afterslip evolution on the crustal ramp of the main himalayan thrust fault following the 2015 mw 7 8 gorkha nepal earthquake abstract current afterslip models of the mw 7 8 gorkha earthquake contradict with the depth ranges of relocated aftershock distribution and inter seismic locked creeping transition zone we use both gps and interferometric synthetic aperture radar insar data to image the afterslip evolution in the first 189 post seismic days i e from 25 april to 1 november 2015 in the study region 51 gps stations are divided into three categories based on their observation time 1 25 stations with both pre and post seismic observations 2 16 stations with only post seismic observations and 3 10 stations with only pre seismic observations the secular tectonic motion and seasonal variations are corrected carefully and directly using the fitted functions from the pre seismic position time series during the inversions we adopt the widely accepted flat ramp flat geometrical model of the main frontal thrust fault mft main himalayan thrust fault mht the preferred weight ratios between gps and insar observations are elaborately determined through comprehensive analysis of model resolution and fitting residuals in contrast to previous afterslip models our preferred afterslip distributes on the crustal ramp of the mht from depths of 11 to 29 km which is verified by further inversions using only gps data and checkerboard resolution tests the seismic moment released by the afterslip in the first six months is 3 42 1019 n m only approximately 4 of the mainshock moment the rupture gap between the mainshock and the 12 may aftershock is filled up with post seismic aseismic slip

the late devensian 22 000 bp irish sea basin the sedimentary record of a collapsed ice sheet margin the late devensian 20 ka bp glacial geology of the irish sea basin 4000 km2 is an event stratigraphy recording the entry of marine waters into a glacio isostatically depressed basin and the rapid retreat of the irish sea glacier as a tidewater ice margin marine limits occur up to 140 m o d across much of the central basin the ice margin was uncoupled from its bed exposing a subglacially scoured topography to glaciomarine processes the irish sea glacier was a major drainage conduit of the last british ice sheet calving of the marine ice margin resulted in fast flow surging of ice streams recorded by drumlin fields around the northern basin margin and tunnel valleys rapid evacuation of the basin may have stranded large areas of dead ice in peripheral zones e g cheshire shropshire lowlands and initiated the collapse of the ice sheet thick wedges of ice contact glaciomarine sediments were deposited during ice retreat as morainal bank complexes by successive tidewater ice margins stabilized at pinning points around the irish sea coast where morainal banks occur on the seaward side of drumlin swarms there is a clear sequential relationship between rapid ice loss from calving ice margins the development of fast flowing ice streams drumlinization and the pumping of subglacial sediment to tidewater raised delta complexes are locally associated with marine limits along the high relief coastal margins of wales east central ireland and the lake district associated valley infill complexes record downslope resedimentation of heterogenous sediments into the marine environment during ice retreat co eval offshore deposits are represented by well stratified glaciomarine complexes that infill a subglacially scoured topography that shows networks of tunnel valleys glaciomarine mud drapes occur well to the south of the maximum limit of grounded ice in the basin e g north devon scilly islands southern ireland the age of these distal sediments previously mapped as pre devensian tills is constrained by amino acid ratios basin rebound following deglaciation was rapid with over 100 m recovery in 3 ka and was followed by a low marine still stand peat accumulating in offshore areas now as much as 55 m below sea level has been drowned by the postglacial eustatic rise in sea level the glacio sedimentary model identified in this paper involving rapid ice retreat and related sedimentation triggered by rising relative sea level suggests that isotatic downwarping is an important mechanism for deglaciating continental shelves

primary surface ruptures of the great himalayan earthquakes in 1934 and 1255 it is unclear where plate boundary thrusts generate giant rather than great earthquakes along the himalayas the source sizes and recurrence times of large seismic events are particularly uncertain since no surface signatures were found for those that shook the range in the twentieth century here we challenge the consensus that these events remained blind and did not rupture the surface we use geomorphological mapping of fluvial deposits palaeo seismological logging of river cut cliffs and trench walls and modelling of calibrated 14c ages to show that the mw 8 2 bihar nepal earthquake on 15 january 1934 did break the surface traces of the rupture are clear along at least 150 km of the main frontal thrust fault in nepal between 85 50 and 87 20 e furthermore we date collapse wedges in the sir valley and find that the 7 june ad 1255 earthquake an event that devastated kathmandu and mortally wounded the nepalese king abhaya malla also ruptured the surface along this stretch of the mega thrust thus in the past 1 000 years two great earthquakes 679 years apart rather than one giant eleventh century ad event contributed to the frontal uplift of young river terraces in eastern nepal the rare surface expression of these earthquakes implies that surface ruptures of other reputedly blind great himalayan events might exist the recurrence times of great himalayan earthquakes are difficult to assess because they rarely rupture the surface field mapping and 14c dating of offset fluvial deposits are used to identify two great himalayan quakes that ruptured the surface along the main plate boundary fault in ad 1255 and 1934

detailed rupture imaging of the 25 april 2015 nepal earthquake using teleseismic p waves we analyze the rupture process of the 25 april 2015 nepal earthquake with globally recorded teleseismic p waves the rupture propagated east southeast from the hypocenter for about 160 km with a duration of 55 s backprojection of both high frequency hf 0 2 to 3 hz and low frequency lf 0 05 to 0 2 hz p waves suggest a multistage rupture process from the low frequency images we resolve an initial slow downdip northward rupture near the nucleation area for the first 20 s stage 1 followed by two faster updip ruptures 20 to 40 s for stage 2 and 40 to 55 s for stage 3 which released most of the radiated energy northeast of kathmandu the centroid rupture power from lf backprojection agrees well with the global centroid moment tensor solution the spatial resolution of the backprojection images is validated by applying similar analysis to nearby aftershocks the overall rupture pattern agrees well with the aftershock distribution a multiple asperity model could explain the observed multistage rupture and aftershock distribution

styles of subglacial glaciotectonic deformation within the context of the anglian ice sheet a substantial proportion of the glacial sediments of east anglia england are chaotic and highly deformed this has been attributed to a direct glaciotectonic deformation or b slumping of glaciomarine sediments we show that interpretation a leads to a classification of subglacial glaciotectonic deposits into sites of constructional deformation where little or no erosion of the preglacial deposits has occurred and styles of deformation are preserved moving up in the sequence and excavational deformation where substantial erosion of preglacial sediments has occurred and deformational styles are superimposed on each other by using glaciological and geotechnical theory we show that the expression of these deformational styles in east anglia is a natural response to the stress fields imposed by the ice sheet and that in consequence their spatial relationships are explicable the depth of deformation is related to the geotechnical properties of till and substrate the stress and effective stress fields and found to be consistent with observations

observations and modeling of coseismic and postseismic deformation due to the 2015 mw 7 8 gorkha nepal earthquake we use space geodetic data to investigate coseismic and postseismic deformation due to the 2015 mw 7 8 gorkha earthquake that occurred along the central himalayan arc because the earthquake area is characterized by strong variations in surface relief and material properties we developed finite element models that explicitly account for topography and 3 d elastic structure we computed the line of sight displacement histories from three tracks of the sentinel 1a b interferometric synthetic aperture radar insar satellites using persistent scatter method insar observations reveal an uplift of up to 70 mm over 20 months after the main shock concentrated primarily at the downdip edge of the ruptured asperity gps observations also show uplift as well as southward movement in the epicentral area qualitatively similar to the coseismic deformation pattern kinematic inversions of gps and insar data and forward models of stress driven creep suggest that the observed postseismic transient is dominated by afterslip on a downdip extension of the seismic rupture a poroelastic rebound may have contributed to the observed uplift and southward motion but the predicted surface displacements are small we also tested a wide range of viscoelastic relaxation models including 1 d and 3 d variations in the viscosity structure models of a low viscosity channel previously invoked to explain the long term uplift and variations in topography at the plateau margins predict opposite signs of horizontal and vertical displacements compared to those observed our results do not preclude a possibility of deep seated viscoelastic response beneath southern tibet with a characteristic relaxation time greater than the observation period 2 years

foraminifera from the irish sea glacigenic deposits at aberdaron western lleyn north wales palaeoenvironmental implications in a sequence of glacigenic sediments at aberdaron foraminifera were obtained from samples located specifically in order to differentiate between opposing models of depositional environment all the diamict samples yielded remarkably uniform assemblages with similar numbers of benthic specimens and benthic species per unit weight of sediment similar planktic benthic ratios and similar ratios of clearly allochthonous to possibly autochthonous elements this is precisely as predicted by the terrestrial model of sedimentation where all of the sediments are interpreted as being derived from the melting of glacier ice rich in marine debris entrained during passage along the irish sea basin the results lend no support to a glacial marine model since no faunal responses to increasingly distal sedimentary environments are observed however the fauna is dominated by the foraminifera elphidium excavatum terquem forma clavata cushman which is commonly assumed to indicate glacial marine conditions the modern distribution of similar assemblages suggests that it is just as likely to represent the cold reduced salinity conditions that would have prevailed in the northern irish sea basin for much of the quaternary

