volcanism in the afar rift sustained by decompression melting with minimal plume influence continental breakup is caused by some combination of heating and stretching1 2 the afar rift system in africa is an example of active continental rifting where a mantle plume probably weakened the lithosphere through thermal erosion and magma infiltration however the location and degree of plume influence today are debated2 3 here we use seismic s to p receiver functions to image the mantle structure beneath afar we identify the transition between the lithosphere and underlying asthenosphere at about 75 km depth beneath the flanks of the continental rift however this boundary is absent beneath the rift itself and we instead observe a strong increase in seismic velocities with depth at about 75 km we use geodynamic modelling to show that the velocity increase at this depth is best explained by decompression melting of the mantle in the absence of a strong thermal plume so although the absence of mantle lithosphere beneath the rift implies a plume may have once been active we conclude that the influence of a thermal plume directly beneath afar today is minimal

the last british ice sheet a review of the evidence utilised in the compilation of the glacial map of britain this paper reviews the evidence presently available as at december 2003 for the compilation of the glacial map of britain see clark c d evans d j a khatwa a bradwell t jordan c j marsh s h mitchell w a bateman m d 2004 map and gis database of glacial landforms and features related to the last british ice sheet boreas 33 359 375 and http www shef ac uk geography staff clark chris britice html in an effort to stimulate further research on the last british ice sheet and promote a reconstruction of ice sheet behaviour based on glacial geology and geomorphology the wide range of evidence that has been scrutinized for inclusion on the glacial map is assessed with respect to the variability of its quality and quantity and the existing controversies in ice sheet reconstructions landforms interpreted as being of unequivocal ice marginal origin moraines ice contact glacifluvial landforms and lateral meltwater channels and till sheet margins are used in conjunction with available chronological control to locate former glacier and ice sheet margins throughout the last glacial cycle subglacial landforms drumlins flutings and eskers have been used to demarcate former flow patterns within the ice sheet the compilation of evidence in a regional map is crucial to any future reconstructions of palaeo ice sheet dynamics and will provide a clearer understanding of ice sheet configuration ice divide migration and ice thickness and coverage for the british ice sheet as it evolved through the last glacial cycle

seismic imaging of melt in a displaced hawaiian plume the precise location of the mantle plume upwelling beneath hawaii is debated seismic data reveal a thick layer of melt in the mantle beneath western hawaii implying that the upwelling plume may be deflected around an ancient resistive root beneath the island

seismic evidence for sharp lithosphere asthenosphere boundaries of oceanic plates the mobility of the lithosphere over a weaker asthenosphere constitutes the essential element of plate tectonics and thus the understanding of the processes at the lithosphere asthenosphere boundary lab is fundamental to understand how our planet works it is especially so for oceanic plates because their relatively simple creation and evolution should enable easy elucidation of the lab data from borehole broadband ocean bottom seismometers show that the lab beneath the pacific and philippine sea plates is sharp and age dependent the observed large shear wave velocity reduction at the lab requires a partially molten asthenosphere consisting of horizontal melt rich layers embedded in meltless mantle which accounts for the large viscosity contrast at the lab that facilitates horizontal plate motions

the late devensian periglaciation of upland scotland abstract a wide variety of late devensian periglacial landforms developed on scottish mountains both before ca 13 000 bp and during the loch lomond stadial of ca 11 000 10 000 bp nearly all such features are now inactive late devensian periglacial weathering produced three types of regolith mantle openwork block deposits sandy diamicts and silt rich frost susceptible diamicts each of which supports a characteristic assemblage of relict landforms on upper slopes these include large scale sorted circles and stripes earth hummocks and nonsorted relief stripes sorted and nonsorted solifluction features massive boulder sheets and lobes and nivation benches talus protalus ramparts rock glaciers and alluvial fans also developed at the base of mountain slopes the distribution of late devensian periglacial features on scottish mountains is locally controlled by topography the response of underlying rocks to periglacial weathering and the limits of former glaciers regional variations in the altitude of certain forms of loch lomond stadial age particularly protalus ramparts and rock glaciers indicate a decrease in former snowfall eastwards across the scottish highlands and northwards from the highland boundary fault several upland periglacial features are also diagnostic of former permafrost and complement palaeotemperature reconstructions based on ice wedge casts and the equilibrium firn line altitudes of stadial glaciers these suggest that under stadial conditions mean january temperatures at 600 m and 1000 m on mountains in the western grampians must have been no higher than 20 c and 23 c respectively and possibly several degrees lower

spreading rate dependence of three dimensional structure in oceanic spreading centres segmentation by transform faults and other types of along axis discontinuity1 is a well described but poorly explained characteristic of oceanic spreading centres here we use numerical experiments to explore the dynamics of mantle flow and melting beneath a mid ocean ridge buoyant upwelling driven by compositional density variations resulting from the extraction of the melt that forms the ocean crust exhibits a spreading rate dependent transition between two dimensional and three dimensional upwelling structures for low spreading rates and mantle viscosities an initial two dimensional structure transforms into a three dimensional one at high spreading rates an initially two dimensional structure remains two dimensional these results suggest that the origin of spreading centre segmentation may be different at fast and slow spreading rates

zemmouri earthquake rupture zone mw 6 8 algeria aftershocks sequence relocation and 3d velocity model 1 we analyze the aftershocks sequence of the zemmouri thrust faulting earthquake 21 may 2003 mw 6 8 located east of algiers in the tell atlas the seismic sequence located during 2 months following the mainshock is made of more than 1500 earthquakes and extends ne sw along a 60 km fault rupture zone crossing the coastline the earthquake relocation was performed using handpicked p and s phases located with the tomodd in a detailed 3d velocity structure of the epicentral area contrasts between velocity patches seem to correlate with contacts between granitic volcanic basement rocks and the sedimentary formation of the eastern mitidja basin the aftershock sequence exhibits at least three seismic clouds and a well defined se dipping main fault geometry that reflects the complex rupture the distribution of seismic events presents a clear contrast between a dense sw zone and a ne zone with scattered aftershocks we observe that the mainshock locates between the sw and ne seismic zones it also lies at the nns sse contact that separates a basement block to the east and sedimentary formations to the west the aftershock distribution also suggests fault bifurcation at the sw end of the fault rupture with a 20 km long n 100 trending seismic cluster with a vertical fault geometry parallel to the coastline juxtaposed another aftershock cloud may correspond to 75 se dipping fault the fault geometry and related sw branches may illustrate the interference between pre existing fault structures and the sw rupture propagation the rupture zone related kinematics and velocity contrasts obtained from the aftershocks distribution are in agreement with the coastal uplift and reflect the characteristics of an active zone controlled by convergent movements at a plate boundary

rupture parameters of the 2003 zemmouri mw 6 8 algeria earthquake from joint inversion of interferometric synthetic aperture radar coastal uplift and gps 1 we study the surface deformation associated with the 21 may 2003 mw 6 8 zemmouri algeria earthquake the strongest seismic event felt in the algiers region since 1716 the thrust earthquake mechanism and related surface deformation revealed an average 0 50 m coastal uplift along 55 km long coastline we obtain coseismic interferograms using envisat advanced synthetic aperture radar asar is2 and radarsat standard beam st4 data from both the ascending and descending orbits of envisat satellite whereas the radarsat data proved useful only in the descending mode while the two radarsat interferograms cover the earthquake area envisat data cover only the western half of the rupture zone although the interferometric synthetic aperture radar insar coherence in the epicenter area is poor deformation fringes are observed along the coast in different patches in the boumerdes area the maximum coseismic deformation is indicated by the high gradient of fringes visible in all interferograms in agreement with field measurements tape differential gps leveling and gps to constrain the earthquake rupture parameters we model the interferograms and uplift measurements using elastic dislocations on triangular fault patches in an elastic and homogeneous half space we invert the coseismic slip using first a planar surface and second a curved fault both constructed from triangular elements using poly3dinv program that uses a damped least square minimization the best fit of insar coastal uplift and gps data corresponds to a 65 km long fault rupture dipping 40 to 50 se located at 8 to 13 km offshore with a change in strike west of boumerdes from n60 65 to n95 105 the inferred rupture geometry at depth correlates well with the seismological results and may have critical implications for the seismic hazard assessment of the algiers region

changes in seismic anisotropy shed light on the nature of the gutenberg discontinuity the boundary between the lithosphere and asthenosphere is associated with a platewide high seismic velocity lid overlying lowered velocities consistent with thermal models seismic body waves also intermittently detect a sharp velocity reduction at similar depths the gutenberg g discontinuity which cannot be explained by temperature alone we compared an anisotropic tomography model with detections of the g to evaluate their context and relation to the lithosphere asthenosphere boundary lab we find that the g is primarily associated with vertical changes in azimuthal anisotropy and lies above a thermally controlled lab implying that the two are not equivalent interfaces the origin of the g is a result of frozen in lithospheric structures regional compositional variations of the mantle or dynamically perturbed lab

reply to comment by j deverchere et al on zemmouri earthquake rupture zone mw 6 8 algeria aftershocks sequence relocation and 3d velocity model

