rates and processes of bedrock incision by the upper ukak river since the 1912 novarupta ash flow in the valley of ten thousand smokes alaska the rates and patterns of bedrock channel incision significantly influence landscape evolution and long term interactions among climate tectonics and erosion unfortunately only sparse field data are available to quantify the controls on river incision rates we exploit the diversion of the upper ukak river by an ash flow in 1912 to measure rates of incision along a newly formed bedrock channel minimum estimates of the rate of incision into intact rock vary from 0 01 to 0 10 m yr 1 this variation reflects differences in channel slope channel width lithologic facies and intensity of jointing as well as the effects of upstream knickpoint migration a streampower type incision model adequately explains the incision rate data provided 1 variations in channel width are prescribed on the basis of field measurements 2 the slope exponent is significantly less than unity n 0 4 0 2 and 3 observed downstream changes in lithologic facies and the intensity of jointing account for the apparent twofold downstream decrease in the coefficient of erosion despite the very rapid rate of incision calibrated stream power erosion coefficients for the ukak river k 2 4 10 4 m 0 2 yr 1 to 9 0 10 4 m 0 2 yr 1 are within the range of previously published estimates two plausible explanations for the low values of the slope exponent n are that incision rate is limited by either 1 a combination of physical weathering and hydrodynamic joint block extraction or 2 block fracture due to bedload impacts modulated on steeper channel segments by suspension of a significant fraction of the sediment load

three dimensional quantitative modeling of clinoform development abstract clinoform geometry pervades stratigraphic sequences across a variety of scales it is a composite surface which records the complex interplay between accommodation sediment supply physiography and hydrodynamics much of the sequence stratigraphic technique employs clinoform geometry to discriminate between the various systems tracts that constitute depositional sequences however many sequence stratigraphic models treat the generation of accommodation and the input of sediment supply as a two dimensional problem by assuming a line source of sediment entering a system impacted by relative sea level fluctuations one common attribute of clinoforms regardless of size and or shape is that their formation is inherently three dimensional therefore the clinoform geometry varies spatially and temporally throughout a region depending on the proximity to the sediment source and the character of the hydrodynamic regime we present a three dimensional stratigraphic model that combines both diffusion and advection to simulate across and along margin sediment transport and deposition this model allows us to examine how the morphology and internal clinoform geometry of deltas vary away from the sediment source in this application we simulate the development of a delta in a low energy environment to understand the importance of along shelf diffusion on clinoform geometry and the morphology of the delta we predict the three dimensional geometry and how it varies throughout a relative sea level cycle our model indicates that when the clinoform rollover is spatially coincident with the shoreline position the clinoform geometry changes dramatically along strike away from the sediment source region throughout a relative sea level cycle for example oblique clinoforms develop near the source region and evolve into an onlapping sequence along strike on the basis of stratal geometry and the technique of sequence stratigraphy this deposit would be interpreted as two different sequences with very different connotations for their formation we surmise that when the clinoform rollover and the shoreline position are separated e g a subaqueous delta the along strike variability of the clinoform geometry diminishes because of the hydrodynamic forces operative across the shelf consequently it is important to determine how clinoforms develop in three dimensions and to ensure that our window of observation is sufficient to discern between local and regional variability

did the 1977 sumba earthquake excite the chandler wobble abstract the potential role of large earthquakes on the excitation of the earth s free wobble has been the subject of various investigations it is nowadays recognized that the coseismic moment released by large earthquakes is not large enough to maintain the wobble and that they cumulatively only cause a very modest secular motion of the pole nevertheless renewed attention was paid to this subject following the observation of a sharp jump in the lageos derived polar motion excitation function at the time of the great 1977 sumba earthquake the static dislocation theory proved unable to explain these abrupt variations simply in terms of coseismic moment release and it was suggested that aseismic movement of blocks of ruptured lithosphere following the main shock could reconcile theoretical predictions with observations geological evidence suggests that the 1977 sumba earthquake was caused by a slab pull force acting along the subducting lithosphere the main shock was followed by a down dip motion of the slab we estimate quantitatively the potential role of this aseismic mass redistribution we find that the polar motion excitation due to the motions of ruptured lithosphere is not compatible with the lageos observed excitation function being in better agreement with the excitation functions derived by other polar motion data sets however we also show that the short term inertia variations due to the slab movements are considerably larger than those due to the main rupture thus possibly making earthquakes produced by slab pull forces an efficient mechanism for exciting the chandler wobble

