examination of the repeatability of two ms6 4 menyuan earthquakes in qilian haiyuan fault zone ne tibetan plateau based on source parameters abstract repeating earthquakes are key evidence for understanding earthquake recurrence and help improve long term seismic risk assessment in 1986 and 2016 two ms6 4 earthquakes occurred in menyuan region near the middle segment of qilian haiyuan fault zone ne tibetan plateau long period waveforms of the two events at teleseismic stations show high degree of similarity however previous solutions on earthquake location and focal mechanism show remarkable discrepancies especially for the 1986 event as well the ruptured faults also remain ambiguous in this study we determined the source parameters of these two earthquakes including the relative location focal depth focal mechanism source duration and rupture directivity the results show that two earthquakes are thrust events in shallow crust and are located within 15 km and the 2016 earthquake ruptured down dip for 6 km along the southwest dipping plane combing the source parameters geological data and deep seismic reflection profiles we infer that these two earthquakes occurred on the same secondary fault of lenglong ling fault the middle segment of qilian haiyuan fault but they ruptured on different sections of the fault although the two events are probably not repeating earthquakes of qilian haiyuan fault zone the seismic risk of m6 thrust earthquake on these secondary faults and even larger strike slip earthquake on lenglong ling fault are not negligible based on the source parameters and ten year gps observations

geometry and rate of faulting in the north baikal rift siberia we present a detailed morphotectonic analysis of late quaternary faulting in the north baikal rift nbr a region characterized by ranges and basins distributed over more than 800 km along strike in eastern siberia remote sensing techniques spot meteor scenes and aerial photographs are used to map the active fault network which displays a general en echelon distribution from the northern lake baikal to the easternmost basin with 30 km spaced overstepping segments of 10 80 km in length most faults have a dominant dip slip component over their cenozoic history the inherited crustal fabric strongly influences the overall geometry of the rifted basins we use 54 14c ages of postglacial terraces near the foot scarps of the muya basin to date offsets measured inside alluvial fans the last main postglacial event in this area appears to be the early holocene optimum dated at 10 2 ka following the onset of deglaciation at 13 ka using these time constraints a detailed leveling across two terraces offset by the taksimo fault west muya basin shows consistent minimum vertical slip rates of 1 6 0 6 mm yr 1 using 30 other active scarps analyzed in the field we find a lower bound for horizontal velocity of 3 2 0 5 mm yr 1 across the nbr a rate close to the one found in the southern rift from global positioning system measurements we then compare directions of slip vectors from holocene field data and slip directions from earthquake fault plane solutions although local discrepancies appear the mean directions of lesser horizontal stress 3 inverted from theses values are n130 e and n155 e respectively which are comparable within uncertainties and favor a rifting obliquity of 30 40 extrapolating our holocene rates we estimate basin ages younger than those generally believed less than 7 ma and propose a spatial and temporal evolution of rifted basins consistent with experimental models of oblique rifting total amounts of extension and vertical throw 7 and 12 km respectively across major faults appear rather constant from the central to the northern rift these results favor a progressive development of asymmetric grabens in a rift zone that widens with times and they indicate a strong rheological control on deformation which seems enhanced by other contributions than the far field effects of the indo eurasian collision

a random discontinuous model of sea ice motion the rate at which the sea ice pack spreads apart exposing the warm ocean to the cold atmosphere controls the air sea heat exchange in the arctic and the production of ice mass the rate of spreading or opening can be estimated from observations of ice motion using a model of the ice pack which accounts for the random manner in which the ice is broken into rigid pieces in a region intersected by many cracks some cracks will typically be opening while others are closing in this case the total of the openings will exceed the average divergence of the region a few measurements of the ice motion cannot resolve the openings at each crack so that any estimate of opening will be accompanied by estimation errors the random model adopted here imagines the leads to be distributed according to the poisson distribution and the relative displacements at any crack to be gaussian under these assumptions it is determined how the total opening is related to the average deformation and how this relationship depends on the size of the region and on the number of points used to determine the average deformation

