shear wave splitting and subcontinental mantle deformation splitting observations are interpreted in terms of the strain induced lattice preferred orientation of mantle minerals especially olivine we consider three hypotheses concerning the origin of the continental anlsotropy 1 strain associated with absolute plate motion as in the oceanic upper mantle 2 crustal stress and 3 the past and present internal deformation of the subcontinental upper mantle by tectonic episodes it is found that the last hypothesis is the most successful namely that the most recent significant episode of internal deformation appears to be the best predictor of q for stable continental regions this is interpreted as fossil anisotropy whereas for presently active regions such as alaska the anisotropy reflects present day tectonic activity in the stable portion of north america there is a good correlation between delay time and lithospheric thickness this is consistent with the anisotropy being localized in the subcontinental lithosphere and suggests that intrinsic anisotropy is approximately constant the acceptance of this hypothesis has several implications for subcontinental mantle deformation first it argues for coherent deformation of the continental lithosphere crust and mantle during orogenies this implies that the anisotropic portion of the lithosphere was present since the deformational episode and rules out the addition of undeformed material to this layer by subsequent underplating or conductive growth of the thermal boundary layer one of the most important issues in the study of orogenies is the need to reconcile the formation of thickened lithosphere with the paradoxically high mantle temperatures often associated with orogenic episodes most efforts to date have focussed on modes of deformation whereby the cold lithospheric mantle is removed by convective instability or delamination and replaced by warm asthenosphere these models however are incompatible with the evidence for preserved coherent lithospheric deformation rather the deformed mantle appears to have been heated in place we suggest that the elevated mantle temperatures may be due to the strain heating accompanying the deformation

functional soil landscape modelling to estimate slope stability in a steep andean mountain forest region abstract landslides are a common phenomenon within the ecuadorian andes and have an impact on soil landscape formation landslide susceptibility was determined in a steep mountain forest region in southern ecuador soil mechanical and hydrological properties in addition to terrain steepness were hypothesised to be the major factors in causing soil slides hence the factor of safety fs was calculated as the soil shear ratio that is necessary to maintain the critical state equilibrium on a potential sliding surface regression tree rt and random forest rf models were compared in their predictive force to regionalise the depth of the failure plane and soil bulk density based on terrain parameters the depth of the failure plane was assumed at the lower boundary of the stagnic soil layer or soil depth respectively depending on soils being stagnic or non stagnic fs was determined in dependence of soil wetness referring to 0 001 0 01 0 1 and 3 mm h 1 net rainfall rates sites with fs 1 at 3 mm h 1 complete saturation were classified as unconditionally stable sites with fs 1 as unconditionally unstable bulk density and the depth of the failure plane were regionalised with rf which performed better than rt terrain parameters explained the spatial distribution of soil bulk density and the depth of the failure plane only to a relatively small extent which is reasonable due to frequent translocation of soil material by landslides nevertheless their prediction uncertainty still allowed for a reasonable prediction of unconditionally unstable sites

linking hydrological infinite slope stability and land use change models through gis for assessing the impact of deforestation on slope stability in high andean watersheds in the ecuadorian andes episodic slope movements comprising shallow rotational and translational slides and rapid flows of debris and soil material are common consequently not only considerable financial costs are experienced but also major ecological and environmental problems arise in a larger geographical area sediment production by slope movement on hillslopes directly affects sediment transport and deposition in downstream rivers and dams and morphological changes in the stream channels in developing countries world wide slope movement hazards are growing increasing population pressure and economic development force more people to move to potentially hazardous areas which are less suitable for agriculture and rangelands this paper describes the methods used to determine the controlling factors of slope failure and to build upon the results of the statistical analysis a process based slope stability model which includes a dynamic soil wetness index using a simple subsurface flow model the model provides a time varying estimate of slope movement susceptibility by linking land use data with spatially varying hydrologic soil conductivity evapotranspiration soil wetness and soil strength properties the slope stability model was applied to a high andean watershed gordeleg catchment 250 ha southern ecuadorian andes and was validated by calculating the association coefficients between the slope movement susceptibility map of 2000 and the spatial pattern of active slope movements as measured in the field with gps the proposed methodology allows assessment of the effects of past and future land use change on slope stability a realistic deforestation scenario was presented past land use change includes a gradual fragmentation and clear cut of the secondary forests as observed over the last four decades 1963 2000 future land use change is simulated based on a binary logistic deforestation model whereby it was assumed that future land use change would continue at the same rate and style as over the last 37 years 1963 2000 c 2002 elsevier science b v all rights reserved

