the origin of teleseismic pn waves multiple crustal scattering of upper mantle whispering gallery phases 1 teleseismic pn arrivals with an extensive coda are observed to offsets beyond 3000 km along the peaceful nuclear explosion seismic profiles quartz and ruby which were recorded in the western part of the former soviet union we interpret these arrivals as multiply reflected sub moho refractions that travel over large distances due to a positive vertical upper mantle velocity gradient which is characteristic for the study area analysis of the observed data shows that the teleseismic pn and its coda contain significant amounts of energy at all frequencies between 0 and 10 hz our modeling results show that crustal scattering may fully explain the teleseismic pn coda contrary to another published model with upper mantle heterogeneity in the 35 130 km depth range these conclusions are based on two dimensional viscoelastic finite difference seismic wave field simulations in 2000 km long and 250 km deep models of the crust and upper mantle the computationally demanding calculations are facilitated by the use of supercomputer systems our preferred model of crustal scattering is consistent with the results of other high resolution wide angle and normal incidence seismic investigations of the crust and upper mantle they show pronounced reflectivity of the lower crust above an almost transparent uppermost mantle down to 80 100 km depth our model includes a high vertical velocity gradient in the upper mantle based on the results from seismic refraction studies we suggest that the teleseismic pn wave travels as an upper mantle whispering gallery phase and that the origin of its long coda is crustal scattering

general features of the uppermost mantle stratification from long range seismic profiles abstract long range seismic studies made by russian institutions during the last two decades reached depths of 700 800 km on the continent peace nuclear explosions were used as a source and 100 km in the ocean ocean bottom stations recording 500 kg explosions in water comparison of the wave fields of these and other seismic profiles in russia western europe and the south atlantic shows that the classical lithosphere asthenosphere model is too simple to explain the observed data a stratified medium with alternating weak and rigid layers is a more realistic model of the upper mantle one of the layers is globally observed at a depth of 80 to 100 km it is located in the thermal lithosphere beneath old platforms at the bottom of the lithosphere under active tectonic areas and inside the asthenosphere below mid oceanic ridges relatively high velocities 8 4 to 8 5 km s are typical for this boundary both in the old platforms and in the high heat flow oceanic areas a change of structural pattern where the block structure of the uppermost mantle is transformed into a horizontally homogeneous one is typical at that boundary level such features suggest that the boundary separates the brittle and more ductile upper mantle layers and may be considered as the bottom of the global mechanical lithosphere

on the origin of the drumlins of the south german alpine foreland ii the sediments underneath abstract the drumlins of the south german alpine foreland have certain characteristics a distinctly limited occurrence within the formerly glaciated areas a well defined time of formation and a typical rather compact shape the character of the sediments of which they are composed and the relation between drumlin sediments and drumlin form have been a matter of discussion for more than 80 years due to the rareness of good exposures in drumlins a few individual drumlins have become better known during the past decades because they overlie interglacial deposits the observations made at these sites allow the following statements 1 1 the drumlins normally consist of sediments of the last wurm glaciation only in exceptional cases do older pleistocene strata or the pre pleistocene substratum molasse sandstone form part of the drumlin body these exceptions are important in so far as they prove that drumlin formation in principle was an erosional process in the area 2 2 the sediments are mainly till but also a gravel till sequence is not uncommon the rare interglacial beds are mainly lake deposits 3 3 the thickness of the sediments on top of the interglacial deposits varies considerably from some metres to several decametres even underneath a thin cover of younger sediments the fine grained and therefore in principle easily deformable interglacial deposits are glaciotectonically undisturbed altogether these observations allow the conclusion that 1 the process of drumlin formation shaped the glacier bed by highly selective but locally vigorous glacial erosion and 2 this process did obviously not or only poorly affect the sediments below the ice sediment interface even though it was composed of readily deformable material therefore the question is not whether there was erosion or not but why there was not much more erosion and disturbance it is suggested that the answer is likely to be found in the unevenness of the decaying permafrost table at the end of the wurm pleniglacial

seismic velocity model of the crust and uppermost mantle around the mirnyi kimberlite field in siberia abstract we present the first detailed seismic velocity models of the crust and uppermost mantle around the mirnyi kimberlite field in yakutia siberia we have digitized vintage seismograms that were acquired in 1981 and 1983 by use of taiga analogue seismographs along two perpendicular seismic profiles the 370 km long northwest striking profile i across the kimberlite pipe was covered by 41 seismographs which recorded seismic signals from 21 chemical shots along the line including one off end shot the perpendicular 340 km long profile ii across profile i ca 30 km to the south of the mirnyi kimberlite field was covered by 45 seismographs which recorded seismic signals from 22 chemical shots including four off end shots each shot involved detonation of between 1 5 and 6 0 tons of tnt distributed in individual charges of 100 200 kg in shallow water both velocity models show normal cratonic structure of the ca 45 km thick crust with only slight undulation of the moho however relatively small seismic velocity is detected to 25 km depth in a ca 60 km wide zone around the kimberlite pipe surrounded by elevated velocity 6 3 km s in the upper crust the lower crust has a relatively constant velocity of 6 8 6 9 km s it appears relatively unaffected by the presence of the kimberlite field extremely large p wave velocity 8 7 km s of the sub moho mantle is interpreted along profile i except for a 70 km wide zone with a normal pn velocity of 8 1 km s below the kimberlite profile ii mainly shows pn velocities of 8 0 8 2 km s with unusually large velocity 8 5 km s in two ca 100 km wide zones at its southwestern end one zone being close to the kimberlite field the nature of these exceptionally large sub moho mantle velocities is not yet understood the difference in velocity in the two profile directions indicates anisotropy but the effect of unusual rock composition e g from a high concentration of garnet cannot be excluded

structure of the crust and upper mantle beneath the great valley and allegheny plateau of eastern pennsylvania 2 gravity modeling and migration of wide angle reflection data linear inversion of p composites for three different profiles suggests that the lower crust beneath eastern pennsylvania consists of material with high averaged p wave velocities 6 8 7 5 km s compared with 6 4 7 1 km s for most crustal models derived for surrounding areas within the appalachians and the grenville province of the canadian shield interpretations of these velocities in terms of rock type are limited by the low resolving power of the data and by the nonuniqueness in inferring rock type from p wave velocity alone the high averaged p wave velocities could be associated with substantial volumes of mafic rock perhaps emplaced by underplating or with high grade metamorphic assemblages of intermediate composition and sedimentary origin similar to those found in the ivrea zone in northern italy because of the sparseness of the s wave data averaged shear wave velocities are not well enough resolved over most depth ranges to distinguish among the different compositional models computations of gravity anomalies for two dimensional models using various linear velocity density relations however suggest that at least part of the crust beneath the scranton gravity high is mafic moreover if the entire basement section beneath this anomaly consists of mafic material then the gravity studies indicate that the lower crust beneath the great valley must be mafic as well migrated shot gathers show a concentration of reflectors at depths between 35 and 45 km a result that is controlled in part by the limited range of offsets used but that is also consistent with recent observations of a highly reflective lower crust reflections that are migrated to depths within the uppermost mantle could be multiples or primary reflections from upper mantle layering although the data are rather sparse the interpretation of these later arrivals as primary reflections is supported by their small ray parameters which suggests that they are not converted phases and by their large relative amplitudes which suggests that they are not multiples layering within the upper mantle could be in the form of alternating high and low velocity zones perhaps related to emplacement of eclogites or garnet granulites in the uppermost mantle during the process of underplating

structure of the crust and upper mantle beneath the great valley and allegheny plateau of eastern pennsylvania 1 comparison of linear inversion methods for sparse wide angle reflection data we use p data extracted from a small number of wide angle recordings of quarry blasts to construct averaged one dimensional velocity models of the crust beneath portions of the great valley newark basin valley and ridge and allegheny plateau of the central appalachians of pennsylvania using the linear form of the equations for p in terms of slowness depth structure we compare inversion results for the extremal backus gilbert and generalized least squares methods although the uncertainties are large the models do show a well constrained increase in midcrustal velocities and crustal thickness beneath the allegheny plateau inversion of precritical reflections from the moho suggests bounds of 7 1 7 6 km s on p wave velocity and 3 9 4 2 km s on s wave velocity near the base of the crust p wave velocity models for the great valley show a crustal thickness between 40 and 45 km with an average velocity between 6 4 and 6 6 km s models for the allegheny plateau show a larger crustal thickness 47 52 km and a much higher average velocity 6 8 6 9 km s estimates of average shear wave velocities for the great valley range from 3 6 to 3 8 km s with crustal thickness estimates between 37 and 44 km for the relatively small number of singular values retained standard errors in depth for models derived by generalized least squares range from 1 to 2 km for the p wave slowness models and from 2 to 4 km for the s wave models extremal depth bounds in general are 2 to 3 times as wide corresponding uncertainties in interval velocity estimated from resolving kernels in slowness range from 0 15 to 0 45 km s for p wave models and from 0 15 to 0 40 km s for s wave models t2 x2 inversion of pmp data gives similar estimates for total crustal thickness and average velocity after correction for refraction effects t2 x2 inversion of pmp data for a fourth profile suggests the possibility of a slight thickening of the crust 47 48 km directly beneath the axis of the great valley gravity low estimates of average vp vs for the crust based on average velocities for models derived by generalized least squares inversion range from 1 73 to 1 77 estimates based on travel time ratios for events interpreted as p wave and s wave reflections from the moho lie between 1 75 and 1 79 for a crust in which the effects of velocity anisotropy can be neglected these estimates correspond to crustal averages between 0 25 and 0 27 for poisson s ratio the one dimensional velocity models derived here provide estimates of the long wavelength component of velocity structure besides demonstrating the maximum resolving power inherent in a limited p data set these averaged models can be used for migrating reflection data and as starting models for determining two dimensional velocity structure

3d first arrival regional calibration model of northern eurasia seismological monitoring of the comprehensive test ban treaty ctbt requires detailed knowledge of travel time characteristics of seismic phases across large areas we use first arrival travel times from several of russian deep seismic sounding dss profiles primarily those from peaceful nuclear explosions pnes to construct a 3d regional travel time model of northern eurasia the method used which can be viewed as a generalization of the existing regionalization techniques is based on apparent velocity based spatial interpolation of the travel times picked from dss records the resulting travel time field is described in terms of an apparent velocity model in the 3d space of geographic coordinates and ray parameter in the travel time calibration this model could be used to construct approximate source specific station correction surfaces for any location within the region and also as a region specific reference model to be used as a background for further calibration effort this approach allows incremental refinement of the model as additional travel time data become available by converting the travel time model into depth a 3d regional velocity model is obtained providing a description of the general features of the upper mantle in northern eurasia