motion tracking of discontinuous sea ice the purpose of this paper is twofold 1 to develop a high resolution sea ice motion tracking system at the geospatial mesoscale 1 100 km2 and 2 to propose an algorithm that measures motion at close proximity to discontinuous regions here we present a motion tracking system that computes differential motion at 400 m resolution and validate the accuracy precision of this system via four studies the first study measures the accuracy against displacements measured from in situ global positioning system gps buoys deployed at the sea ice experiment dynamic nature of the arctic sedna and the surface heat budget of the arctic ocean sheba experiments the estimates are found to be statistically comparable with gps with an average error of 361 9 and 600 6 m for the experiments respectively the second study compares the estimated displacements to those measured by the radarsat geophysical processing system a precision error of 75 7 m is found between the two motion tracking systems the third study uses intensity warping of randomly sampled measurements to evaluate discontinuous motion tracking a one tailed wilcoxon signed rank test is used to validate these measurements at 0 01 results from this paper prove that anisotropic smoothing produces significantly smaller errors at discontinuous locations w 4240 and p 0 001 over conventional isotropic smoothing the fourth study compares displacements measured by anisotropic smoothing against manual measurements this paper demonstrates an average reduction of the estimation error by 50 m with the use of anisotropic smoothing over the conventional isotropic smoothing

surface rupture and slip distribution along the lenglongling fault in the ne tibetan plateau implications for faulting behavior abstract the lenglongling fault lllf is located in the western section of the tianzhu seismic gap along the qilian haiyuan fault zone in the ne tibetan plateau between the 1920 m8 5 haiyuan and the 1927 m8 0 gulang earthquakes there is little information about the paleoseismic history of the lllf and understanding the faulting history of the lllf is important for determining the seismic hazards of both the fault and the seismic gap using uav based photogrammetry high resolution satellite imagery and field investigations we mapped the surface trace of the fault in detail and measured 192 left lateral offsets of geomorphic markers along the fault trace a binned cumulative offset probability density copd distribution was calculated to analyze single event and multi event cumulative offsets as a result we find that the lllf has fresh scarps along the entire 120 km length indicating that the most recent event might have ruptured the full segment of the fault the coseismic offset of the most recent event changes along the fault trace and has an asymmetrical bell shaped distribution the maximum offset was 7 m located in the middle eastern section of the fault and the offset decreases progressively towards both ends the minimum offset located at the western end was 3 0 m and the average coseismic offset was 4 8 m the cumulative offsets of the four most recent paleoearthquakes are multiples of the coseismic offset of the most recent event and show similar slip distributions indicating that the fault ruptures with a characteristic slip the fault slip distribution estimated recurrence interval and estimated moment magnitude imply that the lllf releases accumulated strain energy mainly by repeatedly producing mw 7 5 7 8 earthquakes every 1000 200 years we also show that the binned copd technique performs well to separate single event and multi event cumulative offsets

synoptic ice motion from avhrr imagery automated measurements versus wind driven theory abstract this note describes the application of a recently elucidated theory of automated sea ice motion detection to avhrr imagery it further seeks to point out the unique ability of avhrr to provide synoptic measurements of sea ice velocity which are useful in validating regional scale ice models the measurements are compared with a simple wind driven theory of ice motion and the results lend support to the linearizing assumptions of the model

c band sar observations of marginal ice zone rheology in the labrador sea synthetic aperture radar sar imagery collected during the limex 87 field program in the labrador sea is used to qualitatively interpret the deformation modes in play throughout the experiment the ice cover exhibited two distinct rheologies separated by a clear line of shear a nonlinear viscous outer regime and a quasi brittle inner regime a single constitutive relation capable of effectively modeling both is unlikely within a plastic rate independent formulation rate dependent effects are discussed in relation to favoring brittle fraction in an otherwise ductile material

use of synthetic aperture radar derived kinematics in mapping mesoscale ocean structure within the interior marginal ice zone synthetic aperture radar sar imagery of the marginal ice zone over the western sector of the yermak plateau defined a region of anomalous ice motion that could not be accounted for by simple free drift movement of the sea ice based on daily averaged winds over the same time period from june 29 to july 6 1984 sea ice trajectories within this anomalous region are however consistent with oceanic forcing of the pack ice by a mesoscale eddy that had recently formed off the polar front although the use of such imagery has already been shown to be a diagnostic tool in mapping ocean features at the ice edge the observed correlation 50 to 70 km behind the local ice edge indicates that sar imagery has the potential to define energetic mesoscale and larger oceanic features well within the polar pack ice

