the effect of earth rheology and ice sheet size on fault slip and magnitude of postglacial earthquakes abstract moderate past and present day seismicity is observed in formerly deglaciated regions of north america and europe an understanding of the occurrence of these earthquakes is important for estimating the seismic risk within these areas as well as areas affected by recent ice sheet melting in particular greenland and antarctica we have developed a new finite element approach that allows us to estimate the fault throw for areas once covered by a continental ice sheet the simulation is initialized by loading a two dimensional earth model with an ice sheet the model incorporates a stress field consisting of rebound horizontal background and vertical stresses as well as a fault that can accommodate slip the sensitivity of fault throw and activation time is tested with respect to lithospheric and crustal thickness viscosity structure of upper and lower mantle and ice sheet thickness and width as well as fault location and angle single event seismic displacements of up to 18 5 m are obtained approximately equivalent to an earthquake with a moment magnitude of 8 5 the thickness of the crust and lithosphere are major parameters affecting the total magnitude of fault slip whereas the size of the ice sheet primarily affects the activation time most faults start to move close to the end of deglaciation and movement typically stops for our simulations after one thrusting reverse earthquake however in our simulations faults with a dip of 60 also show several fault movements before and after the end of deglaciation

crustal deformation associated with glacial fluctuations in the eastern chugach mountains alaska the changes of the solid earth in south central alaska in response to two major glacial fluctuations on different temporal and spatial scales have been estimated and we evaluated their influence on the stress state and ongoing tectonic deformation of the region during the recent 1993 1995 bering glacier surge a large transfer of ice from the bagley ice field to the bering glacier terminus region occurred we estimated the elastic displacement of the solid earth due to ice mass redistribution from global positioning system gps measurements at sites near the surging glacier we can account for these displacements by transfer of an ice volume of about 14 km3 from the surge reservoir area to the terminus region we examined the background seismicity ml 2 5 before during and after the surge we found that the occurrence of small earthquakes ml 4 0 in the surge reservoir region increased during the surge time interval possibly in response to a decrease in ice mass this suggests that a small decrease in the vertical stress 3 could be enough to modulate the occurrence of small shallow earthquakes in this dominantly thrust fault setting during this century the southern alaska coastal glaciers have been undergoing an overall decrease in volume based on our compilation of changes in the extent and thickness of the coastal glaciers between the malaspina and bering we calculated surface displacements due to the earth s viscoelastic response to annual thinning and to the cumulative retreat over the last 100 years the uplift of the region due to an average annual thinning rate of 1 6 m yr in the ablation region is 1 12 mm yr for our reference model with a viscosity of 5 1019 pa s for depths between 40 and 200 km the total viscoelastic response due to the retreat over the last century may be as much as a couple of meters within the coastal ablation zone near icy bay the maximum decrease in v between 0 and 10 km was 1 0 mpa which is significant in relation to the stress drops in recent earthquakes 2 to 10 mpa but small in relation to the estimated tectonic stress magnitude therefore the occurrence of an earthquake such as the st elias 1979 ms 7 2 may have been advanced in time however most of the ongoing stress accumulation would be primarily due to tectonic forces

sedimentation in a humid interior extensional basin the cenozoic li basin northern thailand facies distributions in extensional basins are controlled by a combination of factors including local and regional tectonics climate hinterland characteristics and base level changes during the mid cenozoic northern thailand was a region in which active basin formation was occurring as a result of regional extension related to major strike slip faults it was also a time when the climate was relatively humid the li basin is one of about 40 cenozoic basins in northern thailand that have a fill of continental facies and it is also one of a number of basins that contain economic coal deposits analysis of the geographical and temporal distribution of facies in the li basin indicates that it had internal drainage fed by rivers that supplied water and sediment to extensive floodplain and lake environments variations in the sediment supply were an important control on the relative development of fluvial channel and muddy overbank facies during periods of high clastic input and peat swamp and lacustrine facies when clastic input was lower changes in palaeosol type and the occurrence of peat deposits indicate that there was a trend towards drier conditions through the period of deposition of the available sections late oligocene to miocene the li basin succession provides an example of a small 500 km 2 extensional basin formed in a humid climate with interior drainage and periods of low clastic sediment supply these conditions resulted in an association of facies deposited in permanent lakes peat swamps wet and dry floodplains fluvial channels and local alluvial fans the relationships between depositional facies and tectonic climatic and sediment supply controls established in this case study may be applicable to other rift and transtensional basins

a weathering intensity index for the australian continent using airborne gamma ray spectrometry and digital terrain analysis abstract weathering intensity largely controls the degree to which primary minerals are altered to secondary components including clay minerals and oxides as weathering intensity increases there are changes in the hydrological geochemical and geophysical characteristics of the regolith thus once calibrated weathering intensity can be used to predict a range of regolith properties a weathering intensity index wii over the australian continent has been developed at a 100 m resolution using regression models based on airborne gamma ray spectrometry imagery and the shuttle radar topography mission srtm elevation data airborne gamma ray spectrometry measures the concentration of three radioelements potassium k thorium th and uranium u at the earth s surface the total gamma ray flux dose is also calculated based on the weighted additions of the three radioelements regolith accounts for over 85 of the australian land area and has a major influence in determining the composition of surface materials and in controlling hydrological and geomorphological processes the weathering intensity prediction is based on the integration of two regression models the first uses relief over landscapes with low gamma ray emissions and the second incorporates radioelement distributions and relief the application of a stepwise forward multiple regression for the second model generated a weathering intensity index equation of wii 6 751 0 851 k 1 319 relief 2 682 th k 2 590 dose the wii has been developed for erosional landscapes but also has the potential to inform on deposition processes and materials the wii correlates well with site based geochemical indices and existing regolith mapping interpretation of the wii from regional to local scales and its application in providing more reliable and spatially explicit information on regolith properties are described

geochemical and petrographical characteristics of low rank balingian coal from sarawak malaysia its implications on depositional conditions and thermal maturity abstract geochemical and coal petrographical analyses were undertaken on low rank upper pliocene balingian coal from sarawak malaysia in an attempt to reconstruct the conditions during peat accumulation and the subsequent coalification processes chemically the coal in this study is characterised by high moisture low ash yield and low sulphur content the low ash yield and low sulphur content together with the lack of epiclastic partings clearly indicate that it was deposited in ombrotrophic raised bogs the coal was plotted in the type iii terrigenous kerogen zone of the van krevelen diagram with h c value below 0 9 this shows that the coal was derived from plant materials of terrigenous origin and is still immature for petroleum generation the petrographical study reveals nonetheless the expulsion of early generated hydrocarbons from the disintegration of suberinite and also from phlobaphinite and cutinite petrographically the coal is dominated by huminite with low to moderate amounts of liptinite and low amounts of inertinite pointing to predominantly anaerobic deposition conditions in the paleomires with limited thermal and oxidative tissue destruction most of the studied samples are characterised by low tpi and high gi values and are plotted on the marsh field of the diessel s diagram or it could also originate from decomposed wood in forested swamps nevertheless coals originating from both these sources usually generate high ash yield which is not the case for the studied coal this shows that the interpretation as suggested by the diessel s diagram is not valid for the studied coal the coal has a mean random huminite reflectance between 0 26 and 0 35 suggesting a lignite coal rank for the coal nevertheless geochemical classification based on total moisture and calorific value suggests a subbituminous c rank

