basal ice facies and supraglacial melt out till of the laurentide ice sheet tuktoyaktuk coastlands western arctic canada glacially deformed massive ice and icy sediments mi is in the eskimo lakes fingerlands and summer island area of the tuktoyaktuk coastlands western arctic canada show in the same stratigraphic sequences features characteristic of both basal glacier ice and intrasedimental ice basal ice features comprise 1 ice facies and facies groupings similar to those from the basal ice layers of contemporary glaciers and ice sheets in alaska greenland and iceland 2 ice crystal fabrics similar to those from basal ice in antarctica and ice cored moraines on axel heiberg island canada and 3 a thaw or erosional unconformity along the top of the mi is buried by glacigenic or aeolian sediments intrasedimental ice consists of pore ice and segregated ice formed within pleistocene sands deposited before glacial overriding the co existence of basal and intrasedimental ice within the mi is records their occurrence within the basal ice layer of the laurentide ice sheet stagnation of the ice sheet and melt out of till from the ice surface allowed burial and preservation of the basal ice layer on a regional scale the widespread occurrence of supraglacial melt out till with clast fabrics similar to those in the underlying ice suggests that such till can be well preserved during partial thaw of a continental ice sheet in lowlands underlain by continuous permafrost

slip along the hayward fault california estimated from space based synthetic aperture radar interferometry for 3 5 years following the 1989 m 7 1 loma prieta earthquake creep along the southern hayward fault california slowed or ceased slip apparently resumed pre earthquake rates by 1994 except for a locked 3 km long segment at the southern fault tip which had consistently slipped at 9 mm yr before 1989 we use repeated interferometric synthetic aperture radar intsar measurements to map active deformation along the hayward fault while slip rates recovered between 1992 and 1995 if pure strike slip is assumed then the slip rates estimated from intsar range changes between 1992 and 1995 are generally consistent with creepmeter and alignment array measurements along much of the fault and confirm the temporary locking of the southernmost fault segment however along 6 km of the fremont segment intsar slip estimates appear to be at least twice those measured in the field transient vertical slip northeast side up of 2 3 mm yr near the southern tip of the creep patch could explain this observation first order boundary element models of a vertical frictionless fault in an elastic half space predict some but not all of the inferred vertical slip

constraints on the preservation of diamict facies melt out tills at the margins of stagnant glaciers abstract this paper reviews the formation and preservation of diamict facies melt out till generated in situ by the downwasting of stagnant ice at the margins of continental glaciers melt out tills are commonly envisaged as being the product of the top supraglacial or bottom subglacial melt of stagnant debris rich glacier ice but such deposits are relatively uncommon in modern glacier environments where they are thin laterally discontinuous and have a low preservation potential theoretical considerations of the distribution of englacial debris in continental ice sheets show that only the glacier margin is likely to contain the necessary volumes of englacial debris for melt out to be a significant diamict forming process however the application of thaw consolidation theory to the formation of such deposits shows that substantial porewater pressures and self sediment deformations can be induced during melt out especially in matrix rich debris the classic melt out mechanism widely invoked in the literature since 1875 and involving passive in situ aggregation from thawing englacial debris can be seen to operate under restricted conditions diamict facies produced by melt out are likely to form spatially disjunct and laterally discontinuous elements within complex and ice marginal stratigraphics the melt out process is not a mechanism whereby regionally extensive diamiet ite units can be deposited across glaciated basins

segregated intrusive ice of subglacial meltwater origin in retrogressive thaw flow headwalls richardson mountains nwt canada abstract extensive beds of icy sediments are exposed in the headwalls of active retrogressive thaw flows which developed on the aklavik plateau richardson mountains nwt sedimentary and isotopic characteristics defined two units debris rich ice overlain by icy diamicton these units originated from the same glacial sediment deposited during the late wisconsin westward expansion of the laurentide ice sheet the icy diamicton is a result of the development of thaw flows and mass movement processes during the early holocene warm interval which reworked the sediments the ice in the diamicton is characterized by average 18o and d values of 22 6 1 8 and 181 15 respectively which are similar to the modern isotropic composition of precipitation for that area the debris rich ice is more depleted in 18o and d with 18o ranging from 30 to 27 and d ranging from 230 to 210 air bubbles enclosed in the ice have 13c values ranging between 24 and 19 and a co2 concentration nine times higher than the expected concentration of air entrapped in modern glacier ice but similar to that of soil co2 both physical and isotopic properties of the debris rich ice suggest that it is segregated intrusive ice that formed after the retreat of the laurentide ice sheet during permafrost aggradation as sediment laden subglacial meltwater moved through a proglacial talik this article discusses the mechanism involved in the formation of massive segregated intrusive ice and how it differs from both buried glacier ice and holocene massive intrasedimental ice

englacial deltaic sediments as evidence for basal freezing and marginal shearing leirbreen southern norway analyse des depots de geles de limons sables et graviers pres du front du glacier leirbreen les structures demontrent une origine deltaique les sediments ayant ete geles avant leur incorporation au glacier et n ayant pas subit de cisaillement pendant le transport glaciaire on en deduit les mecanismes de variation du glacier

evidence for two zones of debris entrainment beneath the greenland ice sheet investigation of the ice debris and stable isotope characteristics of basal ice exposed at the margin of the greenland ice sheet provides a means of testing and refining models of ice sheet erosion and deposition the basal ice exposed at the ice sheet margin gives evidence of the processes operating at the bed at different locations which can be used to constrain theoretical models predicting varying basal conditions1 2 improved understanding of the effects of isotope fractionation in hydrogen and oxygen caused by freezing processes at the bed which modify the isotope characteristics of the basal ice layers enables us to report evidence of two separate zones of debris entrainment beneath the ice sheet

