detection of lower mantle scatterers northeast of the marianna subduction zone using short period array data short period university of washington northern california and southern california seismic array records of a sequence of deep mariana subduction zone earthquakes show unexpected clear arrivals nearly 90 and 105 s following p we measure slowness arrival time and arrival azimuth of these phases relative to p using array techniques to find where they emanate in the mantle by combining slowness and back azimuth deviations and the move out with depth of the arrivals from different earthquakes we find their most probable origin is through s to p conversion at point scatterers in the mid to lower mantle at 25 7 n 148 2 e 1590 km and 25 5 n 151 0 e 1850 km respectively separated by 300 km these features indicate elastically distinct material in the middle of the lower mantle which if fragments of subducted slabs are not related to contemporary subduction they may represent upwelling convective material from the deep mantle or d but they are not purely thermal in nature as chemically distinct bodies they may represent potential reservoirs of the isotopic and trace element components recognized geochemically

small scale heterogeneity at the top of the lower mantle around the mariana slab abstract short period waveform data recorded at the western us seismic array for 14 mariana deep earthquakes near 19 n show two anomalous wave packets within about 30 s after the arrival of the direct p wave simply called p or p wave one at about 13 s called x1 phase and the other around 29 s called x2 phase we perform array analyses to locate the sources of these phases in the first step we measure arrival time slowness back azimuth and amplitude of these phases relative to p the amplitudes of the x1 and x2 phases correlate with each other for the individual events and vary more than an order of magnitude among the events which cluster in a region spanning less than 50 km the amplitude correlation suggests that the two waves have a similar origin and the large amplitude variation eliminates receiver side reverberation as the origin of the phases the x1 phase has a slowness and an arrival azimuth which are not distinguished from those of p waves across the entire array and has nearly constant delay times regardless of the focal depths from 567 to 605 km the x2 phase arrives as a more emergent wave packet with slowness and azimuth different from those of p in the second step we compute composite semblance coefficients for the cases of p to p and s to p single scattering near the foci the x1 and x2 phases are best interpreted as s to p scattered waves generated in the uppermost lower mantle north of the focal region based on three observations 1 highest composite semblance values 2 scatterer locations mutually consistent between the two event groups near the depths of 500 and 600 km and 3 a reasonable amount of elastic property anomalies required the x1 phase scatterer is determined at 19 8 0 3 n 145 7 0 3 e 710 30 km on the other hand the scatterer of the x2 phase appears to split into two objects one at 20 4 0 4 n 145 4 1 0 e 900 80 km and the other at 20 6 0 4 n 147 4 0 5 e 860 40 km although the geometries of the scatterers of x1 and x2 phases are not constrained horizontal or subhorizontal discontinuities are unlikely the changes in elastic properties associated with these heterogeneous objects probably occur within several kilometers according to their high efficiency at converting short period waves they are thus likely to represent sharp chemical variations in major element composition these objects are located within a thickened high velocity anomaly at the top of the lower mantle which has been determined by previous seismic studies a plausible tectonic interpretation of these objects is that they are fragments of former oceanic crust which are entrained in the pacific slab impinging on the more viscous lower mantle

small scale heterogeneity in the mid lower mantle beneath the circum pacific area abstract data from a western united states short period seismic network are investigated in order to detect anomalous later p wave arrivals within a time window from 50 s to 170 s after direct p waves for deep and intermediate depth earthquakes at circum pacific subduction zones we interpret the anomalous arrivals as s to p scattered waves from heterogeneities in the mid lower mantle the searched regions depths from 4800 km to 2200 km cover approximately 2 of the entire lower mantle the heterogeneous scattering objects are located by array processing of the seismic waves using semblance with careful investigations of arrival time slowness and azimuth of the later phases relative to direct p waves we usually observe two or three later phases which are separated in arrival time by 5 20 s and have similar arrival azimuth and slowness this observation suggests that a few scatterers often form a cluster with a typical spacing of 100 200 km vertically more than ten clusters or groups of s to p scattering objects are detected in the mid lower mantle beneath the circum pacific regions northern kuril izu bonin mariana northern fiji and west coast of south america the s to p scattering objects are found in a depth range from 1100 to 1800 km and the most prominent objects of each region tend to be located around the middle of the depth range the amplitudes of the scattered waves range from 1 to 10 of the direct p waves with exceptionally large values as large as 40 the associated magnitudes of the changes in elasticity is not tightly constrained but probably are nearly 1 and may occasionally exceed 4 of shear velocity considering their high efficiency at converting short period waves wavelengths of 5 10 km the changes in elastic properties at the heterogeneous objects appear to occur within several kilometers seismic tomography studies have not detected prominent seismic wave speed anomalies except for those beneath south america which appear to be located in the former farallon plate and those at north of fiji which appear to be located around the pacific superplume the mid lower mantle heterogeneity should represent sharp chemical variations in major element composition of the lower mantle rocks the most plausible tectonic explanation of the variations is remnant of subducted and folded former oceanic crust which preceded the current subduction of the pacific plate the extreme estimates of low shear velocity 4 may indicate the prominent drops in the shear modulus due to ferro elastic phase transition in stishovite sio 2 our observations imply that heterogeneity of kilometer scale persists for billions of years despite of stirring due to convection and therefore is ubiquitous in the lower mantle it is qualitatively consistent with some recent convection models

