viscosity and finite strength of the mantle as determined from water and ice loads summary some recent examples of transient earth loads lake bonneville utah glacier bay alaska northeast greenland indicate that both the viscosity and finite strength of the mantle are lower than is commonly presumed a time constant 1 e of 4000 years is estimated for lake bonneville and of 1000 years for northeast greenland a strain rate of 10 14 is typical these figures imply viscosities in a homogeneous half space ranging from 1020 to 1021 poises an upper limit of finite strength is set by lake bonneville at a few times 106 dyn cm2 if mountain ranges like the sierra nevada or himalaya are regarded as dynamically supported rather than static systems this low value is not incompatible with other geologic observations

constraints on mantle viscosity and laurentide ice sheet evolution from pluvial paleolake shorelines in the western united states abstract the deformation pattern of the paleoshorelines of extinct lake bonneville were among the first features to indicate that earth s interior responds viscoelastically to changes in surface loads gilbert 1885 here we revisit and extend this classic study of isostatic rebound with updated lake chronologies for lake bonneville and lake lahontan as well as revised elevation datasets of shoreline features the first order domal pattern in the shoreline elevations can be explained by rebound associated with the removal of the lake load we employ an iterative scheme to calculate the viscoelastic lake rebound which accounts for the deformation of the solid earth and gravity field to calculate a lake load that is consistent with the load deformed paleotopography we find that the domal deformation requires a regional earth structure that exhibits a thin elastic thickness of the lithosphere 15 25 km and low sublithospheric maxwell viscosity 10 19 pa s after correcting for rebound due to the lake load shoreline feature elevations reveal a statistically significant northward dipping trend we attribute this trend to continent scale deformation caused by the ice peripheral bulge of the laurentide ice sheet and take advantage of the position of these lakes on the distal flank of the peripheral bulge to provide new insights on mantle viscosity and laurentide ice sheet reconstructions we perform ice loading calculations to quantify the deformation of the solid earth gravity field and rotation axis that is caused by the growth and demise of the laurentide ice sheet we test three different ice reconstructions paired with a suite of viscosity profiles and confirm that the revealed trend can be explained by deformation associated with the laurentide ice sheet when low viscosities below the asthenosphere are adopted we obtain best fits to shoreline data using ice models that do not have the majority of ice in the eastern sectors of the laurentide ice sheet with the caveat that this result can be affected by lateral variations in viscosity we show that pluvial lakes in the western united states can place valuable constraints on the laurentide ice sheet the shape of its peripheral bulge and the underlying mantle viscosity

viscosity structure of the crust and upper mantle in western nevada from isostatic rebound patterns of the late pleistocene lake lahontan high shoreline received 13 july 2005 revised 26 october 2006 accepted 31 january 2007 published 8 june 2007 1 large lakes can both produce and record significant crustal deformation we present an analysis of the isostatic rebound pattern recorded in the shorelines of paleolake lahontan in western nevada using a layered maxwell viscoelastic model the inferred viscosity structure depends on loading history we use three variants of a well documented lake surface elevation model as input and recover corresponding estimates of viscosity and density structure a simple two layer model with an elastic plate over an inviscid half space fits the observed elevation pattern quite well with a residual variance of 32 of the data variance using multilayered finite viscosity models the residual variance is reduced to 20 of the data variance which is very near to the noise level in the higher resolution models the viscosity is below 10 18 pa s over the depth range from 80 to 160 km the minimum viscosity is very similar to the value that has been seen in the eastern great basin from similar analyses of lake bonneville shorelines but the lowviscosity zone is thinner beneath bonneville making small adjustments to a seismically derived density structure allows an improved fit to the shoreline observations additionally we find that small variations in proposed loading models can result in presumably spurious density inversions and suggest that this modeling approach provides a test for loading histories

quantitative identification of erosional lake bonneville shorelines utah abstract although the major shorelines of pleistocene lake bonneville have been recognized for more than 100 years less prominent shorelines have proven difficult to quantitatively identify and correlate since the time of g k gilbert by applying the savitzky golay filter and methodology of hare et al to high resolution lidar data of selected erosional shorelines five distinct correlatable shorelines between the well described bonneville and provo shorelines on the transgressive limb of the lake bonneville hydrograph are documented the results provide a framework for determining whether these transgressive features represent lake oscillations or stillstands during the height of the last glacial maximum in the eastern great basin of the western united states with possible attendant paleoclimate implications

palaeoshorelines of glacial lake kuray chuja south central siberia form sediments and process glacial lake kuray chuja which occupied the kuray and chuja basins during the quaternary period marine isotope stages 2 and 3 left distinct shoreline features around the basin margins at the greatest extent the lake had a surface area of 2951 km2 with wind fetches up to 70 km wind waves constructed erosional erosional accumulative and accumulative strandlines the latter including spits tombolos barrier beaches and offshore bars strandlines range in altitude between c 1600 and 2100 m the range in altitudes demonstrating lake level variations through time the shoreline forms and stratigraphy are detailed particular attention is given to the presence of pocket beaches on rock coasts the alluvial strandlines of which have distinctive alongshore gradients although reasonably ascribed to regional differential tectonic uplift the possibility that the local alongshore gradients are augmented as a process response to alongshore drift of sediment in a sediment starved system of closed coastal cells is explored using a simple numerical model

quaternary palaeolakes in the evolution of semidesert basins with special emphasis on lake bonneville and the great basin u s a abstract this paper reviews attributes of quaternary lakes and lake basins which are often important in the environmental prehistory of semideserts basin floor and basin closure morphometry have set limits on palaeolake sizes lake morphometry and basin drainage patterns have influenced lacustrine processes and water and sediment loads have influenced basin neotectonics information regarding inundated runoff producing and extra basin spatial domains is acquired directly from the palaeolake record including the littoral morphostratigraphic record and indirectly by reconstruction increasingly detailed hypotheses regarding lake bonneville the largest late pleistocene palaeolake in the great basin are subjects for further testing and refinement oscillating transgression of lake bonneville began about 28 ka the highest stage occurred about 15 ka and termination occurred abruptly about 13 ka a final resurgence of perennial lakes probably occurred in many subbasins of the great basin between 11 and 10 ka when the highest stage of great salt lake successor to lake bonneville developed the gilbert shoreline and when the russell shoreline formed 500 600 km away in the carson desert of the lake lahontan basin the highest post gilbert stage of great salt lake which has been one of the few permanent lakes in the great basin during holocene time probably occurred between 3 and 2 ka a set of eighteen general observations regarding geologic aspects of the palaeolake record in semidesert basins is helping to guide quaternary studies in the great basin

recovering the true size of an eocene hyperthermal from the marine sedimentary record 1 hyperthermals episodes of abrupt global warming associated with the massive injection of carbon into the oceans and atmosphere represent possible analogs for future climate change however uncertainties in their magnitude rate and duration arising as a result of mixing processes and changes in carbonate preservation as the sediment record is formed complicate their use in constraining climate sensitivity and the role of carbon cycle feedbacks here we use cgenie an earth system model of intermediate complexity to assess likely magnitude and rate of carbon input taking a small hyperthermal event from the early middle eocene c22nh3 49 2ma as a case study we develop an iterative method combined with a sediment model simulating the formation and mixing of deep sea sediments to converge on an estimate for the true magnitude of the carbon cycle perturbation in the atmosphere and ocean that drives the event in inverting the 0 95 benthic 13 cexcursion recorded atocean drilling program site 1258 we obtain an estimate of at least 1 45 for the atmospheric co2 13 c excursion that drove event c22nh3 we also assess controls on intersite variation of event shape in model sediments and find that sedimentation rate is the strongest determinant of modeled event size with higher sedimentation rate sites recording the atmospheric signal more accurately our revised estimate for the size of c22nh3 implies a total carbon input almost two thirds higher than would be deduced if the recorded 13 c excursion magnitude was taken at face value

intraplate extensional tectonics of the eastern basin range inferences on structural style from seismic reflection data regional tectonics and thermal mechanical models of brittle ductile deformation the general lack of a correlation between earthquakes and surface faulting in the interior of the western u s cordillera has motivated our efforts to evaluate the geometry structural style and mechanism of normal faulting characteristic of this region of intraplate extension to address the problem we have interpreted over 1500 km of seismic reflection data and constructed detailed cross sections of the upper crust rheological models of the continental crust were calculated to examine the possibility of shallow quasi plastic flow and its influence on faulting in the eastern basin range the western colorado plateau and the middle rocky mountains our data and interpretations have revealed the following styles of cenozoic deformation 1 steep to low angle dip normal faulting along the wasatch fault 2 low angle dip and listric normal faulting possibly associated with movement on preexisting thrusts 3 the occurrence of asymmetric mostly eastward tilted tertiary basins that are bounded by low to moderate dipping planar and listric faults and 4 at least three vertically stacked en echelon low angle reflections in the mid to upper crust that dip gently westward from 3 km beneath the wasatch plateau to over 15 km at the utah nevada border these reflections are interpreted as normal detachment faults the structural style of the pervasive low to moderate angle dipping faults cannot be easily reconciled with classic brittle failure theory but the interpreted termination of normal faults at or above the deeper low angle reflections suggests the presence of shallow zones of ductile deformation that may have accommodated slip an important observation based on interpretations of seismic reflection profiles is that normal fault zones dip more gently in the subsurface than their associated scarps in unconsolidated surficial deposits segment boundaries of the wasatch fault zone apparently coincide with the positions of east trending displacement transfer structures in thrust sheets and the position of the precambrian uinta aulacogen suggesting that preexisting crustal structure partly controls the geometry of extension to examine the influence of ductile deformation quasi plastic flow was modeled for appropriate geotherms of the basin range and colorado plateau crusts these models provide constraints on the depth to the frictional quasi plastic transition that occurs as shallow as 8 km in the eastern basin range this depth also corresponds to the approximate depth above which most accurately determined earthquake foci for small earthquakes m 5 5 appear to nucleate at 10 15 km in or near the brittle ductile transition the rheological modeling suggests that a thermally deforming continental lithosphere plays an important role in the evolution of this extending intraplate region large scale low angle reflections may represent decollements and normal faults at the top of upper crustal zones of reduced shearing strength and higher ductility

