extensive dilatancy anisotropy eda inferred from observations of crustal shear waves generated by a refraction experiment in northern scandinavia summary particle motion plots of shear waves have been studied for the section fg of the fennolora seismic experiment shear wave splitting is observed on some records and the polarization of the first arriving shear waves show two peaks at about n35 w and n65 e these results can be interpreted as being due to crack induced anisotropy with the crack direction dominated by a dominant horizontal stress around n35 w this is consistent with in situ stress measurements and focal mechanism studies in scandinavia the results show that seismic refraction experiments may be useful in providing evidence of crack induced anisotropy in the stable continental crust

lithospheric structure in central eurasia derived from elevation geoid anomaly and thermal analysis we present new crustal and lithospheric thickness maps for central eurasia from the combination of elevation and geoid anomaly data and thermal analysis the results are strongly constrained by numerous previous data based on seismological and seismic experiments tomographic imaging and integrated geophysical studies our results indicate that high topography regions are associated with crustal thickening that is at a maximum below the zagros himalaya tien shan and the tibetan plateau the stiffer continental blocks that remain undeformed within the continental collision areas are characterized by a slightly thickened crust and flat topography lithospheric thickness and crustal thickness show different patterns that highlight an important strain partitioning within the lithosphere the arabia eurasia collision zone is characterized by a thick lithosphere underneath the zagros belt whereas a thin to non existent lithospheric mantle is observed beneath the iranian and anatolian plateaus conversely the india eurasia collision zone is characterized by a very thick lithosphere below its southern part as a consequence of the underplating of the cold and stiff indian lithosphere our new model presents great improvements compared to previous global models available for the region and allows us to discuss major aspects related to the lithospheric structure and acting geodynamic processes in central eurasia

flat slab subduction trench suction and craton destruction comparison of the north china wyoming and brazilian cratons abstract the mechanisms of growth and destruction of continental lithosphere have been long debated we define and test a unifying plate tectonic driving mechanism that explains the numerous petrological geophysical and geological features that characterize the destruction of cratonic lithospheric roots data from three archean cratons demonstrate that loss of their roots is related to rollback of subducted flat slabs some along the mantle transition zone beneath the cratons during flat slab subduction dehydration reactions add water to the overlying mantle wedge as the subducting slabs roll back they suck in mantle material to infill the void space created by the slab roll back and this fertile mantle becomes hydrated the roll back causes concomitant lithospheric thinning of the overlying craton so the flux of newly hydrated mantle material inevitably rises causing adiabatic melting generating new magmas that gradually destroy the roots of the overlying craton through melt peridotite reactions calculated fluxes of new mantle material beneath cratons that have lost their roots range from 2 7 trillion to 70 million cubic kilometers which is sufficient to generate enough melt to completely replace the affected parts of the destroyed cratons cratonic lithosphere may be destroyed in massive quantities through this mechanism warranting a re evaluation of continental growth rates with time

shear wave polarizations near the north anatolian fault ii interpretation in terms of crack induced anisotropy summary the polarizations of shear waves recorded by networks of digital thxee component seismometers immediately above small earthquakes near the north anatolian fault in turkey display shear wave splitting on almost all shear wave seismograms recorded within the shear wave window this splitting is incompatible with source radiation patterns propagating through simple isotropic structures but is compatible with effective anisotropy of the internal structure of the rock along the ray paths this paper interprets the phenomena in terms of widespread crack induced anisotropy distributions of stress induced cracks model many features of the observations and synthetic polarization diagrams calculated for propagation through simulated cracked rock are similar to the observed patterns this evidence for widespread crack induced anisotropy lends strong support to the hypothesis of extensive dilatancy anisotropy eda suggested by laboratory experiments in subcritical crack growth the crucial evidence confirming some form of eda would be observations of temporal changes in shear wave splitting as the stress field alters the crack density and crack geometry there is some weak evidence for such temporal changes at one site but further analysis of suitable digital three component seismometer networks in seismic areas is required to confirm eda

seismic structure in the southeastern china using teleseismic receiver functions abstract the southeastern margin of china is an ideal area to study the modern plate interactions the previous models however are poorly constrained with respect to the geometry due to the sparse coverage here we present new observations from a temporary array with 20 stations in southeastern china we isolated converted seismic phases in the p and s wave coda to generate receiver function from the structure of the crust and upper mantle by using h k stacking and common conversion point stacking the geometry of discontinuities above was imaged along the southeastern chinese coastline the ccp section shows moho dips gently northeastward with a mean depth of 30 km the 410 and 660 km discontinuities are at the depth close to iasp91 model this means that we have not seen any significant anomaly from moho and mantle transition zone that corresponded with the geodynamics of plate subducting instead we found that the crust was ruptured by min river fault to depth of the moho we provide a 2d map of moho topography by combining our crustal thickness to that from permanent stations active seismic and obs offshore profiles the map is consistent with previous studies and shows a crust that thins coastward and southwestward in the rate of 1 5 km per 100 km we image the lithosphere asthenosphere boundary at a depth of 60 to 70 km by using s wave to combine with the p wave our crustal structure suggests that min river fault certainly plays an important role in adjusting regional stress field induced by plate interactions in the study area our lithospheric thickness is more consistent with a very strongly attenuated continental lithosphere given the close proximity to the coast this might suggest that the lithospheric mantle transitions to oceanic before the crust does alternatively we may infer that the continental lithosphere has been thermally eroded in this region

reach classifications of the lower mississippi river a classification of the lower mississippi river into geomorphically distinct reaches provides an effective framework within which the influence of numerous morphologic variables can be analyzed a singular realization of the river however requires that a statistical inference be applied to the results which provides a level of assurance to the conclusions a nonparametric method multi response permutation procedures mrpp is employed to evaluate the significance of channel morphology variables within an a priori reach classification based upon sinuosity and valley slope an alternative classification is proffered generated by mrpp which defines homogeneous subpopulations of the river as reaches for the collective response of the channel morphology variables the numeric analyses generate a refinement by further subdivision of the original proposed reach structure within each reach the multivariate response of the system can be studied through space and time within the time period considered here 1880 to 1915 the river channel became progressively wider and shallower these trends are spatially manifest in fewer longer reaches in 1880 and more shorter reaches in 1915 this increased variability is concentrated in the areas affected by the lake county and monroe uplifts

why cold slabs stagnate in the transition zone oceanic lithosphere sinks stagnates and is deflected sub horizontally beneath western pacific island arcs requiring buoyancy in the slab that is inconsistent with a thermal origin the transformation of pyroxene to majoritic garnet occurs by extremely slow diffusion and pyroxene is therefore unlikely to transform at equilibrium pressures and temperatures in the cold interior of slabs we present high resolution numerical simulations showing that when slow diffusion inhibits the dissolution of pyroxene into garnet the slab becomes buoyant relative to the ambient mantle and stagnates whereas when the phase transformations occur in equilibrium there is no effect on the slab we test the model by comparing slab temperature and geometry and find that sub horizontal slabs are more likely colder than average consistent with our numerical simulations