the 3d numerical modeling of subduction dynamics plate stagnation and segmentation and crustal advection in the wet mantle transition zone 1 water content in the mantle transition zone mtz has been broadly debated in the earth science community as a key issue for plate dynamics in this study a systematic series of three dimensional 3d numerical simulation are performed in an attempt to verify a hypothesis regarding the behavior of subducted oceanic plate and the role of crust in the mtz under wet conditions this hypothesis is based on the seismic observations of structural variations associated with large scale flattened high velocity anomalies i e stagnant slabs in the mtz in our model weak low viscosity fault zones wfzs which presumably correspond to the fault boundaries of large subduction earthquakes are imposed on the top part of subducting plates the phase transitions of olivine to wadsleyite and ringwoodite to perovskite magnesiowustite under both dry and wet conditions are considered based on recent high pressure experiments the effect of viscosity reduction of wet garnet is also considered for oceanic crust in the mtz results show that there is a substantial difference in the behaviors of subducting plate and the trace of crustal materials between the models under dry and wet conditions under wet conditions the subducting plate tends to stagnate with a maximum lateral extent of over 1000 km the weaker and denser crustal material garnet rich is fed into the wfzs and is advected faster than the plate main body of peridotite olivine rich thus the viscosity and density contrast between the crustal materials and the peridotite permits the plate segmentation under a wet mtz condition

vibrational and elastic properties as a pointer to stishovite to cacl2 ferroelastic phase transition in ruo2 abstract the high pressure behavior of ruo2 has been investigated using the first principles calculations based on the density functional theory here we report the calculated properties on structure electronic elastic phonon and electron phonon coupling of rutile and cacl2 type ruo2 our calculated lattice constants and bulk modulus agree reasonably well with the available theoretical and experimental data results of our calculations of zone center phonon modes at ambient and high pressures are in good agreement with raman scattering measurements elastic shear modulus and phonon analysis confirm the ferroelastic phase transition from rutile to cacl2 phase in ruo2 it is clearly illustrated that the first transition is associated with macroscopic shear instability which arises from the strong coupling between elastic constants and softening of raman active b1g mode the observed pressure of phase transition in experimental measurements was reproduced more accurately than in previous calculations and the difference between observed and calculated transition pressure is only of the order of few percentage we have also analyzed the rotation angle for o r o corresponding to b1g mode and found that the rotation of bond about 80 is required for transition from rutile to cacl2 phase in ruo2 in addition the mode gruneisen parameter is discussed the electron phonon interaction in both rutile and cacl2 type ruo2 at high pressure is also discussed

mesozoic plate motion history below the northeast pacific ocean from seismic images of the subducted farallon slab the high resolution seismic imaging of subducted oceanic slabs1 2 has become a powerful tool for reconstructing palaeogeography3 the images can now be interpreted quantitatively by comparison with models of the general circulation of the earth s mantle4 here we use a three dimensional spherical computer model of mantle convection5 6 to show that seismic images of the subducted farallon plate provide strong evidence for a mesozoic period of low angle subduction under north america such a period of low angle subduction has been invoked independently to explain rocky mountain uplift far inland from the plate boundary during the laramide orogeny7 the computer simulations also allow us to locate the largely unknown kula farallon spreading plate boundary the location of which is important for inferring the trajectories of suspect terrain across the pacific basin8

