a revised chronology for the growth and demise of loch lomond readvance younger dryas ice lobes in the lochaber area scotland abstract we present a revised varve chronology for the duration of ice dammed lakes that formed in the lochaber district scotland during the loch lomond younger dryas stadial we analysed new varved sequences and combined them with existing varve records to develop the lochaber master varve chronology 2019 lmvc19 published here for the first time it spans an interval of 518 18 vyrs and is considered more secure than its predecessors because i it is anchored by a more robust record of the vedde ash which is dated to 12 043 43 cal yr bp and ii it provides revised estimates of the timings of key regional palaeoclimatic shifts that are fully compatible with those inferred from independently dated non varved records obtained from neighbouring sites the new results indicate that the lochaber ice dammed lakes existed between 12 135 and 11 618 61 cal yr bp but the pattern of glacier advance that led to lake formation was more complex than previously assumed with some ice fronts reaching their maximal positions 300 years before others initiation of ice retreat at 11 800 cal yr bp appears to have coincided with a rise of 2 c in mean july temperatures inferred from chironomid data obtained from the abernethy forest site in the eastern highlands this local climatic shift is thought to have been a delayed response by up to 335 years to a mid stadial northward migration of the north atlantic polar front the delay probably due to the influence of the sw highland icefield subsequent retreat that led to the formation of ice stagnation features throughout large parts of the area was initiated by a further rise in summer air temperature of 3 c at the start of the early holocene final drainage of the lake system occurred 190 years after the initiation of ice retreat while it took a further 200 years for the ice to vacate the rannoch plateau a nearby upland glacial source

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

mass balance flow and subglacial processes of a modelled younger dryas ice cap in scotland we use an empirically validated high resolution three dimensional ice sheet model to investigate the mass balance regime flow mechanisms and subglacial characteristics of a simulated younger dryas stadial ice cap in scotland and compare the resulting model forecasts with geological evidence input data for the model are basal topography a temperature forcing derived from grip 18 o fluctuations and a precipitation distribution interpolated from modern data the model employs a positive degree day scheme to calculate net mass balance within a domain of 112 500 km 2 which under the imposed climate gives rise to an elongate ice cap along the axis of the western scottish highlands at its maximum the ice cap is dynamically and thermally zoned reflecting topographic and climatic con trols respectively in order to link these palaeoglaciological conditions to geological interpretations we calculate the relative balance between sliding and creep within the simulated ice cap forecast areas of the ice cap with the greatest capacity for basal erosion and predict the likely pattern of subglacial drain age we conclude that ice flow in central areas of the ice cap is largely due to internal deformation and is associated with geological evidence of landscape preservation conversely the distribution of stream lined landforms is linked to faster flowing ice whose velocity is predominantly the result of basal sliding the geometry of the main ice mass focuses subglacial erosion in the mid sections of topographic troughs and produces glaciohydraulic gradients that favour subglacial drainage through low order arterial routes

analogue modelling of intraplate strike slip tectonics a review and new experimental results abstract intraplate strike slip zones commonly display intricate 3 d geometries with rapid changes in structural style along strike and with depth strike slip deformation typically results in complex vertical and horizontal sections that can be difficult to interpret coherently physical modelling of strike slip fault systems is a powerful and graphic tool to help in providing a unified picture of the evolution of strike slip zones with considerable spatial and temporal detail a large number of experimental studies have investigated different aspects of strike slip tectonics using materials such as dry sand wet clay or silicone the choice of analogue material and experimental design exerts a strong control on the structures that form in the model here we present a review of different experimental setups used to investigate intraplate strike slip tectonics from the classical riedel experiment to more sophisticated setups using brittle and viscous analogue materials we review our current understanding from models of distributed shear transtension transpression pull apart basins formed in releasing stepovers and popups formed in restraining stepovers in addition we present the results of two new experimental series that investigated 1 the effect of crustal weak zones on strike slip fault zone segmentation and 2 strike slip and transpressional reactivation of extensional basins

the importance of pressurized subglacial water in separation and sliding at the glacier bed l effet de l eau sous glaciaire sous pression sur le processus de glissement est examine a partir d un parametre appele indice de decollement du lit qui exprime les contraintes perpendiculaires au lit et la pression d eau les donnees proviennent de trois glaciers de formes differentes une loi puissance du type de weertman avec un exposant voisin de 3 modifiee pour tenir compte de l effet de la pression des eaux sous glaciaires apparait comme etant la meilleure

