purely erosional cyclic and solitary steps created by flow over a cohesive bed an erodible surface exposed to supercritical flow often devolves into a series of steps that migrate slowly upstream each step delineates a headcut with an associated hydraulic jump these steps can form in a bed of cohesive material which once eroded is carried downstream as washload without redeposition here the case of purely erosional one dimensional periodic or cyclic steps in cohesive material is considered the st venant shallow water equations combined with a formulation for sediment erosion are used to construct a complete theory of the erosional case the solution allows wavelength wave height migration speed and bed and water surface profiles to be determined as functions of imposed parameters the analysis also admits a solution for a solitary step or single headcut of self preserving form

radial qμ structure of the lower mantle from teleseismic body wave spectra abstract we have measured 150 000 p and 130 000 s wave spectral ratios up to 0 8 hz using recordings of 250 deep focal depth 200 km earthquakes from 890 global and regional network stations we have inverted these data to estimate the attenuation parameters t p and t s for p and s waves and a radial profile of the quality factor q for the lower mantle on average t p increases by about 0 2 s and t s increases by about 0 7 s between epicentral distances of 30 and 97 the relatively strong increase of t s t s 4t p suggests that intrinsic shear attenuation is the cause of the overall trend in our data the increase of t p and t s with distance is smaller than predicted by models prem 12 ql6 11 and qlm9 16 assuming prem values for q in the upper mantle where the data lack resolving power the p and s wave spectra are explained best if q increases from about 360 at prem s 670 km discontinuity to 670 in the lowermost mantle the high values for q can be reconciled with previously determined values by invoking a frequency dependence of q that is proportional to 0 1 data that are separated in pacific and circum pacific subsets have slightly different trends estimates of t p and t s for the pacific data which sample the large low shear velocity province of the pacific are higher than the circum pacific estimates thus it appears that the pacific large low shear velocity province has accompanying low q the difference in q in the lowermost 1000 km of the mantle beneath the pacific and beneath the circum pacific is at most 17 lateral variations of this magnitude are marginally resolvable given the uncertainties of our measurements

observational constraints on the fracture energy of subduction zone earthquakes we relate seismologically observable parameters such as radiated energy seismic moment rupture area and rupture speed to the dynamics of faulting to achieve this objective we computed the radiated energy for 23 subduction zone earthquakes recorded between 1992 and 2001 most of these earthquakes have a magnitude m w 7 5 but we also included some smaller m w 6 7 well studied subduction zone earthquakes and six crustal earthquakes we compiled static stress drop estimates for these 29 earthquakes from literature and used a slip weakening model to determine the radiation efficiency of these earthquakes we also determined the rupture speed of these earthquakes from literature from fracture mechanics fracture energy and hence radiation efficiency can be related to the rupture speed the radiation efficiencies estimated from the partitioning of energy as given by the slip weakening model are consistent with the rupture speed estimated for these earthquakes most earthquakes have radiation efficiencies between 0 25 and 1 and are hence efficient in generating seismic waves but tsunami earthquakes and two deep earthquakes the 1994 bolivia and the 1999 russia china border earthquakes have very small radiation efficiencies 0 25 and hence dissipate a large amount of energy during faulting we suggest that differences in the radiation efficiencies of different types of earthquakes could be due to fundamental differences in their rupture mechanics in deep events the energy is probably dissipated in thermal processes in the fault zone while it is possible that the morphology of the trench causes large energy dissipation during the rupture process of tsunami earthquakes