block kinematics of the pacific north america plate boundary in the southwestern united states from inversion of gps seismological and geologic data 1 the active deformation of the southwestern united states 30 41 n is represented by a finite number of rotating elastic plastic spherical caps gps derived horizontal velocities geologic fault slip rates transform fault azimuths and earthquake derived fault slip vector azimuths are inverted for block angular velocities creep on block bounding faults permanent strain rates within the blocks and the rotations of 11 published gps velocity fields into to a common north american reference frame gps velocities are considered to be a combination of rigid block rotations recoverable elastic strain rates resulting from friction on block bounding faults and nonrecoverable strain rates resulting from slip on faults within the blocks the resulting pacific north america angular velocity is similar to some published estimates and satisfies transform azimuths and one spreading rate in the gulf of california earthquake slip vectors in the gulf of california and alaska and gps velocities along coastal california and within the pacific basin published fault slip rates are satisfied except in the southern mojave desert where the motion of the mohave block relative to north america is faster than can be explained by mapped faults the largest blocks the sierra nevada great valley and the eastern basin and range show permanent strain rates after removing elastic strain of only a few nanostrain per year demonstrating approximately rigid behavior observed horizontal strain rates correlate strongly with predicted strain rates from known faults suggesting that the short term strains evident in gps velocities are largely elastic in only about 20 of the region is distributed deformation needed to match the data indicating that a plate tectonic style description of the deformation of the western united states is plausible most blocks rotate about vertical axes at approximately the same rate as the pacific relative to north america suggesting that locally spin rates are communicated from block to block arguing against both floating block and ball bearing mechanisms of block rotation the similarities of the blocks spin rates to that of the pacific suggests that the pacific strongly influences their motions through edge tractions however it is shown that the blocks cannot rotate about the pacific north america pole without spinning counter to the sense of pacific north america shear unlike some other broad plate boundaries in the western united states vertical axis rotations take up very little of the slip rate budget across the region

convergence rate across the nepal himalaya and interseismic coupling on the main himalayan thrust implications for seismic hazard we document geodetic strain across the nepal himalaya using gps times series from 30 stations in nepal and southern tibet in addition to previously published campaign gps points and leveling data and determine the pattern of interseismic coupling on the main himalayan thrust fault mht the noise on the daily gps positions is modeled as a combination of white and colored noise in order to infer secular velocities at the stations with consistent uncertainties we then locate the pole of rotation of the indian plate in the itrf 2005 reference frame at longitude 1 34 3 31 latitude 51 4 0 3 with an angular velocity of 0 5029 0 0072 myr the pattern of coupling on the mht is computed on a fault dipping 10 to the north and whose strike roughly follows the arcuate shape of the himalaya the model indicates that the mht is locked from the surface to a distance of approximately 100 km down dip corresponding to a depth of 15 to 20 km in map view the transition zone between the locked portion of the mht and the portion which is creeping at the long term slip rate seems to be at the most a few tens of kilometers wide and coincides with the belt of midcrustal microseismicity underneath the himalaya according to a previous study based on thermokinematic modeling of thermochronological and thermobarometric data this transition seems to happen in a zone where the temperature reaches 350 c the convergence between india and south tibet proceeds at a rate of 17 8 0 5 mm yr in central and eastern nepal and 20 5 1 mm yr in western nepal the moment deficit due to locking of the mht in the interseismic period accrues at a rate of 6 6 0 4 10 19 nm yr on the mht underneath nepal for comparison the moment released by the seismicity over the past 500 years including 14 m w 7 earthquakes with moment magnitudes up to 8 5 amounts to only 0 9 10 19 nm yr indicating a large deficit of seismic slip over that period or very infrequent large slow slip events no large slow slip event has been observed however over the 20 years covered by geodetic measurements in the nepal himalaya we discuss the magnitude and return period of m 8 earthquakes required to balance the long term slip budget on the mht

sedimentary evidence for deforming bed conditions associated with a grounded irish sea glacier southern ireland along the south coast of ireland a shelly diamict facies the irish sea till has been variously ascribed to subglacial deposition by a grounded irish sea glacier or to glacimarine sedimentation by suspension settling and iceberg rafting observations are presented here from five sites along the south coast to directly address this question at these sites sedimentary evidence is preserved for the onshore advance of a grounded irish sea glacier which glacitectonically disturbed and eroded pre existing sediments and redeposited them as deformation till recession of this irish sea glacier resulted in the damming of ice marginal lakes in embayments along the south coast into which glacilacustrine sedimentation then took place these lake sediments were subsequently glacitectonised and reworked by overriding glacier ice of inland origin which deposited deformation till on top of the succession there is no evidence for deposition of the irish sea diamicts by glacimarine sedimentation at these sites the widespread development of subglacial deforming bed conditions reflected the abundance of fine grained marine and lacustrine sediments available for subglacial erosion and reworking stratigraphical and chronological data suggest that the advance of a grounded irish sea glacier along the south coast occurred during the last glaciation and this is regionally consistent with marine geological data from the celtic sea these observations demonstrate extension of glacier ice far beyond its traditional limits in the celtic sea and on land in southern ireland during the last glaciation and remove the stratigraphical basis for chronological differentiation of surficial glacial drifts and thus the munsterian glaciation in southern ireland copyright 2001 john wiley sons ltd

foraminiferal stratigraphy and environment of late weichselian deposits on the continental shelf off troms northern norway abstract based on the analysis of 8 selected gravity cores from the upper sediment layers of andfjorden and malangsdjupet off northern norway six late weichselian foraminiferal assemblage zones are defined the two oldest assemblage zones 8 and 7 are found in basal tills and contain mixed faunas reworked and deposited by glaciers which reached the shelf edge during the early late weichselian during the earliest phase of the deglaciation of the continental shelf a sparse fauna characterized by buccella frigida zone 6 was deposited zone 5 is dominated by cassidulina laevigata and a fairly high content of planktic foraminifera indicating periods of ice free normal marine surface waters during a glacial advance between 14 000 and 13 000 b p the fauna zone 4 was dominated by elphidium excavatum this fauna reflects near glacial conditions characterized by unstable bottom water conditions the last c 500 years of this period suffered from oxygen depleted bottom waters zone 3 formed between 13 000 and 10 000 b p comprises several species e g cassidulina reniforme nonion barleeanum n labradoricum and cibicides lobatulus during the first 2000 years of this period the fauna reflects a climatic amelioration e g an increase in temperature salinity and current activity probably due to intrusion of atlantic water during the younger dryas zone 3 reflects a climatic deterioration

inversion of surface deformation data for rapid estimates of source parameters and uncertainties a bayesian approach new satellite missions e g the european space agency s sentinel 1 constellation advances in data downlinking and rapid product generation now provide us with the ability to access space geodetic data within hours of their acquisition to truly take advantage of this opportunity we need to be able to interpret geodetic data in a prompt and robust manner here we present a bayesian approach for the inversion of multiple geodetic data sets that allows a rapid characterization of posterior probability density functions pdfs of source model parameters the inversion algorithm efficiently samples posterior pdfs through a markov chain monte carlo method incorporating the metropolis hastings algorithm with automatic step size selection we apply our approach to synthetic geodetic data simulating deformation of magmatic origin and demonstrate its ability to retrieve known source parameters we also apply the inversion algorithm to interferometric synthetic aperture radar data measuring co seismic displacements for a thrust faulting earthquake 2015 mw 6 4 pishan earthquake china and retrieve optimal source parameters and associated uncertainties given its robustness and rapidity in estimating deformation source parameters and uncertainties our bayesian framework is capable of taking advantage of real time geodetic measurements thus our approach can be applied to geodetic data to study magmatic tectonic and other geophysical processes especially in rapid response operational settings e g volcano observatories our algorithm is fully implemented in a matlab based software package geodetic bayesian inversion software that we make freely available to the scientific community

subglacial bedform geomorphology of the irish ice sheet reveals major configuration changes during growth and decay the belated realisation that ribbed rogen moraines form such an integral part of irish geomorphology and the piecemeal approach to previous drumlin mapping is probably responsible for the highly contrasting views of palaeoflow patterns of the irish ice sheet using a high resolution 25 m digital elevation model we present morphological maps of a large part 100 100 km of the so called drumlin belt of north central ireland the landforms comprise mostly ribbed moraine much larger than found elsewhere up to 16 km in length which in places are superimposed on each other contrary to most prior assessments we find the bedform record to contain numerous and overlapping episodes of bed formation ribbed moraine drumlins and crag and tails that provide a palimpsest record of changing flow geometries these demonstrate an ice sheet with a centre of mass and flow geometry that changed during growth and decay using distinctive flow patterns and relative age relationships between them we reconstruct ice sheet evolution into four phases during a single glacial cycle in phase 1 early in the glacial cycle scottish and local ice coalesced to form a northeast centred irish ice sheet as it grew its centre of mass migrated southwards culminating in a major n s divide positioned down the east of ireland phase 2 ca last glacial maximum during retreat the centre of mass migrated at least 120 km northwards and became established in northwest ireland and at this point a dramatic bedforming event produced one of the world s largest and most contiguous ribbed moraine fields phase 3 final deglaciation is thought to be by fragmentation into many topographically controlled minor ice caps phase 4 rather than any dramatic or unexpected behaviour the reconstructed phases indicate a relatively predictable pattern of ice sheet growth and decay with changes in centres of mass and does not require major readvances or ice stream events copyright 2001 john wiley sons ltd