2d model of the crust and uppermost mantle along rift profile siberian craton abstract a two dimensional model of the crust and uppermost mantle for the western siberian craton and the adjoining areas of the pur gedan basin to the north and baikal rift zone to the south is determined from travel time data from recordings of 30 chemical explosions and three nuclear explosions along the rift deep seismic sounding profile this velocity model shows strong lateral variations in the crust and sub moho structure both within the craton and between the craton and the surrounding region the pur gedan basin has a 15 km thick low velocity sediment layer overlying a 25 km thick high velocity crystalline crustal layer a paleo rift zone with a graben like structure in the basement and a high velocity crustal intrusion or mantle upward exists beneath the southern part of the pur gedan basin the sedimentary layer is thin or non existent and there is a velocity reversal in the upper crust beneath the yenisey zone the siberian craton has nearly uniform crustal thickness of 40 43 km but the average velocity in the lower crust in the north is higher 6 8 6 9 km s than in the south 6 6 km s the crust beneath the baikal rift zone is 35 km thick and has an average crustal velocity similar to that observed beneath the southern part of craton the uppermost mantle velocity varies from 8 0 to 8 1 km s beneath the young west siberian platform and baikal rift zone to 8 1 8 5 km s beneath the siberian craton anomalous high pn velocities 8 4 8 5 km s are observed beneath the western tunguss basin in the northern part of the craton and beneath the southern part of the siberian craton but lower pn velocities 8 1 km s are observed beneath the low angara basin in the central part of the craton at about 100 km depth beneath the craton there is a velocity inversion with a strong reflecting interface at its base some reflectors are also distinguished within the upper mantle at depth between 230 and 350 km

comparison of 2 d and 3 d models of the steady wind driven circulation in shallow waters abstract the classical theory of the steady wind driven circulation in shallow waters described by the linear three dimensional equations is generalized to include arbitrary variations of the vertical eddy viscosity the stream function equation is compared to the corresponding equation of a two dimensional model the influence on the solution of various eddy viscosity profiles and or bottom boundary conditions is discussed from the comparison of the equations a parameterization of the bottom stress in terms of transport and wind stress is derived such that the two dimensional model can yield results identical to those of the three dimensional model

sediment deformation beneath glaciers rheology and geological consequences experiments beneath breidamerkurjokull in iceland have led to development of flow laws for the subglacial till relating strain rate to shear stress and effective pressure and assuming either bingham fluid or nonlinearly viscous fluid behavior water pressures in the till are less than ice pressures and it is suggested that this may lead to infiltration of ice into the sediment which inhibits sliding at the ice sediment interface where water pressures are equal or near to ice pressures infiltration does not occur and sliding may result a one dimensional theory of subglacial deformation is developed in which the empirical flow law is coupled with a model of subglacial hydrology and consolidation this predicts stable states in which subglacial sediment either does not deform or a dilatant deforming horizon forms with positive effective pressures at the ice bed interface or unstable states where zero or negative effective pressures are predicted time dependent analyses show that response times following perturbations of the system may be of the order of 103 years and thus that unsteady behavior may be normal on glaciers flowing over unlithified sediment beds it is suggested that the natural variability of material properties in subglacial sediment beds leads to the development of drumlins on the glacier bed it is suggested that unstable deformation at zero or negative effective stress leads to piping in subglacial sediments at the glacier terminus and the growth of sediment floored subglacial tunnels their frequency is that which is sufficient to draw down subglacial water pressures so as to prevent unstable deformation where they discharge large water volumes subglacial sediments flow laterally toward them producing tunnel valleys this sediment is then removed by water flowing along the axial tunnel tunnel valleys can be regarded as the equivalent in soft sediment areas of eskers in bedrock areas

origin of drumlins on the floor of lake ontario and in upper new york state abstract upper new york state usa contains one of the largest drumlin fields 12 000 km2 on the north america continent consisting of some 10 000 drumlins located between lake ontario in the north and the finger lakes drumlin like bedforms have also recently been discovered in deep water 200 m on the nearby floor of the rochester basin in lake ontario the new york state drumlin field was produced under the laurentide ice sheet 18 000 years ago when it extended southwards to terminate against the allegheny plateau outcrops of drumlin cores exposed by erosion along the lake ontario shoreline provide windows into the stratigraphy and sedimentology of the northern part of the field sedimentological description of 10 coastal drumlin cores combined with quantitative morphometric analysis of 1487 drumlins shows that they are the product of subglacial erosion of till sheets separated by glaciolacustrine deposits a two phase subglacial model for drumlin formation is suggested consisting of initial aggradation of extensive till deposits during ice advance followed by erosion and streamlining possibly accompanying stillstand of the ice margin and building of moraines systematic changes in drumlin morphometry and spacing are evident ranging from small numbers 60 closely spaced ovoid drumlins l w ratios between 1 and 3 drumlin shape appears to be systematically related to sediment thickness available for erosional streamlining elongate spindle forms occur on the crests and lee sides of bedrock escarpments where sediment cover is thin larger ovoid drumlins occur in topographic depressions where sediment thickness is greater offshore streamlined forms on the floor of the deep water rochester basin in lake ontario have long axes at right angles to the trend of onshore drumlins these are composed of rock rock drumlins and have an orientation structurally controlled by a newly identified inlier of proterozoic grenville province metasediments

crustal structure of the siberian craton and the west siberian basin an appraisal of existing seismic data abstract we present a digital model sibcrust of the crustal structure of the siberian craton sc and the west siberian basin wsb based on all seismic profiles published since 1960 and sampled with a nominal interval of 50 km data quality is assessed and quantitatively assigned to each profile based on acquisition and interpretation method and completeness of crustal model the database represents major improvement in coverage and resolution and includes depth to moho thickness and average p wave velocity of five crustal layers sediments and upper middle lower and lowermost crust and pn velocity maps and cross sections demonstrate strong crustal heterogeneity which correlates weakly with tectono thermal age and strongly with tectonic setting sedimentary thickness varies from 0 3 km in stable craton to 10 20 km in extended regions typical moho depths are 44 48 km in archean crust and up to 54 km around the anabar shield 40 42 km in proterozoic orogens 35 38 km in extended cratonic crust and 38 42 km in the west siberian basin average crustal vp velocity is similar for the sc and the wsb and shows a bimodal distribution with peaks at ca 5 4 km s in deep sedimentary basins and 6 2 6 6 km s in parts of the wsb and sc exceptionally high basement vp velocities 6 8 7 0 km s at the northern border between the sc and the wsb indicate the presence of magmatic intrusions and are proposed to mark the source zone of the siberian lip the cratonic crust generally consists of three layers and high velocity lowermost crust vp 7 4 km s is observed only locally pn velocities are generally 8 2 km s in the sc and wsb and abnormally high 8 6 8 9 km s around kimberlite fields we discuss the origin of crustal heterogeneity and link it to regional crustal evolution

subducted lithosphere or 530 km discontinuity tomographic images of the mantle west of japan and south kuril islands suggest that in this region the subducted lithospheric slabs instead of penetrating the lower mantle lie flat on top of it van der hilst et al 1991 fukao et al 1992 to test these models with independent data and techniques we analyse the slowness of the p arrivals of kuril japan seismic events at a seismic network in baikal region relative to iasp91 standard earth model the flat lying slab should generate an additional refraction line at epicentral distances less than 30 the presence of this line is very clear in our data the slope of the line and its position relative to the other lines are qualitatively consistent with the estimates of the slab velocity and thickness in the tomographic models however a similar wavefield can be generated by 530 km discontinuity the presence of which is established by long range refraction profiling in the neighbouring regions of northern eurasia

the role of seismic refraction data for studies of the origin and evolution of continental rifts abstract universal attributes of continental rift systems are crustal extension with associated asthenospheric upwelling or modification of the mantle beneath the rift axis continental rifting is thus greatly controlled if not driven by geodynamic processes in the lower lithosphere seismic refraction profiling is a technique for obtaining high resolution data on structures seismic velocities and petrologic conditions in the deep crust and upper mantle status of presently available seismic refraction data in four major cenozoic continental rift systems rhinegraben of central europe rio grande rift of southwestern united states baikal rift of eastern siberia and kenya rift of east africa is reviewed in the light of extent of coverage in area and depth reliability of velocity measurements and outstanding structural and geodynamical problems that remain unanswered for each system evidence of crustal thinning anomalous mantle at the moho as well as shallow and midcrustal velocity anomalies exist in all four examples the rhinegraben is the best constrained system from the point of view of seismic structure models seismic refraction structure data for the kenya rift are sparse and raise more questions than answers since extensive geological volcanological and petrological data available for the east africa system usually make it the standard for models of continental rifting modern high resolution deep seismic refraction profiles in kenya are urgently needed in order to advance understanding of basic continental rifting processes

the yamal peninsula lake baikal deep seismic sounding profile seismograms from three nuclear explosions recorded along a 2400 km long deep seismic sounding profile extending from the yamal peninsula to lake baikal are presented we have constructed a preliminary 1 d compressional velocity model to fit the major travel time features of the data clear differences between the seismograms from each shot imply that the velocity structure of the crust and upper mantle is variable along the profile estimated crustal thicknesses range from 47 km beneath the west siberian rift to 42 km beneath the siberian craton the structure of the upper mantle above the transition zone consists of material with p wave velocities ranging from 8 25 km s at the moho to 8 53 km s at 225 km velocities increase abruptly at 225 km depth to 8 63 km s there is little evidence for a pronounced low velocity zone although small velocity reversals are required to terminate several branches of the travel time curve the uppermantle transition zone discontinuity at 425 km depth consists of a 5 6 first order velocity increase the lower discontinuity has a 4 9 velocity increase over the depth range 656 5 to 659 km

variation in drumlin orientation form and stratigraphy relating to successive ice flows in southern and central nova scotia abstract a strong correspondence exists between striation and drumlin long axes trends in nova scotia the variation in striation trends is largely due to successive ice flow events which inscribed many outcrops with sets of superimposed striations that can be correlated over broad areas of nova scotia a type of drumlin in the nova scotia fields is the lobate or reoriented drumlin which is a form with two principal axes parallel to ice movements established by striations and dispersal of distinctive erratics the internal structure of nova scotia drumlins is generally a layer cake of till sheets the most common situation is a grey core till formed by a southeastward ice flow across grey metasedimentary bedrock and a distinctly red mantle till formed by phases of southward to southwestward ice flow drumlins in the yarmouth field of southern nova scotia exhibit the greatest number of stacked units capped by a coarse textured till that represents deposition by a late stage ice mass centered inland nova scotia drumlins appear to have a multi phase origin the first and major drumlin forming ice flow phase was southeastward nucleating agents for initiation of these drumlins may have been preexisting tills or waterlain deposits individual and lobate drumlin axes imply a late southward drumlin forming ice flow phase parallel to the inferred ice flow trend for the mantle till units based on clast provenance some of these drumlins nucleated from preexisting southeast trending forms

the composition and internal structure of drumlins complexity commonality and implications for a unifying theory of their formation investigation of drumlins is significant to both glaciology and palaeoglaciology but the sheer diversity of their composition and internal structure is often cited as a major obstacle towards a satisfactory unifying explanation of their formation this paper presents the first systematic survey of the vast literature on this subject with the aim of concisely summarising observations and identifying any emergent patterns or commonality that theories of drumlin formation should be able to explain results confirm that investigations are often limited by availability of suitable sediment exposures 40 of studies report data from 5 drumlins and 44 do not specify sample size although borehole data and geophysical techniques can alleviate this problem however it is clear that the constituents of drumlins are incredibly diverse in terms of their composition e g a range of lithologies clast shapes sizes and fabrics structure e g sediments that are sorted homogeneous surface conformable unconformable and evidence of deformation e g ranging from pervasive to non pervasive limited to absent despite this diversity our review leads us to suggest that drumlin composition can be simplified to five basic types i mainly bedrock ii part bedrock part till iii mainly till iv part till part sorted sediments and v mainly sorted sediments this is a potentially significant step in that it reduces the oft cited complexity of drumlin composition and provides a more realistic goal for theories or numerical models of drumlin formation to target the various types can occur within the same drumlin field which leaves us with two possible implications for drumlin formation 1 different types of drumlin are formed seeded by different processes despite being morphologically similar equifinality investigation of drumlin composition may therefore reveal diagnostic processes explanations for these different types of drumlin and we argue that bedrock drumlins are an example 2 a single process occurs across large parts of the ice bed interface to create drumlinised terrain in a variety of sediments investigation of drumlin composition may in this case simply reflect pre existing sediments but importantly the way in which the drumlin forming mechanism modifies is modified by them we argue that the latter simpler explanation applies to all other types of drumlin excluding purely bedrock forms and conclude that the diversity in drumlin composition is no obstacle to a single unifying theory

scales of heterogeneities in the continental crust and upper mantle a seismological characterization of crust and upper mantle can refer to large scale averages of seismic velocities or to fluctuations of elastic parameters large is understood here relative to the wavelength used to probe the earth in this paper we try to characterize crust and upper mantle by the fluctuations in media properties rather than by their average velocities as such it becomes evident that different scales of heterogeneities prevail in different layers of crust and mantle although we cannot provide final models and an explanation of why these different scales exist we believe that scales of inhomogeneities carry significant information regarding the tectonic processes that have affected the lower crust the lithospheric and the sublithospheric upper mantle we focus on four different types of small scale inhomogeneities 1 the characteristics of the lower crust 2 velocity fluctuations in the uppermost mantle 3 scattering in the lowermost lithosphere and on 4 heterogeneities in the mantle transition zone