global mantle heterogeneity and its influence on teleseismic regional tomography abstract a new global p wave tomography model is determined using a flexible grid parameterization this new model better reveals the mantle structure under the polar regions than the previous tomographic models the subducting slabs are generally imaged clearly as high velocity high v zones the young slabs are still subducting in the upper mantle and the mantle transition zone mtz whereas the old and ancient slabs are either stagnant in the mtz or have subducted down to the lower mantle even reaching the core mantle boundary low velocity low v anomalies are generally revealed in the mantle under the hotspot regions it seems that a variety of mantle upwelling plumes exist some strong plumes are visible in the whole mantle under the long living hotspots such as those in south central pacific africa hawaii and iceland whereas weak plumes are visible in only some depth range under the minor hotspots under the intraplate volcanoes in east eurasia bering sea and west alaska significant low v anomalies are revealed in the upper mantle which may reflect hot and wet upwelling associated with corner flows in the big mantle wedge bmw above the stagnant pacific slab in the mtz and perhaps deep slab dehydration as well the subduction triggered magmatism in the bmw may be a new class of mantle plumes we also used the new global model to investigate the influence of whole mantle heterogeneity on the determination of upper mantle tomography under japan with a teleseismic inversion method the results show that the mantle heterogeneities outside the target volume of regional tomography can cause significant changes 0 2 0 4 s to the observed relative travel time residuals of a distant earthquake the pattern of regional tomography remains the same even after correcting for the whole mantle heterogeneity but there are some changes in the amplitude of velocity anomalies in the regional tomography hence it is necessary to correct for the mantle heterogeneities outside the target volume so as to obtain a better regional tomography

unsuccessful initial search for a midmantle chemical boundary with seismic arrays compositional layering of the midmantle has been proposed to account for seismic and geochemical patterns van der hilst and karason 1999 and inferred radiogenic heat source concentrations kellogg et al 1999 compositional layering would require thermal boundary layers both above and below an interface we construct a minimal 1 d model of a mid mantle boundary consistent with the observed nearly adiabatic compressional velocity structure dziewonski and anderson 1981 and the proposed high heat flow from the lower mantle albarede and van der hilst 1999 kellogg et al 1999 ray tracing and reflectivity synthetic seismograms show that a distinct triplication is predicted for short period p waves although topography on a boundary would cause uncertainty in the strength and the range of the triplication many clear observations would be expected we examine data from the us west coast regional networks in the most likely distance range of 60 to 70 for a 1770 km depth boundary and find no evidence for p wave triplications

stirring geochemistry in mantle convection models with stiff plates and slabs abstract numerical models of mantle convection are presented that readily yield midocean ridge basalt morb and oceanic island basalt oib ages equaling or exceeding the apparent 1 8 ga lead isotopic ages of trace element heterogeneities in the mantle these models feature high viscosity surface plates and subducting lithosphere and higher viscosities in the lower mantle the formation and subduction of oceanic crust are simulated by means of tracers that represent a basaltic component the models are run at the full mantle rayleigh number and take account of faster mantle overturning and deeper melting in the past more than 97 of the mantle is processed in these models including the expected excess density of former oceanic crust readily accounts for the depletion of morb source relative to oib sources a novel finding is of gravitational settling of dense tracers within the low viscosity upper mantle as well as at the base of the mantle the models suggest as well that the seismological observation of a change in tomographic character in the deep mantle might be explained without the need to postulate a separate layer in the deep mantle these results expand the range of models with the potential to reconcile geochemical and geophysical observations of the mantle

seismic evidence for a chemical heterogeneity in the midmantle a strong and slightly dipping seismic reflector beneath the mariana subduction zone 1 a clear later phase 80 s after the direct p wave is observed in most of individual seismograms recorded by a short period seismometer network in japan j array from a cluster of deep earthquakes that occurred at the northern mariana subduction zone this phase 1 shows a p wave particle motion 2 arrives later from earthquakes with shallower focal depths 3 has a steeper incident angle than that of p wave and 4 shows a deviation of a few degrees in the arrival azimuth from that of p wave we interpret it as an s to p converted wave which takes off downward from the source and is reflected at a velocity discontinuity reflector below the earthquakes travel time inversion shows that the seismic reflector dips southwest by 20 at 24 25 n 144 75 e and at a depth of 1115 km with a lateral extension at least 100 100 km the location corresponds to the lower edge of a high velocity anomaly in global tomographic models amplitude and waveform analyses suggest a decrease of s wave velocity by 2 6 and an increase of density by 2 9 within the reflector there is almost no difference in p wave velocity 1 between the reflector and the surrounding mantle the estimated thickness of the reflector is 12 km these observations indicate that the observed seismic structure is more likely to be a chemical reservoir rather than a purely thermal anomaly the seismic reflector might be a piece of subducted oceanic crust as suggested by a previous study it also could be related to the break down of the d phase of dense hydrous magnesium silicates at midmantle pressure condition reported by recent mineral physics studies both scenarios imply that mechanical chemical segregation might occur within the subducted slab at midmantle condition