the depth distribution of mantle anisotropy beneath the tonga subduction zone abstract shear wave splitting recorded by a temporary deployment of broadband seismometers located above the tonga subduction zone yields strong constraints on the depth distribution of anisotropy in the mantle beneath the tonga back arc region splitting parameters obtained for local s and teleseismic sks phases were modeled using a ray based method that predicts shear wave splitting on individual phase paths and determines the best fitting values of anisotropic strength orientation and depth extent splitting in teleseismic sks phases is identical to that in s phases from local earthquakes that occur at the base of the transition zone demonstrating that there is no significant splitting due to anisotropy in the lower mantle splitting times for local s phases do not vary significantly with depth and for models in which the strength of anisotropy is laterally uniform they rule out anisotropy in the transition zone finally the observed splitting indicates that anisotropy of more than 0 8 exists in the upper mantle with a fast symmetry axis at 60 w roughly parallel to the absolute plate motion vector of the subducting pacific lithosphere

trench parallel flow beneath the nazca plate from seismic anisotropy shear wave splitting of s and sks phases reveals the anisotropy and strain field of the mantle beneath the subducting nazca plate cocos plate and the caribbean region these observations can be used to test models of mantle flow two dimensional entrained mantle flow beneath the subducting nazca slab is not consistent with the data rather there is evidence for horizontal trench parallel flow in the mantle beneath the nazca plate along much of the andean subduction zone trench parallel flow is attributale utable to retrograde motion of the slab the decoupling of the slab and underlying mantle and a partial barrier to flow at depth resulting in lateral mantle flow beneath the slab such flow facilitates the transfer of material from the shrinking mantle reservoir beneath the pacific basin to the growing mantle reservoir beneath the atlantic basin trenchparallel flow may explain the eastward motions of the caribbean and scotia sea plates the anomalously shallow bathymetry of the eastern nazca plate the long wavelength geoid high over western south america and it may contribute to the high elevation and intense deformation of the central andes

current plate velocities relative to the hotspots incorporating the nuvel 1 global plate motion model nuvel 1 is a new global model of current relative plate velocities demets et al 1990 which differ significantly from those of prior models here we incorporate nuvel 1 into hs2 nuvel1 a new global model of plate velocities relative to the hotspots hs2 nuvel1 was determined from the hotspot data and errors used by minster and jordan 1978 to determine am1 2 which is their model of plate velocities relative to the hotspots am1 2 is consistent with minster and jordan s relative plate velocity model rm2 here we compare hs2 nuvel1 with am1 2 and examine how their differences relate to differences between nuvel 1 and rm2 hs2 nuvel1 plate velocities relative to the hotspots are mainly similar to those of am1 2 minor differences between the two models include the following 1 in hs2 nuvel1 the speed of the partly continental apparently non subducting indian plate is greater than that of the purely oceanic subducting nazca plate 2 in places the direction of motion of the african antarctic arabian australian caribbean cocos eurasian north american and south american plates differs between models by more than 10 3 in places the speed of the australian caribbean cocos indian and nazca plates differs between models by more than 8 mm yr although 27 of the 30 rm2 euler vectors differ with 95 confidence from those of nuvel 1 only the am1 2 arabia hotspot and india hotspot euler vectors differ with 95 confidence from those of hs2 nuvel1 thus substituting nuvel 1 for rm2 in the inversion for plate velocities relative to the hotspots changes few euler vectors significantly presumably because the uncertainty in the velocity of a plate relative to the hotspots is much greater than the uncertainty in its velocity relative to other plates

a physically based model for the topographic control on shallow landsliding a model for the topographic influence on shallow landslide initiation is developed by coupling digital terrain data with near surface through flow and slope stability models the hydrologic model topog o loughlin 1986 predicts the degree of soil saturation in response to a steady state rainfall for topographic elements defined by the intersection of contours and flow tube boundaries the slope stability component uses this relative soil saturation to analyze the stability of each topographic element for the case of cohesionless soils of spatially constant thickness and saturated conductivity the steady state rainfall predicted to cause instability in each topographic element provides a measure of the relative potential for shallow landsliding the spatial distribution of critical rainfall values is compared with landslide locations mapped from aerial photographs and in the field for three study basins where high resolution digital elevation data are available tennessee valley in marin county california mettman ridge in the oregon coast range and split creek on the olympic peninsula washington model predictions in each of these areas are consistent with spatial patterns of observed landslide scars although hydrologic complexities not accounted for in the model e g spatial variability of soil properties and bedrock flow control specific sites and timing of debris flow initiation within areas of similar topographic control

