lunar global shape and polar topography derived from kaguya lalt laser altimetry a global lunar topographic map with a spatial resolution of finer than 0 5 degree has been derived using data from the laser altimeter lalt on board the japanese lunar explorer selenological and engineering explorer selene or kaguya in comparison with the previous unified lunar control network ulcn 2005 model the new map reveals unbiased lunar topography for scales finer than a few hundred kilometers spherical harmonic analysis of global topographic data for the moon earth mars and venus suggests that isostatic compensation is the prevailing lithospheric support mechanism at large scales however simple rigid support is suggested to dominate for the moon venus and mars for smaller scales which may indicate a drier lithosphere than on earth especially for the moon and venus

a continental scale mosaic of the amazon basin using jers 1 sar a methodology example and accuracy assessment are given for a continental scale mosaic of the amazon river basin at 100 m resolution using the jers 1 satellite this unprecedented resource of l band sar data collected by jers 1 during the low flood season of the river amounts to a collection of 57 orbits of the satellite and a total of some 1500 1 k spl times 1 kb images interscene overlap both in the along track and cross track directions allows common reference points to be used to correct individual scene geolocation inaccuracies that have been derived from the satellite ephemeris the set of common reference points is assembled into a matrix formulation that is used to solve for individual scene geometric offsets by correcting for these offsets each scene is placed within a global coordinate system which can then be used as the basis for creating a final visually seamless mosaic the methodology employed in this approach allows for a mathematical foundation to be applied to the mosaicking process as well as providing a unique traceable solution for correctly geolocating satellite imagery

global distribution of large lunar craters implications for resurfacing and impactor populations by using high resolution altimetric measurements of the moon we produced a catalog of all impact craters 20 kilometers in diameter on the lunar surface and analyzed their distribution and population characteristics the most densely cratered portion of the highlands reached a state of saturation equilibrium large impact events such as orientale basin locally modified the prebasin crater population to 2 basin radii from the basin center basins such as imbrium orientale and nectaris which are important stratigraphic markers in lunar history are temporally distinguishable on the basis of crater statistics the characteristics of pre and postmare crater populations support the hypothesis that there were two populations of impactors in early solar system history and that the transition occurred near the time of the orientale basin event

hypocentre determination offshore of eastern taiwan using the maximum intersection method summary the maximum intersection maxi method which derives from the master station method msm determines within a 3 d velocity model the absolute hypocentral location based on observed arrival times first the spatial node that better satisfies the arrival time differences computed at all station pairs plus or minus an error tolerance value in seconds is defined as the preliminary hypocentral solution pred second because pred depends neither on the estimate of origin time nor on the residual root mean square rms residual outliers are objectively detected and cleaned out from the original data set without any iterative process or weighting third a statistical minimization residual rms is conducted in a small domain around the pred node which results in a unique final solution the maxi method is applied to the determination of earthquake hypocentres with the proper station correction terms in the southernmost extremity of the ryukyu subduction zone where several dense seismic clusters occur near the seismogenic plate interface the location of earthquakes recorded at both the taiwanese and japanese networks is obtained for about a thousand events between 1992 and 1997 the process uses a detailed 3 d velocity model based on multiple geophysical data sources obtained in the junction area between subduction and collision east of taiwan the earthquake clustering and the significant drop in residual statistics 1 20 0 80 and 0 35 s for taiwanese catalogue msm and maxim solutions respectively indicate the accuracy of the method which can be used to routinely determine absolute hypocentre location based on observed arrival times

scaling gridded river networks for macroscale hydrology development analysis and control of error a simple and robust river network scaling algorithm nsa is presented to rescale fine resolution networks to any coarser resolution the algorithm was tested over the danube river basin and the european continent coarse resolution networks at 2 5 5 10 and 30 min resolutions were derived from higher resolution gridded networks using nsa and geomorphometric attributes such as river order shape index and width function these parameters were calculated and compared at each resolution simple scaling relationships were found to predict decreasing river lengths with coarser resolution data this relationship can be used to correct river length as a function of grid resolution the length corrected width functions of the major river basins in europe were compared at different resolutions to assess river network performance the discretization error in representing basin area and river lengths at coarser resolutions were analyzed and simple relationships were found to calculate the minimum number of grid cells needed to maintain the catchment area and length within a desired level of accuracy this relationship among geomorphological characteristics such as shape index and width function derived from gridded networks at different resolutions suggests that a minimum of 200 300 grid cells is necessary to maintain the geomorphological characteristics of the river networks with sufficient accuracy

a topological system for delineation and codification of the earth s river basins abstract a comprehensive reference system for the earth s river basins is proposed as a support to river basin management global change research and the pursuit of sustainable development a natural system for delineation and codification of basins is presented which is based upon topographic control and the topology of the river network these characteristics make the system well suited for implementation and use with digital elevation models dems and geographic information systems a demonstration of these traits is made with the 30 arcsecond gtopo30 dem for north america the system has additional appeal owing to its economy of digits and the topological information that they carry this is illustrated through presentation of comparisons with usgs hydrologic unit codes and demonstration of the use of code numbers to reveal dependence or independence of water use activities within a basin

teleseismic location techniques and their application to earthquake clusters in the south central pacific abstract improved methods for single and multiple event hypocenter determinations are developed and applied to the problem of locating earthquake clusters in the south central pacific ocean bayesian statistical methods are used to incorporate a priori information about arrival time variance into the derivation of hypocenter confidence ellipsoids permitting a more realistic calculation of critical parameters in the case where the number of stations is small the diagonal elements of certain projection operators called data importances by minster et al 1974 are used to evaluate network balance the hypocentroid of an event cluster is defined to be the average location of events within the cluster and the deviations of individual hypocenters from the hypocentroid are called cluster vectors the problem of estimating the cluster vectors can be decoupled from the problem of estimating the hypocentroid by a simple but fundamental mathematical result here termed the hypocentroidal decomposition theorem the algorithm based on this analysis appears to have many advantages over other published methods for multiple event location both in its efficient use of available information and its computational speed the application of this method to three clusters of shallow intraplate seismicity in the south central pacific designated regions a b and c demonstrates that the seismicity within each cluster is very localized the rms lengths of the cluster vectors for each group of epicenters are estimated to be only 9 6 and 12 km respectively estimates of the epicentroids are

dynamic modeling suggests terrace zone asymmetry in the chicxulub crater is caused by target heterogeneity we investigate the cause of terrace zone asymmetry in the chicxulub impact crater using dynamic models of crater formation marine seismic data acquired across the crater show that the geometry of the crater s terrace zone a series of sedimentary megablocks that slumped into the crater from the crater rim varies significantly around the offshore half of the crater the seismic data also reveal that at the time of impact both the water depth and sediment thickness varied with azimuth around the impact site to test whether the observed heterogeneity in the pre impact target might have affected terrace zone geometry we constructed two end member models of upper target structure at chicxulub based on the seismic data at different azimuths one model representing the northwest sector had no water layer and a 3 km thick sediment layer the other model representing the northeast sector had a 2 km water layer above a 4 km sediment layer numerical models of vertical impacts into these two targets produced final craters that differ substantially in terrace zone geometry suggesting that the initial water depth and sediment thickness variations affected the structure of the terrace zone at chicxulub moreover the differences in terrace zone geometry between the two numerical models are consistent with the observed differences in the geometry of the terrace zone at different azimuths around the chicxulub crater we conclude that asymmetry in the pre impact target rocks at chicxulub is likely to be the primary cause of asymmetry in the terrace zone

near real time double difference event location using long term seismic archives with application to northern california we present a real time procedure that uses cross correlation and double difference methods to rapidly relocate new seismic events with high precision relative to past events with accurately known locations waveforms of new events are auto matically cross correlated with those archived for nearby past events to measure accu rate differential phase arrival times these data together with delay times computed from arrival time picks are subsequently inverted for the vector connecting the new event to its neighboring events using the double difference algorithm the new seis mic monitoring technique is applied to earthquakes recorded in northern california using near real time data feeds from the northern california seismic network ncsn and the northern california earthquake data center and a locally stored copy of the ncsn seismic archive new events are automatically relocated in near real time tens of seconds relative to a high resolution double difference earthquake catalog for northern california back testing using past events across northern california indi cates that the real time solutions are on average within 0 08 km laterally and 0 24 km vertically of the double difference catalog locations we show that the precision with which new events are located using this technique will improve with time helped by the continued increase in density of recorded earthquakes and growth of the digital seismic archives real time double difference location allows for monitoring spatio temporal changes in seismogenic properties of active faults with unprecedented res olution and therefore has considerable social and economic impact in the immediate evaluation and mitigation of seismic hazards

progressive multiple event location pmel abstract this paper introduces a new method of using earthquake arrival times to simultaneously determine earthquake hypocenters and station corrections progressive multiple event location pmel forms a solution in three major steps 1 hypocenters are located by conventional single event methods using current station correction estimates 2 an annulled data set pavlis and booker 1980 is formed and accumulated using householder transformations and 3 station correction perturbations are calculated from a pseudoinverse solution of the annulled data set in practice pmel converges rapidly we analyze the non uniqueness of pmel estimates in terms of resolution and covariance matrices one of the most important features of pmel is the computer algorithm that we describe which requires only a modest amount of computer memory that is independent of the number of earthquakes to be processed consequently this algorithm can process a virtually unlimited number of earthquakes we apply pmel to a set of 8049 arrival times from 652 earthquakes and 4 explosions recorded by a network in the coso range inyo county california pmel converges after four adjustments to the station corrections the final rms misfit of 0 05 sec is remarkably good and the station correction estimates correlate strongly with surface geology

observations at terrestrial impact structures their utility in constraining crater formation hypervelocity impact involves the near instantaneous transfer of considerable energy from the impactor to a spatially limited near surface volume of the target body local geology of the target area tends to be of secondary importance and the net result is that impacts of similar size on a given planetary body produce similar results this is the essence of the utility of observations at impact craters particularly terrestrial craters in constraining impact processes unfortunately there are few well documented results from systematic contemporaneous campaigns to characterize specific terrestrial impact structures with the full spectrum of geoscientific tools available at the time nevertheless observations of the terrestrial impact record have contributed substantially to fundamental properties of impact there is a beginning of convergence and mutual testing of observations at terrestrial impact structures and the results of modeling in particular from recent hydrocode models the terrestrial impact record provides few constraints on models of ejecta processes beyond a confirmation of the involvement of the local substrate in ejecta lithologies and shows that z models are at best first order approximations observational evidence to date suggests that the formation of interior rings is an extension of the structural uplift process that occurs at smaller complex impact structures there are however major observational gaps and cases e g vredefort where current observations and hydrocode models are apparently inconsistent it is perhaps time that the impact community as a whole considers documenting the existing observational and modeling knowledge gaps that are required to be filled to make the intellectual breakthroughs equivalent to those of the 1970s and 1980s which were fueled by observations at terrestrial impact structures filling these knowledge gaps would likely be centered on the later stages of formation of complex and ring structures and on ejecta