activity along the osning thrust in central europe during the lateglacial ice sheet and lithosphere interactions abstract the osning thrust is one of the major fault systems in central europe with a length of approximately 115 km it underwent a polyphase tectonic evolution in the mesozoic that ranged from extensional movements in the jurassic to reverse faulting and thrusting during inversion in the late cretaceous a series of complex metre scale faults and related fold structures are developed within the upper pleistocene alluvial aeolian complex of the upper senne 1 km away from the thrust the faults dip towards the north and show offsets in a range of several decimetres growth strata indicate a two fold evolution of the structures the faults began as normal faults and were later transformed into reverse faults which resulted in the formation of small scale inversion structures with a typical harpoon shape glaciotectonics can be ruled out as the driving mechanism for these structures because new optically stimulated luminescence osl ages imply that the sedimentary succession was deposited during the late pleistocene between 29 3 2 9 ka and 13 1 1 5 ka at which time the ice margin was much further to the northeast we believe the inversion structures were caused by movement on the osning thrust due to generation of a forebulge of the late pleistocene weichselian ice sheet this led to normal faulting as a consequence of extension in the forebulge area during glaciation the osl ages for the normal fault related growth strata are in a range of 16 13 ka later reverse movements occurred during deglaciation due to the n s directed compressional stress field in northern germany numerical simulations of the deglaciation seismicity point to seismic events with a thrust mechanism in the study area between 15 5 and 12 3 ka bp although normal faulting is also possible in this time period numerous soft sediment deformation structures imply that movement on the osning thrust caused earthquakes with a significant magnitude in the autumn of 1612 an earthquake took place in this area it is very likely that this event is related to background seismicity on this fault although movement due to the influence of the ongoing glacial rebound in fennoscandia is also possible

organic control on shoreface stacking patterns bogged down in the mire in ever wet climates raised mires that are elevated several metres above flood levels can cover significant portions of coastal plains because peat accumulation may keep pace with moderate rates of base level rise the development of raised mires may reduced the areal extent of marine transgressions thick low ash coals are present immediately landward of many vertically stacked shoreface parasequences in cretaceous state of the western interior of north america we suggest that these coals formed in raised mires that stabilized shorelines for long periods of time in such settings the rate of sediment supply including peat accumulation to the coastal environment is partly a function of the rate of change in base level

jura cretaceous oxfordian to cenomanian stratigraphy of the north central bowser basin northern british columbia three new formations of late jurassic and early to mid cretaceous age are defined for a 2000 m thick section of jura cretaceous rocks exposed in the north central bowser basin the currier formation oxfordian to kimmeridgian or tithonian consists of 350 600 m of interbedded shales siltstones sandstones coals and carbonates the mcevoy formation barremian to as young as albian consists of 400 800 m of siltstones and shales with minor sandstones thin coals limestones and conglomerates the devils claw formation in part mid albian to cenomanian consists of 300 600 m of strata characterized by thick pebble and cobble conglomerates with associated coarse sandstones and minor siltstones and shales two successive coarsening upward sequences are identified in the study area the first begins with middle jurassic marine shales of the jackson unit grading upwards to coarser upper jurassic facies of the currier formation the currier formation is conformably or unconformably overlain by siltstones and

land use change and erosional history in a lake catchment system on the canadian prairies abstract the introduction of agriculture in the late 1800s and early 1900s brought about many changes in the natural prairie landscape of western canada the objective of this research project is to evaluate landscape response to land use change by relating observed changes in the sedimentary record of a lake drainage basin to documented land use change that has occurred since the onset of settlement a 52 cm lake sediment core was sectioned into 1 cm layers the sediment was separated into allogenic and authigenic fractions using a wet chemical extraction technique close interval 210pb dating enabled the calculation of sediment and elemental influx rates prior to european settlement erosion rates were low

investigation of coupling between surface processes and induced flow in the lower continental crust as a cause of intraplate seismicity many studies have highlighted the role of coupling between surface processes and flow in the lower continental crust in deforming the crust and creating topographic relief over quaternary timescales on the basis of the rheological knowledge gained it is suggested that intraplate seismicity can also be caused by coupling between surface processes and flow in the lower continental crust this view is shown to be a natural consequence of the modern idea that isostatic equilibrium is maintained by flow in the weak lower crust in response to erosion and sedimentation it is supported by a general correlation between the vigour of surface processes and rates of intraplate seismicity and by instances of seasonal seismicity that correlates with seasonal climate human interference in the environment can affect surface loading for instance deforestation for agriculture or urban development can cause increased erosion rates global warming is expected to cause increased storminess and thus increased erosion rates and or global sea level rise the possibility of increased rates of seismicity resulting from these processes should thus be considered in future hazard assessment copyright 2006 john wiley sons ltd

modelling of stresses in the fennoscandian lithosphere induced by pleistocene glaciations the seismicity observed in fennoscandia is usually explained by tectonic stresses the question of the contribution of stresses induced by glacial isostatic adjustment to the seismicity has not finally been settled yet in order to quantify the isostatic stress field generated by the fennoscandian glacial load we consider layered maxwell viscoelastic half spaces loaded by axisymmetric discs in particular we calculate the maximum shear stress distribution induced by the load model and the associated stress regimes in the lithosphere emphasis is placed on a discussion of the sensitivity of the calculated isostatic stresses to variations in load cross section lithosphere thickness and asthenosphere viscosity we also examine the effects produced by the viscous relaxation of the lithosphere whose viscosity is parameterized according to the stratification expected for temperature activated diffusion creep our results show that the isostatic shear stresses typically reach 2 mpa near the surface at the present time but that their distribution may be modified strongly by the details of the earth and load models investigated the viscous relaxation of the lithosphere becomes particularly important if more than one glaciation is considered since the last ice age in fennoscandia consisted of several glaciations the model of a perfectly elastic lithosphere conventionally employed in models of glacial isostatic adjustment therefore may not be justified when calculating the isostatic stresses

postglacial seismicity offshore mid norway with emphasis on spatio temporal magnitudal variations abstract norway and its continental margin in spite of being located in an intraplate environment is of great interest from a neotectonic perspective influence on neotectonics stems both from the fact that this is a recently deglaciated region in which significant rebound is still occurring and from its proximity both to a rifted continental margin and to failed rift zones passive continental margins and rift related structures are the most seismically active ones within stable continental regions with a number of well documented earthquakes of magnitude 7 and higher as observed around the globe indeed the disparity in seismicity between such regions and plate boundary regions is greater in terms of return times than in terms of maximum magnitude a recent detailed assessment of neotectonics in fennoscandia has shown strong bedrock related evidence for several large magnitude m 7 earthquakes in the northern areas lapland while few if any similar observations have been made farther south a possible explanation for this is that postglacial earthquakes have been occurring on hidden thrusts in the south in fact several major structures have recently been mapped and shown to have capabilities to accommodate m 6 5 7 earthquakes without breaking the surface given that the largest historically known earthquake in fennoscandia is only of the order of m 5 8 it is likely therefore that the potentially largest magnitude in this region may be well above this

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

late cretaceous to recent tectonic evolution of the north german basin and the transition zone to the baltic shield southwest baltic sea abstract in this study we investigate the late cretaceous to recent tectonic evolution of the southwestern baltic sea based on a dense grid of seismic reflection profiles this area covers the baltic sea sector of the salt influenced north german basin and its transition to the salt free baltic shield across the tornquist zone the upper cretaceous to recent structural evolution is discussed by means of individual seismic sections and derived high resolution time structure maps of the main horizons i e the upper cretaceous tertiary and pleistocene the upper cretaceous and tertiary layers reveal numerous significant faults throughout the study area several of these faults propagate upwards across the unconsolidated pleistocene sediments and occasionally penetrate the surface the salt influenced north german basin reveals three major fault trends nw se n s and nne ssw several of these faults are located directly above basement sub salt faults and salt pillows the majority of these faults are trending n s to nne ssw and parallel the direction of the gluckstadt graben faults in the salt free tornquist zone we identify two major shallow fault trends which are nw se and ne sw the majority of these faults are located above basement faults following the direction of the tornquist zone we conclude that generally basement tectonics controls activation and trends of shallow faults if salt is present the ductile salt layer causes a lateral shift between the sub and supra salt faults major plate reorganisation related to the africa iberia europe convergence and the subsequent alpine orogeny caused reactivation of pre existing faults and vertical salt movement in the late cretaceous the change of stress orientation from ne sw to a nw se during neogene caused another phase of fault and salt tectonic reactivation we explain that the ice sheet loading and or present day stress field may have acted in combination causing the recent tectonics and upward extension of the faults