the aftershock sequence of the 2015 april 25 gorkha nepal earthquake l b adhikari 1 u p gautam 1 b p koirala 1 m bhattarai 1 t kandel 2 r m gupta 1 c timsina 1 n maharjan 1 k maharjan 2 t dahal 2 r hoste colomer 3 4 y cano 3 m dandine 3 a guilhem 3 s merrer 3 p roudil3 and l bollinger3 1national seismological centre department of mines and geology lainchaur kathmandu nepal e mail adhikari research gmail com 2regional seismological centre department of mines and geology surkhet birendranagar nepal 3cea dam dif f 91297 arpajon france 4laboratoire de geologie ecole normale superieure cnrs 24 rue lhomond f 75004 paris france

modelling the spatial distribution of present day deformation in nepal how cylindrical is the main himalayan thrust in nepal summary the structure of the himalayas in nepal is characterized by underthrusting of the indian lithosphere beneath the chain along the main himalayan thrust mht the mht is affected by major earthquakes of m 8 that have ruptured segments several hundred kilometres in length the study of historical seismicity underlines the existence of a significant seismic gap between the 1905 kangra and the 1934 bihar nepal earthquake areas in western nepal this contribution presents a numerical model of the interseismic deformation using the adeli 2 d finite element code a parametric study has been performed to estimate the influence of the topography the geometry of the flat ramp flat transition of the mht and its rheology the results of these runs are compared along three cross sections of eastern central and western nepal using various recordings of the active deformation of nepal neotectonics microseismicity gps velocities vertical displacement rates deduced from comparative levellings the results of this study suggest 1 a small amount of aseismic slip along the southern part of the mht and 2 an abrupt change in geometry of the mht between central and western nepal the stress build up in eastern and central nepal is produced by coupling of a bend flat ramp transition of the mht and a brittle ductile transition at the foot of the ramp in western nepal on the other hand stress build up is only induced by a brittle ductile transition located along the low angle part of the mht this difference suggests the presence of a lateral ramp on the mht to allow transition between the central and western nepal geometries of the mht this change in mht geometries between central and western nepal is also clearly marked in the himalayan relief an abrupt decrease in altitude and incision between central and western nepal

on the mechanics of earthquake afterslip we propose a model for earthquake afterslip based on rate and state variable friction laws in the model afterslip is attributed to the interaction of a velocity weakening region at depth within which earthquakes nucleate with an upper region of velocity strengthening frictional behavior the existence of this upper region is supported by independent seismologic observations and the results of laboratory friction experiments in our model afterslip is the result of relaxation of a stress perturbation within the velocity strengthening region which arises when an earthquake propagates into that region from below we derive the stress perturbation and its decay from the friction constitutive law using a simple 1 degree of freedom approximation for the elastic interaction between the fault and its surroundings this approximation is based on thickness averaged displacements and slip velocities within the velocity strengthening region which is assumed to slip as a rigid block coseismic and postseismic slip are coupled through the thickness averaged stiffness k of the velocity strengthening region we assume k to be inversely proportional to the thickness of this region which means that thicker velocity strengthening regions have a greater tendency to arrest coseismic slip we model the afterslip time histories of the 1966 parkfield and 1987 superstition hills earthquakes and relate the model parameters to physical parameters which may govern the rheologic behavior of the faults in accord with field observations our model predicts 1 that afterslip on some faults scales with the thickness of the unconsolidated sedimentary cover and 2 that proportionally more afterslip occurs for earthquakes in which coseismic surface slip is small compared with coseismic slip at depth velocity strengthening frictional behavior is to be expected for faults within poorly consolidated sediments and for those that contain significant gouge zones about 500 m within their shallow regions 3 5 km combining our results with those of recent laboratory friction studies indicates that relatively young faults with little accumulated fault gouge should exhibit little afterslip

line of sight displacement from alos 2 interferometry mw 7 8 gorkha earthquake and mw 7 3 aftershock interferometric synthetic aperture radar insar is a key tool for the analysis of displacement and stress changes caused by large crustal earthquakes particularly in remote areas a challenge for traditional insar has been its limited spatial and temporal coverage especially for very large events whose dimensions exceed the typical swath width of 70 100 km this problem is addressed by the alos 2 satellite whose palsar 2 instrument operates in scansar mode enabling a repeat time of 2 weeks and a swath width of 350 km here we present insar line of sight displacement data from alos 2 palsar 2 observations covering the mw 7 8 gorkha nepal earthquake and its mw 7 3 aftershock that were acquired within 1 week of each event the data are made freely available and we encourage their use in models of the fault slip and associated stress changes the mw 7 3 aftershock not only extended the rupture area of the main shock toward the east but also left a 20 km gap where the fault has little or no coseismic slip we estimate this unslipped fault patch has the potential to generate a mw 6 9 event

deep seismic reflection evidence for continental underthrusting beneath southern tibet the himalaya and adjacent tibetan plateau constituting earth s largest region of elevated topography and anomalously thick crust formed as a consequence of cenozoic collision between india and asia itself considered the archetypal continent continent collision1 3 here we report the first results from an attempt to image the structure of the crust beneath this region using deep seismic reflection profiling our 100 km long profile acquired in the tethyan himalaya shows a mid crustal reflection that prob ably marks the active thrust fault along which the indian plate is underthrusting southern tibet upper crustal reflections with geo metries suggestive of large scale structural imbrication of the upper crust and moho reflections from the base of the double normal thickness crust underlying the region these results lend substantial support to the view that crustal thickening beneath southernmost tibet was accomplished by wholesale underthrusting of indian continental crust beneath the structurally imbricated upper crust comprising the tethyan himalaya

himalayan megathrust geometry and relation to topography revealed by the gorkha earthquake the himalayan mountain range has been the locus of some of the largest continental earthquakes including the 2015 magnitude 7 8 gorkha earthquake competing hypotheses suggest that himalayan topography is sustained and plate convergence is accommodated either predominantly on the main plate boundary fault or more broadly across multiple smaller thrust faults here we use geodetic measurements of surface displacement to show that the gorkha earthquake ruptured the main himalayan thrust fault the earthquake generated about 1 m of uplift in the kathmandu basin yet caused the high himalaya farther north to subside by about 0 6 m we use the geodetic data combined with geologic geomorphological and geophysical analyses to constrain the geometry of the main himalayan thrust in the kathmandu area structural analyses together with interseismic and coseismic displacements are best explained by a steep shallow thrust fault flattening at depth between 5 and 15 km and connecting to a mid crustal steeper thrust we suggest that present day convergence across the himalaya is mostly accommodated by this fault no significant motion on smaller thrust faults is required furthermore given that the gorkha earthquake caused the high himalayan mountains to subside and that our fault geometry explains measured interseismic displacements we propose that growth of himalayan topography may largely occur during the ongoing post seismic phase

amino acid geochronology of raised beaches in south west britain abstract based on 1 the epimerization of l isoleucine to d alloisoleucine d l ratios in patella vulgata littorina littorea l littoralis l saxatilis littorina species and nucella lapillus from raised beaches in south west britain 2 statistical analysis of the d l ratios and 3 lithostratigraphic and geomorphic evaluation three d l stages are proposed the d l ratios for all the species measured are converted to a patella vulgata standard the three d l stages are 1 1 the minchin hole d l stage d l ratios 0 175 0 014 defined at a stratotype in minchin hole cave gower wales 2 2 a provisionally defined but as yet unamed d l stage because of the current unavailability of a suitable stratotype with d l ratios of 0 135 0 014 3 3 the pennard d l stage d l ratios 0 105 0 016 defined at a stratotype in minchin hole cave gower wales two geochronological models of the three high sea level events representing the d l stages are constrained by uranium series age determinations on stalagmite interbedded with marine beds in minchin hole and bacon hole caves gower wales a potential fixed point in model evaluation is an age determination which is equivalent to oxygen isotope sub stage 5e 122 ka the two models are oxygen isotope stage and age ka bp d l stage d l ratio model 1a model 1b model 2 pennard 0 105 0 016 5a ca 80 5e 122 5e 122 5c ca 100 unnamed 0 135 0 014 5e 122 7 194 minchin hole 0 175 0 014 7 186 245 7 186 245 7 216 the ages of the raised beaches are used to constrain the timing and extent of glaciation in the area the extent of the late devensian glaciation is fixed by reference to localities where raised beaches of the pennard d l stage outcrop as well as by using unpublished data on molluscs incorporated into glacial deposits two pre devensian glaciations antedate the minchin hole d l stage the irish sea glaciation of the bristol channel irish sea older drift of south wales fremington till of north devon is ascribed to oxygen isotope 10 or earlier while the paviland welsh glaciation is ascribed to oxygen isotope stage 8 or earlier an earlier glaciation berwyn glaciation is inferred from erratics of known welsh provenance in essex