volumetric analysis of complex lunar craters implications for basin ring formation the transition in hypervelocity impact structures from complex craters to basins is defined by a transition in uplifted central features from peaks to peak rings volumetric and morphologic analyses of the central peaks in complex lunar craters are combined with subsurface data from terrestrial complex impact structures in an effort to characterize the crater to basin transition central peak volumes in lunar craters with rim diameters drc 80 km central peak volume is relatively reduced and a second power law relationship is defined the relative reduction in peak volume in craters with drc 80 km is associated with a relative decrease in peak height and is accompanied by the development of a concentric zone of enhanced floor roughening studies of terrestrial complex impact structures suggest that the amount of uplifted material as judged from its depth of origin continues to increase with increasing rim diameter this suggests that a redistribution of uplifted material away from a centralized peak may occur in the larger craters the volumetric and morphologic changes described occur over a rim diameter range of 51 80 km far below the previously proposed range for the crater to basin transition drc 140 175 km evidence is presented to support a crater to basin transition beginning at drc 51 80 km characterized by a relative reduction in central peak volume and the development of rings of floor roughening which are suggested to be precursors of peak ring development

automated upscaling of river networks for macroscale hydrological modeling 1 we developed a hierarchical dominant river tracing drt algorithm for automated extraction and spatial upscaling of basin flow directions and river networks using fine scale hydrography inputs e g flow direction river networks and flow accumulation in contrast with previous upscaling methods the drt algorithm utilizes information on global and local drainage patterns from baseline fine scale hydrography to determine upscaled flow directions and other critical variables including upscaled basin area basin shape and river lengths the drt algorithm preserves the original baseline hierarchical drainage structure by tracing each entire flow path from headwater to river mouth at fine scale while prioritizing successively higher order basins and rivers for tracing we applied the algorithm to produce a series of global hydrography data sets from 1 16 to 2 spatial scales in two geographic projections wgs84 and lambert azimuthal equal area the drt results were evaluated against other alternative upscaling methods and hydrography data sets for continental u s and global domains these results show favorable drt upscaling performance in preserving baseline fine scale river network information including 1 improved automated extraction of flow directions and river networks at any spatial scale without the need for manual correction 2 consistency of river network basin shape basin area river length and basin internal drainage structure between upscaled and baseline fine scale hydrography and 3 performance largely independent of spatial scale geographic region and projection the results of this study include an initial set of drt upscaled global hydrography maps derived from hydro1k baseline fine scale hydrography inputs these digital data are available online for public access at ftp ftp ntsg umt edu pub data drt

monitoring velocity variations in the crust using earthquake doublets an application to the calaveras fault california we present a technique that greatly improves the precision in measuring temporal variations of crustal velocities using an earthquake doublet or pair of microearthquakes that have nearly identical waveforms and the same hypocenter and magnitude but occur on different dates we compute differences in arrival times between seismograms recorded at the same station in the freqency domain by cross correlation of short windows of signal a moving window analysis of the entire seismograms including the coda gives t the difference in arrival times versus running time along the seismogram the time resolution of the method is an order of magnitude better than the digitization interval the t technique is illustrated with a pair of microearthquakes m 1 7 and 2 0 that occurred before and after the coyote lake california earthquake m 5 9 of august 6 1979 and on the same segment of the calaveras fault that ruptured during the earthquake the coda wave arrivals for some stations are progressively delayed for the second earthquake in the doublet so that its seismogram appears as a stretched version of the earlier event we interpret this systematic variation in t along the coda as a change in the average s velocity in the upper crust in the time interval between the two doublets s wave velocities appear to have decreased by 0 2 in an oblong region 5 10 km in radius at the south end of the aftershock zone

deep fault plane geometry inferred from multiplet relative relocation beneath the south flank of kilauea dense microearthquake swarms occur in the upper south flank of kilauea providing multiplets composed of hundreds of events the similarity of their waveforms and the quality of the data have been sufficient to provide accurate relative relocations of their hypocenters a simple and efficient method has been developed which allowed the relative relocation of more than 250 events with an average precision of about 50 m horizontally and 75 m vertically relocation of these events greatly improves the definition of the seismic image of the fault that generates them indeed relative relocations define a plane dipping about 6 northward although corresponding absolute locations are widely dispersed in the swarm a composite focal mechanism built from events providing a correct spatial sampling of the multiplet also gives a well constrained northward dip of about 5 to the near horizontal plane this technique thus collapses the clouds of hypocenters of single event locations to a plane coinciding with the slip plane revealed by previous focal mechanism studies we cannot conclude that all south flank earthquakes collapse to a single plane there may locally be several planes perhaps with different dips and depths throughout the south flank volume the 6 northward dipping plane we found is too steep to represent the overall flexure of the oceanic crust under the load of the island of hawaii this plane is probably an important feature that characterizes the basal slip layer below the upper south flank of kilauea volcano differences in seismicity rate and surface deformations between the upper and lower south flank could be related to the geometry of this deep fault plane the present work illustrates how high precision relative relocations of similar events in dense swarms combined with the analysis of geodetic measurements can help to describe deep fault plane geometry systematic selection and extensive relative relocation of similar earthquakes could be attempted in other well instrumented highly seismic areas to provide reliable basic information especially useful for understanding of earthquake generation processes

scaling impact melting and crater dimensions implications for the lunar cratering record abstract the dimensions of large craters formed by impact are controlled to a large extent by gravity whereas the volume of impact melt created during the same event is essentially independent of gravity this differential scaling fosters size dependent changes in the dynamics of impact crater and basin formation as well as in the final morphologies of the resulting structures a variety of such effects can be observed in the lunar cratering record and some predictions can be made on the basis of calculations of impact melting and crater dimensions among them are the following 1 as event magnitude increases the volume of melt created relative to that of the crater will grow and more will be retained inside the rim of the crater or basin 2 the depth of melting will exceed the depth of excavation at diameters that essentially coincide with both the inflection in the depth diameter trend and the simple to complex transition 3 the volume of melt will exceed that of the transient cavity at a cavity diameter on the order of the diameter of the moon this would arguably correspond to a moon melting event 4 small lunar craters only rarely display exterior flows of impact melt because the relatively small volumes of melt created can become choked with clasts increasing the melt s viscosity and chilling it rapidly larger craters and basins should suffer little from such a process 5 deep melting near the projectile s axis of penetration during larger events will yield a progression in cen tral structure morphology with growing event magnitude this sequence should range from single peaks through multiple peaks to peak rings 6 the minimum depth of origin of central peak material should co incide with the maximum depth of melting the main central peak in a crater the size of tycho should have had a preimpact depth of close to 15 km

global test of seismic event locations using three dimensional earth models to prepare to update location procedures at the international seismological centre isc we conduct a global test of location accuracy using two 3d earth models and three 1d models jeffreys bullens j b preliminary reference earth model prem ak135 with initial phase arrival times from different distance ranges the 3d models include one spherical harmonic model and one irregular grid model representing two important alternative model parameterizations our tests include a worldwide distribution of reference events from a previous study by smith and ekstrom 1996 and the ground truth database of the prototype international data centre for each test we use phase arrival times associated with the events in the isc bulletin and recompute hypocenters with the same algorithm used in the isc operations with teleseismic arrival times alone 25 the overall accuracy of our recomputed hypocenters is similar using either of the 3d models the teleseismic hypocenters from 3d models are on an average closer to the reference locations than the hypocenters computed using any of the 1d models but the improvement in results using ak135 is small when we use the irregular grid model with teleseismic regional and local initial arrival times together and fix to reference depths the accuracy of the epicenters is improved over the results with teleseismic times alone with a 3d model we are able to invert for depth for a larger fraction of earthquakes and our newly computed depths are more tightly clustered in a subduction zone than depths from the isc bulletin but not as tightly as depths computed by engdahl et al 1998 who used depth phases as well as direct phases in a test of all the locatable events from 1 month of the isc bulletin the irregular grid model improved residuals and formal location uncertainties without introducing large systematic changes in the hypocenters

radiometric normalization of multitemporal high resolution satellite images with quality control for land cover change detection the radiometric normalization of multitemporal satellite optical images of the same terrain is often necessary for land cover change detection e g relative differences in previous studies ground reference data or pseudo invariant features pifs were used in the radiometric rectification of multitemporal images ground reference data are costly and difficult to acquire for most satellite remotely sensed images and the selection of pifs is generally subjective in addition previous research has been focused on radiometric normalization of two images acquired on different dates the problem of conservation of radiometric resolution in the case of radiometric normalization between more than two images has not been addressed this article reports on a new procedure for radiometric normalization between multitemporal images of the same area the selection of pifs is done statistically with quality control principal component analysis pca is used to find linear relationships between multitemporal images of the same area the satellite images are normalized radiometrically to a common scale tied to the reference radiometric levels the procedure ensures the conservation of radiometric resolution for the multitemporal images involved the new procedure is applied to three landsat 5 thematic mapper tm images from three different years august 1986 1987 and 1991 and of the same area quality control measures show that the error in radiometric consistency between the multitemporal images is reduced effectively the normalized difference vegetation index ndvi is calculated using the radiometrically normalized multitemporal imagery and assessed in the context of land cover change analysis

removal of artifact depressions from digital elevation models towards a minimum impact approach artifact depressions in digital elevation models dems interrupt flow paths and alter drainage directions techniques for removing depressions should enforce continuous flow paths in a way that requires the least modification of the dem impacts on the spatial and statistical distributions of elevation and its derivatives were assessed for four methods of removing depressions 1 filling 2 breaching 3 a combination of filling and breaching with breaching constrained to a maximum of two grid cells 4 a combination of filling and breaching based on an impact reduction approach ira the ira removes each depression using either filling or breaching depending on which method has the least impact in terms of the number of modified cells and the mean absolute difference in the dem analysis of a lidar dem of a landscape on the canadian shield showed significant differences in the impacts among the four depression removal methods depression filling a removal method that is widely implemented in geographical information system software was found to impact terrain attributes most severely constrained breaching which relies heavily on filling for larger depressions also performed poorly both depression breaching and the ira impacted spatial and statistical distributions of terrain attributes less than depression filling and constrained breaching the most sensitive landscapes to depression removal were those that contained large i e 10 flat areas because of the occurrence of relatively large depressions in these areas copyright 2005 john wiley sons ltd

digital terrain modelling a review of hydrological geomorphological and biological applications the topography of a catchment has a major impact on the hydrological geomorphological and biological processes active in the landscape the spatial distribution of topographic attributes can often be used as an indirect measure of the spatial variability of these processes and allows them to be mapped using relatively simple techniques many geographic information systems are being developed that store topographic information as the primary data for analysing water resource and biological problems furthermore topography can be used to develop more physically realistic structures for hydrologic and water quality models that directly account for the impact of topography on the hydrology digital elevation models are the primary data used in the analysis of catchment topography we describe elevation data sources digital elevation model structures and the analysis of digital elevation data for hydrological geomorphological and biological applications some hydrologic models that make use of digital representations of topography are also considered

