the bristol mendip foreland thrust belt the thrusts and associated fold structures of the bristol mendip area are interpreted in terms of a thin skinned piggy back foreland thrust belt of variscan age with dominant northward transport strike normal balanced sections and compatible strike parallel sections have been constructed to illustrate the 3 d geometry of the linked thrust system north south shortening of c 20 km 40 is calculated from deformed and restored strike normal sections a thick and extensive thrust wedge of pre old red sandstone basement in the west of the area is responsible for culminations expressed at the surface as the mendip periclines uplifted culminations permit erosion to lower stratigraphic levels in the west and south of the area strike parallel sections and a hanging wall cut off map indicate that the majority of thrusts in the area are mainly oblique ramps rather than simple frontal and lateral ramps or flats the en echelon pattern of the mendip periclines may be related to the oblique ne climb of two of these thrusts the angle of frontal ramp climb through the dinantian stratigraphy is generally low and this explains the presence of numerous klippen of lower on upper carboniferous rocks whilst suggesting that certain thrust sheets were much more extensive than present outcrops indicate early pre thrusting movement on basement lineaments in the variscan foreland created uplifts angular unconformities and a predominance of n s structures in the north of the area

determination of volumetric variations and coastal changes due to historical volcanic eruptions using historical maps and remote sensing at deception island west antarctica abstract deception island is an active volcano in the south shetland islands antarctic its eruptions have been recorded since 1842 the last episode occurring between 1967 and 1970 this study quantifies the geomorphological changes which have taken place as a result of historical volcanic activity on the island the linear and volumetric results obtained for the telefon bay and craters of 1970s where the surtseyan eruption took place in 1967 are presented in detail

bedload transported pedogenic mud aggregates in the lower old red sandstone in southwest wales siltstones which exhibit large scale cross stratification and three dimensional bedforms in the ridgeway conglomerate formation are interpreted as partly representing bedload transported pedogenic mud aggregates the siltstones contain mixed layer swelling clays abundant desiccation cracks calcrete nodules and pseudoanticlinal slip planes which suggest the presence of vertic palaeosols and a hot seasonal climate compaction obliterated much of the original mud aggregate texture which is retained only where quartz grains surround individual aggregates

geodetic observations during the 2009 eruption of redoubt volcano alaska abstract in march 2009 redoubt volcano about 160 km to the sw of anchorage alaska began its most recent explosive eruption deformation induced by this event was recorded by a gps campaign network consisting of 14 benchmarks which had been established in 1991 after the previous eruption the network was partially reoccupied in 2001 and 2008 and no volcanic deformation was detected during that period in response to precursory unrest starting in january 2009 the alaska volcano observatory temporarily deployed continuously recording gps instruments at four of the campaign benchmarks only days before the onset of explosive activity in march 2009 the only gps instrument recording continuously during the months prior to the eruption was the plate boundary observatory pbo station ac17 about 28 km northeast of the volcano s summit data from this station reveals subtle motion radially outward from the volcano beginning as early as may 2008 which reversed with the onset of explosive activity using simple analytical models we link the precursory activity to a point source intrusion of 0 0194 0 03400 0092 km3 in volume at 13 50 17 3310 17 km below sea level bsl superscripts and subscripts refer to upper and lower ends of confidence intervals at the 95 level during the explosive phase about 0 05 0 10 028 km3 of magma was evacuated from a prolate spheroid with its centroid at 9 17 15 176 92 km bsl a semimajor axis of 4 50 10 001 25 km length and a semi minor axis of 0 475 4 00 3 km the effusive activity is inferred to come from the same source decreasing in volume by 0 0167 0 02280 0106 km3 including observations from seismology and petrology we hypothesize a mid crustal two reservoir system with material sourced from 20 km flowing in at about 13 5 km depth and reheating residual material in the proposed spheroid the mixture migrated to shallower depth 2 4 5 km bsl and reheated material there as this residual magma erupted it was replaced by the material from the spheroidal reservoir at 7 11 5 km depth which renders the shallow source undetectable for geodetic instruments in addition to long term displacements we investigate sub daily kinematic positioning solutions and find that large short term positioning offsets correlate with large explosive events spikes in phase residuals plotted along the sky tracks of individual satellites can be related to individual plumes given favorable satellite station geometry which may be of use in volcano monitoring

practical application of the sequential balancing technique an example from the irish variscides the process of sequential restoration presented by cooper trayner 1986 is applied to a n s cross section through the irish variscides to demonstrate that this approach improves the accuracy of thin skinned structural modelling and allows the progressive deformation of a marginal belt to be examined the principles and methods of sequential restoration are illustrated the cross section is restored in four steps and gives a bulk shortening of 52 in this model the fold belt evolved as the basal decollement migrated northwards and considerable ductile shortening by folding and cleavage formation preceded faulting although faulting gradually became more important towards the north the section is divided into four structural domains based upon different deformation histories each is restored independently by removing the ductile strain before restoring the faulting from this example it is clear that many models derived from single step balancing especially those through ductile deformed areas should be re examined

sedimentology and stratigraphy of thetownsend tuff bed lower old red sandstone in south wales and the welsh borders the townsend tuff bed has a highly distinctive internal stratigraphy which allows it to be recognized at a large number of localities scattered over the welsh borders and south wales it is a group of 3 almost directly superimposed normally graded air fall tuffs that originated in distant but powerful plinian eruptions centre unknown and became spread over extensive but practically featureless coastal mud flats the bed occurs in a barren interval within the early lower old red sandstone between a silurian invertebrate vertebrate fauna below and an already devonian vertebrate assemblage above the base of the devonian system in south wales and the welsh borders is accordingly defined as occurring at a regionally uniform lithological contact within the townsend tuff bed

normal vector analysis from gnss gps data applied to deception volcano surface deformation summary surface deformation parameters and its use in volcano monitoring have evolved from classical geodetic procedures up to those based on global navigation satellite systems gnss in particular the most widely used and known global positioning system gps profiting from the automated data processing positioning precision and rates as well as the large storage capacity and low power consumption of its equipments these features have enabled the permanent gnss gps data acquisition to ensure the continuous monitoring of geodetic benchmarks for the evaluation of surface deformation in active tectonic or volcanic areas in deception island antarctica a normal vector analysis is being used to give surface deformation based on three permanently observed gnss gps benchmarks due to data availability both in the past and for near real time use all benchmarks used are inside the monitored volcanic area although the reference is away from thermal springs and or fumaroles unlike the other two the time variation of slope distances to the reference benchmark and of the magnitude and inclination of the normal vector to the triangle defined by the reference benchmark and any other two provides the spatial deformation in the volcanic area covered the normal vector variation in magnitude gives information on compression or expansion here called spatial dilatometer while the changes in inclination gives information on relative uplift or subsidence here called spatial inclinometer in geodesy the triangle is a basic geometric unit and the areal strain is commonly applied in tectonics and volcanism the normal vector analysis conjugates both benefiting from the method s precision simplicity and possibility to model the surface using several triangles the proposed method was applied to gnss gps data collected every austral summer between 2001 2002 and 2009 2010 in deception island the results evidence that deception island acts as a strain marker in the bransfield basin volcano tectonic setting

tectonic evolution of sw wales during the upper palaeozoic during the upper palaeozoic the development of several strike faults strongly influenced the deformation history of sw wales this aspect of the deformation is emphasized in this new description of the tectonic evolution of the region after the caledonian orogeny several strike faults caused crustal extension by normal dip slip and partially controlled the subsidence of depositional basins these faults ceased moving before the initiation of variscan deformation in sw wales two of the earlier faults were reactivated with reverse slip translations during variscan deformation when three strike faults were initiated as a result of gravitational spreading two of the new faults formed sole thrusts for northward translating nappes and the other developed as a subsidiary lag fault the sole thrusts transected some of the pre existing faults causing along strike variation in their motion the strike faults in sw wales were therefore initiated at different times and display contrasting displacement histories

a seismic study of deep geological structure in the bristol channel area sw britain summary results from eight seismic refraction lines 35 90 km long in the bristol channel area are presented the data mostly land recordings of marine shots have been interpreted mainly by ray tracing and time term modelling upper layer velocities through palaeozoic rocks usually fall within the range 4 8 5 2 km s 1 below the carboniferous limestone with a normal velocity of 5 1 5 2 kms 1 the old red sandstone with a velocity of 4 7 4 8 kms 1 acts as a low velocity layer as do parts of the underlying lower palaeozoic succession in the central south wales bristol channel area and the mendips a 5 4 5 5 km s 1 refractor is correlated with a horizon at or near the top of the lower palaeozoic succession under the whole area except for north devon a 6 0 6 2 km s 1 basal refractor has been located and is correlated with precambrian crystalline basement rocks in general this refractor deepens southwards from a series of basement highs which existed before the major movements of the variscan orogeny in south wales resulting in a southerly thickening of the pre upper carboniferous supra basement sequence in north devon a 6 2 km s 1 refractor at shallow depth interpreted as a horizon in the devonian or lower palaeozoic succession overlies a deep reflector that may represent the precambrian crystalline basement