short term surface deformation on the northern hayward fault ca and nearby landslides using polarimetric sar interferometry polinsar in this study we analyze 25 radarsat 2 images from ascending and descending geometries to study the creep rate on the hayward fault and landslide motions near berkeley ca we applied a coherence optimization technique from polarimetric synthetic aperture radar interferometry polinsar to increase the accuracy of the measurements we resolve 3 5 mm year of motion along the hayward fault in agreement with earlier creep estimates we identify a potential motion on secondary fault northeast and parallel to the hayward fault which is creeping at a lower rate of 1 5 mm year in addition we identify a number of landslides along the hills east of the fault that agree with earlier results from advanced interferometric synthetic aperture radar sar analysis and field investigations we investigate four particular slope instabilities one of which was marked as moderately active and three as highly active by earlier field investigations the resolved along hill slope displacement is estimated at 23 mm year our results demonstrate that polinsar is an effective method to increase the interferometric coherence and provide improved resolution of deformation features associated with natural hazards

an investigation of the deforming layer debris rich basal ice continuum illustrated from three alaskan glaciers three small alaskan glaciers with different bed conditions were studied exit glacier had a thin deforming layer and produced subglacial and proglacial glaciotectonic land forms childs glacier also had a thin deforming layer but the upper part was frozen to the ice matanuska glacier had no deforming layer but had subglacial debris rich ice since it has been shown that sediment at the base can account for the majority of ice movement it is suggested that there is a deforming bed debris rich continuum whereby similar processes occur throughout the different subglacial environments these include similar longitudinal deformation patterns compression at the margin extension and simple shear up glacier similar vertical deformation patterns increase in deformation and fabric strength upwards through the sequence leading to the attenuation of stratified ice into dispersed ice and similar and interrelated incorporation processes the major differences were that the processes occurred at a much faster rate within the deforming layer and that probably only the deforming layer will be recorded in the geological record

an ice marginal δ18o record from barnes ice cap baffin island canada barnes ice cap baffin island canada is a remnant of the laurentide ice sheet that separated from it about 8500 years ago owing to recession of the ice cap during the holocene pleistocene age i

the burst like behavior of aseismic slip on a rough fault the creeping section of the haiyuan fault china recent observations suggesting the influence of creep on earthquakes nucleation and arrest are strong incentives to investigate the physical mechanisms controlling how active faults slip we focus here on deriving generic characteristics of shallow creep along the haiyuan fault a major strike slip fault in china by investigating the relationship between fault slip and geometry we use optical images and time series of synthetic aperture radar data to map the surface fault trace and the spatiotemporal distribution of surface slip along the creeping section of the haiyuan fault the fault trace roughness shows a power law behavior similar to that of the aseismic slip distribution with a 0 8 roughness exponent typical of a self affine regime one possible interpretation is that fault geometry controls to some extent the distribution of aseismic slip as it has been shown previously for coseismic slip along active faults creep is characterized by local fluctuations in rates that we define as creep bursts the potency of creep bursts follows a power law behavior similar to the gutenberg richter earthquake distribution whereas the distribution of bursts velocity is non gaussian suggesting an avalanche like behavior of these slip events such similarities with earthquakes and lab experiments lead us to interpret the rich dynamics of creep bursts observed along the haiyuan fault as resulting from long range elastic interactions within the heterogeneous earth s crust

spatiotemporal evolution of surface creep in the parkfield region of the san andreas fault 1993 2004 from synthetic aperture radar the parkfield section of the san andreas fault saf is defined as a transitional portion of the fault between slip release behavior types in the creeping section of the saf to the northwest and the apparently locked section to the southeast the parkfield section is characterized by complex frictional fault behavior because it represents a transition zone from aseismic creep to stick slip regime at least six historic earthquakes of mw 6 have occurred in this area in 1881 1901 1922 1934 1966 and 2004 it was observed in the 2004 mw 6 0 parkfield earthquake that 70 of the total coseismic and postseismic moment release occurred aseismically to understand the saf behavior in this area it is of particular interest to measure and analyze not only the spatial evolution of the surface displacement in this area but also its evolution over time using radar data acquired by the european space agency s european remote sensing ers1 2 satellites we constructed descending interferograms and retrieved time series of surface displacements along the central saf for the decade preceding the 2004 parkfield earthquake we focus on characterizing the space and time evolution of surface creep in the parkfield and cholame sections the spatial pattern of the interseismic displacement rate indicates that tectonic strain was not uniformly distributed along the strike of the fault between 1993 and 2004 our data indicate not only a decrease in the creep rate from the parkfield section to south of highway 46 from 1 4 0 3 cm y to 0 6 0 3 cm y but also a small but significant creep rate increase in the cholame section to 0 2 0 1 cm y the evidence for episodic creep in the cholame section of the saf south east of parkfield is in contrast with previously published interpretations of gps and trilateration data the cholame section of the saf merits close monitoring because it was likely the nucleation site of the 1857 fort tejon earthquake and because it has shown recent evidence of deep slow slip as revealed by deep tremors

two facies interpretation of the basal layer of the greenland ice sheet contributes to a unified model of basal ice formation two exposures of basal ice in alaska and greenland which have previously provided the basis for contrasting models of basal ice development are in fact directly comparable reinterpretation of previous field descriptions combined with new structural and sedimentological data from west greenland facilitates a simple unification of previous models of basal ice development and a common terminology for the field description of basal ice sequences the stratigraphy of the basal ice sequence at any site indicates the subglacial conditions and processes operating up glacier of that site presented here are interpretations of the major sequence types

