monitoring and modelling particle and reach scale morphological change in gravel bed rivers applications and challenges this paper focuses on developments in topographic data acquisition including airborne remote sensing digital photogrammetry differential gps and laser profiling e g lidar technologies that allow rapid acquisition of high resolution and high precision topographic data sets over a range of spatial scales these developments have offered new opportunities for investigating spatial and temporal patterns of morphological change in gravel bed rivers and have contributed to revitalization in three key areas 1 morphometric estimates of sediment transport and sediment budgeting 2 boundary conditions for numerical models including computational fluid dynamics and cellular modelling 3 three dimensional characterisation of morphology that is independent of flow stage the potential is clear but there remain a number of significant challenges including quality control and the effects of error on specific applications and morphologies this paper presents results from two investigations representing field and laboratory analyses of gravel bed river morphology at different spatial scales and for different applications case study 1 is concerned with monitoring and modelling morphological change in a large braided gravel bed river using ground based gps survey and digital photogrammetry derived from airborne imagery case study 2 is an investigation of the mechanisms for infiltration of fine sediment into gravel bed rivers which applies close range laser altimetry in flume experiments to derive very high resolution digital elevation models dems that are used to quantify and analyse changes in bed texture these case studies highlight the strengths and weaknesses of specific technologies and approaches to analysis of channel and floodplain morphology and change and suggest key areas that remain to be fully resolved in particular the critical need to define a specific threshold level of detection associated with each acquisition method and for different fluvial settings e g bar surface sub aqueous zone is emphasised

characterization of site specific gps errors using a short baseline network of braced monuments at yucca mountain southern nevada 1 we use a short baseline network of braced monuments to investigate site specific gps effects the network has baseline lengths of 10 100 and 1000 m baseline time series have root mean square rms residuals about a model for the seasonal cycle of 0 05 0 24 mm for the horizontal components and 0 20 0 72 mm for the radial seasonal cycles occur with amplitudes of 0 04 0 60 mm even for the horizontal components and even for the shortest baselines for many time series these lag seasonal cycles in local temperature measurements by 23 43 days this could suggest that they are related to bedrock thermal expansion both shorter period signals and seasonal cycles for shorter baselines to rep2 the one short braced monument in our network are correlated with temperature with no lag time differences between rep2 and the other stations which are deep braced should reflect processes occurring in the upper few meters of the ground these correlations may be related to thermal expansion of these upper ground layers and or thermal expansion of the monuments themselves even over these short distances we see a systematic increase in rms values with increasing baseline length this and the low rms levels suggests that site specific effects are unlikely to be the limiting factor in the use of similar gps sites for geophysical investigations

nature of the recent vertical ground movements inferred from high precision leveling data in an intraplate setting ne ardenne belgium yearly high precision leveling surveys have been performed from 1993 to 1998 along a 48 km long local network centered on gileppe lake at the foot of the ardenne massif belgium institut geographique militaire and institut geographique national igm ign levelings of 1948 and 1974 yielded additional information the data were corrected for collimation and thermal errors other sources of error earth tides atmospheric refraction rod miscalibration were estimated and corrections were made when necessary random errors of individual surveys range from 0 15 to 0 74 mm km the recorded elevation changes indicate the existence of tilted segments some 5 to 10 km in length with yearly tilt values amounting up to 2 rads fault movements of a few mm yr are also demonstrated the segment limits are spatially stable from one year to the next but very frequent sense reversals of the vertical motions are observed this explains why the total movement over a 20 to 30 year period is barely higher than the yearly displacements various nontectonic causes of vertical ground movement e g monument instability varying water loading of the lake sediment compaction etc have been considered yielding little satisfactory explanation of the patterns of observed elevation changes we propose that the recorded motions which we call reversible fault creep and reversible tilt respectively are a true tectonic signal reflecting the tectonic noise which accompanies the long term deformation of uplifting areas in intraplate settings such movements are characteristic of fault segments which may occasionally generate earthquakes

gps applications for geodynamics and earthquake studies geodetic measurements obtained with the global positioning system gps are increasingly more widely applied in geophysical studies in this paper we review the changes to the technology of gps geodesy over the last five years that are responsible for this increased applicability we survey geophysical investigations employing gps to measure coseismic postseismic and interseismic deformation plate motion and crustal deformation at plate boundaries volcano deformation and the deformation associated with glacial isostatic adjustment and its application to sea level studies we emphasize the use of gps determinations for the modeling of this wide variety of geophysical phenomena we also discuss the recent advent of permanent gps networks for regional geophysical studies as well as the possible future of gps surveying in light of the recent advances

geometry and grain size characteristics of the basal surface of a braided river deposit description of the three dimensional geometry and grain size patterns of fluvial deposits and their relationship to the morphodynamics of the river has been an elusive objective in sedimentology hindered by limited exposure and the time scale of fluvial dynamics in small scale physical models the time scales are short enough to map river morphology and sedimentology during significant and continuous morphological development of the river and its deposits especially for braided rivers using close range digital photogrammetry the dynamics of the river morphology and resulting deposit geometry and sedimentology were captured using digital elevation model differencing techniques combined with automated grain size mapping from image texture analysis using these novel methods we show the temporal development and characteristics of braided river deposit geometry and for the first time map the characteristics and development of the basal surface of braided river deposits in relation to river morphodynamics and formative processes the basal surface has considerable relief wide variation in grain size similar to that of the river as a whole develops progressively over time by switching of channels producing adjacent patches and ribbons of basal incision of different ages and is only partially related to bed scour associated with laterally migrating channel confluences

displacement of surface monuments vertical motion several measurements of vertical ground motion at pinon flat observatory california indicate the overall weakness and instability of the earth s weathered surface with respect to the underlying rock cumulative long period motions of order 0 5 mm per year dominate these records though smaller elastic deformations caused by precipitation loading atmospheric loading and tidal strains are evident at higher frequencies all of these help to characterize the near surface material the long period records suggest that near surface weathering is the dominant influence on monument motion at least at this site on crystalline rock in a semi arid environment rainfall loading gives an average vertical modulus of 2 6 gpa for the material in the uppermost 26 m of the ground compared with 88 gpa for granite under moderate confining stress atmospheric loading gives similar results but indicates the ground is permeable to airflow at periods longer than a few hours earth tide records show poisson s ratio to be 0 09 in contrast to the normative range of 0 2 0 25 establishing that horizontal strains couple only weakly into vertical ones so that vertical strains near the surface are a poor measure of areal strain the form of the ground surface displacement power spectrum indicates that analyses of geodetic surveys would be improved with the inclusion of a monument positioning error budget that increases with time because of ground instability and the generally small rate of crustal tectonic motions deeply emplaced monuments will be needed for observational programs designed to detect short term changes in crustal deformation over baselengths of order 10 km and less

shallow radar sharad sounding observations of the medusae fossae formation mars the sharad shallow radar sounding radar on the mars reconnaissance orbiter detects subsurface reflections in the eastern and western parts of the medusae fossae formation mff the radar waves penetrate up to 580 m of the mff and detect clear subsurface interfaces in two locations west mff between 150 and 155 e and east mff between 209 and 213 e analysis of sharad radargrams suggests that the real part of the permittivity is 3 0 which falls within the range of permittivity values inferred from marsis data for thicker parts of the mff the sharad data cannot uniquely determine the composition of the mff material but the low permittivity implies that the upper few hundred meters of the mff material has a high porosity one possibility is that the mff is comprised of low density welded or interlocked pyroclastic deposits that are capable of sustaining the steep sided yardangs and ridges seen in imagery the sharad surface echo power across the mff is low relative to typical martian plains and completely disappears in parts of the east mff that correspond to the radar dark stealth region these areas are extremely rough at centimeter to meter scales and the lack of echo power is most likely due to a combination of surface roughness and a low near surface permittivity that reduces the echo strength from any locally flat regions there is also no radar evidence for internal layering in any of the sharad data for the mff despite the fact that tens of meters scale layering is apparent in infrared and visible wavelength images of nearby areas these interfaces may not be detected in sharad data if their permittivity contrasts are low or if the layers are discontinuous the lack of closely spaced internal radar reflectors suggests that the mff is not an equatorial analog to the current martian polar deposits which show clear evidence of multiple internal layers in sharad data