structural interpretation of the great earthquakes of the last millennium in the central himalaya abstract a major question about the himalaya remains open does a great earthquake like the mw 8 1 1934 earthquake release all the strain stored by the tibet india convergence during the preceding interseismic period and only that strain or can it also release a background store of energy that remained unreleased through one or more earlier earthquakes and so potentially engender giant events or a relatively random sequence of events to consider this question the history of the great earthquakes of the last millennium is investigated here by combining data provided by the historical archives of kathmandu trenches through surface ruptures isoseismal damage mapping seismites and the instrumental record in the kathmandu basin the location of the epicenter of the 1934 earthquake was determined from the arrival of high energy p waves that caused sedimentary dikes and ground fractures perpendicular to the epicenter azimuth the epicenter of the mw 7 6 1833 earthquake can therefore be determined analogously from dike orientation and its location to the ne of kathmandu indicates an overlap with the mw 8 1 1934 rupture the 1934 earthquake released strain not released by the 1833 earthquake comparison of the historical records of earthquakes in kathmandu with 14c ages from paleo seismic trenches along the himalayan front suggests that 1 the 1344 kathmandu event ruptured the surface as far away as kumaon and was therefore a giant mw 8 6 earthquake and 2 the 1255 event that destroyed kathmandu is attested by surface ruptures in central and western nepal and by seismites in soft sediment as far away as kumaon geometric and rheologic controls for the different types of ruptures during the medium mw 7 great mw 8 and giant mw 8 4 earthquakes are illustrated in structural cross sections it is found that the epicenters of great himalayan earthquakes are located on the basal thrust farther north or close to the locked zone which is defined from geodetic measurements of regional deformation during the interseismic period this suggests that great earthquakes initiate in a wide transition zone between exclusively brittle and exclusively creeping regimes the extent of which depends on the dip of the main himalayan thrust the succession of the great earthquakes during the last millennium has released all the 20 m millennial himalayan convergence even in the central seismic gap which has been locked since 1505 the millennial seismic release rate is close to the convergence rate nonetheless no evidence of a succession of characteristic earthquakes has been found the 1100 1833 and 1934 earthquakes in the eastern himalaya are characterized neither by constant displacement nor by constant recurrence furthermore some great earthquakes do not release all the strain elastically stored by the himalayan and tibetan upper crust after the 1255 event there was still the potential for a slip of several meters for the mw 8 1 1505 event this suggests a rather random release of seismic energy great earthquakes could occur anytime and in any part of the central himalaya furthermore a future giant earthquake of mw 8 6 cannot be excluded

the last ice sheet in north west scotland reconstruction and implications recent models of the last scottish ice sheet suggest that nunataks remained above the ice surface in areas peripheral to the main centres of accumulation this proposition has been investigated on 140 mountains over an area of 10 000 km2 in nw scotland outside the limits of the later loch lomond readvance in this area there is evidence for a single high level weathering limit that separates glacially eroded terrain from higher areas of in situ frost debris this limit occurs at altitudes ranging from 425 to 450 m in the outer hebrides to 950 m on the mainland and is best developed on lithologies that resisted breakdown after ice sheet downwastage interpretation of this weathering limit as a periglacial trimline cut by the last ice sheet at its maximum thickness is supported by 1 joint depth and schmidt hammer measurements that indicate significantly more advanced rock breakdown above the weathering limit 2 a much greater representation of gibbsite a pre late devensian weathering product in the clay fraction of soils above the limit 3 cosmogenic isotope dating of the exposure ages of rock outcrops above and below the limit 4 the sharpness of the limit at some sites and its regular decline along former ice flowlines and 5 shear stress calculations based on the inferred altitude and gradient of the former ice surface reconstruction of the ice surface based on trimline evidence indicates that the mainland ice shed lay near or slightly east of the present watershed and descended northwards from 900 m to ca 550 m at the north coast independent dispersion centres fed broad ice streams that occupied major troughs on skye an ice dome 800 m deflected the northwestwards movement of mainland ice but the mountains of rum were over ridden by mainland ice up to an altitude of ca 700 m the outer hebrides supported an independent ice cap that was confluent with mainland ice in the minches extrapolation of the trimline evidence indicates that most reconstructions of ice extent are too conservative and suggests that low gradient ice streams extended across the hebridean shelf offshore wider implications of this research are 1 that blockfields and other periglacial weathering covers are not all of the same age or significance depending on the resistance of different lithologies to frost weathering 2 that the contrasting degree of glacial modification in the western and eastern highlands of scotland may reflect a former cover of predominantly warm based ice in the former and predominantly cold based ice in the latter and 3 that the approach and techniques developed in this study have potential application for constraining ice sheet models not only in areas peripheral to the main centres of ice accumulation in britain and ireland but also in other mountain areas where nunataks protruded through warm based late pleistocene ice masses

a late pleistocene intertidal boulder pavement from an isostatically emergent coast dundalk bay eastern ireland late pleistocene sequences around dundalk bay eastern ireland record glaciomarine sedimentation near the margin of a grounded ice lobe around 15 ka sp a coastal exposure at cooley point consists of four major facies deposited outside this ice limit 1 a basal mud facies deposited from sediment plumes accumulated following the initial ice marginal retreat inland it contains a well preserved arctic microfauna dominated by the foram elphidium clavatum and the ostracod roundstonia globulifera 2 a flat to undulating boulder facies pavement mostly one clast thick is found pressed into the mud and is characterized by bevelled and striated upper clast surfaces pavement attributes are a result of intertidal activity in a cold climate the boulder source is due to rafting by ice flees from glacigenic debris deposited during an ice advance 3 laminated sand facies drape the pavement and are a result of variable current activity 4 the overlying gravel facies is separated from the sand facies by a marine erosion surface the gravel facies is subaqueous channelized and is overlain by late glacial raised beach ridges locally the gravels have been deformed by ice pressure from partially floating ice flees facies changes record terrestrial submergence and provide evidence for changes in relative sea level during part of the last deglacial cycle the boulder pavement and deformed gravel facies suggest that ice flees and sea ice effects may be more common within stratigraphies along emergent coasts than previously thought though they have a low preservation potential extreme conditions during the deglacial favoured opportunistic microfaunas during mud deposition this event may be related to a major meltwater event within the irish sea basin

coseismic and early postseismic deformation due to the 25 april 2015 mw 7 8 gorkha nepal earthquake from insar and gps measurements analysis of interferometric synthetic aperture radar insar and global positioning system gps data reveals coseismic and early postseismic 4 88 days surface displacements associated with the 25 april 2015 mw 7 8 gorkha nepal earthquake the pattern of early postseismic surface uplift and subsidence is found to be opposite to that of the coseismic motion insar and gps data were jointly inverted for coseismic and postseismic slip on the main himalayan thrust mht we consider a complex ramp flat ramp flat subsurface structure of the mht with four connected fault planes dipping toward north from the main frontal thrust mft the inverted coseismic slip distribution follows an elliptical pattern extending east southeastward from the hypocenter with maximum amplitude of 5 7 m above the upper edge of the midcrustal ramp we infer early postseismic afterslip 4 16 days of 0 2 0 47 m toward downdip of the coseismic slip asperity and another patch with 0 1 0 2 m slip toward east the shallow portion of the mht toward south is found to have remained unruptured during the earthquake nor did it slip aseismically after the earthquake suggesting possibility of large events in the future

electrical structure of the himalaya of central nepal high conductivity around the mid crustal ramp along the mht twelve broadband magnetotelluric mt soundings were performed across the himalaya of central nepal in 1996 in order to determine the electrical structure of the crust and its relation to geological structures and active tectonics the mt impedance tensors were obtained for frequencies between 0 001 and 500 hz the 2 d section derived from joint inversion of te and tm mode after rri and groom bailey decomposition shows high conductivity in the foreland basin 30 m that contrasts with the resistive indian basement 300 m and lesser himalaya 1000 m in addition our mt sounding reveals a major conductive feature beneath the front of the higher himalaya also characterized by intense microseismic activity and the position of a mid crustal ramp along the major active thrust fault mht this high conductivity zone probably reflects metamorphic fluids released during underthrusting of the indian basement and pervading well connected microcracks induced by interseismic stress build up or distributed brittle deformation around the ramp

biofacies and sediments in an emergent late pleistocene glaciomarine sequence skerries east central ireland abstract late devensian sedimentation ca 18 ka b p on the coastal margins of the irish sea basin occurred in shallow water glaciomarine environments around retreating tidewater ice margins high relative sea levels were the result of glacioisostatic crustal depression around the periphery of the last british ice sheet at skerries in east central ireland ice proximal glaciomarine diamict mud sand and gravel facies are selectively preserved in a bedrock depression the coastal exposure about 500 m long can be divided into three lithofacies associations 1 a diamict gravel association resting on bedrock was emplaced by sediment gravity flows and records the downslope reworking of glacial debris released from a retreating ice margin 2 an overlying mud association was deposited from suspended sediment plumes with minor ice rafting and records ice retreat and increasing distality of the site muds contain a mixed foraminiferal microfaunal assemblage typical of open water shallow marine shelves species can be grouped into reworked temperate cosmopolitan and well preserved boreo arctic elements and indicate mixing of derived and retransported temperate species with an in situ glaciomarine fauna 3 at the top of the section a gravel association derived from a nearshore fan delta rests on planated muds and is attributed to wave reworking and slumping of the fan delta front in shallow water during rapid basin rebound this and other sequences elsewhere in the irish sea basin is a record of rapid evacuation of the basin by calving tidewater glaciers and the uplift and erosion of glaciomarine sedimentary sequences in response to rapid late glacial crustal rebound

himalayan strain reservoir inferred from limited afterslip following the gorkha earthquake great himalayan earthquakes are rare analysis of surface motions in the months after the 2015 gorkha earthquake reveals negligible aseismic slip implying that stress may be stored in the crust to be tapped during future great earthquakes