coseismic rotation changes from the 2004 sumatra earthquake the effects of earth s compressibility versus earthquake induced topography summary polar motion is modelled for the large 2004 sumatra earthquake via dislocation theory for an incompressible elastic earth model where inertia perturbations are due to earthquake triggered topography of density contrast interfaces and for a compressible model where inertia perturbation due to compression dilatation of earth s material is included density and elastic parameters are based on a multilayered reference earth both models are based on analytical green s functions propagated from the centre to the earth s surface preliminary and updated seismological solutions are considered in elucidating the effects of improving earthquake parameters on polar motion the large sumatra thrust earthquake was particularly efficient in driving polar motion since it was responsible for large material displacements occurring orthogonally to the strike of the earthquake and to the earth s surface as imaged by grace gravity anomalies over the earthquake area the effects of earthquake induced topography are four times larger than the effects of earth s compressibility for l 2 geopotential components for varying compressional earth properties and seismic solution modelled polar motion ranges from 8 6 to 9 4 cm in amplitude and between 117 and 130 east longitude in direction the close relationship between polar motion direction earthquake longitude and thrust nature of the event are established in terms of basic physical concepts

landsliding and the evolution of normal fault bounded mountains much of the tectonic and climatic history in high relief regions such as the mountains of the western u s basin and range province is contained in the morphology of hillslopes drainage networks and other landforms that range in scale from 10 1 to 101km to understand how these landforms evolve we have developed a numerical landscape evolution model that combines a detailed tectonic displacement field with a set of physically based geomorphic rules bedrock landsliding long recognized as a significant geomorphic process in mountainous topography is for the first time explicitly included in the rule set in a series of numerical experiments we generate synthetic landscapes that closely resemble mountainous topography observed in the basin and range the production of realistic landscapes depends critically on the presence of bedrock landslides and landsliding yields rates of long term erosion that are comparable in magnitude to those of fluvial erosion the erosive efficiency of bedrock landsliding implies that hillslopes may respond very quickly to changes in local base level and that fluvial erosion is the rate limiting process in steady state experimental landscapes our experiments generate power law distributions of landslide sizes somewhat similar to both field and laboratory observations thus even a simple model of bedrock landsliding is capable of quantitatively reproducing mountainous topography and landslide distributions and represents a significant step forward in our understanding of the evolution of normal fault bounded ranges

sequence stratigraphy in active extensional basins implications for the interpretation of ancient basin fills abstract systematic variations in sequences their component units and their stacking patterns exist within rift basins these variations can be related to displacement gradients associated with the large scale 12 50 km segmentation of normal fault zones which control accommodation sediment supply and basin physiography sediment supply is also strongly influenced by the nature of pre rift drainage networks and variations in bedrock lithology high rates of hangingwall subsidence close to the centre of normal fault segments may cancel out the effects of glacio eustatic sea level fall so that accommodation development is normally characterized by the continual addition of new space the resulting sequences lack type 1 sequence boundaries and lowstand systems tracts and stack into aggradational sequence sets the adjacent footwall is subject to uplift which may lead to subaerial exposure and incision generating a composite type 1 sequence boundary away from the fault zone and near segment boundaries slip rates are much lower and hence relative sea level change is dominated by eustasy here falls in relative sea level are important resulting in type 1 sequences sequence stacking patterns reflect not only eustasy and local fault controlled subsidence but also the interaction of these with adjacent uplifting footwalls and or regional uplift tectonic influence on sequence development will be more pronounced during greenhouse times than icehouse times

effects of variations in fault slip rate on sequence stratigraphy in fan deltas insights from numerical modeling results from a newly developed numerical model incorporating tectonic subsidence eustasy and sedimentation are presented for rift basin settings in particular we simulate contemporaneous fan delta deposition subsidence and eustatic sea level variations to investigate the three dimensional nature of depositional sequences in the hanging wall of a normal fault a random walk algorithm is used for sediment delivery from source to shoreline together with a nonlinear three dimensional diffusion equation for sediment movement on steep delta foresets three sediment sources are modeled they are located along strike in areas of low medium and high subsidence rates of hanging wall subsidence eustatic sea level variation and sediment supply are derived from studies of active extensional basins the resulting stratigraphy contains three fan deltas with distinct morphologies and internal stacking patterns sequence boundaries and offlap forced regression are restricted to areas of low subsidence toward the fault tip aggradationally stacked deltaic wedges are along strike where subsidence rates are high near the fault center the simulated geometries compare well to natural examples and highlight along strike sequence variability and the importance of local controls in such settings

centroid moment tensor solutions for october december 1992 abstract centroid moment tensor solutions are presented for 205 earthquakes that occurred during the fourth quarter of 1992 the solutions are obtained using corrections for aspherical earth structure represented by a whole mantle shear velocity model sh8 u4l8 of dziewonski and woodward