on the timing of retreat of the loch lomond younger dryas readvance icefield in the sw scottish highlands and its wider significance abstract it has long been assumed that the last glacier expansion in the scottish highlands the loch lomond readvance llr resulted from a cold reversal that was broadly coeval with the younger dryas episode this view has recently been challenged with the suggestion that glacier ice had disappeared from rannoch moor one of the main ice accumulation centres in the sw scottish highlands by as early as 12 5 ka i e within the first half of the younger dryas here we present new radiocarbon tephrostratigraphical and pollen stratigraphical evidence from one of the key sites on rannoch moor the results of an experiment designed to test this hypothesis our results not only contradict that concept but are fully compatible with other evidence from the sw scottish highlands that suggests that the llr glaciers in this area continued to expand until towards the end of the younger dryas period and may have persisted in some places after the onset of the holocene we consider the possible reasons for this marked divergence in chronology a matter that is crucial to resolve because the precise timing of the demise of the llr glaciers has important palaeoclimatic and other implications in the wider context we also draw attention to problems with the general use of the term younger dryas and why we regard the greenland stratotype unit and term greenland stadial 1 gs 1 a more secure stratigraphic comparator

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

the 14 november 2001 kokoxili tibet earthquake high frequency seismic radiation originating from the transitions between sub rayleigh and supershear rupture velocity regimes seismic array based analysis of the major kokoxili earthquake tibet 14 november 2001 yields an unambiguous reconstruction of the seismic rupture history and relates it to the generated seismic radiation we demonstrate that after a classical sub rayleigh velocity stage the rupture speed has jumped to supershear values close to compressional wave velocity over a 175 km long fault segment before abruptly slowing down in the late part of the earthquake the transition locations between these three phases are correlated with the fault geometry and are associated with the most energetic radiation this observation proves that the rupture velocity changes as theoretically predicted are a primary source of high frequency seismic radiation this result requires reconsidering the origins of seismic damage generally attributed to slip variations

the reconstruction of former ice sheets and their mass balance characteristics using a non linearly viscous flow model on a utilise un modele d ecoulement visqueux non lineaire pour etudier l influence des caracteristiques du bilan de masse des conditions aux limites sur le fond rocheux et de la topographie sous glaciaire sur l etendue et la forme des calottes glaciaires le but est de rendre possible l utilisation des traces geologiques de l extension glaciaire passee pour reconstituer les paleoclimats

superficial simplicity of the 2010 el mayor cucapah earthquake of baja california in mexico the geometry of faults is usually thought to be more complicated at the surface than at depth and to control the initiation propagation and arrest of seismic ruptures the fault system that runs from southern california into mexico is a simple strike slip boundary the west side of california and mexico moves northwards with respect to the east however the m w 7 2 2010 el mayor cucapah earthquake on this fault system produced a pattern of seismic waves that indicates a far more complex source than slip on a planar strike slip fault here we use geodetic remote sensing and seismological data to reconstruct the fault geometry and history of slip during this earthquake we find that the earthquake produced a straight 120 km long fault trace that cut through the cucapah mountain range and across the colorado river delta however at depth the fault is made up of two different segments connected by a small extensional fault both segments strike n130 e but dip in opposite directions the earthquake was initiated on the connecting extensional fault and 15 s later ruptured the two main segments with dominantly strike slip motion we show that complexities in the fault geometry at depth explain well the complex pattern of radiated seismic waves we conclude that the location and detailed characteristics of the earthquake could not have been anticipated on the basis of observations of surface geology alone

relation between continental strike slip earthquake segmentation and thickness of the crust 1 high resolution maps of large continental strike slip earthquake surface ruptures show that they are formed of fault segments these segments are bounded by fault bends step overs or combinations of the two the lowest limit in size for such segments may not be relevant in the understanding of earthquake mechanics as it pertains to the granular properties of fault zones the maximum limit in segment length however is important as it is directly relates to the maximum extent of seismic rupture to measure the length of the segments a new quantitative method based on piecewise linear fitting is developed and is used to automatically retrieve segments from earthquake rupture maps next this approach is tested against a set of ten continental strike slip earthquake ruptures derived from similar high quality maps the test suggests that segments have a maximum length of 18 km independent of regional tectonic setting slip inversions for earthquakes based on seismological and or geodetic data most often are not unique and can show some variability even for one particular event some basic characteristics however such as total moment release or general source geometry seem to persist that are relevant to earthquake mechanics measurements of the maximum horizontal extent of individual slip patches derived from seismic source inversion for strike slip ruptures show that their strike dimension does not increase infinitely with magnitude but instead reaches a maximum value of 25 km these two independent lines of observations complemented by earlier data and analog experiments suggest that it is the thickness of the seismogenic crust that controls the structural scaling of the length of seismic segments and that it is independent of the ultimate size of individual earthquakes