a mechanical and thermal model for the evolution of the williston basin the williston basin is a large circular intracratonic basin containing over 4 km of sediments ranging in age from cambrian to tertiary data on seven formations from over 1300 wells in montana south dakota and north dakota were used to determine the shape of the basin over time by assuming that the lithosphere behaves like an elastic plate on a fluid substrate the shape of the basin could be closely matched using a point load the match was improved by adding the equation of a plane to the equation for elastic deformation before fitting the model to the data the planar adjustment allows for the effects of regional sedimentation or erosion or eustatic sea level changes the mechanical modeling indicates that the elastic strength of the lithosphere in this area has generally increased from the ordovician to the present the geometrical center of the basin migrated less than 20 km over 450 m y the direction and magnitude of tilt of the plane removed from the data is related to tectonic events in western north america the increasing deflection of the basin over time can be explained by a simple thermal model which would explain the thickening of the lithosphere consisting of conductive cooling of a hot region in the lithosphere depths to formations in a single well differ from the subsidence predicted by the elastic model with regional tilt removed because of global sedimentation events and the development in the mesozoic of a foreland thrust basin of which the williston basin became part the mechanical and thermal models constrain possible initiating mechanisms for this basin the thermal modeling and the absence of volcanics in the stratigraphic column rule out a shallow crustal heat source neither wrench faulting nor crustal stretching were likely to have been significant in the formation of the williston basin

response of calcareous nannofossils to the paleocene eocene thermal maximum from a shelf section in jordan abstract the paleocene eocene thermal maximum petm is known as an approximately 200 kyr long lasting interval of extreme global warming accompanied by major alterations in the ocean atmosphere system these include a negative carbon isotope excursion intense carbonate dissolution and biotic changes of marine floras and faunas the current study reports the response of calcareous nannofossils across the paleocene eocene boundary in a paleoshelf setting in jordan core os 28 clearly marked by a negative 13 c org excursion and the occurrence of characteristic excursion taxa e g discoaster araneus rhomboaster spp coccolithus bownii while this section suffers from intense dissolution at the onset of the event and the peak of the isotopic excursion it retains well preserved diverse nannofossil assemblages from the pre petm petm recovery and post petm intervals these assemblages are dominated by two taxa of inferred mesotrophic affinities coccolithus pelagicus toweius spp and show only low abundances of oligotrophic taxa discoaster spp fasciculithus spp sphenolithus spp overall there appear to be only relatively low level changes in the general assemblage composition across the petm during the post petm however there was a gradual decrease in relative abundance of c pelagicus and toweius spp this decline co coccured with a relative increase of coccolithus bownii and coccolithus foraminis and in its later phase was accompanied by an increase in the relative abundance of sphenolithus spp these changes indicate a possible shift towards less fertile conditions following the hyperthermal event the relatively muted signal of biotic change associated with the petm interval at this site was partly a consequence of poor preservation within the key sequence of the studied core on the other hand the low signal may also be indicative for local environment processes such as variations in riverine sourced nutrients salinity turbidity operating on a regional scale these local factors overrode the direct and indirect temperature signals that are the dominant control on nannofossil communities across the petm in open ocean sites finally the assemblages from the jordan section highlight further the overall spatial heterogeneity in reported responses of shelf area communities to the petm interval these heterogeneities have been observed in shelf assemblages from tanzania new jersey and the tethyan margins which again points to the strong influence of regional controls like river input in more marginal settings

morphological analysis of the lake lahontan shoreline and beachfront fault scarps pershing county nevada abstract with the diffusion equation representation of landform evolution providing reference calculations quantitative comparisons between profiles of the high stand of lake lahontan presented here and profiles of the lake bonneville shoreline scarps analyzed elsewhere reveal that the two sets of scarps are nearly identical morphologically when care is exercised in the selection of profiles the lahontan high stand scarps are remarkably reproducible from one profile to the next highly suggestive evidence that the processes that have shaped and changed the shape of these landforms are correspondingly regular slope angle differences of only 2 are both discernible and interpretable features of these late quaternary landforms cut in weakly consolidated alluvium at a level of uncertainty of no more than 50 per cent the mass diffusivity of the lahontan high stand is the same as the lake bonneville shoreline 1 1 gkg 1 gkg 1 m 2 ka this result suggests that much can be learned about the ages of late quaternary fault scarps cut in weakly consolidated alluvium throughout the basin and range province from their morphology alone the beachfront fault scarps themselves truncated by lake lahontan in our study area are morphologically only slightly older 15 to 18 ka bp than the lahontan high stand 12 ka bp

regional to global evolution of impacts of parameterized mountain wave drag in the lower stratosphere abstractmountain ranges are regional features on earth as are the regions of mountain wave drag mwd exerted by dissipating atmospheric gravity waves generated by flow over them however these r

shallow marine response to global climate change during the paleocene eocene thermal maximum salisbury embayment usa the paleocene eocene thermal maximum petm was an interval of extreme warmth that caused disruption of marine and terrestrial ecosystems on a global scale here we examine the sediments flora and fauna from an expanded section at mattawoman creek billingsley road mcbr in maryland and explore the impact of warming at a nearshore shallow marine 30 100 m water depth site in the salisbury embayment observations indicate that at the onset of the petm the site abruptly shifted from an open marine to prodelta setting with increased terrestrial and fresh water input changes in microfossil biota suggest stratification of the water column and low oxygen bottom water conditions in the earliest eocene formation of authigenic carbonate through microbial diagenesis produced an unusually large bulk carbon isotope shift while the magnitude of the corresponding signal from benthic foraminifera is similar to that at other marine sites this proves that the landward increase in the magnitude of the carbon isotope excursion measured in bulk sediment is not due to a near instantaneous release of 12c enriched co2 we conclude that the mcbr site records nearshore marine response to global climate change that can be used as an analog for modern coastal response to global warming

horizontal strain across the wasatch front near salt lake city utah two adjacent geodetic networks span a 105 km extent of the wasatch fault zone in north central utah one of the networks located in the vicinity of salt lake city was observed by the national ocean service national geodetic survey nos ngs in 1962 1963 triangulation mode and again in 1973 1974 combined triangulation trilateration mode to the north in the vicinity of ogden the u s geological survey usgs performed five separate trilateration surveys of the second network during the 1972 1981 interval when fit to a model assuming both temporal and spatial homogeneity for the strain rate the two independent data sets yield mutually consistent strain rate tensors subsets of the nos ngs data however suggest spatial variation in the strain field and a subset of the usgs data indicates a possible temporal variation in the strain rate the quality of the data is such that we are uncertain whether or not these apparent variations represent actual tectonic signals the strain rate tensors for the two complete data sets suggest an underlying deformational pattern characterized by east west e w maximum principal strain extension positive this pattern may also be inferred from regional seismicity and quaternary geology the suspected variations would imply that the area to the north of salt lake city experienced significant e w compression preceding 1978 in contradiction to the underlying strain pattern this compression may be caused by the mountainous block eastward adjacent to the fault zone displacing westward along a shallow angle west dipping detachment surface we speculate on the existence of an e w trending zone of weakness for example secondary faults located north of salt lake city to explain how the stress field to the north may be decoupled from that to the south where e w compression has not been detected while seismic and geologic information contribute some plausibility to our speculations the evidence for the existence of the suspected variations is inconclusive

rapid and sustained surface ocean acidification during the paleocene eocene thermal maximum the paleocene eocene thermal maximum petm has been associated with the release of several thousands of petagrams of carbon pg c as methane and or carbon dioxide into the ocean atmosphere system within 10 kyr on the basis of the co occurrence of a carbon isotope excursion cie widespread dissolution of deep sea carbonates and global warming in theory this rapid carbon release should have severely acidified the surface ocean though no geochemical evidence has yet been presented using boron based proxies for surface ocean carbonate chemistry we present the first observational evidence for a drop in the ph of surface and thermocline seawater during the petm planktic foraminifers from a drill site in the north pacific ocean drilling program site 1209 show a 0 8 decrease in boron isotopic composition 11b at the onset of the event along with a 30 40 reduction in shell b ca similar trends in 11b are present in two lower resolution records from the south atlantic and equatorial pacific these observations are consistent with significant global acidification of the surface ocean lasting at least 70 kyr and requiring sustained carbon release the anomalies in the b records are consistent with an initial surface ph drop of 0 3 units at the upper range of model based estimates of acidification

calcareous nannofossil fluxes and size fluctuations in the middle eocene 48 39 ma from ocean drilling program odp site 1209 in the tropical pacific ocean abstract pelagic carbonates constitute the majority of the ocean sediments particularly since the jurassic and record climatic and oceanic changes cenozoic sediments record glacial and interglacial periods as well as thermal maxima such as the petm paleocene eocene thermal maximum at ca 56 ma or the meco middle eocene climatic optimum that dates back to ca 40 ma the paleogene period shows variations in seawater temperature and atmospheric co2 as well as fluctuations of the carbonate compensation depth ccd in order to understand the actions and feedbacks between climate regulated amongst others by temperature partial pressure of co2 and atmospheric belts ccd fluctuations and pelagic carbonate producers the fluxes assemblages and sizes of calcareous nannofossils were studied from sediments dated between 48 and 39 ma including the meco interval calcareous nannofossils were analysed in from the odp ocean drilling project leg 198 site 1209a shatsky rise located in the tropical pacific the previously proposed age model for site 1209 has been slightly modified based on new calcareous nannofossil biostratigraphy recalibrated according to the gts 2012 in a long term perspective calcareous nannofossil assemblages and taxa size show significant changes during the middle eocene our data suggest that relatively oligotrophic conditions occurred between 48 and 45 ma interrupted by higher trophic conditions between 45 and 39 ma although oligotrophy occurred again during the meco discoaster spp show smaller sizes from 48 to 39 ma mirroring the global temperature decrease at 40 ma during the meco large sized reticulofenestrids with a peak of reticulofenestra umbilicus 14 m occurred whereas smaller but heavily calcified dictyococcites spp peak in the aftermath of the meco calcareous nannofossil fluxes show a significant increase with respect to background values during the caes carbonate accumulation event although they are low during the meco calcareous nannofossil fluxes seem to have had important impact on the oceanic carbon cycles by creating a carbonate flux to the ocean interior likely contributing to the ccd deepening

lithospheric flexure and the evolution of sedimentary basins the sediments that have accumulated in sedimentary basins during geological time represent a load on the lithosphere that should respond by flexure simple elastic and viscoelastic maxwell plate models have been used to examine quantitatively the contribution of flexure to basin formation the models have been used to predict the stratigraphy and gravity anomalies associated with basins for different thermal and loading histories the predictions of the models have been compared with observed stratigraphy and free air gravity anomalies from interior and cratonic basins the best overall fit to the observations is for an elastic plate model in which the flexural strength of the lithosphere increases with age a similar model has recently been used successfully to explain observations from continental margin basins oceanic islands and seamounts and deep sea trench outer rise systems this model explains the increase in the overall width of basins during their evolution as well as the stratigraphy of the basin edges the apparent decrease in the widths of some basins through time can be explained by the model if sediment deposition is followed by erosion of the basin and its edges the models results suggest that the flexural properties of continental and oceanic lithosphere are generally similar and that flexure is an important factor to consider in backstripping studies in which the tectonic subsidence of a basin is isolated and stratigraphic studies in which relative changes of sea level are estimated