seismic scatterers at the shallowest lower mantle beneath subducted slabs abstract data from a western united states short period seismic network are analyzed in order to investigate anomalous later phases within a time window from about 10 s to 120 s after direct p waves for deep and intermediate depth earthquakes in circum pacific subduction zones the anomalous phases are best interpreted as s to p scattered waves wavelengths of 10 km from heterogeneities in the shallow lower mantle depths 950 km several s to p scatterers where elastic properties of the rocks must substantially change within several kilometers are detected in the shallowest 300 km of the lower mantle beneath four circum pacific regions kuril bonin fiji and peru around most of the observed scatterers the seismic tomography models have delineated high seismic velocity anomalies which are associated with recently subducted pacific slab or nazca slab the most likely origin of the scatterers would be basalt which used to form the oceanic crust interestingly enough the majority of the scatterers are located near the bottom boundaries of the slabs given rather moderate degrees of folding and or buckling of the pacific and nazca slabs in the shallowest lower mantle at the study areas the existence of the oceanic crust associated with the most recent slab subduction at the scattering sites is unlikely alternative and more likely explanations include the presence of ancient basaltic rocks localized dehydration of hydrous minerals or a sharp boundary between different rock fabrics such as isotropic and anisotropic lower mantle rocks associated with mantle flow dragged by the slab subduction

understanding seismic heterogeneities in the lower mantle beneath the americas from seismic tomography and plate tectonic history we combine results from seismic tomography and plate motion history to investigate slabs of subducted lithosphere in the lower mantle beneath the americas using broadband waveform cross correlation we measured 37 000 differential p and s traveltimes 2000 pcp p and scs s times along a wide corridor from alaska to south america we invert the data simultaneously to obtain p and s wave velocity models we interpret slab structures and unravel subduction history by comparing our v s tomographic images with reconstructed plate motion from present day up to 120 myr convergence of the pacific with respect to the americas is computed using either 1 the pacific and indo atlantic hot spot reference frames or 2 the plate circuit passing through antarctica around 800 km depth four distinctive fast anomalies can be associated with subduction of the nazca cocos and juan de fuca plates beneath south central and north america respectively and of the pacific plate beneath the aleutian island arc the large fast anomalies in the lowermost mantle which are most pronounced in the s wave models can be associated with late cretaceous subduction of the farallon plate beneath the americas near 2000 km depth the images record the post 80 myr fragmentation of the proto farallon plate into the kula plate in the north and the farallon plate in the northeast near 1000 km depth we infer separate fast anomalies interpreted as the kula pacific juan de fuca and farallon slabs this interpretation is consistent with the volume and length of slabs estimated from the tomographic images and the plate history reconstruction

pedologic and geomorphic impacts of a tornado blowdown event in a mixed pine hardwood forest abstract biomechanical effects of trees on soils and surface processes may be extensive in forest environments two blowdown sites caused by a november 2005 tornado in the ouachita national forest arkansas allowed a case study examination of bioturbation associated with a specific forest blowdown event as well as detailed examination of relationships between tree root systems soils and underlying bedrock the sites occur within mixed shortleaf pine and hardwood forests more than 95 of trees in the severe blowdown areas were either uprooted or suffered trunk break with uprooting more common than breakage within the most heavily damaged areas all uprooted trees were pines while all trees left standing were hardwoods root wads of uprooted trees had a mean surface area of about 3 m 2 and volume of about 2 m 3 though individual sizes were quite variable nearly 4 of the ground surface area was affected by uprootings with a soil volume equivalent to a disturbance of the entire surface area to a depth of 2 4 cm tree size as measured by diameter at breast height was significantly related to the area and volume of root wads r 2 0 55 0 71 respectively with volume of uprooted soil varying as diameter to the 3 power suggesting that the timing of blowdown events relative to tree age or growth stage significantly influences the area of disturbance and the mass and volume of material involved in 93 of cases the roots of the uprooted trees contacted or penetrated the underlying bedrock and in all those cases bedrock was quarried by uprooting only 11 of the tree throws showed evidence of general lateral root turning at the soil bedrock interface in most cases roots penetrated bedrock along joints the propensity for tree roots to penetrate bedrock joints facilitate weathering and excavate bedrock during uprooting supports the idea that tree roots play a predominant role in locally deepening soils