peat accumulating depositional systems of sarawak east malaysia many coal deposits originate in deltaic estuarine and coastal plain settings and a knowledge of interrelationships between the tectonic and depositional elements active at the time of sediment deposition is necessary to formulate basin scale models the prograding coastal depositional systems of sarawak all contain domed peat accumulating environments in which low ash low sulfur peats are being deposited in areas of active clastic siliciclastic sedimentation these depositional systems are as large as 11 400 km2 and individual peat deposits within systems are in excess of 20 m thick and 1000 km2 in area the geographic positions and drainage basin areas of each depositional system are controlled by fault and fold systems although prograding into the same receiving basin individual system geomorphology is variable and ranges from a wave dominated microtidal delta to a wave dominated meso to macro tidal delta coastal plain system to a tide dominated macrotidal estuarine embayment along a 450 km stretch of coastline system variation is a function of sediment supply shelf and embayment geometry wave climate and tidal range these factors which control depositional system geomorphology also control the resulting long axis orientation of the thick domed peat deposits the surface vegetation and internal characteristics of most domed peat deposits however are similar internal characteristics consist of basal high ash high sulfur degraded peats overlain by low ash low sulfur well preserved peats in vertical profile these systems demonstrate variable responses to late pleistocene holocene sea level rise and in these instances the variation is most attributable to local differences in siliciclastic sediment supply which is a function of the drainage basin area

the age palaeoclimate palaeovegetation coal seam architecture mire types paleodepositional environments and thermal maturity of syn collision paralic coal from mukah sarawak malaysia abstract the mukah coal accumulated in the balingian formation where the time stratigraphic position is poorly defined by fauna though a probable late miocene age has always been assigned to this formation samples collected in the present study that yielded an abundance of casuarina pollen associated with occurrences of dacrydium stenochlaena palustris florschuetzia levipoli and also stenochlaena areolaris spores compare closely to zone pr9 of the palynological zonation of the malay basin and can be tied to depositional sequences of malay basin seismic sequences i2000 i3000 indicating an early miocene age for the studied coal the early miocene age shows that the mukah coal was formed during the collision between luconia block dangerous grounds with the borneo that lasted from late eocene to late early miocene the rapid increase of deposition base level caused by the collision is clearly reflected by the architecture of the mukah coal seams that were generally thin and also by the reverse order of the paleo peat bodies the studied coal samples contained large amounts of detrohuminite without the enrichment of liptinite group macerals usually explained by the dominance of herbaceous plants in the paleomires however the pollen assemblages recovered in the present study provide no support for a herbaceous swamp instead the peats were likely formed mainly from forest vegetation based on the recovery of dominant arboreal pollen assemblages in the present study palynomorph assemblages recovered in the present study with abundance of casuarina pollen associated with common occurrences of dacrydium strongly suggest kerangas vegetation and kerapah type peat swamps indicating a very wet climate the occurrence of rattan and pandanus pollens shows that the kerapah type peat swamps were locally bordered by rattan and pandanus swamps this shows that the prevailing use of coal petrography to discern the type of vegetation that was present in the peat forming mires may lead to wrong conclusions therefore a multi disciplinary approach must be applied for a more accurate and reliable spatial interpretation of the type of vegetation that was present in the peat forming mires consistent with the low sulphur content evidence from the palynomorph assemblages recovered from the coal seams shows that the coal forming peat was deposited in freshwater mires with little or no marine influence despite the fact that the accumulation of the mukah coal forming peat took place within a coastal plain setting moreover the fauna present in the host rock formation also suggested a brackish water environment of deposition

ice ages and nuclear waste isolation abstract the greatest natural threats to the integrity of the geological barriers to nuclear wastes isolated in cavities mined at depths between 400 and 800 m are likely during rapid retreats of future ice sheets the next major glacial retreat is expected at ca 70 ka well within the lifetime of high grade nuclear waste but it is not yet clear how long man s greenhouse effect may delay it this contribution discusses the potential problems posed to european waste isolation sites during erosion by ice and over pressurizing of meltwater and gasses in a lithosphere flexed by major ice sheets these depend on the target rocks and the location of the site with respect to the ice streams and margins of future ice sheets of particular size no sites are planned under the centres of future ice sheets in europe where end glacial earthquakes can be expected to reactivate major faults nor where ice can be expected to deepen and lengthen fjords along the atlantic coast sites in the alps may be vulnerable to radical changes in the patterns of glacial troughs the stability and geohydrology of sites in coastal areas beyond future ice margins are threatened by river gorges when sea level falls ca 125 m or in enclosed basins like the mediterranean ever lower the greatest problems are likely in lowland regions exposed by the rapid retreat of thick ice fronts where large lakes on or under thick warm based ice are dammed by more distal cold based ice groundwater in subhorizontal fractures dilated by glacial unloading may reach over pressures capable of hydraulically lifting megablocks of bedrock with fracture permeability and or the ice damming them so that less permeable substrates are susceptible to incisions eroded to depths of ca 360 at locations controlled mainly by ice topography kinematics and history

seismicity and seismotectonics of norway and nearby continental shelf areas the earthquake activity of norway and nearby offshore areas is low to intermediate with few events above magnitude 5 recent significant improvements in instrumental coverage in parallel with a better utilization of older including historical data have shown that the seismicity in the south is predominantly confined to the coastal areas and to the viking graben while from the northern north sea to svalbard the earthquakes in a broad sense follow the continental margin fifty one focal mechanism solutions from these areas about half of them new reveal stress directions that clearly indicate a connection to the plate tectonic ridge push force at least for the areas at a minimum distance from the continental margin along the margin stress directions also indicate a possible connection to postglacial uplift as well as to lithospheric loading effects a dominance of normal faulting on the landward side and reverse faulting on the oceanic side agrees with this interpretation on a regional level the seismicity in these areas correlate quite well with geologic features such as grabens fault zones fault complexes fracture zones and the margin itself indicating that these structures act in a general sense as weakness zones in the presence of a regionally more stable stress field in the northern north sea however an area with quite anomalous stress orientations with strike slip faulting is found in a region transitional between normal and reverse faulting most of the earthquake foci are confined to the presumably brittle parts of the crust but many events are also located quite close to and on both sides of the moho discontinuity

stress transfer in the storegga area offshore mid norway abstract the recently discovered large gas field ormen lange within the storegga submarine slide area offshore mid norway poses important questions as to the origin of these large submarine slides and their possible implications in terms of the safety of the development and the production in this respect the present study was initiated with the main objective of investigating the possibility of stress transfer as triggering mechanism for multiple earthquake occurrence and hence for the storegga submarine slide ca 8200 years before present bp stress changes following different scenario earthquakes along the selected faults in the area are modeled and computed for a number of cases using the coulomb failure criterion we demonstrate the possibility of large earthquakes triggering multiple ruptures along neighbouring fault segments the combined effect of the co seismic slip and strong ground shaking due to a large earthquake m 7 accompanied by the stress transfer on the optimally oriented normal fault planes which are analogous to the slide scar may have played an important role for the triggering of the storegga submarine slide

implications of a ductile crustal layer for the deformation caused by the fennoscandian ice sheet summary previous studies of glacial isostatic adjustment have usually considered earth models with a purely elastic lithosphere a possibly significant deviation from this assumption is the presence of a ductile crustal layer embedded in an otherwise elastic lithosphere such a layer has been suggested for various continental regions on the basis of seismic and tectonic evidence the present study investigates the implications of a ductile crustal layer for the interpretation of glacial isostatic adjustment using a layered incompressible maxwell viscoelastic earth model and a simplified representation of the fennoscandian glaciation the relaxation time and amplitude spectra show that besides the conventional buoyancy mode m0 also present in earth models with a purely elastic lithosphere the ductile layer supports a slowly decaying mode mc which is capable of modifying the deformation markedly thus measures of the absolute deformation such as the stress clearly reflect the presence of the ductile layer in contrast to this are measures of the relative deformation such as the vertical displacement rate and the rate of gravity change to a good approximation these rates are inversely proportional to the relaxation time of the more quickly decaying mode m0 and are therefore less affected by the ductile layer taken together the present study suggests that provided a ductile crustal layer exists its presence should be accounted for in interpretations of the glacial isostatic adjustment following the fennoscandian or smaller glaciations