shoreline processes and the age of the lake lahontan highstand in the jessup embayment nevada the well developed shoreline record of pluvial lake lahontan in the jessup embayment nevada is used to refine the history of late pleistocene lake level fluctuations and to assess controls on shoreline development and distribution controls on the strength and type of shorelines developed include local slope the amount and characteristics of sediment available for transport the availability of accommodation space and length of time the lake level resides at a particular shoreline elevation at the sehoo highstand and during the early part of the regression strong storm winds and waves from the south southeast set up a clockwise net shore drift pattern near the head of the embayment although significant differences in local slope geometry of the shoreline and wave energy existed in the embayment crestal heights of constructional shoreline features formed at the highstand vary 2 6 m in elevation and hence provide a relatively precise marker of the highstand elevation radiocarbon dating of a camel bone preserved in high shoreline deposits indicates that the lake reached its highest elevation of 1338 5 m in the embayment and receded from that elevation immediately prior to 13 070 60 yr b p similar and slightly older radiocarbon ages on gastropod shells preserved in barrier deposits at 1327 m 13 280 110 yr b p and 1331 m 13 110 110 yr b p suggest that the final rise to the highstand was very rapid and that the lake maintained its highest stand for a very brief period of time perhaps only for years or decades the brevity of the highstand is reasonable in light of the recent formation of similar barrier features in modern pyramid lake which formed in less than seven months due to a rapid increase in lake level

towards an understanding of the ca isotopic signal related to ocean acidification and alkalinity overshoots in the rock record abstract in this contribution we explore the idea that the ca isotope proxy has utility as an indicator of carbonate authigenesis i e post depositional precipitation of caco3 within the sedimentary package given the strong contrast in isotopic fractionation factor between the formational and diagenetic environments ca isotopes have the potential to fingerprint carbonate authigenesis when it occurs close to the seawater sediment interface we demonstrate that ca isotopes are particularly applicable to exploring ocean acidification events and potentially ocean anoxic events and focus our attention on ocean acidification related to the paleocene eocene thermal maximum petm we present three scenarios that vary in the magnitude and duration of the carbon fluxes that are simulated using an earth system model of intermediate complexity cgenie and we use the cgenie output to constrain the upper boundary conditions of 1 d reactive transport models of authigenesis and recrystallization in the sedimentary section along with simple mixing calculations the models inform our exploration of the hypothesis that authigenic carbonate induced by a saturation state overshoot during the petm explains recently published ca isotope records and perhaps bulk carbonate records over ocean anoxic event oae 2 our simulations suggest that fractionation factor variability does not explain the petm 44ca records and we propose a 44ca caco3 space framework to assist with the elucidation of authigenic additions over time scales that are short relative to the residence time of ca in the ocean 1 ma ultimately we find that the authigenic zone generated in the sedimentary column may be influenced by alkalinity overshoots or redox state the caco3 produced in this zone can overprint temporal signals with depth dependent signals that reflect lithology and sedimentation rate and need not be spatially uniform even when driven by a global event ultimately we demonstrate the utility of ca isotopes for exploring short time scale climatic events and a quantitative framework to guide interpretations

modification of wave cut and faulting controlled landforms from a casual observation that the form of degraded fault scarps resembles the error function this investigation proceeds through an elementary diffusion equation representation of landform evolution to the application of the resulting equations to the modern topography of scarplike landforms the morphologic observations can be analyzed either in the form of one or more cross strike elevation profiles or in the form of the slope offset plot a point plot of maximum scarp slope versus scarp offset working with either or both of these data representations for nine geologic structures which range in age from 3 to 400 ka b p and in offset from 1 to 50 m we apply analytical solutions for the vertical initial value scarp the vertical continuous offset scarp and the finite slope initial value scarp the model calculations are intrinsically ambiguous yielding as the final answer only the product t in the case of the initial value problem or the product a 1 in the case of the repeated faulting problem here t is the age of a single scarp forming event 2a is the vertical slip rate and is the mass diffusivity a single profile across three sea cliffs along the santa cruz california coast is analyzed as three separate initial value problems a reasonably constrained age for the sea cliff standing above the highway 1 platform returns 11 gkg 1 gkg 1 m2 ka with this we can date the two older sea cliffs in fact we do the converse age estimates for these two older sea cliffs based on a uniform rate of uplift both yield the same as for the lower sea cliff we treat a single profile of the raymond fault in pasadena san marino in terms of the repeated faulting problem for it the uplift rate of r crook and others yields 16 gkg the very substantial preexisting offset across the raymond fault must have been buried leveled some 230 ka b p when the modern topography began to form our analysis of the lake bonneville shoreline scarps reveals a dependence of t on 2a suggestive of nonlinear modification processes this appearance is treated with the finite slope initial value scarp model to determine 1 1 gkg for the lake bonneville shoreline scarps the suggestion of m n machette that approximately 100 000 year old meter high scarps are unobservable in weakly consolidated alluvial terranes of the basin and range and rio grande rift valley provinces can be formulated as 1 gkg the coincidence between this inequality and the lake bonneville shoreline is striking and it suggests that the value of 1 gkg may be generally applicable as a good first approximation to the modification of alluvial terranes within the semiarid regions of the western united states the lake bonneville shoreline is the basis for dating four sets of fault scarps in west central utah the drum mountains fault scarps can be modeled in several different circumstances but the most likely interpretation is that these fault scarps formed as the result of a single episode of normal faulting 3 6 to 5 7 ka b p the younger age is associated with quite low initial slope angles 25 the other three sets of fault scarps show no evidence for finite initial value slopes fault scarps along the eastern base of the fish springs range are very young 3 ka b p we estimate the age of fault scarps along the western flank of the oquirrh mountains to be 32 ka b p which meets the weak geologic constraint that they be older than the lake bonneville shoreline fault scarps along the northeastern margin of the sheeprock mountains are even older 53 ka b p an intriguing consequence of our single event analysis of these scarps is that an 11 5 m offset occurred in a single earthquake

reinterpretation of the exposed record of the last two cycles of lake bonneville western united states a substantially modified history of the last two cycles of lake bonneville is proposed the bonneville lake cycle began prior to 26 000 yr b p the lake reached the bonneville shoreline about 16 000 yr b p poor dating control limits our knowledge of the timing of subsequent events lake level was maintained at the bonneville shoreline until about 15 000 yr b p or somewhat later when catastrophic downcutting of the outlet caused a rapid drop of 100 m the provo shoreline was formed as rates of isostatic uplift due to this unloading slowed by 13 000 yr b p the lake had fallen below the provo level and reached one close to that of great salt lake by 11 000 yr b p deposits of the little valley lake cycle are identified by their position below a marked unconformity and by amino acid ratios of their fossil gastropods the maximum level of the little valley lake was well below the bonneville shoreline based on degree of soil development and other evidence the little valley lake cycle may be equivalent in age to marine oxygenisotope stage 6 the proposed lake history has climatic implications for the region first because the fluctuations of lake bonneville and lake lahontan during the last cycle of each were apparently out of phase there may have been significant local differences in the timing and character of late pleistocene climate changes in the great basin second although the bonneville and little valley lake cycles were broadly synchronous with maximum episodes of glaciation environmental conditions necessary to generate large lakes did not exist during early wisconsin time

deglaciation induced vertical motion of the north american continent and transient lower mantle rheology the last deglaciation event of the current ice age which began approximately 18 000 years ago and ended about 7000 years ago continues to exert a profound influence on the vertical motion of the solid earth in and surrounding the regions which were once ice covered observations of such vertical motions may be employed to constrain the radial viscoelastic structure of the planet and therefore to contribute in an important way to the understanding of geodynamic processes in general in this paper both present day rates of vertical motion as recorded on tide gauges and long time scale records of vertical motion as recorded in 14c controlled relative sea level histories are employed to refine previously constructed models of the radial viscoelastic structure an interesting sidelight to this analysis is the demonstration that the lower mantle viscosity inferred from the vertical motion data could represent a transient rather than the steady state value a fact which would help considerably to reconcile the small viscosity stratification required by the glacial rebound data with the large stratification which seems to be required by some recent analyses of the geoid height anomalies associated with internal density heterogeneity of the mantle which has been revealed by application of seismic tomographic techniques a further product of these new analyses is obtained by the application of the glacial isostatic adjustment model to filter this signal from the secular trends of relative sea level observed on tide gauges from both the east and west coasts of the north american continent these results may be important in the context of recently proposed scenarios of climatic change

response of calcareous nannofossils to the paleocene eocene thermal maximum observations on composition preservation and calcification in sediments from odp site 1263 walvis ridge sw atlantic abstract in this study we present the results of a detailed analysis on calcareous nannofossil assemblages from sediment cores of odp site 1263 southern east atlantic walvis ridge this section represents one of the few complete deep sea sections that document the paleocene eocene thermal maximum petm in the pelagic realm the petm transient event was characterized by a brief but intense interval of global warming a global negative carbon isotope excursion cie and widespread dissolution of seafloor carbonate sediments paired analysis at polarizing light microscope lm and scanning electron microscope sem documents the different behavior of nannofossils through the different phases of the petm at the onset of cie within the cie and during the recovery interval the presence of anomalous specimens and morphotypes within some nannofossil taxa recorded during previous lm high resolution analyses has been further investigated in selected samples at the sem besides the known representatives of the cie petm excursion nanno flora as rhomboaster calcitrapa group and discoaster anartios the analysis revealed the presence of peculiar morphotypes of fasciculithus and deformed specimens of discoaster nobilis group discoaster mediosus and discoaster multiradiatus that are considered related to the anomalous amount of co2 in the ocean atmosphere system during the early phase of petm comparative analyses were performed in few selected samples from other petm sections located at different latitudes in the atlantic and pacific oceans although the anomalous geochemical conditions during the petm cie interval seem to have had some influence on the nannofossil production calcification and assemblage composition it results that local productivity together with post depositional diagenetic conditions were additional important controlling factors on nannofossil assemblages preliminary data from eocene thermal maximum 2 etm2 or elmo suggest that nannofossil malformations are not exclusive of the petm and are associated to other episodes of perturbation of the c cycle

pleistocene deglaciation and the earth s rotation implications for mantle viscosity summary recent results from the analysis of postglacial rebound data suggest that the viscosity of the earth s mantle increases through the transition region models which fit both relative sea level and free air gravity data have viscosities which increase from a value near 1022 poise in the upper mantle beneath the lithosphere to a value of about 1023 poise in the lower mantle in this paper we analyse the effect of deglaciation upon the earth s rotation and thereby show that the observed secular trend polar wander evident in the ils ipms pole path and measurements of the non tidal acceleration of the length of day are both consistent with the viscosity profile deduced from postglacial rebound the two analyses are therefore mutually reinforcing