2 d image of seismic attenuation beneath the deep seismic sounding profile quartz russia we present a 2 d image of the upper mantle attenuation using nuclear explosion data from the ultra long refraction reflection profile quartz our analysis is based on a modified common spectrum technique followed by least squares inversion for q and iterative ray tracing in the velocity structure obtained earlier the resulting attenuation structure corroborates the earlier model for northern eurasia as well as our recent estimate based on the analysis of the long range p n phase and provides significantly more detail than the existing models the resulting upper mantle attenuation structure is characterised by q values ranging from 400 to 1800 down to the depths of 150 190 and probably 400 km the attenuation increases horizontally in se direction away from the baltic shield our model exhibits strong 2 d vertical and horizontal attenuation contrasts a high attenuation layer in the depth range of 120 150 to 160 180 km can apparently be associated with the presence of a partial melts within the base of the lithosphere

mirror symmetry of the crust in the oil gas region of shengli china abstract the concept of mirror image symmetry describes the correlation between the bottom of a sedimentary basin and the top of the underlying mantle the degree of mirror symmetry is analyzed here using thickness data from mesozoic cenozoic sedimentary basins and the moho depth with the purpose of investigating the implications for tectonics and exploratory practices in oil gas bearing basins our attention is focused on different tectonic elements of a multi scale tectonic partition in the oil gas region of shengli southeast of bohai bay china by applying standard least squares analysis methods to both datasets we obtained the average thickness h of the consolidated crust and the mirror symmetry factor a for every tectonic unit thereby allowing us to explore the correlation between the bottom depth of a sedimentary basin and the top of the underlying mantle a detailed analysis of data uncertainties and their potential effects led to small fluctuations of h and a within a narrow band around the mean values of 33 26 km and 1 43 respectively thus the results can be considered valid if they are constrained by these error bounds the issues of crust mantle interaction and the deviation of the crust from isostatic equilibrium are also addressed for their tectonic implications other structural parameters related to the deep rooted crust beneath the tectonic elements that make up the study region such as the ratio r of the thickness of the consolidated crust to the absolute value of the symmetry factor the ratio k of the maximum sediment thickness to the maximum uplift of the mantle and the product kh are also evaluated for their implications in geophysical prospecting the symmetry signature of the crust is compared to the symmetry of other sedimentary basins in china and in the world suggesting symmetry as a feasible prognostic tool in exploration for oil gas reservoirs the key result is that those locations where oil gas reservoirs have been found to date are basins in which the crust mantle interaction is active and the crust is isostatically compensated both of those parameters can be quantitatively constrained conversely oil and gas reserves are poor or nonexistent in regions where the crust mantle interaction is inactive and the crust is far from isostatic equilibrium however an intermediate case between these two extreme scenarios wherein the crust mantle interaction is rather moderate but the crust is in a state close to isostasy cannot be entirely ruled out

an overview of the earth crust under china abstract we assess the results of a number of deep seismic soundings performed in china over the last few decades and study the variations in crustal structure in 18 tectonic units comprised of three platforms and 15 fold systems thickness data on 344 mesozoic cenozoic sedimentary basins as well as data on moho depth are collected in order to discuss the relationship between the thickness of the basins and the average thickness of the consolidated crust in each tectonic unit the degree of mirror image symmetry between mesozoic cenozoic sedimentary basins and the uplifting topmost parts of the mantle is herein analyzed using deep geophysical data on sedimentary basins by applying standard methods of least squares analysis to both datasets we have obtained both the average thickness of the consolidated crust and the mirror image symmetry factor for every platform and tectonic fold system thereby allowing us to explore the correlation between the depths of the bottom of the sedimentary basins and the top of the uplifting mantle the thickness of the consolidated crust in china is found to be between 20 and 63 km following a pattern of gradual thickening from east to west expressed in terms of spatial seismicity and the concentration of seismic energy and according to the sharing out of earthquake hypocenters in the top 80 km of the earth the rheology of the area does not appear to suit the widely accepted jelly sandwich model for the continents which does not seem to be entirely valid in china the findings on the mirror image symmetry factor show that this parameter varies mainly in the range 0 5 to 1 8 compared with each other tectonic unit most of the tectonic systems in china appear to be isostatically compensated tibet is an exception in that the symmetry factor is positive for the gangdise nyainqentanglha 1 0 and himalayan 0 1 fold systems implying that these tectonic zones are far from being in the isostatic equilibrium of the other regions we have also analyzed the zoning characteristics through the logarithmic relationship ln r ln h a using the average thickness of the consolidated crust and the absolute value of the symmetry factor the key finding is that regardless of geographical location all the values of r h a for those sedimentary basins in which oil gas reservoirs have to date been found fall into the narrow range of values between 19 38 and 37 40 there is some appeal in a possible relationship involving the ratio of crustal thickness to symmetry factor more so when the results obtained appear to suggest a prognostic tool for exploratory practice in relation to oil gas reservoirs

seismic models of the lower lithosphere beneath the southern baltic sea between sweden and poland abstract based on recordings from the northern part of the baltic sea black sea profile and eugeno s profile 4 2 d seismic models have been constructed for a profile across the southwestern part of the east european platform from southern sweden to northern poland the thickness of the crust along the profile varies from 33 to 47 km the moho p wave velocity is 8 0 8 3 km s the uppermost mantle has a fine structure with alternating layers of higher and lower velocities down to a depth of about 120 km three alternating high and low velocity layers have been modelled the velocities vary between 8 2 and 8 7 km s in the high velocity layers and 8 0 and 8 5 km s in the low velocity layers a tendency of the depth of the moho and the depth of the uppermost mantle seismic boundaries to increase towards the southeast is observed

geophysical differences in the lithosphere between phanerozoic and precambrian australia abstract cannikin atomic bomb recordings indicate that there are differences in travel times from the aleutian islands test site to phanerozoic and precambrian provinces in australia of up to 1 1 s explosion seismic studies in central and southeastern australia enable travel time corrections for crustal and upper mantle structure to be made to recordings of such teleseismic events structure in the upper 60 km can account for at most about 0 2 s of the residual difference but attempts to constrain the remaining residual time to the region above the lehmann discontinuity at about 200 km depth are difficult to reconcile with explosion seismic models regional differences in seismic velocity structure between phanerozoic and precambrian australia therefore appear to exist at depths greater than 200 km electrical conductivities within the mantle have been investigated using two methods long period electromagnetic depth sounding using magnetometer arrays demonstrates that conductivities increase at about 200 km under phanerozoic australia but not until about 500 km depth under precambrian australia shorter period magnetotelluric measurements can only resolve shallower structures these too indicate a similar trend but with sub crustal conductivities increasing at less than 100 km under phanerozoic australia magma at these depths and shallower may be the source for cainozoic volcanism in eastern australia under precambrian central and northern australia magnetotelluric investigations indicate that pronounced conductivity increases do not occur until depths of 150 200 km are reached oceanic magnetic observations indicate that the australian lithospheric plate as a whole is separating from antarctica at a rate of about 7 cm yr the seismic and conductivity structures under the continental region of this plate indicate that lateral inhomogeneities possibly extend to depths as great as 500 km and are probably caused by the passage of eastern australia over a hot spot hawaiian studies indicate that hot spots are not local features but result from large scale disturbances in the mantle conductivity increases commencing in the depth range 100 250 km may give an indication of uppermost zones within which the palaeozoic lithospherc has been substantially modified resulting in elevated surface heat flow volcanism and seismic travel time anomalies

on the nature of the teleseismic pn phase observed on the ultralong range profile quartz russia the most prominent secondary phase observed in the records from the ultralong profile quartz crossing northern eurasia is the high frequency long range teleseismic pn this phase propagating with the group velocity of about 8 1 to 8 2 km sec to over 3000 km distances dominates the records within the frequency range above about 5 hz within this teleseismic pn we distinguish onsets of several branches having higher apparent velocities between 8 5 and 8 6 km sec using travel time modeling techniques we associate the teleseismic pn with whispering gallery modes traveling within the top 160 km of the mantle the long incoherent coda of this phase results from scattering and from reverberations of seismic waves within the crust the contrast in frequency contents between the teleseismic pn and deeper refracted and reflected phases is explained by the increase of inelastic attenuation within the prominent low velocity zone lvz below the depth of about 150 km

correlation of lg amplitude ratios from peaceful nuclear explosions to crustal structure in northern eurasia because the lg phase is strongly affected by the variations of crustal structure in some areas understanding these factors is important for nuclear test monitoring this study examines the effects of regional tectonic structure on lg propagation by using the peaceful nuclear explosion pne profiles in russia the logarithms of lg sn and lg pcoda pne amplitude ratios within the 0 5 to 3 hz frequency band are measured and correlated with the regional crustal structures both ratios are found to decrease within the areas with thick low velocity sedimentary cover and across tectonic boundaries with abrupt variations of crustal thickness for the offset derivatives of both the logarithmic ratios a linear relationship to the slopes of the moho and the vertical travel times within the sedimentary cover is determined a strong negative slope is observed along both crustal thinning and crustal thickening segments and a positive slope follows the negative slope across a crustal thickening segment therefore crustal thinning appears to affect the lg propagation stronger than crustal thickening which could be due to focusing lg energy within the crustal wave guide the log amplitude regression provided in this article could be useful for predicting lg behavior in areas where amplitude measurements are not available

super deep reflection profiling exploring the continental mantle lid abstract reflections from the continental mantle lithosphere have now been reported from common mid point cmp profiles at numerous sites around the world these reflections include 1 distinct dipping events that appear to originate in the lower crust and continue some distance into the upper mantle 2 kilometer scale discontinuous diffusely distributed or isolated reflections at varying depths 3 continuous sub horizontal reflections tens of kilometers in extent often interpreted as the base of the lithosphere in spite of a wide variation in depth and 4 very deep reflections in the mantle lithosphere 125 km the first category of mantle reflections is most commonly observed in proximity to crustal sutures lending credence to their interpretation as fossil subduction zones isolated discontinuous mantle reflections are by far the most common and though observed in both ancient and modern collisional environments are difficult to interpret due to both their limited extent and a corresponding lack of three dimensional control sub horizontal mantle reflections appear in disparate tectonic environments in at least nine locations worldwide of special note are the various reports of specific reflections at 80 100 km 22 24 s twt in the north sea eastern europe and the urals which suggest a more ubiquitous mantle horizon the deepest events imaged thus far in a controlled source cmp survey are the super deep mantle reflections of the urseis project that have been identified at 135 165 km 35 43 s and 225 km 56 s of the many reported mantle reflections these are the most likely to be associated with the base of the lithosphere although such an interpretation averts the question of why an essentially thermo mechanical transition should be reflective at high frequencies 10 20 hz