helium and carbon isotopic signatures of thermal spring gases in southeast yunnan china abstract late palaeozoic and cenozoic magmatism including pingbian quaternary basaltic volcanoes occurs in southeast yunnan china where seismic tomography evidence indicates magma activity in the uppermost mantle however the characteristics of mantle fluid release remain poorly understood here we report the chemical compositions of hot spring gases in se yunnan and measure the 3he 4he ratios 4he 20ne ratios and 13c values co2 ch4 to determine their origins and the factors influencing their migration except for five samples contaminated by the atmosphere 4he 20ne ratios 0 39 2 39 the rc ra ratios rc is the air corrected 3he 4he ratio ra is the air ratio with 1 4 10 6 range from 0 042 ra to 0 470 ra indicating that the helium is mostly of crustal origin with minor addition of mantle derived helium the calculated maximum proportion of mantle helium was 5 of total helium indicating that mantle 3he leakage correlates with the ductile lower crust the hot spring gases are fractionated by the partial dissolution of co2 in groundwater and the initial 13cco2 values are modelled by rayleigh fractionation within a range of 26 5 to 6 14 the modelled co2 in samples estimated by the he c isotope coupling model originates from the mixing of limestone and organic sediment end members the isotopic signature of ch4 69 2 to 35 9 suggests a thermogenic source and microbial oxidation in some samples furthermore the apparent isotopic temperatures are estimated using fractionation factors for ch4 and co2 suggesting a lack of magmatism in the crust beneath the red river fault zone 188 318 c but partial melting under the bozhushan granitoid plutons 572 688 c the low emission of mantle derived helium is attributed to the low fault permeability and minor active crustal deformation in present day se yunnan which restrain the upward migration of mantle fluids

paleomagnetism from deception island south shetlands archipelago antarctica new insights into the interpretation of the volcanic evolution using a geomagnetic model deception island shows the most recent exposed active volcanism in the northern boundary of the bransfield trough the succession of the volcanic sequence in the island is broadly divided into pre and post caldera collapse units although a well constrained chronological identification of the well defined successive volcanic episodes is still needed a new paleomagnetic investigation was carried out on 157 samples grouped in 20 sites from the volcanic deposits of deception island south shetlands archipelago antarctic peninsula region distributed in 1 volcanic breccia 3 sites and lavas 2 sites prior to the caldera collapse 2 lavas emplaced after the caldera collapse 10 sites and 3 dikes cutting pre and the lowermost post caldera collapse units 5 sites the information revealed by paleomagnetism provides new data about the evolution of the multi episodic volcanic edifice of this quaternary volcano suggesting that the present day position of the volcanic materials is close to their original emplacement position the new data have been combined with previous paleomagnetic results in order to tentatively propose an age when comparing the paleomagnetic data with a global geomagnetic model despite the uncertainties in the use of averaged paleomagnetic data per volcanic units the new data in combination with tephra occurrences noted elsewhere in the region suggest that the pre caldera units f1 and f2 erupted before 12 000 year bc the caldera collapse took place at about 8300 year bc and post caldera units s1 and s2 are younger than 2000 year bc

mid devonian tectonics and sedimentation in the bristol channel area the hangman sandstone group eifelian of north devon contains two continental 9old red sandstone9 formations the trentishoe formation is some 1000 m thick and consists of lithic arenites which petrographically match closely with those in the higher parts of the lower old red sandstone in south wales this formation was derived mainly from erosion of the highest lower old red sandstone in early mid devonian times as a result of end caledonian uplift and erosion in s wales the rawns formation which follows contains 120 m of conglomerates and pebbly sandstones with angular clasts of porphyry tuff quartzite and lithic arenite which do not match with rocks in possible source areas in wales but could have been derived from the lower palaeozoic and precambrian rocks believed to lie at shallow depth to the north of the bristol channel fault zone fault movements along this zone are believed to have generated relatively short lived coarse clastic supply at various times and places around the bristol channel in lower to early mid devonian times in response to end caledonian movements the later production of late namurian to westphalian sands from the bristol channel area was unrelated to these devonian events and represents uplift in response to variscan events in sw england

enhancement of sub daily positioning solutions for surface deformation monitoring at deception volcano south shetland islands antarctica deception island is one of the most visited places in antarctica there are biological geological and archeological features that are major attractions within port foster its horse shoe shaped natural inner bay and two scientific bases that are occupied during austral summers deception island is an active volcano however and needs to be monitored in order to reduce risk to people on the island surface deformation in response to fluid pressure is one of the main volcanic activities to observe automated data acquisition and processing using the global navigation satellite systems allow measurements of surface deformation in near real time nevertheless the positioning repeatability in sub daily solutions is affected by geophysical influences such as ocean tidal loading among others such periodic influences must be accurately modeled to achieve similar repeatability as daily solutions that average them however a single solution each 24 h will average out the deformation suffered during that period and the position update waiting time can be a limitation for near real time purposes throughout the last five austral summer campaigns in deception using simultaneous wireless communications between benchmarks a processing strategy was developed to achieve millimeter level half hourly positioning solutions that have similar repeatability as those given by 24 h solutions for these half hourly solutions a tidal analysis was performed to assess any mismodeling of ocean tide loading and a discrete kalman filter was designed and implemented to enhance the sub daily positioning repeatability with these solutions the volcano dynamic activity resulting in localized surface deformation for the last five austral summer campaigns is addressed although based on only three carefully located benchmarks it is shown that deception has been shortening and subsiding during these last 4 years the method s accuracy in baselines up to a few hundred kilometers assures its applicability to other volcanoes worldwide

past and recent tritium levels in arctic and antarctic polar caps tritium concentration was measured in snow deposited at the grip site central greenland and at the vostok station east antarctica from snow pits covering the period 1980 1990 the objective of the study was to investigate tritium concentrations in polar regions several decades after the bomb peak of the sixties and to put them in the context of available data for environmental tritium in the arctic and the antarctic over the last five decades the tritium content of the samples was measured by mass spectrometry using the helium 3 regrowth method in antarctica the tritium concentrations are in the range 70 110 tu the comparison of the bomb tritium history at different locations show that tritium levels increase moving inland where vapour pressure becomes extremely low and therefore more sensitive to the intrusion of stratospheric air masses highly enriched in tritium although most tritium fallout occurred in the northern hemisphere the tritium levels in central greenland in the 80 s in the range 10 40 tu are significantly lower than at vostok unlike antarctica no such continental effect is observed in greenland due to the higher water vapour content of the air masses as evidenced by the much higher snow accumulation rate whereas tritium fallout in antarctica appears to occur as a result of direct injections of stratospheric tritium during winter arctic fallout are the result of the dominant spring injection of stratospheric air at mid latitude in line with the deposition of other stratospheric tracers

the irish variscides a fold belt developed within a major surge zone an arcuate fold belt characterizes the irish variscides south of the dingle dungarvan line the folds are cross cut by numerous faults which tend to be sinistral in the west and dextral in the east clockwise transection of major fold axes by minor folds and by cleavage has been recorded in the east while anticlockwise transections are common in the west these and other features suggest that north south dextral and sinistral shearing occurred in the east and west respectively this is considered to be a consequence of the morphology of the munster basin which allowed the development of a surge zone in the centre of the fold belt the variscan sole thrust is believed to lie at the base of or within the old red sandstone however to the east thinning of the upper palaeozoic cover sequence forces the sole thrust to cut down laterally stratigraphic section into lower palaeozoic basement in the depocentre the sole thrust surged ahead by propagating along bedding surfaces or possibly a devonian carboniferous extensional detachment beneath the basin while to the east and offshore to the west its propagation was inhibited by the absence of easy decollement horizons within the basement consequently the tip line became strongly arcuate and the thrust developed into a surge zone the sole thrust propagated northwards by stick slip processes much of the deformation within the cover sequence occurred during sticking events particularly fold tightening and accommodation faulting

some comments on two layer extensional models for the evolution of sedimentary basins simple extensional models that involve listric faulting in the brittle upper crust and plastic flow in the lower lithosphere have been shown to account for the subsidence history of various continental sedimentary basins and continental shelves in this paper we present structural evidence that extension in the continental lithosphere during rifting is not uniform we review evidence that the rifting process in major intracratonic rift basins is spasmodic rather than continuous that extension and subsidence within the rift during a tectonic phase is generally accompanied by uplift and erosion of the rift flanks that subcrustal heat input during rifting occurs over an area much broader than the rift proper and that there may be broad regional uplift before and or during rifting to explain the uplift of the flanks during rifting and their postrift subsidence we invoke two mechanisms subcrustal thinning by extension below the flanks and tilted major normal faults in the crust between graben and flanks the uplift and erosion of the flanks due to tilted faults probably do not significantly affect estimates of extension from subsidence analysis but uplift due to both sources can in certain cases be incorrectly attributed to regional uplift or doming we present a simplified analysis of the two layer extensional model for the elementary case in which extension is instantaneous and the crust is thinned by a different amount from the subcrustal lithosphere we provide a simple graphical method of data analysis to obtain the parameters that describe thinning of the crust and lithosphere during extension from the subsidence history application of this method to the central part of the pattani trough in the intracratonic gulf of thailand shows that extension and thinning of the lithosphere of a factor of 2 since late eocene can account for much of the subsidence history and the present day heat flow our analysis suggests that thinning of the crust in this area is 20 greater than thinning of the whole lithosphere assuming that none of the lithosphere is removed from the region of extension during rifting we show by simple geometric examples that a process of nonuniform extension implies that much greater thicknesses of sediment can be deposited in the center of a young basin than in the case of uniform extension of both crust and subcrustal lithosphere such an extensional process produces significant uplift of the flanks of the rift and as a result of erosion of the uplifted areas the effective cross sectional area of the basin can be increased by as much as 10 20 depending on the rate of erosion compared to the area that would have been created by a process of uniform extension finally we show that it may ultimately be possible to compute erosion rates from seismic cross sections of basins