lithospheric density structure beneath the tarim basin and surroundings northwestern china from the joint inversion of gravity and topography abstract intraplate strain generally focuses in discrete zones but despite the profound impact of this partitioning on global tectonics geodynamics and seismic hazard the processes by which deformation becomes localized are not well understood such heterogeneous intraplate strain is exemplified in central asia where the indo eurasian collision has caused widespread deformation while the tarim block has experienced minimal cenozoic shortening the apparent stability of tarim may arise either because strain is dominantly accommodated by pre existing faults in the continental suture zones that bound it essentially discretizing eurasia into microplates or because the lithospheric scale strength i e viscosity of the tarim block is greater than its surroundings here we jointly analyze seismic velocity gravity topography and temperature to develop a 3 d density model of the crust and upper mantle in this region the tarim crust is characterized by high density v s v p and v p v s consistent with a dominantly mafic composition and with the presence of an oceanic plateau beneath tarim low density but high velocity mantle lithosphere beneath southern southwestern tarim underlies a suite of permian plume related mafic intrusions and a type granites sourced in previously depleted mantle lithosphere we posit that this region was further depleted dehydrated and strengthened by permian plume magmatism the actively deforming western and southern margins of tarim the tien shan kunlun shan and altyn tagh fault are underlain by buoyant upper mantle with low velocity we hypothesize that this material has been hydrated by mantle derived fluids that have preferentially migrated along paleozoic continental sutures such hydrous material should be weak and herein strain focuses there because of lithospheric scale variations in rheology rather than the pre existence of faults in the brittle crust thus this world class example of strain partitioning arises not simply from the pre existence of brittle faults but from the thermo chemical and therefore rheological variations inherited from prior tectonism

anabranching rivers their cause character and classification anabranching rivers consist of multiple channels separated by vegetated semi permanent alluvial islands excised from existing floodplain or formed by within channel or deltaic accretion these rivers occupy a wide range of environments from low to high energy however their existence has never been adequately explained they occur concurrently with other types of channel pattern although specific requirements include a flood dominated flow regime and banks that are resistant to erosion with some systems characterized by mechanisms to block or constrict channels thereby triggering avulsion the fundamental advantage of an anabranching river is that by constructing a semi permanent system of multiple channels it can concentrate stream flow and maximize bed sediment transport work per unit area of the bed under conditions where there is little or no opportunity to increase gradient on the basis of stream energy sediment size and morphological characteristics six types of anabranching river are recognized types 1 3 are lower energy and types 4 6 are higher energy systems type 1 are cohesive sediment rivers commonly termed anastomosing with low w d ratio channels that exhibit little or no lateral migration they are divisible into three subtypes based on vegetative and sedimentary environment type 2 are sand dominated island forming rivers and type 3 are mixed load laterally active meandering rivers type 4 are sand dominated ridge forming rivers characterized by long parallel channel dividing ridges type 5 are gravel dominated laterally active systems that interface between meandering and braiding in mountainous regions type 6 are gravel dominated stable systems that occur as non migrating channels in small relatively steep basins anabranching rivers represent a relatively uncommon but widespread and distinctive group that because of particular sedimentary energy gradient and other hydraulic conditions operate most effectively as a system of multiple channels separated by vegetated floodplain islands or alluvial ridges

the ups and downs of north america evaluating the role of mantle dynamic topography since the mesozoic the driving force for transient vertical motions of earth s surface remains an outstanding question a main difficulty lies in the uncertain role of the underlying mantle especially during the geological past here i review previous studies on both observational constraints and physical mechanisms of north american topographic evolution since the mesozoic i first summarize the north american vertical motion history using proxies from structural geology geochronology sedimentary stratigraphy and geomorphology based on which i then discuss the published physical models overall there is a progressive consensus on the contribution of mantle dynamic topography due to buoyancy structures associated with the past subduction at the continental scale a largely west to east migrating deformation pattern suggests an eastward translation of mantle dynamic effects consistent with models involving an eastward subduction and sinking of former farallon slabs since the cretaceous among the existing models the inverse model based on an adjoint algorithm and time dependent data constraints provides the most extensive explanations for the temporal changes of north american topography since the mesozoic at regional scales debates still exist on the predicted surface subsidence and uplift within both the western and eastern united states where discrepancies are likely due to differences in model setup e g mantle dynamic properties and boundary conditions and the amount of time dependent observational constraints toward the development of the next generation predictive geodynamic models new research directions may include 1 development of enhanced data assimilation capabilities 2 exploration of multiscale and multiphysics processes and 3 cross disciplinary code coupling

earthquake prediction a new physical basis summary subcritical crack growth in the laboratory occurs slowly but progressively in solids subjected to low stresses at low strain rates the cracks tend to grow parallel to the maximum compressive stress so that when this stress is aligned over a large enough region the cracks will also be aligned and possess effective seismic anisotropy it is suggested that such subcritical crack growth produces extensive dilatancy anisotropy eda throughout earthquake preparation zones this process is a possible driving mechanism for earthquake precursors observed at substantial distances from impending focal zones and provides in the shear wave splitting which has been observed in several seismic regions a possible technique for monitoring the build up of stress before earthquakes

predicting river width depth and velocity at ungauged sites in england and wales using multilevel models using a dataset of gauged river discharges taken from sites in england and wales we applied linear multilevel models also known as mixed effects models to quantify the variability in discharge and the discharge hydraulic geometry relationships across three nested spatial scales a jackknifing procedure was used to test the ability of the multilevel models to predict hydraulic geometry and therefore width mean depth and mean velocity at ungauged stations these models provide a framework for making predictions of hydraulic geometry parameters with associated level of uncertainty using different levels of data availability results indicate that as one travels downstream along a river there is greater variability in hydraulic geometry than is the case between rivers of similar sizes this indicates that hydraulic geometry is driven by catchment area and therefore hydrology to a greater extent than by natural geomorphological variations in the streamwise direction such as changes in meso habitat types and local channel engineering but these geomorphological variations can still have a major impact on channel structure

meso scale aeolian sediment input to coastal dunes the nature of aeolian transport events abstract observations of aeolian transport in coastal areas have focused on short term experiments because of limitations imposed by instrumentation this paper uses a case study at greenwich dunes prince edward island national park canada to analyze how sediment transport takes place at the beach over periods of weeks to months a monitoring station provided hourly time series of vegetation cover shoreline position fetch distances surficial moisture content presence of ice and snow wind speed and direction and transport processes over nine months analysis shows that high wind speeds may not generate any net transport into the dunes because of the limitations imposed by snow ice cover moisture and short fetch distances despite extreme winds during intense storms such events often lead to wave scarping rather than aeolian sediment input to the foredunes when sediment was transported on the beach the magnitude was regulated by a combination of factors including angle of wind approach fetch distance moisture content and duration of the wind event in particular angle of wind approach and therefore fetch distance may demote a high magnitude wind event with strong transport potential to one with no transport at all which poses challenges for predicting the effects of individual storms over the course of several months a significant proportion of sediment delivery to the foredunes was associated with wind events of low to medium magnitude it is suggested here that large magnitude wind events have low probabilities of resulting in transport towards the foredune because factors such as wave inundation play an increasing role in preventing sediment movement across the beach this has implications for modelling and management and highlights differences between the magnitude and frequency of aeolian transport events in the coastal environment compared to those in deserts and to fluvial sediment transport

effects of the free surface on shear wavetrains summary the behaviour of shear waves is of great importance in identifying and investigating seismic anisotropy in the earth however shear wavetrains recorded at the earth s surface do not always reflect the motion at depth introducing practical problems of interpretation shear wavetrains incident on the surface of an isotropic half space at angles less than critical about 35 are broadly preserved but at greater angles substantial distortions can occur for stations situated close to the source as in local earthquake studies the local sp phase a radially polarized precursor to s may occur the behaviour at the surface of an anisotropic half space is further complicated by the divergence of phase and energy propagation vectors all of these complications suggest that detailed seismogram modelling is essential to any study of shear wave propagation in the earth and in particular to investigations of anisotropy induced shear wave splitting

