comparison of geodetic and glaciological mass balance techniques gulkana glacier alaska u s a the net mass balance on gulkana glacier alaska u s a has been measured since 1966 by the glaciological method in which seasonal balances are measured at three index sites and extrapolated over large areas of the glacier systematic errors can accumulate linearly with time in this method therefore the geodetic balance in which errors are less time dependent was calculated for comparison with the glaciological method digital elevation models of the glacier in 1974 1993 and 1999 were prepared using aerial photographs and geodetic balances were computed giving 6 0 0 7 m w e from 1974 to 1993 and 11 8 0 7 m w e from 1974 to 1999 these balances are compared with the glaciological balances over the same intervals which were 5 8 0 9 and 11 2 1 0 m w e respectively both balances show that the thinning rate tripled in the 1990s these cumulative balances differ by 6 for this close agreement the glaciologically measured mass balance of gulkana glacier must be largely free of systematic errors and be based on a time variable area altitude distribution and the photography used in the geodetic method must have enough contrast to enable accurate photogrammetry

a few parts in 108 geodetic baseline repeatability in the gulf of california using the global positioning system global positioning system gps geodetic measurements of 350 650 km baselines across the pacific north america plate boundary in the gulf of california are presented the analysis employs a four station u s fiducial network and combined carrier phase and pseudorange data water vapor radiometer wvr data at the gulf sites are used to calibrate the gps signal for wet tropospheric path delays residual tropospheric delays are modeled as first order exponentially correlated stochastic processes the measurement precision for horizontal components is a few parts in 108 or better comparison of the gulf data with other geodetic techniques is not yet possible however the system accuracy appears to be about 1 part in 107 based on simultaneous gps solutions of a baseline in california collocated with vlbi the results are encouraging because a high level of precision with gps is demonstrated even with stations located outside a fiducial network and when wet tropospheric path delays are significant typically exceeding 20 cm at zenith

contribution of small glaciers to global sea level observed long term changes in glacier volume and hydrometeorological mass balance models yield data on the transfer of water from glaciers excluding those in greenland and antarctica to the oceans the average observed volume change for the period 1900 to 1961 is scaled to a global average by use of the seasonal amplitude of the mass balance these data are used to calibrate the models to estimate the changing contribution of glaciers to sea level for the period 1884 to 1975 although the error band is large these glaciers appear to account for a third to half of observed rise in sea level approximately that fraction not explained by thermal expansion of the ocean

vertical structure variability in a seasonal simulation of a medium resolution regional model of the eastern south pacific a seasonal simulation from a medium resolution ocean general circulation mode ogcm is used to investigate the vertical structure variability of the southeast pacific sep the focus is on the extra tropical rossby wave etrw variability and associated forcing mechanism some aspects of the model mean state are validated from available observations which justifies a vertical mode decomposition of the model variability the analysis of the baroclinic mode contributions to sea level indicates that the gravest mode is dominant over most of the domain at all frequencies annual variability is on average twice as large as the semi annual variability which is confined near the coast for all the modes the first baroclinic mode contribution to the annual cycle exhibits a clear westward propagation north of the critical latitude the higher order modes only contribute near the coast where they are associated with vertically propagating energy the residual variability which is the energy at all timescales other than annual and semi annual periods peaks offshore between similar to 20 degrees s and similar to 30 degrees s for all baroclinic modes the third baroclinic mode also exhibits a relative maximum variability off the coast of peru south of the critical latitude of the annual cycle similar to 13 degrees s where the peru chile undercurrent is the most intense sensitivity experiments to the atmospheric and boundary forcing suggest that the residual variability results from the non linear interaction between annual rossby waves and the mean flow while the annual etrws in the model result from the summed contribution from both the local wind stress and remote equatorial forcing overall the study extends the classical analysis of sea level variability in the sep based on linear theory and suggests that the peculiarities of the baroclinic modes need to be taken into account for interpreting the sea level variability and understanding its connection with the equatorial variability c 2008 published by elsevier ltd

kinematic gps as a source for airborne gravity reduction in the airborne gravity survey of switzerland an airborne gravity survey of switzerland was performed in a joint project between the swiss federal institute of technology zurich and lacoste and romberg gravity meters inc the survey was flown in a twin otter aircraft equipped by the swiss federal directorate of cadastral surveying the aircraft was outfitted with three global positioning system receivers one for navigational purpose and two as sources of positioning velocity and vertical acceleration for airborne gravity reduction four receivers were installed on the ground as reference stations the gravity data were recorded with a modified lacoste and romberg marine gravimeter at a sampling rate of 1 s modifications included anti alias filters and an absolute encoder for the measuring screw the flights were performed at a barometric altitude of 5100 m above sea level an airborne bouguer anomaly map computed at flight altitude with topographic corrections of up to 167 km and a density of 2670 kg m3 is presented bouguer anomaly values at crossing points between lines flown at comparable altitudes h 10 m show differences varying between 1 1 and 2 7 mgal 10 5 m s2 comparison of the ground bouguer anomaly map upward continued to 5100 m and the one computed from airborne data shows a strong similarity both in amplitude and wavelength

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

the spectrum of gps measurement errors and the accuracy of airborne gravity measurements recent observations georgiadou and kleusberg 1987 kleusberg et al 1989 suggest that errors in gps carrier phase observations at frequencies within the gravity passband of airborne gravity systems may be due mainly to multipath interference further the power spectral density psd of these errors has been found to fall off rapidly with increase in frequency throughout the anticipated gravity passband in the manner of a red spectrum rather than a white which remains constant it is shown that this implies a much greater allowable error in gps derived altitude reference than would be the case if the psd of altitude errors 1 was white 2 had the same shape as that of typical aircraft vertical motion or 3 was dominated by a sinusoidal wave located near the high frequency limit of the gravity passband this enhances the feasibility of airborne gravity for regional scale surveys and perhaps explains why actual measurements have been better than predicted for example given a uniform f 4 distri

the mass balance of circum arctic glaciers and recent climate change the sum of winter accumulation and summer losses of mass from glaciers and ice sheets net surface mass balance varies with changing climate in the arctic glaciers and ice caps excluding the greenland ice sheet cover about 275 000 km2of both the widely glacierized archipelagos of the canadian norwegian and russian high arctic and the area north of about 60 n in alaska iceland and scandinavia since the 1940s surface mass balance time series of varying length have been acquired from more than 40 arctic ice caps and glaciers most arctic glaciers have experienced predominantly negative net surface mass balance over the past few decades there is no uniform recent trend in mass balance for the entire arctic although some regional trends occur examples are the increasingly negative mass balances for northern alaska due to higher summer temperatures and increasingly positive mass balances for maritime scandinavia and iceland due to increased winter precipitation the negative mass balance of most arctic glaciers may be a response to a step like warming in the early twentieth century at the termination of the cold little ice age arctic ice masses outside greenland are at present contributing about 0 13 mm yr 1to global sea level rise

recent glacier mass changes in the gulf of alaska region from grace mascon solutions the mass changes of the gulf of alaska goa glaciers are computed from the gravity recovery and climate experiment grace inter satellite range rate data for the period april 2003 september 2007 through the application of unique processing techniques and a surface mass concentration mascon parameterization the mass variations in the goa glacier regions have been estimated at high temporal 10 day and spatial 2 2 arc degrees resolution the mascon solutions are directly estimated from a reduction of the grace k band inter satellite range rate data and unlike previous grace solutions for the goa glaciers do not exhibit contamination by leakage from mass change occurring outside the region of interest the mascon solutions reveal considerable temporal and spatial variation within the goa glacier region with the largest negative mass balances observed in the st elias mountains including the yakutat and glacier bay regions the most rapid losses occurred during the 2004 melt season due to record temperatures in alaska during that year the total mass balance of the goa glacier region was 84 5 gt a 1 contributing 0 23 0 01 mm a 1 to global sea level rise from april 2003 through march 2007 highlighting the large seasonal and interannual variability of the goa glaciers the rate determined over the period april 2003 march 2006 is 102 5 gt a 1 which includes the anomalously high temperatures of 2004 and does not include the large 2007 winter balance year snowfall the mascon solutions agree well with regional patterns of glacier mass loss determined from aircraft altimetry and in situ measurements

subdecadally resolved paleoceanography of the peru margin during the last two millennia 1 using multiproxy sediment core data from the el nino southern oscillation enso sensitive peru margin subdecadally resolved down to 0 6 year surface productivity and subsurface denitrification are reconstructed for the last 2300 years scanning xrf generated major elemental data ti fe si correlate well with discrete inductively coupled plasma atomic emission spectometry icp aes analyses and together with x radiography core density are used as productivity indices as surface productivity in this marine region is strongly impacted by enso higher lower periods of surface productivity are inferred to represent a persistent normal la nina el nino like state surface productivity and subsurface denitrification appear to have remained intimately coupled during this period due to direct stimulation of requisite subsurface suboxia and or hydrographic restructuring the late holocene peru margin is characterized by persistent moderate productivity and subsurface denitrification punctuated at centennial scale by shorter duration periods of high production and intense denitrification these centennial scale events are likely analogous to modern observations of decadal scale regime shifts but of higher amplitude and provide a background history for future natural changes to this system solar irradiance variability is suggested to have influenced peru productivity as evidenced in numerous high resolution paleorecords from the northern hemisphere