monument motion and measurements of crustal velocities it is usually assumed in geodetic studies that measurement errors are independent from one measurement to the next and that the rate of deformation velocity is constant over the duration of the experiment any temporal correlation between measurements can substantially affect the uncertainty in this velocity estimate when it is determined from the time series of measurements one source of possible long term correlation is motion of the geodetic monument with respect to the deep crust available measurements suggest that this motion introduces errors that have the form of a random walk process we show how such errors affect the uncertainty of velocity estimates for a geodetic experiment of set duration we calculate the velocity uncertainty as a function of the number of observations and of the relative amount of correlated and uncorrelated noise we find that 1 neglecting long term temporal correlations makes the uncertainty in the estimated velocities much too small and that 2 when the correlated and independent noise sources are of similar magnitude the expected improvement in uncertainty from having more measurement is not realized there is almost no improvement in some cases we have also examined the effect of outliers blunders on the velocity uncertainty for a frequency of outliers typical of geodetic field campaigns the previous two conclusions remain unchanged these results suggest that long term correlations have a large effect on estimating deformation rates unless these correlations are small frequent observations give little advantage if frequent observations are planned the amount of correlated noise due to monument instability must be kept small if the full capabilities of the measurement technique are to be realized

a new velocity field for africa from combined gps and doris space geodetic solutions contribution to the definition of the african reference frame afref 1 we analyzed 16 years of gps and 17 years of doppler orbitography and radiopositioning integrated by satellite doris data at continuously operating geodetic sites in africa and surroundings to describe the present day kinematics of the nubian and somalian plates and constrain relative motions across the east african rift the resulting velocity field describes horizontal and vertical motion at 133 gps sites and 9 doris sites horizontal velocities at sites located on stable nubia fit a single plate model with a weighted root mean square residual of 0 6 mm yr maximum residual 1 mm yr an upper bound for plate wide motions and for regional scale deformation in the seismically active southern africa and cameroon volcanic line we confirm significant southward motion 1 5 mm yr in morocco with respect to nubia consistent with earlier findings we propose an updated angular velocity for the divergence between nubia and somalia which provides the kinematic boundary conditions to rifting in east africa we update a plate motion model for the east african rift and revise the counterclockwise rotation of the victoria plate and clockwise rotation of the rovuma plate with respect to nubia vertical velocities range from 2 to 2 mm yr close to their uncertainties with no clear geographic pattern this study provides the first continent wide position velocity solution for africa expressed in international terrestrial reference frame itrf2008 a contribution to the upcoming african reference frame afref except for a few regions the african continent remains largely under sampled by continuous space geodetic data efforts are needed to augment the geodetic infrastructure and openly share existing data sets so that the objectives of afref can be fully reached

sensitivity of crustal deformation instruments to changes in secular rate a variety of instruments including borehole strainmeters water wells creepmeters laser ranging and differential magnetometers are used to monitor crustal deformation in areas that are prone to geologic hazards such as earthquakes and volcanic eruptions in monitoring the deformation one typically examines the data for either a change in rate or a simple offset in the record however one needs to place a statistical confidence level that the detected signal differs from the background noise calculation of the statistical confidence level may be done using the formalism of the matched filter whose output is the signal to noise ratio two ingredients are needed to form a matched filter 1 the power density spectrum of the instrument and 2 the functional form of the signal that we desire to detect using the available crustal deformation data from the parkfield california network the background noise for individual instruments as a function of frequency f is estimated using the traditional method of the power density spectra except for two color laser distance ranging data the power spectra for most of the instruments have a frequency dependence of f n where 2 n 3 the confidence level with which a hypothesized signal is present is determined directly from the signal to noise ratio with the numerator being a function of the signal and the denominator being a function of the power spectrum using a creepmeter as an example a 0 04 mm change occurring over 1 hour a 0 06 mm occurring over 10 hours or 0 20 mm over 100 hours are all signals for which 2 and therefore have only a 5 confidence that these signals could be background noise

assessing the potential for measuring europa s tidal love number h 2 using radar sounder and topographic imager data abstract the tidal love number h 2 is a key geophysical measurement for the characterization of europa s interior especially of its outer ice shell if a subsurface ocean is present we performed numerical simulations to assess the potential for estimating h 2 using altimetric measurements with a combination of radar sounding and stereo imaging data the measurement principle exploits both delay and doppler information in the radar surface return in combination with topography from a digital terrain model dtm the resulting radar range measurements at cross over locations can be used in combination with radio science doppler data for an improved trajectory solution and for estimating the h 2 love number our simulation results suggest that the absolute accuracy of h 2 from the joint analysis of reason radar for europa assessment and sounding ocean to near surface surface return and eis europa imaging system dtm data will be in the range of 0 04 0 17 assuming full radio link coverage the error is controlled by the snr budget and dtm quality both dependent on the surface properties of europa we estimate that this would unambiguously confirm or reject the global ocean hypothesis and in combination with a nominal radio science based measurement of the tidal love number k 2 constrain the thickness of europa s outer ice shell to up to 15 km

a semiautomated multilayer picking algorithm for ice sheet radar echograms applied to ground based near surface data snow accumulation over an ice sheet is the sole mass input making it a primary measurement for understanding the past present and future mass balance near surface frequency modulated continuous wave fmcw radars image isochronous firn layers recording accumulation histories the semiautomated multilayer picking algorithm sampa was designed and developed to trace annual accumulation layers in polar firn from both airborne and ground based radars the sampa algorithm is based on the radon transform rt computed by blocks and angular orientations over a radar echogram for each echogram s block the rt maps firn segmented layer features into peaks which are picked using amplitude and width threshold parameters of peaks a backward rt is then computed for each corresponding block mapping the peaks back into picked segmented layers the segmented layers are then connected and smoothed to achieve a final layer pick across the echogram once input parameters are trained sampa operates autonomously and can process hundreds of kilometers of radar data picking more than 40 layers sampa final pick results and layer numbering still require a cursory manual adjustment to correct noncontinuous picks which are likely not annual and to correct for inconsistency in layer numbering despite the manual effort to train and check sampa results it is an efficient tool for picking multiple accumulation layers in polar firn reducing time over manual digitizing efforts the trackability of good detected layers is greater than 90

detecting strain in the yucca mountain area nevada from repeated surveys of the relative motions between geodetic stations claim black mile 67tjs and wahomie fig 1 from 1991 through 1997 wernicke et al 1 deduce a n65 w strain accumulation rate of 50 9 nanostrains per year 2 across the proposed high level radioactive waste disposal repository at yucca mountain nevada that strain rate is sufficient to indicate a higher than expected earthquake hazard at the repository an earlier 1983 1993 u s geological survey usgs measurement table 1 of the strain accumulation in the network black triangles in fig 1 found a n65 w strain rate of 8 20 nanostrains per year a rate not significantly different from zero 3 although the two measurements are marginally consistent at the 95 confidence level that is the difference 42 22 nanostrains per year is less than 2 standard deviations sd the earthquake hazard implications are somewhat different the usgs strain determination is the better of the two measurements wernicke et al did not include the effects of monument instability in their error budget and as a consequence have significantly underestimated the uncertainties in their measurements moreover in their interpretation of the data they did not give proper weight to the coseismic and postseismic effects of the little skull mountain earthquake june 29 1992 m 5 4

displacement of surface monuments horizontal motion measurements of tectonic deformation depend on both accurate instrumentation and adequate coupling of the apparatus to the earth s crust existing techniques capable of resolving the signals of interest strain rates of 10 n yr are mainly observatory based the limitation in the baselength of these instruments 1 km results in a requirement that the reference monuments be exceptionally stable 10 tzm yr however records from pition flat observatory california show that the actual horizontal displacements for massive near surface monuments eraplaced in competent weathered granite are of the order of 50 tzm yr the low noise level of the strain measurements at this site indicates that this magnitude of monument displacement is abnormally small until high accuracy geodetic techniques are developed sophisticated monuments or monument monitoring devices will be necessary to record faithfully continuous crustal deformation

strain and rotation rate patterns of mainland greece from continuous gps data and comparison between seismic and geodetic moment release we processed data from 100 continuous gps stations to provide new insights into the crustal motion and deformation of central and western greece we used the derived velocity field to evaluate two dimensional strain and rotation rate tensors and we mapped the dilatation and maximum shear strain rates in central peloponnese and epirus we documented a 90 switch in the extension direction which can be explained on the basis of the plate boundary configuration evidence for an extended deformation pattern in central greece was found additionally we detected two pairs of shear belts one in akarnania nw peloponnese and one in north aegean we delineated two rotational domains that dominate the present day pattern moreover we saw no geodetic evidence for north anatolian fault growth toward central greece we translated the geodetic strain rates into rates of seismic moment release and compared them with earthquake catalog based moment rates in the central ionian sea the geodetic strain is completely released seismically which is indicative of a fully coupled seismogenic zone however for most of the study area the geodesy based moment rates are at least 2 times higher than the earthquake based rates we attribute this mainly to earthquake catalog representativity over the long term situation however for the gulf of corinth it is unrealistic to associate the high ratio of geodetic to seismic moment rates only to incompleteness of the earthquake catalog instead long term aseismic deformation must be an important mechanism accommodating a considerable portion of the strain budget especially at its western part