thematic mapper laser profile resolution of holocene lake limit great salt lake desert utah abstract the limit of great salt lake s maximum expansion onto the floor of the great salt lake desert during holocene time is marked by a break in slope which is clearly depicted in terrain models which merge thematic mapper tm multispectral scanner data and aerial profiling of terrain system apts laser profile data mean elevations of apts coincident tm pixels are strongly correlated with reflectance in tm bands 5 and 7 when and where sufficient moisture contrasts among terrain components are high tm apts models and field surveys place the highest holocene standing water at an elevation of 4221 ft 1286 7 m

vertical deformation associated with normal fault systems evolved over coseismic postseismic and multiseismic periods vertical deformation of extensional provinces varies significantly and in seemingly contradictory ways sparse but robust geodetic seismic and geologic observations in the basin and range province of the western united states indicate that immediately after an earthquake vertical change primarily occurs as subsidence of the normal fault hanging wall a few decades later a 100 km wide zone is symmetrically uplifted the preserved topography of long term rifting shows bent and tilted footwall flanks rising high above deep basins we develop finite element models subjected to extensional and gravitational forces to study time varying deformation associated with normal faulting we replicate observations with a model that has a weak upper mantle overlain by a stronger lower crust and a breakable elastic upper crust a 60 dipping normal fault cuts through the upper crust and extends through the lower crust to simulate an underlying shear zone stretching the model under gravity demonstrates that asymmetric slip via collapse of the hanging wall is a natural consequence of coseismic deformation focused flow in the upper mantle imposed by deformation of the lower crust localizes uplift under the footwall the breakable upper crust is a necessary model feature to replicate footwall bending over the observed width 10 km which is predicted to take place within 1 2 decades after each large earthquake thus the best preserved topographic signature of rifting is expected to occur early in the postseismic period the relatively stronger lower crust in our models is necessary to replicate broader postseismic uplift that is observed geodetically in subsequent decades

complex exposure histories of chert clasts in the late pleistocene shorelines of lake lisan southern israel activities of 26 al and 10 be in five chert clasts sampled from two beach ridges of late pleistocene lake lisan precursor of the dead sea in southern israel indicate low rates of chert bedrock erosion and complex exposure burial and by inference transport histories the chert clasts were derived from the senonian mishash formation a chert bearing chalk which is widely exposed in the nahal zin drainage basin the drainage system that supplied most of the material to the beach ridges simple exposure ages assuming only exposure at the beach ridge sampling sites range from 35 to 354 ky using the ratio 26 al 10 be total clast histories range from 0 46 to 4 3 my unrelated to the clasts current position and exposure period on the late pleistocene beach ridges 160 177 m below sea level optically stimulated luminescence dating of fine sediments from the same and nearby beach ridges yielded ages of 20 0 s 1 4 ka and 36 1 s 3 3 ka these ages are supported by the degree of soil development on the beach ridges and correspond well with previously determined ages of lake lisan which suggest that the lake reached its highest stand around 27 000 cal years bp if the clasts were exposed only once and than buried beyond the range of significant cosmogenic nuclide production then the minimum initial exposure and the total burial times before delivery to the beach ridge are in the ranges 50 1300 ky and 390 3130 ky respectively alternatively the initial cosmogenic dosing could have occurred during steady erosion of the source bedrock back calculating such rates of rock erosion suggests values between 0 4 and 12 m my 1 t he relatively long burial periods indicate extended sediment storage as colluvium on slopes and or as alluvial deposits in river terraces some clasts may have been stored for long periods in abandoned pliocene and early pleistocene routes of nahal zin to the mediterranean before being transported again back into the nahal zin drainage system and washed on to the shores of lake lisan during the late pleistocene copyright 2003 john wiley sons ltd

postseismic relaxation driven by brittle creep a possible mechanism to reconcile geodetic measurements and the decay rate of aftershocks application to the chi chi earthquake taiwan we evaluate the effect of coseismic stress changes on the fault slip at midcrustal depth assuming a velocity strengthening brittle creep rheology we show that this model can help reconcile the time evolution of afterslip as measured from geodesy with aftershocks decay we propose an analytical expression for slip of the brittle creeping fault zone bcfz that applies to any dynamic or static stress perturbation including shear stress and normal stress changes the model predicts an initial logarithmic increase of slip with time postseismic slip rate decays over a characteristic time t r a that does not depend on the amplitude of the stress perturbation and it asymptotically joins the long term creep imposed by interseismic stress buildup given that the seismicity rate might be considered proportional to the sliding velocity of the bcfz the model predicts a decay rate of aftershocks that follows omori s law with a mathematical formalism identical to that of dieterich 1994 although based on a different mechanical rationale our model also differs from dieterich s model in that it requires that aftershock sequences and deep afterslip as constrained from geodetic measurements should follow the same temporal evolution we test this for the 1999 chi chi earthquake m w 7 6 and find that both sets of data are consistent with a model of afterslip due to the response of the bcfz the inferred relaxation time t r 8 5 years requires a value for a log v being the coefficient of friction in the range between 1 3 10 3 and 10 2

tide gage measurements of uplift along the south coast of alaska annual mean sea levels along the south coast of alaska are used to measure uplift along the alaska aleutian subduction zone oceanographic effects are removed from the observed annual mean sea levels by subtracting a correction that is proportional to the sea level fluctuations observed in southeast alaska that correction is effective in reducing fluctuations in the observed annual mean sea level as far west as the tip of alaska peninsula additional corrections to remove the eustatic rise in sea level and the apparent fall in sea level due to postglacial isostatic rebound of the land are introduced this corrected sea level record should provide a measure of tectonic subsidence in the area affected by the 1964 alaska earthquake postseismic uplift occurs where coseismic subsidence was observed and postseismic subsidence occurs where coseismic uplift was observed the immediate postseismic response is damped out within the first decade and the subsequent uplift rates appear to be steady over the 1974 1989 interval however some of those rates seem to be too high to be sustained over the 1000 year earthquake recurrence interval appropriate to this area if the interseismic deformation is only to recover the coseismic displacement thus a long term 100 years relaxation in uplift rates is postulated the immediate time constant 5 years postseismic relaxation is attributed to postseismic slip on the plate interface directly downdip from the coseismic rupture the long term time constant 100 years relaxation is attributed to flow in the asthenosphere

upper mantle viscosity derived from the difference in rebound of the provo and bonneville shorelines lake bonneville basin utah twenty four new field measurements of elevation of provo level and bonneville level shoreline terraces provide data for reanalysis of isostatic rebound in the lake bonneville basin analysis of the differential rebound between the provo shoreline maximum rebound of 43 m and the bonneville shoreline maximum rebound of 69 m requires that the latter be an equilibrium shoreline within the possible measurement errors the provo shoreline formed after the elastic lithosphere had attained at least 91 equilibration to the removal of the water load between the bonneville and provo shorelines within the errors the provo may also represent an equilibrium shoreline from the new data presented in this paper the best estimate of the upper limit of effective viscosity of the uppermost mantle assuming a half space model and a 2000 year time interval between the bonneville and provo shorelines is 2 1019 n s m 2 2 1020 p in addition comparison of shoreline rebound profiles for both shorelines with theoretical plate flexure models indicates that the mean flexural rigidity of the basin and range lithosphere in this region is 1 1023 n m or slightly less

evolution of the northern santa cruz mountains by advection of crust past a san andreas fault bend the late quaternary marine terraces near santa cruz california reflect uplift associated with the nearby restraining bend on the san andreas fault excellent correspondence of the coseismic vertical displacement field caused by the 17 october 1989 magnitude 7 1 loma prieta earthquake and the present elevations of these terraces allows calculation of maximum long term uplift rates 1 to 2 kilometers west of the san andreas fault of 0 8 millimeters per year over several million years this uplift in concert with the right lateral translation of the resulting topography and with continual attack by geomorphic processes can account for the general topography of the northern santa cruz mountains

climate model and proxy data constraints on ocean warming across the paleocene eocene thermal maximum article constraining the greenhouse gas forcing climatic warming and estimates of climate sensitivity across ancient large transient warming events is a major challenge to the palaeoclimate research community here we provide a new compilation and synthesis of the available marine proxy temperature data across the largest of these hyperthermals the paleocene eocene thermal maximum petm this includes the application of consistent temperature calibrations to all data including the most recent set of calibrations for archaeal lipid derived palaeothermometry this compilation provides the basis for an informed discussion of the likely range of petm warming the biases present in the existing record and an initial assessment of the geographical pattern of petm ocean warming to aid interpretation of the geographic variability of the proxy derived estimates of petm warming we present a comparison of this data with the patterns of warming produced by high pco2 sim ulations of eocene climates using the hadley centre atmosphere ocean general circulation model aogcm hadcm3l on the basis of this comparison and taking into account the patterns of intermediate water warming we estimate that the global mean surface temperature anomaly for the petm is within the range of 4 to 5 c