glaciation of scotland during the younger dryas stadial a review considerable research effort in recent years has refined our knowledge of the landforms and sedimentary sequences generated by glaciers of the last cold episode in scotland the younger dryas and the chronology of their formation these recent advances have benefited from new technologies such as high resolution digital terrain models numerical ice sheet simulations and cosmic ray surface exposure dating this review presents a summary of recent younger dryas research in scotland particularly focusing on studies from the last two decades the findings of these investigations are compared with those of earlier workers and critically are appraised in terms of their relevance to five key aspects of younger dryas glaciation growth of the ice cap its geometry dynamics mode of decay and likely stadial climate minor differences aside the consensus view appears to favour a relatively thick but areally restricted central ice cap surrounded by satellite ice fields at its centre the ice cap was probably thickest during the first 500 years of the stadial after which it most likely thinned as the climate became increasingly arid outlet glaciers were dynamic only in marginal areas where they produced abundant moraine sequences during deglaciation but throughout much of the stadial central areas of the ice cap effected only minimal landscape modification deglaciation took place by active retreat under a rapidly warming climate overall the stadial was dominated by much colder and drier conditions than present and probably experi enced greater intra annual temperature ranges copyright 2009 john wiley sons ltd

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

evidence for an earthquake barrier model from mw 7 8 kokoxili tibet earthquake slip distribution abstract the slip distribution of the mw 7 8 kokoxili tibet 2001 earthquake has been measured at high resolution using optical correlation of satellite images and provides both the parallel and perpendicular components of the horizontal co seismic slip this reveals a variation of the horizontal slip at a scale of 20 km along strike anti correlation of slip parallel and perpendicular to the fault indicates transfer of slip from the horizontal to the vertical component at the ends of segments these features suggest a rupture model with segments separated by strong persistent geometric barriers the unexpected ending of the rupture south of the main fault can be explain by such a structure but bears important implications for the initiation and rupture directivity of the next earthquake

earthquake scaling fault segmentation and structural maturity abstract slip and length measurements on earthquakes suggest large stress drop variability we analyze an extended set of slip length measurements for large earthquakes m 6 to seek for the possible origin s of this apparent variability we propose that such variability arises from earthquakes breaking a variable number of major fault segments that number depends on the strength of the inter segment zones which itself depends on the structural maturity of the faults we propose new d max l parameterizations based on that idea of multiple segment ruptures in such parameterizations each broken segment roughly scales as a crack while the total multi segment rupture does not stress drop on individual segments is roughly constant only varying between 3 5 to 9 mpa the slight variation that is still observed depends on fault structural maturity more mature faults have lower stress drops than immature ones the new d max l functions that we propose reduce uncertainties with respect to available relationships they thus provide a more solid basis to estimate seismic hazard by integrating fault properties revealed by geological studies

modern glacier characteristics as a basis for inferring former climates with particular reference to the loch lomond stadial abstract studies of the mass balance of modern glaciers have indicated that the equilibrium line altitude ela is the most critical parameter in the link between glaciers and climate average accumulation on a glacier includes components derived from direct precipitation on the glacier surface as well as wind drifting and avalanching of snow and approximates closely to accumulation at the equilibrium line ablation is most usefully predicted by mean summer temperature and there is a close non linear relationship between accumulation and mean summer temperature at the equilibrium line following discussion of methods of reconstructing former glaciers and calculating their equilibrium line altitudes the application of the above relationships to the loch lomond readvance glaciers of highland britain is considered and an outline of the precipitation pattern and the mean summer temperature of the loch lomond stadial is given