an investigation of the debris rich basal ice from worthington glacier alaska u s a this paper examines the debris rich basal ice layer from worthington glacier alaska u s a a small valley glacier overlying rigid bedrock the debris rich basal ice layer studied shows evidence for large scale longitudinal compressive deformation isoclinal folds and nappes similar in style and magnitude features to that reported from push moraines formed in glacial sediments the debris rich ice largely comprised stratified solid ice layers of alternating debris rich and debris poor ice which we suggest results from the tectonic attenuation of folds produced from the deformation of the frozen debris glacier ice and bubble rich ice that comprise the initial basal layer of worthington glacier beneath the glacier lies a thin bed of saturated diamicton which contains evidence of limited movement it is suggested that this is the result of the partial melt out of the debris rich basal ice layer which then behaved as a local and seasonal thin deforming layer it is suggested that this example from a valley glacier flowing over rigid bedrock provides further evidence that the processes ofsediment transport incorporation and deposition in the debris rich basal ice are similar to and linked with those in the deforming layer

mid wisconsinan eolian deposits of the kittigazuit formation tuktoyaktuk coastlands northwest territories canada the kittigazuit formation is a late quaternary sand unit commonly observed throughout the tuktoyaktuk coastlands and in subbottom sediments of the southern beaufort shelf stratigraphic and sedimentology data including sedimentary structures grain surface characteristics and heavy and light mineralogy assist in characterizing the deposit and indicate that it is eolian in origin plant and arthropod macrofossils suggest that although the summer climate during deposition was as warm or slightly warmer than today conditions were likely more arid permafrost is interpreted as being widespread during deposition accelerator mass spectrometry radiocarbon dates indicate that the kittigazuit formation was deposited between 37 and 33 ka bp the unit is therefore interpreted as a mid wisconsinan eolian dune deposit formed by reworking of underlying alluvial sediments of the kidluit formation under nonglacial conditions glaciogenic sediments overlying the kittigazuit formation indicate that glacial ice cover

surficial materials and related ground ice conditions slave province n w t canada surficial mapping and geologic information on the nature and evolution of surficial materials in the slave geologic province indicate that the geotechnical properties and potential ground ice contents associated with these materials depend largely upon their provenance depositional conditions and the postglacial climatic history this information may be used to provide a regional scale view of the distribution of ground ice conditions and terrain sensitivities associated with various surficial materials in till veneers and blankets ground ice content is generally low as suggested by lack of thermokarst and other permafrost features however distinctive surface relief in hummocky till including kettle depressions rim ridges and shallow thaw flowslides may be attributed to massive ice resulting in sensitive till terrain although many outwash sediments have low ice contents near the surface massive ice ranging from 5 to 10 m thick is present in some eskers and ice contact outwash sediments these are associated with thermokarst slope movement and collapse features indicative of meltout or creep of large bodies of massive ice the terrain sensitivity associated with these deposits is typically low to moderate due to the coarse grained nature of the sediments in contrast terrain sensitivity is high and active layer detachment slides are common along the coronation gulf coast where frozen silty clay marine sediments contain a wide range of ice contents results from this study may be applied to a much more extensive area of the glaciated western arctic mainland and adjacent arctic coastal plain in which materials with a similar glacial history are found resume la cartographie et l evolution de depots de surface dans la province des esclaves demontrent que les proprietes geotechniques et le potentiel pour la presence de glace de sol associes aux depots dependent largement de l origine des depots l histoire glaciaire et une connaissance de l histoire climatique postglaciaire cette information peut servir a fournir une vue regionale de la distribution de glace de sol et la sensibilite de terrain associee aux divers depots de surface la quantite de glace de sol dans les couvertures et placages de till peut etre minime telle que suggeree par l absence de thermokarst ou des formes periglaciaires par contre dans le till bossele des structures de contact glaciaire et des glissements retrogressifs par liquefaction resultent en formes de relief distinctives qui peuvent etre attribuees a la glace de sol enfouie meme si certains eskers ont l apparence d avoir de la glace de sol en faible teneur la glace massive d une epaisseur d e5a1 0 mpeut se retrouver ou les eskers demontrent les effets de thermokarst de reptation et des structures d effondrement la sensibilite de terrain associee a ces depots est generalement faible a moyenne a cause d une granulometrie grossiere le long des rivieres ou des sables grossiers littoraux recouvrent les silts argilleux marins geles contenant la glace de sol d une epaisseur variable la sensibilite de terrain est elevee et des glissements par liquefaction sont communs les resultats de cette etude peuvent etre appliques dans l arctique central et de l ouest ou les depots de surface ayant une origine glaciaire semblable sont presents

earthquake potential along the northern hayward fault california the hayward fault slips in large earthquakes and by aseismic creep observed along its surface trace dislocation models of the surface deformation adjacent to the hayward fault measured with the global positioning system and interferometric synthetic aperture radar favor creep at 7 millimeters per year to the bottom of the seismogenic zone along a 20 kilometer long northern fault segment microearthquakes with the same waveform repeatedly occur at 4 to 10 kilometer depths and indicate deep creep at 5 to 7 millimeters per year the difference between current creep rates and the long term slip rate of 10 millimeters per year can be reconciled in a mechanical model of a freely slipping northern hayward fault adjacent to the locked 1868 earthquake rupture which broke the southern 40 to 50 kilometers of the fault the potential for a major independent earthquake of the northern hayward fault might be less than previously thought

massive ice of the tuktoyaktuk area western arctic coast canada the extensive coastal exposure of massive underground ice at peninsula point southwest of tuktoyaktuk northwest territories is believed to be intrasedimental ice the ice grew beneath a frozen d