some geological implications of average quaternary glacial conditions analyses of quaternary landscape evolution tend to focus on events associated with culminations of glacial and interglacial ages but for most of quaternary time environments were intermediate in character average quaternary glacial conditions based on assessment of the marine isotope record approximated those near the stage 2 stage 1 transition and during substages 5b and 5d isotope stages 3 and 4 and substages 5a d lie within one standard deviation of the mean value under average glacial conditions ice sheets lying over northern north america and europe were much more contracted than their full glacial counterparts and the distribution of mountain glaciers reflected a snowline depression of some 500 m geomorphic processes operating under average quaternary conditions contributed importantly to landscape evolution examples of landscapes that may represent such average conditions include cirques and fluvial deposits of the pacific northwest the fjords and strandflat of western norway and atolls of the tropical oceans by examining the geologic record from the perspective of average conditions rather than those of climatic extremes added insight can be gained regarding the evolution of quaternary landscapes

imaging pacific lithosphere seismic discontinuities insights from ss precursor modeling oceanic lithosphere provides an ideal location to decipher the nature of the lithosphere asthenosphere system which is vital to our understanding of plate tectonics it is well established that oceanic lithosphere cools thickens and subsides as it ages according to the conductive cooling models yet this simple realization fails to explain various observations for example old oceanic lithosphere does not subside as predicted further precise imaging of the lower boundary of the oceanic lithosphere has proven challenging here we use ss precursors to image the discontinuity structure across the pacific ocean using 24 years of teleseismic data we image a sharp pervasive velocity discontinuity 3 15 drop over 36 my there is no age depth dependence and we image the discontinuity at an average depth of 60 1 5 km the amplitude and sharpness of the boundary suggests a compositional variation and or layered carbonatitic melt may be required to explain our observations rather than temperature alone the strength and pervasiveness of the boundary suggests that it is likely related to the lithosphere asthenosphere boundary an additional deeper discontinuity at 80 120 km depth is imaged intermittently that in most cases likely represents a continuing negative velocity gradient in depth

the lithosphere asthenosphere boundary in the tien shan karakoram region from s receiver functions evidence for continental subduction 1 significant s to p converted wave energy from the crust mantle and lithosphere asthenosphere boundaries the moho and the lab respectively has been observed in the tien shan and karakoram orogenic belts and used for the determination of the thickness of the crust and the mantle lithosphere the moho lies at depths of 45 65 km in the tien shan and adjacent regions and deepens to 70 km depth in pamir and karakoram the thickness of the lithosphere varies between 90 and 120 km underneath the tien shan and increases to a value of 160 km beneath the tarim basin to the south of the tarim basin the lower boundary of the asian lithosphere can be clearly followed to a depth of 270 km beneath central pamir and karakoram while the indian lithosphere is observed beneath the karakoram dipping from 130 km to 170 km towards the north the observations indicate a scenario of continental collision and subduction consistent with seismicity and the surface wave tomography results

an upper mantle seismic discontinuity beneath the galapagos archipelago and its implications for studies of the lithosphere asthenosphere boundary an upper mantle seismic discontinuity the gutenberg or g discontinuity at which shear wave velocity decreases with depth has been mapped from s to p conversions in radial receiver functions recorded across the galapagos archipelago the mean depth of the discontinuity is 91 8 km beneath the southeastern archipelago and 72 5 km beneath surrounding regions the discontinuity appears deeper beneath the portion of the nazca plate that we infer passed over the galapagos mantle plume than elsewhere in the region we equate the depth of the g discontinuity to the maximum depth extent of anhydrous melting which forms an overlying layer of dehydrated and depleted mantle we attribute areas of shallow discontinuity depth to the formation of the dehydrated layer near the galapagos spreading center and areas of greater discontinuity depth to its modification over a mantle plume with an excess temperature of 115 30 c the g discontinuity lies within a high seismic velocity anomaly that we conclude forms by partial dehydration and a gradual but steady increase in seismic velocity with decreasing depth after upwelling mantle first encounters the solidus for volatile bearing mantle material at the depth of the solidus for anhydrous mantle material removal of remaining water creates a sharp decrease in velocity with depth this discontinuity may also mark a site of melt accumulation results from seismic imaging the compositions of galapagos lavas and rare earth element concentrations across the archipelago require that mantle upwelling and partial melting occur over a broad region within the dehydrated and depleted layer we conclude that the g discontinuity beneath the archipelago does not mark the boundary between rigid lithosphere and convecting asthenosphere

the 21 may 2003 zemmouri algeria earthquake mw 6 8 relocation and aftershock sequence analysis 1 a strong earthquake mw 6 8 struck the coastal region east of algiers and the tell atlas of algeria on 21 may 2003 and was responsible of severe damage and about 2400 casualties the coastal mainshock was followed by a large number of aftershocks the largest reaching mw 5 8 on 27 may 2003 we study the mainshock first major aftershocks and about 900 events recorded by temporary seismic stations using master event approach and double difference dd methods although the seismic station array has a large gap coverage the dd algorithm provides with an accurate aftershocks location the mainshock hypocenter relocation is determined using three major aftershocks 5 0 mw 5 8 chosen as master events the new mainshock location shifted on the coastline 36 83n 3 65e at 8 10 km depth seismic events extend to about 16 km depth and form a n 55 60 e trending and 45 55 se dipping fault geometry up to now it is the unique among the recently studied seismic events of the tell atlas of algeria mainshock and aftershocks relocation the thrust focal mechanism harvard cmt n 57 44 se dip 71 rake and the seismic moment 2 86 1019 nm infer a 50 km long fault rupture that may appear at the sea bottom at 6 to 12 km offshore north of the coastline the zemmouri earthquake occurred along the complex thrust and fold system of the tell atlas and provides with new constraints on the earthquake hazard evaluation in northern algeria

a sharp lithosphere asthenosphere boundary imaged beneath eastern north america although a rigid lithosphere about 100 km of crust and uppermost mantle moving over a weaker asthenosphere a few hundred kilometres of more deformable rock is a widely accepted aspect of plate tectonics the properties of the boundary between them are poorly understood when compressional waves p waves from an earthquake encounter an interface at an angle some of the energy is converted to shear waves or s waves these converted waves can be used to construct an image of the interface based on converted waves recorded in eastern north america the lithosphere asthenosphere boundary has been resolved as a sharp gradient that cannot be explained by thermal gradients alone indicating that the boundary is controlled by melt or high water content in the asthenosphere plate tectonic theory hinges on the concept of a relatively rigid lithosphere moving over a weaker asthenosphere yet the nature of the lithosphere asthenosphere boundary remains poorly understood the gradient in seismic velocity that occurs at this boundary is central to constraining the physical and chemical properties that create differences in mechanical strength between the two layers for example if the lithosphere is simply a thermal boundary layer that is more rigid owing to colder temperatures mantle flow models1 2 indicate that the velocity gradient at its base would occur over tens of kilometres in contrast if the asthenosphere is weak owing to volatile enrichment3 4 5 6 or the presence of partial melt7 the lithosphere asthenosphere boundary could occur over a much smaller depth range here we use converted seismic phases in eastern north america to image a very sharp seismic velocity gradient at the base of the lithosphere a 3 11 per cent drop in shear wave velocity over a depth range of 11 km or less at 90 110 km depth such a strong sharp boundary cannot be reconciled with a purely thermal gradient but could be explained by an asthenosphere that contains a few per cent partial melt7 or that is enriched in volatiles relative to the lithosphere3 4 5 6

crustal structure along the edge transect beneath the kodiak shelf off alaska derived from obh seismic refraction data summary along the edge alaska transect over the kodiak shelf off alaska a deep crustal seismic refraction experiment was carried out in 1994 using an airgun source with a high shot density and closely spaced ocean bottom hydrophones obhs these data clearly define a gently dipping plate boundary that gradually increases from 2 5d at the trench to 5d 250 km landwards of the trench beneath the shelf a landward increase of the velocities in the subducting oceanic crust was found the sedimentary upper plate beneath the continental slope can be divided into a young neogene accretionary prism beneath the lower slope and a more layered structure below the middle and upper slope where a body with elevated velocities 4 2 5 1 km s 1 in the lower part is interpreted as well consolidated sediment of possibly late eocene age acting as the backstop across the inner shelf between kodiak island and kenai peninsula near surface high velocities 6 0 km s 1 document a strong uplift 10 km of the mesozoic and palaeocene accretionary complex and furthermore suggest its seaward extension beneath the outer shelf the most striking feature along the edge transect is the thick low velocity zone lvz that coincides with the arched reflectors in the lower crust beneath the kodiak island kenai peninsula axis on the edge seismic reflection data this lvz is interpreted as indicating underplated low velocity rocks which contribute the same volume of new material as the frontal accretion to the continent the growth of which is rapid totalling 4200 km2 across the kodiak shelf since eocene times a calculation of the material balance shows that an underplating of underthrust sediment alone may not account for the huge volume of the underplated low velocity rocks we speculate that the underplating of continental fragment or more likely seamounts or plateau may be involved in continental growth