modification of wave cut and faulting controlled landforms from a casual observation that the form of degraded fault scarps resembles the error function this investigation proceeds through an elementary diffusion equation representation of landform evolution to the application of the resulting equations to the modern topography of scarplike landforms the morphologic observations can be analyzed either in the form of one or more cross strike elevation profiles or in the form of the slope offset plot a point plot of maximum scarp slope versus scarp offset working with either or both of these data representations for nine geologic structures which range in age from 3 to 400 ka b p and in offset from 1 to 50 m we apply analytical solutions for the vertical initial value scarp the vertical continuous offset scarp and the finite slope initial value scarp the model calculations are intrinsically ambiguous yielding as the final answer only the product t in the case of the initial value problem or the product a 1 in the case of the repeated faulting problem here t is the age of a single scarp forming event 2a is the vertical slip rate and is the mass diffusivity a single profile across three sea cliffs along the santa cruz california coast is analyzed as three separate initial value problems a reasonably constrained age for the sea cliff standing above the highway 1 platform returns 11 gkg 1 gkg 1 m2 ka with this we can date the two older sea cliffs in fact we do the converse age estimates for these two older sea cliffs based on a uniform rate of uplift both yield the same as for the lower sea cliff we treat a single profile of the raymond fault in pasadena san marino in terms of the repeated faulting problem for it the uplift rate of r crook and others yields 16 gkg the very substantial preexisting offset across the raymond fault must have been buried leveled some 230 ka b p when the modern topography began to form our analysis of the lake bonneville shoreline scarps reveals a dependence of t on 2a suggestive of nonlinear modification processes this appearance is treated with the finite slope initial value scarp model to determine 1 1 gkg for the lake bonneville shoreline scarps the suggestion of m n machette that approximately 100 000 year old meter high scarps are unobservable in weakly consolidated alluvial terranes of the basin and range and rio grande rift valley provinces can be formulated as 1 gkg the coincidence between this inequality and the lake bonneville shoreline is striking and it suggests that the value of 1 gkg may be generally applicable as a good first approximation to the modification of alluvial terranes within the semiarid regions of the western united states the lake bonneville shoreline is the basis for dating four sets of fault scarps in west central utah the drum mountains fault scarps can be modeled in several different circumstances but the most likely interpretation is that these fault scarps formed as the result of a single episode of normal faulting 3 6 to 5 7 ka b p the younger age is associated with quite low initial slope angles 25 the other three sets of fault scarps show no evidence for finite initial value slopes fault scarps along the eastern base of the fish springs range are very young 3 ka b p we estimate the age of fault scarps along the western flank of the oquirrh mountains to be 32 ka b p which meets the weak geologic constraint that they be older than the lake bonneville shoreline fault scarps along the northeastern margin of the sheeprock mountains are even older 53 ka b p an intriguing consequence of our single event analysis of these scarps is that an 11 5 m offset occurred in a single earthquake

beaufort chukchi ice margin data from seasat ice motion the motion of sea ice in the summer and fall marginal zone of the beaufort and chukchi seas is observed by tracking ice features in sequential seasat synthetic aperture radar images four examples of ice motion fields are shown and discussed with translation observation density finer than one observation per 5 km for the most part in this region the components of proportional relative motion are shown to commonly have values in the range 0 1 to 0 25 day throughout the marginal zone which itself has a scale of the order of 100 km

active faulting and tectonics of the ningxia hui autonomous region china strike slip thrust and normal faulting all seem to play an active role in the tectonics of ningxia in the southernmost part of the region a major left lateral strike slip fault enters the region from the neighboring gansu province to the west and trends about s65 e this fault is very clear on landsat imagery and on aerial photos and the portion in eastern gansu and ningxia broke in the haiyuan earthquake of december 16 1920 displacements of 5 10 m caused by that earthquake are clear in numerous localities and accord with a revised value of the seismic moment of 1 2 1021n m the eastern end of the haiyuan fault terminates in a narrow south trending fold and thrust zone several other similar north to northwest trending fold and thrust belts are present in the area about 50 200 km northeast of the haiyuan fault and divide it into small apparently relatively undeformed blocks 10 40 km in dimensions the geometry of the structures in the fold and thrust zones and the apparently shallow depths at the time of deformation suggest that current deformation is similar to that that occurred in the fold and thrust belt of the idaho wyoming rocky mountains north of this area both the helan shan a horst and the yinchuan graben are bounded by clear active northerly trending normal faults in some cases with right lateral strike slip components the overall deformation hence seems to include dominant components of east west left lateral strike slip movement northeast southwest crustal shortening and northwest southeast extension we interpret the extension as a response to a northeast directed force applied to the ordos block and both this northeast directed force and the left lateral slip on the haiyuan fault to the eastward displacement of material on the northeast edge of the tibetan plateau with respect to eurasia north of it