middle pleistocene saalian lake outburst floods in the munsterland embayment nw germany impacts and magnitudes abstract during the late saalian drenthe glaciation ice damming of the upper weser valley led to the formation of glacial lake weser the lake drained catastrophically into the munsterland embayment as the western ice dam failed releasing up to 110 km3 of water with a calculated peak discharge of 2 5 105 m3 s to 1 3 106 m3 s geographic information systems gis and high resolution digital elevation models dem were used to map streamlined landforms and channel systems in front of lake overspills geological maps 2450 boreholes and the dem were integrated into the 3d modeling program gocad to reconstruct the distribution of flood related deposits palaeotopographic surfaces and the internal facies architecture of streamlined hills the drainage pathways are characterized by the occurrence of deep plunge pools channels streamlined hills and 4 km long and 12 m deep v shaped megaflutes plunge pools are deeply incised into mesozoic basement rocks and occur in front of three major overspill channels the plunge pools are up to 780 m long 400 m wide and 35 m deep approximately 1 10 5 km downslope of the overspill channels fan shaped arrays of streamlined hills are developed each covering an area of 60 130 km2 indicating rapid flow expansion the hills commonly have quadrilateral to elongated shapes and formed under submerged to partly submerged flow conditions when the outburst flood entered a shallow lake in the munsterland embayment hills are up to 4300 m long 1200 m wide 11 m high and have characteristic average aspect ratios of 1 3 3 they are separated by shallow anabranching channels in the outer zones and up to 30 m deep channels in the central zones hills partly display v shaped chevron like bedforms that have apices facing upslope are 1 6 2 5 km long 3 10 m high 0 8 1 2 m from limb to limb with limb separation angels of 20 35 these bedforms are interpreted as mixed erosional depositional features it is hypothesized that the post saalian landscape evolution of the munsterland embayment has considerably been influenced by catastrophic floods of glacial lake weser creating large and deep valleys which subsequently became the new site of river systems the outburst floods probably followed the east west trending saalian rhine meuse river system eventually flowing into the north sea the strait of dover and the bay of biscay it is speculated that the hondsrug ice stream may have been enhanced or even triggered by the formation and outburst of glacial lakes in the study area

a new model of upper mantle p wave velocity below the baltic shield indication of partial melt in the 95 to 160 km depth range abstract the subcrustal mantle to about a depth of 160 km below the baltic shield can be divided seismically into two main intervals the upper interval between ca 45 and 100 km is characterized by refracted waves with velocities between 8 0 and 8 6 km s interpreted as a sandwich layered model of intermixed high and low velocity layers the lower interval is a ca 40 km thick zone of relatively low average velocity at a depth increasing from 95 km in the southern part to 120 km in the northern part of the shield seismic sections show that isolated bodies in this interval generate scattered reflections with substantial amplitude variation over short distance the maximum velocity difference at the reflectors is 1 0 km s which is larger than in the upper main interval our model is based on a general gap in correlation of seismic arrivals at offsets between 800 and 1100 km at larger offsets we observe continuous linear first arrivals indicating a relatively homogenous layer of high 8 6 km s velocity below a depth of 160 km petrologically the lower reflective interval is explained by partially melted small bodies with patches of carbonatitic or kimberlitic magma of horizontal extent less than 20 km this new model of the upper mantle is based on seismic data from the baltic shield and there is clear indication that it is equally valid for other shield and platform areas

temporal correlation between dyke swarms and crustal extension in the middle palaeozoic vilyui rift basin siberian platform abstract this paper presents results from new 40ar 39ar isotope dating of nine mafic dykes from three large dyke swarms vilyui markha kontai dzherba and chara sinsk of the yakutsk vilyui large igneous province lip in addition to a reconstruction of the subsidence history of the middle palaeozoic vilyui paleorift basin eastern siberian platform all previously published 40ar 39ar and u pb dates are summarized statistical analysis of the dyke ages reveals repeated magmatic events in the study area two major pulses of mafic magmatism are identified one at the frasnian famennian boundary with a main peak at ca 374 1 ma and another in the latest devonian with a peak at ca 363 4 ma the time of maximum intensity of dyke intrusion coincides within uncertainty with rapid subsidence in the vilyui basin the minimum total volume of middle palaeozoic magmatism produced in the yakutsk vilyui lip is 100 215 k km3 which is much less than earlier estimates most of the mafic material within the yakutsk vilyui lip is related to the vilyui basin and associated dyke swarms backstripping analysis of sedimentation in depressions of the vilyui basin was carried out estimates were obtained for the spatial distribution of the stretching factor of the crust and mantle lithosphere averaging 1 17 and 1 44 respectively the amount of extension due to dyke intrusion is estimated to be 6 backstripping analysis of sedimentation in the vilyui basin was used to assess the effect of both intraplate far field forces and upwelling magma flows initiated by a mantle plume a numerical thermomechanical model was developed to investigate the relations between two possible mechanisms by which the vilyui rift was initiated intraplate extension passive rifting and the ascent of a mantle magmatic diapir active rifting a model considering both of these mechanisms shows the contribution of the far field extension forces and the effect of convective flows around the mantle plume assuming a temperature of 1500 c for a heat source operating for 10 myr the best fit model predicts the formation of the vilyui basin under extensional conditions with a depth integrated horizontal driving force of 2 0 1013 n m which corresponds to a lithostatic pressure of 0 73

processing and inversion of refraction and wide angle reflection data from the 1986 nevada passcal experiment we derive averaged one dimensional velocity models for the crust beneath the basin and range in western nevada by inverting p composites extracted from slant stacks of refraction and wide angle reflection data a combination of high cut filtering in the frequency domain with coherency filtering in the p domain has proved effective in smoothing severe static shifts due to lateral heterogeneities and suppressing artifacts due to spatial aliasing we supplement the low frequency information provided by the refraction records with higher frequency arrivals picked from the normal incidence and wide angle reflection sections generalized least squares inversion of data from eight shots for p and s wave velocity structure beneath two perpendicular profiles yields consistent estimates for total crustal thickness p wave 30 31 km s wave 30 32 km and average crustal velocity 6 2 km s 3 4 3 5 km s average poisson s ratio beneath the n s profile is 0 27 0 28 p wave velocities near the base of the crust 7 4 0 3 km s are estimated by inverting precritical reflections from the moho standard errors in depth for these models range from 1 to 3 km extremal depth bounds in general are about twice as large uncertainties in velocity estimated from resolving kernels range from 0 1 to 0 3 km s estimates of poisson1s ratio as a function of depth are characterized by large standard errors reflecting the poor resolution of shear wave velocities the combination of low average p and s wave velocities with a high average poisson s ratio in the upper half of the crust however is consistent with the presence of fluid filled cracks these results highlight the need for three component recording to better resolve shear wave velocity structure

magnetic fabrics of drumlins of the green bay lobe southeastern wisconsin abstract to study if the relief of drumlins of the green bay lobe of the laurentide ice sheet is dominantly the result of depositional or erosional processes we measured the anisotropy of magnetic susceptibility of 2500 samples of the horicon till from five drumlins in southeastern wisconsin these drumlins contain no macroscopic heterogeneities that might otherwise help guide interpretation of deformation kinematics ring shear experiments on this till provided the calibration necessary to relate fabrics based on principal susceptibilities of multiple intact samples to patterns of subglacial till deformation fabric strengths based on orientations of maximum susceptibility and measured from samples collected below the zone of pedogenesis weaken abruptly at depths shallower than 2 m the till lacks evidence of systematically divergent or convergent shear related to drumlin shape most till has been sheared in directions 6 24 to the east of drumlin long axes with shear plane orientations that are unrelated to drumlin morphology an exception is till at shallow depths 2 m where shearing azimuths and shear plane orientations agree more consistently with drumlin trends and morphologies the horicon till was likely deformed in shear during advance of the lobe drumlins formed by erosion of this basal till after glacier flow had shifted to the west when the johnstown moraine was being built a supraglacial till 2 m thick was draped over some of the drumlins during retreat of the lobe these results do not support models of drumlin formation in which sediment deposition helps amplify drumlin relief

global scale analysis of the mantle pds phases a global scale analysis of travel times of the mantle pds phases converted from p to s from the discontinuity at a depth d beneath the receiver is presented most of the data are related to p 410 s and p 660 s recorded by the broadband stations of geoscope incorporated research institutions for seismology iris and other networks in order to provide a good global scale coverage published measurements at 37 stations are complemented by our measurements at 45 stations lateral resolution of our data is many times higher than that of ss and its precursors previously used for similar purposes but we have fewer data in the oceans lateral variations of travel times of the major pds phases are strongly correlated with the lateral p and s velocity variations in the uppermost mantle as revealed by tomographic studies the scaling coefficient between the teleseismic s and p residuals as found from the variations of travel times of the major pds phases is around 3 7 for north america and around 3 3 for the rest of the world almost all the differential travel times t p 660 s t p 410 s are in the range of 1 s relative to the average value of 24 0 s if the lateral variations of the velocities within the mantle transition zone mtz can be neglected the corresponding variations of thickness of the mtz are in the range of 10 km relative to the standard depth of 250 km and do not show significant correlation with either velocities in the upper mantle above the mtz or with the variations of thickness of the mtz as found in some recent studies of precursors to ss there is a weak but marginally significant positive correlation between the variations of thickness of the mtz inferred from our data and the s velocity variations in the mtz as given by su et al 1994 this correlation suggests that both variables contain temperature dependent components lateral variability of the mtz is also manifested by extreme weakness of p 410 s at several locations this may indicate either anomalous topography on 410 km discontinuity or strong broadening of the otherwise sharp discontinuity at some stations there are arrivals that can be interpreted as p 520 s this interpretation implies that the strengh and or sharpness of 520 km discontinuity as well as its depth are laterally variable in a broad range

p wave mantle velocity structure beneath northern eurasia from long range recordings along the profile quartz high resolution seismic sounding of the mantle using two peaceful nuclear explosions pnes along the 3950 km long quartz profile in northern eurasia reveal major unexpected vertical and lateral mantle inhomogeneities in contrast to standard seismological earth models such as prem and iasp91 three rather than two mantle discontinuities are found between 400 and 700 km depth they are located at about 420 550 and 670 km depth lateral variations in depths amount to 10 20 km and associated p wave velocities vary by 0 1 km s 1 in the upper mantle the uppermost layer through which pn propagates extends down to about 100 km depth the mantle below this depth but above the 410 km discontinuity is characterized by alternating high and low p wave velocities in the depth range between 100 and 200 km the velocity fluctuates between 8 3 and 8 7 km s 1 and shows variations from shotpoint to shotpoint average velocities are clearly higher than standard seismological reference models this part of the mantle overlies a low velocity zone between about 200 and 300 km depth this channel also displays substantial lateral variation in depth which could be interpreted as a laterally variable asthenosphere beneath the west siberian basin the asthenosphere seems to be well established whereas it is only poorly defined under the uralian belt and the tectonic units to the northwest with the addition of more data from this and other profiles future aims include two dimensional and three dimensional tomographic modelling as well as modelling of petrological composition of the mantle down to 850 km depth beneath northern eurasia

results of lithospheric studies from long range profiles in siberia several long range seismic profiles obtained during the last ten years in siberia show the complicated lithospheric structure of the siberian platforms the three component observations conducted at distances up to 3000 km made it possible to obtain information on p and s velocities in the crust on p velocity and q factor for the upper mantle and on the seismic boundaries responsible for reflected refracted and converted waves down to a depth of 400 700 km the crustal models are typical of old platforms of eurasia the average thickness of 40 km three layers with p velocities 6 2 6 5 7 0 km s and thicknesses of 10 15 km are distinguished the depth to the m discontinuity varies from 45 50 km beneath the old tunguss depression to 35 40 km beneath the younger vilyui basin the most complicated moho structure is observed in the boundary between the west siberian and the siberian platforms a strong inhomogeneity of p velocity models was revealed for the upper mantle the horizontal inhomogeneities are more larger in the uppermost mantle to depths of 80 100 km where p velocities vary from 8 0 8 2 km s beneath the young west siberian plate to 8 4 8 6 km s beneath some blocks of the siberian craton the fine vertical inhomogeneity was studied with reflections correlated after computer processing of seismograms they outlined several low velocity layers 20 50 km thick the layers were characterized by low q as well intensive waves were recorded from the transition zone between the upper and lower mantle the top of the zone is nearly horizontal in the area its depth is 400 25 km the bottom of the zone lies at about 700 km