zagros phantom earthquakes reassessed the interplay of seismicity and deep salt flow in the simply folded belt unraveling the contributions of main shock slip aftershocks aseismic afterslip and postseismic relaxation to the deformation observed in earthquake sequences heightens our understanding of crustal rheology triggering phenomena and seismic hazard here we revisit two recent earthquakes in the zagros mountains iran which exhibited unusual and contentious aftereffects the mw 6 earthquakes at qeshm 2005 and fin 2006 are both associated with large interferometric synthetic aperture radar insar signals consistent with slip on steep reverse faults in carbonate rocks of the middle sedimentary cover but small aftershocks detected with local seismic networks were concentrated at significantly greater depths this discrepancy can be interpreted in one of two ways either 1 there is a genuine vertical separation between main shock and aftershocks reflecting a complex stress state near the basement cover interface or 2 the aftershocks delimit the main shock slip and the insar signals were caused by shallow updip afterslip phantom earthquakes with very similar magnitudes mechanisms and geographical positions as the original earthquakes here we show that main shock centroid depths obtained from body waveform modeling which in this instance is the only method that can reveal for certain the depth at which seismic slip was centered strongly support the first interpretation at qeshm microseismic aftershock depths are centered at the level of the hormuz formation an infracambrian sequence of intercalated evaporitic and nonevaporitic sediments these aftershocks may reflect the breaking up of harder hormuz sediments and adjacent strata as the salt flows in response to main shock strain at the base of the cover this work bolsters recent suggestions that most large earthquakes in the zagros are contained within carbonate rocks in the midlower sedimentary cover and that the crystalline basement shortens mostly aseismically

major end moraines of younger dryas age on wollaston peninsula victoria island canadian arctic implications for paleoclimate and for formation of hummocky moraine some of the most extensive and massive end moraines of younger dryas age 11 10 14c ka bp yet recognized in north america occur on wollaston peninsula of victoria island on the western part of the peninsula numerous closely spaced end moraines formed in the interval starting 11 100 100 radiocarbon years ago and ending about 10 500 10 200 years ago net recession was generally slow throughout and was punctuated by moraine building and at least two readvances recession is mapped with a resolution that is approximately decadal the moraines form an orderly nested succession and are consistently associated with westward shedding of meltwater which formed a sequence of marine limit deltas we lack firm independent proxy climate evidence needed to assess whether these moraines formed because of cold younger dryas climate rather than because of controls such as topographic setting and water depth but climatic control seems probable the moraines evidently retain glacier ice cores as do most similarly

cryostratigraphy paleogeography and climate change during the early holocene warm interval western arctic coast canada botanical and cryostratigraphic records from northwest canada indicate that the climate of the early holocene was considerably warmer than today tree line was over 100 km farther north and a thaw unconformity dating from 8000 14c years bp formed at the base of an active layer 2 5 times thicker than at present numerous thermokarst lake basins formed in the preceding millennia both the botanical and cryostratigraphic indices described are products of summer conditions previous reconstructions of early holocene climate have not assessed the significance of paleocoastal location on the seasonality and extent of apparent climate warming at present there is a steep gradient in growing season conditions between cooler sites on the beaufort sea coast and warmer inland locations winter conditions are more uniform because both sea and land are snow covered coastal retreat in the region has been rapid due to sea level rising over a gently sloping shelf containing readily erodible sediments the coastlin

melt out till in the edmonton area alberta canada till at two localities in the edmonton area alberta was formed mainly by passive melt out from glacier ice and not by lodgment by active ice or as a result of supraglacially derived flows this interpretation is based on the implications of in situ stratified glacial sediment below and within till and of large unlithified clasts of sediment derived from subtill deposits the interpretation is also supported by more general regional stratigraphic and structural observations such associated properties as subtill deformation a sharply planar till preglacial sediment contact sole marks and fabric support formation by melt out or illustrate local exceptions to this process regionally consistent preferred orientation of clasts is interpreted to represent preferred englacial orientation collective analysis of the principal eigenvectors of individual englacial fabrics and flow or resedimented till fabrics from a modem glacial environment and similar analysis for till at villeneuve near edmonton show the edmonton till to occupy the intermediate position in terms of orientation strength predicted by the melt out hypothesis in places preferred orientation is considered to have been disturbed by flow and diapirism induced by the process of thaw consolidation thus preferred clast orientation in till may show considerable deviation from a regional trend stratigraphy and sedimentology are used to classify the till and to relate individual exposures to regional environments of deposition

numerical modeling of strike slip creeping faults and implications for the hayward fault california abstract the seismic potential of creeping faults such as the hayward fault san francisco bay area ca depends on the rate at which moment slip deficit accumulates on the fault plane thus it is important to evaluate how the creep rate observed at the surface is related to the slip on the fault plane the surface creep rate scr depends on the geometry of locked and free portions of the fault and on the interaction between the fault zone and the surrounding lithosphere using a viscoelastic finite element model we investigate how fault zone geometries and physical characteristics such as frictionless or locked patches affect the observed surface creep when the system is driven by far field plate motions these results have been applied to creep observations of the hayward fault this analysis differs from most previous fault creeping models in that the fault in our model is loaded by a distributed viscous flow induced by far field velocity boundary conditions instead of imposed slip beneath the major faults of the region the far field velocity boundary conditions simulate the relative motion of the stable pacific plate respect to the rigid sierra nevada block leaving the rheology fault geometry and mechanics locked or free to creep patches to determinate the patterns of fault creep our model results show that the fault geometry e g length and depth of creeping and the local rheology influence the surface creep rate scr and the slip on the fault plane in particular we show that the viscoelastic layer beneath the elastic seismogenic zone plays a fundamental role in loading the fault additionally the coupling with the surrounding lithosphere results in a smooth transition from regions free to creep to locked patches

