geological and geographical conditions despite these basic differences both study sites in absolute numbers showed similar extensions of the water bodies at low and mean flow the depths of the groundwater table related to mean flow were also comparable prior to channelization the groundwater conditions in both floodplains favored the formation of wet to moist alluvial forest communities up until today the two river landscapes continue to undergo different developments both river sections are impounded but the machland floodplain still represents a rural site while the vienna site has been utilized more intensively as building land and for urban infrastructure as a consequence of the diverse human interventions in the 19th and 20th century river bed degradation and aggradation of sediments in the floodplains have significantly truncated fluvial dynamics and hydrological connectivity in addition these phenomena have substantially deepened the groundwater table in both study sites the results contribute to the identification of river floodplain type specific reference conditions and provide an additional decision basis for discussing appropriate management strategies in the degraded riverine ecosystems

the role of vegetation and bed level fluctuations in the process of channel narrowing abstract a catastrophic flood ire 1965 on plum creek a perennial sandbed stream in the western great plains removed most of the bottomland vegetation and transformed the single thalweg stream into a wider braided channel following eight years of further widening associated with minor high flows a process of channel narrowing began in 1973 narrowing continues today the history of channel narrowing was reconstructed by counting the annual rings of 129 trees and shrubs along a 5 km reach of plum creek near louviers colorado sixty three of these plants were excavated in order to determine the age and elevation of the germination point the reconstructed record of channel change was verified from historical aerial photographs and then compared to sediment stratigraphy and records of discharge and bed elevation from a streamflow gaging station in the study reach channel narrowing at plum creel occurs in two ways first during periods of high flow sand and fine gravel are delivered to the channel temporarily raising the general bed level subsequently several years of uninterrupted low flows incise a narrower channel second during years of low flow vegetation becomes established on the subaerial part of the present channel bed in both cases surfaces stabilize as a result of vegetation growth and vertical accretion of sediment

delay time tomography of the upper mantle below europe the mediterranean and asia minor summary the method of linearized delay time tomography is applied to retrieve the p velocity heterogeneity of the upper mantle in central europe the mediterranean and asia minor the upper mantle is parametrized in slowness cell functions with lateral dimensions of 1 the model parametrization includes event mislocation vectors and station delay time corrections in all 20 000 parameters describe the model delay time data selected from the isc data base 1964 1982 from regional events and from stations up to 90 of epicentral distance are used about 18 000 events and 937 stations contributed nearly 500 000 delay times we discuss the tomographic method the data processing the cell model employed the computation of the ray geometry the use of composite rays in tomography and the cell hit count the inversions are performed with two different iterative row action methods lsqr and sirt results obtained with the lsqr method will be shown only the spatial resolution is investigated with sensitivity analyses using two different synthetic velocity models a spike model and a model with harmonically varying velocity anomalies the spatial resolution is estimated to be high on the order of the cell size in the mantle below central and southeastern europe the mapped velocity heterogeneity exhibits primarily low velocities around a depth of 200 km and just above the transition from upper to lower mantle this indicates a systematic deviation of the reference model jeffreys bullen from the radially averaged earth structure which may violate the basic assumptions underlying the linearized approach a posteriori investigation of the data also indicates the presence of a low velocity zone and the existence of strong velocity depth gradients

causes of 20th century channel narrowing in mountain and piedmont rivers of southeastern france extensive channel narrowing in southeastern france provides an illustration of geomorphic response to land use changes the study region comprises a range of environments from large piedmont and intramountain gravel bed rivers to small mountain streams field measurements and analysis of historical data demonstrate two distinct periods of channel change from 1850 to 1950 channel narrowing is interpreted to be the result of a recovery process in response to widespread channel destabilization induced by major floods during the second half of the 19th century at the time the largely deforested basins were highly responsive to flooding whereas the recovery process was accelerated by floodplain and basin scale land use changes afforestation and torrential control works which in turn reduced sediment delivery and enabled vegetation development in channels from 1950 to 1970 channel narrowing accelerated in most of the studied rivers this recent phenomenon is considered as a human induced fluvial adjustment directly related to forest development on river margins and human abandonment of intensive floodplain land uses at the same time long profile degradation occurred as a result of long term bedload supply decrease in small mountain streams channel narrowing is mainly explained by channel incision which seems to progress from upstream where sediment sources are progressively stabilized by afforestation copyright 2002 john wiley sons ltd

channel reach morphology in mountain drainage basins a classification of channel reach morphology in mountain drainage basins synthesizes stream morphologies into seven distinct reach types colluvial bedrock and five alluvial channel types cascade step pool plane bed pool rime and dune ripple coupling reach level channel processes with the spatial arrangement of reach morphologies their links to hillslope processes and external forcing by confinement ripar ian vegetation and woody debris defines a process based framework within which to assess channel condition and response potential in mountain drainage basins field investigations demonstrate character istic slope grain size shear stress and roughness ranges for different reach types observations consistent with our hypothesis that alluvial channel morphologies reflect specific roughness configurations ad justed to the relative magnitudes of sediment supply and transport ca pacity steep alluvial channels cascade and step pool have high ratios of transport capacity to sediment supply and are resilient to changes in discharge and sediment supply whereas low gradient alluvial channels pool rime and dune ripple have lower transport capacity to supply ra tios and thus exhibit significant and prolonged response to changes in sediment supply and discharge general differences in the ratio of transport capacity to supply between channel types allow aggregation of reaches into source transport and response segments the spatial distribution of which provides a watershed level conceptual model linking reach morphology and channel processes these two scales of channel network classification define a framework within which to in vestigate spatial and temporal patterns of channel response in moun tain drainage basins