stability morphology and surface grain size patterns of channel bifurcation in gravel cobble bedded anabranching rivers this study presents the first detailed field based analysis of the morphology of bifurcations within anabranching cobble gravel rivers bifurcations divide the flow of water and sediment into downstream anabranches thereby influencing the characteristics of the anabranches and the longevity of river islands the history morphology bed grain size and flow vectors at five bifurcations on the renous river new brunswick canada were studied in detail the angles of bifurcations within five anabranching rivers in the miramichi basin were investigated the average bifurcation angle was 47 within the range of values cited for braided river bifurcations bifurcation angle decreased when anabranches were of similar length shields stresses in channels upstream of bifurcations were lower than reported values for braided rivers stable bifurcations displayed lower shields stresses than unstable bifurcations contrary to experimental results from braided river bifurcations bifurcations in anabranching rivers are stabilized by vegetation that slows channel migration and helps to maintain a uniform upstream flow field the morphology of stable bifurcations enhances their stability a large bar shaped like a shallow ramp that increases in elevation to floodplain level forms at stable bifurcations floodplains at stable bifurcations accrete upstream at rates between 0 9 and 2 5 m a 1 bars may also form within the entrance of an anabranch downstream of the bifurcation node these bars are associated with bifurcation instability forming after a period of stability or an avulsion channel abandonment occurs when a bar completely blocks the entrance to one anabranch the stability of channels upstream of bifurcations and the location of bars at bifurcations influence bifurcation stability and the maintenance of river anabranching in the long term copyright 2006 john wiley sons ltd

thermal expansion of forsterite at high pressures determined by in situ x ray diffraction the adiabatic geotherm in the upper mantle abstract volumes of forsterite were measured by in situ x ray diffraction at simultaneously high pressures and high temperatures up to 14 gpa and 1900 k in a kawai type multi anvil apparatus by fitting the present data to the mie gruneisen debye thermal equation of state with the results of the previous reliable studies we obtained 0 1 31 1 and q 3 2 1 the logarithmic volume dependence of the thermal expansion coefficient was found to be t 8 4 2 the average temperature derivative of the isothermal bulk modulus in the investigated pressure temperature ranges was found to be kt t p 0 028 1 gpa k the isobaric heat capacity and thermal pressure at high pressure and high temperature were estimated using the present volume data the adiabatic geotherm at the top and base of the uppermost mantle are 0 60 2 and 0 34 2 k km the temperature estimated from the 410 km discontinuity depth and the olivine wadsleyite transition pressure suggests a mantle potential temperature of 1520 40 k

modeling of three component lg waves in anisotropic crustal models abstract lg wave synthetic seismograms are presented in order to analyze the influence of anisotropy in the continental crust on their three component waveforms the effect of dry and liquid filled open cracks in the upper crust and petrological anisotropy in the lower crust on waves produced by surface explosions and crustal earthquakes is examined the polarization and especially the amplitude of the transverse component proves to be very sensitive to introduction of weak anisotropy in the crust comparisons of the modeling with lg wave data produced by explosions in southern scandinavia show that a realistic crustal anisotropy can explain observations that the transverse components of these waves are as large as their vertical ones a 10 km thick surficial layer with liquid filled open cracks is our perferred model for southern scandinavia

crustal thickness map of the chinese mainland from teleseismic receiver functions abstract we present a new crustal thickness map of the chinese mainland and adjacent areas based on a compilation of previously published data more than 1900 estimates of crustal thickness from receiver function studies were collected and the weighted averages were used to develop a contour map of crustal thickness beneath the chinese mainland the combined dataset provided good coverage especially over eastern and central china and our analysis revealed crustal thickness variations of the chinese mainland with considerably more detail than in previous models our crustal thickness map shows a large variation from a thickness of less than 30 km in the mesozoic basin of eastern china to over 80 km in the tibetan plateau the thickest crust was found in central tibet while the thinnest continental crust was observed beneath eastern china normal to slightly thick crust 38 51 km was found for the stable precambrian basins and orogenic belts comparison between our model and other models reveals that the models share similar large scale and smaller scale features over large portions of eastern china where the data coverage is good however large differences up to 25 km in crustal thickness occur in areas with complex crustal structure or poor data coverage we also evaluated the quality of previous models by comparing them with our newly compiled point observations of crustal thickness

on the recovery of effective elastic thickness using spectral methods examples from synthetic data and from the fennoscandian shield there is considerable controversy regarding the long term strength of continents te while some authors obtain both low and high te estimates from the bouguer coherence and suggest that both crust and mantle contribute to lithospheric strength others obtain estimates of only 25 km using the free air admittance and suggest that the mantle is weak at the root of this controversy is how accurately te can be recovered from coherence and admittance we investigate this question by using synthetic topography and gravity anomaly data for which te is known we show that the discrepancies stem from comparison of theoretical curves to multitaper power spectral estimates of free air admittance we reformulate the admittance method and show that it can recover synthetic te estimates similar to those recovered using coherence in light of these results we estimate te in fennoscandia and obtain similar results using both techniques te is 20 40 km in the caledonides 40 60 km in the swedish svecofennides 40 60 km in the kola peninsula and 70 100 km in southern karelia and svecofennian central finland independent rheological modeling using a xenolith controlled geotherm predicts similar high te in central finland because te exceeds crustal thickness in this area the mantle must contribute significantly to the total strength te in fennoscandia increases with tectonic age seismic lithosphere thickness and decreasing heat flow and low te correlates with frequent seismicity however in proterozoic and archean lithosphere the relationship of te to age is ambiguous suggesting that compositional variations may influence the strength of continents copyright 2004 by the american geophysical union

understanding the temporal dynamics of the wandering renous river new brunswick canada wandering rivers are composed of individual anabranches surrounding semi permanent islands linked by single channel reaches wandering rivers are important because they provide habitat complexity for aquatic organisms including salmonids an anabranch cycle model was developed from previous literature and field observations to illustrate how anabranches within the wandering pattern change from single to multiple channels and vice versa over a number of decades the model was used to investigate the temporal dynamics of a wandering river through historical case studies and channel characteristics from field data the wandering renous river new brunswick was mapped from aerial photographs 1945 1965 1983 and 1999 to determine river pattern statistics and for historical analysis of case studies five case studies consisting of a stable single channel newly formed anabranches anabranches gaining stability following creation stable anabranches and an abandoning anabranch were investigated in detail long profiles hydraulic geometry channel energy grain size and sediment mobility variables were calculated for each channel within the renous study area the frequency of channel formation and abandonment were similar over the 54 years of analysis indicating that the wandering pattern is being maintained eight anabranches were formed through avulsions five were formed through the emergence of islands from channel bars and 11 anabranches were abandoned the stable anabranch pair displayed similar hydraulic geometry and channel energy characteristics while unstable anabranch pairs did not the anabranch pair that gained stability displayed more similar channel energy characteristics than the anabranch pair that was losing stability abandoning it appears that anabranch pairs with similar energy characteristics are more stable than anabranches where these characteristics are out of balance this is consistent with the hypothesis that anabranch pairs of similar length will be more stable than those with dissimilar lengths copyright 2005 john wiley sons ltd