glaciation and sea level change for ireland and the irish sea since late devensian midlandian time the sea level change around the coast of ireland and the irish sea for the past 20 000 years is primarily the combined result of the glacio isostatic adjustment of the crust to the removal of ice over the british isles and the total eustatic change from the global ice sheets however the isostatic effects due to the removal of ice from northern europe and north america and the addition of meltwater into the oceans also make a significant contribution predictions of sea level change based on glacio hydro isostatic models are compared with observations to constrain the ice volume over ireland at the time of the last glacial maximum and the maximum ice height appears to have been of the order of 600 m the models predict well the spatial variability in sea level change observed across the region for holocene and lateglacial time with levels above present being predicted only for northeastern ireland and north of about morecambe bay the models do not support suggestions that lateglacial levels along the east coast of ireland or the coast of wales were 50 150 m above their present levels consistent models that would produce such large lateglacial highstands are incompatible with all other sea level and glacial evidence for the british isles palaeobathymetry and palaeoshoreline reconstructions for the irish sea indicates that a tenuous landbridge between britain and ireland developed only across the celtic sea between about 18000 and 14000 years bp

the interpretation and classification of subglacially deformed materials abstract a general classification of subglacially deformed materials is proposed based on sediment properties and their relationship to styles of subglacial strain deformation till is defined as homogenized usually diamictic material formed by glacially induced shear of subsole materials three types are recognized type a formed by pervasive ductile deformation type b formed by brittle shear and comminution till produced by the reduction of void space by in situ crushing and abrasion the term glacitectonite is adopted for materials that have undergone subglacial shear but retain some of the structural characteristics of the parent material original structures may be truncated by glacitectonic fabric elements type a or distorted but not truncated type b the principles of strain and material response particle orientation mechanisms fabric development and drainage conditions are reviewed examples of deformation tills and glacitectonites from breidamerkurjokull iceland slettmarkbreen norway loch lomond scotland and east yorkshire england are used to illustrate the nature of subglacially deformed materials and their relationship to former subglacial strain and drainage conditions the geologic evidence suggests a continuum of bed strengths can be recognized in deforming substrata ranging from high strength low strain type b deformation till and comminution till to low strength high strain type a deformation till

fault slip distribution of the 1999 mw 7 1 hector mine california earthquake estimated from satellite radar and gps measurements we use a combination of satellite radar and gps data to estimate the slip distribution of the 1999 m w 7 1 hector mine earthquake a right lateral strikeslip earthquake that occurred on a northwest southeast striking fault in the southern california mojave desert the data include synthetic aperture radar interferograms insar from both ascending and descending orbits radar amplitude image offset fields sario for both ascending and descending azimuth directions and campaign gps observations from 55 stations provided by agnew et al 2002 we model the fault with nine segments derived from the field mapped fault rupture the sario data and aftershock locations we first estimate the dip of each fault segment as well as a single constant strike slip component across each segment resulting in an average dip of 83 to the northeast and slip of up to 5 6 m then we fix the optimal fault segment dip discretize the fault segments into 1 5 km 1 5 km patches and solve for the variable slip distribution using a nonnegative least squares method that includes an appropriate degree of smoothing our preferred solution has both right lateral strike slip and reverse faulting the estimated geodetic moment is 5 93 10 19 n m m w 7 1 similar to seismological estimates indicating that there are insignificant interseismic and postseismic deformation signals in the data we find strike slip displacements of up to 6 0 m and reverse faulting of up to 1 6 m with the maximum slip located just northwest of the epicenter most of the slip is concentrated northwest and south of the epicenter little slip is found on the northeastern branch of the fault the sario data and our modeling indicate that the amount and extent of surface fault rupture were underestimated in the field

glacial deposits at wylfa head anglesey north wales evidence for late devensian deposition in a non marine environment the nature and origin of glacial sediments at wylfa head are described and their significance with regard to sedimentary environments during late devensian deglaciation of the irish sea basin is discussed recent models of deglaciation under glaciomarine conditions are challenged the quaternary sequence at wylfa consists of eroded and glaciotectonically deformed bedrock locally derived lodgement till calcareous silt rich lodgement till containing northern erratics discontinuous units of orange brown silty sand of possible aeolian origin and grey laminated freshwater silts filling a small kettle hole the till units thicken to the south where the surface is drumlinised it is concluded that the landforms and deposits result from a warm based irish sea glacier which moved towards the southwest spatial variation in basal water pressure resulted from localised drainage through zones of more heavily jointed bedrock rapid glacial erosion occurred in areas where subglacial water pressure was relatively high while deposition of the resulting basal sediment took place where water pressures were reduced the glacier also carried basal calcareous silty till onshore which was deposited by lodgement processes none of the deposits at wylfa are interpreted as glaciomarine in origin and there is no evidence at this site for an isostatically induced marine transgression prior to deglaciation

evidence for heinrich event 1 in the british isles in the north irish sea basin isb sedimentary successions constrained by ams 14c dates obtained from marine microfaunas record three major palaeoenvironmental shifts during the last deglacial cycle i marine muds cooley point interstadial dated to between 16 7 and 14 7 14c kyr bp record a major deglaciation of the isb following the late glacial maximum lgm ii terminal outwash and ice contact landforms killard point stadial were deposited during an extensive ice readvance which occurred after 14 7 14c kyr bp and reached a maximum extent at ca 14 14c kyr bp at this time the lowlands surrounding the north isb were drumlinised coeval flowlines reconstructed from these bedforms end at prominent moraines killard point bride st bees and indicate contemporaneity of drumlinisation from separate ice dispersal centres substrate erosion by fast ice flow and subglacial sediment transfer to ice sheet margins in north central ireland bed reorganisation associated with this fast ice flow phase involved overprinting and drumlinisation of earlier transverse ridges rogen type moraines by headward erosion along ice streams that exited through tidewater ice margins this is the first direct terrestrial evidence that the british ice sheet bis participated in heinrich event 1 h1 iii regional mud drapes directly overlying drumlins record high relative sea level rsl with stagnation zone retreat after 13 7 14c kyr bp rough island interstadial elsewhere in lowland areas of northern britain ice marginal sediments and morainic belts record millennial scale oscillations of the bis which post date the lgm advance on to the continental shelf and pre date the loch lomond stadial younger dryas advance in the highlands of western scotland ca 11 10 14c kyr bp in western northwestern and northern ireland killard point stadial h1 ice limits are reconstructed from ice flow lines that are coeval with those in the north isb and end at prominent moraines on the scottish continental shelf possible h1 age ice limits are reconstructed from dated marine muds and associated ice marginal moraines it is argued that the last major offshore ice expansion from the scottish mountains post dated ca 15 14c kyr bp and is therefore part of the h1 event in eastern england the stratigraphic significance of the dimlington silts is re evaluated because evidence shows that there was only one major ice oscillation post dating ca 18 14c kyr bp in these lowlands in a wider context the sequence of deglacial events in the isb widespread deglaciation of southern part of the bis major readvance during h1 ice sheet collapse is similar to records of ice sheet variability from the southern margins of the laurentide ice sheet lis well dated ice marginal records however show that during the killard point readvance the bis was at its maximum position when retreat of the lis was well underway this phasing relationship supports the idea that the bis readvance was a response to north atlantic cooling induced by collapse of the lis 1998 john wiley sons ltd

on the relationship between mw and ml for small earthquakes abstract estimating the moment magnitudes m w of a small earthquake is a challenging task one viable option to measure its size is to calculate its local magnitude m l and convert it to the physically based m w unfortunately to correctly perform such a conversion is not easy moreover even though many studies demonstrate that the equivalence between m l and m w is incorrect for small events these two parameters are sometimes thought to be strictly equivalent regardless of the earthquake s size using random vibration theory we show that below m w 4 the m l of a small earthquake is proportional to the logarithm of its seismic moment and the following relationship holds we test our findings on a high quality data set in the upper tiber valley northern apennines italy composed of events in the range of 0 m l 3 8 for which we compute accurate estimates of m l and m w online material details of the processing procedure figures of the empirical regional attenuation functional and source terms of 1191 events from the alto tiberina fault atf data set and earthquake catalog

slip model of the 2015 mw 7 8 gorkha nepal earthquake from inversions of alos 2 and gps data we use surface deformation measurements including interferometric synthetic aperture radar data acquired by the alos 2 mission of the japanese aerospace exploration agency and global positioning system gps data to invert for the fault geometry and coseismic slip distribution of the 2015 mw 7 8 gorkha earthquake in nepal assuming that the ruptured fault connects to the surface trace of the main frontal thrust mft fault between 84 34 e and 86 19 e the best fitting model suggests a dip angle of 7 the moment calculated from the slip model is 6 08 1020 nm corresponding to the moment magnitude of 7 79 the rupture of the 2015 gorkha earthquake was dominated by thrust motion that was primarily concentrated in a 150 km long zone 50 to 100 km northward from the surface trace of the main frontal thrust mft with maximum slip of 5 8 m at a depth of 8 km data thus indicate that the 2015 gorkha earthquake ruptured a deep part of the seismogenic zone in contrast to the 1934 bihar nepal earthquake which had ruptured a shallow part of the adjacent fault segment to the east