the generation of sar layover and shadow maps from digital elevation models as almost fully automated techniques as well as expert systems obtain more and more importance in the geocoding of synthetic aperture radar sar images the solution to the problem of the identification of homologue points between the sar image and reference system moves into the fields of pattern recognition and feature matching shadow regions which appear as dark regions in the sar image are independent from the backscattering of the imaged terrain due to the multiplicity of signals layover regions appear brighter than the surrounding regions hence the phenomena of layover and shadow are stressed in the present paper the reasons for their occurrence are studied through the digital elevation model representing the earth s surface an algorithm to define layover and shadow regions directly in the geometry of the digital elevation model is presented the results are given in a so called layover and shadow map

a macroscale hydrological data set of river flow routing parameters for the amazon basin 1 continental scale hydrologic routing models also known as macrohydrological routing models have evolved considerably in the past few years as the models have become more sophisticated they have represented a variety of new processes and expanded their data requirements either as input data or as validation for the model output this paper presents a new data set of large scale hydrological river flow routing parameters for the amazon and tocantins basins part of this data set was required by the development of the continental scale hydrological routing model hydra and its application to the amazon basin hydra represents phenomenalike floods backwater effects and seasonal hydrograph much more realistically than the previous generation of macrohydrological routing models the data set contains data on 1 river network at 5 min 9 km resolution 2 time series of monthly means of river discharge and river stage for 122 fluviometric stations spread throughout the basin 3 sinuosity of each of the main rivers measured at 111 river sections in the basin and 4 depth to the water table and transmissivity of the aquifer derived from measurements taken at 81 points throughout the basin

the global rain forest mapping project jers 1 radar mosaic of tropical africa development and product characterization aspects the global rain forest mapping project grfm is an international collaborative effort initiated and managed by the national space development agency of japan nasda the main goal of the project is to produce a high resolution wall to wall map of the entire tropical rain forest domain in four continents using the l band sar onboard the jers 1 spacecraft the processing phase which entails the generation of wide area radar mosaics from the raw sar data was split according to the geographic area in this paper the focus is on the part related to africa the grfm project s goal calls for the coverage of a continental scale area of several million km sup 2 using a sensor with the resolution of tens of meters in the case of the african continent this entails the assemblage of some 3900 high resolution sar scenes into a bitemporal mosaic at 100 m pixel spacing and with known geometric accuracy while this fact opens up an entire new perspective for vegetation mapping in the tropics it presents a number of technical challenge the authors report on the solutions adopted in the grfm africa mosaic development and discuss some quantitative and qualitative aspects related to the characterization and validation of the grfm products in particular the mosaic geolocation and its validation are discussed in detail indeed the internal geometric consistency subpixel accuracy in the coregistration of the two dates and the absolute geolocation residual mean squared error of 240 m with respect to ground control points are key features of the grfm africa mosaic

bidirectional measurements of surface reflectance for view angle corrections of oblique imagery abstract an apparatus for acquiring bidirectional reflectance factor data was constructed and used over four surface types data sets were obtained over a headed wheat canopy bare soil having several different roughness conditions playa dry lake bed and gypsum sand results are presented in terms of relative bidirectional reflectance factors brfs as a function of view angle at a number of solar zenith angles nadir brfs as a function of solar zenith angles and for wheat vegetation indices as related to view and solar zenith angles the wheat canopy exhibited the largest brf changes with view angle brfs for the red and the near infrared nir bands measured over wheat did not have the same relationship with view angle nir red ratios calculated from nadir brfs changed by nearly a factor of 2 when the solar zenith angle changed from 20 to 50 brf versus view angle relationships were similar for soils having smooth and intermediate rough surfaces but were considerably different for the roughest surface nadir brf versus solar zenith angle relationships were distinctly different for the three soil roughness levels of the various surfaces brfs for gypsum sand changed the least with view angle 10 at 30

recognition of supraglacial debris in the tianshan mountains on polarimetric sar images abstract debris cover is widely present in the ablation areas of mountain glaciers such debris plays an important role in glacier mass balance but it complicates the glacier boundary and area estimation when using remotely sensed images automatic recognition of the debris is much more difficult than recognizing bare ice on optical remotely sensed images because the debris has almost the same spectral characteristics of the surrounding terrain in this paper the scattering characteristics of the debris on the c and l band polarimetric sar images are presented and analyzed to study the possibility of recognizing debris thickness and extent the koxkar glacier in the central tianshan mountain range was selected as the study area it was found that debris is distinct from bare ice in cross polarization hv of both the l and c bands the l band volume scattering component acquired from target decomposition increases with debris thickness when the debris is less than 25 cm deep but the volume scattering does not increases if the debris is thicker than 25 cm in contrast the c band sar data does not appear to be sensitive to debris thickness this difference may be caused by different radar penetration depth of the debris on the basis of the polarimetric property analysis two methods were developed to determine the extent of the debris in the first method the simple threshold to distinguish debris from non debris areas is presented using this threshold approximately 90 of the debris can be recognized in the second method by combining more polarimetric features and support vector machines recognition of debris reaches an accuracy greater than 95

validation of a new global 30 min drainage direction map abstract digital drainage direction maps are a prerequisite for analyzing the flow of water on the land surface of the earth for continental or global studies the most appropriate and most frequently used resolution for such data sets appears to be 30 longitude by latitude in this paper we present the new global drainage direction map ddm30 a 30 raster map of surface drainage directions which organizes the earth s land area into drainage basins and provides the river network topology ddm30 was generated by first upscaling two drainage direction maps ddms at higher resolutions the resulting map was then extensively corrected in an iterative manner by comparison against vectorized high resolution river maps and other geographic information finally it was co referenced to the locations of 935 gauging stations provided by the global runoff data centre grdc which again involved manual corrections ddm30 was validated against drainage basin areas from the literature against the given upstream areas of the grdc stations and most importantly against information from hydro1k a data set based on a hydrologically corrected 1 km digital elevation model which is thought to afford the best information on surface drainage currently available at the global scale in the course of the validation the quality of ddm30 was compared to three other 30 ddms the validation results show that ddm30 provides a more accurate representation of drainage directions and river network topology than the other 30 ddms

global event location with full and sparse data sets using three dimensional models of mantle p wave velocity in order to improve on the accuracy of event locations at teleseismic distances it is necessary to adequately correct for lateral variations in structure along the ray paths either through deterministic model based corrections empirical path station corrections or a combination of both approaches in this paper we investigate the ability of current three dimensional models of mantle p wave velocity to accurately locate teleseismic events we test four recently published models two are parameterized in terms of relatively long wavelength spherical harmonic functions up to degree 12 and two are parameterized in terms of blocks of constant velocity which have a dimension of a few hundreds of km these models together with detailed crustal corrections are used to locate a set of 112 global test events consisting of both earthquakes and explosions with p wave travel time data compiled by the international seismological centre isc the results indicate that the supposedly higher resolution block models do not improve the accuracy of teleseismic event locations over the longer wavelength spherical harmonic models for some source locations the block models do not predict the range of observed travel time residuals as well as the longer wavelength models the accuracy of the locations largely varies randomly with geographic position although events in central asia are particularly well located we also tested the effect of reduced data sets on the locations multiple location iterations using 30 p wave travel times indicate that teleseismic events may be located within an area of 1000 km of the true location 66 of the time with only the model based corrections and increasing to 75 if calibration information is available if as few as 8 phases are available then this is possible only 50 of the time further refinement in models and or procedure such as the addition ofp phases azimuth data and consideration of p wave anisotropy may provide further improvement in the teleseismic location of small events

epicentre accuracy based on seismic network criteria summary we establish reliable and conservative estimates for epicentre location accuracy using data that are readily available in published seismic bulletins a large variety of seismic studies rely on catalogues of event locations making proper assessment of location uncertainty critical event location and uncertainty parameters in most global regional and national earthquake catalogues are obtained from traditional linearized inversion methods using a 1 d earth model to predict traveltimes reported catalogue uncertainties are based on the assumption that error processes are gaussian zero mean and uncorrelated unfortunately these assumptions are commonly violated leading to the underestimation of true location uncertainty especially at high confidence levels we find that catalogue location accuracy is most reliably estimated by station geometry we make use of two explosions with exactly known epicentres to develop local network location 0 2 5 accuracy criteria using monte carlo simulations of network geometry we find that local network locations are accurate to within 5 km with a 95 per cent confidence level when the network meets the following criteria 1 there are 10 or more stations all within 250 km 2 an azimuthal gap of less than 110 3 a secondary azimuthal gap of less than 160 and 4 at least one station within 30 km to derive location accuracy criteria for near regional 2 5 10 regional 2 5 20 and teleseismic 28 91 networks we use a large data set of exceptionally well located earthquakes and nuclear explosions beyond local distances we find that the secondary azimuthal gap is sufficient to constrain epicentre accuracy and location error increases when the secondary azimuthal gap exceeds 120 when station coverage meets the criterion of a secondary azimuth gap of less than 120 near regional networks provide 20 km accuracy at the 90 per cent confidence level while regional and teleseismic networks provide 25 km accuracy at the 90 per cent confidence level

across path dn gradient in landsat tm imagery of amazonian forests a challenge for image interpretation and mosaicking abstract an analysis of tropical rain forest covering amazonian lowlands has highlighted a systematic across path east west radiometric gradient within landsat tm imagery visual assessment of 45 and quantitative analysis of 20 amazonian landsat 4 and 5 tm scenes show that the gradient is band dependent and pronounced in visible light bands 1 to 3 but significant also in ir bands 4 to 7 the results show that the scan line location of a pixel explains a considerable amount of the dn variation of forests in the width of the entire scene b1 70 b2 52 b3 44 b4 34 b5 46 b7 39 in digital numbers the difference between east and west side of a scene may be small 9 4 3 10 9 3 respectively but these differences become significant if the images are to be mosaicked or the data are used for mapping relatively subtle differences of natural forests apparently the gradient is a result of at least three factors 1 shadows caused by the undulating terrain 2 anisotropic reflectance of the varying surfaces and 3 atmospheric scattering the phenomenon becomes more significant when the sun is high and the scanning line is close to solar azimuth direction a condition more easily encountered in lower latitudes of the earth

evidence for a large scale remnant of subducted lithosphere beneath fiji we combine spatial variations of p and s wave speeds 1000 fault plane solutions and 6600 well determined hypocenters to investigate the nature of subducted lithosphere and deep earthquakes beneath the tonga back arc we show that perplexing patterns in seismicity and fault plane solutions can be accounted for by the juxtaposition of a steep dipping wadati benioff zone and a subhorizontal remnant of slab that is no longer attached to the actively subducting lithosphere the detached slab may be from a previous episode of subduction along the fossil vitiaz trench about 5 to 8 million years ago the juxtaposition of slabs retains a large amount of subducted material in the transition zone of the mantle such a configuration if common in the past would allow the preservation of a primordial component in the lower mantle