landslides in the central coalfield cantabrian mountains nw spain geomorphological features conditioning factors and methodological implications in susceptibility assessment abstract a geomorphological study focussing on slope instability and landslide susceptibility modelling was performed on a 278 km2 area in the nalon river basin central coalfield nw spain the methodology of the study includes 1 geomorphological mapping at both 1 5000 and 1 25 000 scales based on air photo interpretation and field work 2 digital terrain model dtm creation and overlay of geomorphological and dtm layers in a geographical information system gis and 3 statistical treatment of variables using spss and development of a logistic regression model a total of 603 mass movements including earth flow and debris flow were inventoried and were classified into two groups according to their size this study focuses on the first group with small mass movements 100 to 101 m in size which often cause damage to infrastructures and even victims the detected conditioning factors of these landslides are lithology soils and colluviums vegetation pasture and topography dtm analyses show that high instabilities are linked to slopes with ne and sw orientations curvature values between 6 and 0 7 and slope values from 16 to 30 bedrock lithology carboniferous sandstone and siltstone presence of quaternary soils and sediments vegetation and the topographical factors were used to develop a landslide susceptibility model using the logistic regression method application of zoom method allows us to accurately detect small mass movements using a 5 m grid cell data even if geomorphological mapping is done at a 1 25 000 scale

late quaternary erosion events in lowland and mid altitude tasmania in relation to climate change and first human arrival abstract the establishment of a chronology of landscape forming events in lowland and mid altitude tasmania essential for assessing the relative importance of climatic and human influences on erosion and for assessing present erosion risk has been limited by the small number of ages obtained and limitations of dating methods in this paper we critically assess previous tasmanian studies list published radiocarbon ages considered to be dependable present new radiocarbon and thermoluminescence tl ages for 25 sites around tasmania and consider the evidence for the hypotheses that erosion processes at low and mid altitudes have been 1 purely climatically controlled and 2 influenced both by climatic and anthropogenic increased fire frequency effects a total of 94 dependable finite ages calibrated for radiocarbon and as measured for tl and optically stimulated luminescence osl determinations are listed for deposits comprising dunes colluvium alluvium and loess like aeolian deposits two fall in the 100 ka period 15 fall in the period 65 35 ka and 77 fall in the period 35 0 3 ka there was a sustained increase in erosion recorded in the period 35 15 ka as reflected by a greater number of dated aeolian deposits during this period we considered three possible biases that may have affected the age distribution obtained the limitations of radiocarbon dating sampling bias and preservation bias sampling bias may have favoured more recent dune strata but radiocarbon dating and preservation biases are unlikely to have significantly distorted the age distribution obtained long but intermittent aeolian deposition is recorded at two sites southwood b c 59 28 ka and dunlin dune c 29 14 ka but there is no evidence of regional loess deposits such as found in new zealand the timing of increased erosion in tasmania between 35 and 30 ka approximately coincides with the intermittent ten fold increase of dust accumulation between 33 and 30 ka in the antarctic dome c ice core the absence of widespread erosion before 35 ka the abrupt increase of erosion around this time the frequent association of erosion products with charcoal the arrival of people in tasmania at c 40 cal ka and the known use of fires by aborigines to maintain areas of non climax vegetation suggest that ecosystem disturbance by anthropogenic fires in a drier climate than that presently prevailing may have contributed to erosion in lowland and mid altitude tasmania after 35 ka thus the tasmanian erosion record provides circumstantial support for the proposition that human dispersal in southeast australia was accompanied by significant ecological change

frequency dependent anisotropy in wellington new zealand shear wave splitting measurements are made using teleseismic s scs and sks waveforms recorded at the gdsn broadband station snzo situated in south karori new zealand the average s and sks delay times are around 2 to 3 s among the highest in the world the average scs delay time is significantly smaller around 1 s this discrepancy appears to be due to differences in dominant frequency the most likely cause of frequency dependent anisotropy is oriented heterogeneities with a scale length much smaller than the wavelength the fast polarizations range between 21 and 79 with an average ne sw direction which is sub parallel to the trend of the local geologic structure and the strike of the hikurangi subduction zone azimuthal variations in delay time which cannot be explained by differences in period may be due to a dipping axis of symmetry or laterally varying anisotropy or a more complicated symmetry system