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

effects of lithospheric viscoelastic relaxation on the contemporary deformation following the 1959 mw 7 3 hebgen lake montana earthquake and other areas of the intermountain seismic belt 1 the 1959 mw 7 3 hebgen lake mt normal faulting earthquake occurred in an extensional stress regime near the yellowstone volcanic field time dependent crustal deformation data following this major earthquake were acquired by precise trilateration and gps surveys from 1973 to 2000 around the hebgen lake fault zone modeling the changes of baseline lengths across and near the fault reveals a lateral variation of transient rheology in which the lithosphere is stronger near the hebgen lake fault zone than in the vicinity of the yellowstone volcano system the models also imply that the lower crust is stronger than the upper mantle in agreement with results from studies of postseismic and post lake filling relaxations 100 years in addition evaluations of the postseismic motion produced by the hebgen lake and the 1983 mw 6 9 borah peak id earthquakes indicate that horizontal transient motion of up to 1 mm yr contribute significantly to the contemporary regional crustal deformation near the epicentral areas for the eastern basin and range 500 km south of the hebgen lake fault similar rheologic models were derived from the observed uplift associated with the lake bonneville rebound and were used to evaluate the postseismic deformation associated with six most recent paleoearthquakes of the wasatch fault zone and three m 5 6 historic earthquakes of northern utah the results show 0 1 mm yr of horizontal postseismic motion at present time that are within the horizontal uncertainties of continuous gps velocity from the basin and range and significantly smaller than the contemporary extension of 1 3 mm yr in the wasatch front

the midlatitude lower stratospheric mountain wave valve layer abstractthe vertical propagation and attenuation of mountain waves launched by new zealand terrain during the deep propagating gravity wave experiment deepwave field campaign are investigated new zealand mountain waves were frequently attenuated in a lower stratospheric weak wind layer between z 15 and 25 km this layer is termed a valve layer as conditions within this layer primarily minimum wind speed control mountain wave momentum flux through it analogous to a valve controlling mass flux through a pipe this valve layer is a climatological feature in the wintertime midlatitude lower stratosphere above the subtropical jet mountain wave dynamics within this valve layer are studied using realistic weather research and forecasting wrf model simulations that were extensively validated against research aircraft radiosonde and satellite observations locally wave attenuation is horizontally and vertically inhomogeneous evidenced by numerous regions with wave induced low richardson numbers an

constraints on transient viscoelastic rheology of the asthenosphere from seasonal deformation we discuss the constraints on short term asthenospheric viscosity provided by seasonal deformation of the earth we use data from 195 globally distributed continuous global navigation satellite system stations surface loading is derived from the gravity recovery and climate experiment and used as an input to predict geodetic displacements we compute green s functions for surface displacements for a purely elastic spherical reference earth model and for viscoelastic earth models we show that a range of transient viscoelastic rheologies derived to explain the early phase of postseismic deformation may induce a detectable effect on the phase and amplitude of horizontal displacements induced by seasonal loading at long wavelengths 1 300 4 000 km by comparing predicted and observed seasonal horizontal motion we conclude that transient asthenospheric viscosity cannot be lower than 5 10 17 pa s suggesting that low values of transient asthenospheric viscosities reported in some postseismic studies cannot hold for the seasonal deformation global average

biomineralization within vesicles the calcite of coccoliths coccolithophores are a group of unicellular plant plankton which produce exoskeletons of minute calcite plates called coccoliths despite their small size 1 10 m across coccoliths are remarkably elaborate biomineral structures characterized by precise control of both nucleation and growth of calcite by the organic system they are also of considerable environmental and applied geological importance coccolithophores occur in enormous abundances forming a significant proportion of total marine primary production and carbon fixation especially in open ocean environments their biogeochemical impact is magnified by export of coccoliths to the ocean floor where coccoliths are the largest single component of deep sea sediments forming vast accumulations of calcareous oozes and chalks including the late cretaceous chalks of northwestern europe moreover coccoliths are extensively employed by geologists as marker fossils to determine the ages of sediments especially from drill cores more recently satellite imaging of immense coccolithophore blooms has led to extensive multi disciplinary research into their biology and impact on the marine ecosystem and global carbon cycle e g westbroek et al 1993 paasche 2002 thierstein and young in press biological affinities coccolithophores belong to the algal division or phylum haptophyta other haptophytes are non calcifying and include the well known genera phaeocystis prymnesium pavlova and chrysochromulina they are all characterized by possessing golden brown chloroplasts two smooth flagella and a third flagellum like organelle the haptonema the haptonema shows distinctive coiling behavior and has a quite different microtubular sub structure from flagella molecular genetic data have shown that the haptophytes are a group discrete from other algal protists that probably originated during the precambrian 600 ma protist radiation and acquired chloroplasts subsequently possibly in the late palaeozoic ca 300 400 ma as a result of secondary endosymbiosis medlin et al 1997 molecular genetic phylogenies of the haptophytes are still being developed but all results to date edvardsen

shelf and open ocean calcareous phytoplankton assemblages across the paleocene eocene thermal maximum implications for global productivity gradients abrupt global warming and profound perturbation of the carbon cycle during the paleocene eocene thermal maximum petm ca 55 ma have been linked to a massive release of carbon into the ocean atmosphere system increased phytoplankton productivity has been invoked to cause subsequent co2 drawdown cooling and environmental recovery however interpretations of geochemical and biotic data differ on when and where this increased productivity occurred here we present high resolution nannofossil assemblage data from a shelf section the u s geological survey usgs drill hole at wilson lake new jersey and an open ocean location ocean drilling program odp site 1209 paleoequatorial pacific these data combined with published biotic records indicate a transient steepening of shelf offshelf trophic gradients across the petm onset and peak with a decrease in open ocean productivity coeval with increased nutrient availability in shelf areas productivity levels recovered in the open ocean during the later stages of the event which coupled with intensified continental weathering rates may have played an important role in carbon sequestration and co2 drawdown

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

a reevaluation of the isostatic rebound of lake bonneville recent data pertaining to the uplift of the provo and bonneville shorelines of the late pleistocene lake bonneville are evaluated in a reanalysis using a rigorous model of deformation of a plane earth comprising an elastic layer overlying a viscoelastic channel the new observations constrain the wavelength and amplitude of the uplift of two shorelines formed at two different epochs and they partly resolve the ambiguities in the plausible mechanical parameters found in previous solutions the results indicate that the effective thickness of the elastic lithosphere is 28 to 30 km equal to the seismically determined crustal thickness in the region the estimate of the upper mantle viscosity in the region varies from 1 5 3 4 lo19 pa s to 2 1 5 8 l018 pa s depending on whether the upper mantle is assumed to be of uniform viscosity or the flow is confined to a narrow channel in the asthenosphere the predicted rate of present uplift at the center of the desiccated lake is 0 06 mm yr and 0 03 mm yr for the shallow channel and uniform mantle models respectively these values are beyond the first order leveling accuracies and the question of the existence of a narrow channel in the region cannot be resolved with the available observations

erosion isostatic rebound models for uplift an application to south eastern australia summary a mountain s history includes two distinctive phases one of active tectonism and construction followed by one of erosion and passive isostatic rebound in the first phase uplift is driven by tectonic mechanisms while in the second phase base levels of the terrain are regionally uplifted it is this latter phase that is modelled here the starting model is a mountain range initially in isostatic equilibrium on a viscoelastic plate defined by the effective flexural rigidity d and relaxation time 7 the rate of erosion at any time t is assumed to be proportional to the elevation at that time with an erosional time constant 7 for a given present day topography the uplift erosion gravity and stress can be computed through time as functions of d 7 7 and the time to at which the erosional rebound mechanism became the dominant landscaping process the model has been applied to the highlands of south eastern australia which we assume to be an erosional residue of the palaeozoic lachlan fold belt observations of rivers cutting through cainozoic basalts and other geomorphological indicators of uplift can then be interpreted in terms of the isostatic rebound and there is no need to invoke active tectonic uplift mechanisms the model parameters that fit the observations are t 150 3 50myr dt 2 5 x ioz4nmmyr and to 180 200myr the predicted late palaeozoic fold belt topography is about 75 per cent greater than the present day values topographic depressions are predicted to have occurred along the margins of the formerly elevated areas and the model is relevant to understanding the evolution of basins flanking the highlands within the highland area erosion generally exceeds uplift but in some regions the two are approximately equal in keeping with recent geomorphological observations the flexural stresses associated with the erosion initially increase with time and maximum values in south eastern australia are predicted to occur in late cainozoic time with the stress state near the surface being mainly tensional

evidence of surface water oligotrophy during the paleocene eocene thermal maximum nannofossil assemblage data from ocean drilling program site 690 maud rise weddell sea 1 nannoplankton assemblages at ocean drilling program site 690 maud rise weddell sea experienced an abrupt and dramatic transformation at the onset of the paleocene eocene thermal maximum petm at 55 m y the major assemblage shift suggests a change from colder more productive surface waters to warmer more oligotrophic conditions significant restructuring of assemblages during the later part of the petm indicates that nannoplankton communities were not stable and that surface water conditions changed although they remained warm and oligotrophic combined with benthic foraminiferal assemblage data nannoplankton assemblage results suggest increased sequestration of nutrients in shelf environments and starvation of the open ocean although the petm was a short lived event it appears to have had long term effects on nannoplankton leading to the extinction of fasciculithus a dominant paleocene genus

the lageos constraint on deep mantle viscosity results from a new normal mode method for the inversion of viscoelastic relaxation spectra the recently observed acceleration in the node of the orbit of the lageos satellite has previously been shown to provide a good constraint on the viscosity of the earth s mantle beneath the 670 km seismic discontinuity this paper explores the extent to which the previously inferred lower mantle viscosity may be traded off against variations of other properties of the radial viscoelastic structure we show explicitly that the nontidal acceleration of rotation inferred from the lageos data and predicted as a consequence of the earth s response to the last deglaciation event of the current ice age is relatively insensitive both to variations of lithospheric thickness and to the presence or absence of plausible chemical heterogeneity across the 670 km interface it therefore provides a high quality constraint on the viscosity of the deep mantle with the upper mantle viscosity fixed at the nominal value of 1021 pa s the bounds on lower mantle viscosity lm are such that 2 1021 pa s lm 6 1021 pa s even when allowance is made for the presence of a viscous boundary layer at the base of the upper mantle such as would exist if the mantle convective circulation were layered

does rapid change in ice loading modulate strain accumulation and release in glaciated tectonically active regions there are major glaciated regions of the world that are also seismologically active changes in the thickness of ice due to glacier surges advances or retreats produce stress changes that may be a significant fraction of the tectonic stress accumulated during an earthquake cycle the changes in ice loading can affect both the normal and shear stress on a fault with stresses being enhanced or reduced depending on glacier and fault geometry the stress change has a nearly instantaneous elastic component and a longer time scale viscoelastic component thus i propose that glacier motion can produce geodetically significant horizontal and vertical crustal displacements and can affect strain strain rate and the time of occurrence of earthquakes in regions that are not tectonically active rapid ice motion can also produce locally significant and geodetically detectable crustal deformations

alleviation of a systematic westerly bias in general circulation and numerical weather prediction models through an orographic gravity wave drag parametrization systematic westerly biases in the northern hemisphere wintertime flow of the meteorological office 15 layer operational model and 11 layer general circulation model are described evidence that the failure to parametrize subgrid scale orographic gravity wave drag may account for such biases is presented this evidence is taken from aircraft studies surface pressure drag measurements and studies of the zonally averaged momentum budget a parametrization scheme is described in which the surface stress is proportional to the near surface wind speed and static stability and to the variance of subgrid scale orography the stress is absorbed in the vertical by considering the influence of such gravity wave activity on static stability and vertical wind shear a richardson number dependent wave breaking formulation is devised and the vertical stress profile determined by a saturation hypothesis whereby the breaking waves are maintained at marginal stability it is shown that wave breaking preferentially occurs in the boundary layer and in the lower stratosphere results from a simple zonally symmetric model show how the adjustment to thermal wind balance with a wave drag in the stratosphere warms polar regions by adiabatic descent and decelerates the mean westerlies in the troposphere the influence of the parametrization scheme on integrations of the 11 layer model is described and found to be generally beneficial in a discussion of the reasons why this problem has only recently emerged it is suggested that the satisfactory northern hemisphere winter circulations of previous coarser general circulation models were due to a compensation implied by underestimating both the surface drag and the horizontal flux of momentum by explicitly resolved large scale eddies