the rapid drift of the indian tectonic plate the breakup of the supercontinent gondwanaland into africa antarctica australia and india about 140 million years ago and consequently the opening of the indian ocean is thought to have been caused by heating of the lithosphere from below by a large plume whose relicts are now the marion kerguelen and reunion plumes plate reconstructions based on palaeomagnetic data suggest that the indian plate attained a very high speed 18 20 cm yr 1 during the late cretaceous period subsequent to its breakup from gondwanaland and then slowed to approximately 5 cm yr 1 after the continental collision with asia approximately 50 myr ago the australian and african plates moved comparatively less distance and at much lower speeds of 2 4 cm yr 1 refs 3 5 antarctica remained almost stationary this mobility makes india unique among the fragments of gondwanaland here we propose that when the fragments of gondwanaland were separated by the plume the penetration of their lithospheric roots into the asthenosphere were important in determining their speed we estimated the thickness of the lithospheric plates of the different fragments of gondwanaland around the indian ocean by using the shear wave receiver function technique we found that the fragment of gondwanaland with clearly the thinnest lithosphere is india the lithospheric roots in south africa australia and antarctica are between 180 and 300 km deep whereas the indian lithosphere extends only about 100 km deep we infer that the plume that partitioned gondwanaland may have also melted the lower half of the indian lithosphere thus permitting faster motion due to ridge push or slab pull

an ice cap landsystem for palaeoglaciological reconstructions characterizing the younger dryas in western scotland abstract this paper reviews the contrasting behaviours of ice caps and icefields defines a generic landsystem model that can effectively discriminate between them and applies the model to landform sediment assemblages in an area of western scotland such a model is necessary since many palaeoenvironmental inferences from formerly glaciated terrains are based on the geometry extent and dynamics of reconstructed ice masses the validity of these glacier reconstructions is dependent on the accurate initial interpretation of relict landforms and sediments and their inter relationships a new landsystems model is presented here in which individual geological and geomorphological elements are checked against a set of eight theoretical diagnostic criteria that characterize the style of former glaciation when applied to a 1200 km 2 area of the western scottish highlands the landsystem tool predicts 1 an extensive younger dryas ice cap with a maximum surface elevation of 900 m above sea level implying colder or wetter conditions than previously thought and 2 the survival of an independent mountain icefield in part of the area during deglaciation glaciological theory proxy palaeoenvironmental data and established glacier climate topography relationships support these predictions thereby giving credibility to the landsystem methodology as a generic tool for palaeoglaciological reconstructions

waveform tomography reveals channeled flow at the base of the oceanic asthenosphere understanding the relationship between different scales of convection that drive plate motions and hotspot volcanism still eludes geophysicists using full waveform seismic tomography we imaged a pattern of horizontally elongated bands of low shear velocity most prominent between 200 and 350 kilometers depth which extends below the well developed low velocity zone these quasi periodic fingerlike structures of wavelength 2000 kilometers align parallel to the direction of absolute plate motion for thousands of kilometers below 400 kilometers depth velocity structure is organized into fewer undulating but vertically coherent low velocity plumelike features which appear rooted in the lower mantle this suggests the presence of a dynamic interplay between plate driven flow in the low velocity zone and active influx of low rigidity material from deep mantle sources deflected horizontally beneath the moving top boundary layer

scattered wave imaging of the lithosphere asthenosphere boundary several recent studies have imaged discontinuities interpreted as the lithosphere asthenosphere boundary using receiver function methods these are exciting results since this boundary is fundamental and yet relatively elusive its location is not well imaged nor are its properties well understood the receiver function method provides high depth resolution and the multitude of studies using this method have increased lateral resolution a better global understanding of the location and nature of the boundary is developing which ultimately will have implications for mantle dynamics and planetary evolution however these new results do not all form a clear and consistent picture and in some cases introduce new complexities and questions some apparent contradictions may represent unmodeled earth structure overall interpretation and synthesis requires careful consideration of the approaches and sensitivities of individual studies

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

determination of intrinsic attenuation in the oceanic lithosphere asthenosphere system we recorded p and s waves traveling through the oceanic lithosphere asthenosphere system las using broadband ocean bottom seismometers in the northwest pacific and we quantitatively separated the intrinsic anelastic and extrinsic scattering attenuation effects on seismic wave propagation to directly infer the thermomechanical properties of the oceanic las the strong intrinsic attenuation in the asthenosphere obtained at higher frequency 3 hertz is comparable to that constrained at lower frequency 100 seconds by surface waves and suggests frequency independent anelasticity whereas the intrinsic attenuation in the lithosphere is frequency dependent this difference in frequency dependence indicates that the strong and broad peak dissipation recently observed in the laboratory exists only in the asthenosphere and provides new insight into what distinguishes the asthenosphere from the lithosphere

double difference tomography the method and its application to the hayward fault california we have developed a double difference dd seismic tomography method that makes use of both absolute and relative arrival times by reducing systematic errors using the more accurate relative arrival times the method produces an improved velocity model simultaneously it yields event locations of a quality equivalent to those of the dd location method while avoiding simplifying assumptions of that method we test this method on a synthetic dataset and find that it produces a more accurate velocity model and event locations than standard tomography we also test this method on a hayward fault california earthquake dataset spanning 1984 1998 the earthquakes relocated by this method collapse to a thin line along the fault trace consistent with previous results the dd velocity model has sharper velocity contrasts near the source region than the standard tomography model

subsidence of normal oceanic lithosphere apparent thermal expansivity and seafloor flattening abstract seafloor topography has been a key observational constraint on the thermal evolution of oceanic lithosphere which is the top boundary layer of convection in earth s mantle at least for the first 70 myr the age progression of seafloor depth is known to follow the prediction of half space cooling and the subsidence rate is commonly believed to be 350 m ma 1 2 here we show that based on a new statistical analysis of global bathymetry the average subsidence rate of normal oceanic lithosphere is likely to be 320 m ma 1 2 i e 10 lower than the conventional value we define the normal seafloor as regions uncorrelated with anomalous crust such as hotspots and oceanic plateaus but the lower subsidence rate appears to be a stable estimate not depending on how exactly we define the normal seafloor this low subsidence rate can still be explained by half space cooling with realistic mantle properties if the effective thermal expansivity of a viscoelastic mantle is taken into account in light of a revised model of half space cooling the normal seafloor unperturbed by the emplacement of anomalous crust exists for all ages and the so called seafloor flattening seems to be mostly caused by hotspots and oceanic plateaus

seismic structure of the upper mantle in a central pacific corridor the seismic structure of the tonga hawaii corridor has been investigated by combining two data sets revenaugh and jordan s reflectivity profile from scs reverberations which provides travel times to and impedance contrasts across the major mantle discontinuities and 1500 new observations of frequency dependent phase delays for the three component s ss and sss body waves and the r1 and g1 surface waves which constrain the velocity structure within this layered framework the shear waves turning in the upper mantle showed significant splitting of the sh and sv components indicative of shallow polarization anisotropy the data set was inverted in conjunction with attenuation and mineralogical constraints to obtain a complete spherically symmetric radially anisotropic structure the final model pa5 is characterized by a high velocity anisotropic lid bounded at 68 km depth by a large negative g discontinuity a low velocity anisotropic layer below g extending to a small l discontinuity at 166 km an isotropic steep gradient region between 166 km and 415 km and transition zone discontinuities at 415 507 and 651 km the depth of the radial anisotropy in pa5 is shallower than in most previous studies based on surface waves and higher modes the average value of radial shear anisotropy in the lid 3 7 is consistent with the magnitude expected from the spreading controlled models of olivine orientation while anisotropy in the low velocity zone which is required by our data set could be induced either by paleostrains that took place near the ridge crest or by shearing in the asthenosphere as a result of present day plate motions on the basis of recent work by hirth and kohlstedt we suggest that the g discontinuity is caused by a rapid increase in the water content of mantle minerals with depth marking the fossilized lower boundary of the melt separation zone active during crust formation the high gradient zone between 200 and 400 km is a characteristic feature of convecting oceanic upper mantle and is probably controlled by a steady decrease in the homologous temperature over this depth interval the average shear velocity gradient in the transition zone is lower than in most previous seismic models in better agreement with the predictions for a pyrolitic composition

a detailed subduction structure in the kuril trench deduced from ocean bottom seismographic refraction studies abstract in 1983 we conducted an ocean bottom seismograph obs experiment in the southernmost part of the kuril trench beneath which the pacific plate is subducting under hokkaido island japan the aim of this experiment was to determine crust and upper mantle structure from the oceanic basin to the continental slope by dense seismic refraction profiling using explosives and airguns the total length of the profiles was 560 km along which ten obs s were deployed the observed data were of good quality which enabled us to obtain a detailed velocity structure of the active margin down to 20 30 km we constructed a velocity structure model by ray tracing and amplitude modeling in the oceanic basin the crust has a typical oceanic structure characterized by three layers with p wave velocities of 1 8 3 8 6 5 and 6 5 7 0 km s the velocity gradient in layer 3 increases downward from 0 075 to 0 10 s 1 the moho discontinuity was well constrained by clearly observed p n and p m p phases the total thickness of the oceanic crust was determined to be 8 km and almost constant in the oceanic basin the p wave velocity is 7 9 km s beneath the moho discontinuity which increases downward with a rather small velocity gradient 0 015 0 03 s 1 beneath the continental slope we found relatively low velocity 2 5 to 5 5 5 8 km s material the oceanic moho discontinuity associated with the subducting plate was traced down to a depth of 25 km our seismic data strongly suggest that oceanic layer 2 is smoothly subducting and does not break up to form a wedge structure this result is in remarkable contrast with the velocity structure in the active margin of the ryukyu trench area about 1000 km south of the present experimental area where we found a 12 km thick prominent low velocity wedge is situated 50 150 km landward from the trench axis on the seaward side of the wedge the surface of the igneous basement undulates severely the wedge was probably formed by materials of oceanic origin such a difference in velocity structure suggests that the subduction mechanism in the trench area differs from region to region in the northwestern pacific