upward lightning observations from towers in rapid city south dakota and comparison with national lightning detection network data 2004 2010 1 we report on upward lightning observations from ten tall towers 91 191 m in rapid city south dakota usa and compare with national lightning detection network nldn data a total of 81 upward flashes were observed from 2004 2010 using gps time stamped optical sensors and in all but one case visible flash activity preceded the development of the upward leaders time correlated analysis showed that the nldn recorded an event within 50 km of towers and within 500 ms prior to upward leader development from the tower s for 83 67 81 of the upward flashes a preceding positive cloud to ground stroke cg was detected in 57 46 81 of the cases and a preceding positive intracloud flash ic in 23 19 81 of the cases however 8 of the 19 nldn indicated ic events were actually cg strokes based on optical observations preceding negative intracloud flashes ic were recorded for 2 2 81 of the cases analysis also showed that for 44 36 81 of the upward flashes the nldn reported subsequent negative cloud to ground cg strokes and or ic events at one or more tower locations of the 151 subsequent events 70 105 151 were cg reports and 30 46 151 were listed as ic events the geometric mean median location accuracy and peak current for subsequent events were 194 m 206 m and 12 9 ka 12 4 ka respectively these correlated observations suggest that a majority of the upward lightning flashes were triggered by a preceding flash with the dominant triggering type being the cg flash

joint bulk sound and shear tomography for western pacific subduction zones abstract detailed regional body wave tomographic inversion of the western pacific region has been performed using p and s travel times from common sources and receivers with a joint inversion in terms of bulk sound and shear wave speed variations in the mantle this technique allows the separation of the influence of bulk and shear moduli and hence a more direct comparison with mineral physics information the study region is parameterized with cells of side 0 5 to 2 and 19 layers to a depth of 1500 km while the rest of the mantle was parameterized with 5 5 cells with 16 layers between the surface and the core mantle boundary a simultaneous inversion is made for regional and global structures to minimize the influence of surrounding structures on the regional image a nested iterative inversion scheme is employed with local linearization and three dimensional ray tracing through the successive model updates the results of the regional tomographic inversion reveal the penetration of a subducted slab below the 660 km discontinuity at the kurile kamchatka trench while flattening of slabs above this depth is observed in the japan and izu bonin subduction zones on both the bulk sound and shear wave speed images the penetration of a subducted slab down to a depth of at least 1200 km is seen below the southern part of the bonin trench mariana philippine and java subduction zones fast shear wave speed perturbations associated with the subducted slabs down to the 410 km transition zone are larger than the comparable bulk sound perturbations for all these subduction zones except the philippines the bulk sound signature for the subducted slab is more pronounced than for shear in the philippines talaud new guinea solomon and tonga subduction zones where penetration of the slab into the middle mantle is observed variation in the amplitude ratio between bulk sound and shear wave speed anomalies correlates well with the subduction parameters of the descending slab slabs younger than 90 ma at the trench show bulk sound dominance in the upper mantle while older slabs have a stronger shear wave speed signature spreading of the fast shear wave speed zone between 800 and 1000 km is observed in the areas of deep subducted slab penetration but has no comparable expression in the bulk sound images this high velocity feature may reflect physical or chemical disequilibria introduced to the lower mantle by subducted slabs

structure and evolution of lithospheric slab beneath the sunda arc indonesia tomographic imaging reveals seismic anomalies beneath the sunda island arc indonesia that suggest that the lithospheric slab penetrates to a depth of at least 1500 kilometers the sunda slab forms the eastern end of a deep anomaly associated with the past subduction of the plate underlying the mesozoic tethys ocean in accord with previous studies the lithospheric slab was imaged as a continuous feature from the surface to the lower mantle below java with a local deflection where the slab continues into the lower mantle the deep slab seems to be detached from the upper mantle slab beneath sumatra this complex slab structure is related to the tertiary evolution of southeastern asia and the indian ocean region

signature of remnant slabs in the north pacific from p wave tomography summary a 3 d ray tracing technique was used in a global tomographic inversion in order to obtaintomographicimagesofthenorthpacific thedatareportedbythegeophysical surveyofrussia 1955 1997 wereusedtogetherwiththecataloguesoftheinternational seismologicalcenter 1964 1991 andtheusgeologicalsurveynationalearthquake information center 1991 1998 and the recompiled catalogue was reprocessed the final data set used for following the inversion contained 523430 summary ray paths the whole of the earth s mantle was parametrized by cells of 2 2 and 19 layers the large and sparse system of observation equations was solved using an iterative lsqr algorithm asubhorizontalhigh velocityanomalyisrevealedjustabovethe660kmdiscontinuity beneaththealeutiansubductionzone thishigh velocityfeatureisobservedatlatitudes of up to 70 n and is interpreted as a remnant of the subducted kula plate which disappeared through ridge subduction at about 48ma a further positive velocity perturbation feature can be identified beneath the chukotka peninsula and okhotsk sea extending from 300 to 660km depth and then either extending further down to 800km chukotka or deflecting along the 660km discontinuity okhotsk sea this high velocity anomaly is interpreted as a remnant slab of the okhotsk plate accreted to siberia at 55ma