the ice hill an example of retarded deglaciation in siberia abstract the geological structure of one of the southernmost sites of thick ice beds in the yenisei valley near the arctic circle is discussed the erosion contacts of the foliated and contorted ice abundance of glacial debris and the position between the basal till and ablation cover indicate a glacial origin for the ice layer the ice occurs in the cores of arcuate accretion ridges built of ablation materials the overlying sequence consists of a series of diamicton flows alternating with lacustrine and outwash sediments laterally the ice rock complex changes into thick lacustrine rhythmites underlain by basal tills the ice containing hummocky terrain is often lower than the adjacent lacustrine plain therefore inversion of ice controlled topography is suggested several stages of glaciokarst development are supposed to have occurred after an eastward moving ice lobe stagnated more than 50 ka bp the main depositional events are associated with the middle weichselian draining of ice dammed lake igarka and with early holocene topographic inversion the holocene warming apparently caused diapiric deformation of the buried ice probably because of the density and thickness differences between the ice and the overburden the long history of burial and preservation of the remnants of basal glacier ice was controlled by pleistocene permafrost landscape evolution in northern siberia is governed by such retarded deglaciation in contrast with atlantic environments the thick ablation sequence may be described in terms of a spitsbergen model but the siberian basal tills because of their position within the permafrost must be regarded as exfoliated layers of debris rich ice according to shantzer lavrushin s model the occurrence of buried glacier ice and the mode of distribution of the permafrost shows the relict nature of the latter in areas of modern and former retarded deglaciation intermittent diamicton flows are supposed to mark episodes of climatic amelioration like the pleistocene and holocene diamictons with driftwood at the ice hill such warm diamictons may account for some early holocene and similar puzzling interglacial ice advances

synthetic aperture radar interferometry to measure earth s surface topography and its deformation synthetic aperture radar interferometry insar from earth orbiting spacecraft provides a new tool to map global topography and deformation of the earth s surface radar images taken from slightly different viewing directions allow the construction of digital elevation models of meter scale accuracy these data sets aid in the analysis and interpretation of tectonic and volcanic landscapes if the earth s surface deformed between two radar image acquisitions a map of the surface dis placement with tens of meters resolution and subcentimeter accuracy can be con structed this review gives a basic overview of insar for earth scientists and presents a selection of geologic applications that demonstrate the unique capabilities of insar for mapping the topography and deformation of the earth

first evidences of fast creeping on a long lasting quiescent earthquake normal fault in the mediterranean summary a key issue in our understanding of the earthquake cycle and seismic hazard is the behaviour of an active fault during the interseismic phase locked and creeping faults represent two end members of mechanical behaviours that are given two extreme rupturing hazard levels that is high and low respectively geophysical and space geodetic analyses are carried out over the pollino range an extensional environment within the africa eurasia plate boundary to disclose the behaviour of the long lasting quiescent castrovillari normal fault fault trenching evidenced at least four large earthquakes 6 5 7 0 mw in the past and an elapsed time of 1200 yr since the last event inversion of differential interferometric synthetic aperture radar and global positioning system over a decade shows fast creeping at all depths of the fault plane the velocity strengthening creeping zone reaches maximum rates 20 mm yr 1 against an average rate of about 3 9 mm yr 1 it limits the southern weakening locked part of the fault an essential condition for the generation of a large earthquake on the castrovillari fault as has occurred in the past is a rupture through the velocity strengthening zone the castrovillari fault yields the best evidence for being both a strong and weak fault during its earthquake cycle creeping at rates faster than its tectonically driven ones it must thus consist of a mix of unstable and conditionally stable patches ready to sustain a sizeable earthquake quantifying and mapping the slip rate over the fault plane is important because they influence fault moment budget estimate and helps to constrain constitutive laws of fault zones aseismic slip also redistributes stress in the crust thereby affecting the locations of future earthquakes

multi interferogram method for measuring interseismic deformation denali fault alaska summary studies of interseismic strain accumulation are crucial to our understanding of continental deformation the earthquake cycle and seismic hazard by mapping small amounts of ground deformation over large spatial areas insar has the potential to produce continental scale maps of strain accumulation on active faults however most insar studies to date have focused on areas where the coherence is relatively good e g california tibet and turkey and most analysis techniques stacking small baseline subset algorithm permanent scatterers etc only include information from pixels which are coherent throughout the time span of the study in some areas such as alaska where the deformation rate is small and coherence very variable it is necessary to include information from pixels which are coherent in some but not all interferograms we use a three stage iterative algorithm based on distributed scatterer interferometry we validate our method using synthetic data created using realistic parameters from a test site on the denali fault alaska and present a preliminary result of 10 5 5 0 mm yr 1 for the slip rate on the denali fault based on a single track of radar data from ers1 2

continental transforms a view from the alpine fault abstract continental transform faults are dominantly highly localized strike slip shear zones hundreds of kilometers long that accumulate tens to hundreds of kilometers of displacement from work on the alpine fault we pose the questions what is the deep structure of a continental transform and how does the displacement become localized we review research on the alpine fault and propose a model in which the fault partitions at depth into a steep zone extending into the mantle with largely fault parallel motion and a flat ductile decollement in the lower crust the fault localizes around two thirds of the plate motion within a 100 km wide zone of distributed deformation a review of other active continental fault systems suggests that variation between them may reflect their tectonic origins the nature of the crust in which they develop the presence of a significant oblique component of motion and the displacement rate all however have evidence for the development of a single principal fault zone that carries 50 of the total displacement and extends as a localized zone of shear into the upper mantle we review mechanisms of strain weakening and suggest that localization of a principal fault may be initiated in the seismogenic crust and through a series of positive feedbacks eventually extend through the lower crust into the upper mantle

a simple explanation for the occurrence of the 1911 morgan hill earthquake in the stress shadow of the 1906 san francisco earthquake we propose a new model to overcome an apparent stress shadow paradox the stress shadow of the 1906 san francisco earthquake was so effective in inhibiting earthquake activity that no m 6 earthquakes occurred in the san francisco bay area for more than 70 years after the 1906 earthquake with one exception the 1911 morgan hill earthquake how could this earthquake occur only 5 years after the 1906 earthquake in an area where earthquake activity should have been inhibited our model is characterized by localized locked patches on the morgan hill segment of the calaveras fault surrounded by steadily creeping patches according to this model the tectonic stressing rate on the morgan hill segment is so high that the stress shadow caused by the 1906 earthquake can be dissipated within several years this simple model is consistent with both the surface deformation data and the apparent earthquake recurrence at morgan hill in contrast to two previous models which are either poorly constrained or have difficulty explaining such observations