neotectonics of the sumatran fault indonesia the 1900 km long trench parallel sumatran fault accommodates a significant amount of the right lateral component of oblique convergence between the eurasian and indian australian plates from 10 n to 7 s our detailed map of the fault compiled from topographic maps and stereographic aerial photographs shows that unlike many other great strike slip faults the sumatran fault is highly segmented cross strike width of step overs between the 19 major subaerial segments is commonly many kilometers the influence of these step overs on historical seismic source dimensions suggests that the dimensions of future events will also be influenced by fault geometry geomorphic offsets along the fault range as high as 20 km and may represent the total offset across the fault if this is so other structures must have accommodated much of the dextral component of oblique convergence during the past few million years our analysis of stretching of the forearc region near the southern tip of sumatra constrains the combined dextral slip on the sumatran and mentawai faults to be no more than 100 km in the past few million years the shape and location of the sumatran fault and the active volcanic arc are highly correlated with the shape and character of the underlying subducting oceanic lithosphere nonetheless active volcanic centers of the sumatran volcanic arc have not influenced noticeably the geometry of the active sumatran fault on the basis of its geologic history and pattern of deformation we divide the sumatran plate margin into northern central and southern domains we support previous proposals that the geometry and character of the subducting investigator fracture zone are affecting the shape and evolution of the sumatran fault system within the central domain the southern domain is the most regular the sumatran fault there comprises six right stepping segments this pattern indicates that the overall trend of the fault deviates 4 clockwise from the slip vector between the two blocks it separates the regularity of this section and its association with the portion of the subduction zone that generated the giant m w 9 earthquake of 1833 suggest that a geometrically simple subducting slab results in both simple strike slip faulting and unusually large subduction earthquakes

shear wave anisotropy in the mariana subduction zone to determine the location strength and orientation of seismic anisotropy in the mariana subduction zone beneath guam we evaluated shear wave splitting in local s regional s and scs and teleseismic core phases such as sks recorded at station gumo fast directions from the local s phases have an average azimuth of 45 and splitting times range from 0 1 s to 0 4 s for local s phases from events within the southeastern half of the subducting slab splitting parameters manifest minimal frequency dependence in both fast direction and splitting time however for the remaining local s phases in the data set fast directions vary with frequency content no well constrained splitting parameters were obtained for the regional and teleseismic phases but the particle motions of these unsplit phases are consistent with an average anisotropic fast direction of 45 anisotropy due solely to olivine oriented by slab entrained flow in the mantle wedge would produce local s fast directions at 66 and anisotropy due solely to fossil seafloor spreading in the subducting slab would yield fast directions at 20 to 30 neither of these predictions is consistent with the observed fast directions however the observed splitting including the frequency dependent fast directions can be explained by models containing anisotropy in both the slab and wedge and possibly although not necessarily anisotropy due to recent extension in the overriding philippine sea plate

soil properties on a chronosequence of landslides in montane rain forest ecuador to assess the impact of landslides on soil fertility in south ecuador we compared the properties of shallow translational debris slides with those of adjacent undisturbed soils a chronosequence of four small landslides ca 0 5 ca 2 3 ca 8 10 and ca 20 years old was selected on a 30 50 forest covered east facing slope of the eastern cordillera at 1900 2300 m above sea level a s l all soils were dystric cambisols the mean mass of the soil organic layer sum of all o horizons increased in the order landslide head 46 t ha 1 central part track 101 t ha 1 foot 102 t ha 1 reference soils 291 t ha 1 implying a variation in nutrient storage of the same order in the head area only the oldest landslide had an organic layer all mineral soils were acidic ph in h2o of the a horizon 3 4 5 2 the effective cec of the a horizon ranged from 22 to 141 mmolc kg 1 and the base saturation from 13 to 54 none of these properties was consistently different between landslide and reference soils the a horizons of the soil in the landslide foot area had greater concentrations of most nutrients than those in the landslide head area however differences were not significant the nutrient concentrations in the landslide foot area resembled those in the a horizons of the reference soils thus the most obvious change in soil properties caused by the landsliding was partial or complete removal of the organic layer which was not restored during the ca 20 years covered by the chronosequence this decreased the topsoil fertility of the landslide area