tomographic inversion for three dimensional anisotropy of earth s inner core abstract seismological studies generally suggest that the earth s inner core is anisotropic and the anisotropic structure changes significantly both laterally and with depth previous body wave studies of the inner core have relied on ray tracing or waveform modeling using one dimensional 1d models here we present non linear tomographic inversions of the inner core anisotropy using three dimensional 3d ray tracing spline parameterization and a large collection of pkp differential travel times we adapt a pseudo bending ray tracing pbr method in spherical coordinates for seismic rays that traverse the inner core pkp df phase the method iteratively perturbs each discontinuity point and continuous segment of the ray through 3d earth structure so that its travel time is minimum the 3d anisotropic structure of the inner core is approximated to the first order as 3d heterogeneous but isotropic structure for a given ray the data are corrected using a scaled mantle tomographic model the inner core anisotropy model obtained has the following major features 1 the model has strong hemispherical and depth variation the isotropic velocity in the topmost inner core is greater in quasi eastern hemisphere qeh 40 160 e than in quasi western hemisphere qwh other longitudes the anisotropy is weak in qeh to the depth of 600 700 km below the inner core boundary icb while in qwh the anisotropy increases at much shallower depth about 100 200 km below the icb to about 3 4 then remains at about 2 4 throughout the rest of the inner core 2 the anisotropy form changes abruptly over a depth range of about 150 km at the radius of about 600 km slightly less than half of the inner core radius forming a distinct inner inner core iic the velocity in the iic has maximums at equatorial and polar directions and minimum at an angle of about 40 from the equatorial plane the velocity in the outer inner core oic however changes little for ray directions 0 40 from the equatorial plane 3 despite large variation of the anisotropy the isotropic velocity voigt average throughout the inner core is nearly uniform the results suggest that the oic is likely composed of the same type of iron crystals with uniform chemistry but the iic may be composed of a different type of crystal alignment a different iron phase or a different chemical composition our tests on model parameterization mantle correction and linear and non linear inversion suggest the main features of our model are very robust however fine scale structures are likely to differ particularly in the major transition zones e g in the topmost qwh isotropy to anisotropy between oic and iic change in the form of anisotropy and between qeh and qwh in oic difference in anisotropy strength searches for possible waveform complications from these boundaries need to be aware of the directional dependence and geographical variation to be successful

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

origins of positive cloud to ground lightning flashes in the stratiform region of a mesoscale convective system 1 the origins of positive cloud to ground cg lightning in the stratiform region of a leading line trailing stratiform mesoscale convective system mcs are investigated platforms include radars nldn data and a vhf 3 d lightning mapping system this study examines a small asymmetric mcs that occurred near the colorado kansas border in june 2000 in this storm 39 of the 269 cgs produced over a nearly 5 hour period came to ground within the stratiform region of these 30 initiated in the leading convective line and propagated rearward before coming to ground nine other cgs originated within the stratiform region stratiform cgs were observed to propagate mostly horizontally through vertically thin layers the observations suggest that stratiform charge is a conduit for cg lightning from the convective line and can initiate cgs as well

multiscale seismic tomography and earthquake relocation incorporating differential time data application to the maule subduction zone chile abstract we present a multiscale seismic tomography method incorporating differential time data this is an extension of the double difference tomography method to teleseismic distances using a nested regional global model parameterization it allows inclusion of absolute and differential time data observed at any distance potentially improving resolution of structure in areas where local or regional data are sparse the algorithm named teletomodd is quite flexible and is applicable to a variety of relocation and tomography problems including simultaneously solving for global velocity structure to illustrate the technique we apply it to the maule region of chile where an m w 8 8 earthquake occurred in 2010

adaptive whole earth tomography 1 an approach for seismic tomography is presented which allows the parameterization to be refined during the inversion the objective is to use the data to refine the mesh and the velocity model together and hence both are considered part of the solution some simple rules are used to identify the volumes of a three dimensional model in need of refinement the self adaptive parameterization is applied to an initial mesh built from uniformly distributed spherical triangles and delaunay tetrahedra application of the technique to a typical summary ray p wave arrival time data set shows it to be both feasible and practical for large scale whole earth tomography a noticeable trend in the resulting models as the parameterization is refined is the thinning of the farallon and tethys subduction features imaged in the mid mantle together with an increase in amplitude of the velocity perturbation

regression estimates of design flows for ungaged sites using bankfull geometry and flashiness abstract bankfull geometry data at 22 united states geological survey stream flow gaging sites in the red river basin of minnesota and north dakota were used for developing regression estimates of flows of different return periods regression equations were developed first by using only basin characteristics and then by using only bankfull geometry data as independent variables flashiness was included later as an independent variable in both cases in all 101 regressions were evaluated storage channel slope and bankfull width did not appear in the selected regressions stream flashiness was found to be an important explanatory variable in both bankfull geometry and basin characteristics regressions the bankfull geometry data produced slightly better regression equations than the basin characteristics data the bankfull geometry regressions will be useful to predict design flows and to compare with flow estimates developed by traditional methods for ungaged sites in the red river basin