seismic structure of the uppermost mantle beneath the kenya rift a major goal of the kenya rift international seismic project wrisp 1990 experiment was the determination of deep li ospheric structure in the re action wide angle reflection part of the krisp effort the experiment was designed to obtain arrivals to distances in excess of 400 km phases from interfaces within the mantle vyere recorded from many shotpoints and by design the best data were obtained along the axial profile reflected arrikals from two thin 10 km high velocity layers were observed along this profile and a refracted arrival was observed from the upper high velocity layer these mantle phases were observed on record sections from four axial profile shotpoints so overlapping and reversed coverage was obtained both high velocity layers are deepest beneath lake turkana and become more shallow southward as the apex of the kenya dome is approached the first layer has a velocity of 8 05 8 15 km s is at a depth of about 45 km beneath lake turkana and is observed at depths of about 40 km to the south before it disappears near the base of the crust the deeper layer has velocities ranging from 7 7 to 7 8 km s in the south to about 8 3 km s in the north has a similar dip as the upper one and is found at depths of 60 65 km mantle arrivals outside the rift valley appear to correlate with this layer the large amoungs of extrusive volcanics associated with the rift suggest comp itional anomalies as an explanation for the observed velocity structure however the effects of the large heat anomaly associated with the rift indicate that composition alone cannot explain the high velocity layers observed these layers require some anisotropy probably due to the preferred orientation of olivine crystals the seismic model is consistent with hot mantle material rising beneaith the kenya dome in the southern kenya rift and north dipping shearing along the rift axis near the base of the lithosphere beneath the northern kenya rift this implies lithosphere thickening towards the north and is consistent with a thermal thinning of the lithosphere from below in the south changing to thinning of the lith phere due to stretching in the north

drumlins and catastrophic subglacial floods shaw j kvill d and rains b 1989 drumlins and catastrophic subglacial floods in j menzies and j rose editors subglacial bedforms drumlins rogen moraine and associated subglacial bedforms sediment geol 62 177 202 a number of lines of evidence are shown to be consistent with drumlin formation by catastrophic meltwater floods drumlins are associated with landforms related to such floods and landscapes produced by outburst floods in extragiacial areas contain drumlin like landforms some drumlins which contain mainly residual materials are compared to similar forms covering a wide range of scales and are interpreted to be scour remnant ridges produced by the action of horseshoe vortices on subgiacial materials these vortices are a product of flow separation in turbulent fluids and this interpretation implies drumlin formation by meltwater other drumlin calied cavity fill drumlins have distinctive shapes that are analogous with infilled erosional marks produced by turbulent separated flows these drumlins are interpreted as the infills of cavities eroded upwards into glacier beds by broad subgiacial meltwater sheetflows the sedimentology and internal structure of the cavity fill drumlins indicate rapid deposition from hyperconcentrated flow clast shape surface texture and lithology are consistent with the short distance of giaciofhivial transport predicted by the cavity fill hypothesis estimates of flow discharge 0 6 6 x 107 m3 s total volume of flow 84 1 103 km3 and flow duration 16 162 days are given for the catastrophic flood proposed to have produced the livingstone like saskatchewan drumlin field subgiacially derived floods are used to explain the sudden drainage of extraglacial lakes and major depositional events in proglacial lakes and it is suggested that they might have contributed to the lid of cold freshwater over the north atlantic held to have caused a late glacial cooling event the flood hypothesis requires extensive subgiacial lakes to have occurred beneath the laurentide and fennoscandian ice sheets which if they existed must have influenced the form and behaviour of these major bodies of ice

upper mantle velocity structure beneath the siberian platform summary we present a new velocity model for the continental upper mantle beneath central siberia based on observations of the 1982 rift deep seismic sounding dss profile three peaceful nuclear explosions pne were detonated to provide energy for the 2600 km long profile that extends from the yamal peninsula to the mongolian border se of lake baikal in this paper we model seismic recordings from the northernmost explosion since data from that shot shows unambiguous arrivals from the mantle transition zone discontinuities the analysis combines forward traveltime modelling and waveform matching using reflectivity synthetic seismograms our model for the lithosphere has velocities of 8 25 8 20 km s from the moho to 117km depth between 117 and 123km depth a strong velocity gradient 8 30 8 53 km s is required while a moderate gradient 8 53 8 55 km s l exists between 123 and 136km depth a low velocity zone from 136 to 210km depth terminates this phase arrival branch the gradient again rises between 210 and 233 km and depth culminating in a high gradient zone 8 63 8 80 km s between 233 and 235 km depth below the high gradient zone more moderate gradient 8 80 8 85 km s is required from 235 to 253 km depth terminating in a zone of lower velocity 8 62 8 64 km s from 253 to 400 km depth the upper mantle transition zone consists of two high gradient zones separated by a more moderate gradient the upper zone is best modelled as a 35 km thick velocity gradient 8 64 9 45 km s from 400 to 435 km depth the existence of the velocity gradient is based on the observation that arrivals from this feature can be identified starting at 1580 km range and rapidly become prominent with increasing distance a model with a first order discontinuity predicts significant arrivals at ranges closer than 1580 km our observations contain no compelling evidence for a 520 km discontinuity although a small discontinuity cannot be ruled out the lower transitionzone discontinuity is modelled as a 4 km thick gradient zone 10 25 10 62 km s i from 655 to 659 km depth

rayleigh wave group velocity tomography of siberia china and the vicinity rayleigh waves are used in a tomographic inversion to obtain group velocity maps of east asia 40 e 160 e and 20 n 70 n the period range studied is 30 to 70 seconds seismograms used for this study were recorded at cdsn stations at a temporary broadband seismic array in tibet at several sro stations and kirnos equipped stations established in asia by the former soviet union in siberia in the sakhalin and in mongolia altogether more than 1200 paths were available in the tomographic inversion the study area includes the angara craton the geologically ancient core of asia and the subsequently accreted units the altaids a paleozoic collision complex the sino korean platform a chain of archaen terranes separated by belts of active structures the south china platform a collage of precambrian paleozoic and mesozoic metamorphic and igneous terranes as well as the tibetan plateau an active tectonic feature created in late cenozoic through collision of the indian subcontinent and the asian continent many of these main units are recognizable in the tomographic images as distinctive units tibet appears as a prominent low velocity about 15 from the average structure with western and central tibet often appearing as the areas with the lowest velocities the central asian fold belt and the angara craton are consistently high group velocity areas some lesser tectonic features are also recognizable for example lake baikal is seen as a high velocity feature at periods greater than 40 seconds however the high group velocity feature does not stop near the southern end of lake baikal it extends south southwestward across mongolia the north china plain a part of the platform where extensional tectonics dominate is an area of high velocities as a result of relatively thin crust the south china block the least tectonically active region of china is generally an area of high velocity for periods longer than 40 seconds a nne trending high group velocity gradient clearly exists in eastern china the velocities are noticeably higher in the east from the group velocity maps average dispersion curves at twelve locations were determined and inverted to obtain velocity structures main results of group velocity inversion include 1 a tibetan crust of around 60 km thick with low crustal and upper mantle shear velocities at 3 3 km s and 4 2 km s respectively 2 with the moho constrained at 40 43 km the angara craton and the central asian foldbelt have a v s in excess of 4 6 km s 3 relatively low shear velocities are obtained for tectonically active areas in many parts of the study area where precambrian basement is exposed the process in the crust and upper mantle due to recent tectonic activities have modified the crust and upper mantle velocity structures under the precambrian terranes they are no longer underlain by high velocity crust and mantle

a glaciofluvial origin for drumlins of the livingstone lake area saskatchewan the livingstone lake drumlin field of northern saskatchewan is on the athabasca plains it is draped over high ground underlain by the precambrian athabasca sandstone the drumlins occur in spindle parabolic and transverse asymmetrical forms a map of individual drumlins shows that features of similar form occur together the drumlins are related on a regional scale to even larger landforms there is also an arrangement of drumlins in streams parallel to the assumed flow direction these patterns illustrate spatial organisation of the drumlin forming flows the livingstone lake drumlins are closely related to tunnel valleys large crescentic scours and eskers exposed bedrock reveals widespread scalloping and sichelwannen an argument is made that drumlins are related to these glaciofluvial forms but were created at different times and by different flows than those forming small scale flutings and other lodgment features sediments within the drumlins are mainly primary water sorted deposits some of wh

deep structure of the continental lithosphere in an unextended orogen an explosive source seismic reflection profile in the urals urals seismic experiment and integrated studies urseis 1995 explosive source near vertical seismic reflection data from the urals seismic experiment and integrated studies urseis profile displays an image of orogenic lithosphere to depths of 225 km the reflective crustal section is characterized by dipping crustal scale shear zones and a pronounced crustal root that show no evidence of overprinting by extension and are preserved since late paleozoic collision toward the east the uralian crustal root is composed of a partially subducted volcanic arc while to the west it has affinity with the east european platform the reflection character of the moho varies across tectonic strike and implies that the moho 1 acted as a structural detachment beneath the trans uralian zone 2 forms a tectonic boundary between terranes beneath the east uralian zone 3 consists of a transitional zone from eclogitized lower crust to peridotitic upper mantle in the crustal root 4 is a 3 9 km thick reflective zone beneath the fold and thrust belt and 5 is a boundary 200 m thick in the west mantle reflections at 80 100 km depth 22 24 s may represent a continuation of the main uralian fault into the subcrustal lithosphere alternatively these reflectors may signify paleozoic or younger mantle shear zones or the top of a zone of partial melting in the upper mantle deeper mantle reflections at 140 160 km 35 45 s and 225 km 55 s may image mafic intrusions at the base of the lithosphere or along localized shear zones in the upper mantle

upper mantle structure beneath eastern siberia evidence from gravity modeling and mantle petrology 1 the spatial distribution of large scale lithospheric domains and the boundaries between them may control the emplacement of large ore bodies and as such regional mapping of the lithosphere is relevant to mineral exploration in this study we combine potential field geophysical data and mantle petrology to map major lithospheric structures on the eastern part of the siberian platform the platform consists of several archean and proterozoic terranes that have been mapped from regional magnetic data and basement exposures in the anabar shield we use garnet and chromite concentrates from a chain of paleozoic to mesozoic kimberlites across the platform to construct mantle sections which show significant lateral variation in rock type distribution within the lithospheric mantle these lateral variations correspond to the terranes mapped at the surface and indicate that the terrane boundaries are translithospheric archean terranes are underlain by depleted archean lithosphere more than 200 km thick while the proterozoic terranes are underlain by thinner and less depleted lithosphere geophysical data show more strongly negative bouguer anomalies and a more heterogeneous magnetic anomaly pattern over the archean terranes than on the proterozoic terranes the pattern of the gravity data reflects the lateral variation in mantle composition beneath the terranes as shown by mantle petrology studies we invert gravity and topography data to estimate the flexural strength or elastic thickness te of the lithosphere across the area although on a stable precambrian craton the te is relatively low 30 km across most of the area suggesting a relatively weak lithosphere comparable to that of tectonically much younger areas around the world a 150 km wide zone of very weak lithosphere te 10 km runs n s across the western part of the study area this weak zone coincides with a zone of thickened lower crust and abnormally high sub moho p wave velocities which suggest anisotropy in the upper mantle the kimberlite fields in the archean part of the platform are localized on the flanks of this zone of weak lithosphere we suggest that the low te zone may be a mantle shear zone which has been a preferred conduit for the emplacement of magmas into the lower crust and later has controlled the emplacement of kimberlites in the study area

lidar based volume assessment of the origin of the wadena drumlin field minnesota usa abstract the wadena drumlin field wdf 7500 km 2 in west central minnesota usa is bordered along its outer extremity by the till cored alexandria moraine marking the furthest extent of the southwesterly flowing wadena ice lobe at c 15 000 kyr bp newly available high resolution light detection and ranging lidar data reveal new information regarding the number morphology and extent of streamlined bedforms in the wdf in addition a newly developed quantitative methodology based on relief curvature analysis of lidar elevation based raster data is used to evaluate sediment volumes represented by the wdf and its bounding end moraine these data are used to evaluate models for the origin of drumlins high resolution lidar based mapping doubles the streamlined footprint of the wadena lobe to 16 500 km 2 increases the number of bedforms from 2000 to 6000 and most significantly reclassifies large numbers of bedforms mapped previously as drumlins as mega scale glacial lineations msgls indicating that the wadena ice lobe experienced fast ice flow the total volume of sediment in the alexandria moraine is 71 110 km 3 that in the drumlins and msgls is 2 83 km 3 and the volume of swales between these bedforms is 74 51 km 3 the moraine volume is equivalent to a till layer 6 8 m thick across the entire bed of the wadena lobe suggesting drumlinization and moraine formation were accompanied by widespread lowering of the bed this supports the hypothesis that drumlins and msgls are residual erosional features carved from a pre existing till swales represent missing sediment that was eroded subglacially and advected downglacier to build the alexandria moraine during fast ice flow alternatively the relatively small volume of sediment represented by subglacial bedforms indicates they could have formed rapidly by depositional processes