the 1998 1999 seismic series at deception island volcano antarctica abstract during the 1998 1999 antarctic summer the pattern of seismic activity at deception island volcano changed significantly the change was characterized by the occurrence of an intense swarm of volcano tectonic vt earthquakes more than 2000 vt earthquakes with s p times smaller than 4 s were recorded in the period january february 1999 pure volcanic events were also detected especially long period lp events volcanic tremor and some hybrid events seismic monitoring was performed using two short period small aperture arrays among other instruments based on their signal to noise ratios we selected 863 vt earthquakes 350 lp events and tremor episodes and 9 hybrid events for analysis we estimated apparent slowness and back azimuth for all events using the zero lag cross correlation array technique combining this information with s p times and other indirect evidence we identified two different source regions lp seismicity is located less than 1 1 5 km southwest of the fumarole array site these events are likely to have a hydrothermal origin vt earthquakes and hybrid events are located at depths of 0 3 10 km in an area under the bay of deception island the area extends from the fumarole array to the northeast with epicentral distances that range from 0 5 to 12 km most hypocenters are clustered in a small volume of around 8 km3 the sources of the lp seismicity and the vt earthquakes are spatially distinct which indicates that they are not produced by the same mechanisms moment magnitude analyses of the vt earthquakes provide an average magnitude of 0 5 and very low average stress drop around 1 bar a study of first motion of the p waves suggests that the events in this small source region should have a variety of source mechanisms this is supported by the existence of families of events with the same waveforms the occurrence of repeating fracture processes with low stress drop and small fault dimensions can be explained by the lubrication of pre existing zones of weakness by pressurized fluids the most probable hypothesis that explains the generation of this seismic series at deception island is a seismic series caused by the stress generated by the uplift of the source area due to a magmatic injection in depth we favor this hypothesis since it is compatible with the majority of the characteristics of the seismicity and explains the spatial and temporal behavior of the series

lispb delta a lithospheric seismic profile in britain analysis and interpretation of the wales and southern england section abstract the lithospheric seismic profile in britain lispb shot in 1974 included a 310 km profile lispb delta crossing the palaeozoic welsh basin the western extent of the midland microcraton and the cornubian zone of southern england this first comprehensive analysis of these data has produced a sub horizontally layered seismic and associated gravity model that correlates well with surface geology a north south decrease in crustal velocity and density corresponds to the change from avalonian crust into the rheno hercynian zone at the south end of the profile high velocities and densities in the lowest crustal layer beneath north wales are proposed to result from cenozoic and possibly ordovician igneous intrusive rocks the former derived from an upwelling plume associated with the opening of the north atlantic examination of the load distribution throughout the model shows that it is strongly correlated with the earthquake distribution along lispb delta earthquake focal depth also correlates with heat flow a simple heat flow profile has been derived and the seismic velocity model used to constrain crustal heat production values a long wavelength excursion from published data can be explained in terms of an increase in mantle heat flow resulting from a previously identified deep thermal anomaly beneath the irish sea supplementary material normalised synthetic and true amplitude seismic record sections including picks and modelled phases for shots sp04 sp05 sps1 sps2 are available at http www geolsoc org uk sup18450

mesozoic reactivation of variscan thrusting in the bristol channel area uk new seismic reflection data from the bristol channel area provide direct evidence of a major variscan thrust in the palaeozoic basement beneath the mesozoic bristol channel syncline the thrust has an average southerly dip of about 25 and it rises into the major fault the central bristol channel fault zone cbcfz at the northern margin of the bristol channel syncline the cbcfz is attributed to reactivation in extension of the variscan thrust probably during the early cretaceous there is no evidence for major synsedimentary movement on the cbcfz and the bristol channel syncline does not represent a rollover structure section restoration suggests that the cbcfz has cut up through a previously tilted sequence of triassic and jurassic strata pervasive nnw sse cross faults are interpreted as original variscan transfer faults that have been reactivated in the mesozoic and tertiary

beryllium 10 transport to antarctica results from seasonally resolved observations and modeling 1 cosmogenic 10be measured in polar ice cores has important application in the reconstruction of past solar activity however the processes controlling its atmospheric transport and deposition to the ice sheets are not fully understood here we use the seasonal changes in 10be concentrations in a 10 year monthly resolved ice core record from the law dome site east antarctica in conjunction with echam5 ham general circulation model gcm simulations of 10be and 7be deposition as tools to examine this problem maximum 10be concentrations are observed in the ice core during the austral late summer to early autumn summer autumn while minimum concentrations are observed during the austral winter the gcm simulations corroborated by earlier observations of 10be 7be ratios in antarctica from the georg von neumayer air sampling station suggest that the 10be concentration maximum is linked to direct input of stratospheric 10be from the antarctic stratosphere to the lower levels of the antarctic troposphere during the austral summer autumn this result contrasts with the modeled transport of 10be to greenland where the seasonal maximum in stratospheric input is seen in the late winter to spring synchronous with the timing of the seasonal maximum in midlatitude stratosphere to troposphere exchange our results suggest that a different combination of processes is responsible for the transport of 10be to the antarctic and greenland ice sheets

triassic jurassic development of the st george s channel basin offshore wales uk abstract isopach maps and backstripped tectonic subsidence plots from the triassic jurassic of the st george s channel basin reveal significant departures from current models of extensional basin development i rifting was highly protracted with discrete increments of crustal extension spanning ca 120 my ii substantial syn kinematic sediment on the footwalls of major faults records pure shear sub seismic scale deformation to have been important during regional triassic extension forward modelling of depth converted seismic interpretations is used to test the notion of combined pure and simple shear and to quantify the distribution of crustal extension between large and sub seismic scale faults the models indicate that triassic subsidence was generated by ca 2 5 km extension on major faults and 10 km extension by sub seismic scale faulting in fault bounded compartments jurassic extension was dominated by large scale faults whereas in the areas of overlap between major fault segments jurassic extension was taken up chiefly by sub seismic scale faulting comparison of measured vitrinite reflectance vr and vr modelled from heatflow history yielded by the forward models supports this scheme of episodic pure shear dominated extension this research highlights the inherent difficulty in using seismic interpretation in isolation from quantitative subsidence and or thermal history data to identify syn and post kinematic sedimentary sequences furthermore it provides an opportunity to more fully reconstruct mesozoic basin development in the west of uk area which in the cheshire central and east irish sea basins is largely precluded by erosion of post triassic strata

continuous gps measurements of crustal deformation in garhwal kumaun himalaya we report gps measurements of crustal deformation from five continuous sites in the garhwal kumaun himalaya the motion at these sites confirms strain accumulation on the main himalayan thrust mht under the outer and lesser himalaya with a slip deficit rate of 18 mm year over a width of 100 km apart from secular plate motion these sites also exhibit seasonal variations we model these seasonal variations using the global models of atmospheric and hydrological loads the influence of these loads is maximum in the vertical component which decreases in the north and then in the east component all the four sites in the himalayan region and a site at delhi show consistency between the observed seasonal variations with that predicted by the model however the annual variations in the horizontal component of displacement time series at bdri badrinath gps site are not consistent with the predictions which could be due to local site conditions

volcanic hazard on deception island south shetland islands antarctica abstract deception island is the most active volcano in the south shetland islands and has been the scene of more than twenty identified eruptions over the past two centuries in this contribution we present the first comprehensive long term volcanic hazard assessment for this volcanic island the research is based on the use of probabilistic methods and statistical techniques to estimate volcanic susceptibility eruption recurrence and the most likely future eruptive scenarios we perform a statistical analysis of the time series of past eruptions and the spatial extent of their products including lava flows fallout pyroclastic density currents and lahars the bayesian event tree statistical method hasset is applied to calculate eruption recurrence while the qvast tool is used in an analysis of past activity to calculate the possibility that new vents will open volcanic susceptibility on the basis of these calculations we identify a number of significant scenarios using the gis based voris 2 0 1 and laharz software and evaluate the potential extent of the main volcanic hazards to be expected on the island this study represents a step forward in the evaluation of volcanic hazard on deception island and the results obtained are potentially useful for long term emergency planning

seismological evidence of an active footwall shortcut thrust in the northern itoigawa shizuoka tectonic line derived by the aftershock sequence of the 2014 m 6 7 northern nagano earthquake abstract a destructive m 6 7 earthquake struck northern nagano prefecture on november 22 2014 the main shock occurred on the kamishiro fault segment of the northern itoigawa shizuoka tectonic line istl we used data recorded at 41 stations of the local seismographic network in order to locate 2118 earthquakes that occurred between november 18 and november 30 2014 to estimate hypocenters we assigned low vp models to stations within the northern fossa magna nfm basin thus accounting for large lateral crustal heterogeneities across the kamishiro fault in order to further improve accuracy the final hypocenter locations were recalculated inside a 3d velocity model using the double difference method we used the aftershock activity distribution and focal mechanism solutions of major events in order to estimate the source fault area of the main shock our analysis suggests that the shallow part of the source fault corresponds to the surface trace of the kamishiro fault and dips 30 45 se while the deeper part of the source fault corresponds to the downdip portion of the otari nakayama fault a high angle fault dipping 50 65 se that formed during the opening of the nfm basin in the miocene along its surface trace the otari nakayama fault has been inactive during the late quaternary we verified the validity of our model by calculating surface deformation using a simple homogeneous elastic half space model and comparing it to observed surface deformation from satellite interferometry assuming large coseismic slip in the areas of low seismicity and small coseismic slip in the areas of high seismicity shallowing of the source fault from 50 65 to 30 45 in the upper 4 km in the areas where both surface fault traces are visible is a result of footwall shortcut thrusting by the kamishiro fault off the otari nakayama fault