lithosphere and asthenosphere of the tien shan imaged by s receiver functions 1 the s receiver function technique was applied to the recordings from 36 broad band stations in the tien shan the results reveal a pronounced difference in the properties of the lithosphere asthenosphere of the tien shan and those of the neighboring platforms beneath the tien shan an upper mantle lid with an s velocity of about 4 5 km s is underlain at a depth of about 90 km by a low velocity zone where the s velocity drops to 4 1 4 2 km s trends of p and s travel time residuals are consistent with the presence of melt or other liquids in this zone there is no evidence of any similar layer beneath the platforms the crust is 55 65 km thick beneath most of the tien shan and 45 km below the platforms although it thins to about 45 km near the naryn basin in the central tien shan

drumlins in ice sheet reconstructions with reference to the western pennines northern england abstract drumlin morphology and distribution can be used to determine the palaeoglaciological conditions under which subglacial bedforms were created by late pleistocene ice sheets detailed field mapping of part of the large drumlin fields in northern england in particular the identification of areas of superimposed drumlins has been shown to be of significance in the delimitation of the ice divide within the area the overall distribution of the subglacial bedforms has also been used to define the extent of ice streams within this part of the late devensian dimlington stadial ice sheet based on the physical principles which underlie the deformational model of drumlin formation and present day glaciological information on subglacial ice sheet conditions variations in drumlin morphology have allowed a first attempt at reconstructing areas of high 100 kpa and low

lower slab boundary in the japan subduction zone abstract we have successfully detected the lower boundary of a subducting slab the successive imaging of the lower slab boundary beneath northeastern ne japan is attained by receiver function rf depth conversion analysis using a recent 3d tomographic velocity model we use waveforms from 249 teleseismic events collected by hi net and j array short period stations in ne japan rfs are calculated through frequency domain division of radial components by vertical ones with a water level of 0 001 and a 1 0 hz low pass gaussian filter assuming that all later phases in the radial rfs are due to ps phases converted at discontinuities beneath stations we calculate depth converted rfs mapped onto the cross section with the ccp common conversion point stacking in a cross section the slab surface and the oceanic moho can be imaged down to 120 km depth for the greater depths the rf amplitudes corresponding to them cannot be seen because in the oceanic crust basalt would be completely metamorphosed to eclogite below this depth the lower boundary of the pacific slab can also be traced down to 200 km depth or more it is parallel to the slab surface and the oceanic moho and the thickness between the slab surface and the lower boundary is 80 km finally we estimate a top to bottom slab velocity model that explains the rfs observed at broadband stations with the synthetic rfs this model exhibits a 13 velocity reduction downwards the lower slab boundary which would relatively sharp for the base of the thermal boundary layer therefore this sharp discontinuity is presumably considered to be the subducting g gutenberg discontinuity that is formed by the change of the amount of h 2 o water meaning that the g discontinuity is the chemical boundary at the bottom of the oceanic lithosphere the g discontinuity depth is controlled by the potential temperature of the asthenospheric mantle beneath the mid ocean ridge and hence the observed thickness of 80 km i e the g discontinuity depth corresponds to 1375 c in potential temperature when this boundary is formed

imaging the colliding indian and asian lithospheric plates beneath tibet 1 a high resolution image of the base of the lithosphere from s to p converted seismic waves revealed the collision architecture of the indian and asian continental plates beneath the tibetan plateau the base of the indian lithosphere dips northward from a depth of 160 km beneath the himalayas to a depth of 220 km just south of the bangong suture the base of the asian lithosphere is nearly horizontal at the depth of 160 180 km from central to northern tibet there is a vertical gap of about 50 km between indian and asian lithospheres our observation of a well defined thick lithosphere throughout the entire plateau is not consistent with models of wholesale convective instability of a thickened mantle lithosphere which would predict a very thin asian lithosphere the hypothesized sequential southward subduction of tibetan and asian continental lithospheres leading to the growth of the tibetan plateau if correct cannot be occurring below 180 km depth our results along with available geological and geophysical data strongly support that the plateau is predominantly formed by a relatively coherent north dipping subducted indian continental lithosphere in the south which presently can be traced to the middle of the plateau and a south dipping subducted asian lithosphere in the north at a shallower depth

a seismic reflection image for the base of a tectonic plate a high resolution image for the base of an oceanic plate that is subducting beneath north island new zealand reveals a channel which is interpreted as a sheared zone of ponded partial melts or volatiles this low viscosity channel decouples the plate from mantle flow beneath allowing plate tectonics to work tim stern and co authors use explosion generated seismic waves to form a high resolution image of the base of an oceanic plate that is subducting beneath north island new zealand they find an abrupt seismic wave speed transition less than a kilometre thick at a depth of 100 km dipping at an angle of 15 the presence of a parallel 10 km deeper reflection event shows that the decrease in compressional wave speed is confined to a channel at the base of the plate which the authors interpret as a sheared zone of ponded partial melts or volatiles they conclude that this is independent evidence for a low viscosity channel at the lithosphere asthenosphere boundary that decouples plates from mantle flow beneath and allows plate tectonics to take place plate tectonics successfully describes the surface of earth as a mosaic of moving lithospheric plates but it is not clear what happens at the base of the plates the lithosphere asthenosphere boundary lab the lab has been well imaged with converted teleseismic waves1 2 whose 10 40 kilometre wavelength controls the structural resolution here we use explosion generated seismic waves of about 0 5 kilometre wavelength to form a high resolution image for the base of an oceanic plate that is subducting beneath north island new zealand our 80 kilometre wide image is based on p wave reflections and shows an approximately 15 dipping abrupt seismic wave speed transition less than 1 kilometre thick at a depth of about 100 kilometres the boundary is parallel to the top of the plate and seismic attributes indicate a p wave speed decrease of at least 8 3 per cent across it a parallel reflection event approximately 10 kilometres deeper shows that the decrease in p wave speed is confined to a channel at the base of the plate which we interpret as a sheared zone of ponded partial melts or volatiles this is independent high resolution evidence for a low viscosity channel at the lab that decouples plates from mantle flow beneath and allows plate tectonics to work

the rupture process and location of the 2003 zemmouri boumerdes earthquake mw 6 8 inferred from seismic and geodetic data this work is a study of the earthquake mw 6 8 that occurred on may 21 2003 in zemmouri boumerdes algeria using methodology based on teleseismic data uplift measurements and synthetic aperture radar data as a starting point we fix the two source fault models obtained in this work solution 1 strike 64 dip 50 and rake 97 solution 2 strike 256 dip 40 and rake 91 with a length of 60 km and width of 20 km to calculate the slip distribution that best explains the seismic and geodetic observations the interferometric fringes revealed a strong displacement in the satellite direction 53 cm along the coast of algeria between the cities of boumerdes and zemmouri the inversion of teleseismic body waves for the two focal solution types one plane dipping to the se and the second plane dipping to the nw showed distinct ruptures however both bilateral ruptures included two asperities one near the hypocentre and the other at a shallower location the maximum slip solution 1 3 8 m and solution 2 4 0 m occurred near the hypocentre in both seismic source models the surface displacement model was obtained with okada s equations using the edcmp algorithm the three components of the displacements calculated were projected regarding the satellite direction los line of sight for comparison with the interferogram the geographic location of the fault plane was determined by comparing the uplift measurements with the vertical displacement models calculated with the source at several locations the surface displacements calculated from these source models indicate that the model based on the se plane and the epicentre location at 36 846 n and 3 660 e produces results closer to the interferogram and the uplift measurements

mapping the megathrust beneath the northern gulf of alaska using wide angle seismic data in the northern gulf of alaska and prince william sound we have used wide angle seismic reflection refraction profiles earthquake studies and laboratory measurements of physical properties to determine the geometry of the prince william and yakutat terranes the aleutian megathrust and the subducting pacific plate in this complex region the yakutat terrane is underthrust beneath the prince william terrane and both terranes are interpreted to be underlain by the pacific plate wide angle seismic reflection refraction profiles recorded along five seismic lines are used to unravel this terrane geometry modeled velocities in the upper crust of the prince william terrane to 18 km depth agree closely with laboratory velocity measurements of orca group phyllites and quartzofeldspathic graywackes the chief components of the prince william terrane to hydrostatic pressures as high as 600 mpa 6 kbar a landward dipping reflector at depths of 16 24 km is interpreted as the base of the prince william terrane this reflector corresponds to the top of the wadati benioff zone seismicity and is interpreted as the megathrust immediately beneath the megathrust is a 4 km thick 6 9 km s refractor which we infer to be the source of a prominent magnetic anomaly and which is interpreted by us and previous workers to be gabbro in eocene age oceanic crust of the underthrust yakutat terrane wide angle seismic data magnetic anomaly data and tectonic reconstructions indicate that the yakutat terrane has been underthrust beneath the prince william terrane for at least a few hundred kilometers wide angle seismic data are consistent with a 9 to 10 landward dip of the subducting pacific plate beneath the outer shelf and slope distinctly different from the inferred average 3 to 4 dip of the overlying 6 9 km s refractor and the wadati benioff seismic zone beneath the inner shelf our preferred interpretation of the geophysical data is that one composite plate composed of the pacific plate of a fairly uniform thickness and the yakutat plate of varying thickness is subducting beneath southern alaska