gradual unlocking of plate boundary controlled initiation of the 2014 iquique earthquake a long foreshock series unlocked the south american plate boundary until eventually initiating the m 8 1 iquique chile earthquake two groups publishing in this issue of nature analyse the seismic context of the iquique earthquake that occurred off the coast of northern chile on 1 april 2014 in a seismic zone that had been quiescent since a significant event in 1877 gavin hayes et al identify areas of remaining or elevated earthquake hazard along the megathrust fault in the region and conclude that the 2014 iquique event was not the earthquake that had been anticipated given that significant sections of the northern chile subduction zone have not ruptured in almost 150 years they suggest that it is likely that future megathrust earthquakes will occur south and potentially north of the 2014 iquique sequence bernd schurr et al show that the april 2014 earthquake broke a central fraction of the northern chile seismic gap the last major segment of the south american plate boundary that had yet to rupture in the past century from july 2013 up to the april earthquake they identify three seismic clusters along this part of the plate boundary each lasting a few weeks with earthquakes of increasing peak magnitudes they conclude that these seismic clusters and their slip transients reflect a gradual weakening of the central part of the seismic gap that was instrumental in initiating the final failure on 1 april 2014 northern chile was struck by a magnitude 8 1 earthquake following a protracted series of foreshocks the integrated plate boundary observatory chile monitored the entire sequence of events providing unprecedented resolution of the build up to the main event and its rupture evolution here we show that the iquique earthquake broke a central fraction of the so called northern chile seismic gap the last major segment of the south american plate boundary that had not ruptured in the past century1 2 since july 2013 three seismic clusters each lasting a few weeks hit this part of the plate boundary with earthquakes of increasing peak magnitudes starting with the second cluster geodetic observations show surface displacements that can be associated with slip on the plate interface these seismic clusters and their slip transients occupied a part of the plate interface that was transitional between a fully locked and a creeping portion leading up to this earthquake the b value of the foreshocks gradually decreased during the years before the earthquake reversing its trend a few days before the iquique earthquake the mainshock finally nucleated at the northern end of the foreshock area which skirted a locked patch and ruptured mainly downdip towards higher locking peak slip was attained immediately downdip of the foreshock region and at the margin of the locked patch we conclude that gradual weakening of the central part of the seismic gap accentuated by the foreshock activity in a zone of intermediate seismic coupling was instrumental in causing final failure distinguishing the iquique earthquake from most great earthquakes finally only one third of the gap was broken and the remaining locked segments now pose a significant increased seismic hazard with the potential to host an earthquake with a magnitude of 8 5

monitoring glacier zones and snow firn line changes in the qinghai tibetan plateau using c band sar imagery abstract small glaciers and ice caps in mountainous areas are often sensitive indicators of local and global climate change in this paper typical continental glaciers the dongkemadi and its neighbouring glaciers in the central area of the qinghai tibetan plateau are monitored using multi sensor c band synthetic aperture radar sar imagery the study includes analysis of the alternating processes of ablation and freezing the glacier zones detected on sar images and the changing snow firn line across different days seasons and years experiments show that in late summer the wet snow firn ice boundary which is termed the late summer wet snow firn line wsfl is easily detected on sar images and it is relatively stable over multiple days also the detected late summer wsfl and the recorded yearly equilibrium line which reflects glacier mass balance are close in a positive mass balance year but the detected late summer wsfl is lower than the equilibrium line in a negative mass balance year by combining pit and sar observations it was found that the firn can be divided into two parts on the glaciers the thick firn that lies in the neve basin is distinct on sar images in winter but the firn surrounding the basin with thickness ranging from 0 to 20 cm is difficult to recognize the thick firn line the lower boundary of neve basin is stable in observations eight years apart based on the c band vv polarization sar image experiments field work and existing records the spatiotemporal backscatter signature specific to the typical continental glacier is identified the spatiotemporal backscatter signature helps to understand mass balance proxies and surface melt patterns of the glaciers in sar images

hydrocode simulations of chicxulub crater collapse and peak ring formation we use hydrocode modeling to investigate dynamic models for the collapse of the chicxulub impact crater our aim is to integrate the results from numerical simulations with kinematic models derived from seismic reflection and wide angle velocity data to further our understanding of the formation of large impact craters in our simulations we model the collapse of a 100 km diameter bowlshaped cavity formed in comprehensively fractured crustal material to facilitate wholesale collapse we require that the strength of the target be significantly weakened in the present model we achieve this using acoustic fluidization where strong vibrations produced by the expanding shock wave cause extreme pressure fluctuations in the target at times and positions where the overburden pressure is sufficiently counteracted the frictional resistance is reduced enabling the rock debris to flow our simulations produce a collapsed crater that contains most of the features that we observe in the seismic data at chicxulub in particular we observe a topographic peak ring formed as material that is originally part of the central uplift collapses outward and is thrust over the inwardly collapsing transient crater rim this model for peak ring generation has not been previously demonstrated by numerical simulations and predicts that the peak ring is composed of deeply derived material and that the stratigraphy within the peak ring is overturned c 2002 elsevier science usa

height above the nearest drainage a hydrologically relevant new terrain model summary this paper introduces a new terrain model named hand and reports on the calibration and validation of landscape classes representing soil environments in amazonia which were derived using it the hand model normalizes topography according to the local relative heights found along the drainage network and in this way presents the topology of the relative soil gravitational potentials or local draining potentials the hand model has been demonstrated to show a high correlation with the depth of the water table providing an accurate spatial representation of soil water environments normalized draining potentials can be classified according to the relative vertical flowpath distances to the nearest drainages defining classes of soil water environments these classes have been shown to be comparable and have verifiable and reproducible hydrological significance across the studied catchment and for surrounding ungauged catchments the robust validation of this model over an area of 18 000 km2 in the lower rio negro catchment has demonstrated its capacity to map expansive environments using only remotely acquired topography data as inputs the classified hand model has also preliminarily demonstrated robustness when applied to ungauged catchments elsewhere with contrasting geologies geomorphologies and soil types the hand model and the derived soil water maps can help to advance physically based hydrological models and be applied to a host of disciplines that focus on soil moisture and ground water dynamics as an original assessment of soil water in the landscape the hand model explores the synergy between digital topography data and terrain modeling presenting an opportunity for solving many difficult problems in hydrology

discrimination of alluvial and mixed bedrock alluvial multichannel river networks this paper explores the use of planview morphological metrics to quantitatively describe and distinguish mixed bedrock alluvial multichannel networks from alluvial multichannel networks the geometries of the channel planforms of two bedrock constrained networks mekong and orange rivers are compared with the classic alluvial anastomosed upper columbia river and the wandering ganga river widely recognised indices utilized include channel link count and channel sinuosity with additional emphasis being given to the less common metrics network bifurcation angles and island shape characteristics i e aspect ratio compactness roundness and convexity link count data with one notable exception conform to theoretical expectations bifurcation angles for all four multichannel rivers are significantly greater than angles reported for braiding rivers island convexity clearly discriminates the two alluvial rivers from the two bedrock influenced rivers the width of the macrochannel in which each network develops has a positive influence on the number of channel links and is further related to channel slope variations which in turn are influenced by terrain structure revealed using trend surface analysis the geometry of multichannel networks are often laterally constrained such that the values of channel bifurcation angles and link sinuosity values reduce as the network intensifies and channel links are shortened these latter observations go some way to explain the oft noted relatively straight links seen within multichannel networks which are a necessary adjustment to space filling constraints placed on a network

aftershock seismicity of the 27 february 2010 mw 8 8 maule earthquake rupture zone on 27 february 2010 the mw 8 8 maule earthquake in central chile ruptured a seismic gap where significant strain had accumulated since 1835 shortly after the mainshock a dense network of temporary seismic stations was installed along the whole rupture zone in order to capture the aftershock activity here we present the aftershock distribution and first motion polarity focal mechanisms based on automatic detection algorithms and picking engines by processing the seismic data between 15 march and 30 september 2010 from stations from iris ipgp gfz and university of liverpool we determined 20 205 hypocentres with magnitudes mw between 1 and 5 5 seismic activity occurs in six groups 1 normal faulting outer rise events 2 a shallow group of plate interface seismicity apparent at 25 35 km depth and 50 120 km distance to the trench with some variations between profiles along strike the aftershocks occur largely within the zone of coseismic slip but extend 50 km further north and with predominantly shallowly dipping thrust mechanisms along dip the events are either within the zone of coseismic slip or downdip from it depending on the coseismic slip model used 3 a third band of seismicity is observed further downdip at 40 50 km depth and further inland at 150 160 km trench perpendicular distance with mostly shallow dipping 28 thrust focal mechanisms indicating rupture of the plate interface significantly downdip of the coseismic rupture and presumably above the intersection of the continental moho with the plate interface 4 a deep group of intermediate depth events between 80 and 120 km depth is present north of 36 s within the maule segment a large portion of events during the inter seismic phase originated from this depth range 5 the magmatic arc exhibits a small amount of crustal seismicity but does not appear to show significantly enhanced activity after the mw 8 8 maule 2010 earthquake 6 pronounced crustal aftershock activity with mainly normal faulting mechanisms is found in the region of pichilemu 34 5 s these crustal events occur in a 30 km wide region with sharp inclined boundaries and oriented oblique to the trench the best located events describe a plane dipping to the southwest consistent with one of the focal planes of the large normal faulting aftershock mw 6 9 on 11 march 2010

a reanalysis of the hypocentral location and related observations for the great 1906 california earthquake we determine probabilistic hypocentral locations for the foreshock and mainshock of the great 1906 california earthquake through reanalysis of arrival time observations in conjunction with modern velocity models and advanced event location techniques we obtain two additional observations for the mainshock and one for the foreshock that were not used in previous location studies using a robust likelihood function for event location we generate a usable subset of the predominantly unreliable teleseismic readings and determine new wave type identifications for some of the local and teleseismic readings our locations are much better constrained than those of earlier studies even though we do not assume that the epicenter lies on the san andreas fault as did previous authors we confirm the conclusions of earlier studies that the local and teleseismic arrival time observations can be explained by a single foreshock focus and a single mainshock focus on the san andreas fault and that there is no single unique hypocenter that satisfies all available local observations the maximum likelihood point latitude 37 78 n longitude 122 51 w for our preferred mainshock location indicates a hypocenter to the west of san francisco close to the san andreas fault zone this hypocenter has a 68 confidence error of about 8 km parallel to the san andreas fault and about 24 km perpendicular to the fault and a depth in the midcrust of about 12 7 km the closest point on the san andreas fault to this hypocenter lies about 10 km to the northwest of the widely accepted mainshock epicenter of bolt 1968 our mainshock location is consistent with the association of initial rupture of the 1906 mainshock with a dilatational right bend or step over in the submerged san andreas fault system offshore of the golden gate our foreshock location is less well constrained than our mainshock location but is consistent with the foreshock hypocenter being at the same location as the mainshock hypocenter online material visualization of 3d probabilistic hypocentral locations associated with the 1906 earthquake