pressure sources versus surface loads analyzing volcano deformation signal composition with an application to hekla volcano iceland the load of lava emplaced over periods of decades to centuries induces a gradual viscous response of the earth resulting in measurable deformation this effect should be considered in source model inversions for volcanic areas with large lava production and flow emplacement in small centralized regions if deformation data remain uncorrected constructive load and pressure source interference may result in an overestimate of depth and volume of a magma reservoir whereas destructive signal interference may cause these values to be underestimated in both cases the source geometry preference could be biased the ratio of horizontal and vertical displacements aids the identification of composite signals we provide a method to quantify and remove the lava load deformation signals using deformation at hekla volcano iceland as an example

the development of the deception island volcano caldera under control of the bransfield basin sinistral strike slip tectonic regime nw antarctica

fan delta sedimentation in the silurian coralliferous formation of sw wales implications for the structure of the southern margin of the welsh basin the uppermost llandovery to lower wenlock coralliferous group in sw pembrokeshire is here redefined as a single formation with two members the coralliferous formation is approximately 150 m thick and comprises a basal unit of granule to pebble grade rudite beds the renney slip member overlain by interbedded mudstones and fine sandstones of the deadman s bay member the renney slip member lies unconformably above the skomer volcanic group and includes 12 4 m of coarse grained granule and pebble rich rudites with beds up to 0 94 m thick three lithofacies are recognized within this unit coarse granule rich rudite beds are interpreted as a variety of mass flow deposits some of which have been reworked in a marine environment thick sandstones with planar and ripple lamination are shoreface to offshore transition zone deposits silty mudstones interbedded with very fine grained sandstones represent marine offshore deposits formed largely below mean storm wave base these facies associations and abundant bioturbation indicate an environment with a strong marine influence and a proximal source of coarse grained sediment the renney slip member is reinterpreted in the context of a fan delta depositional model at least seven cycles of deposition are recognized each showing an upwards fining pattern representing deposition from fan delta shoreface transition zone to open marine environments these patterns of deposition are attributed to localized tectonic movements causing variations in relative sea level at the time the renney slip member was deposited the southern welsh basin margin is interpreted as a fault block extensional margin with the landmass of pretannia to the south though fan delta deposition took place southwards against the uplifted footwall of the wenall fault the basin margin lay to the south of the ritec fault

structural controls on palaeozoic basin evolution and inversion in southwest wales the tectonic evolution of sw dyfed is presented in terms of a model of basin evolution and subsequent destruction by reactivation of the basin bounding faults in contractional mode movements along long lived palaeozoic extensional faults were reversed during variscan compression with the pre existing faults accommodating the contraction in addition to the development of a thin skinned thrust and fold system basin analysis of the pre variscan extensional system uses sedimentological and stratigraphical evidence to constrain the timing of movements of the basin bounding faults thus allowing division of the stratigraphy into depositional megasequences related to these extensional movements field examples on all scales illustrate active extension during the palaeozoic structural cross sections through sw dyfed demonstrate the interrelationship of the extensional and contractional deformations with palinspastic restorations of the cross sections illustrating the complexity of the pre variscan template

sedimentology of a devonian fault bounded braidplain and lacustrine fill in the lower part of the skrinkle sandstones dyfed wales the upper devonian to lower carboniferous skrinkle sandstones of the pembroke peninsula are predominantly continental deposits from the post caledonian synrift succession at the southern margin of the upper palaeozoic welsh landmass the lower part of the sandstones record deposition in the 30 10 km tenby angle fault block from which a 6 to 68 m thick interval is described and interpreted as a lacustrine deposit succeeded by a high energy sandy braidplain succession the lacustrine deposit is dominated by red mudstones and ripple cross laminated sandstones interbedded quartzose sandstones form a coarsening upward sequence from the red mudstones in the basin centre suggesting a deltaic origin and a smooth fronted braidplain delta model is proposed the sequence introduces the braidplain succession composed of groups of horizontal low angle laminated and trough cross bedded sandstones these are compared with recent ephemeral stream and sheetflood sediments and their characteristics used to depict a system of mutually erosive sheetflood and channel bodies the latter produced during the rising and falling stages of flood events which alternate to produce a thick multistorey sandstone palaeocurrent data indicate an axial drainage system from the north west running parallel to the main faults of the area this is supported by the maturity and sandy nature of the sediments basin closure towards the south and the postulated bristol channel landmass is inferred

variable pathways residence time and geochemical evolution of seepage beneath the mississippi river levee during the 2011 2015 and 2016 floods abstract seepage beneath artificial levees is a common concern during flooding events risk of levee failure is elevated when piping erodes channels beneath the levee evidenced by the formation of sand boils where transported sediments discharge along the lower mississippi river pathways of floodwater beneath the levee vary with surface geology following deeper paths where the levee overlies fine grained channel fill deposits and shallower higher risk paths where it overlies sand bar deposits shallow organic rich alluvial aquifers are often geochemically stratified into upper oxic and lower anoxic zones raising the possibility of using the geochemical signatures of discharging water from sand boils to differentiate flow pathways a preliminary investigation north of vicksburg ms usa during the 2011 mississippi river flood demonstrated the potential of using geochemistry to identify deep and shallow pathways though the study was limited to cation and trace element analyses sampling during the 2015 and 2016 floods for temperature conductivity redox potential eh dissolved oxygen do major ions trace elements tritium and stable isotope ratios of oxygen hydrogen and strontium facilitated a greater understanding of the nature of flow and geochemical evolution of groundwater in this environment characteristics of deeper flow pathways relative to shallow included 1 lower eh and higher fe and as reflecting anoxic conditions and high fe sediments 2 proportional increases in fe and hco3 indicating reductive dissolution of fe oxyhydroxides and 3 higher ratios of ba ca and sr ca reflecting differences in the elemental composition of minerals with depth tritium results indicate that subsurface flow pathways are dynamic shifting spatially with the rapid changes in hydraulic gradients during and between flooding events estimated residence times of groundwater discharging from sand boils and relief wells ranged from essentially zero discharge of concurrent floodwater up to a quarter century lower strontium isotope ratios 87sr 86sr were observed in the aquifer relative to river water though with no clear variation with flow depth oxygen and hydrogen isotope ratios 18o and 2h show evidence of partial evaporation prior to recharge also with no apparent variation with subsequent flow depth

late yeadonian upper sandstone group incised valley supply and depositional systems in the south wales peripheral foreland basin implications for the evolution of the culm basin and for the silesian hydrocarbon plays of onshore and offshore uk abstract the upper sandstone group of south wales has previously been interpreted as a simple nnw sse trending incised valley that was filled during the late yeadonian namurian g1b data presented in this study indicate a far more complex scenario the group is well developed in the pembrokeshire sub basin but it is absent from the main part of the south wales basin located to the east of the penlan axis the principal source area for sediment flux was the forebulge of the basin located to the north in lower palaeozoic foreland strata variscan flexural uplift of this source area and an accompanying rapid high magnitude fall in sea level produced a very high sediment budget thus during the late yeadonian lowstand of sea level massive amounts of sediment were being generated and transported via an incised valley system across the western part of the south wales peripheral foreland basin the location and orientation of the incised supply system and its related interfluves were controlled by intrabasinal synsedimentary variscan structures many of which were reactivated caledonian extensional faults during the succeeding sea level rise the incised valley was filled initially by fluvio deltaic sands and later by estuarine argillaceous sediments the implications of this combined tectonic sedimentological high resolution sequence stratigraphic model for the evolution of the late namurian crackington formation turbidites of the culm basin are discussed examples of silesian incised valley fill sandstone reservoirs developed in the east midlands oilfield and the southern gas basin are briefly summarised and their spatial and temporal distributions are appraised data generated from these case studies are assessed in terms of their use for the modelling of incised valley fill sequences in foreland basins and other tectonic settings

influence of a transverse basement fault on along strike variations in the geometry of an inverted normal fault case study of the mosha fault central alborz range iran abstract inverted normal faults show variations in structural geometry from footwall shortcut thrusts to hanging wall break back thrusts in the present study we evaluated along strike variations in the geometry of the mosha fault central alborz range iran detailed structural mapping within the taleqan mountains revealed that the mosha fault in the eastern part of the study area is associated with a large basement cored hanging wall anticline thrust over tertiary rocks that occur as a syncline or cut by footwall shortcut thrusts in the western part of the study area however the hanging wall consists of break back thrust sheets of paleozoic mesozoic rocks these thrust sheets occur as a duplex system and have allochthonous masses gravitationally emplaced in the foothills of the taleqan mountains curved fold axial traces and scattered intrusive bodies are observed in the valian valley area where the mosha fault is displaced across a transverse basement fault this basement fault controlled along strike variations in the geometry of the mosha fault during its evolution from a basin bounding fault to an inverted normal fault inversion of the fault in the eastern part of the study area where the fault is relatively steep involved basement rocks in the western part of the study area where the fault is relatively shallowly dipping deformation in the hanging wall is accommodated by thin skinned break back thrust sheets

evidence for hydrothermal venting and sediment volcanism discharged after recent short lived volcanic eruptions at deception island bransfield strait antarctica abstract the results of a combined geophysical and geochemical research programme on deception island an active volcano at 62 43 s 60 57 w in bransfield strait antarctica are presented ultrahigh resolution acoustic data obtained with a topas topographic parameter sonar system and multibeam bathymetry simrad em1000 allow a detailed analysis of submarine vents in port foster the submerged caldera of deception island the data show three different types of seafloor structures low relief mounds high relief mounds wasp nest like and spire like structures we interpret these structures as products of sediment volcanism and seeps caused by heating and boiling of pore fluids in gas charged sediments and related to recent short lived volcanic events possibly those that occurred in 1967 1969 and 1970 in addition subsurface vertical disturbed zones formed by increased amplitude and phase inverse reflectors beneath the mounds suggest the presence of fluidised and brecciated sediments within hydrofracture systems a key finding of this study is that there appears to be a close relationship between the submarine mounds detected by our ultrahigh resolution seismic study geochemical haloes fault pathways and present day thermal anomalies in surface waters we suggest that seafloor hydrofracture systems and subsurface pipes can be re used as fluid migration pathways resulting in hydrothermal seeps and vents on the seafloor possibly up to decades after coeval volcanic eruptions