testing links between river patterns and in channel characteristics using mrpp and anova this study tests the assumption that the characteristics of channels within multiple channel rivers are different from those of single channel rivers some river restoration approaches propose radical transformation of river patterns from multiple to single channels based on the link between river patterns and their in channel characteristics determining the links between river patterns and their in channel characteristics is complicated by differences in geology history climate and discharge among rivers furthermore multiple channel rivers are composed of a mosaic of channel types with a range of in channel characteristics this study minimizes these problems by analysing a single river containing neighbouring single and multiple channel patterns with little change in discharge downstream and by analysing all channel types the study addressed two objectives to determine the hydraulic geometry energy and sediment mobility characteristics of neighbouring single and multiple channel river patterns and to test for statistical differences in these characteristics between patterns the renous river shows a wandering pattern for 11 5 km with multiple channels around semipermanent islands and abandoned channels in the flood plain the river displays a single channel river pattern where channels are confined by their valley walls upstream and downstream of wandering the analysis was conducted at three scales first the confined single channel and wandering multiple channel patterns were compared pattern scale second the confined channel pattern was compared to single and multiple channel sections within the wandering pattern section scale third all channel types were compared channel type scale multi response permutation procedure mrpp and analysis of variance anova were used to analyze differences between channels difference tests found no simple discrimination between the single and multiple channel river patterns of the renous river tests between the single confined and multiple wandering channel patterns found few differences in the in channel variables the tests did find differences between multiple channel sections within the wandering pattern and confined single channels however a greater number of differences were found between multiple channel and single channel sections within the wandering pattern highlighting the variability within the wandering pattern two groups emerged when all channel types were tested for differences perennial main channels containing the thalweg and ephemeral side channels therefore side channels define the in channel characteristics of wandering rivers because few differences were found among main channels in either pattern this analysis suggests that all channel types not just main channels should be investigated to obtain a complete picture of a river pattern prior to any restoration efforts engineers must exercise caution when applying the link between river patterns and in channel characteristics to river restoration efforts

the meandering braided river threshold a reappraisal abstract the concept of a threshold discharge slope q s combination that separates braided from meandering streams is critically re examined partly by review of previous data and partly by analysis of new data from south island new zealand it is argue d that discriminant functions that use mean annual discharge provide a poor physical basis for interpretations based on natural processes while bankfull discharge is also deficient because it is not a fully independent variable the common use of channel rather than valley slope adds a further misleading component because channel slope is partly dependent on channel pattern sinuosity most previous studies have inadequately treated the role of bed particle size in pattern discrimination failing to recognize that active gravel streams must plot higher on a q s chart than sand bed channels irrespective of pattern because of the greater power requirements for bed material movement within any one size class of bed material there is no evidence to indicate a clear discrimination between braiding and meandering only a weak statistical association between pattern and slope discharge values while this association may be explicable in terms of the high shear stress and stream power that accompany high qs values promoting braiding the real prerequisite for braiding appears to be high loads of bed calibre material producing wide shallow channels a factor that is only partly controlled by stream power accordingly the search for a pattern threshold based on discharge and slope seems to be a futile exercise an interpretation of existing pattern discriminant functions from the perspective of the threshold shear stress for particle movement is made it is concluded that in effect these functions merely state that gravel bed streams are more likely to be braided than channels in finer sediment statistically this appears to be valid and reasons for that difference are offered based on the balance between imposed bed material load and channel capacity

magnetotellurics in southwestern sweden evidence for electrical anisotropy in the lower crust magnetotelluric data from measurements conducted on the southwestern part of the baltic shield are analyzed with respect to crustal and upper mantle structures the interpretations have been done using ordinary two dimensional and transverse anisotropic layered models in which distortions of the impedance tensors due to near surface electrical structures are included in the interpretation procedures the anisotropic model is able to explain the gross features of the data whereas the two dimensional model only displays features observed at long periods the two main results from the study with anisotropic models are the interpretation of a possible transverse anisotropic lower crust and a depth to the uppermost conductive layer within the mantle of more than 200 km the minimum depth to the conductive mantle layer is found from a most squares analysis

predicting channel patterns brewer paul lewin j 2001 predicting channel patterns geomorphology 40 pp 329 339 rae2008

shear wave polarizations in the peter the first range indicating crack induced anisotropy in a thrust fault regime summary three component seismograms of small local earthquakes recorded in the peter the first range of mountains near garm tadzhikistan ssr display shear wave splitting similar to that previously observed near the north anatolian fault in turkey the peter the first range is in a region of compressional tectonics whereas the north anatolian fault is a comparatively simple strike slip fault detailed analysis of the turkish records suggests that the splitting is diagnostic of crack induced anisotropy caused by vertical microcracks aligned parallel to the direction of maximum compression preliminary examination of paper records from garm shows that most shear waves arriving within the shear wave window display shear wave splitting and that the polarizations of leading shear waves are consistently aligned in a ne sw direction the area is complicated and the tectonics are not well understood but the ne sw direction is approximately perpendicular to the compressional axis in many of the fault plane mechanisms of the earthquakes these earthquakes are usually at depths between 5 and 12 km although there are some deeper events nearby parallel shear wave polarizations such as those observed are expected to indicate the strike of nearly vertical parallel microcracks which would be aligned parallel to the direction of maximum compression thus the shear wave polarizations in the peter the first range indicate that the directions of principal stress are reversed in the rock above the earthquake foci where thrust faulting is taking place

high resolution mantle tomography of china and surrounding regions 1 a high resolution p wave tomographic model of the crust and mantle down to 1100 km depth under china and surrounding regions is determined by using about one million arrival times of p pp pp and pcp waves from 19 361 earthquakes recorded by 1012 seismic stations the subducting pacific slab is imaged clearly as a high velocity zone from the oceanic trenches down to about 600 km depth and intermediate depth and deep earthquakes are located within the slab the pacific slab becomes stagnant in the mantle transition zone under east china the western edge of the stagnant slab is roughly coincident with a surface topographic boundary in east china the active changbai and wudalianchi intraplate volcanoes in northeast china are underlain by significant slow anomalies in the upper mantle above the stagnant pacific slab these results suggest that the active intraplate volcanoes in ne china are not hot spots but a kind of back arc volcano associated with the deep subduction of the pacific slab and its stagnancy in the transition zone under the mariana arc however the pacific slab penetrates directly down to the lower mantle the active tengchong volcano in southwest china is related to the eastward subduction of the burma microplate the subducting indian and philippine sea plates are also imaged clearly the indian plate has subducted down to 200 300 km depth under the tibetan plateau with a horizontal moving distance of about 500 km high velocity anomalies are revealed in the upper mantle under the tarim basin ordos and sichuan basin which are three stable blocks in china