hydromorphological parameters of natural channel behavior in conditions of the hercynian system and the flysch belt of the western carpathians on the territory of the czech republic abstract a fundamental prerequisite for assessing the current ecological status of streams is the establishment of reference conditions for each stream type that serve as a benchmark the hydromorphological reference conditions reflect the natural channel behavior which is extremely variable significant parameters of natural channel behavior were determined using a combination of four selected statistical methods principal component analysis agglomerative hierarchical clustering correlation and regression macroscale analyses of data about altitude stream order channel slope valley floor slope sinuosity and characteristics of the hydrological regime were conducted for 3197 reaches of major rivers in the czech republic with total length of 15 636 km on the basis of selected significant parameters and their threshold values channels were classified into groups of river characteristics based on shared behaviors the channel behavior within these groups was validated using hydromorphological characteristics of natural channels determined during field research at reference sites classification of channels into groups confirmed the fundamental differences between channel behavior under conditions of the hercynian system and the flysch belt of the western carpathians in the czech republic and determined a specific group in the flattened high areas of mountains in the bohemian massif validating confirmed the distinctions between groups of river characteristics and the uniqueness of each one it also emphasized the benefits of using qualitative data and riparian zone characteristics for describing channel behavior channel slope entrenchment ratio bed structure and d 50 were determined as quantitative characteristics of natural channel behavior

seismic tomography with p and s data reveals lateral variations in the rigidity of deep slabs abstract regional seismic tomography of the northwest pacific island arcs using p and s wave arrival time data with similar path coverage reveals an oceanic lithospheric slab deflected in the mantle transition zone beneath the izu bonin region in good agreement with the results of earlier tomographic and other seismic studies in the region the s wave images however do not show clearly the deflection of the slab this implies that the stagnant lithospheric slab in the transition zone is more likely a bulk sound structure which is strongly supported by our results from joint inversions for bulk sound and shear wavespeeds for the izu bonin region where trench migration has been reported the properties of the deflected slab lying on top of the 660 km discontinuity show strong bulk sound and weak shear signatures in contrast to the descending slab itself there is an indication in the shear images that a component of the former oceanic lithosphere is penetrating into the top of the lower mantle suggesting that a slab split has occurred

heterogeneity within the subducting pacific slab beneath the izu bonin mariana arc evidence from tomography using 3d ray tracing inversion techniques distinct zones of seismic heterogeneity along the izu bonin mariana arc have been investigated using complimenting regional bulk sound shear wave speed and p wave tomographic images the distribution of seismic anomalies and the inferred geometry of the subducting pacific plate have been modelled in unprecedented detail using joint tomography and new p wave model using a 3d inversion algorithm the use of 3d ray tracing techniques and smaller cell parameterizations have greatly enhanced the resolution of gradients therefore the models show much more detail about the structure and physical properties of the subduction zone the well defined features from the multiple wave speed images are used to elucidate the distinct morphology change between slab beneath the izu bonin horizontal slab and mariana vertical arcs and the distribution of physical properties in the mantle and the subducting oceanic lithosphere changes in physical properties within the slab tear at the southern end of the izu bonin arc identified as a bgap or thinningq in the tomographic images could be the result of the distortion of the pacific plate as its shape transforms between near horizontal to near vertical a decrease in the rigidity and strength of the lithosphere the subduction of the marcus necker ridge change in subduction velocity or a combination of all these factors strong slow anomalies exist both in the mantle wedge above and below the slab beneath the izu bonin arc but are not present beneath the mariana arc at the junction between the izu bonin and mariana arcs it appears that the there are two separate pieces of the pacific plate the torn slab north of 268 n and a buckled near vertically dipping slab south of the tear the transition between the two distinct slab morphologies coincides with the location of the ogasawara plateau and the trench d 2005 elsevier b v all rights reserved

morphological patterns of headwater streams based in flysch bedrock examples from the outer western carpathians abstract a channel reach morphology of mountain headwater streams results from the balance between fluvial and hillslope processes a large dataset n 102 of channel reaches coming out from flysch mid mountains was evaluated and compared with streams occurring in other environments two new channel reach morphologies were distinguished with respect to their differences in the ratio of sediment supply to transport capacity bedrock cascades and step rapids the chaining of channel reach morphologies by gradient criteria and the parameters of channel gradient and bankfull width related to the basin area show similar trends when compared to other recent studies by contrast bankfull depth indicates its independence on increasing basin area significant downstream coarsening of bed material occurs only in alluvial stepped bed morphologies cascades step pools and step rapids mainly due to strong slope channel coupling processes moreover the specific ratio of bankfull width and d90 predicts the interlocking of boulder steps as well as well developed step pool morphology an amount of large woody debris is closely related to the activity of strict local forest management in evaluated channels as a significant decrease in large woody debris pieces is observed with increasing basin area

patterns of alluvial rivers the pattern planform of a river can be considered at vastly different scales depending upon both the size of the river and the part of the fluvial system that is under consideration figure 1 for example in the broadest sense river patterns comprise a drainage network dendritic parallel trellis etc figure la the type of pattern is of interest to geomorphologists and geologists who interpret geologic conditions from aerial photographs at another scale a river reach which in figure lb is meandering is of interest to the geomorphologist who is interested in what that pattern reveals about river history and behavior and to the engineer who is charged with maintaining navigation and preventing major instability when a single meander is examined figure 1 c the hydraulics offtow the sediment transport and the potential for bank erosion are of concern in addition the sedimentologist is interested in the distribution of sediment within the bend bed forms within the channel figure ld and sedimentary structures figure ie which also establish a component of roughness for the hydraulic engineer finally the individual grains figure if provide geologic information on the sediment sources the nature of sediment loads and the feasibility of dredging for gravel there is an interaction of hydrology hydraulics geology and geomorphology at all scales which emphasizes the point that the fluvial system as a whole cannot be ignored even though only a component of the system is to be studied in this review only the patterns or planforms of alluvial rivers are discussed although it is apparent that the hydrologic and sediment yield characteristics of the drainage basin figure la as well as its geologic history cannot be ignored in the explanation of the pattern of any river