response of normal faults to glacial interglacial fluctuations of ice and water masses on earth s surface 1 changes in surface loads during glacial interglacial cycles and the associated flexure and rebound of the lithosphere alter the stress field in actively extending regions and may lead to slip rate variations on normal faults in particular loading may cause a period of seismic quiescence that is followed by temporal clustering of earthquakes during and after unloading here we present a suite of finite element experiments to evaluate how the magnitude distribution and temporal evolution of the load as well as rheological parameters of the lithosphere and asthenosphere influence the response of a normal fault the results show that the duration of the seismically quiet period during loading and the intensity of the slip rate increase during unloading are primarily controlled by the magnitude of the load the time lag between the changes in loading and the reaction of the fault is mainly determined by the viscosity of the asthenosphere parameters that play only a minor role for the fault s response include the rate of load removal fault strength and the thickness of the lithosphere our results imply that earthquake recurrence models derived from holocene slip histories may not be representative for the long term evolution of seismogenic faults

postglacial rebound and fault instability in fennoscandia summary the best available rebound model is used to investigate the role that postglacial rebound plays in triggering seismicity in fennoscandia the salient features of the model include tectonic stress due to spreading at the north atlantic ridge overburden pressure gravitationally self consistent ocean loading and the realistic deglaciation history and compressible earth model which best fits the sea level and ice data in fennoscandia the model predicts the spatio temporal evolution of the state of stress the magnitude of fault instability the timing of the onset of this instability and the mode of failure of lateglacial and postglacial seismicity the consistency of the predictions with the observations suggests that postglacial rebound is probably the cause of the large postglacial thrust faults observed in fennoscandia the model also predicts a uniform stress field and instability in central fennoscandia for the present with thrust faulting as the predicted mode of failure however the lack of spatial correlation of the present seismicity with the region of uplift and the existence of strike slip and normal modes of current seismicity are inconsistent with this model further unmodelled factors such as the presence of high angle faults in the central region of uplift along the baltic coast would be required in order to explain the pattern of seismicity today in terms of postglacial rebound stress the sensitivity of the model predictions to the evects of compressibility tectonic stress viscosity and ice model is also investigated for sites outside the ice margin it is found that the mode of failure is sensitive to the presence of tectonic stress and that the onset timing is also dependent on compressibility for sites within the ice margin the evect of earth rheology is shown to be small however ice load history is shown to have larger evects on the onset time of earthquakes and the magnitude of fault instability

transgressive regressive cycles and the occurrence of coal in some upper cretaceous strata of utah cenomanian santonian strata contain about 60 of the known cretaceous coal resources of utah the areal and temporal distribution of these resources can be related to the transgressive regressive history of the western shoreline of the interior cretaceous seaway two orders of transgressive regressive cycles the larger of which corresponds to third order cycles of vail et al are deemed important in analyzing the distribution of coal in utah the largest coal fields are associated with extensive vertical stacking of the deposits of what are here termed fourth order cycles at the transgressive and regressive maxima of third order cycles deposits of transgressive and regressive phases of third order cycles contain only minor amounts of coal this genetic relationship may prove useful in predicting areas of important cretaceous coal resources in deeper parts of structural basins in the rocky mountain region

natural radionuclides in the soils of a small agricultural basin in the canadian prairies and their association with topography soil properties and erosion summary samples taken from the a and b horizons of the soil at 160 sites in a small 178 ha cultivated drainage basin in central saskatchewan were analysed by gamma spectroscopy to determine the concentration of a number of natural radionuclides in the soil the concentration of 40k the 238u daughters 226ra 214pb and 214bi and the 232th daughters228ac 212bi and 208tl was determined a variety of soil properties and topographic variables were measured at each sampling site earlier studies in the basin provided net soil erosion estimates i e net loss or gain for each site the association of isotope activities with topography soil properties and net erosion was evaluated mean isotope activities for the basin were very close to mean values reported earlier for native soils in southern saskatchewan differences in isotope concentrations between the a and b horizons of the soils were related to differences in the degree to which the different isotopes are taken up by plants isotope concentrations in the surface soil were inversely correlated with soil particle size variation in isotope activities within the basin appeared to be linked to soil redistribution by erosion but in a complex manner which reflects size sorting of soil particles by erosion processes erosion processes seem to be at least as important as leaching processes in determining the spatial distribution of natural radionuclides in the surface soils of the study area

glacio seismotectonics ice sheets crustal deformation and seismicity abstract the last decade has witnessed a significant growth in our understanding of the past and continuing effects of ice sheets and glaciers on contemporary crustal deformation and seismicity this growth has been driven largely by the emergence of postglacial rebound models pgm constrained by new field observations that incorporate increasingly realistic rheological mechanical and glacial parameters in this paper we highlight some of these recent field based investigations and new pgms and examine their implications for understanding crustal deformation and seismicity during glaciation and following deglaciation the emerging glacial rebound models outlined in the paper support the view that both tectonic stresses and glacial rebound stresses are needed to explain the distribution and style of contemporary earthquake activity in former glaciated shields of eastern canada and fennoscandia however many of these models neglect important parameters such as topography lateral variations in lithospheric strength and tectonic strain built up during glaciation in glaciated mountainous terrains glacial erosion may directly modulate tectonic deformation by resetting the orogenic topography and thereby providing an additional compensatory uplift mechanism such effects are likely to be important both in tectonically active orogens and in the mountainous regions of glaciated shields in general the short term response to ice fluctuations is similar to the earth s response to fluctuations in water reservoirs with the subsequent increase or decrease in seismicity which depends on the pre existing stress state when the ice fluctuations occur on the spatial scale and magnitude of the late pleistocene glaciation and deglaciation however the viscoelastic response of the earth especially the mantle causes significant changes in crustal deformation and earthquake activity that is spatially extensive and temporally complex the regions of greatest ice thickness and the regions marginal to the late pleistocene ice sheets indicate the most dramatic evidence of earthquake faulting the mantle response to these large ice mass fluctuations and the change in mass between the oceans and land caused and continues to cause measureable crustal deformation at hundreds of kilometres from the ice margins for both tectonically active and cratonic regions palaeoseismic investigations of late pleistocene and holocene faults are an important tool in evaluating earthquake hazard the predicted response of the earth over this time however is very dependent on the model assumed for most regions far more carefully designed field observations are needed to constrain the existing rheological and ice models

late ordovician ashgillian glacial deposits in southern jordan the late ordovician ashgillian glacial deposits in southern jordan comprise a lower and upper glacially incised palaeovalley system occupying reactivated basement and pan african fault controlled depressions the lower palaeovalley incised into shoreface sandstones of the pre glacial tubeiliyat formation is filled with thin glaciofluvial sandstones at the base overlain by up to 50 m of shoreface sandstone a prominent glaciated surface near the top of this palaeovalley fill contains intersecting glacial striations aligned e w and nw se the upper palaeovalley fill comprises glaciofluvial and marine sandstones incised into the lower palaeovalley or where this is absent into the tubeiliyat formation southern jordan lay close to the margin of a late ordovician terrestrial ice sheet in northwest saudi arabia characterised by two major ice advances these are correlated with the lower and upper palaeovalleys in southern jordan interrupted by two subsidiary glacial advances during late stage filling of the lower palaeovalley when ice advanced from the west and northwest thus four ice advances are now recorded from the late ordovician glacial record of southern jordan disturbed and deformed green sandstones beneath the upper palaeovalley fill in the jebel ammar area are confined to the margins of the hutayya graben and have been interpreted as structureless glacial loessite or glacial rock flour petrographic and textural analyses of the deformed sandstones their mapped lateral transition into undeformed tubeiliyat marine sandstones away from the fault zone and the presence of similar sedimentary structures to those in the pre glacial marine tubeiliyat formation suggest that they are a locally deformed facies equivalent of the tubeiliyat not part of the younger glacial deposits deformation is attributed to glacially induced crustal stresses and seismic reactivation of pre existing faults previously weakened by epeirogenesis triggering sediment liquefaction and deformation typical of earthquake generated seismites deformation confined to an area of not more than 4 km wide adjacent to the major fault zone implies earthquake magnitudes of at least 6 mo the high authigenic chlorite content of deformed tubeiliyat sandstones compared to undeformed ones is attributed to a post seismic hydrothermal system driven by compactional dewatering and hydrofracturing of the bedrock which acted as a groundwater recharge area supplied by subglacial meltwater from beneath the ice sheet fluid movement along glacial seismotectonically reactivated faults infiltrated the adjacent tubeiliyat sandstones under pressure and elevated geothermal gradient where chlorite was precipitated from solution d 2005 elsevier b v all rights reserved