contemporary horizontal velocity and strain rate fields of the pacific australian plate boundary zone through new zealand we have inverted velocity solutions from nine geodetic networks distributed across new zealand to derive present day continuous horizontal velocity and strain rate fields at the earth s surface throughout the country the nine networks contain a total of 362 global positioning system gps stations that have been observed at least twice and at least a year apart between 1991 and 1998 the model velocity field is expanded as bicubic spline interpolation functions defined within a curvilinear grid that covers the country and extends into the assumed rigid australian and pacific plates to west and east the inversion jointly minimizes the magnitudes of fitted strain rates and the misfit to the observed velocity data the spline technique allows high spatial resolution of strain rate variations especially in regions with spatially dense gps data expansion of the model velocity field on the surface of a sphere allows arbitrarily large areas to be studied previously known aspects of new zealand plate boundary deformation are highlighted with improved resolution including back arc extension in the taupo volcanic zone rotation of the hikurangi forearc away from this zone in the north island and a band of high shear strain rate under the southern alps to the southeast of the alpine fault our results reveal several new features including a region of enhanced shear straining apparently associated with strike slip faults in the southern north island and a band of contractional straining subparallel and well east of the alpine fault that is similar to features found in numerical and sandbox models of continental collision

automatic extraction and analysis of ice layering in radar sounder data nowadays the interest on the development of orbiting radar sounders for the observation of earth polar areas is increasing in this context the analysis of the structure of the ice stratigraphy is of primary importance for the study of the past history and for the prediction of the evpolution of icy environments however as proven by planetary missions orbiting radar sounders provide a huge amount of data thus the development of automatic techniques for the analysis of these data is of fundamental importance for proper data exploitation in this paper we propose a novel method for the automatic detection of subsurface linear features from radar sounder data acquired in icy regions showing extended layering the proposed method allows the estimation of the position of the linear features with subpixel accuracy moreover each detected linear interface is treated as a single object which is completely described by the position of its points the estimated local width and the contrast this allows the direct measurement of geometrical and radiometric parameters e g slope angle and intensity without the need of further postprocessing steps this paper also proposes some measurements for deriving from the output of the proposed technique important variables that can characterize quantitatively the properties of the detected linear features e g mean depth and mean intensity and their distribution e g number and density of layers the effectiveness of the proposed method is confirmed by the results obtained on several radargrams acquired by the shallow radar on the north pole of mars

noise in gps displacement measurements from southern california and southern nevada 1 time series of position changes estimated from data from 236 continuously recording gps receivers operating in southern california and southern nevada are evaluated for noise models that characterize their temporal correlations the lengths of the time series range between 3 5 and 10 years after adjusting these data for postseismic deformation offsets and annual periodicities i find that about one half of the time series have temporal correlations that are categorized as either flicker or random walk noise the remaining time series can be best categorized as either a combination of flicker and random walk power law noise first order gauss markov plus random walk noise or power law plus broadband seasonal noise a variety of geodetic monuments are used in southern california and nevada including deeply braced designs cement piers pins drilled in outcrop and buildings when i evaluate the noise for each time series in terms of an estimate of the standard error in velocity i find that the sites with the smallest errors are those located in nevada using deeply braced monuments sites that are installed within regions of active pumping both for groundwater and oil had the largest standard errors in velocity comparison of monument stability as measured by standard error in rate with average annual rainfall nearby indicates a marginally significant correlation in addition even though regional filtering removed much of the common mode signals in these time series there still remains a common mode seasonal signal which can and should be removed

monitoring and modelling morphological change in a braided gravel bed river using high resolution gps based survey recent research in fluvial geomorphology has emphasized the direct monitoring of channel topography as a useful tool to better understand the interrelationship between river form and process and in particular to estimate bedload transport rates and reach scale sediment budgets until recently however this morphometric approach has been limited to comparison of repeatedly surveyed cross sections with the associated problems of low frequency sampling and an emphasis on cross stream as opposed to downstream morphological dynamics recent advances in analytical photogrammetry have however permitted the acquisition of data at sufficient resolutions to represent macroform 101 m and microform 10 m channel geometry in fully three dimensions while inherently spatially distributed the photogrammetric approach to land surveying is however restricted to observable areas of the channel and is thus of limited use in the subaqueous zone especially if flows are turbid or highly coloured this paper presents an alternative approach to the study of three dimensional morphological dynamics of a divided reach of the gravelly river feshie scotland in which topographic survey of both exposed and submerged areas of the reach was undertaken using the global positioning system gps survey results from two field programmes in 1998 and 1999 are presented in which a geotronics geotracer 2000 real time kinematic gps receiving unit was used to survey a 200 80 m reach rapid radial survey methods were employed permitting the collection of 2000 survey points per day giving a mean density over the 13 ha reach of 1 1 points per square metre a detailed assessment of survey errors and dem quality is presented and a limit of detection of c 10 cm proposed as an upper threshold for the identification of significant change between dems preliminary interpretation of channel dynamics in 1998 99 reveals relatively little change to the overall macroscale reach structure dem differencing techniques however highlight important local changes including the progradation of submerged bar fronts bar head aggradation and scour along major channel thalwegs and the erosion of fines from sloughs copyright 2000 john wiley sons ltd

interseismic crustal deformation of frontal thrust fault system in the chiayi tainan area taiwan abstract we derive a velocity field using gps data between 1993 and 2007 in the chiayi tainan area located in the deformation front of the taiwan mountain belt the crustal motion with respect to penghu shows large velocities of about 33 44 mm yr in the west northwest to west directions in the western foothills and the velocities decrease westward to 0 5 mm yr in the coastal area significant uplift rates of 5 20 mm yr are observed at sites to the east of the jiuchiunken muchiliao liuchia fault jmlf system we use a block model a buried dislocation model and a two dimensional fault model to invert for fault geometries and slip rates on major frontal thrust faults modeling results from a block model show the inferred long term slip rate of 42 mm yr in the direction of 280 and the maximum back slip rate of 38 mm yr on a 23 east dipping fault extending to 13 km at depth on the other hand the buried dislocation model results in a horizontal decollement at a depth of 8 km with a uniform slip rate of 41 6 mm yr if we connect the top edge of decollement to the surface trace of jmlf as a potential future rupture a 22 east dipping fault is required results from both block model and buried dislocation model suggest the jmlf is nearly fully locked the results of two dimensional fault models show the frontal thrust faults have slip rates of less than 2 mm yr at shallow depths and the inferred decollement is sub horizontal 5 7 at a depth of 10 km with slip rates of 44 46 mm yr results of various approaches show general agreement on fault geometries and slip rates and reveal that the frontal thrust fault system has a high potential for large earthquakes

how do gravel bed rivers braid sedimentary processes and bed forms leading to the onset of braiding were observed in small scale hydraulic models of gravel bed streams the laboratory streams had a variety of combinations of constant discharge and slope but identical bed material particle size distributions from initially straight channels braiding occurred by four different processes deposition and accumulation of a central bar chute cutoff of point bars conversion of single transverse unit bars to mid channel braid bars and dissection of multiple bars in these experiments the chute cutoff mechanism was the most common but the predominant braiding mechanism depends upon sediment mobility excess bed shear stress and the bed form regime at very low excess bed shear stress the central bar process dominates but at higher excess bed shear stress slip face unit bars are more common bed scour at confluences is more pronounced and propogation of alternate convergence scour and divergence deposition is more likely thus chu

distortion of isochronous layers in ice revealed by ground penetrating radar in addition to measuring ice sheet thickness ground penetrating radar can be used to delineate reflections in ice sheets1 2 3 these reflections are generally accepted to result from layers of isochronous deposition of snow and can reveal much about the dynamics of the ice flow here we present ground penetrating radar data from fletcher promontory antarctica which show arches and troughs in isochronous ice layers to a depth of 100 m we demonstrate that the origin of these features can be determined by their growth with depth and many features result from local anomalies in accumulation rate which can be correlated with the ice surface slope one arch appears to be the result of a local anomaly in vertical strain rate its proximity to the ice divide width and growth with depth indicate that this arch is one of a class of features postulated by raymond4 but not previously shown to exist in the field such a feature is an indication of the nonlinear rheology of ice and requires that palaeoclimate records from ice cores extracted from the vicinity of ice divides underlain by similar features should be specifically corrected for such effects on ice flow