mixing by time dependent convection abstract two dimensional numerical flow models are employed to study the mixing of passive heterogeneities in the earth s mantle both simple kinematic models of time dependent flow and dynamic convection models are studied initially small blocks of tracers are inserted into the flow and their progressive dispersal is monitored through time some of the tracers also serve as infinitesimal strain markers three different regimes of mixing are observed a all heterogeneities are rapidly strained and stirred according to a turbulent mixing law where the size of a blob decreases exponentially with time b most heterogeneities are only slowly strained and possibly follow a laminar mixing law with a linear decrease with time of the size of a heterogeneity c the size reduction proceeds rapidly in part of the fluid but some poorly stirred islands persist for a long time all three regimes are found in various kinematic flow models while in the dynamic convection models only regime a is observed the effective strain rate in the exponential turbulent mixing law is more than an order of magnitude smaller than the average flow strain rate when the results from the dynamic convection models with variable viscosity are scaled to the upper mantle mixing over small length scales would be achieved after a few hundred million years for whole mantle convection with a significant increase of viscosity with depth mixing times could be in the order of 1 2 ga in the latter case it appears marginally possible that part of the isotopic heterogeneity observed in oceanic basalts has evolved within the convecting mantle rather than in physically separated reservoirs

melting in the feosio2 system to deep lower mantle pressures implications for subducted banded iron formations abstract banded iron formations bifs consisting of layers of iron oxide and silica are far denser than normal mantle material and should have been subducted and sunk into the deep lower mantle we performed melting experiments on fe2sio4 from 26 to 131 gpa in a laser heated diamond anvil cell dac the textural and chemical characterization of a sample recovered from the dac revealed that sio2 is the liquidus phase for the whole pressure range examined in this study the chemical compositions of partial melts are very rich in feo indicating that the eutectic melt compositions in the feo sio2 binary system are very close to the feo end member the eutectic temperature is estimated to be 3540 150 k at the core mantle boundary cmb which is likely to be lower than the temperature at the top of the core at least in the archean and paleoproterozoic eons suggesting that subducted bifs underwent partial melting in a thermal boundary layer above the cmb the feo rich melts formed by partial melting of the bifs were exceedingly dense and therefore migrated downward we infer that such partial melts have caused iron enrichment in the bottom part of the mantle which may have contributed to the formation of ultralow velocity zones ulvzs observed today on the other hand solid residues left after the segregation of the feo rich partial melts have been almost pure sio2 and therefore buoyant in the deep lower mantle to be entrained in mantle upwellings they have likely been stretched and folded repeatedly by mantle flow forming sio2 streaks within the mantle marble cake mantle packages enhanced by sio2 streaks may be the origin of seismic scatterers in the mid lower mantle

seismic evidence for a sharp lithospheric base persisting to the lowermost mantle beneath the caribbean summary broad band data from south american earthquakes recorded by californian seismic networks are analysed using a newly developed seismic wave migration method the slowness backazimuth weighted migration sbwm using the sbwm out of plane seismic p wave reflections have been observed the reflection locations extend throughout the earth s lower mantle down to the core mantle boundary cmb and coincide with the edges of tomographically mapped high seismic velocities modelling using synthetic seismograms suggests that a narrow 10 15 km low or high velocity lamella with about 2 per cent velocity contrast can reproduce the observed reflected waveforms but other explanations may exist considering the reflection locations and synthetic modelling the observed out of plane energy is well explained by underside reflections off a sharp reflector at the base of the subducted lithosphere we also detect weaker reflections corresponding to the tomographically mapped top of the slab which may arise from the boundary between the nazca plate and the overlying former basaltic oceanic crust the joint interpretation of the waveform modelling and geodynamic considerations indicate mass flux of the former oceanic lithosphere and basaltic crust across the 660 km discontinuity linking processes and structure at the top and bottom of the earth s mantle supporting the idea of whole mantle convection