glacimarine processes and inductive lithofacies modelling of ice shelf and tidewater glacier sediments based on quaternary examples abstract three variables control the type of glacial debris source and where and when debris is introduced to an ocean 1 type of glacial ice source ice sheet or valley glacier 2 condition of a grounded glacier melting freezing or frozen base and cold or warm internal ice and 3 type of glacier front ice shelf or tidewater using these variables in different combinations eight glacimarine regimes are postulated to exist by integrating information from holocene sediment and pleistocene glacimarine sequences with the eight inductive regimes lithofacies relationships are predicted and modelled the models show a complexity of glacimarine lithofacies the importance of recognizing this complexity lies in realistic interpretations of ancient sequences ice shelf sediment may be limited in the geologic record because of tectonic and climatic constraints required for ice shelf formation alternatively in some tidewater glacier regimes larger volumes of glacimarine sediment are produced than in ice shelf regimes ice proximal sediment is distinctive especially near subglacial meltwater stream effluxes ice shelves and tidewater glaciers may produce similar ice proximal lithofacies e g morainal bank associations and laminites in certain regimes however details of lithofacies may aid in distinguishing ice shelf from tidewater regimes ice shelf and tidewater iceberg zone sediment can be distinguished from each other if basal and high level englacial debris can be distinguished ice shelf zone sediment out from the grounding line has a basal debris source high level englacial debris is deposited in more distal ice shelf zones resulting in sediment by pass in corresponding positions of a tidewater glacier regime iceberg rafted debris comprises mixed basal and high level englacial debris deeper water zones receive large volumes of sediment when a melting freezing base grounding line is at the edge of a continental shelf when the grounding line retreats sediment supply may be drastically reduced because of a back sloping continental shelf and trapping by morainal banks cool water bioclastic carbonates may accumulate once a grounding line has retreated although ice shelf iceberg zones are more extensive than those in tidewater regimes ice shelf icebergs have low debris content and resulting ice rafted debris may be scarce the smallest volume of sediment is produced by a frozen base ice sheet ending as a tidewater front and the largest volume by a melting freezing base valley tidewater glacier glacimarine sediment has a relatively high preservation potential near continental interiors or margins however at continental margins mass flow olistostrome and tectonic melange deposits may be preserved with glacimarine diamictites these deposits may be difficult to distinguish from each other especially if metamorphosed such as at a convergent margin the models presented do not fully represent the glacimarine environment because many other variables are omitted however the principal concepts of generating glacimarine lithofacies associations are considered continued research will verify if each regime exists and will provide data on those regimes that exist today to compare and modify these models

a critical review of the glaciomarine model for irish sea deglaciation evidence from southern britain the celtic shelf and adjacent continental slope in support of their glaciomarine model for the deglaciation of the irish sea basin eyles and mccabe cited the occurrence of distal glaciomarine mud drapes onshore in the isles of scilly and north devon and of arctic beach face gravels and sands around the shores of the celtic sea glacial and sea level data from the southern part of the irish sea in the terminal zone of the ice stream and the adjacent continental slope are reviewed here to test this aspect of the model the suggestion that the glacial sequences of both the isles of scilly and fremington in north devon are glaciomarine mud drapes is rejected an actively calving tidewater margin only occurred early in the deglacial sequence close to the terminal zone in the south central celtic sea relative sea levels were lower and therefore glacio isostatic depression less than envisaged in the glaciomarine model geochronological sedimentological and biostratigraphical data indicate that the raised beach sequences around the shores of the celtic sea and english channel were deposited at or during regression soon after interglacial eustatic highstands evidence for ice rafting at a time of high relative sea levels is restricted to a phase s earlier than the late devensian these data indicate that the raised beach sequences have no bearing on the style of irish sea deglaciation copyright 2001 john wiley sons ltd

the glacigenic deposits of western lleyn north wales terrestrial or marine this paper describes a complex sequence of glacigenic sediments occupying a faultbounded depression at aberdaron bay western lleyn the sequence offers an insight into sedimentary environments during deglaciation of the irish sea basin a lower stratified diamict association lda containing contorted units of fine sand silt and displaying strong consistent clast fabrics is overlain by an upper diamict association uda with weaker fabrics and extensive sand and gravel layers and channel fills certain characteristics of the sequence can be explained by a glacimarine depositional model but there are several problems in particular the geometry of the sediments is difficult to explain without recourse to the melting of buried ice an alternative model that overcomes these problems involves the decay of a terrestrial glacier containing reworked marine sediments supraglacial sediment flows released during decay of thinner ice covering the surrounding hills uda would have rapidly buried a thick stagnant ice mass in the aberdaron depression facilitating slow melting and release of basal meltout till lda a model is presented that accounts for the stagnation and in situ decay of a debris rich irish sea glacier and which could explain many of the deposits and landforms surrounding the irish sea basin without recourse to high relative sea levels

density driven deformation structures in glacigenic consolidated diamicts examples from traeth y mwnt cardiganshire wales u k abstract density driven deformation may occur when a sediment of higher bulk wet density is deposited on top of one of a lower bulk wet density and occurs commonly in glacigenic sediments by recognizing density driven deformation of gravels and sands embedded in diamicts it is possible to reconstruct relative preconsolidation states of the diamicts density driven structures indicate that during deformation the diamict behaved as a viscous fluid thus providing important evidence for the viscosity and physical state of diamicts after deposition which has implications for the depositional environment the density driven process and its implications for reconstructing depositional environments is discussed criteria are given for the recognition of density driven deformation stages of gravels and sands deposited on top of a viscous mud

drumlin formation in southern anglesey and arvon northwest wales this is a study of late devensian drumlins formed in southern anglesey and arvon northwest wales this area was affected by ice sheet coalescence when the welsh ice sheet met with the lrish sea ice sheet and drumlins were formed once the two had coalesced it is suggested that the drumlins were the result of net subglacial soft bed erosion and that they represent more resistant cores within the subglacial deforming layer the drumlins have either gravel or till cores and where the core was deformable large scale compressive glaciotectonic structures were seen e g dinas dinlle with local subglacial compression of 59 where the cores were more resistant e g lleiniog these were not deformed but remained as more competent masses within the deforming layer it is suggested that the less competent material flowed around the cores some remaining as a thin carapace but most of the material being removed down glacier leaving the drumlins as erosional remnants in northwest wales there is a multi till sequence that traditionally has been interpreted as having been deposited as the result of separate ice sheet advances and retreats however in this study it is suggested that the different tills were deposited as the result of ice sheet coalescence and that sites such as dinas dinlle do not show evidence of a major readvance in the retreat of the devensian ice but are indicative of continuously changing conditions within the subglacial deforming bed

afterslip and aftershocks in the rate and state friction law istituto nazionale di geofisica e vulcanologia italy ingv centre national de la recherche scientifique cnrs exxonmobil upstream research company

dominant controls of downdip afterslip and viscous relaxation on the postseismic displacements following the mw7 9 gorkha nepal earthquake author s zhao b burgmann r wang d tan k du r zhang r abstract 2017 american geophysical union all rights reserved we analyze three dimensional gps coordinate time series from continuously operating stations in nepal and south tibet and calculate the initial 1 year postseismic displacements we first investigate models of poroelastic rebound afterslip and viscoelastic relaxation individually and then attempt to resolve the trade offs between their contributions by evaluating the misfit between observed and simulated displacements we compare kinematic inversions for distributed afterslip with stress driven afterslip models the modeling results show that no single mechanism satisfactorily explains near and far field postseismic deformation following the gorkha earthquake when considering contributions from all three mechanisms we favor a combination of viscoelastic relaxation and afterslip alone as poroelastic rebound always worsens the misfit the combined model does not improve the data misfit significantly but the inverted afterslip distribution is more physically plausible the inverted afterslip favors slip within the brittle ductile transition zone downdip of the coseismic rupture and fills the small gap between the mainshock and largest aftershock slip zone releasing only 7 of the coseismic moment our preferred model also illuminates the laterally heterogeneous rheological structure between india and the south tibet the transient and steady state viscosities of the upper mantle beneath tibet are constrained to be greater than 1018 pa s and 1019 pa s whereas the indian upper mantle has a high viscosity 1020 pa s the viscosity in the lower crust of southern tibet shows a clear trade off with its southward extent and thickness suggesting an upper bound value of 8 1019 pa s for its steady state viscosity

deglaciation of the irish sea basin a critique of the glaciomarine hypothesis the glaciomarine model for deglaciation of the irish sea basin suggests that the weight of ice at the last glacial maximum was sufficient to raise relative sea levels far above their present height destabilising the ice margin and causing rapid deglaciation glacigenic deposits throughout the basin have been interpreted as glaciomarine the six main lines of evidence on which the hypothesis rests sedimentology deformation structures delta deposits marine fauna amino acid ratios and radiocarbon dates are reviewed critically the sedimentological interpretation of many sections has been challenged and it is argued that subglacial sediments are common rather than rare and that there is widespread evidence of glaciotectonism density driven deformation associated with waterlain sediments is rare and occurs where water was ponded locally sand and gravel deposits interpreted as gilbert type deltas are similarly the result of local ponding or occur where glaciers from different source areas uncoupled they do not record past sea levels and the ad hoc theory of piano key tectonics is not required to explain the irregular pattern of altitudes the cold water foraminifers interpreted as in situ are regarded as reworked from irish sea sediments that accumulated during much of the late quaternary when the basin was cold and shallow with reduced salinities amino acid age estimates used in support of the glaciomarine model are regarded as unreliable radiocarbon dates from distinctive foraminiferal assemblages in northeast ireland show that glaciomarine sediments do occur above present sea level but they are restricted to low altitudes in the north of the basin and record a rise rather than a fall in sea level it is suggested here that the oldest dates around 17 000 yr bp record the first late devensian weichselian marine inundation above present sea level this accords with the pattern but not the detail of recent models of sea level change copyright 2001 john wiley sons ltd