modelling bedload yield in braided gravel bed rivers abstract this paper outlines an approach for estimating the annual bedload yield of a braided channel this procedure is based on the extension of theory of flow and sediment transport in braided rivers recently presented by paola 1996 the revised approach accounts explicitly for the relationship between increasing discharge and varying channel hydraulics and is suitable for use in obtaining bedload transport rate estimates over a range of discharges integration of such estimates using flow duration data allows annual bedload yield to be determined model parameterisation is achieved using topographic survey data for the waimakariri river new zealand comparison of modelled bedload yield with values estimated from repeated topographic surveys indicates that the model is able to accurately predict both the medium term c 30 years mean annual bedload yield of the waimakariri at crossbank the section 17 8 km upstream of the river mouth and also short term fluctuations in bedload yield associated with varying annual flow statistics streamwise patterns of volumetric erosion and deposition determined for a 45 km length of the waimakariri using the model are also in broad agreement with trends identified in topographic survey data for the period 1961 1997 however significant deviations between modelled and surveyed volumes of cut and fill are evident at some locations comparison of model performance with conventional applications of bedload transport equations which tend to underestimate transport rates for braided channels suggests that the approach presented here may represent a significant improvement this is the case because the model quantifies the relationship between braid intensity and spatial variability in flow hydraulics at a cross section output from the model suggests that braided rivers may transport a significant proportion of their annual bedload at lower discharges than those indicated by earlier theoretical approaches results also provide quantitative support for the argument that increased intensity of braiding may promote higher rates of bedload transport in gravel bed rivers

correlated errors in geodetic time series implications for time dependent deformation analysis of frequent trilateration observations from the two color electronic distance measuring networks in california demonstrate that the noise power spectra are dominated by white noise at higher frequencies and power law behavior at lower frequencies in contrast earth scientists typically have assumed that only white noise is present in a geodetic time series since a combination of infrequent measurements and low precision usually preclude identifying the time correlated signature in such data after removing a linear trend from the two color data it becomes evident that there are primarily two recognizable types of time correlated noise present in the residuals the first type is a seasonal variation in displacement which is probably a result of measuring to shallow surface monuments installed in clayey soil which responds to seasonally occurring rainfall this noise is significant only for a small fraction of the sites analyzed the second type of correlated noise becomes evident only after spectral analysis of line length changes and shows a functional relation at long periods between power and frequency of 1 where is frequency and 2 with 2 this type of correlated noise is termed random walk noise and its source is mainly thought to be small random motions of geodetic monuments with respect to the earth s crust though other sources are possible because the line length changes in the two color networks are measured at irregular intervals power spectral techniques cannot reliably estimate the level of 1 noise rather we also use here a maximum likelihood estimation technique which assumes that there are only two sources of noise in the residual time series white noise and random walk noise and estimates the amount of each from this analysis we find that the random walk noise level averages about 1 3 mm yr and that our estimates of the white noise component confirm theoretical limitations of the measurement technique in addition the seasonal noise can be as large as 3 mm in amplitude but typically is less than 0 5 mm because of the presence of random walk noise in these time series modeling and interpretation of the geodetic data must account for this source of error by way of example we show that estimating the time varying strain tensor a form of spatial averaging from geodetic data having both random walk and white noise error components results in seemingly significant variations in the rate of strain accumulation spatial averaging does reduce the size of both noise components but not their relative influence on the resulting strain accumulation model

relative motion between the caribbean and north american plates and related boundary zone deformation from a decade of gps observations global positioning system gps measurements in 1986 1994 and 1995 at sites in dominican republic puerto rico cuba and grand turk define the velocity of the caribbean plate relative to north america the data show eastward motion of the caribbean plate at a rate of 21 1 mm yr 1 standard error in the vicinity of southern dominican republic a factor of 2 higher than the nuvel 1a plate motion model prediction of 11 3 mm yr independent measurements on san andres island and an euler vector derived from these data also suggest a rate that is much higher than the nuvel 1a model available data combined with simple elastic strain models give the following slip rate estimates for major left lateral faults in hispaniola 1 the north hispaniola fault offshore the north coast of hispaniola 4 3 mm yr 2 the septentrional fault in northern dominican republic 8 3 mm yr and 3 the enriquillo fault in southern dominican republic and haiti 8 4 mm yr the relatively high plate motion rate and fault slip rates suggested by our study combined with evidence for strain accumulation and historical seismicity imply that seismic risk in the region may be higher than previous estimates based on low plate rate low fault slip rate models and the relatively low rate of seismicity over the last century

observations of bedload movement bar development and sediment supply in the braided ohau river relative bedload transport rate and hydraulic parameters were measured on two occasions in a reach of the braided gravel bedded ohau river each reach contained a deep fast flowing chute leading to an area of diverging shallow flow which contained a middle bar the measurements are self consistent and indicate that where flow is concentrated in a deep chute shear stress is high but where flow diverges depth slope and shear stress decrease in the first survey the bed was scoured in the chute and sediment transport rates were high but where flow diverged sediment transport rate decreased it appears that deposition leads to bar growth bar growth in turn reduces slope and depth deposition is encouraged and the bar continues to grow vertically laterally and upstream in the second survey no sediment transport was observed despite hydraulic conditions very similar to the first survey the absence of sediment transport is attributed to the cessation of sediment supply to the river channel

noise properties of continuous gps data from concrete pillar geodetic monuments in new zealand and comparison with data from u s deep drilled braced monuments 1 reducing noise levels in geodetic data is critical for the interpretation and modeling of geophysically interesting signals in this paper i estimate noise properties of continuous gps time series collected on concrete pillar monuments and compare them with similar data from deep drilled braced monuments that are considered the most stable three dimensional monuments available i show that the time series noise properties are very similar between the monument types at least for time series up to 4 5 years duration differences between the monument types are therefore not a dominant influence on these time series implying that the less expensive concrete pillar monuments are a valid choice for recording many signals of geophysical interest

active width of gravel bed braided rivers previous analyses have identified the active width of braided rivers the bed area over which bed load flux and short term morphological change occurs as an important element of braiding dynamics and predictions of bed load flux here we compare theoretical predictions of active width in gravel bed braided rivers with observations from sunwapta river and from a generic physical model of gravel braided rivers to provide general observations of the variation in active width and to develop an understanding of the causes of variation bed topography was surveyed daily along a 150 m reach of the pro glacial sunwapta river for a total of four weeks during summer when flow was above threshold for morphological activity in the laboratory detailed digital elevation models dems were derived from photogrammetric survey at regular intervals during a constant discharge run from the field and flume observations there is considerable local and circumstantial variation in active width but also a general trend in average active width with increasing discharge there is also a clear relationship of active width with active braiding index number of active branches in the braided channel network and with dimensionless stream power which appears to be consistent across the range of data from field and physical models thus there is a link between active width and the river morphology and dynamics and the possibility of a general relationship for estimating active width from channel pattern properties or reach scale stream power values from which approximate bedload flux calculations may be made the analysis also raises questions about differences between hydraulically based numerical model computations of instantaneous active width and observation of time integrated morphological active width understanding these differences can give insight into the nature of bedload transport in braided rivers and the relationship to morphological processes of braiding copyright 2011 john wiley sons ltd

new boundary conditions for the west antarctic ice sheet subglacial topography beneath pine island glacier 1 predictions about future changes in the amundsen sea sector of the west antarctic ice sheet wais have been hampered by poorly known subglacial topography extensive airborne survey has allowed us to derive improved subglacial topography for the pine island glacier basin the trunk of this glacier lies in a narrow 250 km long 500 m deep sub glacial trough suggesting a long lived and constrained ice stream two tributaries lie in similar troughs others lie in less defined shallower troughs the lower basin of the glacier is surrounded by bedrock which after deglaciation and isostatic rebound could rise above sea level this feature would impede ice sheet collapse initiated near the grounding line of this glacier and prevent its progress into the deepest portions of wais the inland slope of the bed beneath the trunk of the glacier however confirms potential instability of the lower basin containing sufficient ice to raise global sea by 24 cm

accumulation and erosion of mars south polar layered deposits mars polar regions are covered with ice rich layered deposits that potentially contain a record of climate variations the sounding radar sharad on the mars reconnaissance orbiter mapped detailed subsurface stratigraphy in the promethei lingula region of the south polar plateau planum australe radar reflections interpreted as layers are correlated across adjacent orbits and are continuous for up to 150 kilometers along spacecraft orbital tracks the reflectors are often separated into discrete reflector sequences and strong echoes are seen as deep as 1 kilometer in some cases the sequences are dipping with respect to each other suggesting an interdepositional period of erosion in australe sulci layers are exhumed indicating recent erosion

observations on sediment mobility in a large gravel bed river article this study investigates sediment mobility in a large gravel bed river tagliamento river northeastern italy field data were used to identify the morphological effectiveness of a range of flows floods with recurrence interval b1 to 3 5 year and for a detailed analysis of the partial transport condition the analyses were carried out on three cross sections where a number of areas representative of different morphological units main and secondary channels low and high bars islands were painted grain size of the painted area was measured using a photographic method monitoring of bed mobility during the study period supplied new photographs of the painted areas measurements of size and travel distance of the mobilized particles and estimate of flow depth after each flood event our analyses have shown that with dimensionless shear stress around 0 073 17 n m 2 the morphological effect over the painted areas was primarily partial transport while with stresses n0 1 25 n m 2 the bed experienced full mobility i e all the painted particles were transported or totally buried full sediment mobility was observed on lower morphological units i e main and secondary channels under floods with very high frequency rib1 y whereas on the low bars full mobility occurred under floods with a recurrence interval slightly n1 year instead fine deposition and partial transport conditions were observed on the higher bars even after the largest of the monitored floods ri 3 5 y the analysis of the partial transport condition relies on more than 3500 measurements of particle travel distance travel distances range from a few centimetres up to 22 m the transported particles were generally finer than the painted sediments and the analysis of the sediment transport ratio revealed that partial transport occurred under equal mobility conditions for particles finer than 32 mm and under size selective mobility for coarser fractions this appears to be corroborated for db32 mm by the insensitiveness of particle transport distance to particle sizes even if the exponent 1 of the relationship between the dimensionless shear stress and the maximum transported diameter would suggest that all fractions are transported under equal mobility conditions