stratigraphy and glaciotectonic structures of permafrost deformed beneath the northwest margin of the laurentide ice sheet tuktoyaktuk coastlands canada the upper 5 20 m of ice rich permafrost at three sites overridden by the northwest margin of the laurentide ice sheet in the tuktoyaktuk coastlands western arctic canada comprise massive ice beneath ice rich diamicton or sandy silt the diamicton and silt contain 1 truncated ice blocks up to 15 m long 2 sand lenses and layers 3 ice veins dipping at 20 30 4 ice lenses adjacent and parallel to sedimentary contacts and 5 ice wedges the massive ice is interpreted as intrasedimental or buried basal glacier ice and the diamicton and silt as glacitectonite that has never thawed deformation of frozen ground was mainly ductile in character deformation was accompanied by sub marginal erosion of permafrost which formed an angular unconformity along the top of the massive ice and supplied ice clasts and sand bodies to the overlying glacitectonite after deformation and erosion ceased postglacial segregated ice and ice wedge ice developed within the deformed permafrost

creeping along the ismetpasa section of the north anatolian fault western turkey rate and extent from insar creeping along the north anatolian fault naf at ismetpasa turkey was discovered some thirty years ago about a decade after the first observations of the phenomenon along the san andreas fault in california however little is known about its lateral extent and rate in order to study its three dimensional nature and rupture characteristics we use synthetic aperture radar interferometry insar and elastic dislocation models compared also with field observations interferograms with temporal baselines ranging between 1 25 and 5 years show that the creeping section starts at the western termination of the 1943 m 7 6 earthquake rupture it continues about 70 km to the west overlapping with the eastern part of the 1944 m 7 3 earthquake rupture offsets along strike indicate a maximum creep rate of 11f3 mm year near the mid point of the creeping section decreasing gradually towards the edges near ismetpasa insar data yield 8f3 mm year of creep rate consistent with recent instrumental triangulation and creepmeter measurements modeling of the insar and gps data suggests that the faultcreep occurs most probably at a shallow depth 0 7 km our analysis combined with previous studies suggests that creeping might have commenced following the 1944 earthquake and thus may be a long lasting but transient slip episode d 2005 elsevier b v all rights reserved

glaciohydraulic supercooling a freeze on mechanism to create stratified debris rich basal ice i field evidence debris laden ice accretes to the base of matanuska glacier alaska u s a from water that supercools while flowing in a distributed drainage system up the adverse slope of an overdeepening frazil ice grows in the water column and forms aggregates while other ice grows on the glacier sole or on substrate materials sediment is trapped by this growing ice forming stratified debris laden basal ice growth rates of 0 1 m a 1 of debris rich basal ice are possible the large sediment fluxes that this mechanism allows may have implications for interpretation of the widespread deposits from ice that flowed through other overdeepenings including heinrich events and the till sheets south of the laurentian great lakes

land subsidence in houston texas measured by radar interferometry and constrained by extensometers 1 we present results from a radar interferometry study over the houston galveston texas gulf coast region from the nearly 60 potential interferograms considered an atmospheric artifact assessment is performed and a tractable set of interferograms selected for detailed processing and error analysis the subsequent interferogram time series spanning 1996 1998 is constrained by coincident extensometer data with root mean square error less than 2 5 mm the interferogram time series confirms that historic subsidence in east houston has stopped consistent with current groundwater use patterns broad scale subsidence bowls are observed in west and northwest houston where maximum subsidence rates are in excess of 2 and 4 cm yr 1 respectively linear interferogram phase signatures associated with approximately 1 cm of differential subsidence across faults including the long point fault in northwest houston are observed near the seabrook extensometer a hereto unidentified subsidence bowl with a maximum subsidence rate in excess of 3 cm yr 1 is revealed this study demonstrates that when used in conjunction with a set of traditional geodetic measurements radar interferometry can measure the spatial and temporal evolution of urban land subsidence within even the most challenging of environments

geodetic determination of relative plate motion and crustal deformation across the scotia south america plate boundary in eastern tierra del fuego 1 global positioning system gps measurements provide the first direct measurement of plate motion and crustal deformation across the scotia south america transform plate boundary in tierra del fuego this plate boundary accommodates a part of the overall motion between south america and antarctica the subaerial section of the plate boundary in tierra del fuego about 160 km in length is modeled as a two dimensional strike slip plate boundary with east west strike along the magallanes fagnano fault system the principal fault of this portion of the plate boundary relative plate motion is left lateral strike slip on a vertical fault at 6 6 1 3 mm year based on an assumed locking depth of 15 km the site velocities on the scotia plate side are faster than the relative velocity by an additional 1 2 mm yr suggesting there may be a wider region of diffuse left lateral deformation in southern patagonia the north south components of the velocities however do not support the existence of active large scale transpression or transtension between the south america and scotia plates along this section of the plate boundary

active fault creep variations at chihshang taiwan revealed by creep meter monitoring 1998 2001 1 the daily creep meter data recorded at chihshang in 1998 2001 are presented the chihshang creep meter experiment was set up across the chihshang thrust fault the most active segment of the longitudinal valley fault which is the present day plate suture between the eurasian and the philippine sea plates in eastern taiwan near continuous data recording at two sites revealed different surface fault motions yet similar annual shortening rates 16 2 mm at the tapo site comprising two connected creep meters and 15 0 mm at the chinyuan site three creep meters straddling parallel fault branches four of the five creep meters showed a seasonal variation with the fault moving steadily during the rainy season from april to october and remaining quiescent during the rest of the year the only exception was recorded by the creep meter located on a melange composed hillslope where local gravitational landsliding played an additional role other than tectonic faulting through comparison with daily precipitation data we inferred that moderate rainfall suffices to trigger or facilitate slippage on the surface fault during the transition period of the dry wet season during the observation period from 1998 to 2001 the subsurface seismicity exhibited clusters of microearthquakes on the chihshang fault at depths of 10 25 km recurrent earthquakes occurred regardless of whether the season was wet or dry indicating that the stress relaxation associated with seismicity in the seismogenic zone did not transfer immediately up to the surface the accumulated strain on the chihshang fault at shallow surface levels was released through creep during the wet season in addition to these short term seasonal variations an apparent decrease in the annual slipping rate on the chihshang fault during the last few years deserves further investigation in order to mitigate against seismic hazard