initiation and development of pull apart basins with riedel shear mechanism insights from scaled clay experiments typical pull apart structures were created in scaled clay experiments with a pure strike slip geometry riedel type experiments a clay slab represents the sedimentary cover above a strike slip fault in the rigid basement at an early stage of the development of the deformation zone synthetic shear fractures riedel shears within the clay slab display dilatational behaviour with increasing basal displacement the riedel shears rotate and open further developing into long narrow and deep troughs the shear displacement and the low angle with the prescribed principal basal fault set them apart from tension gashes at a more evolved stage synthetic segments y shears parallel to the basal principal fault develop and accommodate progressive strike slip deformation the y shears connect the tips of adjacent troughs developed from the earlier riedel shears resulting in the typical rhomb shaped structures characteristic for pull apart basins the strait of sicily rift zone with major strike slip systems being active from the miocene to the present comprises pull apart basins at different length scales for which the structural record suggests development by a mechanism similar to that observed in our experiments

the dynamics of ice sheet outlets a comparison of data from aircraft altimetry landsat imagery and radia echo sounding has shown characteristic surface topographies associated with sheet and stream flow the transition between the two is abrupt and occurs at a step in the subglacial topography this marks the onset of basal sliding and high velocities caused by subglacial water it results in crevassed amphitheatre like basins round the head of outlet glaciers it is also the zone of maximum driving stress beyond which values decline rapidly as velocities increase this abrupt transition appears to be topographically controlled since basal temperatures are at the pressure melting point well inland of the change in regime the marie byrd land ice streams exhibit qualitative differences from other ice sheet outlets however the change to lower driving stresses is much more gradual and occurs several hundred kilometres inland such ice streams have particularly low surface slopes and appear in form and flow regime to resemble confined ice shelves rather than grounded ice the repeated association of the transition to rapid sliding with a distinct subglacial feature implies a stabilizing effect on discharge through outlet glaciers acceleration of the ice is pinned to a subglacial step and propagation of high velocities inland of this feature seems improbable rapid ice flow through subglacial trenches may also ensure a relatively permanent trough through accentuation of the feature by erosion this is concentrated towards the heads of outlet glaciers up stream of the region where significant basal decoupling occurs this may be a mechanism for the overdeepening of fjords at their inland ends and the development of very steep fjord headwalls

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

basal water film basal water pressure and velocity of traveling waves on glaciers la theorie de nye et weertman des ondes cinematiques est etendue pour couvrir le cas ou la presence d une abondante quantite d eau au fond ou une pression croissante d eau accroit la vitesse de glissement d un glacier sur son lit on trouve que le rapport entre la vitesse de l onde et la vitesse superficielle du glacier est independante de la quantite d eau ou de sa pression au fond

a reinterpretation of scottish hummocky moraine and its significance for the deglaciation of the scottish highlands during the younger dryas or loch lomond stadial the aim of this paper is to demonstrate that much of the hummocky moraine present within the northern part of the lochlomond readvance ice cap formerly situated in the north west scottish highlands may be interpreted as suites of ice front moraines deposited during active decay these landforms can be used to reconstruct ice cap decay whichleads to important insights into the shrinking form of the ice cap and associated environmental conditions evidence has been collected from 10803 airphotographs and from detailed field survey it is presented at three spatial scales

computerized x ray tomography analysis of three dimensional fault geometries in basement induced wrench faulting abstract computerized x ray tomography applied to sandbox experiments makes it possible to analyze the kinematic evolution as well as the three dimensional geometry of faults in basement controlled wrench faulting with increasing basement displacement the evolution of shear bands developed in the model sand bed is observed as follows 1 the right stepping shears that have a cirque or shell or ship body shape develop on both sides of the basement fault 2 the shears on the one side of the basement fault join those on the other side and therefore each shear surface forms a helicoidal shape shears reach the surface of the sand near or above the basement fault thereby en echelon riedel shears are observed at the surface of the sand 3 lower angle shears and p shears lying within the zone defined by the first riedels have steeper dips and a less pronounced helicoidal aspect than the riedels such three dimensional shape and kinematic evolution of shears in the fault experiments agree well with the similar faults which propagate up through the unconsolidated sediments from a wrench fault in bedrock as observed in the excavated trenches at some active faults in the fault experiments the strike of the riedel shear to the basement fault in dense sand is larger than that in loose sand in reasonable agreement with the directions predicted by the coulomb criterion in terms of the angle of internal friction likewise the geometries of the riedel shears are considered to depend on the overburden materials in natural cases of wrench faulting