thermal structure radial anisotropy and dynamics of oceanic boundary layers defining the oceanic lithosphere as a thermal boundary layer allows to explain to first order age dependent bathymetry and isotropic wave speeds in contrast ss precursors and receiver functions suggest a subhorizontal interface within this layer on top of a radially anisotropic zone comparing a suite of geodynamic scenarios against surface wave dispersion data and seismic discontinuities we find that only weak age dependency of the radially anisotropic zone is compatible with observations we show that this zone is confined from below by a second weaker seismic interface while observed azimuthal anisotropy is consistent with lattice preferred orientation of olivine due to asthenospheric flow underneath the lithosphere radial anisotropy requires additional contributions perhaps from petrological fabrics or melt ponding this implies that seismic reflectors previously associated with the base of the lithosphere are instead associated with preserved structures embedded in it they carry information about plate formation but have little control on plate deformation

implications of grain size evolution on the seismic structure of the oceanic upper mantle abstract we construct a 1 d steady state channel flow model for grain size evolution in the oceanic upper mantle using a composite diffusion dislocation creep rheology grain size evolution is calculated assuming that grain size is controlled by a competition between dynamic recrystallization and grain growth applying this grain size evolution model to the oceanic upper mantle we calculate grain size as a function of depth seafloor age and mantle water content the resulting grain size structure is used to predict shear wave velocity v s and seismic quality factor q for a plate age of 60 myr and an olivine water content of 1000 h 10 6 si we find that grain size reaches a minimum of 15 mm at 150 km depth and then increases to 20 30 mm at a depth of 400 km this grain size structure produces a good fit to the low seismic shear wave velocity zone lvz in oceanic upper mantle observed by surface wave studies assuming that the influence of hydrogen on anelastic behavior is similar to that observed for steady state creep further it predicts a viscosity of 10 19 pa s at 150 km depth and dislocation creep to be the dominant deformation mechanism throughout the oceanic upper mantle consistent with geophysical observations we predict larger grain sizes than proposed in recent studies in which the lvz was explained by a dry mantle and a minimum grain size of 1 mm however we show that for a 1 mm grain size diffusion creep is the dominant deformation mechanism above 100 200 km depth inconsistent with abundant observations of seismic anisotropy from surface wave studies we therefore conclude that a combination of grain size evolution and a hydrated upper mantle is the most likely explanation for both the isotropic and anisotropic seismic structure of the oceanic upper mantle our results also suggest that melt extraction from the mantle will be significantly more efficient than predicted in previous modeling studies that assumed grain sizes of 1 mm

structural characteristics off miyagi forearc region the japan trench seismogenic zone deduced from a wide angle reflection and refraction study abstract the japan trench subduction zone located east of ne japan has regional variation in seismicity many large earthquakes occurred in the northern part of japan trench but few in the southern part off miyagi region is in the middle of the japan trench where the large earthquakes m 7 with thrust mechanisms have occurred at an interval of about 40 years in two parts inner trench slope and near land a seismic experiment using 36 ocean bottom seismographs obs and a 12 000 cu in airgun array was conducted to determine a detailed 2d velocity structure in the forearc region off miyagi the depth to the moho is 21 km at 115 km from the trench axis and becomes progressively deeper landward the p wave velocity of the mantle wedge is 7 9 8 1 km s which is typical velocity for uppermost mantle without large serpentinization the dip angle of oceanic crust is increased from 5 6 near the trench axis to 23 150 km landward from the trench axis the p wave velocity of the oceanic uppermost mantle is as small as 7 7 km s this low velocity oceanic mantle seems to be caused by not a lateral anisotropy but some subduction process by comparison with the seismicity off miyagi the subduction zone can be divided into four parts 1 seaward of the trench axis the seismicity is low and normal fault type earthquakes occur associated with the destruction of oceanic lithosphere 2 beneath the deformed zone landward of the trench axis the plate boundary is characterized as a stable sliding fault plain in case of earthquakes this zone may be tsunamigenic 3 below forearc crust where p wave velocity is almost 6 km s and larger this zone is the seismogenic zone below inner trench slope which is a plate boundary between the forearc and oceanic crusts 4 below mantle wedge the rupture zones of thrust large earthquakes near land e g 1978 off miyagi earthquake are located beneath the mantle wedge the depth of the rupture zones is 30 50 km below sea level from the comparison the rupture zones of large earthquakes off miyagi are limited in two parts plate boundary between the forearc and oceanic crusts and below mantle wedge this limitation is a rare case for subduction zone although the seismogenic process beneath the mantle wedge is not fully clarified our observation suggests the two possibilities earthquake generation at the plate boundary overridden by the mantle wedge without serpentinization or that in the subducting slab

crustal structure of the azores archipelago from rayleigh wave ellipticity data determining the crustal structure of ocean island volcanoes is important to understand the formation and tectonic evolution of the oceanic lithosphere and tectonic swells in marine settings and to assess seismic hazard in the islands the azores archipelago is located near a triple junction system and is possibly under the influence of a mantle plume being at the locus of a wide range of geodynamic processes however its crustal structure is still poorly constrained and debated due to the limited seismic coverage of the region and the peculiar linear geometry of the islands to address these limitations in this study we invert teleseismic rayleigh wave ellipticity measurements for 1 d shear wave speed vs crustal models of the azores archipelago moreover we test the reliability of these new models by using them in independent moment tensor inversions of local seismic data and demonstrate that our models improve the waveform fit compared to previous models we find that data from the westernmost seismic stations used in this study require a shallower moho depth 10 km than data from stations in the eastern part of the archipelago 13 16 km this apparent increase in the moho depth with increasing distance from the mid atlantic ridge mar is expected however the rate at which moho deepens away from the mar is greater than that predicted from a half space cooling model suggesting that local tectonic perturbations have modified crustal structure the 1 d vs models obtained beneath the westernmost seismic stations also show higher wave speeds than for the easternmost stations which correlates well with the ages of the islands except santa maria island we interpret the relatively low vs profile found beneath santa maria island as resulting from underplating which agrees with previous geological studies of the island compared to a recent receiver function study of the region the shallow structure top 2 km in our models shows lower shear wave speed which may have important implications for future hazard studies of the region more generally the new seismic crustal models we present in this study will be useful to better understand the tectonics seismicity moment tensors and strong ground motions in the region

receiver function imaging of lithospheric structure and the onset of melting beneath the galapagos archipelago abstract the galapagos archipelago represents an opportunity to investigate the properties of young oceanic lithosphere the effects of a hotspot anomaly on lithospheric thickness and melting dynamics in a hotspot ridge interaction here we use data recorded by the signet array and permanent station payg on the islands santa cruz and isabela respectively we used p to s ps and s to p sp receiver functions to constrain crust and mantle structure a simultaneous deconvolution method was used to constrain 1 d structure and also for the modeling of robust features a migrated extended multitaper method was used to investigate 3 d structural variations ps images a velocity increase with depth at 11 7 km probably the base of the pre plume crust or old moho sp imaging and modeling images a second deeper velocity increase at 37 7 km depth a velocity decrease with depth is imaged on average at 75 12 km likely associated with the lithosphere asthenosphere boundary this discontinuity is imaged deeper 82 km in the southwest and shallower 66 km in the northeast near the spreading ridge although the trend is consistent with lithospheric thickening with age the thickness is much larger than predicted by conductive cooling models of 0 10 my oceanic lithosphere we infer a compositional contribution to velocity variations finally a velocity increase with depth is imaged at 125 to 145 15 km depth that is likely associated with the onset of melting the discontinuity is imaged deeper in 3 sectors of the galapagos platform ridge region all coincident with the slowest surface wave shear velocity anomalies in the upper 100 km one is located in the southwest in a hypothesized plume location the other two are to the northwest and northeast possibly illuminating multiple plume diversions related to complex plume ridge interactions

imaging the seismic lithosphere asthenosphere boundary of the oceanic plate 1 the seismic lithosphere asthenosphere boundary lab or g discontinuity a seismologically characterized abrupt drop in wave speed in the uppermost mantle is one of the key issues in current geodynamics although plate tectonics started as a theory for the ocean reports on lab for normal oceanic regions are scarce due to paucity of seismic data and whether or not the oceanic lab grows with age is the key issue to be resolved we conduct a systematic survey for the oceanic lab using s to p converted seismic waves along three margins of oceanic plates whose crustal age ranges from 10 myr to 130 myr and we observe laterally continuous oceanic lab images the thickness of the oceanic plate estimated from labs increases with the plate age though scattered suggesting that the evolution of oceanic lithosphere is predominantly governed by temperature and that the oceanic seismic lab represents a boundary that grows with age

periglacial trimlines in the scottish highlands abstract two periglacial weathering limits have been identified on mountains in the highlands of scotland the lower has been interpreted as a periglacial trimline marking the upper limits of loch lomond younger dryas stade glaciers and has been employed to reconstruct the dimensions of parts of the main west highland icefield and certain smaller glaciers and icefields interpretation of the upper weathering limit has been more contentious but recent research has demonstrated 1 significant contrasts in the degree of bedrock weathering above and below this limit 2 that gibbsite a pre devensian weathering product is abundant above the limit but rare in soils farther downslope 3 that the isotopic 26al age of bedrock exposures above the limit greatly exceeds that at lower altitudes and 4 that the altitude of the weathering limit descends regularly along former ice sheet flowlines collectively these attributes suggest that the upper weathering limit is a periglacial trimline defining the maximum altitude of the last ice sheet calculated basal shear stress values are consistent with this interpretation which implies that the mainland ice shed lay at ca 900 m in wester ross and descended gently northwards whilst harris and lewis in the outer hebrides supported an independent ice cap that achieved a maximum altitude of ca 700 m wider implications of this interpretation and the future potential for ice sheet reconstruction are explored