volcano tectonic dynamics of deception island antarctica 27 years of gps observations 1991 2018 abstract deception island south shetland islands is one of the most active volcanoes in antarctica in the 1988 1989 austral summer after the most recent eruptive process on the island 1967 1970 monitoring of volcanic activity through geophysical and geodetic techniques was resumed by spanish and argentinean scientists in order to monitor the island s tectonic and volcanic behavior a geodetic network was deployed currently this network consists of 15 geodetic benchmarks located around port foster deception s inner bay open to the sea two additional geodetic benchmarks were installed outside deception island to be used as reference benchmarks for the differential positioning strategy since 1991 1992 geodetic ground displacement velocities between the successive austral summer antarctic campaigns have been computed and analyzed the overall geodynamic behavior of deception island within the south shetland islands antarctic peninsula and bransfield basin regional environment has been analyzed from geodetic ground displacements results obtained demonstrate that deception and livingston island have a similar behavior derived from the bransfield basin extension and the phoenix micro plate subsidence processes however deception island is also highly influenced by its volcanic activity deception island s volcanic behavior between 1991 and 2018 is shown by the velocity field strain tensors and pressure source evolution obtained from the ground displacements at the geodetic benchmarks during this time period it is possible to identify different inflation and deflation phases separated by transitional or mixed stages of extension without uplift and compression without subsidence the most representative inflation and deflation periods were analyzed in detail to show how they correlate with high and low seismic activity respectively the transitional or mixed stages seem to be the precursors of the next inflation or deflation phase being the bransfield basin rifting and nw se extension the potential related process finally we have analyzed the processes that occurred prior to the volcanic unrests of 1999 2000 and 2012 2013 in both cases an increase in detected seismic activity and or soil and seawater temperature was observed and a mixed phase of extension without uplift seems to be precursory to the volcanic unrest the correlation between the inflation processes identified by ground displacement of the network geodetic benchmarks the increase in seismicity and the increment of soil and seawater temperature makes these transitional mixed phases potential precursors of deception island s volcanic unrest periods

volcano geodesy recent developments and future challenges abstract ascent of magma through earth s crust is normally associated with among other effects ground deformation and gravity changes geodesy is thus a valuable tool for monitoring and hazards assessment during volcanic unrest and it provides valuable data for exploring the geometry and volume of magma plumbing systems recent decades have seen an explosion in the quality and quantity of volcano geodetic data new datasets some made possible by regional and global scientific initiatives as well as new analysis methods and modeling practices have resulted in important changes to our understanding of the geodetic characteristics of active volcanism and magmatic processes from the scale of individual eruptive vents to global compilations of volcano deformation here we describe some of the recent developments in volcano geodesy both in terms of data and interpretive tools and discuss the role of international initiatives in meeting future challenges for the field

variscan compressional structures within the main productive coal bearing strata of south wales the structure of the main productive coal measures within the anthracite zone in the western part of the south wales coalfield is re examined using data from recently operational opencast coal sites variscan thrusts and or folds and bed parallel shear structures are present within all of the sites studied at east pit unaffected by any large scale zone of disturbance bed parallel shear structures are developed along many of the gently dipping coal seams which form a series of simultaneously active detachments representing a process of easy slip thrusting a ne sw striking fold dominated disturbance at gilfach iago is interpreted to overlie a reactivated basement fault a more complex disturbance zone at ffos las combines both e w trending folds and more variably oriented thrusts which together shorten the coal bearing strata by up to 2 km and this is interpreted to be the major variscan frontal thrust ramp in the extreme west of the coalfield the variscan compressional structures within south wales are not consistent with a simple thin skinned thrust system the strain induced by deep seated variscan thrusts was distributed throughout much of the coal bearing sequence by easy slip deformation rather than being localized along a single regional detachment and additional thrusts present around the northern margin of the coalbasin appear to have formed as isolated autochthonous structures the inherent weakness of coal seams across south wales is attributed to the presence of greatly increased fluid pressures which would have been generated both by the maturing coal and by the influx of fluids along deep seated disturbance zones

crustal structure of deception island volcano from p wave seismic tomography tectonic and volcanic implications 1 deception island 62 59 s 60 41 w is an active volcano located in the bransfield strait between the antarctic peninsula and the south shetland islands the island is composed of rocks that date from 0 75 ma to historical eruptions 1842 1967 1969 and 1970 and nowadays most of its activity is represented by vigorous hydrothermal circulation slight resurgence of the inner bay floor and intense seismicity with frequent volcano tectonic and long period events in january 2005 an extensive seismic survey took place in and around the island to collect high quality data for a high resolution p wave velocity tomography study a total of 95 land and 14 ocean bottom seismometers were deployed and more than 6600 air gun shots were fired as a result of this experiment more than 70 000 travel time data were used to obtain the velocity model which resolves strong p wave velocity contrasts down to 5 km depth the joint interpretation of the vp distribution together with the results of geological geochemical and other geophysical magnetic and gravimetric measurements allows us to map and interpret several volcanic features of the island and surroundings the most striking feature is the low p wave velocity beneath the caldera floor which represents the seismic image of an extensive region of magma beneath a sediment filled basin another low velocity zone to the east of deception island corresponds to seafloor sedimentary deposits while high velocities to the northwest are interpreted as the crystalline basement of the south shetland islands platform in general in the tomographic image we observe ne sw and nw se distributions of velocity contrasts that are compatible with the regional tectonic directions and suggest that the volcanic evolution of deception island is strongly conditioned by the bransfield basin geodynamics

experiments on basin inversion above reactivated domino faults abstract results are presented from scaled sand box experiments which investigate the structural inversion of half graben basins generated by the contractional reactivation of extensional domino fault systems the overburden was deformed above a series of rigid basement fault blocks that were extended in a domino manner the models were constructed from either 1 sand with mica interlayers anisotropic behaviour 2 pure sand isotropic behaviour or 3 a sand clay mixture behaviour with increased competence during the extensional phase of deformation sand or alternating sand mica layers were deposited in teh half grabens associated with individual domino faults to simulate a syn extensional stratigraphic sequence together with a component of overall subsidence after termination of the extensional phase sand layers were added to represent a post rift passive subsidence stratigraphy subsequent contraction of the experimental configuration resulted in progressive reactivation of the domino fault system which was accompanied by back rotation of both the footwall and hanging wall in each of the individual fault blocks this produced null points along the profile section of the fault planes which separated net contraction above from net extension below continued shortening of the system led to further contraction being accommodated along footwall shortcut faults it is suggested that these shortcuts developed in response to 1 the accommodation of space problems generated by increased bed length in the graben acquired during extension and 2 by more efficient low angle fault trajectories in keeping with coulomb failure during horizontal to subhorizontal compression during inversion in the anisotropic model folding in the footwall partially suppressed the initiation of footwall shortcut faults footwall shortcut faulting did not occur in experiments where the dips of the original extensional faults were decreased before the inversion in all inversion experiments the contractional deformation associated with the shortening of the half graben was concentrated in the footwall to each domino basin bounding fault a control experiment in which an undeformed sand pack was deposited above an extended series of basement fault blocks revealed that the early extensional architecture formed in the other experiments had a profound influence on the resultant inversion geometries the results show clear similarities to interpreted examples of natural basin inversion structures associated with reactivated domino fault systems as well as to inferred strike slip induced flower structures

seismovolcanic signals at deception island volcano antarctica wave field analysis and source modeling the seismovolcanic signals associated with the volcanic activity of deception island antarctica recorded during three antarctic summers 1994 1995 1995 1996 and 1996 1997 are analyzed using a dense small aperture 500 m seismic array the visual and spectral classification of the seismic events shows the existence of long period and hybrid isolated seismic events and of low frequency quasi monochromatic and spasmodic continuous tremors all spectra have the highest amplitudes in the frequency band between 1 and 4 hz while hybrids and spasmodic tremors have also significant amplitudes in the high frequency band 4 10 hz the array analysis indicates that almost all the well correlated low frequency signals share similar array parameters slowness and back azimuth and have the same source area close to the array site the polarization analysis shows that phases at high frequency are mostly composed of p waves and those phases dominated by low frequencies can be interpreted as surface waves no clear shear waves are evidenced from the energy evaluation we have found that the reduced displacement values for surface and body waves are confined in a narrow interval volcano tectonic seismicity is located close to the array at a depth shallower than 1 km the wave field properties of the seismovolcanic signals allow us to assume a unique source model a shallow resonating fluid filled crack system at a depth of some hundreds of meters all of the seismic activity is interpreted as the response of a reasonably stable stationary geothermal process the differences observed in the back azimuth between low and high frequencies are a near field effect a few episodes of the degassification process in an open conduit were observed and modeled with a simple organ pipe