a distributed slope stability model for steep forested basins a distributed physically based slope stability model dslam based on an infinite slope model a kinematic wave groundwater model and a continuous change vegetation root strength model is presented it is integrated with a contour line based topographic analysis and a geographic information system gis for spatial data extraction and display the model can be run with either individual rainfall events or long term sequences of storms these inputs can be either actual storm records or synthesized random events based on monte carlo simulation the model is designed to analyze rapid shallow landslides and the spatial distribution of safety factor fs in steep forested areas it can investigate the slope stability problem in both temporal and spatial dimensions for example the impact of timber harvesting on slope stability either at a given time or through an extended management period the probability of landslide occurrence for a given year and the delivery of landslide sediments to headwater streams the dslam model was applied in a steep forested drainage of cedar creek in the oregon coast ranges using actual spatial patterns of timber harvesting and measured rainfall during a major storm which triggered widespread landslides in that area in 1975 simulated volume and number of failures were 733 m3 and 4 respectively these values agreed closely with field measurements following the 1975 storm however the effect of parameter uncertainty may complicate this comparison for example when soil cohesion values of 2 0 and 3 0 kpa were used the failure volume changed by factors of 2 04 and 0 41 respectively compared with the average condition of 2 5 kpa used in the simulation for soil depths 30 higher and lower than the standard condition the failure volume changed by factors of 2 0 and 0 27 respectively when maximum root cohesion changed from 12 5 kpa average condition to 10 kpa the failure volume increased 1 73 fold for the case of 15 kpa the failure volume changed by a factor of 0 55 the simulated failures caused by the storm were mostly in hollows the simulations show that the spatial distribution of fs is controlled mainly by topography and timber harvesting patterns and is greatly affected by groundwater flow patterns during major rainstorms most areas with fs 3 0 corresponded with the distribution of blocks clear cut in 1968 and all elements with fs 2 0 were in areas clear cut in 1968 areas with low fs 1 0 1 6 expanded dramatically during the rainstorm and decreased at a slow rate after the storm factors of safety in hollows declined sharply during the storm

teleseismic imaging of subaxial flow at mid ocean ridges traveltime effects of anisotropic mineral texture in the mantle summary deformation of peridotite caused by mantle flow beneath an oceanic spreading centre can result in the development of seismic anisotropy traveltime anomalies and shearwave splitting will develop as seismic energy propagates through such an anisotropic region thus providing a signature of the deformation field at depth in this study we investigate the nature of deformation associated with mantle upwelling for two models of flow in the upper 100 km of the mantle the finite strain fields of the passive upwelling model versus the buoyancy enhanced upwelling model are quite different this suggests that mineral aggregates deform differently in the two models thus developing seismic signatures that are distinguishable numerical estimates of the corresponding mineral textures are made using polycrystal theory for olivine with four operative slip systems the activation of a slip system is determined for each grain on the basis of the local critical resolved shear stress the computed grain deformation reflects a balance between stress equilibrium for the aggregate as a whole and strain continuity between neighbouring grains within the aggregate this approach enables a direct link to be made between the model flow fields and the resulting texture development given these mineral orientation distributions elastic parameters are calculated and wavefronts are propagated through the anisotropic structure traveltimes for teleseismic body waves are computed using ray theory and amplitudes are estimated for an across axis profile extending 100 km from the ridge axis relative p wave residuals of up to 1 s are predicted for the buoyant model with on axis arrivals being earliest since near vertical velocities are fastest beneath the axis on axis p wave arrivals for the passive model are half a second earlier than arrivals 60 km off axis and relative delays continue to increase slowly as distance from the ridge increases s wave splitting of almost a second is predicted for the buoyant model whereas less than a half second of splitting is determined for the passive model

shear wave splitting near guam abstract polarities of shear waves from intermediate focus events underneath guam are studied for records from a group of ten events shear wave splitting with faster arriving e w components are observed this event group occurred within or above one geographic portion of the wadati benioff zone with depths ranging between 57 and 148 km ray tracing calculations were performed for 3 d and 1 d velocity models constructed for the region to determine expected s wave polarities and ray patterns as well as their sensitivities to variations in velocity structure these were used to infer the probable existence of intrinsic anisotropy at depth and to determine the location and magnitude of anisotropy which can explain the observed shear wave splitting the most probable location of the anisotropy is beneath the crust and above or partially within the subducting slab assuming a maximum depth range of 10 120 km for the location of the anisotropy its amount is about 1 which may be viewed as a lower bound plausible causes of the anisotropy include mantle flow and thin sheet like channels filled with lava or water vapor migrating upward from the subducting slab