the quaternary deposits and landforms of scotland and the neighbouring shelves a review abstract a thick sequence of quaternary sediments up to 1000 m has been deposited in the north sea basin and perhaps five major glacial episodes the first occurring prior to ca 1 8 2 1 ma bp and the last during the late devensian can be recognised between the glacial events periods of low salinity arctic marine or glacio marine sedimentation have been dominant although episodes of ameliorated climate when north atlantic drift waters had access to the north sea have been identified a number of horizons in separate boreholes have been correlated with the last interglacial oxygen isotope stage 5e and a sequence of water mass movements around the scottish coasts can be reconstructed for the last ca 125 ka on land sequences of quaternary deposits relating to several glacial and non glacial terrestrial and marine events occur in different areas but due to poor dating correlation between these sequences cannot yet be achieved in particular north east scotland has a complex glacial history with evidence for ice sheet glaciation on at least four occasions evidence from the outer hebrides north east scotland and the north sea basin indicates that the late devensian scottish ice sheet had a rather restricted extent only reaching a short distance offshore along much of the east and west coasts at this time ice free areas existed in north east scotland on the isle of lewis and probably in caithness and orkney whilst part of the outer shelf around st kilda was dry land a marine embayment extended down the east coast of scotland between the scottish and scandinavian ice sheets and independent ice caps existed on the outer hebrides and probably on shetland deglaciation of the greater part of the country took place prior to ca 13 ka bp whilst the climate was still very cold the ice retreat appears to have been orderly with stagnant ice masses being trapped only in topographically suitable locations a number of retreat stages or minor readvances occurred during the general deglaciation the firth of clyde was one of the last areas outside the highlands to be deglaciated and this occurred in a rapid possibly catastrophic fashion shortly prior to ca 13 ka bp despite the mild climate at the start of the lateglacial interstadial it is not known if there was complete deglaciation prior to the loch lomond readvance the readvance glaciers however may have started to advance during the latter part of the interstadial when declining terrestrial temperatures coincided with a period of mild marine conditions the loch lomond readvance maximum can only be dated to some time after ca 10 9 ka bp and it is likely that final ice free conditions were not achieved until the earliest holocene

thickening of young pacific lithosphere from high resolution rayleigh wave tomography a test of the conductive cooling model direct seismic measurements of the thickening of oceanic lithosphere away from the spreading axis are rare due to the remoteness of mid ocean ridges on the east pacific rise at 17 s there were two long term broadband ocean bottom seismometer deployments the melt and glimpse experiments these arrays spanned young pacific plate seafloor ranging in age from 0 to 8 ma combining these two data sets we describe the increase in rayleigh wave phase velocities for 16 100 s period as function of distance from the ridge with two parameterizations an arbitrary function of seafloor age and a simple polynomial function of age on the pacific and nazca plates although resolution analysis shows that 10 to 15 independent pieces of information about the age variation of phase velocity on the pacific plate can be resolved at periods of 50 s the three parameter polynomial model fits the data almost as well indicating a simple pattern of the evolution of structure with age to compare our observations to the predictions for the conductive cooling of the lithosphere we convert a thermal half space cooling model to shear velocity using anharmonic and anelastic contributions the patterns in the velocities are not consistent with simple conductive cooling the conductive cooling model under predicts the changes in phase velocity with age observed in the 20 to 78 s period range we observe significant changes in shear velocity in the asthenosphere at depths greater than conductive cooling should extend the asthenospheric low velocity zone is asymmetric dipping to the west with the lowest velocities beneath the pacific plate west of the spreading center the conductive cooling model also over predicts the shear velocities in the lithosphere by 0 2 km s these anomalies indicate that more complicated mantle flow and significant mantle heterogeneities such as melt are required

ponded melt at the boundary between the lithosphere and asthenosphere the boundary between earth s rigid lithosphere and ductile asthenosphere is marked by a seismic discontinuity laboratory experiments on basaltic magmas show that melts should pond at pressures that correspond to the lithosphere asthenosphere boundary thus magma ponding could explain the observed seismic discontinuity

resolving crustal thickness using ss waveform stacks we image lithospheric interfaces using variations in the character of ss waveform stacks a method we term ss lithospheric interface profiling sslip the variations are caused by reflected phases that is underside reflections ss precursors and topside multiples ss reverberations created at velocity discontinuities near the midpoint of the ss ray path stacks from continental versus oceanic bounce point regions produce distinctly different ss waveforms consistent with the large continent ocean difference in crustal thickness to investigate the potential of ss waveform stacks to constrain moho depths under continents we develop a method to fit continental bounce point stacks with a reference ss waveform convolved with a crustal operator the sslip inferred moho depths agree with the crust 2 0 model in asia for those regions where the ss bounce point density is the highest the sslip depths are correlated correlation coefficient 0 82 with the crust 2 0 values averaged over sample bins of 10 radius the sslip method has broad lateral resolution in comparison to most other methods for resolving crustal thickness but has the potential to sample regions where station coverage may be sparse

late devensian ice sheet in the western grampians scotland a radial pattern of ice flow of the last ice sheet in the largest source area of ice c 5000 km2 in the british isles in western scotland is demonstrated by the dispersal of indicator erratics and by patterns of striae friction cracks and ice moulded landforms three major ice domes and the principal ice divide are identified in the western grampians the ice domes coincided with the highest mountain blocks while it is inferred that the alignment of many of the pre existing valleys controlled much of the outflow of ice forming ice streams within the ice sheet the importance of the rannoch moor basin as a radial provider of ice to surrounding areas was apparently less significant than has hitherto been considered ice flowed into and across the southern part of the basin from the principal ice divide located to the west and south no evidence has yet been found that would support a model of an eastward migrating ice divide either during the build up or during the deglaciation of the late devensian ice sheet

lithospheric structure of the arabian and eurasian collision zone in eastern turkey from s wave receiver functions summary crustal and upper mantle seismic discontinuities beneath eastern turkey are imaged using teleseismic s to p converted phases three crustal phases are observed the moho with depth ranging between 30 and 55 km indicating variable tectonic regimes within this continental collision zone an upper crustal discontinuity at approximately 10 km depth and various crustal low velocity zones possibly associated with recent quaternary volcanism imaging of the upper mantle is complicated by the 3 d geometry of the region in particular due to the bitlis zagros suture zone however several upper mantle s to p converted phase are identified as being the signature of the lithosphere asthenosphere boundary lab the inferred lab for the eastern anatolian accretionary complex indicates that eastern turkey has an anomalously thin between 60 and 80 km lithosphere which is consistent with an oceanic slab detachment model the observed lab phases for the arabian shield and iranian plateau indicate that lithospheric thickness for these stable regions is on the order of 100 to 125 km thick which is typical of continental margins

lateglacial surface exposure dating in the monadhliath mountains central highlands scotland we constrain the deglaciation history of the monadhliath mountains since the last glacial maximum using glacial geomorphology and surface exposure dating collectively these data clarify the glacial history of the monadhliath mountains at the close of the devensian cold period 10be exposure ages indicate deglaciation of the last devensian ice sheet at 15 1 1 4 ka at ca 640 m od the exposure ages are consistent with basal radiocarbon ages from nearby loch etteridge 5 km to the south east 15 3 0 2 kcal bp1 boulders from moraines in three monadhliath corries yielded exposure ages between 11 8 ka and 9 8 ka 470 600 m od suggesting that a lateglacial advance occurred during the younger dryas stadial the limited extent of these younger dryas glaciers in the monadhliath mountains results from the combined effect of a drier climate experienced in the eastern part of the central highlands ice cap and topographical factors our reconstruction largely supports the deglaciation model of golledge et al 2008 and confirms that a sw to ne precipitation gradient dominated scotland during the younger dryas

structure and composition of the aleutian island arc and implications for continental crustal growth we present results of a seismic reflection and refraction investigation of the aleutian island arc designed to test the hypothesis that volcanic arcs constitute the building blocks of continental crust the aleutian arc has the requisite thickness 30 km to build continental crust but it differs strongly from continental crust in its composition and reflectivity structure seismic velocities and the compositions of erupted lavas suggest that the aleutian crust has a mafic bulk composition in contrast to the andesitic bulk composition of continents the silicic upper crust and reflective lower crust that are characteristic of continental crust are conspicuously lacking in the aleutian intraoceanic arc therefore if island arcs form a significant source of continental crust the bulk properties of arc crust must be substantially modified during or after accretion to a continental margin the pervasive deformation intracrustal melting and delamination of mafic to ultramafic residuum necessary to transform arc crust into mature continental crust probably occur during arc continent collision or through subsequent establishment of a continental arc the volume of crust created along the arc exceeds that estimated by previous workers by about a factor of two