east asia seismotectonics magmatism and mantle dynamics abstract in this article we review the significant recent results of geophysical studies and discuss their implications on seismotectonics magmatism and mantle dynamics in east asia high resolution geophysical imaging revealed structural heterogeneities in the source areas of large crustal earthquakes which may reflect magma and fluids that affected the rupture nucleation of large earthquakes in subduction zone regions the crustal fluids originate from the dehydration of the subducting slab magmatism in arc and back arc areas is caused by the corner flow in the mantle wedge and dehydration of the subducting slab the intraplate magmatism has different origins the continental volcanoes in northeast asia such as changbai and wudalianchi seem to be caused by the corner flow in the big mantle wedge bmw above the stagnant slab in the mantle transition zone and the deep dehydration of the stagnant slab as well the tengchong volcano in southwest china is possibly caused by a similar process in bmw above the subducting burma microplate or indian plate the hainan volcano in southernmost china seems to be a hotspot fed by a lower mantle plume associated with the pacific and philippine sea slabs deep subduction in the east and the indian slab s deep subduction in the west down to the lower mantle the occurrence of deep earthquakes under the japan sea and the east asia margin may be related to a metastable olivine wedge in the subducting pacific slab the stagnant slab finally collapses down to the bottom of the mantle which may trigger upwelling of hot mantle materials from the lower mantle to the shallow mantle beneath the subducting slabs and cause the slab plume interactions some of these issues such as the origin of intraplate magmatism are still controversial and so further detailed studies are needed from now

floodplain dynamics of a wandering river dendrochronology of the morice river british columbia canada dendrochronological techniques are used to develop a history of flood occurrence and relative stage for the middle section of the morice river based on flood scars bank undercutting dates and tree establishment dates on fluvial features the morice river is the major tributary of the bulkley river skeena river system northwest british columbia canada reach 2 of the morice river drainage area 3499 km2 is forested and little disturbed by human activity it is presently a wandering multiple channel river and shows evidence of frequent channel changes which have reworked most of the floodplain several times in the last 180 years airphoto analysis and dendrochronology demonstrate that many channels show evidence of two or more periods of activity reoccupation and re excavation of pre existing channel segments is more frequent than development of new channels thirty one significant floods over the past 105 years were detected through dendrochronology of flood scarred trees on the morice river flood scars are predominantly caused by flood transported logs abundant log transport results in damage to channel margin trees during events only slightly above bankfull discharge the record of flood scars on channel margin trees and establishment dates of forest stands on abandoned channels and surfaces show that the morice river has maintained its present regimen for the past 115 years during the neoglacial the morice river was more active than in recent times and its channels occupied twice the present area tree establishment dates show that neoglacial surfaces and channels of the morice river were abandoned during the 1820 s the modern floodplain configuration was assumed by 1870

radon content of groundwater as an earthquake precursor evaluation of worldwide data and physical basis the properties of a worldwide data set of 91 radon 222 rn anomalies the frequency of occurrence the precursor time interval and the distribution of peak amplitudes are correlated with earthquake data such as the respective magnitude and epicentral distance these anomalies were reported as precursors to earthquakes in the united states ussr china japan and iceland although the data set is incomplete and limited by experimental deficiencies several consistent patterns emerge radon anomalies from different tectonic regions show similar patterns the radon anomalies occur at greater epicentral distances for earthquakes of the larger magnitude anomalies preceding large earthquakes m 6 are frequently observed at a distance of 100 to 500 km these distances are larger than several times the rupture dimensions of the future earthquakes the time from the onset of an anomaly to the time of the earthquake the precursor time increases with magnitude but decreases with distance between epicenter and radon station in addition radon anomalies are observed more frequently prior to large earthquakes than prior to small ones indicating that the preparation zone increases in size as magnitude increases the peak amplitude does not scale with magnitude but forms a consistent pattern with epicentral distance in that the larger the earthquake magnitude the farther away the largest amplitudes tend to occur the preparation zone of the earthquake where the anomalies occur forms an almost continuous annulus that expands with time away from the future rupture zone the outer radius of this annulus scales with the earthquake magnitude model calculations indicate that strain fields of at most 10 6 to 10 8 strain caused the radon anomalies if these strains are divided by the appropriate precursor time minimum strain rates from 10 7 day 1 to 10 10 day 1 are obtained such small strains and strain rates suggest that in most cases neither mechanical crack growth induced by dilatancy nor mechanical coupling between pore pressure and the rock matrix caused the anomalies large changes in the orientation of the local strain field however could occur and affect the local stress intensity factor since changes in the stress intensity factor can result in stress corrosion the occurrence of radon anomalies is attributed to slow crack growth controlled by stress corrosion in a rock matrix saturated by groundwater

lithospheric structure in the cathaysia block south china and its implication for the late mesozoic magmatism abstract mesozoic granitoids are widely distributed in south china but the mechanism for generating the felsic magmas is still in debate to understand the possible origin of the granitoids we use joint inversion methods and forward modelling of receiver functions to reveal the lithospheric structure in the cathaysia block the joint inversion of receiver functions and surface wave dispersion with p velocity constraints is applied to a dense array in the cathaysia block and the specific crustal vp vs ratios obtained from a generalized h stacking method are introduced to the traditional joint inversion for passive seismic stations the detailed structures provide valuable knowledge of the geological processes 1 the present day lithosphere is 60 70 km thick which has been thinned since the late mesozoic with reference to geochemical data 2 there is a lack of high vp and vs in the lower crust in this region the results may have limited resolution on the localized magmatic underplating but they do not support the extensive magmatic underplating at the late mesozoic other factors could be the mechanism for the granitoid formation in this region

seismic energy release of the moon previous estimates of the seismic energy released by lunar events have not properly accounted for instrument bandwidth variations in corner frequency and the effects of intense scattering in this paper equations are developed that include all of these effects and give realistic estimates for source parameters these equations are applied to seismograms and displacement spectra from near surface and deep moonquakes to obtain m0 seismic moment s seismic energy release eyr seismic energy released annually by each lunar event class stress drop and mb body wave magnitude the calculations yield m0 3 1021 dyn cm s 2 1017 ergs 400 bars and mb 5 0 for the largest shallow moonquakes and m0 5 1020 dyn cm s 1 1013 ergs 0 1 bars and mb 3 0 for large deep events the average energy released annually is eyr 2 1017 erg yr and eyr 8 1013 erg yr by shallow and deep events respectively overall lunar energy release is dominated by the shallow events the energy released by the deep events may be accounted for by tidal dissipation and deep event stress drops are comparable to and smaller than the calculated tidal stresses a comparison of the above values with those observed terrestrially eyr 1025 ergs and with the energy available from heat flow and tidal dissipation emphasizes the importance of tectonic style e g plate tectonics in determining the characteristics of planetary seismicity

morphodynamics of a 1000 year flood in the kamp river austria and impacts on floodplain morphology this paper investigates the impact of a 1000 year flood in august 2002 on floodplains and valley morphology of an austrian mixed alluvial bed rock river discharges with a recurrence interval between 500 and 2000 years caused distinctive overbank scouring and material deposition in the floodplains after the 1000 year flood those morphologically affected areas were at random intervals documented over the whole longitudinal profile in addition to overbank erosion in curved sections cut offs the river bed locally widened floodplain stripping occurred and local overbank scours were documented along straight parts of the river a hydrodynamic numerical model combined with field measurements was used to analyse the cause of these erosional landforms based on the modelled hydraulic conditions for a one year flood 30 78 m3 s 1 and the catastrophic 2002 event 700 800 m3 s 1 the numerical results allowed a cause effect study with 19 parameters deterministic and statistical analysis anova discriminant analysis showed that the morphodynamic effects of the 2002 flood were influenced by the variability of valley morphology of the kamp river which led partially to supercritical flow during flood constriction these processes were in some cases also anthropogenically influenced lateral constriction and expansion of the valley geometry over short distances led to scouring and aggradation within the inundated areas during the event these morphological features were therefore responsible for the elongated scour holes in the floodplains copyright 2009 john wiley sons ltd