satellite radar interferometry for monitoring ice sheet motion application to an antarctic ice stream satellite radar interferometry sri provides a sensitive means of monitoring the flow velocities and grounding line positions of ice streams which are indicators of response of the ice sheets to climatic change or internal instability the detection limit is about 1 5 millimeters for vertical motions and about 4 millimeters for horizontal motions in the radar beam direction the grounding line detected by tidal motions where the ice goes afloat can be mapped at a resolution of 0 5 kilometer the sri velocities and grounding line of the rutford ice stream antarctica agree fairly well with earlier ground based data the combined use of sri and other satellite methods is expected to provide data that will enhance the understanding of ice stream mechanics and help make possible the prediction of ice sheet behavior

spatial variability in the flow of a valley glacier deformation of a large array of boreholes measurements of the deformation of a dense array of boreholes in worthington glacier alaska show that the glacier moves with generally bed parallel motion strain in the 200 m deep valley glacier is constant near the surface but follows a nonlinear vertical profile below a depth of about 120 m by a depth of 180 m the octahedral strain rate reaches 0 35 yr 1 the three dimensional velocity field shows spatial complexity with significant deviations from plane strain despite relatively simple valley geometry in the vicinity of the 6 10 6 m 3 study volume no evidence was found for time varying deformation or movement along localized shear planes observations were made by repeatedly measuring the long axis geometry of 31 closely spaced boreholes over a 70 day period and three additional holes after 1 full year of deformation the holes were spaced 15 to 30 m apart installation and measurement of such a large number of boreholes required the development of a semiautomated hot water drilling system that creates straight and vertical boreholes with uniform walls the equipment and procedures enables borehole profiles to be measured without the use of hole casing inclinometry measurements collected in the holes were processed analyzed for error and visualized as a fully three dimensional data set the new methods offer unique insight into small scale spatial and temporal variations in the pattern of flow in a valley glacier

evaluation of gps estimates of relative positions from central california 1986 1988 i report estimates of long term precision and accuracy of interstation vectors using the global positioning system gps precision is estimated from three experiments conducted in central california over a period of 1 2 years horizontal precision is 3 to 8 mm for baseline vectors between 100 and 450 km in length and the vertical precision ranges from 11 to 33 mm accuracy is assessed by comparing vlbi estimates with results from 6 gps experiments conducted at mojave and palos verdes over a period of 2 2 years rates for all vector components agree with vlbi within one standard deviation

application of the global positioning system to crustal deformation measurement 1 precision and accuracy in this paper we assess the precision and accuracy of interstation vectors determined using the global positioning system gps satellites these vectors were between stations in california separated by 50 450 km using data from tracking the seven block i satellites in campaigns from 1986 through 1989 we examine the precision of gps measurements over time scales of a several days and a few years we characterize gps precision by constant and length dependent terms the north south component of the interstation vectors has a short term precision of 1 9 mm 0 6 parts in 108 the east west component shows a similar precision at the shortest distances 2 1 mm with a larger length dependence 1 3 parts in 108 the vertical precision has a mean value of 17 mm with no clear length dependence for long term precision we examine interstation vectors measured over a period of 2 2 to 2 7 years when we include the recent results of davis et al 1989 for distances less than 50 km we can describe long term gps precision for baselines less than 450 km in length as 3 4 mm 1 2 parts in 108 5 2mm 2 8 parts in 108 11 7mm 13 parts in 108 in the north south east west and vertical components accuracy has been determined by comparing gps baseline estimates with those derived from very long baseline interferometry vlbi a comparison of eight interstation vectors shows differences ranging from 5 to 30 mm between the mean gps and mean vlbi estimates in the horizontal components and less than 80 mm in the vertical a large portion of the horizontal differences can be explained by local survey errors at two sites in california a comparison which suffers less from such errors is between the rates of change of the baselines the horizontal rates estimated from over 4 years of vlbi data agree with those determined with 1 2 years of gps data to within one standard deviation in the vertical both gps and vlbi find insignificant vertical motion

on the accuracy of marine gravity measurements we have assessed the accuracy of lamont doherty geological observatory s global marine gravity data bank by examining the crossover errors coes at intersecting ship tracks more than 63 000 coes were found having a standard deviation of 22 43 mgal mgal 10 5 m s 2 we use the coes to find and remove linear drifts and dc shifts present in the data set this adjustment reduces the standard deviation to 13 96 mgal coes generally decrease with latitude which we attribute to uncertainties in the eotvos correction high coes occur in areas of high gravity gradients these two features point to poor navigation as the principal source of error in marine gravity surveys coes have generally been decreasing during the last two decades reflecting improvements in instrumentation and quality of navigation a comparison of the shipboard gravity data to seasat derived gravity revealed a 9 mgal bias in the terrestrial data which probably reflects uncertainties in choice of reference field the adjusted data set was used to generate a gravimetric geoid for the nw atlantic ocean by removing this geoid from the seasat sea surface heights a residual geoid was obtained a special feature of this map is an elongate ene trend that appears to correlate with the edge of the gulf stream

investigations on intra annual elevation changes using multi temporal airborne laser scanning data case study engabreen norway key issues of glacier monitoring are changes in glacier geometry and glacier mass as accurate direct measurements are costly and time consuming the use of various remote sensing data for glacier monitoring is explored one technology used and described here is airborne laser scanning the method enables the derivation of high quality digital elevation models dems with a vertical and horizontal accuracy in the sub metre range between september 2001 and august 2002 three laser scanner data acquisition flights were carried out covering the whole area of engabreen norway and corresponding well to the measurement dates for the mass balance year 2001 02 the data quality of the dems is assessed e g by comparing the values with a control area which has been surveyed independently or gps ground profiles measured during the flights for the whole glacier surface elevation change and consequently volume change is calculated quantified and compared with traditional mass balance data for the same time interval for the winter term emergence submergence velocity is determined from laser scanner data and snow depth data and is compared with velocity measurements at stakes the investigations reveal the high potential of airborne laser scanning for measuring the extent and the topography of glaciers as well as changes in geometry area volume

airborne gravimetry from a small twin engine aircraft over the long island sound in january 1990 a test of the feasibility of airborne gravimetry from a small geophysical survey aircraft a cessna 404 was conducted over the long island sound using a bell aerospace bgm 3 sea gravity meter gravity has been measured from large aircraft and specially modified de havilland twin otters but never from small standard survey aircraft the gravity field of the long island sound is dominated by an asymmetric positive 30 rngal anomaly which is well constrained by both marine and land gravity measurements using a trimble 4000 gps receiver to record the aircraft s horizontal position and radar altimeter elevations to recover the vertical accelerations gravity anomalies along a total of 65 km were successfully measured the root mean square rms difference between the airborne results and marine measurements within 2 km of the flight path was 2 6 mgai for 15 measured values the anomalies recovered from airborne gravimetry can also be compared with the gridded regional free air gravity field calculated using all available marine and land gravity measurements the rms difference between 458 airborne gravity measurements and the regional gravity field is 2 7 mgai this preliminary experiment demonstrates that gravity anomalies with wavelengthsas short as 5 km can be measured from small aircraft with accuracies of 2 7 mgal or better the gravity measurements could be improved by higher quality vertical and horizontal positioning and tuning the gravimeter s stabilized platform for aircraft use

geodetic and tectonic analyses along an active plate boundary the central gulf of california the gulf of california is traversed by the shear plate boundary between pacific and north american plates and because of several islands in its central part offers the possibility of direct geodetic measurements of plate motion a geodetic network of 150 km aperture and comprising 11 stations was measured in 1982 and 1986 by laser trilateration methods the deformations deduced from the comparison of the two epochs indicate right lateral shear strain covering the entire gulf rather than localized movements in the eastern part of the network between the axial islands and the sonoran coast significant right lateral shear deformation occurs with a relative displacement of about 23 12 cm over 4 years in the northwestern region canal de ballenas a right lateral displacement of about 17 4 cm is observed whereas in the southwestern part of the network canal sal si puedes the deformation remains very weak this suggests that south of the canal de ballenas the plate boundary is locked a tectonic analysis of neogene and quaternary faults in baja california sonora and the central islands of the gulf permitted the reconstruction of the stress pattern evolution of this area these data also indicate the predominance of right lateral motion on a nw se trending zone within a regional framework characterized by an approximately n s compression and an e w extension the geodetic results are discussed in comparison with the neotectonic analysis and the seismic data available in the area the data suggest a broad strain accumulation zone covering the totality of the central gulf of california a nw se relative velocity of about 8 3 cm yr is found between the two sides of the gulf during the 1982 1986 interval

the alpine swiss french airborne gravity survey summary in february 1998 a regional scale airborne gravity survey was carried out over the french occidental alps within the framework of the geofrance 3 d research program the survey consisted of 18 ns and 16 ew oriented lines with a spacing of 10 and 20 km respectively covering the whole of the western french alps total area 50 000 km2 total distance of lines flown 10 000 km the equipment was mounted in a medium size aircraft dehavilland twin otter flowing at a constant altitude of 5100 m a s l and at a mean ground speed of about 280 km h 1 gravity was measured using a lacoste romberg relative air sea gravimeter type sa mounted on a laser gyro stabilized platform data from 5 gps antennae located on fuselage and wings and 7 ground based gps reference stations were used to determine position and aircraft induced accelerations the gravimeter passband was derived by comparing the vertical accelerations provided by the gravimeter with those estimated from the gps positions this comparison showed that the gravimeter is not sensitive to very short wavelength aircraft accelerations and therefore a simplified formulation for computing airborne gravity measurements was developed the intermediate and short wavelength non gravitational accelerations were eliminated by means of digital exponential low pass filters cut off wavelength 16 km an important issue in airborne gravimetry is the reliability of the airborne gravity surveys when compared to ground surveys in our studied area the differences between the airborne acquired bouguer anomaly and the ground upward continued bouguer anomaly of the alps shows a good agreement the rms of these differences is equal to 7 68 mgal for a spatial resolution of 8 km however in some areas with rugged topography the amplitudes of those differences have a striking correlation with the topography we then argue that the choice of an appropriate density reduction by a factor of 10 per cent for computing the ground topographic corrections over the highest mountains results in significantly reducing the differences between airborne and ground upward continued bouguer anomalies which shows that some of the misfit stems from errors in the ground data