a general method to normalize landsat reflectance data to nadir brdf adjusted reflectance abstract the landsat satellites have been providing spectacular imagery of the earth s surface for over 40 years however they acquire images at view angles 7 5 from nadir that cause small directional effects in the surface reflectance there are also variations with solar zenith angle over the year that can cause apparent change in reflectance even if the surface properties remain constant when landsat data from adjoining paths or from long time series are used a model of the surface anisotropy is required to adjust all landsat observations to a uniform nadir view primarily for visual consistency vegetation monitoring or detection of subtle surface changes here a generalized approach is developed to provide consistent view angle corrections across the landsat archive while this approach is not applicable for generation of landsat surface albedo which requires a full characterization of the surface bidirectional reflectance distribution function brdf or for correction to a constant solar illumination angle across a wide range of sun angles it provides landsat nadir brdf adjusted reflectance nbar for a range of terrestrial monitoring applications the landsat nbar is derived as the product of the observed landsat reflectance and the ratio of the reflectances modeled using modis brdf spectral model parameters for the observed landsat and for a nadir view and fixed solar zenith geometry in this study a total of 567 conterminous united states conus january and july 2010 landsat 5 thematic mapper tm and landsat 7 enhanced thematic mapper etm images that have swath edge overlapping paths sensed in alternating backscatter and forward scattering orientations were used the average difference between landsat 5 tm and landsat 7 etm surface reflectance in the forward and backward scatter directions at the overlapping landsat scan edges was quantified the conus july view zenith brdf effects were about 0 02 in the landsat visible bands and about 0 03 0 05 and 0 06 in the 2 1 m 1 6 m and near infrared bands respectively comparisons of landsat 5 tm and landsat 7 etm nbar derived using modis brdf spectral model parameters defined with respect to different spatial and temporal scales and defined with respect to different land cover types were undertaken the results suggest that because the brdf shapes of different terrestrial surfaces are sufficiently similar over the narrow 15 landsat field of view a fixed set of modis brdf spectral model parameters may be adequate for landsat nbar derivation with little sensitivity to the land cover type condition or surface disturbance a fixed set of brdf spectral model parameters derived from a global year of highest quality snow free modis brdf product values are provided so users may implement the described landsat nbar generation method

geomorphometric attributes of the global system of rivers at 30 minute spatial resolution in this paper we explore the geomorphometric characteristics and integrity of a 30 0 longitude latitude spatial resolution representation of the global system of potentially flowing rivers we quantify several geomorphometric attributes of digital simulated topological network stn 30p depicting potential flow pathways across the entire non glacierized surface of the earth this data set was examined with respect to several metrics describing individual grid cells river segments and complete drainage systems nearly 60 000 grid cells constitute the global non glacierized land mass the cells are organized into more than 30 000 distinct river segments belonging to approximately 6200 drainage basins stn 30p flow paths and drainage basins are classified as order one through six using the classification system of strahler stn 30p flow pathways depict rivers draining a global land area of 133 1 10 6 km 2 these pathways show a total length of 3 24 10 6 km at 30 0 spatial resolution the relationships between stn 30p order and interior river segment numbers accumulated sub basin areas and accumulated length within individual basins yield high correlation coefficients average r 2 0 96 for continents and globe mean values across individual continents and river orders for the bifurcation ratio 3 15 to 4 44 drainage area ratio 3 74 to 5 77 and basin length ratio 2 02 to 3 27 fall well within the ranges tabulated at finer spatial scales a basin shape index sba l a 0 5 defined as a function of potential mainstem length and drainage area varies between 1 0 and 5 0 for basins 25 000 km 2 and shows a global mean of 2 12 the structure of stn 30p potential river systems is consistent with those of rivers analyzed at finer spatial scales as demonstrated by the numerical similarity of the several geomorphometric indices analyzed however for a particular basin indices from stn 30p will be based on a condensed set of river orders relative to those derived at finer scales a first order stn 30p river is roughly equivalent to an order five to six river derived from 1 62 500 scale maps while 30 0 spatial resolution was found to represent well the 522 basins with areas 25 000 km 2 that drain 82 of the land mass it cannot be used with high confidence in characterizing the geomorphometry of the remaining smaller basins for global climate and biogeochemical studies a composite of the 30 0 resolution and finer spatial resolutions appears to be necessary q 2000 elsevier

quantitative measurement method for impact basin characteristics based on localized spherical harmonics abstract characteristics of impact basins are important fundamental knowledge for assessing basin forming impacts and their influence on surficial and interior structural evolutions for lunar and planetary bodies to estimate impact basin characteristics based on spherical harmonic expressions of topographic figures we propose a quantitative method that we apply it to actual lunar topographic data the estimated basin locations center are almost coincident with those determined by visual inspection however the numbers of ring structures differ from previously reported ones the relation between the ring height and the ring diameter coincides well with those reported previously some older basins show discrepancies in the height diameter relation which probably reflect the degree of degradation by subsequent small impacts we recognize a power law relation between the diameters of a ring and a neighboring ring structure that relation suggests that the formation volume and modification of the melt cavity control the formation and size of peak ring and multi ring structures these relations which are thought to reflect the mechanism of the collapse stage of basin formation impact provide helpful constraints for elucidating the long standing problem of how multi ring impact basins are formed

applying a three dimensional velocity model waveform cross correlation and cluster analysis to locate southern california seismicity from 1981 to 2005 we compute high precision earthquake locations using southern california pick and waveform data from 1981 to 2005 our latest results are significantly improved compared to our previous catalog by the following 1 we locate events with respect to a new crustal p and s velocity model using three dimensional ray tracing 2 we examine six more years of waveform data and compute cross correlation results for many more pairs than our last analysis and 3 we compute locations within similar event clusters using a new method that applies a robust fitting method to obtain the best locations satisfying all the differential time constraints from the waveform cross correlation these results build on the relocated catalogs of hauksson and shearer 2005 and shearer et al 2005 and provide additional insight regarding the fine scale fault structure in southern california and the relationship between the san andreas fault saf and nearby seismicity in particular we present results for two regions in which the seismicity near the southern saf seems to align on dipping faults

global system of rivers its role in organizing continental land mass and defining land to ocean linkages the spatial organization of the earth s land mass is analyzed using a simulated topological network stn 30p representing potential flow pathways across the entire nonglacierized surface of the globe at 30 min longitude latitude spatial resolution we discuss a semiautomated procedure to develop this topology combining digital elevation models and manual network editing stn 30p was verified against several independent sources including map products and drainage basin statistics although we found substantial inconsistency within the extant literature itself a broad suite of diagnostics is offered that quantitatively describes individual grid cells river segments and complete drainage systems spanning orders 1 through 6 based on the strahler classification scheme continental and global scale summaries of key stn 30p attributes are given summaries are also presented which distinguish basins that potentially deliver discharge to an ocean exorheic from those that potentially empty into an internal receiving body endorheic a total of 59 122 individual grid cells constitutes the global nonglacierized land mass at 30 min spatial resolution the cells are organized into 33 251 distinct river segments which define 6152 drainage basins a global total of 133 1 106 km2 bear stn sop flow paths with a total length of 3 24 106 km the organization of river networks has an important role in linking land mass to ocean from a continental perspective low order river segments orders 1 3 drain the largest fraction of land 90 and thus constitute a primary source area for runoff and constituents from an oceanic perspective however the small number n 101 of large drainage systems orders 4 6 predominates draining 65 of global land area and subsuming a large fraction of the otherwise spatially remote low order rivers along river corridors only 10 of land mass is within 100 km of a coastline 25 is within 250 km and 50 is within 750 km the global mean distance to river mouth is 1050 km with individual continental values from 460 to 1340 km the mediterranean black sea and arctic ocean are the most land dominated of all oceans with land ocean area ratios of 4 4 and 1 2 respectively remaining oceans show ratios from 0 55 to 0 13 we discuss limitations of the stn 30p together with its potential role in future global change studies stn 30p is geographically linked to several hundred river discharge and chemistry monitoring stations to provide a framework for calibrating and validating macroscale hydrology and biogeochemical flux models

river reach length and slope estimates for large scale hydrological models based on a relatively high resolution digital elevation model application of regular grid based distributed hydrological models requires information related to river drainage networks such as flow directions flow accumulated areas basin delineation and length and slope of river reaches for every grid cell most of those data may be extracted automatically from digital elevation models dem however when dealing with large basins available dems are usually in higher spatial resolution than the model grid upscaling procedures have therefore been developed to extract low resolution flow directions and flow accumulated areas from relatively high resolution dems this paper presents a new methodology which extends the upscaling method to automatically extract length and slope of river reaches for large scale grid based hydrological models the proposed method is new and is believed to be the first attempt to produce such information automatically from dems the methodology was applied to parts of the uruguay river basin in south america using the globally wide available dem produced by the shuttle radar topography mission srtm 90m quality of results was assessed by comparing calculated river lengths with distances measured over vectorized river networks which were assumed to be correct it was shown that the proposed methodology adequately assigns river lengths to every model cell while ensuring that the whole length of the streams is considered the effect of dem resolution on calculated river length errors was analyzed by resampling the srtm dem to three different cell sizes with best results obtained for the higher resolution dem the modification of the original high resolution dem through the process known as stream burning was also tested largely improving the quality of the results finally optimal distance transforms were used for the calculation of distance increments instead of euclidean local distances giving results that were generally better the quality of results for calculated slope values could not be assessed because no reliable data were available for comparison

elliptical structure of the lunar south pole aitken basin abstract the south pole aitken basin sp a is the largest and oldest basin on the moon the basin has usually been interpreted to exhibit a degraded circular structure but here we demonstrate that the topography iron and thorium signatures of the basin are well described by ellipses with axes measuring 2400 by 2050 km and centered at 53 191 e topography abundances of iron thorium and the distribution of mare basalts are all elevated in the northern halves of the ellipses we also identify an outer topographic ellipse whose semiminor axis scales with the main topographic ellipse by approximately 2 taken together these data imply that the basin was created by an oblique impact along an azimuth of approximately 19 measured counterclockwise from longitude 191 e the geometry of the elevated central farside topography surrounding sp a suggests that it predates the impact the elliptical ring structures of sp a and their scaling relationships will help to understand the formation of large and elliptical basins elsewhere in the solar system this refined basin shape will also inform local geology geochemistry and geophysics of the region