offsets of late quaternary morphology rate of slip and recurrence of large earthquakes on the chang ma fault gansu china the chang ma fault in the western qilian shan gansu province shows evidence of consistent left lateral displacements despite a complex en echelon geometry we have measured short and long term offsets on two n70 80 e striking segments of the fault along the southern edge of the ta quen kou basin where it cuts late quaternary terraces transverse ridges and drainage channels to analyze the offsets of such structures at one site in the eastern part of the basin we ran topographic profiles parallel and perpendicular to the fault over a distance of about 5 km spectral analysis and comparison of longitudinal profiles north and south of the fault allowed us to separate horizontal offsets of structures of different wavelengths apparent on air photos and satellite images transverse profiles were used to determine the vertical throw whose variations appear to result from changes in the fault strike small horizontal offsets of ridge crests and valley slopes are about 55 m along the n70 e striking segment of the fault this displacement corresponds to an uplift of the northern block of about 27 m implying that the fault dips about 73 to the south the measurements also constrain horizontal projection of the slip vector to about n78 e a larger horizontal offset 500 m of morphological swells of longer wavelength 1 6 km is visible on the longitudinal profiles assuming that periglacial erosion has reshaped the surface of the lateral slopes and tops of ridges during the wurm glacial period the smallest offsets of adjacent ridge crests may postdate the begining of the holocene yielding an average rate of left lateral slip on the fault of 5 5 2 2 mm yr in the last 10 2 kyr in the western part of the ta quen kou basin a somewhat slower rate of holocene slip 4 6 4 mm yr is obtained measurement of the horizontal displacement due to the 1932 earthquake there 6 2 0 6 m would imply that the recurrence interval for similar earthquakes at this second site is 1350 540 years

research on snow and ice this review unlike its predecessor martinelli et al 1979 is an intentionally selective survey of recent advances in selected areas of snow and ice research i have chosen to concentrate on studies relating to large scale aspects of the cryosphere and to consider their wider significance for other disciplines results obtained by new measurement techniques and the application of remote sensing methods are also stressed at the same time the broad lines of advance in glaciological research as represented in books conference themes and major field or laboratory programs are noted and a detailed bibliography is appended

spatial scaling of arctic sea ice deformation 1 arctic sea ice deformation arises from spatial gradients in the ice velocity field this deformation occurs across a wide range of spatial scales from meters to thousands of kilometers we analyze 7 years of sea ice deformation data from the radarsat geophysical processor system rgps covering the western arctic ocean we find that the mean deformation rate is related to the spatial scale over which it is measured according to a power law with exponent 0 2 over a scale range from 10 to 1000 km e g deformation rate doubles for a 30 fold reduction in scale both the exponent and the deformation rate have distinct annual cycles the exponent becomes more negative in summer as the ice pack weakens and internal stresses are not as readily transmitted over long distances the deformation rate reaches a minimum in late winter when the ice pack is strongest the deformation also exhibits considerable localization in which the largest deformation rates are confined to smaller and smaller areas as the scale of measurement decreases this supports a model for sea ice based on granular or fracture mechanics the scaling exponent in the power law relationship tends to be larger in magnitude where the concentration of multiyear ice is low consistent with a thinner and weaker ice pack with decreasing multiyear ice in the arctic and a thinning ice pack an increase in the deformation rate has already been documented from buoy data however the net effect of several deformation thickness feedbacks is still uncertain