layer optimized sar processing and slope estimation in radar sounder data englacial layers in antarctica and greenland are indicators of the dynamic rheological and subglacial configuration of the ice sheets airborne radar sounder data is the primary remote sensing solution for directly observing englacial layers and structures at the glacier catchment to ice sheet scale however when traditional along track synthetic aperture radar sar processing is applied steep layers can disappear limiting the detectability and interpretability of englacial layer geometry this study provides a reconstruction algorithm to address the problem of destructive phase interference during the radargram formation we develop and apply a novel sar processor optimized for layer detection that enhances the signal to noise ratio snr of specular reflectors the algorithm also enables the automatic estimation of layer slope we demonstrate the algorithm using data acquired at the institute ice stream west antarctica

estimation of intraplate strain accumulation in the new madrid seismic zone from repeat gps surveys the new madrid seismic zone nmsz a region within the eastern portion of the north american plate where great earthquakes occurred in 1811 1812 provides a type example of large earthquakes within a relatively stable continental interior assessing the scale and causes of deformation in such regions as well estimation of the recurrence interval for the large earthquakes within them has long been recognized as an important but challenging issue for which the advent of space based geodesy provides an important new tool here we report initial results from two global positioning system gps surveys of a geodetic network spanning the new madrid seismic zone because the expected strain signal is small the data were analyzed in three different ways first site velocities were estimated and analyzed for spatial gradients parallel and perpendicular to the trend of the major strike slip faults inferred from seismicity this analysis suggests but does not require a few millimeters per year of right lateral shear across the southern portion of the seismic zone consistent with the earthquake focal mechanisms second we divided the network into near field subnetworks and found possibly significant shear associated with approximately e w shortening within the southern nmsz and possible n s shortening across the left step connecting the presumed strike slip faults third we compared the strain observed along individual baselines to that predicted from the results of earlier near field surveys which combined gps and triangulation data in the southern part of the seismic zone we found general agreement with the earlier study although our data suggest lower strain rates hence after only 2 years of measurements the gps data suggest but do not yet require detectable strain accumulation however given that great earthquakes occur in the area and that our results are reasonably consistent with the results of other geodetic studies using different data and with earthquake mechanisms it seems likely that we are seeing strain accumulation in the southern nmsz a simple interpretation of the data as showing about 3 to 5 mm yr 1 of right lateral fault parallel motion implies a 1000 to 3300 year recurrence for great earthquakes with 5 to 10 m slip assuming all the accumulating strain is released seismically this recurrence interval may be an underestimate if the observed strains are largely postseismic effects of the 1811 1812 earthquakes a possibility suggested by the observation that plate wide data show less motion across the nmsz future surveys should resolve this issue as the longer measurement spans yield more precise velocity estimates

earthquake prediction a critical review summary earthquake prediction research has been conducted for over 100 years with no obvious successes claims of breakthroughs have failed to withstand scrutiny extensive searches have failed to find reliable precursors theoretical work suggests that faulting is a non linear process which is highly sensitive to unmeasurably fine details of the state of the earth in a large volume not just in the immediate vicinity of the hypocentre any small earthquake thus has some probability of cascading into a large event reliable issuing of alarms of imminent large earthquakes appears to be effectively impossible key word earthquake prediction

continuous gps measurements across the western alps 1996 1998 summary global positioning system gps data are analysed from three permanent sites two in the western alps grasse france and zimmerwald switzerland and the third in the po basin torino italy for the 2 5 year period from 1 january 1996 to 1 july 1998 an analysis of the stochastic properties of the position time series reveals a significant amount of spatially and temporally correlated noise which best fits a model combining white noise and flicker noise the coloured noise is drastically reduced by spatially filtering the time series suggesting that it is not due to site specific evects such as monument motion but rather to noise sources common to the three sites such as reference frame satellite orbit or earth orientation errors we find velocity uncertainties 95 per cent confidence interval of 2 7 mm yr 1 at gras 2 3 mm yr 1 at zimm and 2 9 mm yr 1 at tori the residual velocity in the eurasian reference frame is statistically greater than zero at zimm only with 2 4 2 3 mm yr 1 of motion in a nw direction these uncertainties place an upper bound on the expected deformation in the western alps velocities relative to stable eurasia do not exceed 3m m yr 1 corresponding to a maximum strain rate of 0 03 mstrain yr 1 over the gras tori zimm triangle

methodological sensitivity of morphometric estimates of coarse fluvial sediment transport abstract the estimation of fluvial sediment transport rate from measurements of morphological change has received growing recent interest the revival of the morphological method reflects continuing concern over traditional methods of rate determination but also the availability of new survey methods capable of high precision high resolution topographic monitoring remote sensing of river channels through aerial digital photogrammetry is a potentially attractive alternative to labour intensive ground surveys however while photogrammetry presents the opportunity to acquire survey data over large areas data precision and accuracy particularly in the vertical dimension are lower than in traditional ground survey methods this paper presents results of recent research in which digital elevation models dems have been developed for a reach of a large braided gravel bed river in scotland using both digital photogrammetry and high resolution rtk gps ground surveys a statistical level of change detection is assessed by comparing surfaces with independent check points the methodological sensitivity of the annual channel sediment budget 1999 2000 to the threshold is presented results suggest that while the remote survey methods employed here can be used to develop qualitatively convincing moderate precision dems of channel topography rmse 0 21 m the remaining errors imply significant limits on reliable change detection which lead to important information losses tests at a 95 confidence interval for change detection show that over 60 of channel deposition and 40 of erosion may be obscured by the lower level of precision associated with photogrammetric monitoring when compared to ground survey measurements this bias reflects the difficulty of detecting the topographic signature of widespread but shallow deposition on bar tops

a unified analysis of crustal motion in southern california 1970 2004 the scec crustal motion map 1 to determine crustal motions in and around southern california we have processed and combined trilateration data collected from 1970 to 1992 vlbi data from 1979 to 1992 and gps data from 1986 to 2004 a long temporal coverage required in part by the occurrence of several large earthquakes in this region from a series of solutions for station positions we have estimated interseismic velocities coseismic displacements and postseismic motions within the region from 31 n to 38 n and east to 114 w the final product includes estimated horizontal velocities for 1009 gps 190 trilateration and 16 vlbi points with ties between some of these used to stabilize the solution all motions are relative to the stable north american reference frame snarf as realized through the velocities of 20 gps stations this provides a relatively dense set of horizontal velocity estimates with well tested errors for the past quarter century over the plate boundary from 31 n to 36 5 n these velocities agree well with those from the plate boundary observatory which apply to a later time period we also estimated vertical velocities 533 of which have errors below 2 mm yr most of these velocities are less than 1 mm yr but they show 2 4 mm yr subsidence in the ventura and los angeles basins and in the salton trough our analysis also included estimates of coseismic and postseismic motions related to the 1992 landers 1994 northridge 1999 hector mine and 2003 san simeon earthquakes postseismic motions increase logarithmically over time with a time constant of about 10 days and generally mimic the direction and relative amplitude of the coseismic offsets

sharad sounding radar on the mars reconnaissance orbiter 1 sharad shallow radar is a sounding radar provided by agenzia spaziale italiana asi as a facility instrument on the mars reconnaissance orbiter mission its 20 mhz center frequency and 10 mhz bandwidth complement the lower frequency relatively narrower bandwidth capability of the marsis sounding radar a joint italian u s team has guided the experiment development and is responsible for data analysis and interpretation the radar transmits signals at a 700 hz pulse repetition frequency prf and collects reflections from both the surface and near subsurface of mars vertical and horizontal resolutions are respectively 15 m free space and 3 6 km cross track by 0 3 1 km along track the scientific objective of sharad is to map in selected locales dielectric interfaces to at least several hundred meters depth in the martian subsurface and to interpret these results in terms of the occurrence and distribution of expected materials including competent rock soil water and ice a signal to noise ratio of 50 db for a specular surface return is achieved with 10 w of radiated power by using range and azimuth focusing in ground data processing preprocessed data as well as range and azimuth focused data will be formatted according to planetary data system pds standards and be made available from the asi science data center asdc and from the geosciences node of the planetary data system pds important targets for sharad include the polar layered deposits sedimentary stacks especially in terra meridiani buried channel systems buried impact craters volcanic complexes and shallow ice deposits in equilibrium with the atmosphere