drumlin formation by subglacial meltwater erosion some drumlins are shown to belong to a family of remnant erosional ridges associated with subglacial meltwater the lengths of these ridges vary in scale from a few tens of millimetres to over 5 km similar form elements are illustrated for three scales of forms it is concluded that some drumlins are composed of preexisting sediment or bedrock left upstanding in ridges as a result of the removal of surrounding materials this erosional theory is related to an earlier theory in which drumlins are held to result from the infilling of subglacial cavities the unifying factor for both theories is the role of sheets of subglacial meltwater

thermal state and composition of the lithospheric mantle beneath the daldyn kimberlite field yakutia abstract the proton microprobe has been used to study the distribution of trace elements in garnet and chromite concentrates from the udachnaya kimberlite and three smaller low grade kimberlites from the daldyn kimberlite field garnet thermobarometry and classical p t estimates for megacrystalline peridotite xenoliths both suggest a paleozoic geotherm beneath the daldyn area that is close to a 35 mw m 2 conductive model finer grained xenoliths with t c scatter above this geotherm high temperature sheared xenoliths lie near or above a 40 mw m 2 model geotherm at 1150 1400 c the higher t results are interpreted as the result of short term heating caused by magmatic intrusion and perturbation of a relatively cool conductive geotherm especially near the base of the lithosphere the stratigraphic distribution inferred from nickel temperature t ni of garnets with different major element chemistry indicates that the lithosphere is strongly layered in terms of rock type depleted lherzolites predominate to depths of ca 150 km harzburgites comprise up to 60 of the volume between 150 and 180 km and these are underlain by a mixture of depleted and metasomatically enriched lherzolites zinc temperatures t zn indicate that chromite bearing peridotites are essentially absent at depths 190 km high t lherzolite garnets carry a distinctive trace element fingerprint showing enrichment in zr ti y and ga interpreted as due to the infiltration of asthenosphere derived melts this melt related metasomatic signature becomes the dominant one at ca 220 230 km depth and this is interpreted as the base of the lithosphere this depth also corresponds approximately to the lehman discontinuity at the top of a pronounced low velocity zone observed in deep seismic sounding experiments across this part of the siberian platform the techniques used here provide a means of mapping the lithosphere in terms of thermal structure lithology and fluid related processes both lateral 3 d and temporal 4 d variations may be mapped using readily available garnet and chromite concentrates from the widespread kimberlite intrusions across the siberian platform

deep seismic sounding with nuclear explosives in the soviet union a large geophysical program of exploration that uses deep seismic sounding has been under way in the soviet union for decades underground nuclear explosives have been used as strong seismic sources since 1971 the wide spacing between these seismic sources for example 500 kilometers has permitted seismic exploration of inaccessible areas in traverses up to 3000 kilometers in length during the same time an ultra deep drilling program has also been under way the data gathered have been used to elucidate details of the crust as well as to describe layering and inhomogeneities in the underlying mantle by soviet account deep seismic sounding has been instrumental in confirming the existence of numerous sedimentary structures containing oil and gas fields in western and eastern siberia 36 refs 1 tab 5 figs

genesis of boston harbor drumlins massachusetts abstract drumlins in boston harbor are composed of two superposed silty sandy diamicton units and subordinate sand and gravel the lower compact undifferentiated diamicton is interpreted as a pre wisconsin till based on truncated weathering profiles preserved below an erosion surface the upper less compact diamicton contains numerous discontinuous and poorly sorted lenses and stringers of sand and sandy gravel that tend to parallel the erosion surface the upper diamicton and subordinate sandy gravel lenses are interpreted to date from the late wisconsin glaciation along the exposed sections of the long island drumlin complex the preserved weathering profile on the lower diamicton is thicker beneath the drumlin axes and is either thin or missing in the interdrumlin areas this suggests that glacial erosion and streamlining of pre wisconsin deposits and their weathering profile took place after the weathering profile developed and before subsequent deposition of the overlying diamicton unit the latter drapes the erosional drumlin form without contributing substantially to relief of the drumlin form

high velocities in the uppermost mantle of the siberian craton abstract anomalous high seismic velocities up to 8 8 km s have been reported suvorov et al 1985 in the mantle beneath the kimberlite areas of siberia high mantle velocities were also observed on some geon center profiles carried out using nuclear explosions egorkin et al 1987 to obtain clear general signatures of the mantle structure in siberia and the role of the high velocity blocks the geon data were analyzed and compared with other geophysical information this analysis showed that the largest blocks of 300 400 km width with velocities up to 8 6 km s are observed beneath the tunguss depression and in the southern part of the craton near its boundary with the baikal rift zone the blocks penetrate to depths of 100 110 km where they are underlain by low velocity zones or a horizontally homogeneous layer there is no evidence of these blocks in the gravity field velocity anisotropy is proposed as a main cause of the anomalous high velocities although the crossing profiles show that such velocities are observed in different directions the yakutia kimberlite fields are located in the region with average sub moho velocity of 8 3 8 4 km s but with higher velocity at depths of 70 80 km

an investigation of upper mantle heterogeneity beneath the archaean and proterozoic crust of western canada from lithoprobe controlled source seismic experiments abstract observations of upper mantle reflectivity at numerous locations around the world have been linked to the presence of a heterogeneous distribution of rock types within a broad layer of the upper mantle this phenomenon is observed in wide angle reflection data from lithoprobe s alberta basement transect the sarex and deep probe experiments of 1995 and trans hudson orogen transect the thore experiment of 1993 sarex and deep probe image the archaean lithosphere of the hearne and wyoming provinces whereas thore images the archaean and proterozoic lithosphere of the trans hudson orogen and neighbouring areas finite difference synthetic seismograms are used to constrain the position and physical properties of the reflective layer sarex deep probe modelling uses a 2 d visco elastic finite difference routine thore modelling uses a pseudospectral algorithm in both cases the upper mantle is parameterized in terms of two media one medium is the background matrix the other is statistically distributed within the first as a series of elliptical bodies such a scheme is suitable for modelling 1 variations in lithology e g a peridotite matrix with eclogite lenses or 2 variations in rheology e g lenses of increased strain within a less strained background the synthetic seismograms show that the properties of heterogeneities in the upper mantle do not change significantly between the two lithoprobe transects beneath the trans hudson orogen in saskatchewan the layer is best modelled to lie at depths between 80 and 150 km based on observations from perpendicular profiles anisotropy of the heterogeneities is inferred beneath the precambrian domains of alberta 400 km to the west upper mantle heterogeneities are modelled to occur between depths of 90 and 140 km in both cases the heterogeneous bodies within the model have cross sectional lengths of tens of kilometers vertical thicknesses less than 1 km and velocity contrasts from the background of 0 3 to 0 4 km s based on consistency with complementary data and other results the heterogeneous layer is inferred to be part of the continental lithosphere and may have formed through lateral flow or deformation within the upper mantle

the p wave upper mantle structure beneath an active spreading centre the gulf of california summary detailed analysis of short period travel time dt d and wave form data reveals the upper mantle structure beneath an oceanic ridge to depths of 900 km more than 1400 digital seismograms from earthquakes in mexico and central america recorded at scarlet yield 1753 travel times and 58 direct measurements of dt d as well as high quality stable waveforms the 29 events combine to form a continuous record section from 9 to 40 with an average station spacing of less than 5 km first the travel times are inverted using the tau method of bessonova et al the resultant model is adjusted to agree with the experimental p values further constraints arise from the observed relative amplitudes of mantle phases which are modelled by trial and error using wkbj synthetic seismograms chapman wiggins model gca which is appropriate for western mexico north of 20 latitude is similar to existing upper mantle models for shield tectonic continental and arc trench regimes below 400 km but differs significantly in the upper 350 km gca velocities are very low in this depth range the model catches up with the others with a very large velocity gradient from 225 to 390 km this well resolved feature is consistent with the shear wave model tna for western north america of grand helmberger the abundant data from 20 to 30 control the detailed shape of the 660 km discontinuity very large velocity gradients lie both above 620 660 km and below 661 680km a 2 8 per cent velocity change

upper mantle heterogeneity in the northern part of eurasia abstract a two dimensional velocity model of the upper mantle has been compiled from a long range seismic profile crossing the west siberian young plate and the old siberian platform it revealed considerable horizontal and vertical heterogeneity of the mantle a sharp seismic boundary at a depth of 400 km outlines the high velocity gradient transition zone its base lying at a depth of 650 km several layers with different velocities velocity gradients and wave attenuation are distinguished in the upper mantle they likewise differ in their inner structure for instance the uppermost 50 70 km of the mantle are divided into blocks with velocities from 7 9 8 1 to 8 4 8 6 km s 1 comparison of the travel time curves for the siberian long range profile with those compiled from seismological data for europe distinguished large scale upper mantle inhomogeneities of the eurasian continent and allowed for the correlation of tectonic features and geophysical fields the velocity heterogeneity of the uppermost 50 100 km of the mantle correlates with the platform age and heat flow i e the young plates of western europe and western siberia have slightly lower velocities and higher heat flows than the ancient east european and siberian platforms at greater depths 150 250 km the upper mantle velocities increase from the ocean to the inner parts of the continent the structure of the transition zone differs significantly beneath western europe and the other parts of eurasia the sharp boundary at a depth of 400 km traced throughout the whole continent as the boundary reflecting intensive waves transforms beneath western europe into a gradient zone this transition zone feature correlates with positions of the north atlantic west europe geoid and heat flow anomalies

high frequency wave propagation in the uppermost mantle short period three component recordings of the seismic wave field of peaceful nuclear explosions recorded on deep seismic sounding profiles quartz and ruby i collected in 1984 and 1988 respectively in northern russia are used to constrain the nature of the high frequency teleseismic p n phase which can be observed for receiver distances of 3000 km we suggest that this phase is caused by velocity fluctuations in the upper mantle acting as scatterers to test this hypothesis and to determine the properties of the upper mantle scatterers the elastic reflectivity method one dimensional isotropic models was used to model the coda of the high frequency teleseismic p n phase both the observed data and the synthetic record sections were analyzed by examining the coda decay rates of the teleseismic p n phase at 5 hz synthetic seismograms are computed for different models based on the global model iasp91 with an added zone of randomly distributed velocity fluctuations lamellae just below the crust mantle boundary these models may be characterized by the thickness of the scattering layer l the vertical heterogeneity correlation length a and the heterogeneity standard deviation the numerical simulation of the wave propagation in these models generated a high frequency teleseismic p n phase with a well pronounced long coda a comparison of the modeling results with the observations shows clearly that a velocity model containing fluctuations in the upper mantle can easily explain the presence of a high frequency teleseismic p n comparing the coda decay rates of synthetic seismograms with the observation we tried to constrain the properties of the velocity fluctuations in the upper mantle l a and in the distance range of the uninterfered high frequency teleseismic p n phase beyond 1300 km the coda decay rates for our best fitting model are similar to the observed ones this model has a 75 km thick zone of scatterers below the moho containing lamellae with an average thickness of 2 km and a rms velocity perturbation of 5 the modeling results show also that two other possible models the whispering gallery phase along the crust mantle boundary and scattering in the lower crust taken alone are not able to explain the coda properties of the high frequency teleseismic p n phase