δd and δ18o variations of the magmatic system beneath deception island volcano antarctica implications for magma ascent and eruption forecasting abstract geochemistry of volatiles in active volcanoes provides insights into the magmatic processes and evolution at depth such as magma evolution and degassing which can be implemented into volcanic hazards assessment deception island is one of the most active volcanoes in antarctica with more than twenty explosive eruptions documented over the past two centuries hydrogen and oxygen isotopic variations in the volatiles trapped in the deception island rocks glass and melt inclusions in phenocrysts provide essential information on the mechanisms controlling the eruptive history in this volcanic suite thus understanding the petrological and related isotopic variations in the island has the potential to foresee the possible occurrence and its main eruptive features of a future eruption the new isotopic results of this study combined with exhaustive petrologic knowledge reveal in deception island i fast ascent and quenching of most magmas preserving pre eruptive magmatic signal of water contents and isotopic ratios with local modification by rehydration due to glass exposition to seawater and by meteoric and fumarolic waters ii a plumbing system s variable with time and currently dominated by closed system degassing leading to explosive eruptions iii control on the interactions of ascending magmas with the surface waters producing hydrovolcanic activity throughout the two main fault systems in deception island and at different magma stagnation depths these results can be considered in further studies of volcanic monitoring to improve the capability to interpret geophysical data and signals recorded during volcanic unrest episodes and hence forecast volcanic eruptions and related hazards

the stratigraphy and setting of the precambrian rocks of the llangynog inlier dyfed south wales detailed mapping of the precambrian rocks of the llangynog inlier made possible by a series of new exposures has allowed the establishment for the first time of the 1100 m thick succession within the precambrian rocks of the area all boundaries of the precambrian rocks with younger strata in the area are either faults or unconformities some 350 400 m of rhyolitic lavas form the oldest rocks seen in the area they are extensively silicified and devitrified and show little of their original texture although flow banding is visible in some outcrops and the presence of perlitic and snowflake textures imply that originally they were glassy in part these lavas are succeeded by a varied succession dominated by volcaniclastic siltstones showing evidence of shallow water deposition and containing medusoids and trace fossils of ediacaran age interbedded in the sediments are basaltic lavas autobreccias and rare hyaloclastites displaying textural features characteristic of submarine eruption and rhyolitic pumiceous and shardic ash flow tuffs the name coomb volcanic formation is proposed for this succession within which are recognized two members a lower castell cogan rhyolite member succeeded by the coed cochion volcaniclastic member in association are varied intrusions comprising both dolerites and dacites a palaeoenvironmental model built on evidence of petrography palaeontology and sedimentology is that of shallow water to emergent volcanic islands

volcano deformation and eruption forecasting recent advances in global positioning system gps tilt and interferometric synthetic aperture radar insar have greatly increased the availability of volcano deformation data these measurements combined with appropriate source models can be used to estimate magma chamber depth and to provide information on chamber shape and volume change however kinematic models cannot constrain magma chamber volume and provide no predictive

geodetic implications on block formation and geodynamic domains in the south shetland islands antarctic peninsula abstract the south shetland islands archipelago is dynamically complex due to its tectonic surroundings most islands are part of a formerly active volcanic arc although deception penguin and bridgeman islands as well as several submarine volcanoes are characterized by active back arc volcanism geodetic benchmarks were deployed and the movement of the lithosphere to which they were fixed measured to provide geodynamic insight for the south shetland islands bransfield basin and antarctic peninsula area based on surface deformation these benchmarks data add spatial and temporal coverage to previous results the results reveal two different geodynamic patterns each confined to a distinct part of the south shetland islands archipelago the inferred absolute horizontal velocity vectors for the benchmarks in the northeastern part of the archipelago are consistent with the opening of the bransfield basin while benchmark vectors in the southwestern part of the archipelago are similar to those of the benchmarks on the antarctic peninsula in between snow deception and livingston islands represent a transition zone in this area the horizontal velocity vectors relative to the antarctic plate shift northeastwards from n to nw furthermore the south shetland islands benchmarks except for that at gibbs elephant islands indicate subsidence which might be a consequence of the slab roll back at the south shetland trench in contrast the uplift revealed by the antarctic peninsula benchmarks suggests glacial isostatic adjustment after the larson b ice shelf breakup

sandbox model studies of inversion tectonics abstract scaled plane strain sandbox models have been used to simulate basement controlled structural inversion in a sedimentary overburden two basement configurations were tested in the first one reversal of movement along vertical and normal faults that controlled a graben relief induced only a partial recovery of displacement along the pre existing overburden faults the inversion produced new reverse faults in the footwall of the pre existing overburden faults the reactivated normal faults and the new reverse faults defined wedge shaped fault blocks at the edges of the inverted structure in the second configuration the relationship between inversion and tilted fault blocks was tested when a tilting basement block does not move parallel to its bounding fault a compression is induced in the overburden which generates an inverted structure bounded by new reverse faults both experiments show that structural inversion not only reactivates pre existing faults but also generates new faults in the overburden faults related to inversion are the result of horizontal compression either associated with rotation of one of the fault blocks or with vertical uplift of basement blocks

the irish variscides problems perspectives and some solutions a review is presented of interpretations made to date of the irish variscides and the various models of late palaeozoic crustal evolution an examination is then made of the factors controlling variscan strain in ireland including lithological competence basement fabric and basement cover thickness from this the difficulties of recognizing variscan fronts and fold belts are emphasized in order to determine whether all putative variscan strain is indeed variscan in age new time temperature data vitrinite reflectance apatite fission track populations are discussed along with offshore data a case is then presented for recognizing quite distinct episodes of both variscan and post variscan heating and deformation some of the implications for the variscides to the east are briefly examined and the suitability of a regional escape tectonics model is tested

balanced cross section construction from seismic sections in areas of extensional tectonics abstract the application of the technique of balanced section construction initially developed for areas of compressional folding and faulting is reviewed with reference to extensional tectonics a number of examples are discussed where these techniques have been successfully applied in the north sea the interpretation of geoseismic sections is considered to be greatly assisted by careful application of geometrical balance and a consideration of strain even in areas of low crustal extensions the nature of seismic sections however places limitations on the validity of balancing which must be borne in mind with such interpretations and wherever possible the balancing of a geoseismic section should be confirmed by complete depth conversion the rapid testing of the integrity of the geoseismic section by attempting to balance the section at the interpretational phase can eliminate many problems as well as allowing the fullest use to be made of the geophysical information

caldera unrest detected with seawater temperature anomalies at deception island antarctic peninsula increased thermal activity was detected to coincide with the onset of volcano inflation in the seawater filled caldera at deception island this thermal activity was manifested in pulses of high water temperature that coincided with ocean tide cycles the seawater temperature anomalies were detected by a thermometric sensor attached to the tide gauge bottom pressure sensor this was installed where the seawater circulation and the locations of known thermal anomalies fumaroles and thermal springs together favor the detection of water warmed within the caldera detection of the increased thermal activity was also possible because sea ice which covers the entire caldera during the austral winter months insulates the water and thus reduces temperature exchange between seawater and atmosphere in these conditions the water temperature data has been shown to provide significant information about deception volcano activity the detected seawater temperature increase also observed in soil temperature readings suggests rapid and near simultaneous increase in geothermal activity with onset of caldera inflation and an increased number of seismic events observed in the following austral summer

a mountain front model for the variscan deformation of the south wales coalfield access to the considerable geological database of british coal together with seismic evidence of subsurface relationships has enabled the development of a structural model for the south wales coalfield detailed site investigations are used as key examples the simple broad synclinal nature of the coalfield masks a more complex structural system thrusting of variscan age is largely confined to the lower and middle coal measures and throughout the central and northern coalfield is dominantly a forethrust system however along the south crop a major backthrust system is developed which in places penetrates the upper coal measures the south crop shows features analogous with a mountain front and is interpreted as a triangle zone in which pre existing basement faults have facilitated uplift the lack of thrusting within the upper coal measures in contrast to the underlying lower and middle coal measures suggests they have acted as a passive roof to the thrust system geographical variation in the intensity of the deformation can be related to the proximity of and buttressing against the caledonian massif although broadly analogous with current models of foreland basin development and deformation the south wales coalfield demonstrates the importance of pre existing massifs and lineaments in determining the precise evolution of an area

global mapping functions for the atmosphere delay at radio wavelengths i have developed expressions for calculating the ratios mapping functions of the line of sight hydrostatic and wet atmospheric path delays to their corresponding zenith delays at radio wavelengths for elevation angles down to 3 the coefficients of the continued fraction representation of the hydrostatic mapping function depend on the latitude and height above sea level of the observing site and on the day of the year the dependence of the wet mapping function is only on the site latitude by comparing with mapping functions calculated from radiosonde profiles for sites at latitudes between 43 s and 75 n the hydrostatic mapping function is seen to be more accurate than and of comparable precision to mapping functions currently in use which are parameterized in terms of local surface meteorology when the new mapping functions are used in the analysis of geodetic very long baseline interferometry vlbi data the estimated lengths of baselines up to 10 400 km long change by less than 5 mm as the minimum elevation of included data is reduced from 12 to 3 the independence of the new mapping functions from surface meteorology while having comparable accuracy and precision to those that require such input makes them particularly valuable for those situations where surface meteorology data are not available

the global distribution of natural tritium in precipitation simulated with an atmospheric general circulation model and comparison with observations abstract the description of the hydrological cycle in atmospheric general circulation models gcms can be validated using water isotopes as tracers many gcms now simulate the movement of the stable isotopes of water but here we present the first gcm simulations modelling the content of natural tritium in water these simulations were obtained using a version of the lmdz general circulation model enhanced by water isotopes diagnostics lmdz iso to avoid tritium generated by nuclear bomb testing the simulations have been evaluated against a compilation of published tritium datasets dating from before 1950 or measured recently lmdz iso correctly captures the observed tritium enrichment in precipitation as oceanic air moves inland the so called continental effect and the observed north south variations due to the latitudinal dependency of the cosmogenic tritium production rate the seasonal variability linked to the stratospheric intrusions of air masses with higher tritium content into the troposphere is correctly reproduced for antarctica with a maximum in winter lmdz iso reproduces the spring maximum of tritium over europe but underestimates it and produces a peak in winter that is not apparent in the data this implementation of tritium in a gcm promises to provide a better constraint on 1 the intrusions and transport of air masses from the stratosphere and 2 the dynamics of the modelled water cycle the method complements the existing approach of using stable water isotopes