measuring dynamic topography an analysis of southeast asia 1 theoretical models of dynamic topography generated by subducting slabs and consistent with the observed geoid predict 1 2 km of subsidence on wavelengths of 102 103 km the demonstrable existence of such subsidence has important implications for understanding sedimentary basin formation relative sea level changes as well as the earth s viscosity and density structure here we present the results of a combined analysis of subsidence data from oceanic marginal basins and their fringing continental shelves we have chosen to analyze a large area of southeast asia where dynamical predictions are believed to be well constrained by the history of subduction our joint analysis constrains the maximum amplitude of dynamic subsidence to be 300 m with a range of 0 500 m significantly less than predicted actively spreading marginal basins have no resolvable dynamic subsidence but after removing the effects of crustal thickness variation a few inactive marginal basins are consistently 200 500 m deeper than normal adjacent continental sedimentary basins record a possible dynamic subsidence of 0 500 m although wavelengths are shorter than expected 102 km there is also disagreement between the predicted and observed distribution of anomalous subsidence as well as inconsistencies in initiation and duration these results suggest that mass excess within the mantle represented by subducted slabs has little discernible effect on surface topography instead subsidence and marine inundations throughout southeast asia are predominantly controlled by lithospheric extension and or by foreland loading the spatial and temporal distribution of anomalous subsidence suggests that it might not be caused by dynamic topography associated with subducting slabs a large discrepancy between predicted and observed dynamic topography could be reconciled by changing the density structure of subducted slabs by supporting mass excess with a marked increase in viscosity at depth or by decoupling slabs from the surface with a very low viscosity layer

geophysical evidence on segmentation of the tancheng lujiang fault and its implications on the lithosphere evolution in east china abstract the north south trending tancheng lujiang tanlu fault belt extends from northeast china to the dabie sulu orogenic belt for a length of more than 3000 km this fault belt probably has close links with the lithosphere evolution seismic activity and mineral resource concentration in east china surface geological mapping and studies on sedimentation and basin formation have indicated segmentation at the southern middle and northern domains of the fault here we employ geophysical constraints to evaluate these fault segments unlike previous geophysical studies focused on laterally varying crust mantle seismic velocity structure across the fault in this study we have integrated a variety of geophysical data sets such as crustal p wave velocity earthquake occurrence and released seismic energy seismogenic layer thickness surface heat flow and geothermal field to understand the deep structure and strength of the lithosphere along the tanlu segmented fault belt the results demonstrate remarkable crustal scale north to south segmentation this major fault the geophysical evidence and some geochemical constraints suggest that the tanlu fault belt probably served as a channel for melt and fluid percolation and exerted a significant control on the lithosphere evolution in east china

valley confinement as a factor of braided river pattern for the platte river abstract the platte river in nebraska has evolved in the twentieth century from a predominantly braided river pattern to a melange of meandering wandering anastomosed island braided and fully braided reaches identifying the factors that determine the occurrence of a fully braided main channel was the objective of this study aerial photography gage flow data ground surveyed cross sections bed material samples and the results of sediment transport modeling were used to examine factors that control spatial change in main river pattern of the central platte river valley confinement is identified as the determining factor of braided river in nine of eleven divisions of the central platte river flow reduction and the interruption of sediment supply are identified as determining factors preventing fully braided river in the remaining two of eleven reaches valley confinement the topography which limits the width of the floodplain was initially measured as width between historical banks predevelopment river banks this metric was later refined to width between confining features historical banks remnant bars bridge abutments protected banks and levees under existing conditions the main channel of the central platte river is fully braided when valley confinement width between confining features is 600 m or less and begins to divide into the multiple channels of an anastomosed pattern when valley confinement width between confining features exceeds 600 m when platte river flow is divided between two to four major anabranches a fully braided pattern in the main channel of the main anabranch requires a more confined valley of 400 m or less valley confinement is demonstrated to be the dominant factor in determining river pattern in the central platte river although this factor is not normally considered in the continuum of channel pattern model conclusions from this study can be used to increase the occurrence of fully braided main channel in the central platte river to aid habitat recovery for endangered or threatened bird species that favor this river pattern consideration of valley confinement with river continuum factors can aid river managers by improving predictions of river pattern in response to management actions

seismic evidence for significant lateral variations in lithospheric thickness beneath the central and western north china craton abstract we have migrated teleseismic s receiver functions to construct detailed lithospheric structure images that cover the three constituent parts of the north china craton ncc our images show that in contrast to the eastern ncc where significantly thinned lithosphere 60 100 km is widespread the central and western ncc are characterized by the coexistence of both preserved thick and dramatically thinned lithosphere the thick lithosphere 200 km is present beneath the stable ordos plateau and the thinned lithosphere up to 80 km is found in the late cenozoic yinchuan hetao and shaanxi shanxi rift areas with sharp changes occurring over a lateral distance of

channel planform as a non controlling factor in fluvial sedimentology the case of the squamish river floodplain british columbia abstract channel planform styles demonstrate a continuum of variability whereas end member situations may exhibit diagnostic sedimentologic characteristics non end member situations may be exceedingly difficult to reliably differentiate the relevance of channel planform based sedimentologic differentiation of fluvial depositional units has been questioned for some time e g jackson 1978 bridge 1985 brierley 1989a despite reservations outlined in these papers facies models and interpretations of depositional suites in the rock record continue to be applied in terms of channel planform style this paper describes a test of this principle in one particular depositional setting the squamish river in southwestern british columbia is a high energy gravel based river in a fjord setting in a 20 km reach this river displays a distinct downstream gradation in channel planform type from braided through wandering gravel bed to meandering assemblages of bedform scale facies units on bar surfaces in this river do not differ by planform type brierley 1989a rather facies associations relate directly to the pattern of morphostratigraphic units on bar surfaces brierley 1991a when analysed in floodplain exposures sediment sequences which are equivalent to morphostratigraphic units are termed elements these elements are defined in terms of their geometry bounding surface and sediment characteristics detailed analysis of floodplain deposits in the braided wandering gravel bed and meandering reaches of the squamish river demonstrates that just as assemblages of bedform scale facies cannot be differentiated by planform style neither can assemblages of floodplain elements indeed for the squamish river the type character and spatial association of these elements cannot be differentiated reliably at the channel planform scale this indicates the limited relevance of planform differentiation of sedimentary environments under transitional planform situations such as those of high energy gravel bed rivers in confined valleys in such situations sediment inventory at the element scale provides greater insight into mechanisms of floodplain evolution than can be provided by interpretation at either the channel bedform or channel planform scales

slope induced changes in channel character along a gravel bed stream the allt dubhaig scotland changes in channel character along a small river in the scottish highlands are described using measurements in seven reaches over a 3 km length with no significant tributaries but a decline in slope from 0 02 to o ooo15 because of local baselevel control this decline in slope is associated with rapid downstream fining of the gravel bed followed by an abrupt transition to a sand bed the channel pattern alters progressively rather than abruptly in the sequence 1 near braided 2 meandering with active point bar chutes 3 meandering with active outer bank talweg 4 stable equiwidth sinuous the changes in channel pattern and hydraulic geometry are predicted better by rational approaches based on critical shear stress or other physical cdncepts than by purely empirical discriminant or trend equations measurements in five reaches confirm a downstream decrease in shear stress and the amount and calibre of bedload it is argued that the downstream changes in channel character in this stream are induced by profile concavity inherited from deglacial conditions are typical of many streams in mountainous areas and can be understood in terms of slope induced changes in hydraulic properties