the effect of global seismicity on the polar motion of a viscoelastic earth we evaluate the polar drift of a stratified viscoelastic earth generated by 20 years of global seismicity from the centroid moment tensor catalog 1977 1997 our estimate is better than that of soldati and spada 1999 because it accounts for the effects previously neglected of earthquakes at depths larger than 80 km in fact we show that deep focus and intermediate depth focus seismic events tend to affect the earth s inertia tensor more significantly than shallow ones specifically we find that the mean rate of polar drift evaluated over a 6 year time interval immediately following the seismic event due to a vertical dip slip source at the bottom of the asthenosphere 280 km depth in our model is 5 times larger than that generated by an analogous source located at the boundary between lithosphere and asthenosphere 80 km depth we conclude nevertheless that global seismic activity is not able to alter significantly the rotational parameters of the earth according to our computations the changes that it induces in the inertia tensor result in an average polar drift that is still significantly smaller than the observed one

earthquakes and relative sealevel changes 1 using a spherical model of postseismic deformation for the first time we have computed the global contribution of large earthquakes to the relative sealevel variations in the twentieth century we have found that great earthquakes have the overall tendency to produce a sealevel rise and that they affect the measurements taken at those tide gauge sites that are commonly employed to obtain global estimates of sealevel rise though on a global scale most of the signal is associated with thrust events on a regional scale the effects of great transcurrent earthquakes cannot be neglected depending on the viscosity of the asthenosphere the contribution of earthquakes to the long term sealevel changes amounts to at least 0 1 mm yr thus the climate driven long term sealevel changes deduced by tide gauge observations may be slightly but not negligibly overestimated

self organization and scaling relationships of evolving river networks the power spectra s of linear transects of earth s topography is often observed to be a power law function of wave number k with exponent close to 2 s k k 2 in addition river networks are fractal trees that satisfy several power law relationships between their morphologic components a model equation for the evolution of earth s topography by transport limited erosional processes which produces fractal topography and fractal river networks is presented and its solutions are compared in detail to real topography the model is the diffusion equation for sediment transport on hillslopes and channels with the diffusivity constant on hillslopes and proportional to the three halves power of discharge in channels the dependence of diffusivity on discharge is consistent with sediment rating curves we study the model in two ways in the first analysis the diffusivity is parameterized as a function of elevation and a taylor expansion procedure is carried out to obtain a differential equation for the landform elevation which includes the spatially variable diffusivity to first order in the elevation the solution to this equation is a self affine or fractal surface with linear transects that have power spectra s k k 1 8 independent of the age of the topography consistent with observations of real topography the hypsometry produced by the model equation is skewed such that lowlands make up a larger fraction of the total area than highlands as observed in real topography in the second analysis we include river networks explicitly in a numerical simulation by calculating the discharge at every point we characterize the morphology of real river basins with five independent scaling relations between six morphometric variables scaling exponents are calculated for seven river networks from a variety of tectonic environments using high quality digital elevation models river networks formed in the model match the observed scaling laws and satisfy tokunaga side branching statistics

large earthquakes and earth rotation the role of mantle relaxation by means of a radially stratified spherical model and using the available moment tensor solutions we evaluate the contribution of large earthquakes to polar drift in the last two decades in contrast to previous analyses which only considered the elastic response of the earth to the release of seismic moment we account for mantle rheology and thus for the time dependent postseismic inertia changes driven by global seismicity we confirm that during the last twenty years the global seismic activity has not significantly altered the rotational parameters of the earth however we find that for values of asthenospheric viscosity suggested by recent studies of postseismic stress diffusion the delayed relaxation of the mantle amplifies the average rate of polar drift by a factor of 1 2 to 1 7 depending on the width of the asthenosphere even on a decade time scale

landscape response to tectonic forcing digital elevation model analysis of stream profiles in the mendocino triple junction region northern california the topographic evolution of orogens is fundamentally dictated by rates and patterns of bedrock channel incision quantitative field assessments of process based laws are needed to accurately describe landscape uplift and denudation in response to tectonics and climate we evaluate and calibrate the shear stress or similar unit stream power bedrock incision model by studying stream profiles in a tectonically active mountain range previous work on emergent marine terraces in the mendocino triple junction region of northern california provides spatial and temporal control on rock uplift rates digital elevation models and field data are used to quantify differences in landscape morphology associated with along strike northwest to southeast changes in tectonic and climatic conditions analysis of longitudinal profiles supports the hypothesis that the study area channels are in equilibrium with current uplift and climatic conditions consistent with theoretical calculations of system response time based on the shear stress model within uncertainty the profile concavity of the trunk streams is constant throughout the study area 0 43 as predicted by the model channel steepness correlates with uplift rate these data help constrain the two key unknown model parameters the coefficient of erosion k and the exponent associated with channel gradient n this analysis shows that k cannot be treated as a constant throughout the study area despite generally homogeneous substrate properties for a reasonable range of slope exponent values n best fit values of k are positively correlated with uplift rate this correlation has important implications for landscape evolution models and likely reflects dynamic adjustment of k to tectonic changes due to variations in orographic precipitation and perhaps channel width sediment load and frequency of debris flows the apparent variation in k makes a unique value of n impossible to constrain with present data