making use of the world reference base diagnostic horizons for the systematic description of the soil continuum application to the tropical mountain soil landscape of southern ecuador abstract the world reference base for soil resources wrb fao iuss working group wrb 2007 at present does not acknowledge the spatial soil continuum but provides a sound basis to do so using methods from statistical learning theory to develop digital soil maps is much more efficient and precise while regionalising soil diagnostic properties instead of complex entities such as the soil units assigned by the wrb particularly in providing spatial soil information displayed in digital soil maps any aggregation of this spatial soil information to soil units means a loss of information the soil landscape can be systematically described in its spatial continuum simply by the vertical order and extent of the wrb diagnostic horizons the diagnostic horizons are related in their thickness to a standard depth and listed from top to bottom in order of appearance typical diagnostic horizon thickness and occurrence probability were predicted from terrain parameters by classification and regression trees cart throughout the research area in southern ecuador the two disadvantages of cart abrupt prediction class boundaries and dependence on the dataset were addressed by hundredfold model runs on different data subsets leading to a range of possible predictions prediction uncertainty was included in the digital soil maps by calculating these predictions means and standard deviations as well as by horizon occurrence probability prediction model performance was evaluated by means of hundredfold external cross validation terrain parameters were found to have a strong influence on diagnostic topsoil properties however no influence on the vertical profile differentiation was observed hence predicting horizon thickness and subsoil diagnostic properties was difficult the systematic description of the soil continuum of this particular soil landscape resulted in histic and stagnic soil parts dominating the first 100 cm of the soil column for most of the area

seismic anisotropy and mantle flow seismic anisotropy in the mantle is primarily due to deformation induced lattice preferred orientation lpo of olivine crystals the aim of this paper is to better understand how such lpo is produced by flow and to learn whether observations of seismic anisotropy can be used to infer the local direction of flow within the mantle the basis of the work is a two dimensional theory which describes how lpo evolves during an arbitrary time dependent deformation ribe 1989 i investigate the evolution of lpo beneath ocean ridges above subducted slabs and in thermal convective flows the ocean ridge model predicts that the seismic anisotropy produced at a fast spreading ridge should be greater in magnitude than that produced at a slow spreading ridge and that the fast axis should be more nearly horizontal the subduction zone model predicts that strong seismic anisotropy should be produced above subducted slabs with the fast axis aligned with the slab regardless of the subduction angle the evolution of lpo in typical convective flows is extremely complex and depends strongly on such factors as the mode of heating and the surface boundary conditions in general there is no simple relation between the lpo and the local flow direction in any of the models considered the attempt to use seismic anisotropy to map flow patterns on a global scale is therefore probably unwarranted however the lpo does become aligned with the flow direction when the flow is a progressive simple shear such a flow occurs in limited portions of the mantle beneath the lithosphere at a fast spreading ridge above subducted slabs and in boundary layers beneath rigid surfaces such as continents observations of seismic anisotropy may therefore indicate the sense of shear at shallow depths in the mantle

mantle anisotropy beneath northwest pacific subduction zones to assess the location strength and orientation of seismic anisotropy in the southern kuril japan and izu bonin subduction zones we analyzed shear wave splitting in local s phases and teleseismic sks phases fast directions from these phases are roughly parallel to the direction of absolute pacific plate motion wnw in izu bonin roughly parallel to the strike of the trench nne in central honshu and roughly n in the southern kuril back arc in the vicinity of sakhalin island assuming that the orientation and strength of anisotropy does not vary with depth modeling of splitting times from local s and teleseismic phases recorded at sakhalin island requires that the maximum depth of anisotropy lies between 480 km and 950 km in contrast splitting times for local s phases from events in izu bonin rule out anisotropy in the transition zone all the data are consistent with a model in which the lower transition zone 520 660 km and lower mantle are largely isotropic and in which anisotropy occurs intermittently in the upper transition zone 410 520 km possibly due to preferred orientation of spinel assuming that splitting in the upper mantle is produced by preferred orientation of olivine the observed fast directions indicate that the geometry of back arc strain varies systematically between subduction zones the relationship of fast directions and plate motions suggests that the subducting slab exerts significant control on back arc flow but that flow correlated with upper plate deformation must also exist