slip rate variations on faults during glacial loading and post glacial unloading implications for the viscosity structure of the lithosphere abstract many active faults in extensional and contractional tectonic settings experienced a slip rate increase after the last glacial period when the volume of nearby glaciers and lakes decreased this post glacial slip rate increase is caused by transient stresses that are generated by the unloading induced rebound and superimposed on the tectonic background stress field as the latter is different for normal and thrust faults the response to loading and unloading should depend on the fault type here we use finite element models including a fault in rheologically layered lithosphere to explore the conditions under which both normal and thrust faults experience a post glacial slip rate increase the results show that a post glacial slip rate increase occurs on normal faults if the lower crust is stronger than the lithospheric mantle whereas thrust faults accelerate if the lower crust is weaker than the lithospheric mantle these findings imply that the response of faults to mass fluctuations on the earth9s surface may provide constraints on the rheological stratification of the lithosphere we use our results to make predictions on the viscosity structure of the basin and range province and northern scandinavia where palaeoseismological data document a pronounced increase in seismicity as a result of post glacial unloading and rebound

stress and fault parameters affecting fault slip magnitude and activation time during a glacial cycle stress and fault parameters affecting fault slip magnitude and activation time during a glacial cycle

some seismological and geometric features of intraplate earthquakes to understand the nature and cause of intraplate earthquakes we carried out a systematic search for common features associated with them various geological geophysical and seismic data were analyzed and geometric and seismic parameters were compared for 29 intraplate events m 4 5 occurring worldwide the results suggest that intraplate earthquakes occur by the reactivation of pre existing zones of weakness in a compressional stress regime which is generally oriented parallel to the absolute direction of plate motion two styles of faulting were observed for type a earthquakes observed in the eastern united states eastern china western europe and west africa deformation occurs by strike slip motion on steeply dipping faults type b events are usually associated with thrust or normal faulting and were observed in eastern canada fennoscandia australia and peninsular india focal depths did not explain the differences between type a and type b earthquakes rather the differences are due to the perturbation of a regional stress field by a local stress field the regional stress field for type a events is primarily due to ridge push forces the method of stress perturbation varied from region to region the earthquakes in the type b category were further divided into three subcategories type b1 occurring in eastern canada and fennoscandia type b2 occurring in australia peninsular india and central brazil and type b3 occurring in the gulf coast of the u s the inferred causes of the perturbing stresses are deglaciation intracontinental resistive forces resulting from the collision of plates and the deposition of a large thickness of sediments respectively type a events were found to be associated with intersecting faults and generally supported the intersection model of talwani 1988 and had analogs in plate boundary events

reply to comment by hampel et al on stress and fault parameters affecting fault slip magnitude and activation time during a glacial cycle reply to comment by hampel et al on stress and fault parameters affecting fault slip magnitude and activation time during a glacial cycle

the post glacial landscape evolution of the north german basin morphology neotectonics and crustal deformation the recent evolution of the north german basin ngb which is presently a low seismic area was partly affected by glacial loading and unloading of the ice masses major stresses acting within the ngb are induced by the north atlantic ridge push the ongoing alpine collision and the post glacial rebound of fennoscandia present day horizontal stresses within the ngb are directed generally nw se but fan and bend north of 52 n towards nne major basement faults are directed nw se minor faults ne sw and nne ssw and are clearly detectable in geomorphological and satellite lineaments furthermore the drainage pattern and the distribution of lakes in northern germany follow exactly block boundaries and hence mark zones of present day subsidence the understanding of the post glacial morphology and reactivation of faults requires a view into the very heterogeneous crust and upper mantle below the ngb the re adjustment of the individual fault blocks during post glacial relaxation of the lithosphere leads to differential crust dependent uplift and probably to the formation of urstrom valleys the urstrom valleys and terminal moraines in northern germany appear to parallel the major tectonic lineaments and lithospheric block boundaries the lithospheric memory is expressed in the post glacial landscape evolution of the ngb

probabilistic and deterministic seismic hazard results and influence of the sedimentary more basin ne atlantic abstract seismic hazard assessments have been conducted for the ormen lange gas field in the norwegian sea on the flank of the more basin the study used logic tree based probabilistic methods combined with semi deterministic methods for hazard contributions from mapped faults and the hazard was computed in terms of peak ground acceleration pga and spectral acceleration the probabilistic seismic hazard results were complemented by deterministic modelling in 1d wave number integration and 2d finite difference crustal models the deterministic modelling first of all elucidated the shaking duration problem indicating that thick offshore sediment structures like the ones in the more basin may significantly extend the shaking duration of an earthquake the presence of sedimentary layers with large velocity contrasts are responsible for this observation and a conventional soil amplification analysis would not have revealed this phenomenon a modelling along similar lines as indicated in the present paper may be recommended in certain vulnerable situations and in geologic provinces with thick sedimentary layers with significant internal velocity contrasts even though large earthquakes most likely have occurred in the region during the postglacial period the study could not resolve if the huge storegga slide which occurred about 8100 yb was triggered by an earthquake

three dimensional numerical modeling of slip rate variations on normal and thrust fault arrays during ice cap growth and melting 1 changes in the volumes of ice caps considerably alter the stress state of the lithosphere by generating a transient signal that is added to the tectonic background stress field these stress field changes in turn affect crustal deformation and in particular the slip behavior of existing faults here we use three dimensional finite element models to investigate how arrays of normal and thrust faults near a growing and subsequently melting ice cap are influenced in their slip evolution the results show that regardless of fault dip both types of faults experience a decrease in their slip rate during ice cap advance and an increase in their slip rate during ice cap retreat if they are located beneath the ice cap in contrast faults outside the ice cap that are loaded on their footwall or hanging wall only show the opposite pattern their slip rate increases during glacial loading and decreases during subsequent unloading if the load is located along strike of the fault that is at one of its tips the slip behavior of normal and thrust faults is different the normal fault shows a slip rate increase during unloading the thrust fault during loading our results explain the location and timing of deglaciation induced paleoearthquakes in scandinavia and the contrasting slip histories reported from normal faults in the basin and range province which are located at different positions relative to the former yellowstone ice cap more generally our findings imply that a uniform slip behavior of faults in formerly glaciated regions should not be expected

can deglaciation trigger earthquakes in n america a spherical self gravitating viscoelastic earth model is used to calculate the spatial and temporal evolution of the glacially induced lithospheric stress and fault stability in north america the predicted onset time of a pulse of earthquake activities the mode of failure and the magnitude of instability are investigated for three sites with different distance from the former ice margin it is found that glacial unloading is able to trigger paleo earthquakes within the ice margin near charlevoix 47 5 n 70 1 w and in wabash valley 38 5 n 87 w outside the ice margin however rebound stress decays away from the former ice margin thus glacial unloading is unlikely to have triggered the large m8 earthquakes in new madrid 36 6 n 89 5 w