effect of subductions and trends in seismically induced earth rotational variations in the past the influences of large earthquakes on earth rotation and on changes of the gravity field have been the subject of extensive investigations though it is now recognized that earthquakes cannot excite the chandler wobble and that they only drive a very modest secular drift of the earth s spin axis their rotational signatures present some intriguing peculiarities in fact they preferentially drive the rotation axis toward a well defined direction i e 0 140oe and systematically induce negative variations of the earth s oblateness in the first part of this work the static dislocation theory is employed to ascertain the origin of these two remarkable trends this task is accomplished by considering the effects of seismicity on earth rotation during the last two decades we find that the above tendencies are operating even on a yearly time scale and we explain their nature by means of simple geometrical and physical arguments we also find that the trend of the pole toward 140oe is essentially due to the seismicity which characterizes the western pacific subduction zones the seismic excitation function takes for shallow thrust earthquakes a direction roughly opposite to the excitation function associated with mass injection along active subduction zones this point highlights the potential effects of aseismic mass rearrangement at subduction zones on the secular drift of the pole our findings based on a simple model of steady state subduction show that in the last two decades this process substantially acts to counterbalance the polar drift due to global seismic activity we verify that this balance between earthquake and subduction induced rotational signatures also characterizes the time variations of the dynamic oblateness which is intrinsically independent of the inertia changes that drive polar motion from these results which may potentially have some impact on the interpretation of long term polar motion we conclude that the pole of rotation cannot be significantly perturbed by tectonic motions on a decade time scale

coseismic deformations detectable by satellite gravity missions a case study of alaska 1964 2002 and hokkaido 2003 earthquakes in the spectral domain 1 coseismic deformations observed on the earth surface or modeled by conventional dislocation theory cannot be compared directly with those observed by gravity satellite missions because of the spatial resolution limit of the missions and the signal attenuation of the gravity field coseismic deformations in the spectrum domain should be considered instead for this purpose the conventional dislocation theory e g sun and okubo 1993 for a spherical earth model can be used because it is expressed in the form of a spherical harmonic in this study analytical expressions of degree variances of the coseismic geoid and gravity changes for shear and tensile sources are derived and calculated for three real earthquakes those results are compared with expected errors of the gravity recovery and climate experiment grace to elucidate whether or not coseismic geoid and gravity changes are detectable by gravity satellite missions behaviors of the degree variances for four independent seismic sources are investigated results indicate that both the gravity and geoid changes are near two orders of magnitude larger than the precession of the gravity missions in low harmonic degrees on the basis of these results we derived the minimum magnitudes of earthquakes detectable by grace we concluded that coseismic deformations for an earthquake with a seismic magnitude above m 7 5 are expected to be detected by grace

an invasion percolation model of drainage network evolution stream networks evolve by headward growth and branching away from escarpments such as rift margins the structure of these networks and their topographic relief are known to be fractal1 3 but no model so far has been able to generate the observed scaling properties here i present a statistical model of network growth in which stream heads branch and propagate at a rate that depends only on the local strength of the substrate this model corresponds to the process of invasion percolation4 with the added requirement of self avoidance it is a self organized critical system5 with properties similar to those of standard percolation models6 a description based on self avoiding invasion percolation reproduces the known scaling behaviour of stream networks and may provide a valuable tool for delineation of drainage patterns from digital topographic data sets7 8

controls on post mid cretaceous landscape evolution in the southeastern highlands of australia insights from numerical surface process models the tectonic and geomorphic evolution of the southeastern australian highlands has been a subject of controversy among geophysicists geologists and geomorphologists for several decades we employ a numerical surface process model that includes long range fluvial transport hillslope diffusion and landsliding in order to quantitatively assess the tectonic lithological and structural controls on the landscape evolution and denudation history of se australia we constrain fluvial erosion parameters for our model by fitting river profiles rockfall and landsliding are the most important processes controlling the concentration of erosion in river valleys we therefore model hillslope evolution using a very low diffusion coefficient and a threshold slope for landsliding the initial prebreakup topography of the highlands provides a fundamental control on their subsequent evolution together with the style and rate of fluvial incision secondary controls are exerted by lateral variations in lithology and local tectonic uplift along faults our modeling results indicate that 1 the observed highlands morphology requires that the drainage divide was established at its present location prior to opening of the tasman sea whether the divide is inherited from paleozoic orogeny or resulted from mesozoic syn rift uplift cannot be established however 2 in contrast to traditional interpretations escarpment retreat does not appear to be the fundamental process eroding the highlands and 3 the observed barbed river drainage may be imprinted as a result of lithological variation it does not necessarily evolve through capture the driving mechanism that is most consistent with the inferred uplift pattern of the southeastern highlands appears to be magmatic underplating