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

the subsurface character of meteor crater arizona as determined by ground probing radar ground probing radar has provided new two dimensional stratigraphic and structural information on meteor crater arizona four 50 mhz transects inside the crater and one 100 mhz transect on a northeast radial across the exterior ejecta blanket were carried out the frequencies used were in relation to the desired depth of investigation greater than 50 m at 50 mhz and 30 m for 100 mhz the results obtained inside the crater show that the water table can be clearly detected at depths of 65 m as can the contact between the crater wall and the infilling allochthonous breccia lens in addition we were able to detect 1 point reflectors from relatively coherent blocks 1 5m within the breccia lens 2 a zone 7 m thick relatively free of point reflectors from the immediate fall back unit 3 a series of subhorizontal reflectors a few meters apart due to bedding in the post impact crater sediments and 4 five separate subhorizontal reflectors from what we interpret to be a series of postimpact paleo water table levels in the breccia lens the ejecta blanket transect indicates a 4 10 m thick ejecta layer and the underlying moenkopi formation sandstone as well as the moenkopi kaibab contact and bedding within the kaibab formation in addition reverse faults with displacements up to 4 m were detected in the bedrock as well as changes from subhorizontal to 30 in the dip of the bedrock as the crater rim is approached from the northeast beneath the ejecta blanket the total uplift observed at the crater rim is around 55 m the radar data indicate uplift effects out to a radial distance of 400 m from the rim farther than that determined from drilling 300 m the results demonstrate the utility of continuous ground probing radar cross sections in studying the near subsurface 50 m character at meteor crater this relatively rapid low cost technique can be extended to other structures but confident interpretation requires supplemental ground truth constraints

earthquake locations in southern california obtained using source specific station terms we relocate 297 400 events recorded by the southern california seismic network scsn between 1975 and 1998 using spatially varying station terms to improve relative location accuracy our method uses existing scsn p and s picks a smooth one dimensional velocity model and an iterative grid search approach based on the l1 norm we apply empirical corrections for three dimensional structure by computing station timing corrections that continuously vary as a function of source position station terms for each event are obtained by smoothing the residuals from nearby events using a natural neighbor delaunay tessellation of the seismicity and then iterating until a stable set of locations and station terms is achieved our approach achieves relative location accuracy comparable locally to master event methods but can be applied uniformly over large regions median estimated standard errors for our final locations are 328 m in horizontal position and 741 m in depth our locations exhibit much less scatter particularly in depth than those of the scsn catalog and a greater tendency to align into linear and planar features suggestive of fault structures our results appear comparable to and in some cases better than previous scsn relocation studies using joint hypocenter velocity inversion techniques plots of daytime versus nighttime events permit discrimination between clusters of natural and artificial seismicity we observe no simple relationship between the maximum depth of seismicity and surface geology

assessment of different topographic corrections in landsat tm data for mapping vegetation types 2003 different methods for topographic correction of landsat thematic mapper images have been assessed in the context of mapping vegetation types the best results were obtained with a variation of the c method which takes into account the overcorrection of low illuminated slopes by the original c method the performance of this method was tested using two criteria the changes in the spectral characteristics of the image and the reduction in standard deviation of each vegetation type after the correction

improving teleseismic event locations using a three dimensional earth model abstract a comparison is made between seismic event locations derived from standard spherically symmetric earth models jb prem iasp91 and a recent earth model sp and a published data set of 82 well located earthquakes with a more even global distribution iasp91 and prem are shown to offer similar errors in event location and origin time estimates with respect to the jb model the three dimensional 3d model sp for the earthquakes the improvements are smaller corrections for crustal thickness beneath source and receiver are found to be of similar magnitude to the mantle corrections but use of station corrections together with the three dimensional mantle model provide the best locations

measurement and analysis of lunar basin depths from clementine altimetry altimetric profiles from the clementine lidar are used to calculate the depths of 29 large craters and basins on the moon plotting the depths of the best preserved structures together with values for simple and complex craters measured in pre clementine studies reveals an inflection in the depth diameter d d curve in addition to the one revealed by pre clementine data this inflection occurs in the diameter range that corresponds to the morphologic transition from complex crater to basin the best empirical power law fit for basin depths is log10 d 0 41 log10 d 0 57 this relationship is characterized by a lower slope than that for complex craters demonstrating that this morphologic transition corresponds to a further decrease in the depth of an impact structure relative to its diameter with increasing size qualitative consideration of possible causes for the second inflection leads to the conclusion that it is most likely a consequence of a short term modification mechanism that influences fundamental crater morphology such as the increasing influence of gravity with diameter thicknesses of maria in the major basins are calculated by assuming that their unfilled depths would follow thed drelation results are compared with previous estimates and yield thicknesses that are generally greater than those determined by studies of flooded craters and less than those obtained from analysis of gravity

lateral heterogeneity of lunar volcanic activity according to volumes of mare basalts in the farside basins estimates for volumes of mare basalts are essential to understand the thermal conditions of the lunar mantle and its lateral heterogeneity in this study we estimated the thicknesses and volumes of mare basalts within five farside basins apollo ingenii poincare freundlich sharonov and mendel rydberg using pre mare craters buried by mare basalts and post mare craters that penetrated non penetrated mare basalts employing topographic and multiband image data obtained by selene kaguya furthermore using the grail crustal thickness model and the mare volumes estimated by this and previous studies we investigated the relationship between the volumes of the mare basalts and the crustal thicknesses the results suggest that the minimum crustal thicknesses within the basins were a dominant factor determining whether magma erupted at the surface and that the critical crustal thicknesses for magma eruption were 10 km on the farside and 20 km on the nearside the total areas of the regions in which magmas could erupt at the surface are 10 times larger on the nearside than on the farside a comparison between the mare volumes within the mare basins on the nearside and the farside shows that magma production in the farside mantle might have been 20 times smaller than that in the nearside mantle implying a stronger dichotomy than previously estimated these results suggest that the mare hemispherical asymmetry should be attributed to both the difference in the crustal thickness distribution and the difference in the quantity of magma production between the nearside and farside mantles

carving and adaptive drainage enforcement of grid digital elevation models 1 an effective and widely used method for removing spurious pits in digital elevation models consists of filling them until they overflow however this method sometimes creates large flat regions which in turn pose a problem for the determination of accurate flow directions in this study we propose to suppress each pit by creating a descending path from it to the nearest point having a lower elevation value this is achieved by carving i e lowering the terrain elevations along the detected path carving paths are identified through a flooding simulation starting from the river outlets the proposed approach allows for adaptive drainage enforcement whereby river networks coming from other data sources are imposed to the digital elevation model only in places where the automatic river network extraction deviates substantially from the known networks an improvement to methods for routing flow over flat regions is also introduced detailed results are presented over test areas of the danube basin

topographic information of sand dunes as extracted from shading effects using landsat images topographic variations affect the reflectance properties of the earth s surface and are often removed in remote sensing studies especially when significant terrain variations exist in this study however we show that shading effects assessed by landsat can be treated as a signal that stores important topographic information especially when the spectral characteristics of a surface are homogenous the coastal transverse dunes of the ashdod area and the desert linear dunes of nizzana both located in israel were selected to investigate the abovementioned idea the dune heights in these areas are 10 m on average relative to their surroundings and have maximum slopes of 33 an innovative method for extracting slope aspect and height data for sand dunes using landsat thematic mapper tm and enhanced thematic mapper plus etm images was developed based on the regularity and periodicity of dunes landscapes using two landsat images representing different sun zenith and azimuth angles reflectance values of each image were converted to cos i values i incident angle between the surface normal and the solar beam radiation applying histogram matching methods the slope and aspect of each pixel were determined as those that give the best prediction of the observed value of cos i height profiles were then extracted using simple trigonometric relationships the accuracies of heights and slopes along selected profile lines were to the order of 1 m and 3 respectively at a spatial resolution of 15 m best results were obtained when the images included one from the summer and the other from the winter corresponding to maximum difference in solar zenith and azimuth angles errors in heights were attributed to surface heterogeneity e g presence of biogenic soil crusts in the rainy season geometric correction errors cast shadows and bidirectional reflectance distribution function brdf effects comparison to advanced thermal emission and reflection radiometer aster 3d information showed that the proposed method is better in representing the topographic variation of the area than the digital elevation model dem produced by aster

exchanges of sediment between the flood plain and channel of the amazon river in brazil sediment transport through the brazilian sector of the amazon river valley a distance of 2010 km involves exchanges between the channel and the flood plain that in each direction exceed the annual flux of sediment out of the river at obidos 1200 mt yr 1 the exchanges occur through bank erosion bar deposition settling from diffuse overbank flow and sedimentation in flood plain channels we estimated the magnitude of these exchanges for each of 10 reaches of the valley and combined them with calculations of sediment transport into and out of the reaches based on sediment sampling and flow records to define a sediment budget for each reach residuals in the sediment budget of a reach include errors of estimation and erosion or deposition within the channel the annual supply of sediment entering the channel from bank erosion was estimated to average 1570 mt yr 1 1 3 the obidos flux and the amount transferred from channel transport to the bars 380 mt yr 1 and the flood plain 460 mt yr 1 in channelized flow 1230 mt yr 1 in diffuse overbank flow totaled 2070 mt yr 1 1 7 the obidos flux thus deposition on the bars and flood plain exceeded bank erosion by 500 mt yr 1 over a 10 16 yr period sampling and calculation of sediment loads in the channel indicate a net accumulation in the valley floor of approximately 200 mt yr 1 over 16 yr crudely validating the process based calculations of the sediment budget which in turn illuminate the physical controls on each exchange process another 300 400 mt yr 1 are deposited in a delta plain downstream of obidos the components of the sediment budget reflect hydrologic characteristics of the valley floor and geomorphic characteristics of the channel and flood plain which in turn are influenced by tectonic features of the amazon structural trough

global river slope a new geospatial dataset and global scale analysis abstract a rivers longitudinal gradient i e slope is a key parameter in fluvial hydrology hydraulics and geomorphology it affects a multitude of fluvial variables such as flow velocity and sediment transport limitations in river slope data both its availability and accuracy constrain the fidelity of fluvial modeling particularly at larger or global scales traditional slope calculation algorithms cannot accurately predict river slopes as these are based on cell by cell calculation which is only suitable for hillslopes and small mountainous streams this paper presents a methodology for calculating global river slope and a procedure to upscale it for relatively coarse resolution suitable for global scale modeling the methodology is based on a simple principle of calculating slope from elevation depression over the length of a river segment which is automated to allow global scale calculations version 1 0 of the global river slope glors geospatial dataset is introduced and shown to be a step improvement over a previous product nhdplus for the contiguous united states and compares favorably to observed slope data collected from the literature statistical analysis of earth s continents and large basins highlights interesting spatial trends a semi empirical regression analysis between basin average river slope and other basin scale parameters show that terrain slope accounts for 67 of the variability in basin average river slope with average discharge sediment load and basin temperature contributing additional improvements to global predictions of 3 4 and 3 respectively