natural tritium deposition over antarctica and estimation of the mean global production rate tritium content was measured in snow deposited in antarctica before the first arrival of artificial tritium 1954 both at dome c 74 39 s and south pole the mean tritium values at the time of precipitation are equal to 32 2 and 26 3 tu at south pole 1939 1942 and dome c 1951 respectively a seasonal pattern of natural tritium fallout identical to the artificial pattern with a winter maximum is observed in the south pole profile the deposition rate of natural tritium is 0 6 and 0 2 tritium atoms cm 2 sec 1 at south pole and dome c respectively its geographical variation over antarctica appears quite similar to that existing for artificial tritium clearly showing that the same mechanisms govern the deposition of natural and artificial tritium in particular tritium injection over polar regions during antarctic winter a mean deposition rate of 0 37 tritium atoms cm 2 sec 1 over antarctica is derived giving an estimated mean global production rate of 0 2 tritium atoms cm 2 sec 1 this strongly suggests that natural tritium results only from cosmic ray production

subsidence analysis of eastern avalonian sequences implications for iapetus closure basin subsidence analysis employing the backstripping method indicates that fundamentally different basin generating mechanisms controlled silurian basin development in northern england and in wales accelerating subsidence with time suggests that the dominant control on basin formation in northern england was flexure of the eastern avalonian lithosphere mid wales however displays dominantly decelerating subsidence suggesting an extensional control the errors involved with the backstripping method particularly concerning lower palaeozoic application have been addressed in conjunction with sedimentological and tectonic data the subsidence patterns for the windermere supergroup indicate deposition in a flexurally loaded foreland basin which migrated southwards with time similar data for the powys supergroup of mid wales imply an extensional control on silurian deposition possibly in a strike slip setting however later poidoli and early devonian welsh sedimentation may represent the onset of foreland basin deposition the new data are consistent with a diachronous closure of the iapetus ocean related to rotational collision of eastern avalonia with laurentia during the early silurian early silurian oblique collision produced transtension in wales subsequent rotation of eastern avalonia produced more orthogonal collision thus continental flexure was felt initially in northern england in late wenlock times followed by migration of the resultant foreland basin to the southeast into wales in early devonian times the versatility of the backstripping method is shown by this application to lower palaeozoic sequences

geomorphology of the post caldera monogenetic volcanoes at deception island antarctica implications for landform recognition and volcanic hazard assessment abstract deception island is one of the most active volcanoes in antarctica with more than 20 monogenetic eruptions during the holocene the latest episodes of 1967 1969 and 1970 have shown that volcanic activity on deception island can become a concern for tourists scientists and military personnel working on or near the island the objective of this work is to identify eruptive processes and the geomorphic evolution of post caldera monogenetic volcanic edifices at deception island by morphometric analyses supported by field observations morphometric analysis has been used since the 1970s to analyse scoria cones but it has rarely been applied to other monogenetic volcanoes such as tuff cones and tuff rings tuff cones and tuff rings represent the most common landforms during deception island s recent geological past with over 70 scattered eruptive vents inside and along the caldera rim these volcanic landforms have been studied based on field observations and later digital elevation model analyses their geometry ranges from 10 to 100 m in height and diameters vary between 300 and 2500 m the morphometric data suggest that tuff cones have a more circular crater than tuff rings with a significant separation between the two landforms using the height hco and basal width wco parameters tuff cones have hco wco ratios with values between 0 04 and 0 16 and outer slopes between 7 and 34 tuff rings have lower hco wco ratios that are between 0 01 and 0 04 and lower outer slopes between 3 and 21 this study shows that basic shape parameters in combination with slope angle analysis can be used to discriminate among different types of monogenetic volcanoes the initial eruptive related morphometric diversity however prevents correlation of eruption ages with morphometric parameters or constructing a relative chronology of the monogenetic eruptions this work provides a better comprehension of the potential evolution of a future eruption and a broader understanding of volcanic hazards on deception island

isotopic and trace element constraints on mixing and melting models of marginal basin volcanism bransfield strait antarctica bransfield strait is a narrow marginal basin separating the south shetland islands from the northern end of the antarctic peninsula quaternary volcanism occurs in the strait as subaerial and submarine volcanoes aligned on the inferred axis of rifting and as two subaerial off axis volcanoes on the northern margin of the strait the bransfield strait lavas are similar to published analyses from other marginal basins ranging from basalts and basaltic andesites to trachytes they exhibit moderate enrichments in alkali and alkaline earth elements relative to high field strength elements that are typical of many back arc basin basalts the seamount basalts have trace element chemistry similar to enriched mid ocean ridge basalts e morb but with variously higher alkali and alkaline earth element concentrations and frequently lower nb low pressure fractional crystallization accounts for most of the compositional variation within individual volcanoes but it does not explain intervolcano differences even though the volcanoes are closely spaced and presently or recently active melting of depleted mantle mixed with 0 5 2 crust or sediment explains the isotopic and trace element variations not accounted for by magma chamber processes the off axis volcanoes are the products of less partial melting than the on axis volcanoes one of the off axis volcanoes also contains more of an enriched component in its source some of the lavas have rb sr too low to account for their 87sr 86sr perhaps due the loss of rb during mantle metasomatism or interaction between slab derived fluids and the mantle source of the basalts strontium neodymium and 207pb 204pb isotopic signatures remained constant during the transition from tertiary island arc volcanism to quaternary marginal basin volcanism but 206pb 204pb increased high cen smn of basalts from some volcanoes requires residual garnet in the source thus the young 15 25 ma at the trench subducted slab is either deeper than 60 km beneath the volcanoes or it has fractured and is no longer a coherent barrier to melts generated below it

the recent seismo volcanic activity at deception island volcano abstract this paper reviews the recent seismic studies carried out at deception island south shetland islands antarctica which was monitored by the argentinean and spanish antarctic programs since 1986 several types of seismic network have been deployed temporarily during each antarctic summer these networks have consisted of a variety of instruments including radio telemetered stations autonomous digital seismic stations broadband seismometers and seismic arrays we have identified two main types of seismic signals generated by the volcano namely pure seismo volcanic signals such as volcanic tremor and long period lp events and volcano tectonic vt earthquakes their temporal distributions are far from homogeneous volcanic tremors and lp events usually occur in seismic swarms lasting from a few hours to some days the number of lp events in these swarms is highly variable from a background level of less than 30 day to a peak activity of about 100 events h the occurrence of vt earthquakes is even more irregular most vt earthquakes at deception island have been recorded during two intense seismic crises in 1992 and 1999 respectively some of these vt earthquakes were large enough to be felt by researchers working on the island analyses of both types of seismic events have allowed us to derive source locations establish seismic source models analyze seismic attenuation calculate the energy and stress drop of the seismic sources and relate the occurrence of seismicity to the volcanic activity pure seismo volcanic signals are modelled as the consequence of hydrothermal interactions between a shallow aquifer and deeper hot materials resulting in the resonance of fluid filled fractures vt earthquakes constitute the brittle response to changes in the distribution of stress in the volcanic edifice the two vt seismic series are probably related to uplift episodes due to deep injections of magma that did not reach the surface this evidence however indicates the high potential for future volcanic eruptions at deception island

intrusion triggering of the 2010 eyjafjallajokull explosive eruption the ash cloud that brought chaos to european air traffic in april this year was the result of emissions from an icelandic volcano that had been intermittently active for about 18 years a combination of detailed space based geodetic measurements and seismic monitoring of the eyjafjallajkull volcano in the run up to the ash producing explosive summit eruption reveals an unusual deformation pattern that may be attributed to its off rift setting with relatively cool subsurface structure and limited magma at shallow depth as to the predictability of such a dramatic reawakening the immediate precursors to the initial eruption of the volcano in 2010 were subtle and difficult to detect but the clear signs of volcanic unrest during the weeks months and years preceding it may provide better clues to the catastrophic explosion

variscan structure of the inner bristol channel uk major variscan structures under the bristol channel are concealed beneath a mesozoic and quaternary cover mapping of reflectors on offshore seismic sections reveals two major wnw ese striking thrusts within the underlying palaeozoic sequence the more southerly with a moderate ssw dip has previously been identified as the bristol channel thrust another thrust the previously undescribed gravel margin thrust has been identified in the eastern part of the inner bristol channel and lies in the footwall of the bristol channel thrust it has a similar strike but steeper dip and extends to anticipated precambrian basement depths the bristol channel and gravel margin thrusts together juxtaposed the contrasting palaeozoic successions of south wales and sw england before mesozoic reactivation reflection packages identified on the offshore seismic sections are tentatively correlated with specific onshore palaeozoic sequences interpretation of the offshore seismic sections in conjunction with geological mapping along the north devon coast shows that the bristol channel and gravel margin thrusts have orientations and geometries typical of several mesoscale thrusts observed and measured at foreland point north devon along strike structural changes beneath the inner bristol channel seen on seismic sections provide evidence additional to earlier refraction and structural studies for the offshore continuation of the nw se trending watchet cothelstone hatch fault and its linkage with the previously described central bristol channel fault zone the bristol channel and gravel margin thrusts are interpreted to be offset from the cannington park thrust in north somerset by a 14 16 km variscan dextral strike slip displacement across the watchet cothelstone hatch fault the bristol channel gravel margin thrust and the cannington park thrust are interpreted as syngenetic structures linked by their lateral ramp the watchet cothelstone hatch fault using all the above information the overall structure of the variscides of the inner bristol channel is re evaluated and a new tectonic model is presented the structures discussed in this paper at a scale portrayed by commercial seismic data and published geological maps may represent merely the tips of linked thrusts that have previously been mapped down to mid crustal depths on birps seismic sections from the south west approaches traverse we show that enough data now exist to resolve outstanding problems of the concealed variscan structure in the inner bristol channel providing local structural detail that can be incorporated into the wider tectonic framework of nw europe