the long term control of vegetation and woody debris on channel and flood plain evolution insights from a paired catchment study in southeastern australia abstract numerous case studies have demonstrated that alluvial and semi alluvial rivers in se australia have undergone dramatic metamorphosis in historical times however very few studies place these changes within a long term evolutionary context as a consequence the magnitude of and ultimate controls on the changes to river form and processes are not fully appreciated in this study a paired catchment analysis is undertaken between two moderate sized sand bed rivers in east gippsland australia from the thurra river direct insight is gained into the predisturbance control exerted by riparian vegetation and wood in a lowland alluvial river this river is effectively in the same condition today as it was at the time of the arrival of europeans in australia in contrast the adjacent cann river which has been settled by europeans for 150 years but was previously very similar to the thurra river exhibits stark differences today channel morphodynamics observed within the thurra river when coupled with historical and geomorphic evidence for the former condition of the cann river provide a detailed reference by which the recent changes to the cann river are measured chronostratigraphic evidence from both flood plains places recent channel behavior within an evolutionary context extending well into the pleistocene since european settlement the study reach of the cann river has experienced a 360 increase in channel depth a 240 increase in channel slope a 700 increase in channel capacity and up to a 150 fold increase in the rate of lateral channel migration the contemporary condition of the cann river channel differs profoundly to that which has prevailed over at least the previous 27 ka the first order control on the historical channel metamorphosis is the removal of riparian vegetation and woody debris wd numerous thresholds have been crossed as a result of historical channel changes particularly the relationship between average length of woody debris pieces and channel width consequently channel recovery will not simply be achieved by reintroducing the pre existing riparian vegetation and woody debris load devising sound management strategies and realistic management targets for the cann river or any similarly altered river requires an understanding of the long term channel and flood plain evolutionary history as well as the underlying controls on historical changes

wandering miramichi rivers new brunswick canada abstract six rivers within the miramichi basin of new brunswick display long sections with multiple channels that surround semi permanent islands linked by single channels this type of anabranching river may be termed wandering displaying a similar planimetric pattern to wandering rivers in western canada this research addresses three objectives 1 to provide a detailed description of the location pattern characteristics and boundary conditions of wandering miramichi rivers 2 to compare the pattern characteristics among wandering rivers within the miramichi basin and to other wandering meandering and braided rivers and 3 to investigate formative processes for wandering miramichi rivers wandering rivers within the miramichi region occur in larger valleys located downstream of an abrupt change in bedrock from resistive to more erosive bedrock lithology larger rivers display greater braid indices than smaller rivers wandering miramichi rivers display more similarities to meandering rivers than braided rivers exhibit an anabranching pattern yet have characteristics markedly different from anastomosed rivers energy levels mid channel bar formation migration rates and width depth ratios are all within the meandering range lower than braided and higher than anastomosed once anabranches are created larger rivers apparently maintain a greater number of anabranches because of greater discharge wandering miramichi rivers may represent another anabranching river pattern type different from anastomosed and previously described wandering rivers

seismic image and origin of the changbai intraplate volcano in east asia role of big mantle wedge above the stagnant pacific slab abstract we determined p wave tomography of the crust and upper mantle under the changbai volcanic area in northeast asia by using 289 318 arrival time data from 4802 local earthquakes and 9599 teleseismic events a prominent low velocity anomaly is clearly imaged in the crust and upper mantle down to about 410 km depth beneath the changbai volcano a broad high velocity anomaly is revealed in the mantle transition zone and deep earthquakes occurred actively there suggesting that the subducting pacific slab is stagnating in the mantle transition zone under east asia our results suggest that the formation of the changbai and other intraplate volcanoes in northeast asia is related to the upwelling of hot and wet asthenospheric materials in the big mantle wedge above the stagnant pacific slab hence the active intraplate volcanoes in northeast asia are not hotspots related to deep mantle plumes but are caused by plate tectonic processes in the upper mantle

crustal and lithospheric structure of northeast china from s wave receiver functions abstract lithospheric thickness is closely associated with lithospheric response to tectonic forces or thermal processes analysis of s wave receiver functions srfs from a dense seismic array has revealed lithospheric thickness variations along a 1200 km long profile that spans all major geological terranes of northeast china the srf images identify the shallowest moho and lithosphere asthenosphere boundary lab depths beneath the rifted songliao basin thus spatially correlating well with the thick sediment accumulation these features can be explained by a pure shear regime operating in the lower crust and upper mantle suggesting the predominance of roughly symmetric lithosphere stretching from continental rifting in contrast thicker lithosphere in western and eastern terranes of ne china indicates the lithosphere in these regions was not strongly affected by the extensional processes during the late mesozoic flat lab structure beneath the erguna and xing an terranes along with the overlying relatively deeper moho beneath the great xing an range suggests the north south gravity lineament may not be a trans lithospheric structure

distinct lateral variation of lithospheric thickness in the northeastern north china craton abstract a detailed knowledge of the thickness of the lithosphere in the northeastern north china craton ncc is important for understanding the significant tectonic reactivation of the craton in the mesozoic and cenozoic time we achieve this goal by applying the newly proposed wave equation based migration technique to the s receiver functions recently collected in the region distinct negative signals are identified below the moho in all the s receiver function migrated images and stacks which we interpret as representing the s to p conversions from the lithosphere asthenosphere boundary lab the imaged lab is as shallow as 60 70 km in the southeast basin and coastal areas and deepens to no more than 140 km in the northwest mountain ranges and continental interior these observations indicate widespread lithospheric thinning in the study region in comparison with the 180 km lithospheric thicknesses typical of most cratonic regions the revealed topography of the lab generally agrees with the lateral variation in upper mantle seismic anisotropy previously measured through sks splitting analysis in particular a sharp lab step of 40 km is detected at the triple junction of the basin and mountains at almost the same place where an abrupt change from nw se to ne sw in fast polarization direction of shear waves was found these findings suggest a close correlation between the seismic anisotropy and hence deformation of the upper mantle the lithospheric thickness and the surface tectonics of the northeastern ncc while the thinned lithosphere and the nw se fast shear wave polarizations in the east areas probably are related to the dominant nw se tectonic extension in the late mesozoic cenozoic time the thicker lithosphere and the ne sw fast polarization direction in the west mountain ranges may reflect earlier contractional deformations of the region synthetic tests indicate that the lab beneath the northeastern ncc is a well defined zone 10 20 km thick combined with seismic tomography results and geochemical and petrological data this suggests that complex modification of the lithosphere probably accompanied significant lithospheric thinning during the tectonic reactivation of the old craton

numerical modeling of gravel bed river response to meander straightening the coupling between the evolution of bed pavement and long profile 1 artificial meander straightening rectification was conducted in the early 1960s along the sainte marguerite river canada in order to facilitate highway construction along the valley previous studies talbot and lapointe 2002 confirm that vertical reprofiling coupled with pavement coarsening in the degrading reach were the main responses counteracting the disequilibrium in gravel transport rates triggered at rectification of this system numerical simulations using sedrout2 0 a one dimensional hydraulic and sediment transport model and validated against the observed channel response show the important role played by an advancing wave of pavement coarsening down the rectified reach in modulating the bed degradation response simulations extending into the future reveal an asymptotically slowing approach to equilibrium in the middle of the 21st century with a response half time of the order of 10 years in near threshold gravel bed systems like the sainte marguerite river pavement coarsening after rectification buffers the system against extreme degradation most significantly for watershed management this also appears to severely limit the extent of propagation of degradation upstream of the rectification