submarine landforms and ice sheet flow in the kvitoya trough northwestern barents sea high resolution geophysical and sediment core data are used to investigate the pattern and dynamics of former ice flow in kvitoya trough northwestern barents sea a new swath bathymetric dataset identifies three types of submarine landform in the study area streamlined landforms meltwater channels and cavities iceberg scours subglacially produced streamlined landforms provide a record of ice flow through kvitoya trough during the last glaciation flow directions are inferred from the orientations of streamlined landforms drumlins crag and tail features ice flowed northward for at least 135 km from an ice divide at the southern end of kvitoya trough a large channel cavity system incised into bedrock in the southern trough indicates that subglacial meltwater was present at the former ice sheet base modest landform elongation ratios and a lack of mega scale glacial lineations suggest that although ice in kvitoya trough was melting at the bed and flowed faster than the likely thin and cold based ice on adjacent banks a major ice stream probably did not occupy the trough retreat was relatively rapid after 14 13 5 14c kyr b p and probably progressed via ice sheet bed decoupling in response to rising sea level there is little evidence for still stands during ice retreat or of ice proximal deglacial sediments relict iceberg scours in present day water depths of more than 350 m in the northern trough indicate that calving was an important mass loss mechanism during retreat

a quantitative three dimensional depositional model of gravelly braided rivers a quantitative three dimensional depositional model of gravelly braided rivers has been developed based largely on the deposits of the sagavanirktok river in northern alaska these deposits were described using cores wireline logs trenches and ground penetrating radar profiles the origin of the deposits was inferred from observations of 1 channel and bar formation and migration and channel filling interpreted from aerial photographs 2 water flow during floods and 3 the topography and texture of the river bed at low flow stage this depositional model quantitatively represents the geometry of the different scales of strataset the spatial relationships among them and their sediment texture distribution porosity and permeability in the model are related to sediment texture the geometry of a particular type and scale of strataset is related to the geometry and migration of the bedform type e g ripples dunes bedload sheets bars associated with deposition of the strataset in particular the length to thickness ratio of stratasets is similar to the wavelength to height ratio of associated bedforms furthermore the wavelength and height of bedforms such as dunes and bars are related to channel depth and width therefore the thickness of a particular scale of strataset i e medium scale cross sets and large scale sets of inclined strata will vary with river dimensions these relationships between the dimensions of stratasets bedforms and channels mean that this depositional model can be applied to other gravelly fluvial deposits the depositional model can be used to interpret the origin of ancient gravelly fluvial deposits and to aid in the characterization of gravelly fluvial aquifers and hydrocarbon reservoirs

a cascading failure during the 24 may 2013 great okhotsk deep earthquake on 24 may 2013 the largest ever recorded deep earthquake occurred beneath sea of okhotsk a multiple point source inversion procedure is applied to constrain source process of this earthquake based on waveform modeling of both direct p and sh waves and near surface reflected pp and ssh waves our results indicate that the earthquake consists of six major subevents separated in space and time encompassing a horizontal dimension of 64 4 km along n160 e and a downward depth extension of 35 4 km the geographic distribution and focal mechanisms of the inferred subevents and foreshock aftershock locations do not fit into plane rupture we suggest that the earthquake can be best explained by a cascading failure of shear instability within preexisting weak zones in the region with the perturbation of stress generated by a shear instability triggering another

strong ground motions in north america from the bolivia earthquake of june 9 1994 mw 8 3 the bolivia earthquake was remarkable for being felt in north america as far as 8680 km from the epicenter this paper examines the characteristics of ground motions in north america from the perspective of strong motion seismology data on ground motions is mostly from high gain stations but we also have two strong motion accelerograms the largest accelerations and highest frequencies are associated with the p and pcp phases which also correlate with the felt reports in several instances felt locations are associated with a combination of favorable factors most are in a distance range where p wave amplitudes tend to be relatively high as observed in the empirical correction factors for body wave magnitude and in regions with relatively high values of q in the lithosphere in addition site effects structural amplification or both seem to contribute to the selective detection of the earthquake in the regions where some people noticed it motions were far below design spectra for earthquake resistant design and far below levels likely to be associated with damage

the 2013 okhotsk deep focus earthquake rupture beyond the metastable olivine wedge and thermally controlled rise time near the edge of a slab the 2013 m8 3 okhotsk earthquake involves two primary mechanisms of deep focus earthquake rupture mineral phase transformation of olivine to spinel and thermal shear instability backprojection imaging of broadband seismograms recorded by the north american and european networks indicates bilateral rupture toward ne and sse the rupture paths of the ne segment and other regional m7 earthquakes are confined in narrow regions along the slab contours consistent with the phase transformation mechanism however the sse rupture propagates a long distance across the slab and aftershocks are distributed across a 60 km wide zone beyond the plausible thickness of the metastable olivine wedge favoring thermal shear weakening while the ne rupture is only visible at high frequencies the sse rupture is consistently observed across a broad frequency range this frequency dependent rupture mode can be explained by lateral variations of rise time controlled by thermal thinning of the slab near its northern end