quaternary extension in southern tibet field observations and tectonic implications we summarize evidence for quaternary and active faulting collected in the field during three sino french expeditions to southeastern tibet 1980 1982 detailed mapping of quaternary and active faults as well as microtectonic measurements indicate that normal faulting has been the dominant tectonic regime north of the himalayas in the last 2 0 5 m y the maximum horizontal principal stress in south tibet appears to be only the intermediate principal stress 2 1 being vertical south of the chord joining the eastern and western syntaxes of the himalayan arc extensional strains are principally localized within seven regularly spaced rift zones three of which have been studied in some detail the extension direction is determined to be n96 e 7 mainly from statistical averaging of strikes of newly formed normal faults throw rates on normal faults are evaluated for different time spans 2 0 5 m y 60 40 kyr and 10 2 kyr b p using structural and topographic reliefs as well as synglacial and postglacial vertical offsets the rate of quaternary extension is about 1 m y 1 along an 1100 km long ese traverse across south tibet this corresponds to a spreading rate of 1 0 6 cm yr this rate and the divergent horizontal projections of slip vectors of earthquakes along the himalayan front constrain the rate at which rigid india underthrusts southern tibet to be 2 1 cm yr although most of the normal faults appear to be independent of and nearly orthogonal to the e w mesozoic tertiary tectonic fabric the yadong gulu rift appears to be guided for over 130 km by the older oblique ne sw nyainqentanglha range and fault zones along it this reactivated zone is the most prominent left lateral strike slip fault system in se tibet excepting this zone and the vicinity of the se extremity of the karakorum fault quaternary strike slip faulting is rare in south tibet i e south of the chord between the syntaxes of the himalayan arc north of the chord the tectonic style is different there minor conjugate strike slip faulting is widespread and appears to control quaternary normal faulting which is more diffuse and subdued than in south tibet along the chord the presence of a major zone of active right lateral en echelon strike slip faults karakorum jiali fault zone probably reflects the greater facility of eastward extrusion in north central tibet in response to the northward push of india the eastern himalayan syntaxis may be an obstacle to such extrusion movements south of the chord

identification of sea ice types in spaceborne synthetic aperture radar data an approach for identification of sea ice types in spaceborne synthetic aperture radar sar image data is presented the unsupervised classification approach involves cluster analysis for segmentation of the image data followed by cluster labeling based on previously defined look up tables containing the expected backscatter signatures of different ice types measured by land based scatterometer the particular look up table used for labeling a segmented image is selected based on the seasonal and meteorological conditions at the time of data acquisition the extensive scatterometer observations and experience accumulated in field campaigns during the last 10 years were used to construct these look up tables these tables are expected to evolve as sea ice observations from the european ers 1 sar become available this paper presents the classification approach its expected performance the dependence of this performance on radar system performance and expected ice scattering characteristics results using both aircraft and simulated ers 1 sar data are presented the results are compared to limited field ice property measurements and coincident passive microwave imagery an algorithm based on this experimental approach has been implemented in the geophysical processor system at the alaska sar facility for classification of sea ice data in ers 1 c band sar data the importance of an integrated postlaunch program for validation and improvement of this approach is discussed

fault scarps related to the 1739 earthquake and seismicity of the yinchuan graben ningxia huizu zizhiqu china surface faulting accompanying the great yinchuan pingluo earthquake of 1739 in ningxia huizu zizhiqu ningsia hui autonomous region produced two sections of fault scarps 3 5 and 16 5 km long and separated from one another by 65 km along strike the scarps are on the west side of the yinchuan graben along the east flank of the helan shan holan mountains the east side of the faults is downthrown and surface offsets at the fault are as much as 5 3 m on the hongguozigou northern section and 4 6 m on the suyukou southern section actual net displacement may be slightly less near the north end of the set of faults the great wall is offset by about 2 7 m vertically and about 3 m right laterally on scarps more than 2 m high a free face has persisted for the 245 yr since the scarps were formed in 1739 free faces commonly are 2 to 3 m high the 1739 fault displacement occurred at least in part along an older fault scarp that is estimated from profile analysis to be about 12 000 yr old the historical record of destructive earthquakes in the yinchuan graben since 1010 a d includes only one near m 8 in 1739 and only two of approximately m 6 5 one in 1143 and the other in 1477 average recurrence intervals for major earthquakes comparable to that of 1739 in the yinchuan graben probably are measured in thousands and possibly ten thousand or more years