an integrated global model of present day plate motions and plate boundary deformation summary in this paper we present a global model gsrm 1 of both horizontal velocities on the earth s surface and horizontal strain rates for almost all deforming plate boundary zones a model strain rate field is obtained jointly with a global velocity field in the process of solving for a global velocity gradient tensor field in our model we perform a least squares fit between model velocities and observed geodetic velocities as well as between model strain rates and observed geological strain rates model velocities and strain rates are interpolated over a spherical earth using bi cubic bessel splines we include 3000 geodetic velocities from 50 different mostly published studies geological strain rates are obtained for central asia only and they are inferred from quaternary fault slip rates for all areas where no geological information is included a priori constraints are placed on the style and direction but not magnitude of the model strain rate field these constraints are taken from a seismic strain rate field inferred from normalized focal mechanisms of shallow earthquakes we present a global solution of the second invariant of the model strain rate field as well as strain rate solutions for a few selected plate boundary zones generally the strain rate tensor field is consistent with geological and seismological data with the assumption of plate rigidity for all areas other than the plate boundary zones we also present relative angular velocities for most plate pairs we find that in general there is a good agreement between the present day plate motions we obtain and longterm plate motions but a few significant differences exist the rotation rates for the indian arabian and nubian plates relative to eurasia are 30 13 and 50 per cent slower than the nuvel1a estimate respectively and the rotation rate for the nazca plate relative to south america is 17 per cent slower on the other hand caribbean north america motion is 76 per cent faster than the nuvel 1a estimate while crustal blocks in the india eurasia collision zone move significantly and self consistently with respect to bounding plates only a very small motion is predicted between the nubian and somalian plates by integrating plate boundary zone deformation with the traditional modelling of angular velocities of rigid plates we have obtained a model that has already been proven valuable in for instance redefining a no net rotation model of surface motions and by confirming a global correlation between seismicity rates and tectonic moment rates along subduction zones and within zones of continental deformation

the effects of survey frequency on estimates of scour and fill in a braided river model an erratum has been published for this article in earth surface processes and landforms 27 7 2002 795 estimates of scour and fill in rivers that are derived by differencing topographic surfaces are known to be negatively biased by local compensation of scour and fill between surveys but the magnitude of bias is not well known this study examines the effect of survey frequency on volumes of scour and fill over a period of active channel braiding in a small scale river model a 100 min high temporal resolution time series of digital elevation models is artificially coarsened by selectively removing models the resulting four overlapping time series have survey intervals of 10 min 20 min 50 min and 100 min cumulative scour and fill volumes for the 100 min period are compared between the four series it is concluded that the decay in measured volumes of scour and fill with increased survey interval can be described using inverse functions cumulative scour fill volumes are approximately 420 per cent greater over the study period for 10 min survey intervals than for a 100 min interval after the 100 min period of competent flow nearly 65 per cent of the channel area experienced significant compensation of scour and fill several compensation mechanisms were identified in association with braided channel kinetics including lateral channel migration the migration of bed forms and channel avulsion it is demonstrated that by negatively biasing scour fill and net estimates this error significantly affects morphological approaches to the estimation of bed load sediment transport copyright 2002 john wiley sons ltd

crustal velocity and strain rate fields in italy and surrounding regions new results from the analysis of permanent and non permanent gps networks summary we present a new geodetic velocity solution for italy and the surrounding areas obtained from an analysis of continuous and survey mode global positioning system observations collected between 1991 and 2002 we have combined local regional and global networks into a common reference frame velocity solution providing a new detailed picture of the regional scale deformation field in the central mediterranean our velocity estimates are computed with respect to a new stable eurasian reference frame constraining the kinematics of the greater african eurasian plate boundary system in the study area we provide strain rate values for the main seismotectonic districts which are in good agreement with the seismic deformation inferred from earthquake focal mechanisms the southern tyrrhenian area calabria the apennines the southeastern alps the southern dinarides and the albanides display deformation rates at the order of 20 30 nanostrain yr 1 the corsica sardinia block moves according to eurasian plate motions and there is no indication that the opening of the tyrrhenian is still active the pelagian and sicilian domains are separated by a northwest southeast discontinuity the sicily channel rifted area and marginally significant relative motion between the pelagian plateau and the african plate is also observed the southern tyrrhenian is affected by north south compression and accommodates up to 50 per cent of the africa eurasia relative plate motion whereas the calabrian arc exhibits 2 mm yr 1 northwest southeast extension the observed deformation pattern suggests the presence of a major approximately north south tectonic discontinuity separating the sicilian and calabrian domains an extensional boundary observed along peninsular italy coincides with the distribution of seismogenic faults along the axis of the apennines this boundary separates a tyrrhenian and an adriatic domain with diverging velocities orientated north nnw ward and northeastward respectively the apennines are extending perpendicularly to the chain axis at rates of less than 3 mm yr 1 and only in the outer northern apennines indications of active shortening are observed insignificant deformation is observed in the western po plain and the western alps while the central and eastern alps display north south shortening the eastern adriatic domain is shortening perpendicular to the dinaric front with strain rates increasing from north to south the locus of collision between the aegean balkan system and the adriatic and ionian domains is marked by the kephalonia fault system which accommodates up to 20 1 mm yr 1 of right lateral motion the deformation pattern observed in the peri adriatic domain is well described by a counter clockwise rotation of the adriatic microplate around a pole located in the western alps

gps derived crustal velocity tectonic deformation and strain in the indian himalayan arc abstract the present study elucidates velocity of the indian plate from 2013 to 2016 with the help of six continuously operating permanent global positioning system gps stations and tracks the crustal motion and direction directly by means of space based geodetic measurements the gps derived velocity estimates were computed with respect to 2008 international terrestrial reference frame itrf 08 and carried out almost all along the arc in the indian himalayan region ihr the velocity vectors indicate that the indian plate is moving towards the ne direction average velocity of 46 95 0 23 mm yr with higher movement towards the eastward direction 36 11 0 17 mm yr compared to the northward direction 29 02 0 16 mm yr variations in the plate motion between iisc and permanent gps stations suggest that presently the convergence rate is about 8 06 0 28 mm yr and 5 71 0 17 mm yr for higher himalaya and lesser himalaya respectively in addition the deformation rate was also calculated on the basis of baseline shortening between igs stations iisc and lhaz and permanent gps stations the results suggest that the deformation is about 11 68 1 32 mm yr above the main central thrust mct and 6 74 1 20 mm yr above the main boundary thrust mbt with respect to the indian plate iisc while it is 20 60 1 76 mm yr above the mct and 11 42 1 21 mm yr above the mbt with respect to eurasian plate lhaz the strain rate through gps measurement reveals that the maximum strain is accumulated in the central part of the himalaya between the mbt and mct indicating vulnerability of the central indian himalaya for future earthquakes

analysis of deformation data at parkfield california detection of a long term strain transient analysis of more than a decade of high quality data particularly those from the two color electronic distance meter edm in the parkfield california area reveals a significant transient in slip rate along the san andreas fault this transient consists of an increase in fault slip rate of 3 3 0 9 mm yr during 1993 0 to 1998 0 the most reliable fault creep instruments show a comparable increase in slip rate suggesting that the deformation is localized to the fault which breaks the surface there was also an increase in precipitation around 1993 it is unlikely however that this anomaly is due directly to hydrology as its spatial distribution is what would be expected for increased slip on the san andreas fault the increase in slip rate corresponds temporally to a dramatic increase in seismicity including the four largest earthquakes in the period 1984 1999 that occurred along a 6 km segment of the fault just to the north of the edm network there was also a previously reported anomaly in borehole shear strain gwyther et al 1996 that closely corresponds temporally to the transient in edm data solely on the basis of edm data the transient can be modeled as a slip event on a 10 km long segment of the fault the calculated shear strains from this model however are not consistent with the observed ones a compatible model can be found if there is increased aseismic slip to the northwest in conjunction with the four earthquakes support for this northwestern slip is provided by a recent study of slip rate based on microearthquake activity we speculate that this northwestern event served to load the fault to the southeast with the stress being partially released by the observed slip

inference of accumulation rate patterns from deep layers in glaciers and ice sheets the spatial pattern of accumulation rate can be inferred from internal layers in glaciers and ice sheets non dimensional analysis determines where finite strain can be neglected shallow layer approximation or approximated with a local one dimensional flow model local layer approxima tion and where gradients in strain rate along particle paths must be included deep layers we develop a general geophysical inverse procedure to infer the spatial pattern of accumulation rate along a steady state flowband using measured topography of the ice sheet surface bed and a deep layer a variety of thermomechanical ice flow models can be used in the forward problem to calculate surface topography and ice velocity which are used to calculate particle paths and internal layer shapes an objective tolerance criterion prevents over fitting the data after making site specific simplifications in the thermomechanical flow algorithm we find the accumulation rate along a flowband through taylor mouth a flank site on taylor dome antarctica using a layer at approximately 100 m depth or 20 of the ice thickness accumulation rate correlates with ice surface curvature at this site gradients along flow paths critically impact inference of both the accumulation pattern and the depth age relation in a 100 m core