high resolution reconstruction of the last ice sheet in nw scotland reconstructions of the last late devensian british ice sheet have hitherto been based on assumptions regarding its extent and form here we employ observational evidence for the maximum altitude of glacial erosion trimlines on mountains that protruded through the ice palaeonunataks to reconstruct the form of the ice sheet over 10 000 km2 of nw scotland contrasts in the clay mineralogy of soils and exposure ages of rock surfaces above and below these trimlines confirm that they represent the upper limit of late devensian glacial erosion the reconstruction yields realistic values of basal shear stress and is consistent with independent evidence of ice movement directions the ice sheet reached 950 m altitude over the present n s watershed descended northwards and north westwards was deflected around an ice dome on skye and an independent outer hebrides ice cap and probably extended across the adjacent shelf on a bed of deforming sediments

underplating in the himalaya tibet collision zone revealed by the hi climb experiment we studied the formation of the himalayan mountain range and the tibetan plateau by investigating their lithospheric structure using an 800 kilometer long densely spaced seismic array we have constructed an image of the crust and upper mantle beneath the himalayas and the southern tibetan plateau the image reveals in a continuous fashion the main himalayan thrust fault as it extends from a shallow depth under nepal to the mid crust under southern tibet indian crust can be traced to 31 n the crust mantle interface beneath tibet is anisotropic indicating shearing during its formation the dipping mantle fabric suggests that the indian mantle is subducting in a diffuse fashion along several evolving subparallel structures

estimating the return times of great himalayan earthquakes in eastern nepal evidence from the patu and bardibas strands of the main frontal thrust the return times of large himalayan earthquakes are poorly constrained despite historical devastation of cities along the mountain range definitive links between events and specific segments of the main frontal thrust mft are not established and paleoseismological records have not documented the occurrence of several similar events at the same location in east central nepal however recently discovered primary surface ruptures of that megathrust in the a d 1255 and 1934 earthquakes are associated with flights of tectonically uplifted terraces we present here a refined longer slip history of the mft s two overlapping strands patu and bardibas thrusts in that region based on updated geomorphic neotectonic mapping of active faulting two 1 3 km long shallow seismic profiles and logging of two river cut cliffs three paleoseismological trenches and several pits with constraints from 74 detrital charcoals and 14 cosmogenic nuclide ages the amount of hanging wall uplift on the patu thrust since 3650 450 years requires three more events than the two aforementioned the uplift rate 8 5 1 5mm yr thrust dip 25 5 n and apparent characteristic behavior imply 12 17 5m of slip per event on the bardibas thrust discrete pulses of colluvial deposition resulting from the coseismic growth of a flexural fold scarp suggest the occurrence of six or seven paleo earthquakes in the last 4500 50 years the coeval rupture of both strands during great himalayan earthquakes implies that in eastern nepal the late holocene return times of such earthquakes probably ranged between 750 140 and 870 350 years

gps measurements of present day convergence across the nepal himalaya the high elevations of the himalaya and tibet result from the continuing collision between india and asia which started more than 60 million years ago1 4 from geological and seismic studies of the slip rate of faults in asia5 it is believed that approximately one third of the present day convergence rate between india and asia 58 4mmyr 1 is responsible for the shortening uplift and moderate seismicity of the himalaya great earthquakes also occur infrequently in this region releasing in minutes the elastic strain accumulated near the boundary zone over several centuries and accounting for most of the advance of the himalaya over the plains of india the recurrence time for these great earthquakes is determined by the rate of slip of india beneath tibet which has hitherto been estimated indirectly from global plate motions6 from the slip rates of faults in asia7 8 from seismic productivity9 and from the advance of sediments on the northern ganges plain10 here we report geodetic measurements using the global positioning system gps of the rate of contraction across the himalaya which we find to be 17 52 2 mm yr 1 from the form of the deformation field we estimate the rate of slip of india beneath tibet to be 20 5 2 mmyr 1 strain sufficient to drive one or more great himalayan earthquakes with slip similar to that accompanying the magnitude 8 1 bihar nepal 1934 earthquake may currently be available in western nepal

mechanics of fault junctions a sharp bend in a fault must be part of a triple junction and slip on the three fault segments at the junction must have a vector sum of zero in order to avoid an unphysical 1 r stress singularity accompanying the slip a volume change occurs at the junction either a void opens or intense local deformation is required to avoid material overlap the energy absorbed due to the volume change is proportional to the slip increment times the total past slip accumulated at the junction at a new junction the energy absorbed is a small fraction of the energy released by slip on the fault system but after a number of earthquakes proportional to shear modulus over confining stress the junction becomes a strong barrier to further slip although slip occurs more easily on old rupture surfaces than on fresh fractures the growing barrier strength of junctions requires that there be some fresh fracture in earthquakes perhaps a small fraction of the surface that slips in any earthquake is fresh fracture which could provide the instability needed to explain earthquakes a numerical model in two dimensional static plane strain shows even without accounting for energy absorbed at the junction that a bend in a fault acts as a barrier if slip is impeded on the associated fault spur the stress concentration at the bend will tend to induce slip on the spur slip occurring on the spur unstably with a drop in the coefficient of friction can induce increased slip on the main fault segments with no change in the coefficient of friction a fault junction provides a natural realization of barrier and asperity models without appealing to arbitrary variations of fault strength the location of the fresh fracture that occurs after a junction becomes a strong barrier remains an unanswered question it is likely to be initiated near the stress concentration at the old junction a model simulating the effect of fresh fracture near old junctions might explain earthquakes without appealing to an unstable friction law anywhere

lower edge of locked main himalayan thrust unzipped by the 2015 gorkha earthquake faults are unlocked by earthquakes analysis of seismic data from the 2015 nepal earthquake shows that only part of the main himalayan thrust fault was unzipped by the quake leaving much of the fault locked and ready to slip in a future event

geodetic imaging of potential seismogenic asperities on the xianshuihe anninghe zemuhe fault system southwest china with a new 3 d viscoelastic interseismic coupling model we use gps and interferometric synthetic aperture radar insar measurements to image the spatial variation of interseismic coupling on the xianshuihe anninghe zemuhe xaz fault system a new 3 d viscoelastic interseismic deformation model is developed to infer the rotation and strain rates of blocks postseismic viscoelastic relaxation and interseismic slip deficit on the fault surface discretized with triangular dislocation patches the inversions of synthetic data show that the optimal weight ratio and smoothing factor are both 1 the successive joint inversions of geodetic data with different viscosities reveal six potential fully coupled asperities on the xaz fault system among them the potential asperity between shimian and mianning which does not exist in the case of 1019 pa s is confirmed by the published microearthquake depth profile besides there is another potential partially coupled asperity between daofu and kangding with a length scale up to 140 km all these asperity sizes are larger than the minimum resolvable wavelength the minimum and maximum slip deficit rates near the moxi town are 7 0 and 12 7 mm yr respectively different viscosities have little influence on the roughness of the slip deficit rate distribution and the fitting residuals which probably suggests that our observations cannot provide a good constraint on the viscosity of the middle lower crust the calculation of seismic moment accumulation on each segment indicates that the songlinkou selaha s4 shimian mianning s7 and mianning xichang s8 segments are very close to the rupture of characteristic earthquakes however the confidence level is confined by sparse near fault observations

radar interferogram filtering for geophysical applications the use of sar interferometry is often impeded by decorrelation from thermal noise temporal change and baseline geometry power spectra of interferograms are typically the sum of a narrow band component combined with broad band noise we describe a new adaptive filtering algorithm that dramatically lowers phase noise improving both measurement accuracy and phase unwrapping while demonstrating graceful degradation in regions of pure noise the performance of the filter is demonstrated with sar data from the ers satellites over the jakobshavns glacier of greenland

calcium carbonate dissolution in the upper 1000 m of the eastern north atlantic recent analyses suggest that considerable caco3 dissolution may occur in the upper water column of the ocean 1500 m this study uses the distribution of particulate calcium from high resolution suspended matter sampling along the climate variability and predictability co2 repeat hydrography a16n transect in 2003 to estimate caco3 dissolution in the top 1000 m of the north atlantic dissolution rates were also approximated using changes in total alkalinity measurements along isopycnal surfaces water masses were found to be undersaturated with respect to aragonite at intermediate depths 400 1000 m in the eastern tropical north atlantic the caco3 dissolution rate in this region is estimated to be 0 9 mmol caco3 m 2 d 1 indicating this region is a hotspot for upper water column caco3 dissolution compared to the atlantic basin as a whole dissolution rates calculated from particulate calcium distributions outside of this region were significantly lower 0 2 mmol caco3 m 2 d 1 and are comparable to previous estimates of caco3 dissolution flux for the atlantic ocean the magnitude of upper water column dissolution rates compared to measured surface ocean caco3 standing stocks suggests that biologically mediated caco3 dissolution may be occurring in the top 1000 m of the atlantic