experimental evidence for crustal control over seismic fault segmentation strike slip faults are described as continuous structures while they are actually formed of successive segments separated by geometrical complexities although this along strike segmentation is known to affect the overall dynamics of earthquakes the physical processes governing the scale of this segmentation remain unclear here we use analogue models to investigate the structural development of strike slip faults and the physical parameters controlling segmentation we show that length of fault segments is regular along strike and scales linearly with the thickness of the brittle material variations of the rheological properties only have minor effects on the scaling relationship ratios between the segment length and the brittle material thickness are similar for coseismic ruptures and sandbox experiments this supports a model where crustal seismogenic thickness controls fault geometry finally we show that the 2 geometrical complexity acquired during the strike slip fault formation withstands cumulative displacement thus inherited complexity impedes the formation of an ever straighter fault and might control the length of earthquakes ruptures

extent and timing of the last glacial maximum in southwestern alaska a glacier complex composed of confluent alpine glaciers island ice caps and piedmont lobes covered much of the alaska peninsula and kodiak island during the last glacial maximum lgm because this glacier complex formed the southeastern border of beringia its dynamics may have been important in the timing and feasibility of the northwest coast route for human migration into lower latitude north america radiocarbon dates from stratigraphic sections on kodiak island and in the bristol bay lowlands bracket the lgm in southwestern alaska between 23 000 and 14 700 yr b p reconstruction of ice thickness based on glacier trimlines moraines and calculations of basal shear stress depict the alaska peninsula glacier complex flowing to the outer edge of the continental shelf in the gulf of alaska equilibrium line altitudes elas were 300 to 700 m lower than today and approached sea level on the southwestern alaska peninsula in northeastern areas where elas were higher bedrock topography largely controlled ice flow except where ice saddles bridged straits and inlets

fractal analysis applied to characteristic segments of the san andreas fault fractal theory is applied in a quantitative analysis of the san andreas fault saf geometry the method which directly measures the increase in total fault length with a decrease in ruler size gives the fractal dimension d and scaling properties for the chosen length band 0 5 1000 km a physical interpretation of d is that it measures the irregularity of the fault trace in the selected band the fault is subdivided into six segments of distinctive seismic behavior a main fault trace which shows either maximum coseismic slip or creeping was selected for analysis with three alternative branches examined for the saf system south of san bernardino branches of the fault trace are not considered in this work fractal dimensions calculated for the different segments range from 1 0008 to 1 0191 and are different from 1 0 to the 95 confidence interval these small changes reflect the overall smoothness of the main fault trace significant variations in d among segments indicate heterogeneities in the fault smoothness along strike d also changes significantly from the short length band to the long length band where the demarcation point ranges from 1 to 2 km the short length band has larger d values a slight correlation is obtained between the fractal dimension of the main trace and the extent of subparallel faulting this indicates some correspondence between the main fault trace irregularity and the complexity of subsidiary fault traces in plan view

discontinuous fault zones abstract many tectonic faults and tension fractures are at least initially composed of separate segments this note deals with a little explored reason for this phenomenon which in faulting has obvious implications both for the migration of hydrocarbons and for the sealing capacity of faults theoretical arguments based on coulombmohr s theory of shear failure and on a theorem for the integrability of vector fields lead to the expectation that in general non uniform and truly three dimensional stress fields will impede the formation of smooth coherent fault surfaces this is in contrast to the stress fields that are associated with plane deformation examples are given and special attention is drawn to the role of tectonic stress fields with horizontal principal stresses that change with depth in magnitude and direction

paleogene building of the bolivian orocline tectonic restoration of the central andes in 2 d map view using available information on the magnitude and age of tectonic shortening as well as paleomagnetically determined tectonic rotations we have run a series of 2 d map view restorations of the central andes neogene shortening in the foreland belt induced only slight orogenic curvature of the central andes the constraints on the ages of the large observed fore arc rotations average of 37 counterclockwise in southern peru and 29 clockwise in northern chile indicate that the bolivian orocline formed during the eocene oligocene as a consequence of differential shortening focused in the eastern cordillera to minimize local block rotations along the fore arc the restoration that best fits the central andean rotation pattern requires about 400 km of total paleogene plus neogene shortening near the arica bend this value corresponds to the upper bound of estimates of maximum horizontal shortening for the central andes along strike variations in horizontal shortening in the back arc induced bending of the continental margin block rotations with fore arc along strike extension and or orogen parallel transport of upper crustal material toward the symmetry axis of the orocline

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