seismic heterogeneity in the mantle strong shear wave signature of slabs from joint tomography abstract the primary source of information on heterogeneity within the earth comes from seismic tomography a powerful tool for examining the character of heterogeneity comes from the comparison of images of bulk sound and shear wavespeed extracted in a single inversion since this isolates the dependencies on the elastic moduli however particularly in such multi parameter inversions there are many hidden facets which can have a strong influence on the results such as the weightings between parameters and in the misfit functions joint inversion with restricted data sets giving comparable cover for p and s waves provides useful checks on more inclusive studies and can provide relatively high resolution in some areas the relative behaviour of bulk sound and shear wavespeed can provide a useful guide to the definition of heterogeneity regimes for subduction zones a large part of the tomographic signal comes from s wavespeed variations in the upper mantle and transition there can be significant bulk sound speed contributions for younger slabs and in stagnant slabs associated with slab roll back for subducted oceanic lithosphere older than about 90 ma shear wavespeed variations nearly always are dominant and so the p wave images are controlled by shear modulus variations the narrow segments of fast wavespeeds in the depth range 900 1500 km in the lower mantle are dominated by s variations with very little bulk sound contribution deep in the mantle there are many fast features without obvious association with subduction in the last 100 ma which suggests long lived preservation of components of the geodynamic cycle

stagnant slab a review a stagnant slab is a subducted slab of oceanic lithosphere subhorizontally deflected above across or below the 660 km discontinuity this phenomenon has now been widely recognized beneath subduction zones around the circum pacific and in the mediterranean collaboration of seismic and electromagnetic observations mineral physics measurements and geodynamic modeling has begun to provide a consistent picture of stagnant slab

thresholds in small rivers hypotheses developed from fluvial morphological research in western germany the objective of this study was the formulation of fluvial morphological regularities for small rivers with a wide range of morphological and geological characteristics in north rhine westphalia germany based on a statistical research methodology such empirical quantitative information on reference conditions is required for the restoration of small rivers in the former highly industrialised ruhr area following the approach of some classic empirical works in fluvial morphology of the last century several natural reference rivers in the entire research area have been observed in order to provide a statistical correlation between independent and dependent morphological variables regressions between valley floor slope bankfull discharge and stream power on the one hand and several variables describing the longitudinal profile and river planform on the other hand have shown some significant results the regularities found are a quantitative contribution to the establishment of reference conditions as well as a useful tool for the restoration of small rivers if the specific properties and values of the underlying random sampling are taken into account in addition the relation between stream power and sinuosity shows the likely existence of a threshold exceeding a stream power of 100 w m the sinuosity decreases after an increase for lower stream power values comparable thresholds were found for the relation between stream power and pool depth as well as stream power and step steepness the thresholds could be explained by a change in the type of energy dissipation due to different physio geographical settings in highland rivers within forested v shaped valleys here large woody debris seems to increase the channel roughness and possibly replaces the significance of coarse grained bed material pool depth and step steepness as contributors to energy dissipation

spatial and temporal evolution of the subducting pacific plate structure along the western pacific margin 1 tomographic images of the subducting pacific plate beneath the izu bonin mariana arc illustrate a progression of geometries from shallow dipping to vertical from north to south along the arc recent advances in technology and inversion techniques have improved resolution of slab structure beneath the western pacific island arcs but reasons for the variation in geometry and morphology are still poorly understood by comparing high resolution tomographic images of the western pacific and updated paleogeographic reconstructions we are able to link the spatiotemporal evolution of the subducting pacific plate back to the mid miocene we have reconstructed tectonic motions along the kurile japan izu bonin mariana arc system and the ryukyu arc to provide an independent additional interpretation of the subducting pacific plate using the most current plate motion data we then investigate the plausibility of our model and three other proposed models based on the interpreted slab structure from tomographic images the new reconstruction agrees with the basic characteristics of former trench retreat models but illustrates the importance of the collision of the ogasawara plateau with the trench in the mid miocene and its subsequent effect on the slab structure at depth and the impact of other aseismic ridge collisions along the plate boundary the combination of evidence in changed physical properties imaged with tomography and the current interpreted slab morphology can be analyzed with the past plate motions to understand subduction zone processes