response of salt structures to ice sheet loading implications for ice marginal and subglacial processes abstract during the past decades the effect of glacioisostatic adjustment has received much attention however the response of salt structures to ice sheet loading and unloading is poorly understood our study aims to test conceptual models of the interaction between ice sheet loading and salt structures by finite element modelling the results are discussed with regard to their implications for ice marginal and subglacial processes our models consist of 2d plane strain cross sections which represent simplified geological cross sections from the central european basin system the model layers represent i sedimentary rocks of elastoplastic rheology ii a viscoelastic diapir and layer of salt and iii an elastoplastic basement on top of the model a temporarily variable pressure simulates the advance and retreat of an ice sheet the durations of the individual loading phases were defined to resemble the durations of the pleistocene ice advances in northern central europe the geometry and rheology of the model layers and the magnitude spatial distribution and timing of ice sheet loading were systematically varied to detect the controlling factors all simulations indicate that salt structures respond to ice sheet loading an ice advance towards the diapir causes salt flow from the source layer below the ice sheet towards the diapir resulting in an uplift of up to 4 m the diapir continues to rise as long as the load is applied to the source layer but not to the crest of the diapir when the diapir is transgressed by the ice sheet the diapir is pushed down up to 36 m as long as load is applied to the crest of the diapir during and after ice unloading large parts of the displacement are compensated by a reversal of the salt flow plastic deformation of the overburden is restricted to the area immediately above the salt diapir the displacements after unloading range between 3 1 and 2 7 m larger displacements are observed in models with deep rooted diapirs thicker ice sheets longer duration of the loading phase thicker salt source layers and lower viscosity of the salt the rise or fall of diapirs triggered or amplified by ice sheet loading are likely to affect glacigenic deformation erosion and deposition above the diapir and within the rim synclines ice load induced uplift in front of an ice sheet will provide favourable conditions for the formation of push moraines for example by creating a topographic obstacle and inclining potential detachments subglacial subsidence of salt structures will enhance erosion by providing a preferential drainage pathway and fracturing of the overburden of the salt structure and thereby contribute to the incision of tunnel valleys however the resulting displacements are probably too low to have a marked effect on the advance or retreat pattern of the ice sheets

earthquakes along the passive margin of greenland evidence for postglacial rebound control an intriguing observation in greenland is a clear spatial correlation between seismicity and deglaciated areas along passive continental margins a piece of evidence for earthquake triggering due to postglacial rebound another piece of evidence for induced seismicity due to deglaciation derives from earthquake source mechanisms sparse low magnitude seismicity has made it difficult to determine focal mechanisms from greenland earthquakes on the basis of two normal faulting events along deglaciated margins and from the spatial distribution of epicenters earlier investigators suggested that the earthquakes of greenland are due to postglacial rebound this interpretation is tested here by using more recent data broadband waveforms of teleseismic p waves from the august 10 1993 mb 5 4 and october 14 1998 mb 5 1 earthquakes have been inverted for moment tensors and source parameters both mechanisms indicate normal faulting with small strike slip components the 1993 event strike 348 9 dip 41 0 rake 56 3 focal depth 11 km seismic moment 1 03 1024 dyne cm and mw 5 3 the 1998 event strike 61 6 dip 58 0 rake 95 5 focal depth 5 km seismic moment 5 72 1023 dyne cm and mw 5 1 these and the two prior events support the theory that the shallow part of the lithosphere beneath the deglaciated margins is under horizontal extension the observed stress field can be explained as flexural stresses due to removal of ice loads and surface loads by glacial erosion these local extensional stresses are further enhanced by the spreading stress of continental crust and reactivate preexisting faults earthquake characteristics observed from greenland suggest that the dominant seismogenic stresses are from postglacial rebound and spreading of the continental lithosphere

significance of jurassic radiolarians from the cache creek terrane british columbia the discovery of new radiolarian localities in the western belt of the cache creek terrane in southern british columbia possibly changes its upper age limit from late triassic to early or middle jurassic it favors a middle jurassic rather than a late triassic age of amalgamation for the cache creek terrane and quesnellia parts of superterrane i in southern british columbia the new jurassic ages also mean that the western cache creek terrane could be equivalent in age to the bridge river hozameen terrane in british columbia and to terranes containing the tethyan fusulinid yabeina in northwest washington and the klamath mountains of california

quantitative topographic analysis of gilgai soil morphology abstract for a gilgai soil complex we estimated the effect of overland and intrasoil substance flows on vertisol development using concepts of topographic control of lateral substance movement by gravity rather than direct observations and measurements of these processes first we studied relationships between gilgai microtopographic characteristics and some vertisol morphological properties namely depth to parent material c and calcium carbonate enriched bca horizons secondly we checked if microtopographic characteristics of the c horizon surface influence some vertisol properties by examining the bca horizon depth we used digital models of quantitative topographic variables we concluded that the dominant mechanism controlling the c horizon depth is pedoturbation also pedoturbation can be important in the development of the bca horizons however variations in the c and the bca horizon depths are not dictated by pedoturbation only our analysis showed that key factors influencing the c and the bca horizon depths are overland and intrasoil lateral migration and accumulation of water solution and solid substances the c horizon depth depends on the landsurface topographic characteristics namely horizontal vertical and mean curvatures specific catchment area topographic and stream power indices the bca horizon depth is significantly affected by the same set of topographic attributes of both the landsurface and the c horizon surface the bca and the c horizon depths as a rule depend more on specific catchment area topographic and stream power indices than on horizontal vertical and mean curvatures of the landsurface and the c horizon surface this is because specific catchment area topographic and stream power indices take into account a relative location of a point in a microcatena utilization of quantitative topographic variables allows us to explain 82 of variation in the bca horizon depth and to suggest that topography is the main factor in the bca horizon formation

induced stresses and fault potential in eastern canada due to a realistic load a preliminary analysis summary in order to understand the causal relation between postglacial rebound and earthquakes a simple disc load model is used to 1 calculate stresses induced in the lithosphere and mantle by glacial loading melting and postglacial rebound and 2 evaluate the effect of glacial loading rebound on the failure potential for earthquakes in the upper crust the dependence of the failure potential and the actual mode of failure on the coefficient of friction the ambient tectonic stress magnitude direction the stress due to the overlying rocks and lithospheric thickness are investigated prominent features of this paper are the inclusion of 1 a viscoelastic mantle and thus the migration of stress and 2 the ambient tectonic stress and overburden stress contributions in the calculation of the total stress field it is assumed that throughout the earth there are optimally oriented pre existing virtual faults that are initially close to but not at failure thus a time dependent quantity called dfsm related to the coulomb mohr failure criterion can be defined such that a negative value of dfsm would advocate faulting or earthquake activities whereas a positive value of dfsm would promote stability the results indicate that under all combinations of tectonic stress magnitude and overburden stress crustal loading promotes fault stability directly underneath the load upon the removal of the load thrust faulting is predicted within the ice margin if the horizontal stress s induced by the overburden is greater than or equal to the vertical component s of the overburden stress 121 where sjs under this condition theory predicts that faulting or earthquake activity should have reached a maximum immediately after deglaciation if the horizontal stress induced by the overburden is less than the vertical component of the overburden stress 1 l then theory predicts fault stability within the ice margin the theory predicts fault instability both north and south of the ice margin the mode of failure however is completely determined by the value of i the trade off between the tectonic stress magnitude and the overburden stress parameter 1 is also investigated it is shown that a larger tectonic stress magnitude can be used to compensate a smaller value of 1 the results of this analysis show that variations in the coefficient of friction lithospheric thickness and a ductile zone below the upper crust do not significantly affect the above conclusions

will earthquake activity in eastern canada increase in the next few thousand years knowledge of whether earthquake activity will increase in the next few thousand years is important for the planning of nuclear waste repositories assuming that fault instability portends earthquak

new constraints on 1 7 gyr of brittle tectonic evolution in southwestern finland derived from a structural study at the site of a potential nuclear waste repository olkiluoto island abstract the brittle deformation history of southwestern finland was reconstructed through paleostress inversion of fault slip data from outcrops and drill cores at the site of a planned nuclear waste repository seven distinct paleostress states have been resolved spanning 1 7 ga of geological history 1 nw se to nnw sse transpression acted soon after 1 75 ga when conditions leading to brittle deformation were first attained 2 n s to ne sw transpression caused partial reactivation of 1 3 nw se extension followed during the gothian event and at the time of rapakivi magmatism 4 renewed ne sw transtension occurred between 1 60 and 1 30 ga forming the nw se elongated satakunta graben 5 a significant and so far unrecognised phase of ne sw compression has been found to postdate both rapakivi granites and 1 27 ga olivine diabase sills 6 e w transpression followed during the early stages of the mesoproterozoic sveconorwegian orogeny and predated 7 almost coaxial e w extension of the late sveconorwegian orogenic collapse our results prove that the shield s crust fragmentation i e generation of new fractures was short lived in comparison to its jostling phase i e reactivation of old fractures the shield thus reached structural maturity with respect to its saturation with brittle structures already in the late mesoproterozoic we predict that that future stress changes will most probably be accommodated by reactivation of the existing and inherited brittle structures rather than by formation of new deformation zones