time variable gravity signal during the water impoundment of china s three gorges reservoir 1 beginning in 2003 china s three gorges reservoir will start water impoundment in phases by 2009 it will be holding 40 km3 of water flooding a stretch of middle yangtze river about 600 km in length the water impoundment process represents a geophysical controlled experiment offering a unique opportunity for detailed studies of a classical forward inverse modeling problem of surface loading while wang 2000 studied the large loading effects on a local scale we aim for longer spatial scales upwards from several hundred km specially on the time variable gravity signals that can be detected by the newly launched grace satellite mission whose 5 year lifetime until 2007 will span the major impoundment period our results using the green s function method adopting the prem elastic earth model indicate that the per year geoid height increase is above the grace observational sensitivity out to harmonic degree 20 and to degree 50 corresponding to a wavelength of 800 km when integrated over the 5 year period

an airborne gravity study of eastern north carolina the naval research laboratory nrl has developed a prototype airborne gravity measurement system the core of the system is a lacoste and romberg air sea gravity meter mounted on a three axis stable platform corrections to the gravimeter data for altitude and variations in altitude are determined from a combination of highly precise radar and pressure altimeters the original prototype system was designed for use over oceanic areas we recently incorporated the pressure measurement to extend use of the airborne system to terrestrial regions where occasional radar altitudes over points of known topographic height can be obtained the radar heights are used to relate the pressure altitudes to absolute altitudes and to determine the slopes of the isobaric surfaces vertical accelerations due to horizontal velocity over a curved rotating earth the eotvos correction and precise two dimensional positions are determined from a texas instrument p code global positioning system the updated system was tested

gps measurements from the ladakh himalaya india preliminary tests of plate like or continuous deformation in tibet observations of relative motion in a geodetic network in ladakh india and across southern tibet indicate slow shear on the karakorum fault rapid east west extension across the whole of southern tibet and constant arc normal convergence between india and southern tibet along the himalayan arc measurements of ten campaign style and six permanent sites with global positioning system gps precise geodesy provide these bounds on the style and rates of the large scale deformation in the tibet himalaya region divergence between sites at leh ladakh india and shiquanhe western tibet as well as slow relative motion among sites within the ladakh network limit right lateral slip parallel to the karakorum fault to only 3 4 5 mm yr this low rate concurs with a recent estimate of 3 4 mm yr for late holocene time but disagrees with the much higher rate of 30 35 mm yr that has been used to argue for plate like behavior of the tibetan plateau convergence between ladakh and the indian subcontinent at 18 8 3 mm yr at 224 17 1 differs little from estimates of convergence across the central segment of the himalaya finally lengthening of the baseline between leh ladakh and lhasa in southeastern tibet at 17 8 1 mm yr or between leh and bayi farther to the southeast at 18 3 mm yr is consistent with an extrapolation of rates of east west extension of the tibetan plateau based both on shorter gps baselines e g lhasa simikot and on diverging slip vectors of earthquakes in the himalaya we interpret these results to indicate that tibet behaves more like a fl uid than like a plate

variegated glacier alaska usa a century of surges a 1995 surge of variegated glacier alaska usa is discussed in the context of its six 20th century predecessors especially the previous surge in 1982 83 which was studied in detail the average time between surge initiations is 15 years the 1995 surge was considerably weaker than its predecessors having a single phase or at most a very weak second phase the 1995 surge confirms that there is a seasonal cycle with surge initiation in winter and termination in the first part of the melt season and a correlation between weather and both surge termination date and surge extent two days of record high temperature correlated with the termination of the 1995 surge the most obvious issue is the absence of a strong second surge phase as there was in the 1982 83 surge culminating in a surge extent more in line with that of the predecessors this is considered in the light of a simple criterion for surge initiation and re initiation which depends upon the evolving basal shear stress

crustal deformation measurements in central japan determined by a global positioning system fixed point network a global positioning system gps fixed point network has been operating in the kanto and tokai districts of central japan since april 1988 to detect crustal deformation associated with the convergence of the eurasian pacific north american and philippine sea plates and to monitor the deformation cycles of frequent large interplate and intraplate earthquakes this 10 station network established by the national research institute for earth science and disaster prevention nied is the first continuously monitoring network of its kind we determine deformation within the network using two consecutive days of data every 2 weeks for the first 17 months of operations we use a station and orbit relaxation method which relies exclusively on data collected within the nied network except for 1 week of global gps tracking data which is used to determine initial station positions with respect to the global reference frame we detect relative to a station on the eurasian plate in central japan significant westward motion of 28 mm yr of the northern tip of the philippine sea plate which is subducting beneath the eurasian plate at the suruga trough our results support finite element models of collision of the izu block with the eurasian plate based on earthquake focal mechanisms and plate block motions of the japanese archipelago determined from conventional geodetic measurements over the last century we detect southwestward motion of 18 mm yr of the southeastern tip of the eurasian plate confirming expected surface extension of the subducted plate parallel to the suruga trough axis significant vertical uplift with a velocity of 20 mm yr is suggested at a site inland of the tokai district located in the akaishi uplift zone and at a site on hatsushima island in sagami bay the general tendency of vertical movements of the other sites agrees with vertical velocities obtained from 70 years of geodetic leveling and with quaternary vertical displacements determined from geomorphological and other geological evidence we detect no significant crustal motion across the fossa magna tectonic zone in central japan often considered a plate boundary across the tokyo metropolitan area nor across the sagami trough associated with the subduction of the philippine sea plate beneath northeast japan our results demonstrate the power of regionally based continuously monitoring gps networks for obtaining temporally dense measurements of small horizontal and vertical crustal movements across plate boundary zones

recent plate motions and crustal deformation reports by u s workers on geodetic measurements of recent plate motions or crustal deformation published in 1987 1990 are reviewed the review begins with global plate motions proceeds through plate boundaries in california alaska and the pacific northwest and finishes with volcanic phenomena monument stability and longevity and gps relative position measurements 184 refs

postseismic strain following the 1989 loma prieta earthquake from gps and leveling measurements postseismic deformation in the 5 years following the 1989 loma prieta earthquake has been measured with the global positioning system and precise leveling postearthquake velocities at distances greater than 20 km from the coseismic rupture are not significantly different from those observed in the 20 years prior to the earthquake however velocities at stations within 20 km of the rupture exceed preearthquake rates and exhibit unanticipated contraction normal to the strike of the san andreas fault system a combination of forward modeling and nonlinear optimization suggests that the observed postseismic deformations were caused by aseismic oblique reverse slip averaging 2 9 cm yr on the san andreas fault and or the loma prieta rupture zone and 2 4 cm yr reverse slip along a buried fault within the foothills thrust belt the best fitting sources of postseismic deformation are all located at depths of less than 15 km we find no evidence for accelerated flow or shear below the loma prieta rupture in the first 5 years following the earthquake the inferred postseismic slip is likely to have been caused by the coseismic stress change updip of the 1989 rupture

evaluation of the 1984 alaska global positioning system campaign with the bernese gps software during the summer of 1984 five ti 4100 global positioning system gps receivers were used to measure an eight station network in alaska and canada previously measured with mobile very long baseline interferometry vlbi systems with baselines ranging from 300 km to almost 2700 km the observations have been processed in the network mode with the bernese gps software using orbit improvement techniques the comparisons of the gps and vlbi solutions established through a seven parameter helmert transformation show an agreement of the order of 0 1 ppm for all solutions no significant scale factor between gps and vlbi coordinates could be detected these results demonstrate for the first time the power of orbit improvement in conjunction with network processing of gps phase observations

map based methods for estimating glacier equilibrium line altitudes we examine the validity of two methods for estimating glacier equilib rium line altitudes elas from topographic maps the ela determined by contour inflection the kinematic ela andthe mean elevation of the glacier correlate extremely well with the ela determined from mass balance data observed ela however the range inglacierelevations above sea level is much larger thanthe variation in ela mak ing this correlation unhelpful the data were normalized and a reasonable correlation r 2 0 59 was found between observed and kinematic ela the average of the normal ized kinematic elas was consistently located down glacier fromthe observed ela con sistent withtheory thenormalized mean elevationoftheglacierexhibitedno correlation and suggests that the toe headwall altitude ratio is not a good approximation for the ela kinematic waves had no effect on the position of the kinematic ela therefore topographic maps of glacier surfaces can be used to infer the position of the ela and provide a method for estimating past elas from historic topographic maps