the relationship between channel avulsion flow occupancy and aggradation in braided rivers insights from an experimental model experimental modelling of an aggrading braided river has allowed investigation of the relationship between the frequency of channel avulsion a f the duration of time that the braidplain is occupied by flow the spatial pattern of braidplain sedimentation and how these respond to a change in sediment supply s s model results demonstrate a strong positive relationship between s s and a f and that there is no downstream change in a f over the short braidplain distances ca 100 m modelled herein although a f is strongly dependent on s s the degree of channel switching does not influence the rate or spatial pattern of braidplain sedimentation all experiments used a single central input for water and sediment and the channels occupied the centre of the alluvial basin for a longer period of time than the margins for all sediment supply rates and distances downstream despite this spatio temporal pattern in flow occupancy braidplain sedimentation rates were nearly uniform both downstream and across the basin and increased at approximately the same rate as increases in s s as a consequence less frequent and possibly short lived flows at the margins of the braidplain deposited and preserved more sediment per unit time in comparison with the centre of the basin where flow occupancy was higher an approximate order of magnitude change in sediment supply resulted in only a factor of two change in bed slope probably due to both an increase in channelization and adjustment of the channel form that maintained sediment transport through the basin this result suggests that linear diffusion models are unlikely to be applicable in landscape evolution models that possess aggrading multi thread rivers which are capable of self adjustment in channel number and form

feasible optimality of vegetation patterns in river basins 1 we examine mechanisms leading to organization of vegetation patterns within the channel network structure of a semi arid new mexico river basin under the controlling influence of water stress we compare the actual pattern of water stress within the basin to patterns resulting from two algorithms of local stress optimization which proceed from an initial fully random vegetation distribution here we show that the distribution of vegetation and basin water stress derived from an algorithm that maintains local optimization within the network flow path exhibits considerably better agreement with the actual distribution than one that ignores the network structure of the basin these results suggest the pattern of actual vegetation observed within the basin corresponds to a condition of feasible optimality in which organization is constrained by the stochastic nature of local interactions mediated by the network configuration the principles of such organization have important consequences regarding the interaction between land cover change and hydrological dynamics in river basins as well as the biogeographical evolution of landscapes

observations on the movement of coarse gravel using implanted motion sensing radio transmitters motion sensing radio transmitters were implanted in cobbles 72 92 mm diameter and placed in a stream in south west idaho for 43 days during a snowmelt period the radios transmit different pulse rates depending on whether the rocks are at rest or in motion every 30 s a datalogger samples the receiver and records the pulse rate of the transmitters such information can be used to assess numerous properties of particle transport that are beyond the capabilities of conventional tracking methods conclusions include i rocks are more likely to move on rising hydrograph limbs than on falling hydrograph limbs ii the average shields parameter is 0 046 iii rocks move only a fraction of the time between initial and final motion during an event iv the distributions of motion and rest periods are best modeled by gamma functions rather than exponential but the distributions approach exponential as the tails are trimmed copyright 2004 john wiley sons ltd