moment tensors state of stress and their relation to post glacial rebound in northeastern canada summary in the stable craton of northeastern canada moderate seismicity as well as glacial isostatic adjustment gia has been observed we investigate five earthquakes with moment magnitudes between 3 6 and 4 1 that have occurred in northern hudson bay since 2007 which may be triggered by gia focal mechanisms of the earthquakes are determined using a waveform fitting procedure for surface waves in which the best double couple mechanism is obtained through a grid search over strike dip and rake all events exhibit a thrust fault mechanism in general agreement with mechanisms of previously analysed earthquakes in that area stress inversion results incorporating our new mechanisms as well as previously published results exhibit significant differences from previously calculated stresses from gia models for the first time maximum horizontal stress direction shmax is compared to the modelled stress values for northeastern canada we find that the maximum horizontal stress direction strikes roughly nnw sse in contrast to previously inferred ne sw orientation of shmax our results indicate that the local stress field in northern hudson bay deviates from regional stresses resulting from the existence of a roughly e w oriented zone of faulting which is not included in existing gia models

seismo and neotectonics in finnmark kola and the southern barents sea part 2 seismological analysis and seismotectonics abstract a detailed review and analysis of seismological data acquired since 1979 from finnmark kola and the southern barents sea has provided a much improved delineation of the earthquake activity in that region in the barents sea the seismicity is confined only to the western areas while the finnmark kola coastal areas show some seismicity only north and east of murmansk in the rybachi cape tereberski region further inland there are several clear seismicity lineations that to some extent can be correlated with postglacial faults including the ne sw striking stuoragurra fault in finnmark the spatial correlation between seismicity and mapped faults is interpreted in general as a reflection of broad zones of weakness that respond to the present day stress field a detailed analysis of the earthquakes in this area has also shown a dynamic consistency in that they reveal a reverse faulting pattern that is consistent with a detailed geological study that includes a core drilling the dominant horizontal stress direction in this region is nnw sse consistent with the ridge push effect

soft sediment deformation at the base of the neoproterozoic puga cap carbonate southwestern amazon craton brazil confirmation of rapid icehouse to greenhouse transition in snowball earth stratigraphic and isotopic data identify the lower 45 m of the araras group on the southwest margin of the amazon craton as a neoproterozoic platform cap carbonate deposited below wave base upon varanger glacial diamictites of the puga formation the basal beds consist of moderately deep water pinkish dolomudstone with stratiform to wavy fenestral microbialites locally cut by tube like structures and fenestral nonmicrobial planar laminites with tepee like features above the basal carbonates are deep water bituminous lime mudstones with alternating thin calcite crusts and lime mudstone laminae commonly disrupted by calcite crystal fans pseudomorphs after aragonite the basal contact of the puga cap exhibits soft sediment deformational structures principally load casts that are here attributed to rebound induced seismicity acting upon both recently deposited carbonate sediments and underlying unconsolidated diamictite these features constitute the first clearly recognized sedimentological evidence for the rapid change from icehouse to greenhouse conditions as postulated in the snowball earth model of neoproterozoic glaciation

postglacial faulting in eastern canada nature origin and seismic hazard implications abstract at more than 70 locations in southeastern canada and the adjacent united states tiny bedrock faults displace glacial striations that are about 10 000 years old these reverse faults mostly of small displacement occur in a broad arc from western ontario to newfoundland the faults lie near the margin of the laurentian ice sheet strike generally tangential to it and imply compression nearly normal to the ene directed contemporary regional stress these observations and some age relationships suggest that the faults formed very soon after deglaciation perhaps in the first few thousand years after ice melting in each place and probably represent the release of stresses caused by flexural deformation of the upper crust although the individual offsets are small the faults are believed to be pervasive and individual outcrops reflect amounts of stress relief consistent with stresses implied by the postglacial tilt of nearby lake shorelines

suppression of earthquakes by large continental ice sheets the interior regions of antarctica and greenland are aseismic no earthquake larger than body wave magnitude 4 5 5 0 is known for either except along coastal zones or continental shelves here i advance an explanation for this lack of seismic activity in terms of pressure effects produced by the continental ice sheets that mantle both continents

coals associated with tidal sediments in the wilcox group paleogene south texas abstract the several coal seams in 50 m of wilcox strata on the chacon creek east lignite property in south texas are closely associated with tidal sediments the coal bearing sequence is underlain by greenish bioturbated sandstone deposited in open marine water the sediments between the coals and cutting the coals consist of coarsening and fining upward sequences of interbedded sandstone and mudstone with lenticular wavy and flaser bedding and ripple laminated and cross bedded sandstone the sediments contain marine dinoflagellates and palynomorphs of an inland flora most of the sediment accumulated in tidal channels each coal is underlain by rooted strata usually an underclay palynomorphs in the lignite suggest the peat accumulated in low lying swamps dominated by tupelo trees these swamps lay along the landward margin of a tidal channel complex the channel complex probably extended 10 to 30 km inland from the main coastline repeated regressive and transgressive episodes with corresponding expansion and contraction of the peat swamps within the estuarine complex would explain the coal bearing sequence at chacon creek east

characteristics of peat deposits in the mississippi river delta plain abstract variations in organic rich sediment peat from the mississippi river delta plain can be explained by differences in three interrelated parameters a depositional setting b balance between subsidence and detrital influx and c marine inundation variations are observed in geometry of the overall deposits organic matter content and the mineralogy of peats and related ashes using a vibracorer samples were collected from two brackish areas avery island sale cypremort and barataria basin and one freshwater area gueydan geometries of the deposits are different for the two brackish settings interdistributary peats of barataria basin tend to be discontinuous and somewhat thicker than blanket peats of avery island sale cypremort the freshwater peat is an elongate body in a pleistocene channel cut peats in all areas average 90 moisture content dried peat averages 81 3 organic matter with a bulk density of 0 12 g cm3 holocene differential compaction has been minimal less than 4 conventional ash values indicate different distributions of organic material for the two brackish areas for the area containing interdistributary peats approximately 5 0 of the subsurface contains more than 70 organic matter whereas for blanket peats 14 of the section has more than 70 organic matter mineralogical data collected on low temperature ashes indicate that major minerals in brackish peat consist of kaolinite quartz and water soluble salts while minerals from freshwater samples are primarily kaolinite and quartz x ray diffraction and electron microscopy show the presence of smectite illite abundant siliceous spicules framboidal pyrite biotite pyroxene and rutile in the insoluble fraction suitability of these deposits as coal precursors has been discussed by several workers superficial examination of data generated so far suggests that only thin coal seams with high ash would be produced however the presence of decomposing siliceous sponge spicules in the ash and the possibility of ash being leached by fresh groundwater suggest that much ash may be lost during early diagenesis hence this environment may have more potential as a modern coal forming model than first appeared

on a possible connection between three major earthquakes in california and oil production abstract the 1983 coalinga m 6 5 the 1985 kettleman north dome m 6 1 and the 1987 whittier narrows m 5 9 earthquake sequences each occurred beneath major producing oil fields and caused an aftershock sequence whose epicentral extent coincides approximately with that of the overlying oil field despite this coincidence a causal relationship between these sequences and oil production has been discounted because the earthquakes were located at depths of the order of 10 km whereas oil production is confined to the topmost several km moreover because all three oil fields coalinga kettleman north dome and montebello are situated on anticlines that have undergone recent uplift as a consequence of horizontal tectonic compression of the crust natural earthquakes are not unexpected a mechanical connection between oil production and the earthquake sequence is suggested however by the observation that in each case the total seismic deformation was just that required to offset the force imbalance caused by oil production specifically for each of the three sequences m 0 2 m c where m 0 is the sum of the seismic moments is the modulus of rigidity m is the mass of the fluid removed due to oil production is the fraction of the upper crust that is seismogenic and c is the average upper crustal density in essence net extraction of oil and water reduces slightly the average density of the upper crust causing an isostatic imbalance the ductile lower crust deforms in response to this imbalance thus increasing the load on the seismogenic layer which fails seismically to thicken the crust so as to restore static equilibrium locally accordingly earthquakes near the base of the upper crust may be an expected outcome of major oil production from growing anticlines irrespective of the depths of the producing formations