evolution of the mariana convergent plate margin system the mariana convergent plate margin system of the western pacific provides opportunities for studying the tectonic and geochemical processes of intraoceanic plate subduction without the added complexities of continental geology the system s relative geologic simplicity and the well exposed sections of lithosphere in each of its tectonic provinces permit in situ examination of processes critical to understanding subduction tectonics its general history provides analogs to ancient convergent margin terranes exposed on land and helps to explain the chemical mass balance in convergent plate margins the mariana convergent margin s long history of sequential formation of volcanic arcs and extensional back arc basins has created a series of volcanic arcs at the eastern edge of the philippine sea plate the trenchward edge of the overriding plate has a relatively sparse sediment cover rocks outcropping on the trench s inner slope are typical of the early formed suprasubduction zone s lithosphere and have been subjected to various processes related to its tectonic history pervasive forearc faulting has exposed crust and upper mantle lithosphere many large serpentinized peridotite seamounts are within 100 km of the trench axis from these we can learn the history of regional metamorphism and observe and sample active venting of slab fluids ocean drilling recovered suprasubduction zone lava sequences erupted since the eocene that suggest that the forearc region remains volcanologically dynamic seismic studies and seafloor mapping show evidence of deformation throughout forearc evolution large portions of uplifted southern forearc are exposed at the larger islands active volcanoes at the base of the eastern boundary fault of the mariana trough vary in size and composition along strike and record regional differences in source composition their locations along strike of the arc are controlled in part by cross arc structures that also facilitate formation of submarine volcano chains extending from the base of the fault westward into the back arc basin the western boundary is the west mariana ridge the western portion of the volcanic arc active prior to formation of the mariana trough the trough evolved in a two stage extension process of rifting and subsequent seafloor spreading the back arc basin varies along strike from rifted arc lithosphere with scattered volcanoes but no real spreading center in the north to a complex mid ocean type spreading center south of 20 n the change from initial rifting to true seafloor spreading is also evident across the mariana trough from rifted topography near the west mariana ridge to spreading ridges in the central to eastern basin south of 20 n this morphologic change indicates an early stage of extension with basin and range type topography predominant and volcanism restricted to fissure eruptions along fault block boundaries the spreading ridges and abyssal hill morphology evolved later as new lithosphere was generated at elongate volcanic ridges located in the center of rift valleys the center of extension intersects the active volcanic front differently at either end of the mariana trough in the north extension is by rifting of arc lithosphere where it intersects the arc in the south a major strike slip fault extends from the trench axis across the forearc through the volcanic arc and into the back arc basin arc magmas apparently leak along this fault zone into the forearc and the back arc spreading center the complexity of interrelated tectonism and magmatism in this convergent margin is daunting but studies of arc systems such as this provide the best hope of interpreting many of the exposed terranes accreted to continents comparison of subaerial terranes with recent studies of intraoceanic convergent margins will add to our understanding of plate interactions and of the evolution of the volcanic arcs and extensional back arc basins generated within such environments

the role of woody vegetation in stabilizing slopes in the cincinnati area ohio tree roots markedly stabilize colluvium on steep hillsides in the cincinnati area ohio according to detailed analysis of a landslide complex on the south side of rapid run creek a tributary of the ohio river the shear surface of the slide developed near the interface between bouldery silty clay colluvium and underlying calcareous ordovician shale and it broke woody roots that penetrated through the colluvium and into the underlying bedrock measurements of positions sizes and tensile strengths of the roots indicate that the average shear strength contributed by the roots was about 5 7 kn m 2 of the shear surface the average strength contributed by residual friction of the soil was about 0 7 kn m 2 the tree roots increased the factor of safety against sliding nine fold root strength allows forested colluvium mantled hillslopes in the cincinnati area to resist sliding at slope angles as high as 35 whereas similar slopes devoid of trees are subject to sliding at slope angles of 12 to 14 the contribution of tree roots to slope stability should be evaluated before removal of trees for development of hillsides

quantitative analysis of land surface topography land surface topography significantly affects the processes of runoff and erosion a system which determines slope aspect and curvature in both the down slope and across slope directions is developed for an altitude matrix also the upslope drainage area and maximum drainage distance are determined for every point within the altitude matrix a fortran 66 program performs the analysis