the basal ice layer of glaciers and ice sheets abstract in many glaciers and ice sheets there is a basal ice layer bil in which the ice is conditioned primarily by processes operating at the bed the bil is chemically and physically distinctive and is characterised by a component of basally derived sediment the bil is a rheological control on ice sheet dynamics an indicator of subglacial conditions and processes an agent of subglacial geologic processes the source of a substantial proportion of glacial sediments a limit to the downward extension of the climate record from deep ice cores if debris characteristics of the bil are preserved in glacial sediments former glacier conditions can be inferred analysis of stable isotopes gas and cation composition ice crystallography debris composition and structural glaciology has elucidated many mechanisms for bil formation common elements can be identified from a range of locations key issues are entrainment of ice and debris from the bed formation of new ice metamorphism of existing ice in the bil and thickening of the bil by deformation a distinction can be made between basal ice formed by accretion of material from the bed stratified facies and basal ice formed by metamorphic processes within the ice close to the bed dispersed facies

fault structure and mechanics of the hayward fault california from double difference earthquake locations 1 the relationship between small magnitude seismicity and large scale crustal faulting along the hayward fault california is investigated using a double difference dd earthquake location algorithm we used the dd method to determine high resolution hypocenter locations of the seismicity that occurred between 1967 and 1998 the dd technique incorporates catalog travel time data and relative p and s wave arrival time measurements from waveform cross correlation to solve for the hypocentral separation between events the relocated seismicity reveals a narrow near vertical fault zone at most locations this zone follows the hayward fault along its northern half and then diverges from it to the east near san leandro forming the mission trend the relocated seismicity is consistent with the idea that slip from the calaveras fault is transferred over the mission trend onto the northern hayward fault the mission trend is not clearly associated with any mapped active fault as it continues to the south and joins the calaveras fault at calaveras reservoir in some locations discrete structures adjacent to the main trace are seen features that were previously hidden in the uncertainty of the network locations the fine structure of the seismicity suggests that the fault surface on the northern hayward fault is curved or that the events occur on several substructures near san leandro where the more westerly striking trend of the mission seismicity intersects with the surface trace of the aseismic southern hayward fault the seismicity remains diffuse after relocation with strong variation in focal mechanisms between adjacent events indicating a highly fractured zone of deformation the seismicity is highly organized in space especially on the northern hayward fault where it forms horizontal slip parallel streaks of hypocenters of only a few tens of meters width bounded by areas almost absent of seismic activity during the interval from 1984 to 1998 when digital waveforms are available we find that fewer than 6 5 of the earthquakes can be classified as repeating earthquakes events that rupture the same fault patch more than one time these most commonly are located in the shallow creeping part of the fault or within the streaks at greater depth the slow repeat rate of 2 3 times within the 15 year observation period for events with magnitudes around m 1 5 is indicative of a low slip rate or a high stress drop the absence of microearthquakes over large contiguous areas of the northern hayward fault plane in the depth interval from 5 to 10 km and the concentrations of seismicity at these depths suggest that the aseismic regions are either locked or retarded and are storing strain energy for release in future large magnitude earthquakes

cryostructures in permafrost tuktoyaktuk coastlands western arctic canada the shape and distribution of ice and sediment within frozen ground constitute its cryostructure observations on perennially frozen sediments in the tuktoyaktuk coastlands enable six cryostructures to be identified 1 structureless 2 lenticular 3 layered 4 reticulate 5 crustal and 6 suspended these cryostructures can be transitional or composite five cryofacies types can also be identified according to volumetric ice content and grain size they can be grouped into cryofacies assemblages the utility of the descriptive classification of ice rich sediments is illustrated from a palaeothaw layer at crumbling point

osl age and stratigraphy of the strauss sand sheet in new mexico usa abstract the strauss sand sheet occurs in south central new mexico usa and northern chihuahua mexico covering an area of about 4740 km2 its chronology is determined by 19 osl ages the sand sheet formed primarily during three phases of eolian deflation and deposition each phase with a separate sand source and under different climatic and environmental circumstances the first phase of eolian sedimentation occurred 45 to 15 ka with the deposition of unit 1 the sand source for the first phase was beach related features along the eastern shoreline of pluvial lake palomas in mexico the glacial age climate was cool wet and windy because of the southern path of the jet stream at that time after 15 ka with the onset of warmer conditions of the bolling allerod the shutting down of the palomas sand source and wet conditions of the younger dryas the sand sheet stabilized with weak soil development in unit 1 by 11 ka the climate shifted to holocene drying conditions and the second phase of sand accumulation began forming unit 2 the sand source was the local deflation of the previously deposited unit 1 sand the sand sheet stabilized again by 1 9 ka with slightly wetter late holocene climate a weak soil formed in unit 2 sand about a d 1500 and extending to about a d 1850 or later an a horizon formed on the sand sheet probably in response to a desert grassland vegetation during the period of wet climate of the little ice age in an anthropogenic third phase of eolian activity after a d 1850 the vegetation was likely disturbed by overgrazing and the unit 2 and a horizon unit 3 sands were deflated resulting in the deposition of a thin layer of massive eolian sand unit 4 across the sand sheet by about a d 1900 mesquite shrubs had increased in abundance and deflated sand largely from unit 2 began to accumulate around the shrubs forming coppice dunes unit 5 mesquite coppice dunes continued to increase in number and volume during the twentieth century and at present dominate most of the sand sheet this third phase of eolian deflation deposition is ongoing today