an introduction to the global positioning system and some geological applications receivers equipped to measure dual frequency carrier phase signals from satellites of the global positioning system gps have been capable under special conditions of determining relative horizontal positions among stations separated by one to a few hundred kilometers with a precision of one to several millimeters since the early 1980s the major obstacles to making this capability routine extending it to all parts of the globe and extending it to longer station separations have been equipment cost limitations in the gps satellite constellation arduous data analysis uncertainties in satellite orbits uncertainties in propagation delays associated with variable tropospheric water vapor and difficulties in resolving carrier phase cycle ambiguities recent improvements have occurred in all these areas the increasing ease and reduced cost of gps data acquisition and analysis are having a significant impact on studies of near fault crustal deformation and earthquake processes until recently the province of conventional terrestrial geodetic techniques the enhanced satellite constellation improved models and establishment of global tracking networks have extended several millimeters horizontal positioning capability to station separations of 1000 km or more in virtually all parts of the world this enables study of new classes of tectonic problems that previously were difficult to attack with any geodetic technique examples include a complete kinematic description of ongoing crustal deformation in broad complex continental plate boundary zones and measurement of relative plate motion at convergent boundaries where global models may be poorly constrained

mass balance in the glacier bay area of alaska usa and british columbia canada 1995 2011 using airborne laser altimetry the glacier bay region of southeast alaska usa and british columbia canada has undergone major glacier retreat since the little ice age lia we used airborne laser altimetry elevation data acquired between 1995 and 2011 to estimate the mass loss of the glacier bay region over four time periods 1995 2000 2000 05 2005 09 2009 11 for each glacier we extrapolated from center line profiles to the entire glacier to estimate glacier wide mass balance and then averaged these results over the entire region using three difference methods normalized elevation area weighted method and simple average we found that there was large interannual variability of the mass loss since 1995 compared with the long term post lia average for the full period 1995 2011 the average mass loss was 3 93 0 89 gt a 1 0 6 0 1 m w e a 1 compared with 17 8 gt a 1 for the post lia 1770 1948 rate our mass loss rate is consistent with grace gravity signal changes for the 2003 10 period our results also show that there is a lower bias due to center line profiling than was previously found by a digital elevation model difference method

estimating volume change of mountain glaciers using srtm and map based topographic data this paper describes a method for estimating the volume change of mountain glaciers using the shuttle radar topography mission srtm c band data 2000 and a digital elevation model dem generated from topographic maps this approach was developed with srtm data and topographic maps of 1 25 000 scale 1977 from the akshiirak glaciers tien shan central asia the dem for 1977 was generated using 10 m contour lines from 18 map sheets covering the akshiirak massif and surrounding area the nominal vertical accuracy of the maps is 3 3 m the standard deviation of the differences between the map derived dem and the srtm data on glacier free areas of less than 25deg is 6 3 m a single localized region in the western periphery of the study area with systematic error in the srtm data from 20 to 12 m on a 30 km spatial scale was found and excluded from the error analysis assuming a 10 m map error on the upper snow covered glacier areas the estimated root mean square error of the glacier surface change is 8 2 m from 1977 to 1999 the average glacier surface thinning is 15 1 m and the estimated volume loss is 6 15 km3 the rate of the akshiirak glacier volume loss has increased by 2 7 times compared with historical data from 1943 to 1977 the srtm data show an opportunity for quantifying climatic and dynamic surface elevation changes in mountain glaciers ice cloud and land elevation satellite icesat laser altimetry and srtm data could also be used for the estimation of short term surface changes of mountain glaciers

airborne and spaceborne dem and laser altimetry derived surface elevation and volume changes of the bering glacier system alaska usa and yukon canada 1972 2006 using airborne and spaceborne high resolution digital elevation models and laser altimetry we present estimates of interannual and multi decadal surface elevation changes on the bering glacier system alaska usa and yukon canada from 1972 to 2006 we find 1 the rate of lowering during 1972 95 was 0 9 0 1 m a 1 2 this rate accelerated to 3 0 0 7 m a 1 during 1995 2000 and 3 during 2000 03 the lowering rate was 1 5 0 4 m a 1 from 1972 to 2003 70 of the area of the system experienced a volume loss of 191 17 km 3 which was an area average surface elevation lowering of 1 7 0 2 m a 1 from november 2004 to november 2006 surface elevations across bering glacier from mcintosh peak on the south to waxell ridge on the north rose as much as 53 m up glacier on bagley ice valley about 10 km east of juniper island nunatak surface elevations lowered as much as 28 m from october 2003 to october 2006 nasa terra modis observations from may to september 2006 indicated muddy outburst floods from the bering terminus into vitus lake this suggests basal englacial hydrologic storage changes were a contributing factor in the surface elevation changes in the fall of 2006

global plate velocities from the global positioning system we have analyzed 204 days of global positioning system gps data from the global gps network spanning january 1991 through march 1996 on the basis of these gps coordinate solutions we have estimated velocities for 38 sites mostly located on the interiors of the africa antarctica australia eurasia nazca north america pacific and south america plates the uncertainties of the horizontal velocity components range from 1 2 to 5 0 mm yr with the exception of sites on the pacific and nazca plates the gps velocities agree with absolute plate model predictions within 95 confidence for most of the sites in north america antarctica and eurasia the agreement is better than 2 mm yr we find no persuasive evidence for significant vertical motions 3 standard deviations except at four sites three of these four were sites constrained to geodetic reference frame velocities the gps velocities were then used to estimate angular velocities for eight tectonic plates absolute angular velocities derived from the gps data agree with the no net rotation nnr nuvel 1a model within 95 confidence except for the pacific plate our pole of rotation for the pacific plate lies 11 5 west of the nnr nuvel 1a pole with an angular speed 10 faster our relative angular velocities agree with nuvel 1a except for some involving the pacific plate while our pacific north america angular velocity differs significantly from nuvel 1a our model and nuvel 1a predict very small differences in relative motion along the pacific north america plate boundary itself our pacific australia and pacific eurasia angular velocities are significantly faster than nuvel 1a predicting more rapid convergence at these two plate boundaries along the east pacific rise our pacific nazca angular velocity agrees in both rate and azimuth with nuvel 1a

global positioning system network analysis with phase ambiguity resolution applied to crustal deformation studies in california a 5 year campaign is in progress in central and southern california to monitor tectonic motions using observations of the global positioning system gps satellites evidence from geological and space geodetic data indicates that significant horizontal deformations of order 10 mm yr are occurring west of the san andreas fault along the california margin we demonstrate using data from initial epoch measurements in january 1987 that the goal of measuring horizontal deformations with an accuracy of 5 mm yr over the duration of the campaign should be readily achievable the gps network was designed to span a wide range of baseline lengths within california and across north america to aid in phase ambiguity resolution an important factor in achieving highest accuracy baseline determinations we present an efficient algorithm for multisession network analysis of gps data with simultaneous orbit determination and ambiguity resolution using this algorithm with the california data we demonstrate the improvement obtained in station position and satellite orbit estimation when the phase ambiguities are resolved we demonstrate several millimeters 1 part in 108 short term repeatability over five single session daily analyses for horizontal baseline components and length and several tens of millimeters for the vertical comparison with the independently determined very long baseline interferometry baseline between mojave and owens valley suggests that the accuracy is at the same level as the repeatability we show that simultaneous multisession analyses with ambiguity resolution improve the baseline and satellite orbit estimates compared to the single session analyses with the single session analyses we were able to resolve all phase ambiguities on baselines within california with the multisession analyses we were able to resolve the phase ambiguities for most of the network over regional and continental scales

interdecadal sea surface temperature sea level pressure coupled variability in the south pacific ocean 1 the main coupled sea surface temperature sst sea level pressure slp variability at interdecadal timescale in the south pacific is studied by means of correlation and combined complex empirical orthogonal function cceof analyses the sst slp coupled variability presents a bidecadal cycle from mid 1950s to 1970s and a decadal cycle from 1980s to early 1990s reproducing the enso like interdecadal oscillation particularly the first sst slp cceof mode describes the bidecadal cycle characterized by westward progression of sst and slp anomalies along the tropical pacific while the second sst slp cceof mode shows the decadal cycle with eastward development during both bidecadal and decadal cycles the sst fluctuations in the eastern equatorial pacific and along the western coast of south america are primarily forced by equatorial zonal wind variability specially during the bidecadal cycle the alongshore sst variability south of 30 s is maintained and reinforced by meridional coastal wind fluctuations associated with a stationary slp pattern off southern chile this stationary slp pattern appears connected to sst fluctuations in the central tropical pacific

assessment of global positioning system measurements for studies of crustal deformation the u s geological survey has been using the global positioning system gps to perform repeated surveys of networks of different sizes since january 1986 the intersite distances from these various networks are 223 km for a single line connecting the palos verdes and vandenberg sites in southern california 30 50 km for a network of three sites south of the san francisco bay near loma prieta 9 30 km for a network located near hebgen lake montana 7 12 km for a network of sites in the vicinity of parkfield california and 240 m for a line located at the goldstone antenna complex in the mojave desert the lengths quoted do not include the intersite distances for the fiducial sites included in the solutions for orbit determination which can be up to 8000 km we have attempted to assess the long term precision and accuracy of determinations of relative site position for a range of line lengths this assessment has consisted of several different studies in assessing precision we have generally investigated repeatability usually about a best fit linear temporal trend the smallest fractional repeatability was yielded by the measurements on the palos verdes to vandenberg line the root mean square rms residual about the best fit line for these determinations was 6 mm 0 03 parts per million or ppm for the north component 11 mm 0 05 ppm for the east component and 40 mm 0 18 ppm for the vertical component for these determinations gps data from 3 4 consecutive days were combined to produce a single estimate of the vector separation we also used the day to day scatter from these measurements to perform an analysis of variance and found that these multiday determinations can be significantly more precise than estimates determined from a single observing session the worst results were obtained for the loma prieta network where we obtained rms residuals of 11 12 mm 0 3 0 4 ppm for north 14 18 mm 0 3 0 6 ppm for east and 18 21 mm 0 4 0 7 ppm for vertical we cannot definitely explain these poor results but we have evidence to indicate that this poor scatter is due to the short observing session 4 5 hours compared to 6 5 hours for the palos verdes to vandenberg results in assessing accuracy we compared the gps results to those from independent techniques at parkfield we compared the gps estimates of fault parallel motion to those from creep meters and alignment arrays and found excellent agreement within 1 2 mm yr 1 not only for the slip but also for the variation of slip along the san andreas fault we compared the loma prieta and hebgen lake line length estimates to those obtained from a geodolite a high precision laser distance measurement device that the u s geological survey has used for 20 years for studies of crustal deformation if we model the geodolite minus gps line length differences l as l l where l is the line length then we find 0 6 0 5 mm and 0 1 0 1 mm km 1 the uncertainties quoted are one standard deviation from this comparison we conclude that at this level of significance there is no detectable difference between lengths determined from geodolite and gps data finally we compared the gps estimates of the palos verdes to vandenberg line length to those obtained from very long baseline interferometry vlbi the mean difference between the six gps estimates of line length and a best fit line through the vlbi estimates was 1 mm and the rms difference was 12 mm 0 05 ppm close to the standard deviation of the gps measurements for this predominantly east west line