estimate of the rigidity of eclogite in the lower mantle from waveform modeling of broadband s to p wave conversions broadband usarray recordings of the 21 july 2007 western brazil earthquake mw 6 0 depth 633 km include high amplitude signals about 40 s 75 s and 100 s after the p wave arrival they are consistent with s wave to p wave conversions in the mantle beneath northwestern south america the signal at 100 s denoted as s1750p has the highest amplitude and is formed at 1 750 km depth based on slant stacking and semblance analysis waveform modeling using axisymmetric finite difference synthetics indicates that s1750p is generated by a 10 km thick heterogeneity presumably a fragment of subducted mid ocean ridge basalt in the lower mantle the negative polarity of s1750p is a robust observation and constrains the shear velocity anomaly vs of the heterogeneity to be negative the amplitude of s1750p indicates that vs is in the range from 1 6 to 12 4 the large uncertainty in vs is due to the large variability in the recorded s1750p amplitude and simplifications in the modeling of s1750p waveforms the lower end of our estimate for vs is consistent with ab initio calculations by tsuchiya 2011 who estimated that vs of eclogite at lower mantle pressure is between 0 and 2 due to shear softening from the poststishovite phase transition

elasticity of single crystal periclase at high pressure and temperature the effect of iron on the elasticity and seismic parameters of ferropericlase in the lower mantle

longevity of treethrow microtopography implications for mass wasting abstract this study examines and compares methods of dating pit mound microtopography formed by tree uprooting and provides 14 c evidence for the longevity of these landforms microtopography can often by dated by reference to known meteorological phenomena or within certain age constraints by dendrochronologic means we used 14 c analysis of buried wood and charcoal in treethrow mounds in michigan and wisconsin u s a to arrive at estimates of the geochronometric ages of treethrow mounds results indicate that mounds in these areas often persist for more than 1000 years which are two to five times longer than published estimates by less reliable methods the longevity of treethrow mounds in these regions is ascribed to l sandy porous soils which minimize runoff 2 a continuous mat of forest litter and vegetation cover 3 surface concentrations of gravel which may act as an armor 4 large initial size of the features and 5 soil freezing implications are that rates of mass movement due to uprooting may be substantially less than studies from other regions suggest

weathering and clay formation in semi arid calcareous soils from northeastern brazil abstract despite the great number of studies exploring the inter profile genetic relationships in a catena the microrelief and microtopographic features have been overlooked this study investigated the role of microrelief surfaces convex flat and concave on the mineral formation and pedogenesis in soils derived from limestones in ne brazil soil profiles were studied in different micro landscape surfaces and soil samples were taken by horizon for chemical weathering indexes and mineralogical analyses mineralogy was determined in samples from diagnostic subsurface horizons which were subjected to the proper chemical treatment for identification x ray diffraction xrd and quantification newmod ii and thermogravimetry tg of the phyllosilicates the xrd patterns showed similar composition among the parental material of the studied profiles the chemical also showed similar dynamics along the surfaces however the concave surface had soils with a higher degree of weathering when compared to others the clay minerals identified on the convex and flat surfaces were vermiculite illite smectite and kaolinite while on the concave surface only illite and kaolinite were found based on the information generated by the newmod ii there was an increase in the amount of kaolinite towards the concave surface from 21 on the convex surface to 50 of pure kaolinite crystals on the concave surface these data were supported by the tg curves our results evidence that microrelief features marked by low topographic amplitudes are determinant for the formation and distribution of phyllosilicates in calcareous soils and thus may be of key importance for predicting the occurrence of contrasting mineralogy in soils derived from calcareous rock

dipping low velocity layer in the mid lower mantle evidence for geochemical heterogeneity data from western united states short period seismic networks reveal a conversion from an s to a p wave within a low seismic velocity layer greater than or equal to the 4 percent velocity difference compared to the surrounding mantle in the mid lower mantle 1400 to 1600 kilometers deep east of the mariana and izu bonin subduction zones the low velocity layer about 8 kilometers thick dips 30 to 40 southward and is at least 500 kilometers by 300 kilometers its steep dip large velocity contrast and sharpness imply a chemical rather than a thermal origin ancient oceanic crust subducted into the lower mantle is a plausible candidate for the low velocity layer because of its broad thin extent