on the possibility of a folded crustal layer stored in the hydrous mantle transition zone abstract previous numerical studies of mantle convection focusing on subduction dynamics have indicated that viscosity rheological heterogeneity in the subducting plates and the surrounding mantle may have a primary effect on the behavior of subducting plates meanwhile the existence of a low viscosity layer lvl beneath the mantle transition zone mtz has been suggested by several geodynamic studies we investigated the effects of a rheologically weaker crustal layer in a hydrous wet mtz with an underlying lvl on the behavior of subducting plates and determined the trace of crustal material using a numerical simulation model of subduction dynamics in three dimensional regional spherical geometry the combined effect of a rheologically weaker crustal layer and an lvl beneath the mtz produces characteristic transient behavior of the crustal layer whose trace shows a folded loop like feature in the wet mtz along with a folded subducting slab in the lvl this phenomenon is caused by mechanical interaction of the crustal layer with an upward positive bending force due to the main body of the subducting slab folding in the lvl and an enhanced downward negative buoyancy force due to an increase in density from the garnet to the post garnet phase of crustal material the transiently folded crustal layer behind the root of the stagnant slab is also observed this result is consistent with seismological evidence suggesting a piece of subducted oceanic crust in the uppermost lower mantle beneath the subducting slab in the mariana trench over half of the subducted crust is temporarily stored in the mtz however this stored crustal material begins to penetrate into the lower mantle within 10 myr a relatively short timeframe relative to the overturn time of mantle convection eventually most of the crustal material is entrained into the lower mantle but a non negligible portion remains stored in the mtz for 50 myr after the beginning of the accumulation of subducted crust in the mtz

subducting slabs stagnant in the mantle transition zone the p wave velocity structure beneath the western pacific is found from the international seismological center first arrival data special attention was paid to the deep structure beneath the wadati benioff zone we discretized the whole mantle into blocks with finer blocks in the region of interest to obtain the velocities of all the blocks this way of discretization minimizes a problem with tomographic studies of regional scale difficulty in making corrections for the effects outside the region of interest our solution is iterative with the alternate step of the relocation of earthquakes using the whole mantle model of inoue et al 1990 as a starting model a first order smoothness constraint was imposed to suppress the possible fluctuation of the solution around the initial model the essential result depends little on whether the reference spherical model is smooth or discontinuous near 400 and 670 km depths we examined the resolution by calculating the resolving kernels for selected blocks and by reconstructing the checkerboard test patterns of velocity perturbation and the test structures of subducting lithosphere the resolution is depth dependent but in general good enough to see the slab configuration beneath the southern kurile japan izu bonin arcs and the java arc it is relatively poor beneath the northern kurile and mariana arcs the seismic image of subducting slab beneath the southern kurile to bonin arcs bends to subhorizontal near the leading edge of the wadati benioff zone and extends continentward over a distance of more than 1000 km the subhorizontal portion of the slab connects a high velocity blob to the bottom that reaches a depth of at least 800 km across the 670 km discontinuity under the japan arc although the image of the java slab directly penetrates the 670 km discontinuity it then bends to a shallow dip with a considerable spread reaching a depth of about 1200 km these results suggest that descending slabs of lithosphere in the western pacific tend to be stagnant in the transition zone under a subtle control of the 670 km discontinuity although stagnant slab materials eventually descend into the lower mantle they no longer maintain their original configuration below the 670 km discontinuity

on seismological reference models and the perceived nature of heterogeneity a key ingredient in understanding earth structure is the integration of seismological information with results from mineral physics for both the dominant radial dependence of material properties and the 3d structure revealed by seismic tomography in each case an important role is played by reference models for the internal structure of the earth originally constructed to meet seismological needs representations of the travel times of seismic phases are required for the location of seismic events and these have been supplemented by models that match the frequencies of the free oscillation of the earth which have played a major role in characterising seismic sources through the centroid moment tensor derived from long period records parameterised models were introduced to combat the computational demands of inversion and have been extensively used however in such models e g prem the form of the seismic parameters is prescribed to have a functional behaviour such as a cubic based on mathematical convenience rather than physical requirements any 1d models face the challenge of the significant lateral heterogeneity at the top and bottom of the mantle as well as the more subtle variations in between it may well be possible to capture the long wavelength components of 3d heterogeneity but the nature of available data sources means that it will be difficult to achieve comparable p and s definition for the whole mantle in many circumstances reference models are used for comparison with models constructed for different data sets it is then best that e g a cratonic reference model is used to judge results from cratons regionalisation of travel time observations provides a means of constructing such reference models for a broad range of tectonic environments when coupled with suitable path corrections it is possible to make a good account of regional 2d variations it is desirable that reference models used for interpretation of seismic tomography are tied as clearly as possible to mineral physics results with a representation based on the bulk modulus k shear modulus g and density rather than just the p and s wavespeeds comparator models for different mineral compositions and temperature regimes have the potential to aid the interpretation of tomographic images particularly in the separation of the influences of temperature and composition

estimating the probability of river channel adjustment river channels respond not only to natural external controls and natural controls internal to individual drainage basins but also to the influence of human activity although many site specific instances of change have been documented the complexity of the process interactions means that very little is known about the general nature of different styles of adjustment or their relative sensitivity to drainage basin controls data obtained from the thames basin southeast england are used in a probabilistic approach to differentiate between four styles of river channel adjustment and a variety of drainage basin characteristics adopting a probabilistic approach quantifies the degree of confidence attributable to any prediction of river channel adjustment while acknowledging that certainties are difficult to obtain in studies of the natural environment this approach could thus allow environmental planning decisions to be made with a quantified degree of uncertainty four multivariate logistic regression models are described which use a combination of continuous and categorical variables to associate drainage basin characteristics with four styles of river channel adjustment derived from a reconnaissance evaluation survey in comparison it is shown that laterally migrating river channels are the most common natural channel type in the thames basin and their probability of occurrence rises to 71 per cent in sand gravel environments in channels regulated by low weirs deposition is the most likely channel activity where gradients are lower than 0 0040 whilst above this threshold the majority of channels are morphologically inactive in urban channels many of which are also lined by concrete the likelihood of obtaining a stable channel is mostly in excess of 80 per cent in channels straightened during this century deposition is most likely in gradients below 0 0050 whereas erosional enlargement is most probable above this value in channels which were initially channelized prior to this century deposition gives way to stability at a threshold gradient of 0 0080