reevaluation of the chandler wobble seismic excitation from recent data abstract since 1977 seismic moment tensors of major earthquakes have been systematically determined while high accuracy polar motion data have been made available from space techniques the seismic excitation of the chandler wobble during the period 1977 1983 has been obtained using the centroid moment tensor solutions of 1287 strong and moderate earthquakes occurring during that period changes in the earth inertia tensor induced by earthquakes which are derived from the elastic theory of dislocation are assumed to be step functions of time from a comparison between the derived synthetic chandler wobble and the observed one it turns out that seismic excitation is far too small by about two orders of magnitude to explain the chandler wobble amplitude variations during 1977 1983 in particular the increase in the wobble amplitude between 1980 and 1983 during the last two decades seismic moments of major earthquakes remained on the level of 10 27 to 10 28 dyne cm whereas in the past events of high magnitudes corresponding to seismic moments on the order of 10 30 to 10 31 dyne cm have been frequently reported as the later values are those needed to explain the amplitude variations of the chandler wobble the problem of the validity of magnitude estimations in the past and frequency of occurrence of great earthquakes is raised as well as the question of validity of previous positive conclusions on the influence of earthquakes on the chandler wobble excitation

self similarity and multifractality of fluvial erosion topography 1 mathematical conditions and physical origin it is suggested that the scaling laws satisfied by fluvial erosion topography and river networks reflect a basic self similarity or multifractality property of the topographic surface within river basins by analyzing the symmetries of fluvial topography we conclude that this self similarity or multifractality condition should be expressed in a particular way in terms of the topographic increments within subbasins we then analyze whether self similar or multifractal topographies can be stationary or transient solutions of dynamic evolution models of the type h t u where u is the uplift rate is the fluvial erosion rate is a vector of erodibility parameters and is hydraulic shear stress the hydraulic stress on a channel bed is assumed to satisfy amsn where a is contributing area s is slope and m and n are parameters we allow u to vary randomly in time and to vary randomly in space and determine conditions on these random functions as well as the parameters m and n under which the topography may remain in a self similar or multifractal state simulation shows that self similar states are attractive also for non self similar boundary and initial conditions

formulation of coseismic changes in earth rotation and low degree gravity field based on the spherical earth dislocation theory in this paper we present analytical formulas to compute the coseismic earth rotation change polar motion and length of day and low degree gravity field change based on a spherical dislocation theory using the preliminary reference earth model and our formulas we calculate coseismic changes in earth s rotation and low degree stokes coefficients caused by the four largest earthquakes since 1960 the results verify that the present method is consistent with previous studies but the method cannot be verified by the observations a case study on the 2011 tohoku oki earthquake mw 9 0 indicates that the coseismic earth rotation change depends on the magnitude and source parameters and results show a difference between a point source and finite fault model we also investigate the effect of seawater redistribution on coseismic earth rotation change but the effect is small and can be neglected

drainage basin responses to climate change recent investigations have shown that the extent of the channel network in some drainage basins is controlled by a threshold for overland flow erosion the sensitivity of such basins to climate change is analyzed using a physically based model of drainage basin evolution the golem model simulates basin evolution under the action of weathering processes hillslope transport and fluvial bedrock erosion and sediment transport results from perturbation analyses reveal that the nature and timescale of basin response depends on the direction of change an increase in runoff intensity or a decrease in vegetation cover will lead to a rapid expansion of the channel network with the resulting increase in sediment supply initially generating aggradation along the main network followed by downcutting as the sediment supply tapers off by contrast a decrease in runoff intensity or an increase in the erosion threshold will lead to a retraction of the active channel network and a much more gradual geomorphic response cyclic changes in runoff intensity are shown to produce aggradational degradational cycles that resemble those observed in the field cyclic variations in runoff also lead to highly punctuated denudation rates with denudation concentrated during periods of increasing runoff intensity and or decreasing vegetation cover the sediment yield from threshold dominated basins may therefore exhibit significant variability in response to relatively subtle environmental changes a finding which underscores the need for caution in interpreting modern sediment yield data

denudation vertical crustal movements and sedimentary basin infill denudation and vertical crustal movements are linked through the isostatic equation for conservation of lithospheric mass recent empirical results from a wide range of sources are presented on the rates of these processes denudation alone can cause non tectonic isostatic surface uplift of the right magnitude predicted by theory a case is made following ahnert for a single linear relationship although with much scatter between denudation rate and mean drainage basin relief for large basins some recent determinations of denudational time constants have neglected to include tectonic and isostatic terms which oppose the reduction of relief by denudation application of diffusional transport models to determine the rate of sediment deposition are severely limited by inherent one dimensionality and neglect of suspended and washload contributions basin infill sequences may be used to determine past sediment transfer coefficients from a hinterland but problems arise in the apportionment of the various hinterland fluxes that occur in real world three dimensional basins sediment yields in smaller half graben and growth fold basins must reflect the magnitude of drainage basins and the complex local controls upon sediment yields examples are given from extensional basins in the western usa and greece the length of tectonic relief produced in tilt blocks and growth folds will control the area of drainage basin developed through the fractal form of hack s law and hence the magnitude of deposition in sedimentary basins adjoining tectonic uplands