experimental evidence of dynamic scaling and indications of self organized criticality in braided rivers the evolution of an experimental braided river produced in our laboratory has been monitored and analyzed it has been shown that in addition to the spatial scaling revealed by sapozhnikov and foufoula georgiou 1996a braided rivers also exhibit dynamic scaling this implies that a smaller part of a braided river evolves identically in the statistical sense to a larger one provided the time is renormalized by a factor depending only on the ratio of the spatial scales of those parts the small value of the estimated dynamic exponent z is interpreted as an indication that the evolution of small channels in a braided river system is to a large extent forced by the evolution of bigger channels the presence of dynamic scaling is further interpreted as indicating that braided rivers may be in a critical state and behave as self organized critical systems in a recent paper sapozhnikov and foufoula georgiou 1996a evidence was presented that natural braided rivers ex hibit anisotropic scaling self affinity in their geometrical structure within a range of scales spanning the width of the narrowest channel to the width of the braid plain in simple words within these scales if a small part of a braided river is stretched in a certain way along the mainstream direction and a certain different way along the perpendicular direction then this stretched part looks statistically the same as a bigger part of the river such anisotropically scaled objects are called self affine fractals and are characterized by two fractal exponents nx and ny the ratio nx ny characterizes the scaling anisotropy and the fractal dimension d 5 ny 2 nx 1 1 ny e g see sapozhnikov and foufoula georgiou 1995 indicates how densely the object fills the space in sapozhnikov and foufoula georgiou 1996a three natu ral braided rivers of different scales and different hydrological and sedimentological characteristics aichilik and hulahula in alaska and brahmaputra in bangladesh were analyzed for spatial scaling using the logarithmic correlation integral lci method developed by sapozhnikov and foufoula georgiou 1995 interestingly enough it was observed that despite their different scales 0 5 15 km in braid plain width slopes 7 3 10 23 8 310 25 and types of bed material gravel to sand all three rivers exhibited anisotropic spatial scaling with almost the same fractal exponents nx 5 0 72 0 74 and ny 5 0 51 0 52 the x axis being oriented along the river and the y axis being in the perpendicular direction in simple terms this im plies that if parts of a braided river are stretched by l along the mainstream direction and by l n y n x l 0 7 along the perpen dicular direction the resulting images will look statistically similar to each other similarity within a braided river at the same time the invariance of nx and ny between braided rivers of different sizes and hydrology sedimentology suggests that the same anisotropic scaling as above applied to different riv ers will result in statistically similar images apart possibly from a normalization factor to account for the different mass of each river note that mass here refers to the area i e number of pixels covered with water the presence of such a statistical scale invariance in the spatial structure of braided rivers apart from being interesting in its own right might indicate the presence of universal features in the underlying mechanisms responsible for the formation of braided rivers and deserves further theoretical and experimental investiga tion braided rivers besides their complex geometry at any in stant of time are also highly dynamic systems characterized by intensive erosion sediment transport and deposition and fre quent channel shifting as they evolve predicting the evolution of braided rivers in terms of frequency and magnitude of chan nel shifting is of paramount importance where hydraulic struc tures or land developments are planned or where field use must be made of maps and air photos it is of great practical and theoretical value therefore to study the evolution of braided rivers in addition to their spatial structure in view of the evidence for spatial static scaling in braided rivers the question is asked here as to whether they also show dynamic scaling the presence of dynamic scaling would imply that space and time can be appropriately rescaled such that the evolution of the spatial structure of parts of the river of dif ferent size would be statistically indistinguishable the pres ence of dynamic scaling would also provide a highly desirable integrated framework for studying simultaneously the spatial and temporal structure of braided rivers

fluvial fan deltas linking channel processes with large scale morphodynamics 1 alluvial fan deltas are built by aggrading and avulsing river channels a numerical model of flow and sediment transport in channels is combined with a condition for channel avulsion to describe evolution of the fan surface the model combines elements of two recent approaches 1 diffusional models of depositional basin filling which describe the evolution of overall morphology and 2 cellular models of channel evolution which provide simplified descriptions of channel dynamics here the cellular formulation is used simply as a template for discretizing a standard set of equations describing flow and sediment transport within channels the basic formulation is thus grid invariant and the results are in actual rather than arbitrary time and length scales the model captures the interaction between microscale channel morphodynamics including converging and diverging flow and avulsion and morphodynamics at the macroscale fan it provides a starting point for the study of a wide range of topics including the three dimensional stratigraphy of fan delta deposits and the response of fan deltas to engineering activities