active tectonic studies in the united states 1987 1990 the techniques and instrumentation used in active tectonic studies are discussed and recent results are reviewed it is suggested that a critical mass of data on several particular regions has been accumulated making possible critical debates and attempts to assess earthquake hazards particular attention is given to studies of the pacific northwest region basin and range deformation studies and distributed deformation and hidden earthquake sources also included is a comprehensive bibliography for the period

postglacial crustal doming stresses and fracture formation with application to norway abstract postglacial doming of fennoscandia is estimated to have reached a maximum uplift value of 850 m vertical uplift of this magnitude generates stresses that affect the tectonic activity in the domed area using a simple model of a circular elastic plate subject to deflection it is shown that the maximum tensile stresses generated by this uplift occur in the centre of the dome and at the surface reach a numerical value of nearly 30 mpa this tensile stress is an order of magnitude greater than the typical in situ tensile strength of the uppermost part of the crust so that tension fractures are easily generated by this stress tension fractures can under certain conditions reach crustal depths of several hundred metres but if they propagate to greater depths they change into normal faults the tensile stresses at the surface decrease in magnitude with distance from the centre of the dome and become compressive in the marginal parts of the uplifted crustal plate at the surface of these parts the maximum shear stress exceeds 10 mpa because the inferred driving stresses stress drops in earthquakes are commonly only several mpa it follows that the driving shear stress in these marginal parts is large enough to initiate or reactivate seismogenic faults these model results are in broad agreement with data on the current seismotectonics of fennoscandia the formation and reactivation of tensile and shear fractures in fennoscandia as a result of postglacial uplift is likely to increase the hydraulic conductivity of the solid rocks that constitute the uppermost part of the crust this conclusion is supported by reported observations which indicate that the production of groundwater in wells in many areas in norway varies positively with the maximum postglacial uplift

cretaceous sedimentation and tectonics tyaughton methow basin southwestern british columbia the mesozoic tyaughton methow basin straddles the fraser yalakom pasayten straight creek fypsc strike slip fault zone between six tectono stratigraphic terranes in southwestern british columbia data from hauterivian cenomanian basin fill provide constraints for reconstruction of fault displacement and paleogeography the early cretaceous eastern margin of the basin was a region of uplifted jurassic plutons and active intermediate volcanism detritus shed southwestward from that margin was deposited as the marine jackass mountain group albian inner to mid fan facies of the jackass mountain group can be correlated across the yalakom fault suggesting 150 25 km of post albian dextral offset deposits of the jackass mountain group overlap the major strike slip zone fypsc if that zone represents the eastern boundary of the tectono stratigraphic terrane wrangellia then accretion of wrangellia to terranes to the east occurred before late early cretaceous time the western margin of the basin first b

lithofacies and depositional environments of the telkwa coal measures central british columbia canada abstract albian coal measures of the skeena group in the telkwa coalfield comprise more than 500 m of conglomerate sandstone siltstone mudstone and coal that were deposited during two regressive transgressive cycles the stratigraphic sequence is divisible into four lithostratigraphic units the basal unit unit 1 is about 100 m thick and comprises conglomerate sandstone mudstone coal and seatearth deposited in a fluvial environment on a deeply eroded volcanic basement gravel and sand were deposited in braided channels and bars and mud accumulated in floodplains peat accumulated in poorly drained backswamps in the northern part of the study area coal seams thin and split a result of periodic flooding of peat swamps with sediment laden water from nearby streams deposition of unit i ended with marine transgression unit ii consists of up to 140 m of silty mudstone bioturbated and cross bedded chert and muscovite rich sandstone and rare thin carbonaceous mudstones deposited in a shallow marine environment the sands were deposited as distributary channels and mouth bars muds were deposited in bays and thin discontinuous peat accumulated in local salt marshes unit iii averages 90 m in thickness and comprises bioturbated and rippled chert and muscovite rich sandstone siltstone carbonaceous mudstone and thick coal seams deposited in a variety of low energy paralic environments sand and mud were deposited and biogenically reworked in tidal flats and siltstone accumulated in a restricted nearshore marine environment to the east peat accumulated in freshwater coastal domed mires which periodically prograded over tidal flats all but the lowermost coal seams pinch out eastward into brackish and nearshore marine sediments the ash yield of many coals increases towards their seaward margin locally the sulphur yield of the coal is high reflecting occasional inundation by brackish water the coals were deposited during regressive maximum and are characterized by an essentially vertical stacking pattern comprising an aggradational parasequence set the major coals are considered to have been deposited at the turnaround between progradation and retrogradation unit iv is over 150 m thick and is composed of chloritic sandstone overlain by silty mudstone deposited in a marine environment the basal sandstone is a transgressive lag deposit silty mudstone is the predominant lithofacies and was deposited in a nearshore shallow marine environment

soft sediment deformation of late pleistocene sediments along the southwestern coast of the baltic sea ne germany a 1 460 m long profile of a late glacial subglacial glacio fluvial glacio limnic and glacio deltaic sequence exposed at a cliff section on usedom island sw baltic sea coast is described the sequence is up to 31 m thick and shows sedimentary structures typical of a glacial setting soft sediment deformation is encountered and is associated with changes in lithology these deformations include liquefaction slumping and faulting as the most plausible cause earthquake induced shaking is discussed the associated neotectonic activity is seen as a consequence of the postglacial isostatic crustal rebound as the deglaciation earthquake ratio diminishes with time and as the rebound is phasing out no large earthquakes are anticipated for northern germany although in conclusion the lithosphere of the north german basin has to be regarded as weakened by repeated ice loading and deloading

effect of ice sheet growth and melting on the slip evolution of thrust faults abstract field investigations suggest that postglacial unloading and rebound led to the formation or re activation of reverse faults even in continental shields like scandinavia here we use finite element models including a thrust fault embedded in a rheologically layered lithosphere to investigate its slip evolution during glacial loading and subsequent postglacial unloading the model results show that the rate of thrusting decreases during the presence of an ice sheet and strongly increases during deglaciation the magnitude of the slip acceleration is primarily controlled by the thickness of the ice sheet the viscosity of the lithospheric layers and the long term shortening rate in contrast the width of the ice sheet the rate of deglaciation or the fault dip have an only minor influence on the slip evolution in all experiments the slip rate variations are caused by changes in the differential stress the modelled deglaciation induced slip acceleration agrees well with the occurrence of large earthquakes soon after the melting of the fennoscandian ice sheet which led to the formation of spectacular fault scarps in particular in the lapland fault province furthermore our model results support the idea that the low level of seismicity in currently glaciated regions like greenland and antarctica is caused by the presence of the ice sheets based on our models we expect that the decay of the greenland and antarctica ice sheets in the course of global warming will ultimately lead to an increase in earthquake frequency in these regions

frost and soils implications for paleosols paleoclimates and stratigraphy abstract frost is a pedogenetic agent this paper describes the use of frost features in soil for paleoclimatic and stratigraphic interpretation it is possible to differentiate periods of frost activity from those of temperate pedogenesis by macroscopic and microscopic criteria and to distinguish between soils with pre syn and epigenetic frost effects an experimental approach is necessary to determine initial frost effects because they are usually difficult to observe at natural active sites work with ecologists also clarifies the evolution of frost affected soils under climatic and vegetational constraints vegetation has important effects on the thermal and hydraulic regimes of soils and on erosion susceptibility the recognition of fossil cryosoils often allows the reconstruction of sequences of paleoclimatic events in periods or environments with little or no micropaleontological evidence the interrelations between frost and other pedogenetic processes allow a better understanding of climatic evolution and deterioration throughout the neogene and especially during the quaternary and the holocene most of the inherited frost features in european soils are younger than 480 ka bp the differentiation between frost and tectonic perturbations is very important for calculation of soil erosional budgets