geomorphic limits to climate induced increases in topographic relief recognition of the potential for strong dynamic coupling between atmospheric and tectonic processes has sparked intense cross disciplinary investigation and debate on the question of whether tectonics have driven long term climate change or vice versa it has been proposed that climate change might have driven the uplift of mountain summits through an isostatic response to valley incision because isostasy acts to compensate mean elevations the debate hinges on the question of whether climate change can significantly increase topographic relief or more precisely increase the volume of missing mass between summits and ridges here we show that in tectonically active mountain ranges geomorphic constraints allow only a relatively small increase in topographic relief in response to climate change thus although climate change may cause significant increases in denudation rates potentially establishing an important feedback between surficial and crustal processes neither fluvial nor glacial erosion is likely to induce significant isostatic peak uplift

self organization of river networks to threshold states numerical models in which grid cells self organize so that the shear stress in each cell equals a predetermined threshold value are remarkably successful in producing the fundamental structure of river networks such models are a reasonable approximation of networks characterized by near constant dimensionless shear stress bed shear stress7sol bed grain size with each cell s threshold value being proportional to median bed grain size previous work has shown that this is the case for channels cut into alluvium and that the characteristic narrow range of is different for gravel and sand bed channels channels in the italian apennines that are slowly incising into weak bedrock but which are covered by a veneer of gravel for most of the time are shown to be characterized by the same as alluvial gravel bed channels thus threshold models capture the fundamental behavior of many river networks even in areas of long term bedrock incision

normal fault control on bedrock channel incision and sediment supply insights from numerical modeling 1 the evolution of footwall drainage basins sediment supply and hanging wall stratigraphy in rift basins is investigated using a coupled numerical model of detachment limited stream network evolution and coarse grained fan delta deposition the response of bedrock channel networks to repeated footwall uplift events leads to increasing sediment supply over tens of thousands of years as the networks initiate and then expand followed by relatively constant sediment supply as the stream networks reach their maximum spatial extent the distinct time lag between the onset of tectonic activity and attainment of maximum sediment supply leads to stratigraphies that are initially aggradational and then progradational much of the variation in sediment supply is the product of the complex response and reorganization of the stream networks to faulting related perturbations and is not directly related to specific faulting events increasing fault displacement drives the system toward a new steady state with a higher sediment supply but is initially expressed as a retrogradation as sediment supply lags behind increased displacement the converse is true for a decrease in fault displacement which is initially expressed as progradation continual stochastic variation in recurrence interval leads to a system that does not achieve a steady state and as a result exhibits continual variation in sediment supply the model results emphasize the local tectonic controls on stratigraphic architectures developed within extensional basins and the complex manner in which stream network growth and response to tectonic activity can be expressed in the stratigraphic record

active normal fault evolution in greece revealed by geomorphology and drainage patterns active normal fault systems in greece are associated with characteristic geomorphology and drainage patterns that are recognizable in satellite images and digital topography some allowance must be made for the nature of the footwall rocks which can exert an important influence on these patterns and we examine the three main types in greece hard mesozoic limestone relatively soft schist volcanic rocks or flysch and very soft neogene sediments drainage and geomorphology can be used to identify active faults that were previously unknown but can also reveal information about plio quaternary fault evolution and interaction that may be inaccessible by other means we illustrate such processes with examples showing the migration of normal fault systems into their hanging walls and the change in normal faulting activity from nw se faults to e w faults both of which are common in greece

earthquake clustering inferred from pliocene gilbert type fan deltas in the loreto basin baja california sur mexico a stacked sequence of pliocene gilbert type fan deltas in the loreto basin was shed from the footwall of the dextral normal loreto fault and deposited at the margin of a marine basin during rapid fault controlled subsidence fan delta parasequences coarsen upward from marine siltstone and sandstone at the base through sandy bottomsets and gravelly foresets to gravelly nonmarine topsets each topset unit is capped by a thin shell bed that records marine flooding of the delta plain several mechanisms may have produced repetitive vertical stacking of gilbert deltas 1 autocyclic delta lobe switching 2 eustatic sea level fluctuations 3 climatically controlled fluctuations in sediment input and 4 episodic subsidence produced by temporal clustering of earthquakes we favor hypothesis 4 for several reasons but hypotheses 2 and 3 cannot be rejected at this time earthquake clustering can readily produce episodic subsidence at spatial and temporal scales consistent with stratigraphic trends observed in the loreto basin this model is supported by comparison with paleoseismological studies that document clustering on active faults over a wide range of time scales earthquake clustering is a new concept in basin analysis that may be helpful for understanding repetitive stratigraphy in tectonically active basins