the measurement of river bank erosion and lateral channel change a review a detailed review and chronological survey is presented of the various techniques which have been used for the measurement of river bank erosion and channel change the techniques are classified according to the time scales involved long intermediate and short and each is discussed with respect to accuracy and repeatability the methods covered include sedimentological evidence botanical evidence historical sources planimetric resurvey repeated cross profiling erosion pins and terrestrial photogrammetry prospects for future developments are also discussed

improving depth resolution of teleseismic tomography by simultaneous inversion of teleseismic and global p wave traveltime data application to the vrancea region in southeastern europe summary over the years teleseismic tomography has developed to be a sophisticated method to study the earth s upper mantle on a regional scale using data from tomographic experiments with temporary station networks one faces some inherent problems which include limited resolution at depth and artefacts due to a plane wave approximation at the bottom of the model volume simultaneous inversion of dense regionally recorded teleseismic and global p wave traveltime data provides an opportunity to overcome these specific problems the calculation of the entire ray path using a 3 d ray tracing algorithm and a non linear iterative inversion scheme allow to localize heterogeneities in the earth s mantle and to improve resolution at depth application of a variable parametrization scheme provides not only a regional high resolution model but additionally allows to include a priori constrained structures such as a crustal model derived from independent studies we investigated the effect of different inversion strategies for a priori constrained model parameters and found that for upper mantle studies one must allow further perturbation of the known velocity structure during inversion to avoid artefacts down to the mantle transition zone we apply this approach to the romanian vrancea region in southeastern europe the results show a near vertical narrow high velocity body underneath that region extending down to 280 km depth approximately outlining the narrowly spaced seismogenic volume and a deeper differently oriented positive anomaly coupled to the shallower segment at the latter s southwestern edge at north northwest and west of the vrancea region we find an extended region of decreased seismic p wave velocity down to 200 km depth being interpreted as a shallow lithosphere asthenosphere boundary and asthenospheric mantle flow due to lateral migration of the high velocity body from synthetic reconstruction tests we found that inversion of the combined data set of regionally recorded teleseismic and global traveltime data enhances resolution up to depths greater than could be resolved by the teleseismic data alone

interconnection of ferro periclase controls subducted slab morphology at the top of the lower mantle abstract the electrical conductivity of mantle rocks during phase transformation from ringwoodite to silicate perovskite and ferro periclase was measured at 25 gpa and various temperatures ranging from 1300 to 1900 k the electrical conductivity was high at the initial stage of annealing suggesting that ferro periclase forms interconnected layers in aggregates of silicate perovskite and ferro periclase that are representative of lower mantle rock at 1900 k the electrical conductivity quickly decreased and reached that of silicate perovskite suggesting the cut off of the interconnected ferro periclase because of rounding of crystals below 1700 k the high conductivity values were maintained for experimental duration the interconnection of ferro periclase which has a lower viscosity than silicate perovskite can be maintained in a cold descending slab over geological time scales 1 my indicating that a colder slab is less viscous than the warmer mantle surrounding it the low viscosity slab can be prevented from penetrating into the deeper part of the lower mantle by the high viscosities encountered at a depth of 1000 km referred to as the viscosity hill that cause stagnation at this depth as observed by seismic tomography

measured current and close electric field changes associated with the initiation of upward lightning from a tall tower 1 we examine in detail the simultaneous lightning current waveforms close electric field changes and lightning location system data for upward lightning discharges initiated from the gaisberg tower gbt from 2005 to 2009 out of 205 upward flashes most of them 87 or 179 205 were initiated from the tower top without any nearby preceding lightning activity called self initiated whereas 26 upward flashes 13 were initiated from the tower top with immediately preceding nearby lightning activity called nearby lightning triggered including 15 positive ground flashes one negative ground flashes and 10 cloud discharges the possible reasons for self initiated upward flashes dominating at the gbt could be the field enhancement due to the gaisberg mountain above the surrounding terrain and low altitude of charge region during non convective season september to march since we note that self initiated lightning at the gbt occurred predominantly 79 or 142 179 during non convective season on the other hand the majority 85 or 22 26 of nearby lightning triggered upward flashes at the gbt occurring during convective season april to august and 80 nearby lightning triggered upward flashes out of 81 upward flashes observed at the ten tall towers in rapid city in south dakota of usa occurring during summer seasons could be due to the result of high altitude of charge region the triggering flashes were detected to be within 1 and 18 km distance and the time intervals between them and upward lightning initiation are in the range of 0 3 to 90 7 ms