quiescent phase evolution of a surge type glacier black rapids glacier alaska u s a black rapids glacier a surge type glacier in the alaska range most recently surged in 1936 37 and is currently in its quiescent phase mass balance ice velocity and thickness change have been measured at three to ten sites from 1972 to 1994 the annual speed has undergone cyclical fluctuations of as much as 45 about the mean speed ice thickness and surface slope did not change enough to cause the speed fluctuations through changes in ice deformation which indicates that they are being driven by changes in basal motion the behavior of black rapids glacier during this quiescent phase is significantly different from that variegated glacier another well studied surge type glacier in alaska the present medial moraine configuration of black rapids glacier indicates that a surge could occur at any time however ice velocity data indicate that the next surge may not be imminent we believe that there is little chance that the next surge will cross and dam the delta river

consequences of regime shifts for marine food webs climate mediated ecological regime shifts can re structure entire ecosystems from primary producers to top predators as a consequence major trophodynamic pathways change with the altered mix of dominating species four cases of ecosystem regime shifts forced by climate variability are presented north sea central baltic sea central north pacific and humboldt current ecosystems and the effect on food chains is elucidated different types of trophodynamic control mechanisms set in motion through the impact of climate variability and the potential impact of regime shifts on biogeochemical cycles are discussed

airgrav results a comparison of airborne gravity data with gsc test site data sander geophysics sgl has developed an airborne gravimeter system that uses three orthogonal accelerometers mounted on a three axis gyroscopically stabilized platform the system called airgrav airborne inertially referenced gravimeter was designed specifically for airborne use this has resulted in an instrument with significant advantages over the modified sea gravimeters commonly used for airborne surveying the main benefit of the new instrument is that it is more stable in attitude and less subject to noise from horizontal accelerations

airborne surface profiling of glaciers a case study in alaska a relatively lightweight and simple airborne system for surface elevation profiling of glaciers in narrow mountain valleys has been developed and tested the aircraft position is determined by kinematic global positioning system gps methods the distance to the glacier surface is determined with a laser ranger the accuracy is about 0 3 m sufficient to permit future changes to be observed over short time intervals long term changes can be estimated by comparison of profiles with existing maps elevation profiles obtained in 1993 94 from three glaciers in central and south central alaska are compared with maps made about 1950 the resulting area averaged seasonally corrected thickness changes during the interval are gulkana glacier central alaska range 11 m worthington glacier central chugach mountains 7 m and bear lake glacier kenai mountains 12 m all three glaciers retreated during the interval of comparison the estimated uncertainty in the average thickness change is 5 m which is mainly due to errors in the existing maps constraints on the accuracy of the maps are obtained by profiling in proglacial areas

improved sea level monitors for measuring vertical crustal deformation in the shumagin seismic gap alaska we have improved the relative vertical deformation detection capability of a network of sea level gauges in the shumagin seismic gap alaska an examination of the present noise levels suggests that the network is now capable of providing relative vertical deformation data that is quieter than data from leveling the global positioning system very long baseline interferometry or satellite laser ranging

interferometric global positioning system three dimensional positioning source for airborne gravimetry the naval research laboratory nrl and the national geodetic survey recently collaborated on an experiment to test interferometric mode global positioning system gps tracking as a source of altitude and vertical acceleration for airborne gravity measurement reduction a texas instruments ti 4100 gps receiver and an extremely precise radar altimeter were installed in an nrl p 3 orion aircraft a second ti 4100 was located at a fixed base station of known location carrier phase data from four gps satellites were recorded from the fixed and airborne receivers and postprocessed to produce three dimensional displacements of the airborne station relative to the base station differences in gps and radar altimeter coordinate systems were modeled and removed the resulting gps and radar altitudes were compared the two unfiltered 1 hz data sets differed by an rms of 20 cm when aircraft dynamics were controlled by autopilot in straight and level flight during hand flown maneuvers such as turns climbs and descents rms differences varied from 40 to 80 cm a significant portion of the differences can be attributed to remaining coordinate system discrepancies and to uncompensated geometric effects due to aircraft motion we have also examined vertical acceleration time series produced by doubly differencing both data sets by applying a low pass filter which allows resolution of features with wavelengths of 20 km and greater at nominal aircraft speeds of 100 m s the rms difference between the radar and gps derived vertical accelerations was less than 2 mgal 2 10 5 m s2 during straight and level flight it should be possible to improve this accuracy and wavelength resolution with future improvements in measurement and processing techniques the results of this experiment show that the incorporation of interferometric mode gps tracking into the airborne gravity measurement system will make possible rapid and relatively inexpensive gravity surveys over any type of terrain while simultaneously providing accurate measurements of ground height profiles beneath the aircraft

carrier phase ambiguity resolution for the global positioning system applied to geodetic baselines up to 2000 km the global positioning system gps carrier phase data are biased by an integer number of cycles a successful strategy has been developed and demonstrated for resolving these integer ambiguities for geodetic baselines of up to 2000 km in length resulting in a factor of 3 improvement in baseline accuracy and giving centimeter level agreement with coordinates inferred by very long baseline interferometry in the western united states for this experiment a method using pseudorange data is shown to be more reliable than one using ionospheric constraints for baselines longer than 200 km an automated algorithm exploits the correlations between the many phase biases of a gps receiver network to enable the resolution of ambiguities for very long baselines a method called bias optimizing has been developed which unlike traditional bias fixing does not require an arbitrary confidence test bias optimizing is expected to be preferable to bias fixing for poorly configured networks in order to enable ambiguity resolution for long baselines it is recommended that future gps networks have a wide spectrum of baseline lengths ranging from 1000 km and that gps receivers be used which can acquire dual frequency p code data

geodetic airborne laser altimetry of breidamerkurjokull and skeidararjokull iceland and jakobshavns isbrae west greenland

airborne gravity is here the achievement of practical and useful airborne gravity exploration for petroleum is a major culmination of more than twenty years of research and development commercial surveys have now been conducted for three years the precision and anomaly resolution attainable are twice as good as that of current shipborne gravity data this paper presents data to demonstrate the precision of airborne gravity and discusses its usefulness with simultaneous magnetics and topography industrial acceptance of the method portends a new era in geophysical exploration for oil and gas which gives promise to double the effectiveness of explorations on land in both time and cost

airborne measurement of glacier surface elevation by scanning laser altimeter airborne scanning laser altimetry is a relatively new technique for remote sensing ofground elevation a laser ranger is scanned across a swath beneath the aircraft producing a two dimensional distribution of elevations when combined with d ata on aircraft position and orientation smooth snow covered glaciers are ideal surfaces for las er scanning since they are highly refl ective a new prototype laser sys tem is des cribed together with results from hardangerjokulen norway an a nalys is o f the data shows that noise levels are very low at around 2 cm and th at repeatability between over lapping swaths is approximately 10 cm this is consistent with an absolute accuracy of 15 cm or better from manufacturer s and other measurements swath widths of over i km are attainable allowing complete coverage of sma ll to medium siz ed glaciers using para l lel oight tracks the hi g h accuracy and dense even coverage about 20000 points per km 2 gives good quality derived products such as de m s and enables reliable measure ment of glacier volume change scanning laser a ltimetr y has many advantages over photogrammetry whi ch was previously the only remote se nsing method o f measuring elevations over large a reas but which performs poorly over snow covered glaciers

airborne gravimetry using a strapped down lacoste and romberg air sea gravity meter system a feasibility study marine gravimeters mounted on stabilized platforms are commonly used in aircraft to perform airborne gravity measurements the role of the stabilized platform is to level the sensor mechanically whatever the aircraft attitude however this compensation is generally insufficient due to the sensitivity of modern gravity sensors correcting the offlevel error requires that an offlevel correction calculated from positioning data be added to gravimeter measurements which complicates not only the processing but also the assessment of precision and resolution this paper is a feasibility study describing the levelling of a completely strapped down lacoste and romberg gravimeter for airborne gravimetry operation by means of gps positioning data it focuses on the calculation of the sensor offlevel correction needed for the complete gravity data processing the precision of the offlevel correction that can be achieved in terms of gps data precision and gravity wavelengths is theoretically studied and estimated using the gravity and gps data acquired during the alpine swiss french airborne gravity survey carried out in 1998 over the french western alps while a 1 cm precision of gps determined baseline coordinates is sufficient to achieve a 5 mgal precision of the offlevel correction we maintain that this precision has to reach 1 mm to ensure a 1 mgal precision of the offlevel correction at any wavelength without a stabilized platform the onboard instrumentation becomes significantly lighter furthermore the correction for the offlevel error is straightforward and calculated only from gps data thus the precision and the resolution of airborne gravity surveys should be estimated with a better accuracy