the poisson ratio of the australian crust geological and geophysical implications the poisson ratio which depends on the vp vs ratio provides much tighter constraints on the crustal composition than either the compressional or the shear velocity alone the crustal poisson ratio can be determined from the joint analysis of the travel times of waves converted at the moho and of crustal multiples reflected at the top of the moho we have analyzed the records of the permanent stations installed on the australian continent complemented by the data of the skippy experiment the results reveal substantial variations in the poisson ratio in the different tectonic units for the proterozoic crust an increase of the poisson ratio with increasing crustal thickness is systematically observed while for the phanerozoic crust the poisson ratio tends to decrease for increasing crustal thicknesses these observations are in remarkable agreement with the results of the deep seismic soundings that were performed in the former soviet union the variations observed in the proterozoic provinces can perhaps be explained by underplating of mafic materials at the base of the crust fl 2000 elsevier science b v all rights reserved

subcrustal low velocity layers in central india and their implications a 2 d subcrustal velocity model for the central indian continental lithosphere has been derived by travel time and relative amplitude modeling of a digitally normalized analog seismic record section of the hirapur mandla dss profile using a ray tracing technique some prominent wave groups with apparent velocities slightly higher than the moho reflection phase pmp are identified on the normalized record sections assembled with a reduction velocity of 6 km s 1 we interpret these phases as the wide angle reflections from subcrustal lithospheric boundaries comparison of synthetic seismograms with the observed record section shows that the observed phases cannot be explained either by multiples or by the p to s converted phase pms from the moho subcrustal velocity models either with a velocity increase or with a single low velocity layer lvl also do not provide a satisfactory fit we infer that a subcrustal velocity model with two alternate lvls velocity 7 2 km s 1 separated by a 6 km thick high velocity layer velocity 8 1 km s 1 can satisfy both the observed travel times and amplitudes the prominent reflection phases are modeled at depths of 49 51 57 and 60 km it is inferred that the subcrustal lithosphere in the central indian region has a lamellar structure with varying structural and mechanical properties the alternating lvls occurring at relatively shallow depths below moho may be associated with the zones of weakness and lower viscosity suggesting continued mobility with a possible thermal source in the upper mantle this explains the source of observed high heat flow values in the central indian region

mantle heterogeneities and their significance results from lithoprobe seismic reflection and refraction wide angle reflection studiesthis article is one of a series of papers published in this special issue on the theme lithoprobe parameters processes and the evolution of a continent lithoprobe contribution 1486 within lithoprobe s 10 transects data from more than 20 000 km of multichannel seismic mcs reflection profiling and 12 refraction wide angle reflection r war surveys were acquired while the

do subglacial bedforms comprise a size and shape continuum understanding the evolution of the ice bed interface is fundamentally important for gaining insight into the dynamics of ice masses and how subglacial landforms are created however the formation of the suite of landforms generated at this boundary subglacial bedforms is a contentious issue that is yet to be fully resolved bedforms formed in aeolian fluvial and marine environments either belong to separate morphological populations or are thought to represent a continuum of forms generated by the same governing processes for subglacial bedforms a size and shape continuum has been hypothesised yet it has not been fully tested here we analyse the largest data set of subglacial bedform size and shape measurements ever collated 96 900 bedforms our results show that flutes form a distinct population of narrow bedforms however no clear distinction was found between drumlins and megascale glacial lineations msgls which form a continuum of subglacial lineations a continuum of subglacial ribs also exists with no clear size or shape distinctions indicating separate populations furthermore an underreported class of bedform with no clear orientation to ice flow quasi circular bedforms overlaps with the ribbed and lineation continua and typically occurs in spatial transition zones between the two potentially merging these three bedform types into a larger continuum

oscillating turbulent boundary layer with suspended sediments a dynamic boundary layer model with simultaneous interactions between constant oscillatory and turbulent flow suspended sediments and erosion is developed the model appears to be verified as well as the existing data permits in purely oscillatory flow most of the state variables appear to be associated with a turbulent kinetic energy maximum developing near the bottom and phase angle 2 and propagating upward thereafter the maximum horizontal sediment flux is approximately proportional to the third power of the maximum turbulent stress a channel flow with constant pressure gradient may be strongly reduced by the presence of waves the waves may also increase the suspended sediment concentration significantly

studies of mantle structure of u s s r territory on long range seismic profiles long range seismic sounding carried out during the last few years on the territory of the u s s r has shown a basic inhomogeneity of the uppermost mantle as well as evidence of regularities in the distribution of its seismic parameters the following data were used times and apparent velocities of p and s waves for investigation of mantle velocities converted waves for seismic discontinuity model studies and wave attenuation for q factor estimation strong regularities were distinguished in the distribution of average seismic velocities for the uppermost mantle in their dependence on the age and type of geostructure and on their position relative to the central part of the continent old platforms and the inner part of the continent are marked by velocities under the mohorovicic discontinuity of more than 8 2 8 3 km s 1 young platforms and outer parts of the continent by 8 0 8 2 km s 1 and orogenic and rift zones by 7 8 8 0 km s 1 the difference becomes more pronounced at a depth of about 100 200 km for the old platform mantle velocities of 8 5 8 6 km s 1 are typical beneath the orogenic and rift areas inversion zones with velocities less than 7 8 km s 1 are observed the converted waves show fine inhomogeneities of the crust and uppermost mantle the presence of many discontinuities with positive and negative changes of velocity and anisotropy of seismic waves in some of the layers wave attenuation allowed the determination of the q factor in the mantle it varied from one region to another but a close relation between q and p wave velocity is the main cause of its variation

new middle cambrian and middle ordovician palaeomagnetic data from siberia llandelian magnetostratigraphy and relative rotation between the aldan and anabar angara blocks abstract whether siberia was a coherent tectonic unit throughout the phanerozoic or whether significant rotations occurred in early palaeozoic times between the anabar angara and aldan blocks is still a matter of debate addressing this problem a detailed palaeomagnetic study of sections of mid cambrian and llandeillian age has been carried out along the river lena river maya river kulumbe and river stolbovaya with a total of 403 collected hand samples a section of llandeilian age was also investigated on the russian platform near st petersburg the studied rocks are carbonates or fine grained terrigenous sediments of reddish and greyish colors stepwise thermal demagnetization experiments reveal a rather simple directional behavior in most samples after removal of a secondary magnetizations at low to intermediate temperatures a high temperature component is isolated which is carried by magnetite and or hematite positive reversal tests and fold tests clearly demonstrate the primary character of the latter component while only reversed polarity directions are obtained in the lower two thirds of the llandeilo six magnetozones of normal polarity are found in the upper llandeilo which mark the end of the moyero reverse superchron together with previously published paleomagnetic data our new results show rather systematic difference in declinations of 20 between the aldan and anabar angara blocks this argues in favor of a relative rotation between these two blocks with an euler pole of rotation located at latitude 62 n and longitude 117 our interpretation is further supported by existing results from deep sounding seismic experiments yielding a very similar pole of rotation

updates to the regional seismic travel time rstt model 1 tomography a function of global monitoring of nuclear explosions is the development of earth models for predicting seismic travel times for more accurate calculation of event locations most monitoring agencies rely on fast distance dependent one dimensional 1d earth models to calculate seismic event locations quickly and in near real time rstt regional seismic travel time is a seismic velocity model and computer software package that captures the major effects of three dimensional crust and upper mantle structure on regional seismic travel times while still allowing for fast prediction speed milliseconds we describe updates to the rstt model using a refined data set of regional phases i e pn pg sn lg using the bayesloc relative relocation algorithm the tomographic inversion shown here acts to refine the previous rstt public model rstt201404um and displays significant features related to areas of global tectonic complexity as well as further reduction in arrival residual values validation of the updated rstt model demonstrates significant reduction in median epicenter mislocation 15 3 km using all regional phases compared to the iasp91 1d model 22 1 km as well as to the current station correction approach used at the comprehensive nuclear test ban treaty organization international data centre 18 9 km

observation of high frequency teleseismic p n on the long range quartz profile across northern eurasia short period three component recordings of the seismic wave field of peaceful nuclear explosions pnes on long range profiles are used to determine the fine structure of the mantle lithosphere by analyzing the frequency content of the recorded phases and applying different band pass filters to the data it is possible to divide the wave field into two distinctly different constituents low frequency body waves traveling along fermat paths first arrivals and the high frequency teleseismic or long range pn phase traveling with a group velocity of 8 1 km s and accompanied by a long incoherent coda this high frequency teleseismic pn phase is observable from about 750 km where it separates from the faster first arrival to the maximum recording distance of 3145 km it is recorded from shots at different locations and appears to be almost unaffected by the major tectonic feature along the profile the urals the frequency spectrum of this pn phase contains more high frequency energy up to 12 hz than first arrivals that penetrate deeper into the upper mantle the teleseismic high frequency pn arrival has a remarkable coda which is incoherent between closely spaced stations the coda duration is dependent on the component of motion being shortest on the vertical and longest on the transverse component we propose a velocity model that is characterized by a zone extending from the crust mantle boundary to a depth of about 100 km this zone has randomly distributed spatially anisotropic velocity fluctuations we propose that these velocity heterogeneities are stretched in the horizontal direction this zone forms a scattering waveguide that confines the high frequency teleseismic pn there are indications that below this pn waveguide either the scale of the velocity fluctuations or the q factor changes this is expressed in a separation of the teleseismic pn phase from the phase diving deeper into the mantle lithosphere

the velocity structure of the australian shield from seismic travel times abstract travel times between sources and stations in the australian shield are used to develop p and s wave velocity models for the precambrian shield of western and central australia errors in travel times are minimized by using sources for which locations and origin times are constrained by local data or fault scarps apparent velocities between 1500 and 2200 km for p 8 8 km sec and s 4 8 km sec require a high velocity lid and the maximum range of observation of this branch 2200 km requires that the lid extend to a depth of 205 20 km because of the distribution of sources and receivers there are no observations from the shield at ranges greater than 2300 km so we use times from stations in phanerozoic eastern australia and published global summary times as a guide for interpretation at greater ranges allowing for known differences in teleseismic travel time residuals between the precambrian shield and eastern australian the p times are best fit by a model that has a small velocity inversion at the base of the lid and the s times are best fit by a model with a more substantial reduction in velocities however both p and s wave travel times can be satisfied with models that have velocities below 210 km that are concordant with global averages such as iasp91 thus the velocities inferred beneath the lid are low relative to those of the lid but not necessarily low relative to global averages

structural regularities in the lithosphere of continents and plate tectonics abstract two fundamental but competing earth science concepts have been under discussion in russia the first one that of endogenous regimes is based on the assumption that permanent vertical relationships or long term interactions between the crust and upper mantle control crustal evolution significant horizontal movements of the lithosphere as required by the second concept that of global plate tectonics would destroy these crust mantle interactions certain regular features of the crust and upper mantle support the endogenous regime concept and are difficult to explain in terms of conventional plate tectonics in particular the close correlation between near surface features and deep 400 km mantle inhomogeneities suggests that many geological structures are deeply rooted in the mantle moreover geophysical studies have failed to reveal a well defined and continuous asthenosphere at relatively shallow depths 100 km that would allow lithospheric plates to be transported over large distances and the rheology of the lithosphere itself is found to be sufficiently inhomogeneous as to cast doubt on the principle of thin rigid plates in contrast palaeomagnetic and other data require that horizontal movements of many near surface geological structures must have taken place to explain this apparent contradiction it is suggested here that the crust and its connected deep root are capable of gliding along one of the deep mantle phase transition zones with respect to the inner earth

inhomogeneities of the eurasian mantle structure from the traveltimes of the nuclear explosions recorded by the finnish seismic network during 1961 1985 summary during the period 1961 1985 hundreds of nuclear explosions from the area of the soviet union and china were well recorded at finnish seismological stations the seismic waves recorded on the baltic fennoscandian shield penetrated through the mantle of the siberian platform the ural mountains and the east european platform from the known crustal models the functions describing the increase of the average velocities of sedimentary cover and crystalline complex of the crust with thickness were found the corrections for sedimentary cover and crustal thickness were included the large amount of data permitted the calculation of traveltimes of p waves for three sectors up to distances of about 5000 km in all mantle models the boundaries 400 and 700 km were found comparison of the results shows a difference in the traveltimes of the order of 5 s at a distance of about 4000 km which reflects the mantle structure differentiation for depths greater than 700 km lowest velocities for latitudinal direction and highest velocities for longitudinal direction the average s wave velocity model of the mantle was obtained using the traveltimes of s wave first arrivals high values of the vp vs ratio were found in the depth interval 200 400 km while in other depth intervals they were close to 1 73 our 1 d models are compared with and discussed in connection with other models of the east european and siberian platforms as well as with global tomographic solutions