a unified continental thickness from seismology and diamonds suggests a melt defined plate thick rigid continents move over the weaker underlying mantle although geophysical and geochemical constraints on the exact thickness and defining mechanism of the continental plates are widely discrepant xenoliths suggest a chemical continental lithosphere 175 kilometers thick whereas seismic tomography supports a much thicker root 250 kilometers and a gradual lithosphere asthenosphere transition consistent with a thermal definition we modeled ss precursor waveforms from continental interiors and found a 7 to 9 velocity drop at depths of 130 to 190 kilometers the discontinuity depth is well correlated with the origin depths of diamond bearing xenoliths and corresponds to the transition from coarse to deformed xenoliths at this depth the xenolith derived geotherm also intersects the carbonate silicate solidus suggesting that partial melt defines the plate boundaries beneath the continental interior

predictions and observations for the oceanic lithosphere from s to p receiver functions and ss precursors the ocean lithosphere is classically described by the thermal half space cooling hsc or the plate models both characterized by a gradual transition to the asthenosphere beneath scattered waves find sharp seismic discontinuities beneath the oceans possibly from the base of the plate active source studies suggest sharp discontinuities from a melt channel we calculate synthetic s to p receiver functions and ss precursors for the hsc and plate models and also for channels we find that the hsc and plate model velocity gradients are too gradual to create interpretable scattered waves from the base of the plate subtle phases are predicted to follow a similar trend as observations flattening at older ages therefore the seismic discontinuities are probably caused by a thermally controlled process that can also explain their amplitude such as melting melt may coalesce in channels although channels 10 km thick should be resolvable by scattered wave imaging

gibbsitic soils on former nunataks implications for ice sheet reconstruction x ray diffraction analyses of soils above and below a periglacial trimline developed across the basalts of the trotternish escarpment isle of skye scotland demonstrate that gibbsite is restricted to soils above the trimline this suggests that the gibbsite is a relict of pre late devensian weathering and that the trimline did not develop after the last ice sheet achieved its maximum thickness the sharpness of the boundary between frost weathered regolith and gibbsitic soils upslope and ice scoured bedrock associated with gibbsite free soils downslope suggests that the trimline represents the altitude of the last ice sheet at its maximum thickness rather than a former boundary between passive cold based ice and erosive warm based ice these findings illustrate how identification of high level periglacial trimlines and associated contrasts in clay mineralogy provide a means for constraining reconstructions of the form of the last ice sheets

crustal evolution of the southwestern kuril arc hokkaido japan deduced from seismic velocity and geochemical structure abstract the southwestern kuril arc which is not affected by a series of accretion and collision processes is one of the most important experimental sites among the world arc trench systems for investigating the evolution of arc crust published petrological and seismic studies have shown that in south central hokkaido the upper part of the kuril arc crust is thrusting upward toward the west while the lower part is descending downward in the same direction among several hypotheses for formation of continental crust we discuss the role of delamination of the island arc lower crust based on geochemical and seismic velocity structure models seismic velocity structure is obtained from an onshore offshore seismic survey across the southwestern kuril arc trench system the structure in the back arc area shows a thick accretionary complex formed by paleogene accretion and collision based on published seismic results this accretionary complex is considered to continue on land to the cretaceous accretionary complex observed in the hidaka belt the structure of the kuril arc appears characteristic of upper crustal andesitic rocks 6 0 6 2 km s and thick middle to lower crust 6 5 7 3 km s based on published geochemical study we consider a geochemical model of simple crustal evolution explaining the mechanism of generation of andesitic rocks on the kuril arc each volume of andesitic basaltic and mafic layers estimated from the geochemical model is consistent with those obtained from the seismic velocity model crustal composition estimated from the geochemical model and major element chemistry of the volcanic rocks in the kuril arc indicate that mechanical delamination is insufficient to cause the oceanic island arc crust to evolve into continental crust

water rich sublithospheric melt channel in the equatorial atlantic ocean the lithosphere asthenosphere boundary is the most extensive boundary on earth separating the mobile plate above from the convecting mantle below but its nature remains a matter of debate using an ultra deep seismic reflection technique here we show a systematic seismic image of two deep reflectors that we interpret as the upper and lower limits of the lithosphere asthenosphere boundary beneath a 40 70 million year old oceanic lithosphere in the atlantic ocean these two reflections correspond to 1 260 c and 1 355 c isotherms and bound a low velocity channel suggesting that the lithosphere asthenosphere boundary is thermally controlled we observe a clear age dependency of this sublithospheric channel its depth increases with age from 72 km where it is 40 myr old to 88 km where it is 70 myr old whereas its thickness decreases with age from 18 km to 12 km we suggest that partial melting facilitated by water is the main mechanism responsible for the low velocity channel the required water concentration for melting increases with age nevertheless its corresponding total mass remains relatively constant suggesting that most of the volatiles in the oceanic sublithospheric channel originate from a horizontal flux near the ridge axis

lithospheric structure across the california continental borderland from receiver functions due to its complex history of deformation the california continental borderland provides an interesting geological setting for studying how the oceanic and continental lithosphere responds to deformation we map variations in present day lithospheric structure across the region using ps and sp receiver functions at permanent stations of the southern california seismic network as well as ocean bottom seismometer obs data gathered by the asthenospheric and lithospheric broadband architecture from the california offshore region experiment albacore which enhances coverage of the borderland and provides first direct constraints on the structure of the pacific plate west of the patton escarpment noisiness of obs data makes strict handpicking and bandpass filtering necessary in order to obtain interpretable receiver functions using h and common conversion point stacking we find pronounced lithospheric differences across structural blocks which we interpret as indicating that the outer borderland has been translated with little to no internal deformation while the inner borderland underwent significant lithospheric thinning most likely related to accommodating the 90 clockwise rotation of the western transverse range block west of the patton escarpment we find that the transition to typical oceanic crustal thickness takes place over a lateral distance of 50 km we detect an oceanic seismic lithosphere asthenosphere transition at 58 km depth west of the patton escarpment consistent with only weak age dependence of the depth to the seismic lithosphere asthenosphere transition sp common conversion point stacks confirm wholesale lithospheric thinning of the inner borderland and suggest the presence of a slab fragment beneath the outer borderland

active thrust faulting offshore boumerdes algeria and its relations to the 2003 mw 6 9 earthquake 1 we investigate the active seismogenic fault system in the area of the 2003 mw 6 9 boumerdes earthquake algeria from a high resolution swath bathymetry and seismic survey a series of 5 main fault propagation folds 20 35 km long leave prominent cumulative escarpments on the steep slope and in the deep basin fault activity creates plio quaternary growth strata within uplifted areas such as a rollover basin on the slope and piggyback basins in the deep ocean most thrusts turn to fault propagation folds at the sub surface and depict ramp flat trajectories we find that the two main slip patches of the 2003 mw 6 9 boumerdes earthquake are spatially correlated to two segmented cumulative scarps recognized on the slope and at the foot of the margin the overall geometry indicates the predominance of back thrusts implying underthrusting of the neogene oceanic crust

comment on zemmouri earthquake rupture zone mw 6 8 algeria aftershocks sequence relocation and 3d velocity model by a ayadi et al although often difficult to characterize the relationship between a seismic rupture its aftershock sequence and cumulative subsurface or surface faulting or folding is an important challenge to modern seismology and seismotectonics among other benefits it helps document fault length slip and magnitude relationships reconstruct the evolution of the rupture process through historical and prehistorical times and identify the complexity of the deformation in its path toward the surface this approach is a prerequisite to any seismic hazard assessment but is particularly difficult for faults whose surface trace projects offshore a specific effort to identify and quantify the source parameters of large earthquakes in coastal areas is therefore needed not only in subduction zones but also in areas of slow rate and or diffuse deformation

trans pacific upper mantle shear velocity structure 1 we use 50 tonga fiji events recorded at the broadband trinet array southern california to develop a pure path upper mantle shear velocity model across the pacific at the epicentral distances of 70 95 multibounce s waves up to s5 are observed including their triplicated branches which become particularly clear after stacking since these s wave multiples turn at various depths simultaneously modeling their differential traveltimes and waveforms provides strong constraints on the radial velocity structure we parameterize the velocity model according to a priori information from the previous oceanic models so that we can take a grid search approach to fully investigate possible interdependencies among the model parameters we construct synthetics with a reflectivity code and study both the sh and sv components by modeling the whole recordings from events at different depths with different mechanisms we are able to separate shallow low velocity zone lvz features from deeper structure our preferred model pac06 contains a fast lid vsh 4 78 km s 1 vsv 4 58 km s 1 with a thickness of 60 km the underlying lvz is prominent with the lowest velocities vsh 4 34 km s 1 and vsv 4 22 km s 1 occurring at a depth of 160 km these velocities are below the estimates of solid state lvz suggesting the presence of partial melt the anisotropy vsv vsh of pac06 extends to 300 km depth which is constrained by s5 turning at this depth besides the 406 km and 651 km discontinuities pac06 also has a small 1 velocity jump at 516 km we consider these main features of pac06 to be well determined since pac06 explains a large data set from various events therefore it is ideally suited for comparing with mineralogical models

surface and near surface effects on seismic waves theory and borehole seismometer results a simple plane wave model is adequate to explain many surface versus borehole seismometer data sets using such a model we present a series of examples which demonstrate the effects of the free surface near surface velocity gradients and low impedance surface layers on the amplitudes of upcoming body waves in some cases these amplitudes are predictable from simple free surface and impedance contrast expressions however in other cases these expressions are an unreliable guide to the complete response and the full plane wave calculation must be performed large surface amplifications are possible even without focusing due to lateral heterogeneities or nonlinear effects both surface and borehole seismometer site responses are almost always frequency dependent ocean bottom versus borehole seismic data from the 1983 ngendei seismic experiment in the southwest pacific are consistent with both a simple plane wave model and a more complete synthetic seismogram calculation the borehole seismic response to upcoming p waves is reduced at high frequencies because of interference between the upgoing p wave and downgoing p and sv waves reflected from the sediment basement interface however because of much lower borehole noise levels the borehole seismometer enjoys a p wave signal to noise advantage of 3 to 7 db over nearby ocean bottom instruments