intrathermocline eddies in the coastal transition zone off central chile 31 41 s 1 the three dimensional structure and the origin of mesoscale anticyclonic intrathermocline eddies ites in the coastal transition zone ctz off central chile 31 41 s were analyzed through the combination of data from oceanographic cruises and satellite altimetry and the application of an eddy resolving primitive equation ocean model coupled with a numerical experiment using a passive tracer in this region ites are represented by subsurface lenses 100 km diameter 500 m thickness or vertical extension of nearly homogeneous salinity 34 5 and oxygen deficient 1 0 ml l 1 waters properties which are linked to the equatorial subsurface water mass essw transported poleward by the peru chile undercurrent pcuc in the coastal band at least five to seven ites were observed simultaneously in the area between 31 and 38 s during winter cruises in 1997 and 2009 satellite data indicated that the ites identified from in situ data moved westward each at a mean speed of 2 km d 1 and transported a total volume of 1 106 m3 s 1 1 sv the lifespan of each ite ranged from a few months to 1 year model results indicate that ites become detached from the pcuc under summer upwelling conditions in the coastal zone

vertical energy flux at enso time scales in the subthermocline of the southeastern pacific the question of how energy is redistributed in the ocean has renewed the interest for the processes leading to midlatitude subthermocline variability at low frequency here we investigate a process that has been disregarded although potentially relevant for climatic studies dealing with the planetary energy budget the focus is on the southeastern pacific where an efficient oceanic teleconnection takes place linking the remote surface equatorial momentum forcing with the subthermocline through the vertical propagation of low frequency long wavelength extratropical rossby waves etrw a high resolution model is used to document the vertical energy flux associated with etrw at interannual to decadal time scales the analysis of a long term 1958 2008 simulation reveals that the vertical energy flux can be interpreted to a large extent as resulting from the coastally forced etrw as far south as 35 s so that heat content variability can be predicted along theoretical trajectories originating from the coast below the thermocline it is shown that the vertical energy flux associated with the el nino southern oscillation forms beams below the thermocline that account for a large fraction of the total vertical energy flux at interannual time scales extreme el nino events are the dominant contributor to this flux which is hardly impacted by mesoscale activity the energy beams experience a dissipation processes in the ocean below 1000 m that is interpreted as resulting from vertical turbulent diffusion our results suggest that the etrw at enso time scales are strongly dissipated at the surface but still can modulate the heat content in the deep ocean of the southeastern pacific

delineation of a complexly dipping temperate glacier bed using short pulse radar arrays we have defined the complex bed topography for a section of a small temperate glacier using 50 mhz monostatic short pulse radar data and a synthetic aperture array processing method the data were collected on a 100 m by 340 m array grid in the upper stem of gulkana glacier central alaska u s a the array processing was based on a modified three dimensional 3 d kirchhoff migration integral and implemented with a synthetic aperture approach that uses sequences of overlapping sub arrays to generate depth images in vertical planes typical sub array beam patterns are generally 5 at the 6 db level giving a flashlight like searching capability without distorting the wavelet shape the bed topography was constructed using normal reflections picked from 3 d array depth images in some instances reflections were imaged outside the data coverage area the bed surface dips steeply both parallel and transverse to the direction of ice flow the maximum observed depth is roughly 140 m the 3 d method resolved bed dips up to 45 in regions of steepest dip it improved depth accuracy by 36 compared with raw data and by 15 compared with standard two dimensional 2 d migration over 12 db of signal to noise improvement and improved spatial resolution was achieved compared to raw data and 2 d migration false bottom layering seen in the raw data and in 2 d migrations is not observed in the 3 d array results furthermore loss of bottom reflections is shown by the 3 d migration to be attributable to the dip and curvature of the reflector and not scattering losses or signal clutter from englacial inclusions

verification of airborne positioning using global positioning system carrier phase measurements two experiments have been conducted to determine the accuracy with which an aircraft can be positioned in flight using carrier phase measurements from satellites of the navstar global positioning system gps in each experiment a photogrammetric camera was flown over a calibration area providing ground control that enabled aerotriangulation to be performed on ground targets or conversely for the camera position to be independently determined gps measurements were used to determine the position of an antenna located on the aircraft at the time of each photo and using the fixed antenna camera vector to determine the positions of the camera the gps derived camera positions were then used to compute the positions of the ground targets in an experiment in texas the differences between the conventional and gps based aerotriangulation display biases of 1 3 cm horizontally and 28 cm vertically and rms differences of about 2 cm 3 cm and 6 cm in north east and height respectively the camera positions derived from the aerotriangulation showed similar biases when compared to the gps derived camera positions and rms differences of about 7 cm in the horizontal and 9 cm in height because of edge effects in the photography the actual precision is slightly better a second experiment in washington revealed biases of several meters apparently due to unresolved coordinate system differences however a helmert transformation in this case produced rms differences between gps derived and photogrammetrically determined ground positions of 3 5 cm while these results demonstrate the need for care in relating gps results to other geodetic measurements they also show the great potential of gps carrier phase measurements for precise kinematic positioning and a variety of remote sensing applications

early mesozoic rift basins of eastern north america and their gravity anomalies the role of detachments during extension two end member models of extension involving detachments have been developed one model incorporates a fault that soles at mid crustal level overlying a broad region of pure shear in the lower crust the second referred to as the simple shear model includes a detachment continuing through the entire crust and terminating in a region of concentrated extension in the lower crust both models predict basins with no localized thermal effect with the inclusion of flexural isostasy both models predict footwall uplift whose amplitude and wavelength are controlled by the detachment geometry and the lithospheric strength a gravity anomaly over the hanging wall block distinguishes the simple shear model from the intracrustal detachment model the early mesozoic basins of the eastern north america believed to have formed as the result of the normal slip reactivation of a paleozoic thrust system as the atlantic opened are associated with distinctive hanging wall gravity highs these gravity highs the basin geometry the lack of a thermal subsidence phase in the rift basins and the presence of a highly extended and heated region to the east suggest that the simple shear model may be applied the simple shear model fits the outer hanging wall anomaly and permits a region of lower crustal extension to be mapped these basins contain an abundance of basalt flows and diabase sills despite the lack of evidence for regional heating or thermal subsidence implying that a source external to the basin must exist for this magmatic material the detachment fault may facilitate the movement of the molten mafic material into the rift basins from an offshore region of greater heating and extension the addition of 2 km of mafic material along the model detachment accounts for the observed inner gravity high and the lack of a negative gravity anomaly across these basins the match of this modified simple shear model to the observed gravity suggests that the region of greater extension seaward of the hinge zone is the source for the widespread dikes and sills within the basins and the coastal plain and helps explain the geochemical homogeneity of these intrusives and extrusives along 2000 km of the eastern seaboard

laser profiling over antarctic ice streams methods and accuracy we assess the accuracy and precision of the u s national science foundation s support office for aerogeophysical research soar laser profiling system for mapping topography and detecting surface elevation changes of west antarctic ice streams the procedures used to process calibrate and validate the laser navigation and global positioning system gps data are presented the primary objective is to produce surface elevations with the best possible resolution repeat surveys of a grid of lines over whillans ice stream and ice streams c and e were conducted in the 1997 98 and 1999 2000 seasons the procedure has been calibrated using special test flights conducted over areas that have been surveyed with precise geodetic gps equipment mounted on snowmobiles after calibration agreement between the two surfaces is 10 cm rms the accuracy and precision of the procedure have been evaluated at points where laser flight lines cross over one another the accuracy of the system is found to range from 0 09 to 0 22 m

seasonal variability of coastal upwelling and the upwelling front off central chile 1 we analyze sea surface temperature sst and chlorophyll a chl a satellite data to study the seasonal variability of the upwelling off central chile data from an oceanographic cruise are used to illustrate the vertical characteristics of the upwelling front and the geostrophic flow the mean offshore extension of the sst front in summer is 110 km there sst changes from 13 5 c near the coast to 14 5 15 c offshore hydrographic data show that the thermocline becomes progressively shallower toward the coast but that at a certain distance it abruptly bends to form a horizontal front that extends until 50 m depth satellite data show that the chl a decays exponentially offshore and a concentration of 1 mg m 3 indicates the offshore limit of the frontal region the sst front observed most of the year is absent in winter when the coastal water is only slightly colder than the oceanic one however relatively higher chl a values remain present near the coast during winter northwest of punta lavapie 37 15 s the frontal region is located progressively farther offshore suggesting that a branch of an equatorward surface jet separates from the coast to form a meander which is associated with a filament of cold water and an anticyclonic eddy observed frequently in this zone during summer hydrographic data show that isotherm and current disturbances related to mesoscale eddies can extend several hundreds of meters below the surface in contrast the coastal jet is quite shallow extending until 150 m depth