short period observation of the 520 km discontinuity in northern eurasia short period three component recordings of the seismic wave field of peaceful nuclear explosions pnes along several long range profiles in northern eurasia are analyzed to study the structure of the upper mantle we use the data to search for evidence of the disputed 520 km discontinuity in the mantle transition zone here we present short period evidence for the existence of this proposed mantle discontinuity on three long range profiles in siberia we observe in the distance range from 2400 to 2600 km a typical change of the apparent velocity of the first arrivals and the appearance of two characteristic travel time branches we interpret these phenomena as being caused by the proposed upper mantle discontinuity to determine the optimum one dimensional p wave velocity model synthetic seismograms were calculated with the reflectivity method by comparing them with the observed data we estimate the p wave velocity contrast across the 520 km discontinuity to be 0 25 0 05 km s while the velocity gradient below the boundary is 0 001 0 0005 1 s this result indicates that in the mantle transition zone both phase transitions and variations in chemical composition can occur

low velocity layers in the subcrustal lithosphere beneath the deccan traps region of western india abstract travel times and relative amplitude modeling of a seismic record section from the koyna dss profile in the deccan traps region has yielded a velocity model for the indian continental subcrustal lithosphere the observed record section assembled with a reduction velocity of 6 km s 1 and using digitized data from analog deep seismic sounding dss recorders reveals a prominent wave group with an apparent velocity similar to but about 3 s after the reflected p phase from the moho pmp at a reduced time of 7 5 to 6 5 s and recording distance range from 70 to 95 km we interpret this strong amplitude phase as the reflection from an interface in the subcrustal lithosphere comparison of synthetic seismograms for a range of velocity models with the observed record section shows that the observed phase under investigation cannot be explained either by a reflected phase from a subcrustal velocity discontinuity with a single velocity increase or by the p to s converted phase pms from the moho subcrustal velocity models with a single low velocity layer lvl do not seem to give a satisfactory fit to the amplitude observations on the field record section we prefer a subcrustal velocity model with alternating lvl at least two with a velocity of 7 0 7 4 km s 1 separated by a thin high velocity layer in this model the synthetic amplitudes of the reflected phase from the top of the deeper lvl at 56 km depth well match those of the observed reflection phase it is inferred that the continental subcrustal lithosphere in this region of the indian shield has a lamellar structure with significant vertical variation of structural and mechanical properties the alternating lvl occurring at relatively shallow depths below the moho velocity decreasing from 8 3 to 7 4 km s 1 may be associated with zones of weakness and lower viscosity the lvl in the subcrustal lithosphere as well as the lvl inferred in the upper and the lower crust krishna et al 1989 together with the observed depth distribution of seismicity in this region suggest a well defined rheological stratification of the continental lithosphere with varying material properties

crustal and uppermost mantle velocity structure of northern eurasia along the profile quartz the velocity structure of the crust and uppermost mantle beneath the dss profile quartz in northwestern russia is determined using a linearized seismic tomography scheme the analysis is performed on the northern 2200 km of the profile spanning from the kola peninsula the timan pechora basin and the uralian fold belt to the west siberian basin refracted and reflected phases recorded from 28 chemical and two nuclear shot points are analyzed the inversion technique allows determination of the p wave velocity structure and estimation of the depth of the crust mantle discontinuity resolution analysis shows that the upper crustal structure and sections of the lower crust and uppermost mantle are well resolved the modeled velocity and crustal thickness anomalies are confirmed by the resulting structure of the resolution matrix poorer ray coverage in parts of the lower crust and most sections of the uppermost mantle limits their resolvable structures a thick over 10 km high velocity block vp 7 0 km sec in the lower crust of the precambrian beneath the kola peninsula crustal thinning and a wide range of compressional velocities in the sedimentary basin structures and a significant crustal root beneath the uralian fold belt 42 to 45 km moho depth with high lower crustal velocities exceeding 7 0 km sec were identified in the tectonic structure of northwestern eurasia

streamlined erosional residuals and drumlins in central british columbia canada abstract the upland lowland pattern in the plateau region of central british columbia canada forms an extremely large anastomosing channel network with the uplands representing interfluves between channels the study area landscape is remarkably similar in form to water produced channel systems and qualitatively resembles flood landscapes from the channelled scablands and the margins of the laurentide ice sheet numerical shape analysis of the area erosional residuals gives similar results as those derived from known flood landscapes the length to width ratios of the uplands l w 2 38 r2 0 89 are similar to those reported for braid bars and erosional residuals formed by glacial outburst floods thus the study area landscape records a megaflood or floods that almost completely immersed the landscape drumlins with in places ubiquitous hairpin furrows locations downstream from steep slopes facing into the flow and eroded into till and bedrock similarly reflect regional scale meltwater flow that immersed the landscape the regional flow submerged the anastomosing channels at the time of drumlin formation drumlins likely formed as the anastomosing network developed divergent drumlin orientations probably reflect either late flow or separate drumlin forming events that did not appreciably alter the anastomosing system

detection of underside p reflections at mantle discontinuities by stacking broadband data underside p reflections at mantle discontinuities are difficult to observe directly on seismograms mainly because of their low amplitude it is shown that stacking seismograms obtained at several epicentral distances but having their pp bounce points in the same region enables the identification of such phases this method is applied to data from japanese and taiwan events recorded by the nars array and other broadband european stations discontinuities at about 670 and 300 km are revealed beneath northern eurasia

wave propagation in a multiple scattering upper mantle observations and modelling summary a striking feature of russian long range seismic refraction data from peaceful nuclear explosions is the observation of a high frequency teleseismic p phase which travels with a group velocity of 8 0 km s l out to distances of several thousands of kilometres modelling using the reflectivity method shows that this phase can be understood as the response of an upper mantle that contains random rms velocity fluctuations of about 44 per cent superimposed on a positive velocity gradient this class of model explains the existence of the teleseismic p its high frequency content and its coda length a teleseismic p can only be generated if velocity fluctuations are strong enough to cause multiple scattering and occur on a subwavelength scale cross correlation properties of p and s wave velocity fluctuations exert a substantial influence on the wavefield a completely unexpected phase can be observed if the fluctuations are imposed on a negative gradient

scales of structure in the lithosphere images of processes advances in deep seismic sounding observations of the lithosphere on continents allow to identify various scales of heterogeneities in the crust mantle transition in this paper a fresh look is taken at the dynamic properties of seismic waves propagating through this zone ranging from the lower crust well into the lithospheric mantle as observed in near vertical reflection and wide angle refraction experiments the abrupt termination of near vertical reflections at the moho and the coincident presence of a strong coda accompanying the supercritical pmp reflection phase in record sections of continental seismic wide angle refraction experiments reveal a new property of the crust mantle boundary the moho forms a sandwiched mix of crust mantle material between lower crust and topmost mantle in combination with a step in mean velocity a significant change in scale of the structural dimensions and of velocity variance this view is strongly supported by the recognition of the subcrustal lithosphere as a high frequency 5 10 hz scattering wave guide for long distance propagation of the pn phase over more than 3000 km detected during seismic experiments in russia using peaceful nuclear explosions evidence is brought forward that this high frequency wave guide is likely to be present also in the phanerozoic upper mantle of western europe it is furthermore hypothesized that the global propagation of teleseismic sn or corresponding pn waves observed on continents and oceans combined with the recording of strong pmp codas for wave paths on continents points to a world wide change of scale of structure and velocities near the moho a change in scale of heterogeneities under almost all physical and chemical conditions indicates possibly a differential horizontal movement or decoupling of crust and upper mantle at the level of the moho the global presence of the scattering pn wave guide with a preferred horizontal elongation is hypothetically described as a seismic image of processes in the lithospheric mantle locations of present day tectonic activity where horizontal decoupling between crust and mantle are likely to occur e g subduction at continent continent collision zones change of tectonic regimes and continental transform faults are discussed

on the nature of mantle heterogeneities and discontinuities evidence from a very dense wide angle shot record abstract a seismic survey with a receiver spacing of 50 m provided one of the most densely sampled wide angle seismic reflection images of the lithosphere this unique data set recorded by an 18 km long spread reveals that at wide angles the shallow subcrustal mantle features high amplitude reflectivity which contrasts with a lack of reflectivity at latter travel times this change in the seismic signature is located at approximately 120 150 km depth which correlates with the depth estimates of the lithosphere asthenosphere boundary lab of previous dss studies this seismic signature can be simulated by two layer mantle model both layers with similar average velocities differ in their degree of heterogeneity the shallow heterogeneous layer and the deeper and more homogeneous one correlate with the lithosphere and the asthenosphere respectively studies involving surface outcrops of ultramafic massifs and mantle xenoliths infer that the upper mantle is a heterogeneous mixture of ultramafic rocks lherzolites harzburgites pyroxenites peridotites dunites and small amounts of eclogites laboratory measurements of physical properties of these mantle rocks indicate that compositional variations alone can account for the wide angle reflectivity a temperature increase would homogenize the mixture decreasing the seismic reflection properties due to melting processes it is proposed that this would take place below 120 150 km 1200 c the lab

implications of seismic scattering below the 8 discontinuity along pne profile kraton abstract strong scattered arrivals are observed in the 800 1400 km offset range of the four peaceful nuclear explosion pne seismic sections along the 3500 km long e w trending russian profile kraton they give evidence of an 85 km thick inhomogeneous scattering layer in the upper mantle which has a slightly reduced 1 average p wave velocity compared to the layers above and below the top of the anomalous zone is the 8 discontinuity at 100 km depth which is constrained by a clear travel time delay of up to 2 s consistently observed at 900 1000 km 8 offset in the four pne seismic sections we model the inhomogeneous zone below the 8 discontinuity by random velocity fluctuations the full waveform seismic response of a suite of stochastic velocity models is calculated using a two dimensional finite difference scheme the calculated seismic sections resemble the pne data for models where the random fluctuations have a horizontal correlation length of 5 10 km a vertical correlation length not greater than 5 km and a standard deviation of about 2 of the average background velocity fluctuations with significantly larger correlation lengths give rise to coherent scattered arrivals and considerably shorter correlation lengths lead to significantly weaker scattering none of which resemble the observed data the preferred seismic velocity model is in agreement with an upper mantle model in which the low velocity zone below the 8 discontinuity may contain small amounts of partially molten material alternatively the combined effects of rheological weakening and small scale anisotropy may also account for the low velocity scattering layer

a model for sediment re entrainment and transport in shallow basin flows abstract a finite element vertically integrated mean flow model and a boundary layer turbulence sediment model are combined the resulting model is first order three dimensional enabling predictions of sediment re entrainment transport and fallout in shallow basins of arbitrary smooth shape the model is well behaved and appears to be realistic

pleistocene stratigraphy of the boston harbor drumlins massachusetts abstract evidence from the boston harbor drumlins indicates that two superposed tills were deposited during glacier advances which were separated by a long nonglacial interval at long and peddocks islands argillans and truncated clay filled fractures along with discontinuities in clay mineral composition define the till contacts physical indicators separating the tills are not apparent at other exposures where till boundaries were defined solely by discontinuities in clay mineral composition the weathering profile in the upper part of the lower till indicates extensive weathering under a climate similar to that of today and probably similar to that of the sangamon interglaciation the depth of the weathering profile the sequence of clay mineral alteration products and the presence of pedogenic features in the upper part of the lower till are comparable to sangamonian weathering profiles in the midwestern united states implying that the lower till is illinoian or older