3d_fault_offsets a matlab code to automatically measure lateral and vertical fault offsets in topographic data application to san andreas owens valley and hope faults measuring fault offsets preserved at the ground surface is of primary importance to recover earthquake and long term slip distributions and understand fault mechanics the recent explosion of high resolution topographic data such as lidar and photogrammetric digital elevation models offers an unprecedented opportunity to measure dense collections of fault offsets we have developed a new matlab code 3d fault offsets to automate these measurements in topographic data 3d fault offsets mathematically identifies and represents nine of the most prominent geometric characteristics of common sublinear markers along faults especially strike slip in 3 d such as the streambed minimum elevation top free face and base of channel banks or scarps minimum laplacian maximum gradient and maximum laplacian and ridges maximum elevation by calculating best fit lines through the nine point clouds on either side of the fault the code computes the lateral and vertical offsets between the piercing points of these lines onto the fault plane providing nine lateral and nine vertical offset measures per marker through a monte carlo approach the code calculates the total uncertainty on each offset it then provides tools to statistically analyze the dense collection of measures and to reconstruct the prefaulted marker geometry in the horizontal and vertical planes we applied 3d fault offsets to remeasure previously published offsets across 88 markers on the san andreas owens valley and hope faults we obtained 5 454 lateral and vertical offset measures these automatic measures compare well to prior ones field and remote while their rich record provides new insights on the preservation of fault displacements in the morphology

an advection diffusion model for222rn transport in near shore sediments inhabited by sedentary polychaetes abstract a porewater solute transport model is proposed to explain the dissolved radon distributions in four profiles from a near shore marine site the macro infauna at the site is dominated by clymenella torquata a sedentary deposit feeding polychaete that actively irrigates its burrow the model includes both an advective component that takes into account the e g c torquata mechanism of burrow irrigation as well as enhanced diffusion like transport brought about by mobile infauna because it explains the existence of subsurface radon minima with a constant source function and is based on the known irrigations habits of c torquata the model provides good fit to observed radon profiles and may be applicable to other solutes that display depth dependent minima sediment advection velocities individual burrow irrigation rates and enhanced diffusion coefficients are estimated based on a minimization of chi squared for model fits to the 222 rn data of each profile the net advection velocity ranged from 0 19 to 0 91 cm d 1 and enhanced diffusion ranged from 13 to 30 times effective molecular diffusion these values are comparable to those determined by previous investigators using other transport models in similar sediments the range of burrow irrigation rates 0 16 0 78 ml h individual is somewhat lower than the average rate for c torquata that had been determined in the laboratory

formation of an aggregate scale in arctic sea ice 1 the ice pack covering northern seas is a mixture of thick ridged and rafted ice undeformed ice and open water conventional eulerian arctic sea ice models use a plastic yield surface to characterize the constitutive behavior of the pack an alternative is to adopt a discontinuous lagrangian approach and explicitly model the formation of leads and pressure ridges we use a lagrangian ice model that consists of thousands of discrete polygonal floes 1 4 km in width at the beginning of a simulation the ice floes are frozen together in a square domain we apply a linearly varying wind stress that deforms the pack by stretching the viscous elastic joints between adjacent floes fractures propagate along joints forming a crack pattern in the model ice pack the crack pattern defines a system of large plates 10 100 km in width that are aggregates of many individual floes the average size of the plates is determined by a competition between the rate of crack creation and the speed of the relaxation wave that travels outward from a newly broken joint and reduces stresses in the surrounding pack simulation results are used to characterize the formation of the aggregate structure and to determine how the rate of crack creation and the average area of the aggregate plates depends on tensile strength the wind stress gradient and the size of the individual floes after the formation of the aggregate scale plate structure subsequent deformation occurs at the plate boundaries since the usual state of the ice pack is a state of failure an interesting situation is created in which the initial wind driven deformation creates the material conditions or aggregate structure under which subsequent deformation occurs

sea ice displacement from seasat synthetic aperture radar images obtained by a synthetic aperture radar on seasat have been used to measure sea ice displacements over a three day interval in october 1978 the position of a natural ice feature was measured on 5 october and again on october 8 the difference in these two positions is a displacement the displacement of many features was measured the tracked features lie roughly along a line and are quite dense about 2 km apart over a distance of 865 km the displacements are about 20 km displacement errors grow with distance from shore becoming as large as 3 km the graph of displacement versus distance has occasional discontinuities of several kilometers displacement discontinuities are accurate to 0 07 km along track and 3 of their magnitude across track