anastomosis and the continuum of channel pattern anastomosing rivers are characterized by multiple channels separated by islands excised from the floodplain their status relative to the continuum concept of channel pattern is assessed with channel pattern defined in terms of three variables flow strength bank erodibility and relative sediment supply using an ordinal scaling l ow m oderate h igh the traditional forms of straight meandering and braided have respective representations of l l l m l m l m and h h m h in terms of those variables the anastomosing pattern is on average represented by l l m h but not so definitively as other forms specification of the third element sediment supply is particularly hampered by the paucity of data but aggradation a characteristic of many anastomosing rivers can be thought of as symptomatic of a moderately high rate of supply relative to the ability for onward transport a sufficiently high rate of supply to a channel with low flow strength and resistant banks would induce shoaling and or lateral constriction that locally forces flow out of the main channel and ultimately leads to the cutting of anabranches a flow regime characterized by concentrated floods of relatively large magnitude is also regarded as highly conducive to the formation of new channels where low bank erodibility constrains channel capacity anastomosis may in certain cases represent a transitional form of channel pattern but there is no denying the longevity of some anastomosing systems

presence of an intralithospheric discontinuity in the central and western north china craton implications for destruction of the craton detailed knowledge of lithospheric structure is essential for understanding the long term evolution and dynamics of continents we present an image of lithospheric structure across the central and western north china craton ncc derived using s and p receiver functions from a dense seismic array a negative velocity discontinuity is identified at 80 100 km depth within the thick lithosphere 160 200 km similar to that observed in many other cratonic regions and roughly at the same depth as the base of the lithosphere in the eastern ncc the intralithospheric discontinuity may indicate an ancient mechanically weak layer within the overall strong cratonic lithosphere and probably also existed beneath the eastern ncc before the mesozoic the presence of such a weak layer could have facilitated simultaneous lithospheric modification at the base and the middle of the lithosphere in the eastern ncc especially under the strong influence of the mesozoic pacific subduction leading to the severe lithospheric thinning and destruction recorded in this region the weak layer probably did not strongly affect the stability and evolution of the central and western ncc and other cratonic regions where effects from plate boundary processes were weak our seismic images integrated with geological data provide new insights into structural heterogeneities in the subcontinental lithospheric mantle and their roles in the dynamic evolution of continents

variations of the effective elastic thickness over china and surroundings and their relation to the lithosphere dynamics abstract the effective elastic thickness te characterizes response of the lithosphere to a long term tectonic loading as a proxy of the lithospheric strength te can be used to address mechanical behavior and deformation of the blocks with complex geological structure here we use the multitaper coherence method to determine spatial variations of te in china and surroundings based on the topography and bouguer gravity anomaly data the results show that the te values are high 70 km over the cratons e g india craton the siberian craton north china block and also variations of these values are significant over these blocks low te corresponds to the young orogens e g himalayas altun shan qilian shan longmenshan qinling dabie and daxing anling taihang mountains etc combined with other data the lateral variations of te within the north china and south china blocks and the tibetan plateau indicate that the lithospheric strength in china mainland depends on both lithospheric structure and mantle dynamics we guess that during the mesozoic cenozoic period the strength of the lithosphere might have been significantly altered by the thermodynamic processes associated with the india eurasia collision in the southwest and the subduction of the pacific plate in the east the te variations also play a major role in the lithospheric evolution and deformation since the mesozoic

intensive hydration of the mantle transition zone beneath china caused by ancient slab stagnation the mantle transition zone beneath china is anomalously hydrated geochemical analyses of basalts erupted above the mantle transition zone in northeast china indicate that water may have been added to this zone during the dehydration of subducted slabs on two separate occasions over the past one billion years

shear wave polarizations near the north anatolian fault i evidence for anisotropy induced shear wave splitting summary the turkish dilatancy projects tdp1 in 1979 and tdp2 in 1980 recorded small earthquakes near the north anatolian fault with closely spaced networks of three component seismometers in order to investigate the possibility of diagnosing dilatancy from its effects of shear wave propagation this paper examines the polarizations of shear wavetrains recorded in the shear wave window immediately above the earthquake foci abrupt changes in the orientation and or ellipticity of the shear wave polarizations are almost always observed during the first few cycles following the initial shear wave arrival on each seismogram the horizontal projections of the polarizations of the first shear wave arrivals at any given station show nearly parallel alignments with approximately the same orientations at each of the recording sites with one exception it is difficult to explain this uniform alignment over a wide area in terms of scattering at the irregular surface topography or by earthquake focal mechanisms we demonstrate that the shear wave splitting is likely to be the result of anisotropy in the region above the earthquake foci which could produce polarizations displaying the observed alignments the temporal change of the azimuth of alignment observed at one locality between 1979 and 1980 may be due to the release of a local stress anomaly by a very near earthquake

theory of time dependent rupture in the earth at a velocity x which is a well defined function of k this propagation is stable and quasi static and is referred to as subcritical crack growth we shall use the terms stable quasistatic and subcritical to mean propagation at velocities much less than the sonic velocities of the medium this behavior results from stress induced corrosion at the crack tip the principal corrodent for the present application being h20 this behavior has been firmly established in the laboratory for mode i tensile cracks in a wide variety of materials ineluding silicates and silicate glasses see cholz 1968a 1972a martin 1972 wiederhorn and bolz 1970 atkinson 1979 lawn and wilshaw 1975 knott 1973 the form of the relationship between k and x does not vary significantly with the material only the parameters in the law vary as an example we show in figure 1 data on subcritical crack growth in quartz after atkinson 1979 the empirical relationship is found to take the form

isostasy flexure and dynamic topography abstract a fundamental scientific question is what controls the earth s topography although the theoretical principles of isostasy flexure and dynamic topography are widely discussed the parameters needed to apply these principles are frequently not available isostatic factors controlling lithospheric buoyancy are frequently uncertain and non isostatic factors such as lithospheric bending towards subduction zones and dynamic topography are hard to distinguish the question discussed here is whether a set of simple rules that relate topography to lithospheric structure in various tectonic environments can be deduced in a way that missing parameters can be approximated or does each area behave differently making generalizations problematic we contribute to this issue analyzing the asia africa arabia europe domain following a top down strategy we compile a new crustal thickness map and remove the contribution of the crust from the observed elevation then the challenge is to interpret the residual topography in terms of mantle lithosphere buoyancy and dynamics based on systematic relationships between tectonic environments and factors controlling topography we argue that crustal buoyancy and mantle lithospheric density can be approximated from available geological data and that regions near mantle upwelling or downwelling are easily identified by their extreme residual topography yet even for other areas calculating lithospheric thickness from residual topography is problematic because distinguishing variations in mantle lithosphere thickness from sub lithospheric dynamics is difficult fortunately the area studied here provides an opportunity to examine this issue based on the conjunction between the afar plume and the mid ocean ridge in the nearby gulf of aden and southern red sea we constrain the maximal amplitude of dynamic topography to 1 km this estimate is based on a narrow definition of dynamic topography that only includes sub lithospheric processes and using mid ocean ridges as reference where mantle lithosphere buoyancy is zero