the role of trees in the geomorphic system of forested hillslopes a review abstract forested hillslopes form a special geoecosystem an environment of geomorphic processes that depend strongly on forest ecology including the growth and decay of trees changes in structure disturbances and other fluctuations hence the following various functions of trees are reviewed here their role in both biomechanical and biochemical weathering as well as their importance for the hillslope geomorphic subsystem and for transport of soil material via tree uprooting and root growth special attention is paid to tree uprooting a process considered the most efficient and most frequent biogeomorphological indicator of bio physical activity within forest in complex terrain trees have varied implications for soil formation in different environments boreal to tropical forests and altitudes in this paper an attempt has been made to emphasize how trees not only modulate geomorphic processes but also how they act as a direct or indirect agent of microrelief formation the most striking example of which being widespread and long lasting pit and mound microtopography based on the analyzed literature it seems that some problems attributed to forest ecology can have a fundamental effect on forested hillslope dynamics a relationship which points to the need for its integration and interpretation within the field of geomorphology the biology of individual trees has a key influence on the development of e g rock faces weathering front migration and changes in the soil biomantle within upper and lower forest belts additionally forms and sediments depend largely on the horizontal and vertical extent volume and structure of root systems as well as on active processes taking place in the root zone and rhizosphere furthermore although trees to a large extent stabilize slope surfaces their presence can also have a dual effect on slope stability due to tree uprooting a process which in some circumstances can trigger mass movements e g debris avalanches so far several attempts at quantifying the influence of trees on slopes have been made via the use of mathematical equations enabling researchers to calculate 1 the root plate volume of uprooted trees 2 the amount of soil displacement due to tree root growth and 3 rates of erosion sedimentation and soil creep in light of the reviewed literature the most urgent issue appears to be the need for a thorough study of the interactions and feedbacks occurring between trees and geomorphic systems e g soil mixing and biotransport by trees in different climate zones altitudes and time frames especially in terms of the development of forest ecosystems during the holocene

roots rock and regolith biomechanical and biochemical weathering by trees and its impact on hillslopes a critical literature review the role of trees and forests as a critical component of the biosphere and critical zone and of the earth system more generally is widely appreciated less known and acknowledged are the geomorphological functions of tree roots although their importance has been widely referred to in soil studies paleopedology and paleobotany tree roots and their impact on weathering processes and soil production were incorporated in the devonian plant hypothesis and tree root casts served as a key evidence of recognition of past soils in geology sedimentology and paleopedology however knowledge of biomechanical and biochemical weathering induced by vascular plant roots mainly trees has been rarely utilized in geomorphic studies biogeomorphic and pedologic studies in recent decades have highlighted the importance of tree uprooting in which roots play a primary role in soil development regolith disturbance and bedrock mining other important functions of roots were also recognized e g soil displacement by growing roots infilling of stump holes and root cavities root groove development direct and indirect effects taking place in the rhizosphere and mycorrhizosphere mainly biochemical weathering of minerals support by microbial communities and symbiotic fungi and changes in porosity permeability and hydrology of soils in the root zone however further studies are urgently needed because many aspects of biochemical and biomechanical weathering are not well understood this is especially true with respect to taxa specific impacts variations in root architectures edaphic settings ecological relationships and geographic ranges result in substantially different biogeomorphic impacts of different tree species additionally the same species in different environmental settings may have different effects

surface processes and interactions with forest vegetation on a steep mudstone slope stolowe mountains sw poland abstract in this study we recognize complex physical biotic abiotic interactions on a steep forested slope in the moderately elevated mountain terrain of the sudetes central europe using geomorphological pedological and dendrochronological methods on the forested hillslopes of mt rogowa kopa the evidence of disturbance in natural systems is widespread in the geomorphic subsystem its most obvious manifestation is the origin and disappearance of pit and mound microtopography resulting from tree uprooting 82 pit and mound associations have been mapped on a test slope providing quantitative data for calculating sediment flux the flux is around 2 10 4 m 3 m 1 year 1 hence less than suggested in the literature but within the same order of magnitude nevertheless in the long term such a transport rate is comparable with the one typical for creep while it affects a greater thickness of hillslope regolith tree bending and abrupt changes in tree ring width are indicators of disturbed tree growth causally linked to soil creep of mudstone derived regolith eccentric growth is best recorded in wet years and in younger trees which have to adapt to the pre existing pit and mound surface topography we offer a conceptual model that links biotic and abiotic factors and discuss implications of the widespread tree uprooting we suggest that veneers of angular clasts and occasional larger boulders are not necessarily residuals of washed pleistocene solifluction mantles but may result from root plate degradation after uprooting recent catastrophic wind events may through tree uprooting lead to structural changes in cover deposits so that they lose their inherited periglacial signatures