generalized hydraulic geometry insights based on fluvial instability analysis and a physical model 1 the power law dependencies between channel morphology and river flows known as at station hydraulic geometry hg have been recently shown to have exponents that systematically vary with scale contributing area to explain these empirical trends a generalized hg model whose parameters are explicit functions of scale was derived by dodov and foufoula georgiou 2004 based on a statistical multiscaling formalism in this paper we attempt to provide a physical explanation for this scale dependence the hypothesis we pose is that it arises from the scale dependence of fluvial instability which induces systematic variation in river planform geometry e g sinuosity meander wavelength and radius of curvature and consequent variations in channel cross sectional shape with scale in other words we postulate that the scale dependent hg is a direct consequence of the systematic increase of channel cross sectional asymmetry over reaches of increasing scale to test this hypothesis we employ both a direct analysis of observations and also a physical model of meandering rivers which is based on linearization of the fully coupled equations of mass and momentum balance for water and sediment we show that the hg emerging from this physical model is scale dependent and agrees with the empirical observations and the statistical multiscaling model

unusual strong ground motion across japan from the 680 km deep 30 may 2015 ogasawara islands earthquake the mw 7 9 earthquake beneath the ogasawara islands on 2015 may 30 at 680 km depth about 100 km deeper than other seismicity in the vicinity produced significant shaking over a broad area of japan in the epicentral distance range 1000 2000 km usually deep earthquakes in the subducting pacific slab develop a band of large ground motion along the east coast of northern japan due to efficient guiding of high frequency 1 hz waves in the subducting slab however for this very deep earthquake the large ground acceleration arises from relatively low frequency 1 hz s wave pulses with a long tail of long period 0 1 hz signals the arrival of the slab guided high frequency signal was very late and weak compared with normal pacific slab events numerical simulation of seismic wave propagation reveals that the observed low frequency pulses are the direct s wave from the very deep source followed by a large sv to p conversion at the free surface with near critical s wave incidence these phases produce a long period shear coupled pl s pl wave by constructive interference between wide angle p and s reflections in the crust and incoming s wave to the crust the s pl wave travels several hundred kilometers at regional distances with reinforcement from continuing s wave input from the very deep source such an unusual observation of strong low frequency strong ground motion was due to its very great source depth outside the main slab so the high frequency pacific slab guided wave was weak

the significance of long period ground motion at regional to teleseismic distances from the 610 km deep mw 8 3 sea of okhotsk earthquake of 24 may 2013 this study was conducted with support from grantsin aid from the japan society of promotion sciences 17 k01322

the search for a topographic signature of life landscapes are shaped by the uplift deformation and breakdown of bedrock and the erosion transport and deposition of sediment life is important in all of these processes over short timescales the impact of life is quite apparent rock weathering soil formation and erosion slope stability and river dynamics are directly influenced by biotic processes that mediate chemical reactions dilate soil disrupt the ground surface and add strength with a weave of roots over geologic time biotic effects are less obvious but equally important biota affect climate and climatic conditions dictate the mechanisms and rates of erosion that control topographic evolution apart from the obvious influence of humans does the resulting landscape bear an unmistakable stamp of life the influence of life on topography is a topic that has remained largely unexplored erosion laws that explicitly include biotic effects are needed to explore how intrinsically small scale biotic processes can influence the form of entire landscapes and to determine whether these processes create a distinctive topography

the mechanism of the deep bolivia earthquake of june 9 1994 we analyzed the iris broad band seismograms for the june 9 1994 bolivia earthquake the largest deep focus earthquake ever recorded we inverted the record sections with a duration of 330 sec which include p pp and sp phases and obtained a dip slip mechanism dip rake strike 13 4 1 or 89 103 95 with a scalar moment of mo 2 9 10 21 nm mw 8 2 this mechanism is similar to that obtained from long period 175 to 250 sec rayleigh and love waves 83 100 90 mo 3 0 10 21 nm mw 8 3 the main rupture was preceded by about 10 sec by a cluster of smaller events with a total moment of 1 2 10 20 nm mw 7 3 the main rupture starts at about 20 km east or northeast of the initial break and propagates horizontally in the east to northeast direction the source duration is 40 sec and the rupture dimension is about 40km if a fault area of 40 40km is assumed the stress drop is 110 mpa an inversion of body waves p pp and sp with 6 basis moment tensors yielded a best fit solution with a 10 implosive component this result is of marginal significance and its confirmation would require more detailed information on the structures near the source region pp bounce points and stations the observed amplitude of the radial mode 0s 0 1226 sec is consistent with a double couple model with less than 2 isotropic component