automated georeferencing and orthorectification of amazon basin wide sar mosaics using srtm dem data frequently large synthetic aperture radar sar mosaics are not precisely georeferenced because topographic distortions are not removed during the mosaicking process due to the lack of adequate digital elevation models dems the shuttle radar topography mission srtm has recently provided high resolution dem data with nearly global coverage and makes it possible to rectify sar mosaics though techniques are available for rectifying individual scenes of sar imagery using dem data these methods encounter difficulties when rectifying sar mosaics because abrupt geometric discontinuities occur in sar mosaics at scene boundaries this paper introduces an automated method to removing topographic distortions from sar mosaics and producing orthorectified mosaics without accessing original sar images the procedures include sar image simulation from dems two staged image matching between sar mosaics and the simulated image automated tie point derivation and screening piecewise image rectification for localized adjustment and production of orthorectified mosaics the method is used to orthorectify both high water and low water global rain forest mapping project sar mosaics covering the entire amazon basin validation results show that one pixel i e 92 m positioning accuracy root mean square error was achieved in both cases compared to 14 16 pixel errors i e 1288 1472 m of the original mosaics

farside gravity field of the moon from four way doppler measurements of selene kaguya the farside gravity field of the moon is improved from the tracking data of the selenological and engineering explorer selene via a relay subsatellite the new gravity field model reveals that the farside has negative anomaly rings unlike positive anomalies on the nearside several basins have large central gravity highs likely due to super isostatic dynamic uplift of the mantle other basins with highs are associated with mare fill implying basalt eruption facilitated by developed faults basin topography and mantle uplift on the farside are supported by a rigid lithosphere whereas basins on the nearside deformed substantially with eruption variable styles of compensation on the near and farsides suggest that reheating and weakening of the lithosphere on the nearside was more extensive than previously considered

estimating cell to cell land surface drainage paths from digital channel networks with an application to the amazon basin cell to cell surface flow paths are commonly derived from gridded digital elevation models dem by choosing the direction of steepest descent to one of the eight surrounding cells however adequate dems often are not available we developed a topography independent method for creating gridded land and stream drainage direction maps based on corrected vector river networks we applied it to the digital chart of the world river network in the amazon basin gridded at 0 0058 resolution in this basin low relief and poor topographic data have prevented the effective use of dem based methods we geo registered 224 hydrographic gages against the processed network and compared extracted vs published drainage areas drainage areas ranged from 227 to 4 620 000 km 2 median relative error was 4 5 increasing in smaller basins to 94 in basins 2000 km 2 the effective limit of reliability may differ from 2000 km 2 across the basin the drainage direction map and derivative datasets represent an improvement over existing datasets for regional research in the amazon basin methods exploiting vector networks complement terrain approaches and combined they may yield advances in the automated extraction of drainage maps and handling of topologically realistic river systems q 2005 elsevier b v all rights reserved

estimation of supraglacial debris thickness using a novel target decomposition on l band polarimetric sar images in the tianshan mountains debris is widely distributed in the ablation zones of mountain glaciers in the tianshan mountains supraglacial debris can accelerate or hamper glacier ablation depending on its thickness thus it plays an important role in the mass balance of debris covered glaciers this paper proposes a novel method to estimate supraglacial debris thickness by using l band polarimetric synthetic aperture radar a new model based target decomposition is used to extract the surface scattering double bounce and volume scattering components the surface scatter model uses the extended bragg scatter which considers the depolarization effect for rough surfaces the volume scatter model uses elliptical scatterers which approximate the shape of the solids in the debris the volume scattering power is related to the dielectric properties of the debris the radar wavelength the incidence angle and the elliptical scatter shape once the target decomposition is performed the debris thickness can be inverted from the volume scattering power and other known parameters through comparison with a large number of field measurements the inversion is shown to be reasonable and the accuracy is validated to be 0 12 m based on the inversion map in the study area the debris thicknesses of the koxkar glacier and its neighboring glaciers are presented and analyzed

water levels in the amazon basin derived from the ers 2 and envisat radar altimetry missions article i nfo this study sets out to analyze the stages of water bodies in the amazon basin derived from the processing of ers 2 and envisat satellite altimetry data for envisat gdr measurements for both ice 1 and ice 2 tracking algorithms were tested for ers 2 the ice 2 data produced by the oscar project was used water level time series over river segments of very different width from several kilometers to less than a hundred of meters were studied the water level time series that can be derived from narrow riverbeds are enhanced by off nadir detections conversely the off nadir effect may degrade the series over large bodies if not properly accounted for comparison at crossovers and with in situ gauges shows that the quality of the series can be highly variable from 12 cm in the best cases and 40 cm in most cases to several meters in the worse cases cautious data selection is clearly a key point to achieve high quality series indeed low quality series mostly result from inclusion of outliers in the data set finally retained for the computation of the series ice 2 and ice 1 tracking algorithms in the envisat data perform almost equally well envisat altimetry is clearly an improvement on ers 2 altimetry

anomalous moscoviense basin single oblique impact or double impact origin 1 the moscoviense basin is the most prominent mare basalt filled impact basin on the farside highlands of the moon the moscoviense basin has been studied extensively because of its characteristic geological and mineralogical context and distinct mare volcanism the success of kaguya s direct farside gravity recovery and global laser altimetry revealed that the moscoviense basin shows unique characteristics not only for geological and mineralogical but also for the geophysical contexts we measured geomorphological features of the moscoviense basin and the asymmetry suggests an oblique impact formation process moho undulation beneath the moscoviense basin however can hardly be explained by a single oblique impact formation process we propose an alternative hypothesis for the moscoviense basin formation which is called double impact scenario this scenario simultaneously accounts for the anomalously large mantle plug asymmetric surface geo morphology and excavation of olivine rich material originally located beneath the thickest crust on the moon on the basis of a set of monte carlo simulations we statistically examine the occurrence of a small spatial separation of two nearby basins the probability of double impact as seen on the moscoviense basin where the two impacts occurred 80 km apart is estimated to be about 50

hand a new terrain descriptor using srtm dem mapping terra firme rainforest environments in amazonia optical imagery can reveal spectral properties of forest canopy which rarely allows for finding accurate correspondence of canopy features with soils and hydrology in amazonia non floodable swampy forests can not be easily distinguished from non floodable terra firme forests using just bidimensional spectral data accurate topographic data are required for the understanding of land surface processes at finer scales topographic detail has now become available with the shuttle radar topographic mission srtm data this new digital elevation model dem shows the feature rich relief of lowland rain forests adding to the ability to map rain forest environments through many quantitative terrain descriptors in this paper we report on the development of a new quantitative topographic algorithm called hand height above the nearest drainage based on srtm dem data we tested the hand descriptor for a groundwater topographic and vegetation dataset from central amazonia the application of the hand descriptor in terrain classification revealed strong correlation between soil water conditions like classes of water table depth and topography this correlation obeys the physical principle of soil draining potential or relative vertical distance to drainage which can be detected remotely through the topography of the vegetation canopy found in the srtm dem data

errors in hypocenter location picking model and magnitude dependence abstract the location procedures of seismic events are influenced by two major classes of errors the error in picking individual seismic phases and modeling error due to the departure of the real earth from the reference model used in the location both classes of error influence the estimate of location and it is difficult to separate them the role of picking errors can be assessed by a nonlinear analysis using a monte carlo procedure arrivals times are perturbed with random numbers drawn from a normal distribution and the event is relocated using these perturbed arrival times by repeating the procedure many times a cluster of locations is obtained which can be used to investigate the effects of picking errors on the hypocenter this analysis is insensitive to velocity model errors as these are fixed for a given combination of stations and phases some care must be exercised when analysing multidimensional distributions in two dimensional slices because of a projection effect the modeling error due to the influence of lateral heterogeneity in the earth is examined by comparing the locations of the same event using different combinations of phases and network geometries which reinforces the need to use arrivals other than p for accurate depth resolution the sensitivity of p arrivals to changes in depth are swamped by model errors and inclusion of depth sensitive phases such as pp is highly recommended the effect of picking errors on location is found to be much smaller than the mislocation caused by neglecting lateral heterogeneity when only p arrivals are used consequently the monte carlo analysis which is primarily aimed at picking errors only is most appropriate when multiple phases have been used to more accurately constrain the hypocenter especially for the depth component altering the type of phase data used in the location plays a similar role in changing the network geometry in that both are mechanisms that influence the nature of the constraint on the hypocenter by relocating events with network geometries corresponding to the different magnitudes it is found that the location of the event can be affected significantly by the magnitude and when using robust statistics to describe earthquake residuals the mislocation can occur in a systematic manner the effect is marked in regions with significant lateral variations in seismic velocities for example low magnitude events in the flores sea are found to be dragged toward australia as a result of the fast paths to australian stations relative to the iasp 91 reference velocity model

a real time procedure for progressive multiplet relative relocation at the hawaiian volcano observatory a real time procedure has been set up to select and relocate relatively similar events recorded by the u s geological survey hawaiian volcano observatory hvo hawaii seismic network at the observatory it allows the relocation of such similar events with an uncertainty whose order of magnitude is 50 m horizontally and 100 m vertically as a first step a systematic exploration of the volcano to find similar events within the seismicity recorded between years 1988 and 2000 has been undertaken and allows events to be gathered into large multiplets a generalized relative relocation of these similar events has been performed and a database has been built from the result of this relocation incoming earthquakes are routinely compared to this database and relocated and the database is updated preliminary results are presented and discussed manuscript received 21 may 2001

geometric optical bidirectional reflectance modeling of a conifer forest canopy a geometric optical forest canopy model that treats conifers as cones casting shadows on a contrasting background explains the major anisotropies in bidirectional reflectance measurements of a conifer forest canopy taken from the literature the model uses parallelray geometry to describe the illumination and viewing of conifers as three dimensional cones cones are randomly placed and overlap freely cone size height is distributed lognormally and cone form described by the apex angle of the cone is a negative exponential function of height the cones are first presumed to be solid dark gray lambertian objects located on a lighter gray lambertian background to add realism translucence is added and light is allowed to pass through cones with negative exponential attenuation both computer simulation and analytical closed form expressions are implemented the results show a good qualitative agreement with the directional reflectance measurements of the conifer stand indicating that the three dimensional nature of the canopy is a key factor in determining its directional reflectance

the transition from complex crater to peak ring basin on the moon new observations from the lunar orbiter laser altimeter lola instrument impact craters on planetary bodies transition with increasing size from simple to complex to peak ring basins and finally to multi ring basins important to understanding the relationship between complex craters with central peaks and multi ring basins is the analysis of protobasins exhibiting a rim crest and interior ring plus a central peak and peak ring basins exhibiting a rim crest and an interior ring new data have permitted improved portrayal and classification of these transitional features on the moon we used new 128 pixel degree gridded topographic data from the lunar orbiter laser altimeter lola instrument onboard the lunar reconnaissance orbiter combined with image mosaics to conduct a survey of craters 50 km in diameter on the moon and to update the existing catalogs of lunar peak ring basins and protobasins our updated catalog includes 17 peak ring basins rim crest diameters range from 207 km to 582 km geometric mean 343 km and 3 protobasins 137 170 km geometric mean 157 km several basins inferred to be multi ring basins in prior studies apollo moscoviense grimaldi freundlich sharonov coulomb sarton and korolev are now classified as peak ring basins due to their similarities with lunar peak ring basin morphologies and absence of definitive topographic ring structures greater than two in number we also include in our catalog 23 craters exhibiting small ring like clusters of peaks 50 205 km geometric mean 81 km one humboldt exhibits a rim crest diameter and an interior morphology that may be uniquely transitional to the process of forming peak rings a power law fit to ring diameters d ring and rim crest diameters dr of peak ring basins on the