sedimentology of an ice contact glaciomarine delta carey valley northern ireland an extensive late pleistocene delta body related to a water plane at 100 m above sea level is exposed in the upper carey valley northern ireland exposures along the modern river show a lowermost facies association of massive diamict and poorly sorted gravel deposited as sediment gravity flows overlain by a gravelly foreset and topset facies association recording the progradation of a large glacier fed delta diamict facies were emplaced as subaqueous debris flows associated gravels are chaotically bedded and were deposited by the downslope slumping of poorly sorted boulder gravel their subtle grading characteristics can be linked with a variety of mass flow processes sediment gravity flow facies originated upvalley from rapidly deposited sediments which accumulated near the exit of a narrow subglacial channel below an ice margin fronting in water subsequent ice retreat allowed the growth of a gilbert type delta regional evidence shows that the delta top records high relative sea levels in response to isostatic downwarping around the periphery of the last british ice sheet the sedimentology and structure of the carey valley infill may be typical of high level glaciomarine deltas preserved in topographic lows around the coastline of north britain

sedimentation in an ice contact subaqueous setting the mid pleistocene north sea drifts of norfolk u k in east anglia the mid pleistocene north sea drifts extend over some 1500 km2 of the coastal zone of north norfolk they are the oldest pleistocene glacial sequences exposed in britain deposited during the anglian glaciation ca 450 ka bp laminated and stratified pebbly mud diamict facies of the north sea drifts are widely regarded as the product of subglacial deposition below a terrestrial ice margin in this paper these facies are identified as the product of subaqueous deposition in front of the margin of an ice sheet terminating in a large water body laminated stratified and massive diamict facies were deposited by the rain out of fine grained sediment from suspension and coarse debris from floating ice combined with downslope sediment gravity flow intraformational folds are the product of episodic downslope slumping and identify a regional paleoslope to the east away from a major ice marginal moraine ridge the cromer ridge exposures at cromer show bulldozed ice contact subaqueous sediments and ice thrust chalk rafts a fall in water level emplaced shelly shoreface sands and beach gravels which are loaded into the underlying diamicts as large pan shaped sag basins with diapiric structures at their margins comparable sedimentary sequences are exposed elsewhere around the southern north sea basin a glaciomarine setting in response to glacio isostatic depression around the anglian ice sheet is suggested

pre and post seismic deformation related to the 2015 mw7 8 gorkha earthquake nepal we analyze time series from continuously recording gps stations in nepal spanning the pre and post seismic period associated to the m w7 8 gorkha earthquake which ruptured the main himalayan thrust mht fault on april 25th 2015 the records show strong seasonal variations due to surface hydrology after corrections for these variations the time series covering the pre and post seismic periods do not show any detectable transient pre seismic displacement by contrast a transient post seismic signal is clear the observed signal shows southward displacements consistent with afterslip on the mht using additional data from stations deployed after the mainshock we invert the time series for the spatio temporal evolution of slip on the mht this modelling indicates afterslip dominantly downdip of the mainshock rupture two other regions show significant afterslip a more minor zone updip of the rupture and a region between the mainshock and the largest aftershock ruptures afterslip in the first 7 months after the mainshock released a moment of 12 8 0 5 10 19 nm which represents 17 8 0 8 of the co seismic moment the moment released by aftershocks over that period of time is estimated to 2 98 10 19 nm geodetically observed post seismic deformation after co seismic offset correction was thus 76 7 1 0 aseismic the logarithmic time evolution of afterslip is consistent with rate strengthening frictional sliding according to this theory and assuming a long term loading velocity modulated on the basis of the coupling map of the region and the long term slip rate of 20 2 1 1 mm yr afterslip should release about 34 0 1 4 of the co seismic moment after full relaxation of post seismic deformation afterslip contributed to loading the shallower portion of the mht which did not rupture in 2015 and stayed locked afterwards the risk for further large earthquakes in nepal remains high both updip of the rupture area of the gorkha earthquake and west of kathmandu where the mht has remained locked and where no earthquake larger than m w7 5 has occurred since 1505

structural segmentation controlled the 2015 mw 7 8 gorkha earthquake rupture in nepal the ongoing collision of india with asia is partly accommodated by slip on the main himalayan thrust mht the 25 april 2015 m w 7 8 gorkha earthquake is the most recent major event to rupture the mht which dips gently northward beneath central nepal although the geology of the range has been studied for decades fundamental aspects of its deep structure remain disputed here we develop a structural cross section and a three dimensional geologically informed model of the mht that are consistent with seismic observations from the gorkha earthquake a comparison of our model to a detailed slip inversion data set shows that the slip patch closely matches an ovalshaped gently dipping fault surface bounded on all sides by steeper ramps the gorkha earthquake rupture seems to have been limited by the geometry of that fault segment this is a significant step forward in understanding the deep geometry of the mht and its effect on earthquake nucleation and propagation published models of fault locking do not correlate with the slip patch or our fault model in the vicinity of the earthquake further suggesting that fault geometry was the primary control on this event our result emphasizes the importance of adequately constraining subsurface fault geometry in megathrusts in order to better assess the sizes and locations of future earthquakes

geological evidence for neotectonic activity during deglaciation of the southern sperrin mountains northern ireland in the southern sperrin mountains northern ireland stacked glacigenic sequences that accumulated during deglaciation ca 17000 13000 yr bp overlie a basement of jointed and mascerated bedrock the glacigenic sequences comprise interbedded glaciotectonic shears diamictic breccias and rock rafts at one site a normal fault with a metre scale vertical displacement cuts through part of the sequence and is overlain by a glacial diamict sediments at an adjacent site show that faulting and associated hydrothermal activity was related to neotectonic reactivation of pre existing caledonian lineaments caused by ice unloading from stratigraphical and directional evidence fault reactivation occurred early in the deglaciation after north central ireland ice had retreated southwards into lowland areas but before sperrin mountain ice readvanced from the north this relationship provides evidence for the relative timing of neotectonic activity in northern ireland and demonstrates the effects of glacio isostatic unloading near ice sheet centres copyright 1999 john wiley sons ltd

the late devensian glaciation of the eastern lleyn peninsula north wales evidence for terrestrial depositional environments the glacial deposits of the eastern lleyn peninsula record the advance coalescence and subsequent retreat and uncoupling of welsh and irish sea ice sheets during the late devensian cold stage during advance a thick sheet of basal diamict was deposited over much of the area and during retreat and uncoupling which occurred after 14 5 ka the eastern part of the area was dominated by the formation of a large sandur system draining from the retreating margin of the irish sea ice sheet subsequent stages of retreat are marked by a series of arcuate cross valley moraines formed either by ice contact deposition during stillstand or by structural deformation during minor snout oscillation in the western part of the area sedimentation was controlled by a series of dead ice ridges running parallel to the retreating ice margin and this led to the development of a complex assemblage of localised depositional environments including ice front alluvial fans marginal sandur troughs and pro glacial lake basins all formed under supraglacial ice marginal conditions no evidence of glaciomarine deposition is recorded 1998 john wiley sons ltd

rupture process of the mw 7 9 2015 gorkha earthquake nepal insights into himalayan megathrust segmentation we investigate the rupture process of the 25 april 2015 gorkha earthquake mw 7 9 using a kinematic joint inversion of teleseismic waves strong motion data high rate gps static gps and synthetic aperture radar sar data the rupture is found to be simple in terms of coseismic slip and even more in terms of rupture velocity as both inversion results and a complementing back projection analysis show that the main slip patch broke unilaterally at a steady velocity of 3 1 3 3 km s this feature likely contributes to the moderate peak ground acceleration 0 2 g observed in kathmandu the 15 km deep rupture occurs along the base of the coupled portion of the main himalayan thrust and does not break the area ranging from kathmandu to the front the limitation in length and width of the rupture cannot be identified in the preearthquake interseismic coupling distribution and is therefore discussed in light of the structural architecture of the megathrust

magnitude calibration of north indian earthquakes this article is concerned primarily with the evaluation of the size and location of northern indian and southern tibetan earthquakes during the last 200 yr it draws attention to the problems of assessing intensity of early and more recent earthquakes in a built environment which is different from that for which the intensity scale has been constructed and to the way in which isoseismals are drawn through a re evaluation of intensities and a reassessment of isoseismals a formula for the estimation of surface wave magnitude using isoseismal radii is derived this formula is used to estimate the surface wave magnitudes of 16 earthquakes that occurred in the region between 1803 and 1900 this study shows that it is possible to calculate accurate surface wave magnitudes for earthquakes that occurred before the advent of the scale and that there is no need to resort to empirical formulae for the assessment of the size and seismic moment release of pre 20th century earthquakes also derived are formulae for the conversion of ms to m0 in total locations surface wave magnitudes and m0 estimates are presented for 43 important events that occurred in the region between 1803 and 1974 eight of which were in the lower crust or were subcrustal we find that the m0 ms scaling for india yields smaller ms than the global relation and that the methodology used can help to evaluate more realistic slip rates as well as to address other issues related to earthquake hazard in northern india

interseismic coupling on the main himalayan thrust we determine the slip rate and pattern of interseismic coupling on the main himalayan thrust along the entire himalayan arc based on a compilation of geodetic interferometric synthetic aperture radar and microseismicity data we show that convergence is perpendicular to the arc and increases eastwards from 13 3 1 7 mm yr to 21 2 2 0 mm yr these rates are comparable to geological and geomorphic estimates indicating an essentially elastic geodetic surface strain the interseismic uplift rate predicted from the coupling model closely mimics the topography suggesting that a small percentage of the interseismic strain is permanent we find that the fault is fully locked along its complete length over about 100 km width we don t find any resolvable aseismic barrier that could affect the seismic segmentation of the arc and limit the along strike propagation of seismic ruptures the moment deficit builds up at a rate of 15 1 1 10 19 n m yr for the entire length of the himalaya