a generalized exner equation for sediment mass balance 1 the advance of morphodynamics research into new areas has led to a proliferation of forms of sediment mass balance equation without a general equation it is often difficult to know what these problem specific versions of sediment mass balance leave out to address this we derive a general form of the standard exner equation for sediment mass balance that includes effects of tectonic uplift and subsidence soil formation and creep compaction and chemical precipitation and dissolution the complete equation 17 allows for independent evolution of two critical interfaces that between bedrock and sediment or soil and that between sediment and flow by eliminating terms from the general equation it is straightforward to derive mass balance equations applicable to a wide range of problems such as short term bed evolution basin evolution bedrock uplift and soil formation and carbonate precipitation and transport dropping terms makes explicit what is not being considered in a given problem and can be done by inspection or by a formal scaling analysis of the terms scaling analysis leads directly to dimensionless numbers that measure the relative importance of terms in the equation for example the relative influence of spatial versus temporal changes in sediment load on bed evolution combining scaling analysis with time averaging shows how the relative importance of terms in the equation can change with timescale for example the term representing bed evolution due to temporal change in sediment load tends to zero as timescale increases

modeling s wave amplitude patterns for events in the kurile slab using three dimensional gaussian beams 1 the shear velocity structure of the subducted kurile slab is modeled using shear wave amplitude residual spheres we measure long period sh and scsh phase amplitudes for 10 intermediate and deep focus earthquakes recorded at world wide standardized seismograph network and canadian seismic network stations from 1967 to 1986 after correction for source radiation pattern geometric spreading and empirical receiver upper mantle effects the data for intermediate depth kurile slab events show smoothly varying amplitude residual sphere patterns with low amplitudes concentrated in the direction down the slab dip the data are modeled using three dimensional dynamic ray tracing and a three dimensional gaussian beam method starting models are taken from previous p and s wave arrival time residual sphere studies three dimensional ray tracing indicates that ray patterns and resulting amplitudes are very sensitive to the depth extent of the slab and to the position of the event relative to the across slab velocity gradient this sensitivity allows us to place some constraints on the kurile slab geometry position of each event within the slab and penetration depth of coherent slab structure our final slab model is defined by an asymmetric error function that peaks at 4 higher velocity than preliminary reference earthquake model 25 km from the top of the slab the total width of the thermal anomaly averages 140 km the slab is tabular and extends to 670 km in the northern half of the kurile subduction zone in the southern half of the subduction zone the slab flattens along the 670 km discontinuity and deflects laterally persisting to 750 km depth

a cellular model of braided rivers a broad sheet of water flowing over non cohesive sediment typically breaks up into a network of interconnected channels called a braided stream fig 1 the dynamics of such networks are complex channels migrate laterally split rejoin and develop bars with the flow shifting unpredictably from one part of the network to another many processes are known to operate in a braided river1 3 but it is unclear which of these are essential to explain the observed dynamics we describe here a simple deterministic numerical model of water flow over a cohesionless bed that captures the main spatial and temporal features of real braided rivers the patterns arise from local scour and deposition caused by a nonlinear dependence of bedload sediment flux on water discharge although the morphology of the resulting network depends in detail on the sediment transport rule used in the model our results suggest that the only factors essential for braiding are bedload sediment transport and laterally unconstrained free surface flow

toward a unified science of the earth s surface opportunities for synthesis among hydrology geomorphology geochemistry and ecology 1 the earth s surface is shaped by the interaction of tectonics water sediment solutes and biota over a wide range of spatial and temporal scales and across diverse environments development of a predictive science of earth surface dynamics integrates many disciplines and approaches including hydrology geomorphology ocean and atmospheric science sedimentary and structural geology geochemistry and ecology this paper discusses challenges opportunities and a few example problems that can serve as pathways toward this integration