recovering paleoearthquake slip record in a highly dynamic alluvial and tectonic region hope fault new zealand from airborne lidar knowing the slip amplitudes that large earthquakes produced in prehistorical times is one key to anticipate the magnitude of large forthcoming events it is long known that the morphology is preserving remnants of paleoearthquake slips in the form of fault offset landforms however the measured offsets that can be attributed to the most recent paleoearthquakes are generally few along a fault so that they rarely allow recovering the slip distributions and largest slips of these earthquakes we acquired 1 m resolution airborne lidar data on a 30 km stretch of a fast slipping strike slip fault eastern hope fault new zealand located in a region of high alluvial dynamics where landforms are rapidly evolving data analysis reveals 200 offset landforms only 30 allow a good to moderate quality offset measurement from these good to moderate quality measures we recover the slip length distributions and largest slips of the four most recent large paleoearthquakes and find evidence of 4 6 prior events the record suggests that large earthquake slip recurred in multiples of about 4 m along the 30 km stretch although they have larger uncertainties the more numerous lower quality offsets that we also measured reveal a similar earthquake slip record this shows that although offset landforms are partly degraded in dynamically active landscapes they store valuable information on paleoearthquake slips this information might be recovered provided that the morphology is analyzed at high resolution and continuously over a significant fault length remote lidar data are powerful to perform such analyses

extracting sea ice data from satellite sar imagery with the prospect of operational satellite sar s by the end of the decade there is a clear need to develop automated algorithms for the extraction of geophysical data about sea ice from highresolution radar imagery to this end we have developed techniques for distinguishing ice from open water and for resolving the details of deformation within areas 100 km square imaged by seasat sar the classification of ice and open water is based on the creation of a second band of image data consisting of the local variance of the original brightness the first band being a local average brightness in the space of these two variables ice and open water are separated into two distinct clusters the deformation is found on a 3 4 km mesh by local cross correlations of the brightness the strategy is to find a coarse displacement field with a highly averaged image and to proceed through a hierarchy of images with increasing resolution improving the accuracy of the displacements at each step comparison with manually determined displacement shows room for improvement in regions of high deformation by using smaller areas for cross correlation the concentration and deformation data are used together to determine localized regions of the scene where open water is produced or lost

the field of crustal velocity in asia calculated from quaternary rates of slip on faults rates of quaternary faulting when treated as measures of strain rates within regions several times larger than the depths of brittle faulting yield a velocity field for asia that matches the average relative velocity between the indian and eurasian plates over the past 2 myr nuvel 1a and the velocity of shanghai with respect to eurasia measured with very long baseline interferometry vlbi by using rates of slip on discrete surfaces faults to define average strain rates we explicitly assume that the large scale deformation can be treated as that of a continuum depending on the jcales over which strain rates are averaged 87 to 93 per cent of the assumed strain ites are fit within assigned 1 sigma uncertainties and 97 to 99 per cent are fit within 2 sigma the internal consistency of these data and the agreement with independent rates nuvel 1a and vlbi test the validity of treating large scale deformation of continents as that of a continuum in the calculated velocity field a large fraction 85 per cent of india s convergence with eurasia is absorbed by crustal or lithospheric thickening among consistently misfit assumed strain rates are those dominated by high rates of strike slip faulting strain associated with 20 30 mm a 1 of slip on the altyn tagh karakax and karakorum faults is inconsistent with the distributions of strain in surrounding regions we conclude that these rates all of which are based on correlations of ages of offset landforms with changes in global climate and not on radiometric dating have been systematically overestimated lateral transport out of india s northward path is relatively minor south china is calculated to move east southeast at less than 10 mm a 1

faulting associated with large earthquakes and the average rate of deformation in central and eastern asia we determine approximate average rates of deformation in portions of eastern and central asia for the last 80 years these rates are based on estimates of source dimensions average displacements seismic moments and orientations of faults of all large earthquakes m 7 5 and as many other major earthquakes m 7 0 as possible in asia since 1900 a major part of this study is the compilation of these data for separate parts of asia we combine seismic moment tensors to estimate the average rotational strain or deformation tensors for these regions for the last 80 years we estimate that shortening across the tien shan has occurred at 11 mm yr between 5 and 19 mm yr left lateral shear on easterly trending planes in mongolia in northwestern tibet gansu and ningxia and on the xianshuihe fault in western sichuan has been very rapid more than 10 mm yr in each region and apparently as rapid as 40 mm yr in northwestern tibet gansu and ningxia slower rates of a few to 10 mm yr appear to characterize east west extension and conjugate north south shortening of tibet the earthquake history of the himalaya is consistent with rates of underthrusting of more than 10 mm yr but is probably less than the convergence rate of india with eurasia of about 50 mm yr the overall strain field is consistent with a large part of india s penetration into eurasia being absorbed by the extrusion of material out of india s way as a result southeast china moved at about 21 mm yr east southeast with respect to eurasia in the last 80 years with an uncertainty of about a factor of 2 in this estimated rate