airborne gravity and precise positioning for geologic applications airborne gravimetry has become an important geophysical tool primarily because of advancements in methodology and instrumentation made in the past decade airborne gravity is especially useful when measured in conjunction with other geophysical data such as magnetics radar and laser altimetry the aerogeophysical survey over the west antarctic ice sheet described in this paper is one such interdisciplinary study this paper outlines in detail the instrumentation survey and data processing methodology employed to perform airborne gravimetry from the multi instrumented twin otter aircraft precise positioning from carrier phase global positioning sys tem gps observations are combined with measurements of acceleration made by the gravity me ter in the aircraft to obtain the free air gravity anomaly measurement at aircraft altitude gps data are processed using the kinematic and rapid static kars software program and aircraft vertical acceleration and corrections for gravity data reduction are calculated from the gps position solu tion accuracies for the free air anomaly are determined from crossover analysis after significant editing 2 98 mgal rms and from a repeat track 1 39 mgal rms the aerogeophysical survey covered a 300 000 km 2 region in west antarctica over the course of five field seasons the grav ity data from the west antarctic survey reveal the major geologic structures of the west antarctic rift system including the whitmore mountains the byrd subglacial basin the sinuous ridge the ross embayment and siple dome these measurements in conjunction with magnetics and ice penetrating radar provide the information required to reveal the tectonic fabric and history of this important region

interannual to interdecadal sea surface temperature variability along the western coast of south america 1 interannual and interdecadal regional scale sea surface temperature sst variability along peru and chile are described based on 9 coastal stations and global sst in the period 1951 1999 enso related interannual variability dominates the low passed time series along the coast with maximum amplitudes in the tropics decreasing southward at tropical latitudes interdecadal variance is about one third of the interannual variance while they are of similar amplitude in the midlatitudes 36 s the correlation between the low frequency coastal modes and the pacific and atlantic sst suggests that the coastal sst variability comprises two main large scale climate processes the enso cycle at interannual timescale and a basin wide perhaps even a global scale interdecadal oscillation

central and south america gps geodesy casa uno in january 1988 scientists from over 25 organizations in 13 countries and territories cooperated in the largest global positioning system gps campaign in the world to date table 1 43 gps receivers collected approximately 590 station days of data in american samoa australia canada colombia costa rica ecuador new zealand norway panama sweden united states west germany and venezuela the experiment was entitled casa uno an acronym for central and south america and uno is the spanish word for one designating first epoch measurements the casa uno experiment was the first civilian effort implementing a global gps satellite tracking network scientific goals of the project include measurement of strain in the northern andes measurement of subduction rates for the cocos and nazca plates beneath central and south america and measurement of relative motion between the caribbean plate and south america a second set of measurements are planned in 1991 casa dos and should provide preliminary estimates of crustal deformation and plate motion rates in the region the casa series of experiments are intended to be carried out over at least one decade

earthquakes and sea level space and terrestrial metrology on a changing planet the complacency with which man inhabits continent ocean margins or plate boundaries is based on the assumption that sea level rise and periodic seismicity are acceptable risks the forecast of future sea level or future seismicity is essential for informed assessment of these risks the historical data from which forecasts may be derived are in each case of limited antiquity and uneven spatial distribution developments in space geodesy and crustal deformation metrology in the past two decades offer the means to acquire a homogeneous global data set for monitoring relative vertical and horizontal motions of the earth s surface to within several millimeters these new tools are reviewed in terms of their application to forecasting trends in sea level rise and forecasting damaging earthquakes

ice wastage on the kerguelen islands 49 s 69 e between 1963 and 2006 1 we observed the wastage of ice masses on the kerguelen islands indian ocean 49 s 69 e using historical information and recent satellite data overall the total ice covered area on the islands declined from 703 to 552 km2 between 1963 and 2001 a reduction of 21 the area of cook ice cap the main ice body decreased asymmetrically from 501 to 403 km2 west flowing glaciers lost 11 of their area while east flowing glaciers lost 28 after 1991 the retreat rate accelerated from 1 9 km2 a 1963 1991 to 3 8 km2 a 1991 2003 between 1963 and 2000 the ice volume loss was 25 30 km3 equivalent to an area average ice thinning rate of 1 4 1 7 m a the glacial retreat took place in the climatic context of a relatively low level of precipitation compared to the 1950s and a 1 c warming that occurred between 1964 and 1982 the acceleration of the ice losses since at least the 1990s indicates that the state of the ice bodies on the kerguelen islands is still far from balanced together with other studies in patagonia south georgia and heard island our analysis is consistent with a pattern of strong and accelerated wastage of ice masses influenced by the southern ocean

evolving force balance at columbia glacier alaska during its rapid retreat 1 changes in driving and resistive stresses play an essential role in governing the buoyancy forces that are important controls on the speed and irreversibility of tidewater glacier retreats we describe changes in geometry velocity and strain rate and present a top down force balance analysis performed over the lower reach of columbia glacier our analysis uses new measurements and estimates of basal topography and photogrammetric surface velocity measurements made between 1977 and 2001 while assuming depth independent strain sensitivity tests show that the method is robust and insensitive to small changes in the calculation parameters spatial distributions of ice speed show little correspondence with driving stress instead spatial patterns of ice speed exhibit a nonlinear correspondence with basal drag primary resistance to flow comes from basal drag but lateral drag becomes increasingly more important throughout the retreat which may account for observed increases in speed maximum basal drag is always located in a prominent constriction located 12 km upstream from the preretreat terminus once the terminus retreated into deep water off the terminal moraine marking the modern maximum extent the upstream location of this maximum basal drag helped to promote thinning and decrease effective pressure in the lower region by limiting replenishing ice flow from upstream an increase in both ice velocity and calving resulted initiating what appears to be an irreversible retreat

interdecadal variability of the thermocline along the west coast of south america 1 using gridded mbt and xbt data for the period 1955 2002 we analyze the interdecadal variability of the thermocline along the western coast of south america between the equator and 32 s results show a relatively small but coherent interdecadal oscillation of the depth of different isotherms representing the thermocline along the region this oscillation is well correlated with interdecadal sst anomalies at the end of the 1960s the thermocline was on average 10 m shallower than during the beginning of the 1980s while sst anomalies changed from 0 3 c to 0 5 c during the same period the transition from shallow to deep thermocline depths during the mid 1970s is consistent with the change from cold to warm conditions observed at the surface changes in the depth of the thermocline base may modify the properties of the subsurface water that feeds the coastal upwelling with further consequences for the ecosystem of the region

cretaceous tectonic evolution of south china a preliminary synthesis abstract the cretaceous tectonic evolution of south china is characterized by widespread extensional basin and dome generation voluminous magma intrusion eruption and associated polymetallic mineralization all of which are of world wide interests that have stimulated the attention of geologists for more than half a century due to the lack of a comprehensive understanding of regional tectonic evolution and geodynamics of south china many controversies regarding the nature and origin of these features remain this paper attempts to make a review by synthesizing existing structural petrological geochronological and geochemical data of the cretaceous structures and magmas which guides us to propose a three stage tectono thermal evolutionary history of south china during the cretaceous period the earliest cretaceous 145 137 ma tectonic stage was characterized by syn orogenic shortening deformation and metamorphism under a nw se compressional setting which generated voluminous porphyry cu au ore bearing adakitic rocks in the lower yangtze river belt and gneissic granites in the coastal area its geodynamic origin was interpreted as combined effects of the pacific izanagi ridge subduction beneath the lower yangtze river belt and the pacific subduction beneath the cathaysia block this syn orogenic shortening stage was followed by a post orogenic stage 136 86 ma comprising two episodes of alternate extensional and shortening events the extension 136 118 ma in the earlier episode was dominated by a nw se extensional regime it led to significant taphrogenesis manifested by large scale extensional basins and voluminous magma intrusion eruption this extensional event was associated with a combination of the slab window opening during the ridge subduction and the rollback of the subducted pacific slab the subsequent nw se transpressional event led to cessation of active marginal magmatism and resulted in tectonic inversion of previous rift basins this transpression lasted from 117 ma to 108 ma and its driving mechanism was attributed to the collision between the eastern asian margin and the west philippine block the extension 107 86 ma in the later episode was dominated by a wnw ese extensional regime which led to a second phase of basin subsidence and produced numerous a and i type granites and bimodal volcanoes the tectonic regime then changed at ca 85 ma to wnw ese oriented transpression causing inversion of the late cretaceous rift basins and cessation of extension related magmatism the change of stress field from wnw ese extension to wnw ese transpression was related to the variations of the subducted slab dynamics i e the transition from either the ese ward retreat to wnw ward subduction of the pacific slab or the alternate stress during slab break off during the latest cretaceous a drastic change of regional tectonic stress orientation from wnw ese to n s occurred in south china the third stage predominated by n s extension was developed which caused a new phase of regional crustal subsidence along the youngest e w trending extensional structures

an optimized method to calculate the geodetic mass balance of mountain glaciers understanding the effects of climate on glaciers requires precise estimates of ice volume change over several decades this is achieved by the geodetic mass balance computed by two means 1 the digital elevation model dem comparison seqdem allows measurements over the entire glacier however the low contrast over glacierized areas is an issue for the dem generation through the photogrammetric techniques and 2 the profiling method sepm is a faster alternative but fails to capture the spatial variability of elevation changes we present a new framework ssd that relies upon the spatial variability of the elevation change to densify a sampling network to optimize the surface elevation change quantification our method was tested in two small glaciers over different periods we conclude that the sepm overestimates the elevation change by 20 with a mean difference of 1 00 m root mean square error rmse 3 00 m compared with results from the seqdem method a variogram analysis of the elevation changes showed a mean difference of