teleseismic peak ground accelerations from the 24 may 2013 sea of okhotsk deep earthquake abstract the 2013 sea of okhotsk deep earthquake m w 8 3 which was recorded by many global seismic stations with adequate coverage of azimuth and distance provided an opportunity to understand the global characteristics of ground shaking peak ground accelerations pgas from the sea of okhotsk earthquake decreased with distance up to 120 and peaked at a distance of 140 150 the variation as a function of distance is similar to that of the 1994 bolivia earthquake pga values at distances between 40 and 85 are associated with vertical components of direct p waves and the values are in a range from 10 4 to 10 2 m s the average decay with distance agrees with that of the p wave amplitude predicted by the ray theory using lower mantle attenuation in a range of previously obtained models frequencies characterizing the pga decay are between 0 8 and 1 8 hz in agreement with observations from other deep earthquakes the p wave radiation pattern can affect the decay curves of pga with distance by changing the amplitude of p waves in the frequency range spatial variations in pga can depend on the tectonic setting large values of pga are observed in stable continents and old seas whereas small values are observed in tectonically active regions considering observations from the sea of okhotsk deep earthquakes it is likely that pga values have a positive correlation with shear velocity variations at depths of around 100 150 km below the stations

quantification of chemical weathering rates across an actively eroding hillslope abstract chemical weathering rates for landscapes are difficult to quantify because the timescales over which weathering occurs are often unknown in this study we use timescales defined by prior cosmogenic nuclide analyses and a suite of geochemical measurements to calculate weathering rates in saprolite and soil and to determine how these rates vary across an eroding hillslope we also estimate the relative contributions of solute and erosional mass loss to landscape lowering analyses were conducted on a soil mantled hillslope developed on a granodiorite pluton in southern nsw australia mass loss in solution accounts for 35 to 55 of the total mass loss from the hillslope saprolite close to the soil saprolite boundary is less weathered at the ridge than at distance from the ridge the calculated flux of silica from the saprolite is 5 tons km 2 yr 1 and does not vary with distance from the ridge or overlying soil thickness the assumption of steady state but spatially variable erosion rates with a temporally constant thickness of soil and saprolite allows us to calculate the downslope variation in the rate of solute losses soil silica weathering rates initially increase from 12 tons km 2 yr 1 at the ridge crest to 20 tons km 2 yr 1 on the convex region of the hillslope and then decrease to 13 tons km 2 yr 1 by the time soils have been transported 45 50 m soils closer to the surface are more weathered than deeper soils this geochemical stratification suggests that the soil column does not become thoroughly vertically mixed as soils move down slope dependence of solute loss on transport distance may explain the previously noted discrepancy between the observed soil thickness and that predicted based on curvature variation of solute loss with transport distance may also contribute to the linear dependence of soil thickness on distance from the ridge

rupture complexity of the 1994 bolivia and 2013 sea of okhotsk deep earthquakes the physical mechanism of deep earthquakes depth 300 km remains enigmatic partly because their rupture dimensions are difficult to estimate due to their low aftershock productivity and absence of geodetic or surface rupture observations the two largest deep earthquakes the recent great 2013 sea of okhotsk earthquake m 8 3 depth 607 km and the great 1994 bolivia earthquake m 8 3 depth 637 km together provide a unique opportunity to compare their rupture patterns in detail here we extend a travel time sub event location method to perform full teleseismic p waveform inversion this new method allows us to explain the observed broadband records with a set of sub events whose model parameters are robustly constrained without smoothing we find that while the okhotsk event is mostly unilateral rupturing 90 km along strike with a velocity over 4 km s the bolivia earthquake ruptured about half this distance at a slow velocity about 1 5 km s and displayed a major change in rupture direction we explain the observed differences between the two earthquakes as resulting from two fundamentally different faulting mechanisms in slabs with different thermal states phase transformational faulting is inferred to occur inside the metastable olivine wedge within cold slab cores whereas shear melting occurs inside warm slabs once triggered