rapid active thrusting along the northwestern range front of the tanghe nan shan western gansu china the western part of the tanghe nan shan range southwest of subei western gansu china is presently growing on thrust ramps splaying from the left lateral altyn tagh fault late cenozoic thrusting has folded and sliced oligocene miocence red beds into an imbricate wedge capped by warped and uplifted quaternary terraces that form a 2 to 5 km wide ledge north of the steeply faceted range front seismic scarps 1 5 to 4 5 m high cut young fans along the outer thrusts carbon 14 dating of organic remains collected on strath terraces constrains the chronology of deposition and incision by the streams most of the fans and terraces in the southern part of the subei basin appear to have been emplaced after the last glacial maximum particularly during the early holocene optimum 9 5 ka measurements of the shapes of the warped terraces constrain minimum and maximum throws on the outer thrusts the minimum vertical throw of 34 2 m of a surface dated at 8411 530 years b p at one site provides a minimum vertical uplift rate of 4 1 0 5 mm yr the maximum possible uplift 115 15 m of the oldest terrace surface whose probable age is 15 to 18 ka places an upper bound on the uplift rate of 7 2 mm yr the thrust geometry at depth and the cumulative shortening 10 20 km deduced from balancing sections logged across the imbricate thrust wedge are consistent with a shortening rate of about 5 mm yr and an onset of thrusting at about 4 2 ma such a shortening rate implies a significant northward decrease in slip rate along the altyn tagh fault the recent growth of the western qilian mountain ranges thus appears to be intimately coupled with sinistral motion on the altyn tagh fault and the extrusion of tibet

processes and imagery of first year fast sea ice during the melt season an analysis of first year fast sea ice during the melt season has been made by using surface measurements and aircraft radar and photographic imagery obtained during a field study near prince patrick island in the canadian archipelago from june 13 to july 13 1982 and satellite imagery from landsat and seasat distinct changes observed in the properties of the snow layer and the sea ice were a temporary increase in small scale surface roughness caused by formation of nodules of ice at the snow ice interface extensive snow melt and surface flooding development of surface water drainage networks and low topography around fractures and seal breathing holes and a rapid draining of much of the surface water from the extensive salinity profiles obtained two zones of rapid desalination in the first year ice were observed one zone extending from the air ice interface downward toward the center of the ice sheet that resulted from surface warming and drainage of the surface melt water through the ice and the other zone extending from the sea ice interface upward toward the center of the ice sheet that resulted from heating and separation of seawater and ice caused by a layer of low salinity meltwater beneath the ice formed from surface meltwater runoff aircraft radar imagery detected changes in the amount of surface water and in the development of topography surrounding drainage features similar changes were detected in coincident landsat multispectral scanner mss imagery of the study area and in seasat radar imagery and landsat mss imagery of the prince of wales strait from july 1978

neogene and quaternary faulting in and along the qinling shan the structure of the qinling shan mountain range shaanxi china involves major east south east strike slip faults field observations made during two expeditions in 1983 and 1984 show that the faults are active and may have undergone several tens of kilometres of post eocene left lateral displacement the faults cut the morphology sharply and offset left laterally small channels their trace is marked by cataclastic to mylonitic non coaxial deformation zones at least 50 100 m wide the qinling faults allow the eastward extrusion of south china and may be considered the easternmost continuation of the altyn tagh fault system they link extensional tectonics in northeastern china to the himalayan collision

sea ice tracking by nested correlations spatial differences in sea ice displacement affect ice stress ice production and the mass balance of the ice cover our concepts about the spatial structure of this field have been undernourished because of a paucity of data with high spatial detail and because of the tedium of extracting such measurements from images manually a method is described that measures displacements from synthetic aperture radar digital imagery with fine spatial resolution and does so fully automatically many small areas of ice common to two images are identified by correlating the two images the strategy is to acquire a crude displacement field first from highly averaged images and to refine this field with images of successively higher resolution the median discrepancy between automatically and manually measured displacements is three pixels 0 075 km the algorithm operates successfully on compact ice with large floes and modest rotation rates we believe it will prove applicable to most of the arctic ice cover throughout the year