seismic excitation of the polar motion 1977 1993 the mass redistribution in the earth as a result of an earthquake faulting changes the earth s inertia tensor and hence its rotation using the complete formulae developed bychao andgross 1987 based on the normal mode theory we calculated the earthquake induced polar motion excitation for the largest 11 015 earthquakes that occurred during 1977 0 1993 6 the seismic excitations in this period are found to be two orders of magnitude below the detection threshold even with today s high precision earth rotation measurements however it was calculated that an earthquake of only one tenth the size of the great 1960 chile event if happened today could be comfortably detected in polar motion observations furthermore collectively these seismic excitations have a strong statistical tendency to nudge the pole towards 140 e away from the actually observed polar drift direction this non random behavior similarly found in other earthquake induced changes in earth rotation and low degree gravitational field bychao andgross 1987 manifests some geodynamic behavior yet to be explored

why are earthquakes nudging the pole towards 140 e earthquakes have collectively the tendency to displace the pole of rotation of the earth towards a preferred direction 140 e this trend which is still unexplained on quantitative grounds has been revealed by computations of earthquake induced inertia variations on both a secular and a decade time scale purpose of this letter is to show that the above trend results from the combined effects of the geographical distribution of hypocenters and of the prevailing dip slip nature of large earthquakes in this century our findings are based on the static dislocation theory and on simple geometrical arguments

impact of global seismicity on sea level change assessment 1 we analyze the effect of seismic activity on sea level variations by computing the time dependent vertical crustal movement and geoid change due to coseismic deformations and postseismic relaxation effects seismic activity can affect both the absolute sea level changing the earth s gravity field and hence the geoid height and the relative sea level rsl i e the radial distance between seafloor and geoid level by using comprehensive seismic catalogs we assess the net effect of seismicity on tidal relative sea level measurements as well as on the global oceanic surfaces and we obtain an estimate of absolute sea level variations of seismic origin we modified the approach adopted in our previous analysis considering the issue of water volume conservation by applying the sealevel equation and we improved our computational methods enabling us to evaluate the effect of an extremely large number of earthquakes on large grids covering the whole oceanic surface these new potentialities allow us to perform more detailed investigations and to discover a quantitative explanation for the overall tendency of earthquakes to produce a positive global relative sea level variation our results confirm the finding of a previous analysis that on a global scale most of the signal is associated with a few giant thrust events and that rsl estimates obtained using tide gauge data can be sensibly affected by the seismically driven sea level signal the recent measures of sea level obtained by satellite altimetry show a wide regional variation of sea level trends over the oceanic surface with the largest deviations from the mean trend occurring in tectonically active regions while our estimates of average absolute sea level variations turn out to be orders of magnitude smaller than the satellite measured variations we can still argue that the mass redistribution associated with aseismic tectonic processes may contribute to the observed regional variability of sea level variations a detailed study of these tectonic contributions is important to acquire a complete understanding of the global sea level variations and will be the subject of future investigations

geologic constraints on bedrock river incision using the stream power law denudation rate in unextended terranes is limited by the rate of bedrock channel incision often modeled as work rate on the channel bed by water and sediment or stream power the latter can be generalized as ka m s n where k represents the channel bed s resistance to lowenng whose variation with lithology is unknown a is drainage area a surrogate for discharge s is local slope and m and n are exponents whose values are debated we address these uncertainties by simulating the lowering of ancient river profiles using the finite difference method we vary m n and k to match the evolved profile as closely as possible to the corresponding modern river profile over a time period constrained by the age of the mapped paleoprofiles we find at least two end member incision laws ka 0 3 0 5 s for australian rivers with stable base levels and k f a 0 1 0 2 s n for rivers in kauai subject to abrupt base level change the long term lowering rate on the latter expression is a function of the frequency and magnitude of knickpoint erosion characterized by k f incision patterns from japan and california could follow either expression if they follow the first expression with m 0 4 k varies from 10 7 10 6 m 0 2 yr for granite and metamorphic rocks to 10 5 10 4 m 0 2 yr for volcaniclastic rocks and 10 4 10 2 m 0 2 yr for mudstones this potentially large variation in k with lithology could drive strong variability in the rate of long term landscape change including denudation rate and sediment yield