fault slip rates at depth from recurrence intervals of repeating microearthquakes unique attributes in sequences of recurring similar microearthquakes at parkfield california provide a means for inferring slip rate at depth throughout the active fault surface from the time intervals between sequence events application of the method using an 11 year microseismicity record revealed systematic spatial and temporal changes in the slip rate that were synchronous with earthquake activity and other independent measures of fault zone slip if this phenomenon is found to be generally common behavior in active faults it forms the basis for a method to monitor the changing strain field throughout a seismogenic fault zone

variations in creep rate along the hayward fault california interpreted as changes in depth of creep variations in surface creep rate along the hayward fault are modeled as changes in locking depth using 3d boundary elements model creep is driven by screw dislocations at 12 km depth under the hayward and other regional faults inferred depth to locking varies along strike from 4 12 km 12 km implies no locking our models require locked patches under the central hayward fault consistent with a m6 8 earthquake in 1868 but the geometry and extent of locking under the north and south ends depend critically on assumptions regarding continuity and creep behavior of the fault at its ends for the northern onshore part of the fault our models contain 1 4 1 7 times more stored moment than the model of burgmann et al 2000 45 57 of this stored moment resides in creeping areas it is important for seismic hazard estimation to know how much of this moment is released coseismically or as aseismic afterslip

basin width control of faulting in the naryn basin south central kyrgyzstan 1 in central asia s tien shan deformation is distributed across the wide orogen a characteristic of intracontinental mountain building active faults are commonly found within intramontane basins that separate its constituent ranges in order to explore the controls on this intramontane basin deformation we study the naryn basin of south central kyrgyzstan a series of five balanced cross sections reveals a transition in patterns of faulting from faults confined to basin margins to faults focused within the basin center the 20 km wide eastern naryn basin displays deformation attributed to low angle splays of the northern basin bounding fault in the 40 km wide western naryn basin the pattern of deformation linked to the northern range remains but is accompanied by steeper faults that dip both south and north without being directly linked to the basin bounding fault we compare these cross sections to synthetic aperture radar interferometry insar measurements of surface deformation profiles of insar derived surface deformation rates across the naryn basin reveal that in the west deformation is distributed across the broad basin interior whereas in the east rapid uplift is concentrated at the margin of the narrower basin from the geodetic and structural data we infer that in the western naryn basin deformation has migrated away from the northern basin margin and into the interior deformation of the eastern basin interior however remains linked to the basin bounding fault a simple mechanical model demonstrates that basin width may control basin deformation whereby basin interior faulting in the narrow eastern naryn basin is inhibited by the overburden of adjacent ranges citation goode j k d w burbank and b bookhagen 2011 basin width control of faulting in the naryn basin south central kyrgyzstan tectonics 30 tc6009 doi 10 1029 2011tc002910

sar monitoring of progressive and seasonal ground deformation using the permanent scatterers technique spaceborne differential radar interferometry has proven a remarkable potential for mapping ground deformation phenomena e g urban subsidence volcano dynamics coseismic and postseismic displacements along faults as well as slope instability however a full operational capability has not been achieved yet due to atmospheric disturbances and phase decorrelation phenomena these drawbacks can often be at least partially overcome by carrying out measurements on a subset of image pixels corresponding to natural or artificial stable reflectors permanent scatterers ps and exploiting long temporal series of interferometric data this approach allows one to push the measurement precision very close to its theoretical limit in the order of spl sim 1 mm for c band european remote sensing ers like sensors in this paper the detection of both time uniform and seasonal deformation phenomena is addressed and a first assessment of the precision achievable by means of the ps technique is discussed results highlighting deformation phenomena occurring in two test sites in california are reported fremont in the southern bay area and san jose in the santa clara valley

basal till fabric and deposition at burroughs glacier glacier bay alaska basal till and debris rich ice in the basal transport zone of burroughs glacier southeast alaska were studied to develop a model for till deposition and to acquire new pebble fabric measurements from till at a modern glacier studies of till deposition and fabric measurements from modern glacial deposits are important for studying the genesis of pleistocene and pre pleistocene glacial sediment basal till at burroughs glacier is deposited at the ice margin by the melting of basal debris rich ice that stagnated progressively from the bottom upward beneath moving ice during deglaciation the debris rich ice is typically 1 3 m thick and has very high sediment content ranging from 60 to 70 by volume the long axes of pebbles in the debris rich ice and in other parts of the basal transport zone of the glacier are typically well oriented parallel to ice flow the average s 1 eigenvalue for nine fabrics measured in the basal transport zone is 0 8092 0 067 the basal till is massive matrix supported silty sandy diamicton striated lodged boulders and crag and tails are common on the till surface s 1 eigenvalues calculated from 27 pebble fabrics measured in the till range from 0 4930 no fabric to 0 8261 the average value is 0 6757 0 092 the range of values is nearly identical to that reported for fabrics from undeformed lodgment till by dowdeswell and sharp 1986 although the final process of till deposition at burroughs glacier is passive melt out from stagnant debris rich ice the nature and pebble fabric of the till are inherited from active ice processes specifically the progressive stagnation of debris rich ice beneath active ice evidence of differential movement shear within the debris rich ice during deposition is reflected in a change in fabric azimuth with depth in the till beveled bullet boulders and shear surfaces these features are typically thought to be characteristic of lodgment till or brittle deformation of subglacial sediment the melt out process is passive because of the very high debris content of the debris rich ice if the same sequence of till deposition occurred in older glacial deposits and the debris content of the basal ice was high the final process of melt out would not be reflected in properties of the sediment