glacial topographic interactions in the teton range wyoming 1 understanding interactions among tectonics topography climate and erosion is fundamental to studies of mountainous landscapes here we combine topographic analyses with modeled distributions of precipitation insolation and flexural isostasy to present a conceptual model of topographic evolution in the teton range wyoming and test whether efficient glacial relief production has contributed to summit elevations the conceptual model reveals a high degree of complexity inherent in even a relatively small glaciated mountain range back tilting has caused topographic asymmetry with the greatest relief characterizing eastern catchments in the center of the range two high summits grand teton and mount moran rise hundreds of meters above the surrounding landscape their elevations set by the threshold hillslope angle and the spacing between valleys hosting large erosionally efficient glaciers only basins 20 km2 held glaciers capable of eroding sufficiently rapidly to incise deeply and maintain shallow downvalley gradients on the eastern range flank glacial erosion here was promoted by 1 prevailing westerly winds transporting snow to high relief eastern basins leading to cross range precipitation asymmetry 2 the wind blown redistribution of snow from open western headwaters into sheltered eastern cirques with the associated erosion driven migration of the drainage divide increasing eastern accumulation areas and 3 tall steep hillslopes providing shading snow influx from avalanching and insulating debris cover from rockfalls to valley floor glaciers in comparison the topographic enhancement of glacial erosion was less pronounced in western and smaller eastern basins despite dramatic relief production insufficient rock mass is removed from the teton range to isostatically raise summit elevations

nannoplankton malformation during the paleocene eocene thermal maximum and its paleoecological and paleoceanographic significance the paleocene eocene thermal maximum petm is characterized by a transient group of nannoplankton belonging to the genus discoaster our investigation of expanded shelf sections provides unprecedented detail of the morphology and phylogeny of the transient discoaster during the petm and their relationship with environmental change we observe a much larger range of morphological variation than previously documented suggesting that the taxa belonged to a plexus of highly gradational morphotypes rather than individual species we propose that the plexus represents malformed ecophenotypes of a single species that migrated to a deep photic zone refuge during the height of petm warming and eutrophication anomalously high rates of organic matter remineralization characterized these depths during the event and led to lower saturation levels which caused malformation the proposed mechanism explains the co occurrence of malformed discoaster with pristine species that grew in the upper photic zone moreover it illuminates why malformation is a rare phenomenon in the paleontological record

rheology of the lithosphere inferred from postseismic uplift following the 1959 hebgen lake earthquake 1 we have modeled the broad postseismic uplift measured by geodetic leveling in the epicentral area of the 1959 mw 7 3 hebgen lake montana earthquake a normal faulting event in the northern basin and range province to fit the observed uplift we calculate synthetic postseismic deformation using the relaxation response of a gravitational viscoelastic earth to the earthquake for a model with an elastic plate overlying a viscoelastic half space we find that the elastic thickness is 38 8 km which is close to the local crustal thickness the half space viscosity is estimated at 4 1018 0 5 pa s the leveling data do not require a viscous lower crust but permit a lower bound viscosity of 1020 pa s the observed broad uplift cannot be explained by physically plausible afterslip on and below the coseismic fault however local deformation across the coseismic surface rupture requires shallow afterslip reaching the surface the postseismic deformation induced by the estimated viscoelastic structure decays exponentially with a time constant of 15 years because of coupling between the elastic layer and the viscoelastic substrate this relaxation time is significantly longer than the 2 year maxwell relaxation time of the viscous half space itself our result suggests the importance of postseismic relaxation in interpreting high precision global positioning system velocities for example our model results suggest that postseismic transient velocities from both the 1959 hebgen lake and the 1983 mw 6 9 borah peak earthquakes are currently as large as 1 2 mm yr

ocean warming not acidification controlled coccolithophore response during past greenhouse climate change current carbon dioxide emissions are an assumed threat to oceanic calcifying plankton coccolithophores not just due to rising sea surface temperatures but also because of ocean acidification oa this assessment is based on single species culture experiments that are now revealing complex synergistic and adaptive responses to such environmental change despite this complexity there is still a widespread perception that coccolithophore calcification will be inhibited by oa these plankton have an excellent fossil record and so we can test for the impact of oa during geological carbon cycle events providing the added advantages of exploring entire communities across real world major climate perturbation and recovery here we target fossil coccolithophore groups holococcoliths and braarudosphaerids expected to exhibit greatest sensitivity to acidification because of their reliance on extracellular calcification across the paleocene eocene thermal maximum 56 ma rapid warming event the biogeography and abundance of these extracellular calcifiers shifted dramatically disappearing entirely from low latitudes to become limited to cooler lower saturation state areas by comparing these range shift data with the environmental parameters from an earth system model we show that the principal control on these range retractions was temperature with survival maintained in high latitude refugia despite more adverse ocean chemistry conditions deleterious effects of oa were only evidenced when twinned with elevated temperatures

calcareous plankton evolution and the paleocene eocene thermal maximum event new evidence from tanzania the biotic response of calcareous microplankton at the paleocene eocene thermal maximum petm climate event principally comprised poleward migrations the appearance of excursion taxa and elevated turnover in calcareous nannoplankton here we examine whether this relatively muted evolutionary signal may be due to the quality of the stratigraphic and fossil record by analysing exceptionally well preserved microfossils from an expanded hemipelagic petm section in southern tanzania tdp site 14 both nannofossils and planktonic foraminifera show major abundance declines at the onset of the petm that are not explained by dilution or dissolution the petm onset is also marked by the extinction of eight nannofossil species possibly as many as 12 and the intra petm assemblages are quite distinct from background and dominated by coccolithus including the excursion taxon c bownii this biotic response is not clearly biased in favour of particular ecological groups although the nannofossil excursion taxa were all warm water favouring and there was a net diversity loss within cool water favouring eutrophic groups a shift from toweius to coccolithus dominated assemblages is suggestive of increased oligotrophy although the presence of abundant gladiolithus indicates upper photic zone oligotrophy throughout the time interval represented by the tdp site 14 section the significant plankton assemblage shifts diversity decline and possible reduction of calcareous plankton production and or export suggest the rapid onset of highly disruptive environmental change at the petm onset this change must have included rapid temperature increase and heat stress may have played a role in shaping the petm assemblage compositions causing a limited number of extinctions and favouring taxa from warmer areas of the groups ecological range however the muted evolutionary response in these plankton groups indicates that they were highly resilient to this environmental change and through adaptation to the new conditions e g the excursion taxa but probably principally through range shifts i e migration or simply the ability to acclimatize the vast majority of the biodiversity survived and thrived again once conditions returned to normal

rising of the lowest place on earth due to dead sea water level drop evidence from sar interferometry and gps 1 the dead sea water level has been dropping at an exceedingly increasing rate since 1960 and between 1993 and 2001 the interval of the insar data examined in this study it has dropped at an average rate of 0 88 m per year such a water level change could potentially give rise to a resolvable lithospheric rebound and regional uplift with spatial extent and amplitude that are controlled by the effective mechanical properties of the crust and upper mantle combined we measure that deformation for the years 1993 to 2001 using 149 short baseline interferograms made of 31 ers 1 and ers 2 synthetic aperture radar sar images and continuous gps data from the survey of israel recorded between 1997 and 2011 the uplift rate at the dead sea is small up to 4 mm year and the basin topography is almost a mirror of the displacement introducing a strong trade off between uplift and stratified atmosphere noise to overcome this complication we impose a linearity constraint on the satellite to ground line of sight los phase changes based on the steady uplift observed by a continuous gps station in the area of interest and simultaneously solve for the los change rate digital elevation model dem errors and the elevation phase correlation while the los rate and dem errors are solved for each pixel independently the elevation phase correlation is solved for each sar acquisition independently using this approach we separated the stratified atmospheric delay from the ground displacement we observed a regional uplift around the dead sea northern basin with maximum uplift close to the shorelines and diminishing to zero by the mediterranean coast we modeled the effect of water load changes using a homogeneous elastic half space and found a good agreement between modeled and observed ground displacements using elastic properties that are compatible with seismic and gravity data down to a depth of 15 km below the dead sea basin suggesting that the response of the crust to the sea level drop is controlled mainly by the elastic properties of the upper crust immediately below the dead sea basin

mechanical problems in geodynamics and work done in china the subject of geodynamics concerns the dynamics of the global motion of the earth of the motion in the earth s interior and its interaction with surface features together with mechanical processes in the deformation and rupture of geological structures a brief historical review is given from sir i newton maclauwin jacobi poincare poisson lame darwin rayleigh and love who dealt with the homogeneous sphere to leibenson takeuchi and meinesz concentrating on layered spheres and after the advent of plate tectonics on the use of numerical simulation to the analyses of tectonic features earthquake mechanism the application of nonlinear dynamics by discussing the forward and inverse mechanical problems and the questions facing the inverse problems of searching for the structural parameters driving forces etc are raised in more detail thereafter some works accomplished in china on the global and regional stress fields analyses tectonic features analyses mantle flow studies experimental studies of rocks and their constitutive relations are presented finally the interdisciplinary nature of the subject is emphasized and the main mechanical problems that need special attention are then proposed

the growth of geological structures by repeated earthquakes 1 conceptual framework in many places earthquakes with similar characteristics have been shown to recur if this is common then relatively small deformations associated with individual earthquake cycles should accumulate over time to create geological structures following this paradigm we show that existing models developed to describe leveling line changes associated with the seismic cycle can be adapted to explain geological features associated with a fault in these models an elastic layer containing the fault overlies a viscous half space with a different density fault motion associated with an earthquake results in immediate deformation followed by a long period of readjustment as stresses relax in the viscous layer and isostatic equilibrium is restored deformation is also caused as a result of the loading and unloading due to sediment deposition and erosion in this paper the parameters that control the growth of dip slip structures are identified we find that the flexural rigidity of the crust or the apparent elastic thickness provides the main control of the width of a structure the loading due to erosion and deposition of sediment determines the ratio of uplift to subsidence between the two sides of the fault the flexure due to sediment load is much more important in this respect than whether the fault is normal or reverse in character we find that in general real structures are associated with apparent elastic thicknesses of 4 km or less and thus with very low flexural rigidities