extended equilibrium beach profiles abstract the idea of an equilibrium beach profile has been a useful concept in both theoretical and practical coastal engineering studies in essence the subject has thus far evolved to a choice of shape functions which are described by a small set of parameters additional efforts have attempted to relate these parameters to more fundamental quantities such as average grain size of the bottom sediment wave environment geometric aspects of the beach and the like this approach has a long history and can rightly claim a certain level of success however the usual collections of shape functions are well known to have difficulties very near the shoreline let alone on the nearshore portion of the beach this study extends the equilibrium profile up to and somewhat past the shoreline three shape functions are used in conjunction with a taylor expansion for the nearshore and above water portions of the profile a nonlinear fitting technique is applied to estimate the model s best parameter values moreover reduced versions of the proposed models can be employed for prediction based only on parameters related to sediment characteristics or wave conditions and geometry of the visible beach the approach is compared with data from the east coast of australia the east coast of north america and the south shore of the mediterranean sea

sedimentology and sequence stratigraphy of a transfer zone coarse grained delta miocene suez rift egypt this study focuses on miocene sedimentation and stratigraphic evolution in a major transfer zone at the northern tip of the thal fault segment gulf of suez the succession generally shoals upwards from offshore mudstone containing pro delta turbidites into conglomeratic delta foresets and topsets with sandstone dominated shoreface facies coexisting laterally despite this upward shoaling key stratal surfaces marking abrupt changes in relative sea level allow the succession to be divided into four stratal units the stacking pattern of the stratal units suggests an initial relative sea level rise that generated a major marine flooding surface a relative sea level fall followed resulting in widespread exposure and incision during the ensuing relative sea level rise a lowstand coarse grained delta and coeval shoreface succession prograded several kilometres basinward the stratigraphic development of the transfer zone delta is in marked contrast to that of aggradationally stacked deltas that occur near the centre of the baba sidri fault segment further south at the transfer zone low rates of subsidence and accommodation development coupled with a high sediment supply derived from a large fault tip drainage catchment have produced a strongly progradational delta subject to marked changes in relative sea level in the fault centre location however higher rates of accommodation development coupled with lower rates of sediment supply from footwall catchments have produced aggradationally stacked deltas the results from this study have implications for sequence stratigraphic models and hydrocarbon exploration within extensional basins

global postseismic gravity changes of a viscoelastic earth a spherically symmetric earth model with a viscoelastic mantle and an inviscid core is used to study the gravitational perturbation due to a lithospheric shear dislocation in the coseismic and postseismic regime our approach is based on a quasi static solution of the equilibrium equations taking advantage of the normal mode technique for a layered incompressible earth with linear viscoelastic rheology we perform a systematic study of space and time evolution of gravity changes associated with a wide selection of seismic sources investigating the effects of several different mantle viscosity profiles our results show that the gravitational signal is sensitive not only to the viscosity of the asthenosphere but also to that of the mantle including the portion below the 670 km discontinuity as a case study we compute the coseismic and postseismic gravity perturbation due to the 1964 alaska earthquake the last section is devoted to the analysis of the postseismic relaxation rates of the gravitational perturbation following that earthquake for several different viscosity profiles of the mantle our results show that experimental attempts to obtain reliable detection of static and quasi static gravitational perturbation associated with seismic events would be of great importance in understanding the dynamic and viscosity profile of both upper and lower mantle

three dimensional numerical modeling of coarse grained clastic deposition in sedimentary basins a three dimensional numerical model of clastic deposition in sedimentary basins is used to investigate the development of coarse grained deltas in response to relative sea level changes the model incorporates fully three dimensional sediment delivery and deposition together with incised channel formation and slope failure a combined random walk steepest descent algorithm is used to simulate sediment delivery from a drainage basin outlet to the depositional shoreline together with a nonlinear three dimensional diffusion equation for modeling slope dependent sediment erosion transport and deposition when sediment channels transport pathways are out of a specified grade advective erosion occurs thereby increasing the total sediment supply delivered to the basin multiple sediment sources into a basin can be simulated together with tectonic subsidence and eustatic sea level changes the model results presented display many of the key features observed in both modern and ancient coarse grained deltas during periods of slowly changing and high relative sea level highstands a broad delta front progrades approximately radially away from the sediment source conversely incised channels are developed during rapid falls of relative sea level leading to localized deposition of deltaic lobes at the mouths of these channels the incised channels initiate at the exposed delta front and propagate backward toward the sediment source the rate of growth of incised channels is shown to be an important control on delta morphology sediment distribution and lowstand lobe size and location lobes are particularly well developed during periods of slowly changing low relative sea level lowstands periods of rapid rise of relative sea level lead to flooding and infilling of incised channel systems and a rapid landward shift in deposition transgressions incised channels and delta lobes are best developed in a model where tectonic subsidence is similar to that expected for hanging wall sourced deltas in extensional half graben settings in contrast both channels and lobes are less well developed in a model where tectonic subsidence is similar to that expected for footwall sourced deltas in such settings many of the features developed in the models are by their nature three dimensional and two dimensional analysis of the model results can lead to erroneous interpretations of the causes of along strike variability these aspects of sequence variability have important implications for the application of the sequence stratigraphic methodology to many sedimentary basins