historic hydrovolcanism at deception island antarctica implications for eruption hazards deception island antarctica is the southernmost island of the south shetland archipelago in the south atlantic volcanic activity since the eighteenth century along with the latest volcanic unrest episodes in the twentieth and twenty first centuries demonstrates that the volcanic system is still active and that future eruptions are likely despite its remote location the south shetland islands are an important touristic destination during the austral summer in addition they host several research stations and three summer field camps deception island is characterised by a quaternary caldera system with a post caldera succession and is considered to be part of an active dispersed monogenetic volcanic field historical post caldera volcanism on deception island involves monogenetic small volume vei 2 3 eruptions such forming cones and various types of hydrovolcanic edifices the scientific stations on the island were destroyed or severely damaged during the eruptions in 1967 1969 and 1970 mainly due to explosive activity triggered by the interaction of rising or erupting magma with surface water shallow groundwater and ice we conducted a detailed revision field petrology and geochemistry of the historical hydrovolcanic post caldera eruptions of deception island with the aim to understand the dynamics of magma water interaction as well as characterise the most likely eruptive scenarios from future eruptions we specifically focused on the crimson hill estimated age between 1825 and 1829 and kroner lake estimated age between 1829 and 1912 eruptions and 1967 1969 and 1970 events by describing the eruption mechanisms related to the island s hydrovolcanic activity data suggest that the main hazards posed by volcanism on the island are due to fallout ballistic blocks and bombs and subordinate dilute pdcs in addition deception island can be divided into five areas of expected activity due to magma water interaction providing additional data for correct hazard assessment on the island

data assimilation strategies for volcano geodesy abstract ground deformation observed using near real time geodetic methods such as insar and gps can provide critical information about the evolution of a magma chamber prior to volcanic eruption rapid advancement in numerical modeling capabilities has resulted in a number of finite element models targeted at better understanding the connection between surface uplift associated with magma chamber pressurization and the potential for volcanic eruption robust model data fusion techniques are necessary to take full advantage of the numerical models and the volcano monitoring observations currently available in this study we develop a 3d data assimilation framework using the ensemble kalman filter enkf approach in order to combine geodetic observations of surface deformation with geodynamic models to investigate volcanic unrest the enkf sequential assimilation method utilizes disparate data sets as they become available to update geodynamic models of magma reservoir evolution while the enkf has been widely applied in hydrologic and climate modeling the adaptation for volcano monitoring is in its initial stages as such our investigation focuses on conducting a series of sensitivity tests to optimize the enkf for volcano applications and on developing specific strategies for assimilation of geodetic data our numerical experiments illustrate that the enkf is able to adapt well to the spatial limitations posed by gps data and the temporal limitations of insar and that specific strategies can be adopted to enhance enkf performance to improve model forecasts specifically our numerical experiments indicate that 1 incorporating additional iterations of the enkf analysis step is more efficient than increasing the number of ensemble members 2 the accuracy of the enkf results are not affected by initial parameter assumptions 3 gps observations near the center of uplift improve the quality of model forecasts 4 occasionally shifting continuous gps stations to provide variability in the locations of observations results in better model predictions than utilizing fixed locations when the number of available instruments is limited 5 spotty insar data coverage on the flanks of a volcano due to topographic shadows and or atmospheric interference does not adversely impact the effectiveness of enkf if the available coverage is 50 and 6 snow or glacial obstruction in the center of uplift can adversely impact enkf forecasts by utilizing these strategies we conclude that the enkf is an effective sequential model data fusion technique for assimilating multiple geodetic observations to forecast volcanic activity at restless volcanoes

chemical and isotopic snow variability in east antarctica along the 2001 02 itase traverse as part of the international trans antarctic scientific expedition itase project a traverse was carried out from november 2001 to january 2002 through terre adelie george v land oates land and northern victoria land for a total length of about 1875 km the research goal is to determine the latitudinal and longitudinal variability of physical chemical and isotopic parameters along three transects one west east transect we following the 2150 m contour line about 400 km inland of the adelie george v and oates coasts and two north south transects inland terre adelie and oates coast talos dome victoria land the intersection between the we and oates coast victoria land transects is in the talos dome area along the traverse eight 2 m deep snow pits were dug and sampled with a 2 5 cm depth resolution for spatial variability 1 m deep integrated samples were collected every 5 km 363 sampling sites in the snow pit stratigraphy pronounced annual cycles with summer maxima were observed for nssso4 2 msa no3 and h2o2 the seasonality of these chemical trace species was used in combination with stable isotope stratigraphy to derive reliable and temporally representative snow accumulation rates the study of chemical isotopic and accumulation rate variability allowed the identification of a distribution pattern which is controlled not only by altitude and distance from the sea but also by the complex circulation of air masses in the study area in particular although the talos dome area is almost equidistant from the southern ocean and the ross sea local atmospheric circulation is such that the area is strongly affected only by the ross sea moreover we observed a decrease in concentration of aerosol components in the central portion of the we transect and in the southern portion of the talos dome transect this decrease was linked to the higher stability of atmospheric pressure due to the channelling of katabatic winds

3d mechanical stratigraphy of a deformed multi layer linking sedimentary architecture and strain partitioning abstract stratigraphic influence on structural style and strain distribution in deformed sedimentary sequences is well established in models of 2d mechanical stratigraphy in this study we attempt to refine existing models of stratigraphic structure interaction by examining outcrop scale 3d variations in sedimentary architecture and the effects on subsequent deformation at monkstone point pembrokeshire sw wales digital mapping and virtual scanline data from a high resolution virtual outcrop have been combined with field observations sedimentary logs and thin section analysis results show that significant variation in strain partitioning is controlled by changes at a scale of tens of metres in sedimentary architecture within upper carboniferous fluvio deltaic deposits coupled vs uncoupled deformation of the sequence is defined by the composition and lateral continuity of mechanical units and unit interfaces where the sedimentary sequence is characterized by gradational changes in composition and grain size we find that deformation structures are best characterized by patterns of distributed strain in contrast distinct compositional changes vertically and in laterally equivalent deposits results in highly partitioned deformation and strain the mechanical stratigraphy of the study area is inherently 3d in nature due to lateral and vertical compositional variability consideration should be given to 3d variations in mechanical stratigraphy such as those outlined here when predicting subsurface deformation in multi layers

deep structure of the vale of glamorgan south wales uk the deep structure of the vale of glamorgan is investigated using recently acquired seismic data reflection sections from a commercial seismic survey in the vale enable the carboniferous limestone old red sandstone and silurian sequences to be mapped in the subsurface the old red sandstone sequence thins westwards under the southern part of the vale and in the southwest corner of the vale the base of the old red sandstone is interpreted to overstep across the underlying silurian sequence in an analogous manner to its regional overstep in west wales the precambrian basement surface is not clearly represented on the sections but may coincide with the base of a reflective sequence observed in places along one of the reflection lines basement depth estimates from the reflection sections are compared with estimates derived from a new time term analysis of data from long seismic refraction lines basement depths remain uncertain to 1 2 km but appear to be greater under the central part of the vale than under the western part and along the south coastal zone a linked system of variscan forethrusts is traced to outcrop in the core of the cowbridge anticline but none involves major displacement the ty9n y nant moel gilau fault system of the south wales coalfield is shown to be a component of the linked fault system and its current net extension is attributed to mesozoic reactivation of a variscan thrust involving only limited displacement the individual thrusts appear to connect to a basal thrust that may extend northwards into or under the south wales coalfield the amount of displacement along the basal thrust cannot be determined reliably but it may exceed 10 km and involve large scale repetition of palaeozoic sequences under the vale

cenozoic tectonic extension and inversion of the jizhong basin hebei northern china abstract seismic reflection profiles have revealed three major phases of tectonic extension in the jizhong basin during tertiary time the basement faults characterized by listric planar rotational normal faults controlled the development of the sedimentary basin which migrated progressively eastward inversion structures including partially reactivated normal faults a hangingwall back thrust and newly developed reverse faults and folds have involved all sedimentary sequences identifiable in the seismic section probably indicating quaternary tectonic inversion this inversion was probably related to the e w directed shortening in this part of china induced by the overall india eurasia collision

kinematics and segmentation of the south shetland islands bransfield basin system northern antarctic peninsula 1 new gps measurements demonstrate tectonic segmentation of the south shetland islands platform regarded as a microplate separating the antarctic peninsula from the oceanic portion of the antarctic plate king george greenwich and livingston islands on the central and largest segment are separating from the antarctic peninsula at 7 9 mm a moving nnw roughly perpendicular to the continental margin smith and low islands on the small southwestern segment are moving in the same direction but at 2 2 3 0 mm a the elephant island subgroup in the northeast moves at 7 mm a relative to the peninsula like the central group but toward the wnw this implies that it is presently coupled to the scotia plate on the northern side of the south scotia ridge transform boundary thus the uplift of these northeasternmost islands may be caused by scotia antarctic plate convergence rather than by subduction of thickened oceanic crust