estimation of current plate motions in papua new guinea from global positioning system observations plate tectonic motions have been estimated in papua new guinea from a 20 station network of global positioning system sites that has been observed over five campaigns from 1990 to 1996 the present velocities of the sites are consistent with geological models in which the south bismarck woodlark and solomon sea plates form the principal tectonic elements between the pacific and australian plates in this region active spreading is observed on the woodlark basin spreading centre but at a rate that is about half the rate determined from magnetic reversals the other major motions observed are subduction on the new britain trench seafloor spreading across the bismarck sea seismic lineation convergence across the ramu markham fault and left lateral strike slip across the papuan peninsula these motions are consistent with a 8 2 myr 1 clockwise rotation of the south bismarck plate about a pole in the huon gulf and a rotation of the woodlark plate away from the australian plate second order deformation may also be occurring in particular manus island and northern new ireland may be moving northward relative to the pacific plate at 5 8 mm yr 1 significant at the 95 but not at the 99 confidence level which may suggest the existence of a north bismarck plate

airborne gravity measurements over mountainous areas by using a lacoste romberg air sea gravity meter this paper introduces a new approach to airborne gravity data reduction well suited for surveys flown at high altitude with respect to gravity sources mountainous areas classical technique is reviewed and illustrated in taking advantage of airborne gravity measurements performed over the western french alps by using a lacoste romberg air sea gravity meter the part of nongravitational vertical accelerations correlated with gravity meter measurements are investigated with the help of coherence spectra beam velocity has proved to be strikingly correlated with vertical acceleration of the aircraft this finding is theoretically argued by solving the equation of the gravimetric system gravity meter and stabilized platform the transfer function of the system is derived and a new formulation of airborne gravity data reduction which takes care of the sensitive response of spring tension to observable gravity field wavelengths is given the resulting gravity signal exhibits a residual noise caused by electronic devices and short wavelength eotvos effects the use of dedicated exponential filters gives us a way to eliminate these high frequency effects examples of the resulting free air anomaly at 5100 m altitude along one particular profile are given and compared with free air anomaly deduced from the classical method for processing airborne gravity data and with upward continued ground gravity data the well known trade off between accuracy and resolution is discussed in the context of a mountainous area

advances in aerogeophysics and precise positioning gravity topography and high resolution applications airborne magnetic surveys have long been a primary tool for geologic mapping resource exploration hazard evaluation and tectonic studies recent advances in precise positioning have enabled other geophysical tools such as laser and radar altimeters and the gravity meter to be mounted on airplanes and contribute to geologic and environmental studies the principal advantages of airborne geophysical surveys over ground based studies result from enhanced experiment design including improved access to remote and contaminated areas optimized sampling rapid sampling rate and tremendous potential for interdisciplinary studies

updated estimates of glacier volume changes in the western chugach mountains alaska and a comparison of regional extrapolation methods and 2001 2004 average net balance rates ranged between 3 1 to 0 16 m yr 1 for the tidewater and 1 5 to 0 02 m yr 1 for the nontidewater glaciers we tested several methods for extrapolating these measurements to all the glaciers of the western chugach mountains using a process similar to cross validation predictions of individual glacier changes appear to be difficult probably because of the effects of glacier dynamics which on long multidecadal timescales complicates the response of glaciers to climate in contrast estimates of regional contributions to rising sea level were similar for different methods mainly because the large glaciers whose changes dominated the regional total were among those measured for instance the above sea level net balance rate of columbia glacier 3 1 0 08 km 3 yr 1 water equivalent weq or an equivalent rise in sea level sle of 0 0090 0 0002 mm yr 1 was nearly half of the total regional net balance rate of the western chugach mountain glaciers 7 4 1 1 km 3 yr 1 weq or 0 020 0 003 mm yr 1 sle between 1950 1957 and 2001 2004 columbia glacier is a rapidly retreating tidewater glacier that has lost mass through processes largely independent of climate tidewater glaciers should therefore be treated separately when performing regional extrapolations

wind driven interdecadal variability in the eastern tropical and south pacific 1 simulated interface elevation anomalies with a reduced gravity model forced by observed wind stress are used to investigate the origin of thermocline depth fluctuations in the eastern tropical and south pacific at interdecadal timescales it is found that interdecadal thermocline depth fluctuations in the eastern equatorial pacific and along the western coast of the americas are fundamentally driven by zonal wind fluctuations in the western equatorial pacific thus positive negative interface elevation anomalies which correspond to shallower deeper thermocline depths in the eastern tropical pacific and along the west coast of central and south america are related to easterly westerly anomalies in the western sector of the equatorial pacific however off equatorial wind fluctuations maintain and reinforce the interdecadal variability observed along the eastern equatorial pacific and along the west coast of south america in the latter region equatorial off equatorial wind forcing is relatively more important equatorward poleward of 30 s in the eastern equatorial pacific interface elevation anomalies are negatively correlated with sea surface temperature sst at interdecadal timescales according to our results the sst interdecadal anomalies are in part 50 60 driven by wind fluctuations likely through the modulation of vertical advection of cold waters which depends primarily on the thermocline depth forced remotely or locally by winds this relationship was especially strong during the 1970s and 1980s a period characterized by the larger zonal wind stress interdecadal fluctuations observed in the western equatorial pacific

precise regional baseline estimation using a priori orbital information a solution using gps measurements acquired during the casa uno campaign has resulted in 3 4 mm horizontal daily baseline repeatability and 13 mm vertical repeatability for a 729 km baseline located in north america the agreement with vlbi is at the level of 10 20 mm for all components the results were obtained with the gipsy orbit determination and baseline estimation software and are based on five single day data arcs spanning the 20 21 25 26 and 27 of january 1988 the estimation strategy included resolving the carrier phase integer ambiguities bias fixing utilizing an optimal set of fixed reference stations fiducials and constraining gps orbit parameters by applying a priori information derived from initial multi day trajectory fits to broadcast ephemeris data a multi day january 20 27 gps orbit and baseline solution has yielded similar 2 4 mm horizontal daily repeatabilities for the same baseline consistent with the constrained single day arc solutions the application of weak constraints to the orbital state for single day data arcs produces solutions which approach the precise orbits obtained with unconstrained multi day arc solutions this work suggests that the general availability of nominal ephemerides based on many days of global tracking data would be very valuable and practical for regional geodesy allowing for high precision with single day network solutions when combined with a continental scale fiducial network

taku glacier alaska u s a on the move again active deformation of proglacial sediments taku glacier is one of the few glaciers in alaska u s a that has advanced over the last century 7 km since 1890 this advance slowed substantially during the past decade but in summer 2001 the glacier terminus began to readvance at a rate of 30 cm d 1 the advance produced dramatic proglacial sediment deformation up to 200 m in from of the terminus two to three large bulges and several secondary bulges developed in the proglacial sediments as a result of glacial compression along a 1 km wide portion of the terminus the bulge nearest the terminus was 10 m high and 65 m wide the middle bulge 7 m high advanced at 15 cm d 1 and the distal bulge 3 m high and 50 m wide at 9 cm d 1 crenulations and prominent fractures developed in the overlying vegetation layer the frontal lobes of the bulges were steep and overlaid a shear zonc where sediments were being thrust up and over the ground surface ice proximal push moraines 1 10 m high formed along much of the 9 km wide terminus although deformation was minimal at some locations

hydrographic conditions off northern chile during the 1996 1998 la nina and el nino events 1 the evolution of oceanographic conditions in the upwelling region off northern chile 18 24 s between 1996 and 1998 including the 1997 1998 el nino is presented using hydrographic measurements acquired on quarterly cruises of the chilean fisheries institute with sea surface temperature sst sea level and wind speeds from arica 18 5 s iquique 20 5 s and antofagasta 23 5 s and a time series of vertical temperature profiles off iquique spatial patterns of sea surface temperature and salinity from may 1996 to march 1997 followed a normal seasonal progression though conditions were anomalously cool and fresh starting in march 1997 positive anomalies in sea level and sea surface temperature propagated along the south american coast to 37 s maximum sea level anomalies occurred in two peaks in may july 1997 and october 1997 to february 1998 separated by a relaxation period maximum anomalies 2 c and 0 1 practical salinity units psu extended to 400 m in december 1997 within 50 km of the coast march 1998 presented the largest surface anomalies 4 c and 0 6 psu strong poleward flow 20 35 cm s 1 occurred to 400 m or deeper during both sea level maxima and weaker 10 cm s 1 equatorward flow followed each peak by may 1998 sst had returned to the climatological mean and flow was equatorward next to the coast however offshore salinity remained anomalously high owing to a tongue of subtropical water extending southeast along the peruvian coast conditions off northern chile returned to normal between august and december 1998 the timing of the anomalies suggests a connection to equatorial waves the progression of the 1997 1998 el nino was very similar to that of 1982 1983 though with different timing with respect to seasons

occurrence types and genesis models of hot dry rock resources in china as a significant part of geothermal resources the hot dry rock hdr resources have drawn more and more attentions because it potentially can provide clean stable and huge potential of high temperature geothermal energy china started research on hdr resources since 1990s relatively later than advanced countries until now researches on the genetic mechanisms and the occurrence of hdr resources are still inadequate which hinders the exploration and precise potential estimation of hdr resources in china based on the geological indicators of the occurrence of hdr resources by combining the genetic analysis of hdr resources in the world and crustal structure in china we classified the hdr resources into four types i e the high radioactive heat production type the sedimentary basin type the modern volcano type and the inner plate active tectonic zone type this classification could provide geological guidance for hdr resource targeting in certain areas and facilitate further developments