proto iceland plume caused thinning of irish lithosphere abstract the lithosphere asthenosphere boundary lab separates the rigid lithospheric plates from the hot convective mantle in the region of the north atlantic this boundary is widely influenced by the spreading head of the proto iceland plume p kumar et al the lithosphere asthenosphere boundary in the north west atlantic region earth planet sci lett 236 2005 249 257 that also caused the evolution of the british tertiary volcanic province btvp with the giant s causeway basalts as famous landmark using teleseismic shear wave receiver functions we map the lab underneath ireland and find a distinctive lithospheric thinning of about 30 km towards the northern part of the island as this region is part of the btvp we explain the lithospheric thinning in agreement with geochemical results by thermal erosion originating from the head of the proto iceland plume

the global attenuation structure of the upper mantle 1 a large data set of fundamental mode rayleigh wave amplitudes is analyzed to derive a new global three dimensional model of shear wave attenuation in the upper mantle the amplitude observations span a range of periods between 50 and 250 s and are derived from earthquakes with mw 6 0 that occurred between 1993 and 2005 four separate factors may influence an amplitude anomaly intrinsic attenuation along the raypath elastic focusing effects along the raypath uncertainties in the strength of excitation and uncertainties in the response at the station in an earlier paper dalton and ekstrom 2006a dependence of the retrieved attenuation structure on these terms was shown to be significant and an approach was developed to invert the amplitudes simultaneously for each term the new three dimensional attenuation model qrfsi12 which is the subject of this paper is derived using this method the model contains large lateral variations in upper mantle attenuation 60 to 100 and exhibits strong agreement with surface tectonic features at depths shallower than 200 km at greater depth qrfsi12 is dominated by high attenuation in the southeastern pacific and eastern africa and low attenuation along many subduction zones in the western pacific resolution tests confirm that the change in pattern of attenuation above and below 200 km depth can be determined with confidence using the fundamental mode data set the new model is highly correlated with global models of shear wave velocity particularly in the uppermost mantle suggesting that the same factors may control both seismic attenuation and velocity in this depth range however forcing the lateral perturbations in attenuation to match those found in global velocity models decreases the data variance reduction which suggests that subtle differences between patterns of attenuation and velocity are robust

constraints on the anisotropic contributions to velocity discontinuities at 60 km depth beneath the pacific strong sharp negative seismic discontinuities velocity decreases with depth are observed beneath the pacific seafloor at 60 km depth it has been suggested that these are caused by an increase in radial anisotropy with depth which occurs in global surface wave models here we test this hypothesis in two ways we evaluate whether an increase in surface wave radial anisotropy with depth is robust with synthetic resolution tests we do this by fitting an example surface wave data set near the east pacific rise we also estimate the apparent isotropic seismic velocity discontinuities that could be caused by changes in radial anisotropy in s to p and p to s receiver functions and ss precursors using synthetic seismograms we test one model where radial anisotropy is caused by olivine alignment and one model where it is caused by compositional layering the result of our surface wave inversion suggests strong shallow azimuthal anisotropy beneath 0 10 ma seafloor which would also have a radial anisotropy signature an increase in radial anisotropy with depth at 60 km depth is not well resolved in surface wave models and could be artificially observed shallow isotropy underlain by strong radial anisotropy could explain moderate apparent velocity drops 6 in ss precursor imaging but not receiver functions the effect is diminished if strong anisotropy also exists at 0 60 km depth as suggested by surface waves overall an increase in radial anisotropy with depth may not exist at 60 km beneath the oceans and does not explain the scattered wave observations

weak interplate coupling by seamounts and repeating m 7 earthquakes subducting seamounts are thought to increase the normal stress between subducting and overriding plates however recent seismic surveys and laboratory experiments suggest that interplate coupling is weak a seismic survey in the japan trench shows that a large seamount is being subducted near a region of repeating earthquakes of magnitude m 7 both observed seismicity and the pattern of rupture propagation during the 1982 m 7 0 event imply that interplate coupling was weak over the seamount a large rupture area with small slip occurred in front of the seamount its northern bound could be determined by a trace of multiple subducted seamounts whereas a subducted seamount itself may not define the rupture area its width may be influenced by that of the seamount

seismic imaging of thickened lithosphere resulting from plume pulsing beneath iceland ocean plates conductively cool and subside with seafloor age plate thickening with age is also predicted and hot spots may cause thinning however both are debated and depend on the way the plate is defined determining the thickness of the plates along with the process that governs it has proven challenging we use s to p sp receiver functions to image a strong persistent lab beneath iceland where the mid atlantic ridge interacts with a plume with hypothesized pulsating thermal anomaly the plate is thickest up to 84 6 km beneath lithosphere formed during times of hypothesized hotter plume temperatures and as thin as 61 6 km beneath regions formed during colder intervals we performed geodynamic modeling to show that these plate thicknesses are inconsistent with a thermal lithosphere instead periods of increased plume temperatures likely increased the melting depth causing deeper depletion and dehydration and creating a thicker plate this suggests plate thickness is dictated by the conditions of plate formation

the gutenberg discontinuity melt at the lithosphere asthenosphere boundary the lithosphere asthenosphere boundary lab beneath ocean basins separates the upper thermal boundary layer of rigid conductively cooling plates from the underlying ductile convecting mantle the origin of a seismic discontinuity associated with this interface known as the gutenberg discontinuity g remains enigmatic high frequency ss precursors sampling below the pacific plate intermittently detect the g as a sharp negative velocity contrast at 40 to 75 kilometer depth these observations lie near the depth of the lab in regions associated with recent surface volcanism and mantle melt production and are consistent with an intermittent layer of asthenospheric partial melt residing at the lithospheric base i propose that the g reflectivity is regionally enhanced by dynamical processes that produce melt including hot mantle upwellings small scale convection and fluid release during subduction

low seismic velocities below mid ocean ridges attenuation versus melt retention the first comprehensive seismic experiment sampling subridge mantle revealed a pronounced low velocity zone between 40 and 100 km depth below the east pacific rise epr that has been attributed to substantial retained melt fractions of 0 3 2 such high melt fractions are at odds with low melt productivity and high melt mobility inferred from petrology and geochemistry here we evaluate whether seismic attenuation can reconcile subridge seismic structure with low melt fractions we start from a dynamic spreading model which includes melt generation and migration and is converted into seismic structure accounting for temperature pressure composition phase and melt dependent anharmonicity and temperature pressure frequency and hydration dependent anelasticity our models predict a double low velocity zone a shallow approximately triangular region due to dry melting and a low velocity channel between 60 and 150 km depth dominantly controlled by solid state high temperature seismic attenuation in a damp mantle with only a minor contribution of 0 1 melt we test how tomographic inversion influences the imaging of our modeled shear velocity features the epr experiment revealed a double low velocity zone but most tomographic studies would only resolve the deeper velocity minimum experimentally constrained anelasticity formulations produce vsas low as observed and can explain lateral variations in near ridge asthenospheric vs with 100 k temperature variations and or zero to high water content furthermore such qs formulations also reproduce low asthenospheric vs below older oceans and continents from basic lithospheric cooling models although these structures are compatible with global qs images they are more attenuating than permitted by epr data

glacial trimlines to identify former ice margins and subglacial thermal boundaries a review and classification scheme for trimline expression abstract reconstructions of former ice sheets and glaciers provide important palaeoglaciological information about their behaviour in response to climate changes glacial trimlines record both the margin positions and palaeo ice thickness enabling the production of empirically constrained 3 dimensional reconstructions however the literature review into the characteristics interpretation and use of glacial trimlines here presented shows that these features have been under utilised and are poorly described in the existing literature with a confusing terminology currently in use a new classification scheme and terminology for trimline identification and interpretation is developed to better facilitate further research into these common features of glacierised and formerly glaciated landscapes

sedimentology stratigraphy and glacier dynamics western scottish highlands glacial sediments of the western scottish highlands are comprehensively described and characterized here for the first time enabling the first glacial stratigraphy for the area to be proposed this classification is based on the results of extensive geological mapping and field investigation of sedimentary sequences and their structures x ray diffraction and particle size distribution analyses and comparison with deposits formed in contemporary glaciated environments these new data are subsequently appraised in terms of their implications for late pleistocene glacier evolution and dynamics together the data suggest that much of the landscape is palimpsest and can be attributed to the weichselian late devensian glaciation subsequent glacier advance during the younger dryas did little to modify the area suggesting that ice flow was dominated by sliding on a meltwater lubricated rigid bed with deformation of basal sediments playing a more limited role final deglaciation was marked by a significant increase in basal meltwater flux reflecting the warming climate and increasing precipitation these new palaeoglaciological and palaeoenvironmental insights advance our understanding of former glacier dynamics in the western scottish highlands improve our knowledge of pleistocene landscape evolution of this area and enable comparisons to be made with sedimentary sequences elsewhere