great salt lake and precursors utah the last 30 000 years sediment cores up to 6 5 m in length from the south arm of great salt lake utah have been correlated radiocarbon ages and volcanic tephra layers indicate a record of greater than 30 000 years a variety of approaches have been employed to collect data used in stratigraphic correlation and lake elevation interpretation these include acoustic stratigraphy sedimentologic analyses mineralogy geochemistry major element c o and s isotopes and organics paleontology and pollen the results indicate that prior to 32 000 year b p an ephemeral saline lake playa system was present in the basin the perennial lake which has occupied the basin since this time rose in a series of three major steps the freshest water conditions and presumably highest altitude was reached at about 17 000 year b p the lake remained fresh for a brief period followed by a rapid increase in salinity and sharp lowering in elevation to levels below that of the present great salt lake the lake remained at low elevations and divided at times into a north and south basin until about 8 000 year b p since that time with the exception of two short rises to about 1290 m the lake level has remained near the present elevation of 1280 m

reservoir induced deformation and continental rheology in vicinity of lake mead nevada lake mead is a large reservoir in nevada formed by the construction of the 221 m high hoover dam in the black canyon of the colorado river the lake encompasses an area of 635 km2 and the total volume of the reservoir is 35 5 km3 filling started in february 1935 on the basis of a first order leveling in 1935 several levelings were carried out to measure the deformation induced by the load of the reservoir subsidence in the central parts of the lake relative to the first leveling was around 120 mm 1941 218 mm 1950 and 200 mm 1963 the subsidence pattern clearly shows relaxation of the underlying basement due to the water load of the lake which ceased after 1950 modeling of the relaxation process by means of layered viscoelastic compressible flat earth models with a detailed representation of the spatial and temporal distribution of the water load shows that the thickness of the elastic crust underneath lake mead is 30 3 km the data are also consistent with a 10 km thick elastic upper crust and a 20 km thick viscoelastic lower crust with 1020 pa s as a lower bound for its viscosity the subcrust has an average viscosity of 1018 0 2 pa s a surprisingly low value the leveling data constrain the viscosity profile down to 200 km depth

lake bonneville constraints on lithospheric thickness and upper mantle viscosity from isostatic warping of bonneville provo and gilbert stage shorelines the deformed shorelines of the late pleistocene lake bonneville provide an excellent opportunity to analyze the response of the earth to surface loads of relatively short wavelengths 400 km and short duration 30 kyr recently revised estimates of the lake loading history and an expanded compilation of shoreline elevations for the bonneville 1550 m provo 1440 m and gilbert 1300 m shorelines have prompted us to reexamine the deflection the earth model we use is identical with that employed by nakiboglu and lambeck and consists of an elastic plate overlying a maxwell viscoelastic channel and a rigid base our calculation differs from that of nakiboglu and lambeck in two respects we used a significantly more detailed load model and we compared our results with observations from three distinct shorelines the lake elevation history spans 32 kyr in 18 piecewise linear segments the water load is computed at each time step from a digital terrain model 4 4 km cell size and a specified lake elevation we find that the use of three separate shorelines significantly reduces the acceptable region of parameter space the effective elastic lithospheric thickness is 23 2 km the mantle viscosity is 1 2 0 2 1020 pa s and the depth to a significant viscosity increase is no less than 300 km though it might be much more examination of the residual deflections differences between observed and computed shoreline elevations reveals a regional tilt down to the ne of 6 10 5 which we attribute to collapse of the peripheral bulge produced by the laurentide ice sheet

tomography the geoid and plate motions the dynamics of the earth s mantle and its relationship to mantle structure as revealed by seismic tomography the geoid and plate motions are discussed in a critical review of u s research from the period 1987 1990 sections are devoted to plates and mantle convection seismic anomalies flow and the geoid subducted slabs and the 670 km discontinuity the physical properties of the mantle plumes and computational and experimental modeling efforts also included is a comprehensive bibliography for the period 248 refs

transient mountain waves and their interaction with large scales abstract the impact of transient mountain waves on a large scale flow is examined through idealized numerical simulations of the passage of a time evolving synoptic scale jet over an isolated 3d mountain both the global momentum budget and the spatial flow response are examined to illustrate the impact of transient mountain waves on the large scale flow additionally aspects of the spatial response are quantified by potential vorticity inversion nearly linear cases exhibit a weak loss of domain averaged absolute momentum despite the absence of wave breaking this transient effect occurs because over the time period of the large scale flow the momentum flux through the top boundary does not balance the surface pressure drag moreover an adiabatic spatial redistribution of momentum is observed in these cases which results in an increase decrease of zonally averaged zonal momentum south north of the mountain for highly nonlinear cases the zonally averaged momentum field shows a region of flow de

fault behavior and characteristic earthquakes examples from the wasatch and san andreas fault zones paleoseismological data for the wasatch and san andreas fault zones have led to the formulation of the characteristic earthquake model which postulates that individual faults and fault segments tend to generate essentially same size or characteristic earthquakes having a relatively narrow range of magnitudes near the maximum analysis of scarp derived colluvium in trench exposures across the wasatch fault provides estimates of the timing and displacement associated with individual surface faulting earthquakes at all of the sites studied the displacement per event has been consistently large measured values range from 1 6 to 2 6 m and the average is about 2 m on the basis of variability in the timing of individual events as well as changes in scarp morphology and fault geometry six major segments are recognized along the wasatch fault on the basis of the most likely number of surface faulting events 18 that have occurred on segments of the wasatch fault zone during the past 8000 years an average recurrence interval of 400 666 years with a preferred average of 444 years is calculated for the entire zone geologic data on the distribution of slip associated with prehistoric earthquakes and slip rates along the south central segment of the san andreas fault suggest that the m 8 1857 earthquake is a characteristic earthquake for this segment comparisons of earthquake recurrence relationships on both the wasatch and san andreas faults based on historical seismicity data and geologic data show that a linear constant b value extrapolation of the cumulative recurrence curve from the smaller magnitudes leads to gross underestimates of the frequency of occurrence of the large or characteristic earthquakes only by assuming a low b value in the moderate magnitude range can the seismicity data on small earthquakes be reconciled with geologic data on large earthquakes the characteristic earthquake appears to be a fundamental aspect of the behavior of the wasatch and san andreas faults and may apply to many other faults as well

pleistocene deglaciation and the earth s rotation a new analysis summary this paper is concerned with an analysis of the effect of the pleistocene glacial cycle upon the earth s rotation we demonstrate that two important geophysical observables may be explained as aspects of the rotational response to surface mass loading by ice sheets these are the astronomically observed non tidal component of the acceleration of planetary rotation and the secular drift of the rotation pole relative to the surface geography which is evident in the ils pole path the former observation is shown to provide an unambiguous constraint upon the viscosity of the planetary mantle and requires a depth dependence of this parameter which is the same as that which has previously been inferred in studies of the relative sea level variations and free air gravity anomalies associated with post glacial rebound the observed secular drift of the pole cannot provide an independent estimate of the viscosity of the mantle because it depends jointly upon mantle viscosity and lithospheric thickness with the viscosity profile fixed by the rebound data the observed speed of polar wander suggests a continental lithospheric thickness which is in excess of that appropriate for old ocean basins but nevertheless in accord with independent constraints

normal faulting and flexure in an elastic perfectly plastic plate abstract an elastic perfectly plastic plate model has been developed to analyze the flexure associated with normal faulting the model consists of a thin layer which is completely cut by a normal fault overlying a fluid substratum for a given applied bending moment at the fault the relationship between the amount of displacement on the fault and the extent of the failure zone can be calculated the model is applied to the wasatch front region in the eastern basin and range province usa to determine the correlation of its parameters with geological and geophysical data in the vicinity of a major normal fault the wasatch fault along which there has been 3 4 km of late cenozoic uplift in this region most seismic activity occurs away from the wasatch fault in a zone 30 km wide roughly centered 30 km east of the fault this activity occurs at depths of 15 km or less in order to match the observations the lithospheric layer must have a flexural rigidity of 0 5 to 1 1 1022 n m and a yield stress of 1 2 kb and must have zero applied bending moment at the fault the effective mechanical thickness of the lithosphere in this region is 20 25 km these results indicate that the lithosphere in long term mechanical studies in the eastern basin and range is thin and weak evaluating these results as compared to the seismic lithospheric thickness and temperature regime of the region produces some interesting correlations with studies in oceanic regions

the impact of mountain waves on an idealized baroclinically unstable large scale flow abstractthe feedback of mountain waves and low level blocking on an idealized baroclinically unstable wave passing over an isolated ridge is examined through numerical simulation theoretical analy

plate dynamics caribbean map corrections and hotspot push summary in 1986 the author s previous paper describing a simple mathematical model for the forces driving the plates had an rms error of 1 62 per cent in its best case the model included slab pull and its global and local reactions proportional to speed times age 3 2 viscous drag due to shear under moving plates and in the flow towards mantle sinks at midocean ridges and sources at subduction zones ridge push proportional to plate age and friction at continental collision zones strengths of the various forces were found by least squares fitting three different improvements now reduce the error to 1 14 per cent they are 1 revision of the n s american plate boundary east of the caribbean sea to run along the 15 20 fracture zone ii removal of a transform segment from the caribbean subduction zone and iii allowing for hotspot push hotspots cause upward flow in the mantle which spreads outwards under the lithosphere above and pushes two plates apart if their boundary runs nearby in a way which is calculated the results and their statistical significance are estimated by a method given by backus park garbasz 1981 modified slightly because three of the equations in the model are linearly dependent on the remainder all the physical mechanisms envisaged in this work as driving plates turn out to be significant except local reaction to slab pull the effect of which is very small anyway

structure and dynamics of an alpine potential vorticity banner a detailed analysis is undertaken of the primary alpine shear zone that occurred on 1 october 1999 during the mesoscale alpine programme this shear zone emanates from the south western alpine tip in north westerly flow conditions develops in response to the alpine scale flow splitting and separates the northerly mistral wind to the south west of the alps from the quasi stagnant air within the alpine wake the study is based on in situ flight level and dropsonde data from two research aircraft the data are used for the construction of an objective analysis in a cross section perpendicular to the shear zone and for diagnostic computations of the potential vorticity pv flux between vertically stacked flight legs the observed flow structure is compared with simulation results of the swiss model and the non hydrostatic canadian mesoscale compressible community model mc2 operating at horizontal resolutions of 14 and 3 km respectively immediately downstream of the topography the observed shear zone has a surprisingly quasi steady structure that becomes evident provided a slow westward migration is accounted for further downstream the shear zone shows increased signs of transience near the surface it has an overall width of 150 km but narrows to about 25 km near the top of the mistral inversion at a height of 2 km detailed analysis shows that the shear zone has a complex substructure consisting of at least three positive and three negative pv filaments these shear lines are characterized by a pronounced vertical coherence in the mixed layer and throughout most of the inversion layer one of the banners is also evident in low level tracer constituents diagnostic computations of the pv flux along the banners using the generalized bernoulli theorem reveal that most of the associated pv flux is due to vertically oriented vorticity within the inversion layer within the shear zone there is a spanwise circulation of appreciable strength it consists of a deformation flow with the axes of deformation oriented perpendicular to the shear zone this deformation flow in effect squeezes the pv banners and thereby makes them resilient with respect to dissipation and barotropic instabilities detailed intercomparison with numerical model results shows that models with a grid spacing below 15 km are able to capture the overall structure of the shear zone the mc2 model in addition credibly replicates some of the finer scale sub structure of the shear zone in particular at low levels the high predictability and steadiness of the pv banners supports the idea that individual banners are generated by flow separation and or gravity wave breaking events upstream it is argued that the overall width of the shear zone is thus in effect determined by the geometry of the upstream topography and the dynamical processes that govern the downstream advection of the pv banners copyright 2003 royal meteorological society