gps derived crustal deformation analysis of kachchh zone of 2001 m7 7 earthquake western india abstract in this study we present the first estimates of crustal deformation using the time series 2009 2015 from gps network of gujarat gng comprising 10 gps continuous and 5 campaign mode stations in the seismically active kachchh region the gps data were processed using gamit globk glorg software and results reveal very low amount of intra plate deformation in this part of the indian plate international terrestrial reference frame itrf velocity of sites deduced in this study indicates 46 51 mm yr of motion with one sigma uncertainty a maximum of 3 0 0 5 mm yr of deformation has been estimated in the kachchh region however estimated strain rate from the velocity field indicates a maximum strain of 5 nano strain yr our results indicate deformation of a weak zone where earthquakes may trigger due to the combination of local as well as regional stress the analysis of strain tensors near the major fault systems kmf khf swf and gf indicates strike normal compression in the area the low rate of deformation derived in the present study is important to understand the seismic hazard level in this part of the indian intra plate

a method for estimating the mean bed load flux in braided rivers prediction of bed load flux remains a significant problem in understanding braided river morphodynamics for geomorphic and engineering applications two sets of data from laboratory experiments on braided networks performed at the university of trento italy and at the university of alberta canada provide the basis for development of a dimensionless bed load function and for testing a simple predictive model measured total sediment transport rates time averaged at equilibrium channel configuration collapse to a single dimensionless relationship based on dimensionless stream power bed load fluxes predicted by the parker and bagnold functions and cross section average hydraulic parameters under predict the bed load flux particularly at low shear stress this is consistent with previous observation and theory demonstrating the significant influence of transverse variability of the hydraulic parameters in controlling and predicting bed load flux a simple method for adjusting for this lateral variation is proposed for computing the sediment transport rate using topographic cross sections of braided rivers results show good agreement with the measured values suggesting that simple assumptions combined with the mean morphology of the channel may be sufficient to estimate mean bed load flux model predictions also highlight the significance of active bed width rather than bed shear stress as a fundamental ingredient in the prediction of the bed load rate and therefore as an important morphological property to be modelled the model also predicts similar behaviour in the at a station variability of bed load and in the importance of variation of active width relative to bed shear stress in the transport process

continuous monitoring of surface deformation at long valley caldera california with gps continuous global positioning system gps measurements at long valley caldera an active volcanic region in east central california have been made on the south side of the resurgent dome since early 1993 a site on the north side of the dome was added in late 1994 special adaptations for autonomous operation in remote regions and enhanced vertical precision were made the data record ongoing volcanic deformation consistent with uplift and expansion of the surface above a shallow magma chamber measurement precisions 1 standard error for absolute position coordinates i e relative to a global reference frame are 3 4 mm north 5 6 mm east and 10 12 mm vertical using 24 hour solutions corresponding velocity uncertainties for a 12 month period are about 2 mm yr in the horizontal components and 3 4 mm yr in the vertical component high precision can also be achieved for relative position coordinates on short 10 km baselines using broadcast ephemerides and observing times as short as 3 hours even when data are processed rapidly on site comparison of baseline length changes across the resurgent dome between the two gps sites and corresponding two color electronic distance measurements indicates similar extension rates within error 2 mm yr once we account for a random walk noise component in both systems that may reflect spurious monument motion both data sets suggest a pause in deformation for a 3 5 month period in mid 1995 when the extension rate across the dome decreased essentially to zero three dimensional positioning data from the two gps stations suggest a depth 5 8 1 6 km and location west side of the resurgent dome of a major inflation center in agreement with other geodetic techniques near the top of a magma chamber inferred from seismic data gps systems similar to those installed at long valley can provide a practical method for near real time monitoring and hazard assessment on many active volcanoes

new gps constraints on the kinematics of the apennines subduction abstract we present the velocity field of the italian area derived from continuous gps observations from 2003 to 2007 the gps sites were installed by different institutions and for different purposes they cover the whole country with a mean inter site distance of about 60 km and provide a valuable source of data to map the present day kinematics of the region the absolute itrf2005 rotation poles and rates of eurasia africa and adriatic plates are estimated to study the kinematics along their boundaries in the apennines belt the corsica sardinia block coherently moving as the eurasia plate is used as reference of the upper plate for the apennines subduction zone we apply a simple kinematic model to estimate the rates and spatial pattern of the subduction along the apennines we identify at least four different independently moving lower plates i e the adriatic diverging and internally segmented ionian sicily and africa converging plates with different subduction rates the conservative estimates of the subduction rate are 5 mm yr in the calabrian arc 1 5 mm yr in sicily and 0 9 mm yr in the northern apennines this variegate mixture of behaviors seems to reflect the variable lithospheric thickness and composition of the lower plates inherited from the mesozoic rifting an unexpected along strike contraction is observed along the western side of the central northern apennines velocities are estimated both relative to eurasia and relative to the deep and shallow hotspot reference frames hsrf the hotspot representation seems more coherent with the geophysical and geological constraints along the subduction system in which the adriatic and ionian plates move sw ward and their deeper slab portions provide an obstacle to the opposite relative mantle flow all these patterns better reconcile if the subduction process is conceived as a passive feature controlled by the far field plate velocities and the relative eastward mantle flow acting on a disrupted slab

deformation across the pacific north america plate boundary near san francisco california we have detected a narrow zone of compression between the coast ranges and the great valley and we have estimated slip rates for the san andreas rodgers creek and green valley faults just north of san francisco these results are based on an analysis of campaign and continuous global positioning system gps data collected between 1992 and 2000 in central california the zone of compression between the coast ranges and the great valley is 25 km wide the observations clearly show 3 8 1 5 mm yr 1 of shortening over this narrow zone the strike slip components are best fit by a model with 20 8 1 9 mm yr 1 slip on the san andreas fault 10 3 2 6 mm yr 1 on the rodgers creek fault and 8 1 2 1 mm yr 1 on the green valley fault the pacific sierra nevada great valley motion totals 39 2 3 8 mm yr 1 across a zone that is 120 km wide at the latitude of san francisco standard deviations are one the geodetic results suggest a higher than geologic rate for the green valley fault the geodetic results also suggest an inconsistency between geologic estimates of the san andreas rate and seismologic estimates of the depth of locking on the san andreas fault the only convergence observed is in the narrow zone along the border between the great valley and the coast ranges

the bifrost project gps determined 3 d displacement rates in fennoscandia from 800 days of continuous observations in the swepos network abstract this presentation summarizes results obtained from 800 days of operation of swepos the swedish permanent gps array located in the area of the fennoscandian land uplift swepos is the main measuring device for the bifrost project aiming primarily at determination of crustal motions and changes in global sea level in conjunction with postglacial rebound as a future prospect the project will contribute to determine present day changes in the oceanic water budget as well as strive for a more complete understanding of the viscoelastic structure of crust and mantle we show solutions of site positions obtained from the daily processing of the gps observations we determine their variations in time discerning them from plate or frame orientation and discuss a number of perturbation effects among these the possibility of random walk monument motion is considered the feasibility of single site solutions rather than baseline pairs is demonstrated on the basis of 800 days of operation of the permanent network data analysis is able to confirm the general rebound pattern comparison with both modelling results and evidence from mareograph and precise levelling shows high rates of vertical surface displacement from gps measurements in the centre of the pleistocene glaciation region we discuss the possibility of rate biases due to problems with the terrestrial reference frames

the mars observer laser altimeter investigation the primary objective of the mars observer laser altimeter mola investigation is to determine globally the topography of mars at a level suitable for addressing problems in geology and geophysics secondary objectives are to characterize the 1064 nm wavelength surface reflectivity of mars to contribute to analyses of global surface mineralogy and seasonal albedo changes to assist in addressing problems in atmospheric circulation and to provide geodetic control and topographic context for the assessment of possible future mars landing sites the principal components of mola are a diode pumped neodymium doped yttrium aluminum garnet laser transmitter that emits 1064 nm wavelength laser pulses a 0 5 m diameter telescope a silicon avalanche photodiode detector and a time interval unit with 10 ns resolution mola will provide measurements of the topography of mars within approximately 160 m footprints and a center to center along track foot print spacing of 300 m along the mars observer subspacecraft ground track the elevation measurements will be quantized with 1 5 m vertical resolution before correction for orbit and pointing induced errors mola profiles will be assembled into a global 0 2 deg x 0 2 deg grid that will be referenced to mars center of mass with an absolute accuracy of approximately 30 m other data products will include a global grid of topographic gradients corrected individual profiles and a global 0 2 deg x 0 2 deg grid of 1064 nm surface reflectivity