improving sparse network seismic location with bayesian kriging and teleseismically constrained calibration events monitoring the comprehensive nuclear test ban treaty will require improved seismic location capability for small magnitude events the international monitoring system ims is well suited to locate events that are large enough to be recorded at teleseismic distances however small events are likely to be recorded on a sparse subset of ims stations at regional to upper mantle distances less than 30 and sparse network locations can be strongly effected by travel time errors that result from path specific velocity model inaccuracies in an effort to improve sparse network location capability we outline a procedure that applies empirical corrections to travel times determined with an appropriate velocity model more specifically bayesian kriging and calibration events constrained with a global network are used to estimate epicenter specific travel time corrections for a test sparse network of stations we calculate travel time residuals for the calibration events relative to the ak135 velocity model travel time residuals are assigned to the respective calibration epicenter forming a set of spatially varying travel time correction points the spatial set of correction points is declustered to reduce the dimension of the observations with minimal reduction in accuracy of the travel time corrections we then use the declustered set of calibration points and bayesian kriging to form continuous travel time correction surfaces for each station of the test network the effectiveness of travel time correction surfaces is evaluated by locating with and without corrections a subset of the 1991 racha earthquake sequence caucasus mountains for which we have accurate locations that were independently determined with a dense local network when no travel time correction is applied the mean horizontal distance between the local and test network locations is 42 km and there is a distinct bias in sparse network locations toward the north northwest the mean difference between local and sparse network locations is cut to 13 km when corrections are applied and the bias in location is significantly reduced when calibration events in the racha vicinity are not used to make the correction surfaces there is still a significant improvement in location with mean mislocations of 15 km when corrections are not applied only one of the locally determined locations lies within the associated 90 coverage ellipse determined with the test sparse network however by using travel time corrections and estimates of model uncertainty determined using kriging representative error ellipses are obtained this study demonstrates that kriging correction surfaces based on global network constrained calibration events can improve the ability to accurately locate lower magnitude events while providing representative coverage ellipses

relocating earthquakes with empirical traveltimes a strategy is proposed to incorporate effects of 3 d velocity variations on earthquake locationsusing empirical traveltimes etts traveltime residuals are interpolated from those predictedusing a

digital elevation model networks demon a model of flow over hillslopes for computation of contributing and dispersal areas current algorithms for computing contributing areas from a rectangular grid digital elevation model dem use the flow routing model of o callaghan and mark 1984 which has two major restrictions 1 flow which originates over a two dimensional pixel is treated as a point source nondimensional and is projected downslope by a line one dimensional moore and grayson 1991 and 2 the flow direction in each pixel is restricted to eight possibilities we show that large errors in the computed contributing areas result for any terrain topography divergent convergent or planar we present a new model called digital elevation model networks demon which avoids the above problems by representing flow in two dimensions and directed by aspect demon allows computation of both contributing and dispersal areas demon offers the main advantage of contour based models e g moore et al 1988 the representation of varying flow width over nonplanar topography while having the convenience of using rectangular grid dems

improved regional and teleseismic p wave travel time prediction and event location using a global 3d velocity model a global validation dataset of 116 seismic events and 20 977 associated pn and p arrivals is used to assess travel time prediction and event location accuracy for the global scale 3d p wave velocity model called llnl g3dv3 simmons et al 2012 strong regional trends that are observed for ak135 travel time residuals are largely removed when llnl g3dv3 is used for prediction the 25th 75th quantile spread of travel time residuals is reduced by 30 40 at teleseismic distances and the spread is reduced by 60 at regional distances 16 epicenter error decreases when more data are used to constrain event locations until more than 40 arrivals times are used at which point epicenter error reduction tends to plateau median epicenter errors for the ak135 and llnl g3dv3 models plateau at 8 0 and 5 5 km respectively for teleseismic p datasets median epicenter errors for the ak135 and llnl g3dv3 models plateau at 12 0 and 4 0 km respectively for regional pn datasets we demonstrate that spatially correlated travel time residual errors for the ak135 model lead to increasing epicenter error when 40 to 100 pn arrivals are used to constrain the location the effect of correlated error is mitigated by llnl g3dv3 for which epicenter error steadily decreases to 4 km when 100 pn arrivals are used the median area of 0 95 epicenter probability bounds for ak135 and llnl g3dv3 are 1811 and 758 km2 respectively the ak135 ellipses are inflated to achieve the desired rate of true events occurring inside the probability region whereas llnl g3dv3 error ellipses based on empirical residual distributions cover the true location at the expected rate because location bias is minimal

precise hypocentre relocation of microearthquakes in a high temperature geothermal field the torfajokull central volcano iceland the torfaj okull volcanic system is one of approximately 30 active volcanoes comprising the neovolcanic zones of iceland the central volcano of the system is the largest silicic centre in iceland with a caldera of approximately 12 km diameter its high temperature geothermal system is one of the most powerful in iceland torfaj okull is a source of persistent seismicity where both high and low frequency earthquakes occur to study this microseismicity in detail a temporary array of 20 broad band seismic stations was deployed between 2002 june and november these temporary stations were embedded in the permanent south iceland lowland sil network and data from nine adjacent sil stationswere included in this study aminimum one dimensional 1 d velocity model with station corrections was computed for earthquake relocation by inverting manually picked p and s wave arrival times from events occurring in the torfaj okull volcanic centre and its surroundings high frequency earthquakes from the torfaj okull volcanic centre were then relocated calculating a non linear probabilistic solution to the earthquake location problem subsequently we correlated the waveforms of these 121 events 2000 observations to define linked events calculated the relative traveltime difference between event pairs and solved for the hypocentral separation between these events the resulting high resolution pattern shows a tighter clustering in epicentre and focal depth when compared with original locations earthquakes are mainly located beneath the caldera with hypocentres between 1 and 6 km depth and lie almost exclusively within the geothermal system a sharp cut off in seismicity at 3 km suggests either that there is a marked temperature increase or that this is a structural boundary no seismic activity was observed in the fissure swarms to the northeast ne and southwest sw of the volcanic centre

evaluation and correction of angular anisotropic effects in multidate spot and thematic mapper data spot xs oblique data are compared with landsat thematic mapper tm vertical data at two different times under the assumption that analogous spectral bands are equivalent the differences in spectral responses observed over land cover classes are attributed to the effects of angular anisotropic reflection this article shows that land cover classes cannot easily be characterized by their anisotropy the magnitude of anisotropy varies strongly with the radiometric processing levels i e absolute calibration or normalization but has no significant impact on the overall classification results the normalization method based on the use of pseudoinvariant objects is sufficiently effective as to correct most anisotropic disturbances and should facilitate an alternative use of spot and tm data

transition from complex craters to multi ringed basins on terrestrial planetary bodies scale dependent role of the expanding melt cavity and progressive interaction with the displaced zone 1 the observed differences between complex craters and multi ringed basins are described and a combined transient cavity displaced zone melt cavity model is explored to account for the observations in this nested melt cavity model the increasing influence of the percentage of the target undergoing impact melting at the sub impact point with increasing size the differential melt scaling of cintala and grieve 1998 causes fundamental changes in the nature of the transient cavity its relationship to the displaced zone and its short term collapse behavior the transition from complex craters to two ring basins involves expansion of the melting front into the displaced zone formation of a two component excavation cavity and a concomitant radial expansion outward of the zone of maximum elastic rebound the short term modification stage is then dominated by the strength differences between the fluid melt in the inner cavity and rocks of the displaced zone the highly shocked rocks at the outer margin of the expanded parabolic melting front rebound to form the expanded peak ring moving upward and laterally inward easily displacing fluid melt filling the inner depression at larger sizes differential melt scaling causes the peak ring diameter to expand relatively more rapidly than the basin rim and upon collapse the increased volume of melt ponds in the rebounded melt cavity inside the expanding peak ring as the transient melt cavity further increases proportionally in size it penetrates through the base of the displaced zone with significant consequences the resulting modification stage now incorporates into the collapse process inward and upward movement along the base of the displaced zone listric failure occurs inward into the fluid melt cavity beginning at the edge of the melt cavity and extending out along the base of the displaced zone up to the base of the rim structural uplift at 1 5 crater radii this forms an additional outer ring and a resulting megaterrace modifying the radial ejecta on the collapsed rim to form a domical facies at multi ring basin scales the significantly deeper penetration that occurs in the expanding melt cavity accounts for the maximum crustal thickness decrease that occurs inside the peak ring in the final basin early onset and higher density of peak ring basins on mercury is predicted by higher mean impact velocity and differential melt scaling

southern california hypocenter relocation with waveform cross correlation part 2 results using source specific station terms and cluster analysis we obtain precise relative relocations for more than 340 000 southern california earthquakes between 1984 and 2002 by applying the source specific station term ssst method to existing p and s phase picks and a differential lo cation method to about 208 000 events within similar event clusters identified with waveform cross correlation the entire catalog is first relocated by using existing phase picks a reference 1d velocity model and the ssst method of richards dinger and shearer 2000 we also perform separate relocations of imperial valley events by using a velocity model more suited to this region next we apply cluster analysis to the waveform cross correlation output to identify similar event clusters we re locate earthquakes within each similar event cluster by using the differential times alone keeping the cluster centroid fixed to its initial ssst location we estimate standard errors for the relative locations from the internal consistency of differential locations between individual event pairs these errors are often as small as tens of meters in many cases the relocated events within each similar event cluster align in planar features suggestive of faults we observe a surprising number of such faults at small scales that strike nearly perpendicular to the main seismicity trends in general the fine scale details of the seismicity reveal a great deal of structural com plexity in southern california fault systems

tonga slab deformation the influence of a lower mantle upwelling on a slab in a young subduction zone there are fundamental geographic variations in the deformation of slabs in the transition zone the seismic energy release and morphology of the tonga slab show that it is deforming faster and has accumulated more deformation than any other slab we show that tonga overlies the edge of the large scale pacific superplume there is no substantial aseismic penetration into the lower mantle beneath tonga consistent with initiation of subduction during the eocene other major subduction systems overlay seismically fast structures for long lived subduction systems the lower mantle tends to pull down on slabs while in tonga the lower mantle pushes upward partially accounting for the intense deformation the perturbation to the state of slab stress due to large scale mantle flow is 10 to 40 mpa nearly as large as that expected from slab pull