mantle structure beneath indonesia inferred from high resolution tomographic imaging we investigated mantle structure beneath the indonesian region by means of tomographic inversions of traveltime residuals of direct p and the surface reflected depth phases pp and pwp the hypocentres and phase data used in the inversions were derived from the reprocessing of data reported to international data centres which include data from the australian skippy project we used more than 6 0 10 data from more than 50 000 globally distributed earthquakes recorded at a subset of nearly 3000 seismological stations worldwide the use of depth phases improved the sampling of the upper mantle structure in particular beneath the back arc regions the mapping of distant aspherical mantle structure into the study region was minimized by combining a high resolution regional with a low resolution global inversion the inversion was linearized around the ak135 reference velocity model and a combination of minimum norm and gradient damping was applied to constrain the solution inversion of different subsets of the data and test inversions of synthetic data indicate that resolution is sufficient to substantiate the conclusions pertinent to the complex large scale structure of the subducted slab beneath the indonesian archipelago the tomographic images confirm previous evidence for regional slab penetration into the upper part of the lower mantle but suggest a more complex trajectory of mantle flow beneath indonesia the implied lateral variation in the shape of the upper mantle slab is generally in good agreement with inferences from seismicity the data reveal a seismic anomaly beneath the sunda arc which is detected to at least 1500 km in depth and forms the eastern end of a deep anomaly associated with the past subduction of lithosphere of the mesozoic tethys ocean below java the lithospheric slab is probably continuous from the earth s surface to the lower mantle but beneath sumatra the deep slab seems to be detached from the seismogenic slab the high resolution images suggest that the subducted slab is deflected in the transition zone beneath the banda arc and that the descending slabs form a spoon shaped structure north of the banda sea we detect the two opposing subducted slabs of the molucca sea plate this is consistent with previous studies but our images suggest that the westward subduction has a significantly steeper dip than the eastward subduction slab structure beneath the banda and molucca seas is explained in the context of the continent arc collision between australia and the southeast indonesian island arc and the arc arc collision between sangihe and halmahera inversion of traveltime residuals of direct s phases a novelty for this region largely confirms the inferences from the p wave data even though less detail is resolved

deep seismic expression of an ancient plate boundary in europe seismological results on the structure of the upper mantle below europe reveal a marked contrast in seismic properties between precambrian and younger parts of europe the precambrian craton in eastern europe is characterized by high shear wave velocities which can be explained by low temperatures the transition to low seismic velocities below phanerozoic europe coincides with the crustal boundary zone of the craton and exists to depths of at least 140 kilometers despite the long and complex tectonic history of the plate boundary zone the transition is remarkably sharp which rules out any significant lateral transport of asthenospheric material across the suture zone

evolution of mantle structure beneath the northwest pacific evidence from seismic tomography and paleogeographic reconstructions 1 plate motions and subducting slab morphology are intricately connected and through the integration of seismicity tomographic images and relative plate motions the evolution of mantle structure can be interpreted tomographic images of p wave shear wave speed and bulk sound speed perturbations of the northwest pacific region have been interpreted to define the extent and geometry of the subducting pacific plate we have found that the subducted pacific plate beneath the japan and kurile arcs is coherent but is very complex at the junction of the two arcs near the hokkaido corner as the slab subduction angle decreases from north to south while the slab thickens the pacific slab beneath the japan arc is slightly thinner and subducting through the upper mantle at a less steep angle than the slab beneath the kurile arc as the slab reaches the 660 km discontinuity it becomes stagnant and lies in a horizontal position on top of the transition zone both beneath the izu and japan arcs in contrast the slab beneath the kurile arc is subducting at a steeper angle and penetrates through the transition zone into the lower mantle the difference in slab morphology appears to be due to a combination of change in dip of the subducting plate and the convergence velocity of the pacific plate along the margin a new paleogeographic reconstruction of northeast asia was assembled to evaluate the plate motions that could explain the foundation of the current slab morphology the plate reconstruction was based on euler pole motions of the pacific philippine amurian okhotsk and north american plates relative to stable eurasia plate the new tectonic model illustrates the collision of the japan and kurile arcs the opening of the kurile basin disparity in pacific plate velocities along the arc and different rates of trench retreat along the izu japan and kurile segments of the western pacific margin the plate motion model was interpreted in conjunction with the physical properties of the mantle imaged with the p wave and joint tomography to assess the evolution of the pacific plate morphology since the mid miocene and to provide constraints on the plausible plate motions in the region

toward quantifying uncertainty in travel time tomography using the null space shuttle 1 the solution of large linear tomographic inverse problems is fundamentally non unique we suggest to explore the non uniqueness explicitly by examining the null space of the forward operator we show that with the null space shuttle it is possible to assess robustness in tomographic models and we illustrate the concept for the global p wave model mit p08 we found a broad range of acceptable solutions compatible with the travel time data the root mean square rms velocity perturbations vary from 0 2 to 0 6 in the lowermost mantle and from 0 3 to 1 3 in the upper mantle such large variations in average amplitudes prohibit meaningful inferences on temperature or chemical variations in the earth from tomographic models alone on a global scale much short wavelength structure resides in the null space of the forward operator suggesting that the data do not everywhere resolve structure on the smallest length scale 200 km allowed by the block parameterization used in mit p08 and similar models this indicates that great care should be taken when interpreting such structure as a practical measure we suggest that only those structures for which the wave speed perturbations do not change sign within the range of models permitted by the data should be considered robust with this criterion the model null space analysis shows that the high velocity anomalies in the lower mantle which are often interpreted as remnants of slabs of subducted lithosphere are required by the seismic data low velocity anomalies underneath for instance hawaii iceland and africa show varying degrees of robustness