postglacial rebound at the northern cascadia subduction zone postglacial rebound is the response of the earth to the decay of ice sheets a postglacial rebound model explains crustal tilting and rapid uplift at the northern cascadia subduction zone that occurred during retreat of the cordilleran ice sheet observations explained by the model include the shoreline tilts of two proglacial lakes that formed at 13 5 14 ka 14c yr ago and rapid sea level fall land uplift at 12 12 5 ka modelled mantle viscosity values range from 5 1018 to 5 1019 pa s and are consistent with previous viscosity inferences from observations of crustal deformation following subduction zone earthquakes 1018 1019 pa s no lower limit to subduction zone mantle viscosity is apparent from our model but viscosity values equal to or larger than 1020 pa s are de nitely ruled out our modelled subduction zone viscosity values are smaller than most upper mantle viscosity estimates derived from postglacial rebound studies of tectonically less active regions 1020 1021 pa s the rapid observed uplift at 12 ka requires in addition to a low mantle viscosity rapid unloading from a sudden collapse of remaining coastal portions of the southern cordilleran ice sheet the sudden collapse provides 0 18 m of global eustatic sea level rise approximately 0 7 of the sea level rise associated with melt water pulse ia predictions of a global postglacial rebound model ice 3g with a 1021 pa s upper mantle viscosity were previously applied to geodetic data from this region to isolate signals associated with the earthquake cycle owing to the low viscosity values and resulting rapid recovery of glacial deformation our model predicts present day postglacial rebound uplift rates at least 10 times smaller than ice 3g less than about 0 1 mm yr as the ice 3g adjustments were substantial this indicates the need for re evaluation of the geodetic data 2000 elsevier science ltd all rights reserved

slip rate variations on faults in the basin and range province caused by regression of late pleistocene lake bonneville and lake lahontan late pleistocene regression of two large pluvial lakes lake bonneville and lake lahontan caused considerable lithospheric rebound in the basin and range province usa here we use finite element models to show how lake growth and regression affect the temporal and spatial slip evolution on faults near the former lakes our results show that fluctuations in the volume of lake bonneville caused along strike slip variations on the wasatch normal fault with a pronounced slip rate increase on its northern and central parts during lake regression the response of normal and strike slip faults near the ring shaped lake lahontan depends on their location within the rebound area faults located in the centre of rebound show a slip rate increase during lake regression whereas strike slip faults at the periphery decelerate all slip rate variations are caused by differential stress changes owing to changing lake levels regardless of the individual fault response

quasi static response of a layered viscoelastic half space to general surface loading abstract analytical solutions to a prestressed multilayered elastic half space subjected to general surface loads are derived using the cartesian system of vector functions the solutions are then applied to the maxwell viscoelastic medium with time dependent surface loading by means of the correspondence principle and the normal mode method the number of layers in the model and the pattern of surface load at least in principle are unrestrained this theoretical result is convenient for numerical calculation and is applicable to the study of postglacial rebound the inversion of physical parameters of the earth s interior the analysis of the evolution of a sedimentary basin and so forth as a numerical example the evolution of the williston basin is investigated the present study differs from an earlier analysis of that basin in two aspects a four layered model is taken instead of a two layered one and the surface sediment loading is treated as rectangular parallelopipeds with time dependent heights rather than as a point load the computed subsidence curves agree quite well with the data from drilling wells

coastal conglomerates around the hadjer el khamis inselbergs western chad central africa new evidence for lake mega chad episodes this paper reports on a study dealing with the rhyolitic inselbergs of hadjer el khamis that formed palaeoislands during lake mega chad events field observations have shown that 1 conglomeratic patches of immature to mature clasts are preserved at the feet of the hadjer el khamis inselbergs 2 in cross section their pro le reveals a well de ned cliff platform junction at a constant elevation 325 m the monolithological clasts show all degrees of roundness from angular cobbles to well rounded pebbles this wide range of maturity suggests a coastal origin for these cobbles the system was permanently fed with angular clasts which were progressively worn by waves cobbles that were wave worked for the longest time are the best rounded the cliff platform junction is the result of erosion by waves which attacked and undercut the inselberg cliffs during lake mega chad events asymmetrical erosion pro les moreover suggest a wind regime dominated by sw to ne oriented winds these interpretations have two implications the elevation of the cliff platform junction is an indication of the highest water level of lake mega chad at 320 325 m which is in agreement with other observations elsewhere in the basin the sw to ne oriented winds show that monsoon related winds were prevalent during lake mega chad events suggesting the inter tropical convergence zone was located higher in latitude than today copyright 2003 john wiley sons ltd

viscosity estimates for the crust and upper mantle from patterns of lacustrine shoreline deformation in the eastern great basin the deformed shorelines of lake bonneville constitute a classic source of information on lithospheric elastic thickness and upper mantle viscosity we describe and apply a new model to a recently augmented data set new data better constrain both the complex spatio temporal pattern of the lake load and the crustal deformation response to that load the history of lake level fluctuations has been significantly refined and somewhat modified this is due to both more radiocarbon dates from within the bonneville basin and to an improved calibration of the radiocarbon timescale itself the data which constrain the crustal deformation pattern consist of ages and shoreline elevations from several hundred points which sample three major levels of lake bonneville and corresponding elevations from the high stands of three smaller lakes situated to the west of lake bonneville the data from the smaller lakes help elucidate the pattern of deflection which occurred beyond the edge of the big lake the geometry of the earth model incorporates an arbitrary number of layers overlying a half space and the rheology of each level can accommodate an arbitrary number of maxwell viscoelastic elements in parallel the inverse modeling comprises three complementary approaches for the simplest configurations we performed a direct search of the parameter space and delineated the irregular boundary of the subspace of acceptable models for more complex configurations we constrained the elastic parameters to their seismically determined values and then solved for viscosity versus depth profiles by either expressing the log viscosity versus log depth profile as a series of specially constructed orthogonal polynomials or by allowing each of 8 10 layers plus the half space to have an independently determined viscosity we found that the data do not strongly support nor can they conclusively exclude a more complex rheology than simple maxwell viscoelasticity the orthogonal polynomial solution exhibits an essentially monotonic decrease in viscosity with depth the most rapid change occurs at shallow depths decreasing from 1023 pa s at 3 km to 102o pa s at 30 km the decrease is much more gradual below with only another factor of 5 decrease between 30 and 300 km depth the unconstrained solution exhibits a rapid decrease in viscosity with depth from 2x 10 24 pa s in the top 10 km to 4x 1017 pa s at a depth of 40 km a nearly isoviscous asthenospheric region extends from 40 to 150 km and is underlain by a mantle lithospheric region with increased viscosity 2x 102o pa s extending from 150 to 300 km depth and by a uniform viscosity 1019 pa s half space below

interseismic deformation at the nankai trough japan subduction zone uplift along the coast of southwestern japan following the 1944 tonankai ms 8 0 and 1946 nankaido ms 8 2 earthquakes has been inferred from the 1950 1985 tide gage records although uplift rates vary with geographic position the temporal dependence at each site can be described as the superposition of an exponentially decaying time constant 5 years transient significant only in the first decade postseismic and a steady interseismic rate the steady interseismic uplift rate is defined only over the 1956 1985 interval but the linearity in time ofthat uplift record is such that uplift over the remainder of the interseismic cycle 80 years might reasonably be expected to occur at the same rate moreover the spatial pattern and magnitude of the steady uplift rate are reasonably close to those predicted by a simple dislocation model of subduction however the currently observed steady uplift rate is not consistent with the uplift rate inferred from geodetic leveling for the final half of the previous earthquake cycle thus either the hypothesis of a steady interseismic uplift rate after the first decade postseismic is wrong or the strain accumulation pattern for one earthquake need not be the same as for the preceding earthquake on the same segment

a study of the earth s response to surface loading with application to lake bonneville summary analytical solutions are presented for the deformation of a three layered plane earth with elastic viscoelastic rheology and subject to time dependent vertical surface loads the models investigated are 1 elastic or viscoelastic layers overlying an inviscid fluid 2 viscoelastic half space 3 elastic layer over a viscoelastic layer with different boundary conditions at the base of the second layer emphasis is given to the interdependence between the dominant parameters of thickness of the elastic layer the effective viscosity of the viscoelastic layer the change in viscosity with depth and the wavelength and duration of loading the models have been applied to the loading and unloading of the late pleistocene pluvial lake bonneville using the load histories given by crittenden the studies differ from earlier analyses of the bonneville uplift in several important aspects including a rigorous treatment of the horizontal and vertical coupling between the elastic and viscoelastic media the mantle is treated as viscoelastic rather than as a viscous medium the wavelength information has been introduced by using a more realistic model for the load geometry and the effect of the wasatch fault has been considered the models indicate that the two principal parameters defining the rebound are the effective viscosity of the upper mantle and the effective thickness of the elastic layer and that those two parameters can be separated only if both wavelength and amplitude information of the deformation is available at more than one epoch observations of uplift at one epoch are not sufficient to resolve the thickness of the elastic layer and the effective viscosity of the upper mantle but upper bounds for these quantities are well established as 30km and 1 2 10 poise respectively the uplift results do not confirm or deny the possibility of a low viscosity channel in the upper mantle but this can be resolved only if the uplift data are supplemented with observations of the present uplift rate the published rates are controversial but if valid they point to a thin 15 km elastic layer and a relatively narrow 200km low viscosity channel while the models predict uplift near the centre of the former lake they also predict that the peripheral regions should be subsiding appreciably if flow is confined into a shallow channel of low viscosity observations reported by anderson bucknam suggests such behaviour likewise the present rate of uplift changes sign at some distance from the centre of the lake and detailed observations of warping of the shorelines and repeated levelling in the area may yield further constraints on the rebound model copyright