sensitivity test of the geodetic network in las canadas caldera tenerife for volcano monitoring abstract a 17 benchmark geodetic network in the volcanic area of the teide caldera canary islands has been utilised several times since 1982 to detect crustal movements associated with volcanic activity within the network as well as a procedure for solving configuration problems the network is located on the mid western side of the caldera where there are two different morphological zones that both have benchmarks the authors performed a sensitivity test of this geodetic network for volcano monitoring purposes to do so we use a deformation model to calculate surface displacement caused by a dike intrusion in a homogenous half space the depth and location of dike are changed to study the variation of the effects produced displacements the size and location of the intruded dike are found to play a major role in determining both the displacement pattern and magnitude when the dike is close to the surface there is an inversion of the surface displacement pattern and very large surface displacement at certain benchmarks such phenomena can serve as precursors of such dike eruptions our study show a clear need to extend the existing geodetic network to cover the full island for volcano monitoring purposes

echo source discrimination in single pass airborne radar sounding data from the dry valleys antarctica implications for orbital sounding of mars the interpretation of radar sounding data from mars where significant topographic relief occurs will require echo source discrimination to avoid the misinterpretation of surface echoes as arising from the subsurface this can be accomplished through the identification of all radar returns from the surface in order to positively identify subsurface echoes we have developed general techniques for this using airborne radar data from the dry valleys of antarctica these data were collected in a single pass including taylor glacier ice covered lake bonney and an ice free area of taylor valley the pulsed radar 52 5 67 5 mhz was coherently recorded our echo discrimination techniques included a radar simulator using a digital elevation model dem to predict the location and shape of surface echoes in the radar data real and simulated echo strengths were used to calculate a signal to clutter ratio this was complemented by the cross track migration of radar echoes onto the surface these migrated echoes were superimposed on the dem and imagery in order to correlate with surface features using these techniques enabled us to identify a number of echoes in the radar data as arising from the surface and to identify subsurface echoes including a continuous reflector under the main trunk of taylor glacier and multiple reflectors beneath the terminus of taylor glacier surface based radar confirms the thickness of the glacier at three crossing points the results illustrate the importance of using complementary techniques the usefulness of a dem and the limitations of single pass radar sounding data

instantaneous geodetic positioning at medium distances with the global positioning system we evaluate a new method of global positioning system gps data analysis called instantaneous positioning at spatial scale lengths typical of interstation spacings in a modern crustal motion network this method is more precise and versatile than traditional gps static and kinematic processing of multi epoch batches of data the key to instantaneous positioning is the ability to resolve integer cycle phase ambiguities with only a single epoch of dual frequency phase and pseudorange data rendering receiver cycle slips irrelevant we estimate three dimensional relative coordinates and atmospheric zenith delay parameters independently every 30 s over a 12 week period for baseline distances of 50 m 14 km and 37 km horizontal precision of a single epoch coordinate solution is about 15 mm and vertical precision is about 7 8 times worse removing that component of each time series which repeats with a period of exactly 1 sidereal day and thus manifests signal multipath reduces the scatter by about 50 in all components solution averaging of the high frequency time series can be performed using any number of measurement epochs to further improve coordinate precision we demonstrate that the daily coordinates estimated with instantaneous positioning are more precise by 20 50 per coordinate component than those estimated with 24 hour batch processing spectral analysis of the single epoch solutions indicates that the flicker noise characteristic of gps time series observed in lower frequency bands also affects gps solutions in the frequency band 0 01 mhz to 10 mhz we argue that the flicker noise is induced by tropospheric effects since modern gps receivers are capable of observing at frequencies as high as 10 hz our technique significantly overlaps and complements the frequency band of broadband seismology and benefits other research areas such as earthquake geodesy volcanology and gps meteorology

southern california permanent gps geodetic array error analysis of daily position estimates and site velocities we analyze time series of daily positions estimated from data collected by 10 continuously monitoring global positioning system gps sites in southern california during the 19 month period between the june 28 1992 mw 7 3 landers and january 17 1994 mw 6 7 northridge earthquakes each time series exhibits a linear tectonic signal and significant colored noise spectral power at frequencies in the range 5 yr 1 to 0 5 d 1 is dominated by white noise or possibly fractal white noise and is several orders of magnitude higher than what would be expected from random walk noise in this short period range attributed by others to geodetic monument motions estimating a single slope for the time series power spectra suggests fractal white noise processes with spectral indices of about 0 4 site velocity uncertainties assuming this fractal white noise model are 2 4 times larger than uncertainties obtained assuming a purely white noise model a combination white noise plus flicker noise spectral index of 1 model also fits the data and suggests that the velocity uncertainties should be 3 6 times larger than for the white noise model we cannot adequately distinguish between these two noise models nor can we rule out the possibility of a random walk signal at the lowest frequencies these questions await the analysis of longer time series in any case reducing the magnitude of low frequency colored noise is critical and appears to be best accomplished by building sites with deeply anchored and braced monuments otherwise rate uncertainties estimated from continuous gps measurements may not be improved significantly compared to those estimated from infrequent campaign mode measurements

how rigid is the stable interior of the north american plate we analyze data from eight permanent gps stations broadly distributed through the interior of the north american plate and use the resulting velocities to estimate an euler vector describing motion of stable north america as a single rigid plate the site velocities fit the single plate model with a mean residual of 1 3 mm yr the residuals do not appear to reflect post glacial rebound and tests for differential motion between eastern and western north america at the new madrid seismic zone show no resolvable motion within uncertainties the residuals likely reflect observational error and thus our estimate of the stability of the plate interior is likely an upper bound

measurements in a braided river chute and lobe 1 flow pattern sediment transport and channel change this paper and its companion ashworth et al this issue discuss measurements of channel change and associated flow and sediment transport processes in a representative chute and bar reach within a proglacial gravel bed river the sunwapta river in the canadian rockies during a week in which water discharge through the reach increased then decreased a sediment wave passed into and partly along the reach at first the chute aggraded then sediment was eroded from the chute and deposited in a prograding lobe to one side of the original bar head between two distributaries measurements of velocity shear stress and gravel transport rate revealed day to day changes in the divergent pattern of flow and sediment transport the off center location of the lobe reflected an initial asymmetry in the pattern of flow and sediment transport but as the lobe grew the flow and transport gradually switched away to the other distributary width averaged bed load transport rates do not agree well with average rates inferred from bar head deposition or from volumes and spatial patterns of scour and fill the indirect estimates are considered more reliable than those based on direct sampling for necessarily brief durations by the end of the study the new lobe had almost accreted onto the original bar head supporting the idea that most braid bars are of compound origin temporal and spatial patterns in grain size distributions of the bed bed load and deposited sediment are discussed in the companion paper

automated mapping of near bed radio echo layer disruptions in the greenland ice sheet abstract one of the key processes for modulating ice flow is the interaction between the ice and the bed but direct observations of the subglacial environment are sparse and difficult to obtain in this study we use information from an extensive radio echo sounding dataset to identify areas of the greenland ice sheet where internal layers have been influenced by near bed processes based on an automatic algorithm for calculating the slope of the internal radio echo layers we identify areas with disrupted layer stratigraphy we find that large parts of the northern portion of the ice sheet are influenced by locally confined mechanisms that produce up warping or folds in the layer stratigraphy inconsistent with the surface and bed topography this is particularly evident at the onset of ice streams although less dynamic areas close to the ice divide also contain imprints of layer disturbances our results show that the disturbances are found in many different flow and thermal regimes and underscore the need to understand the mechanisms responsible for creating them

reconciling geodetic and geological rates of vertical crustal motion in intraplate regions abstract tectonic motion rates of individual faults and regional deformation in an intraplate setting are estimated based on the analysis of ten yearly surveys of a regional levelling network in ne ardenne w europe owing to the frequency and number of measurement epochs much greater than in classical comparisons of general surveys the tectonic and near surface components of ground motion are clearly separated the marked temporal variability in ground motion strongly depends on the amount of precipitation fallen during the six months preceding each survey and the subsequent drying off of the subsoil at the time of the surveys moreover the ground response to this influence varies from place to place leading to high differential movements at the local scale taking into account the percentage of surveyed faults which moved tectonically during the time of the study i calculate fault motion rates of 0 06 0 09 mm yr similar to geological rates moreover the data indicate that one way for intraplate normal faults to accommodate tectonic strain aseismically is intermittent fault creep with short episodes of a few mm displacement separated by many year long time intervals of fault quiescence a flexural deformation shows the superposition of a tilt event on a trend corresponding to a tilt rate of 0 16 rad yr for a 2 8 km long segment