geomorphic edge effects in response to abiotic and anthropogenic disturbances in forest ecosystems of the gorce mountains western carpathians abstract in the present paper we report on the only known example of a hummocky meadow in poland the area of the hala dluga in the gorce mountains is a hotspot of complex geomorphic edge effects that have been widely studied in relation to human impacts and forest disturbances applying an interdisciplinary approach we aimed to study the geomorphic activity in edge conditions between two contrasting ecosystems a high mountain meadow and a forest several methods were applied geomorphic mapping radiocarbon dating soil analysis geomorphometry wood anatomy and investigations of historical maps these methods enabled us to reconstruct the history of the hala dluga over the past ca 300 years and to evaluate geomorphic activity and soil dynamics in this area the treethrow pit mound microtopography hummocky meadow buckelwiese of this area was formed under forest conditions but due to long term human impacts linked to sheep grazing and mowing was preserved as a distinct topography for at least 100 years while this topography was still clearly visible in the 1950s when it was first reported it is currently gradually disappearing under trees that have formed a belt around the study area soils of the study site were disturbed by tree uprooting with many key features identified during the soil profile analysis spots of coarse partly oriented sandstone fragments in pits patches of organic matter in the metamorphic b horizon and a large number of root remnants and pieces of charcoal in different parts of treethrow mounds and pits we suggest a non linear or even polygenetic soil evolution due to altered vegetation and disturbance regimes the evaluation of wood remnants revealed that the majority of uprooted tree species were picea abies l h karst and larix decidua mill we conclude that in the gorce mountains geomorphic edge effects can form hotspots of geomorphic activity driven by human impacts natural disturbances and the specific hydrological regime in the highest parts of the massif

long wavelength character of subducted slabs in the lower mantle abstract the high resolution seismic tomography provides the detailed information about the fate of the subducted plates in the mantle while the slab deformation in the transition zone is quite complex and differs among the individual subduction zones it could be generally concluded that most slabs seem to penetrate into the lower mantle the character of the fast seismic velocity anomalies however changes when the slabs cross the 670 km discontinuity while in the upper mantle tomography resolves relatively narrow plate like structures in the lower mantle it rather indicates thick blobs of seismically fast material such thickening of the downgoing slabs is traditionally attributed to the effect of the viscosity increase in the lower mantle here we study the deformation of the slabs in the lower mantle in a viscous model with a non linear composite rheology including the diffusion creep the dislocation creep and a power law stress limiter we perform numerical simulations of the subduction process in a 2d cartesian domain and concentrate especially on the effect of the change of the rheological parameters across the 670 km boundary on the slab deformation in the upper part of the lower mantle the thickening or the buckling of the plate is indeed observed in the models with relatively low yield stress 0 1 gpa of the stress limiting mechanism and with a viscosity increase at the 670 km discontinuity further we show that both the major mantle phase transitions and the strength of the crust layer have significant consequences for the creation of the buckling instabilities in the lower mantle

estimating the effect of tree uprooting on variation of soil horizon depth by confronting pedogenetic simulations to measurements in a belgian loess area 1 spatial patterns of soil often do not reflect those of topographic controls we attempted to identify possible causes of this by comparing observed and simulated soil horizon depths observed depths of e bt bc c1 and c2 horizons in loess derived soils in belgium showed a weak to absent relation to terrain attributes in a sloping area we applied the soil genesis model soilgen2 16 onto 108 1 1 m2 locations in a 1329 ha area to find possible causes two scenarios were simulated model 1 simulated soil development under undisturbed conditions taking slope aspect and loess thickness as the only sources of variations model 2 additionally included a stochastic submodel to generate tree uprooting events based on the exposure of trees to the wind outputs of both models were converted to depths of transitions between horizons using an algorithm calibrated to horizon depths observed in the field model 1 showed strong correlations between terrain attributes and depths for all horizons although surprisingly regression kriging was not able to model all variations model 2 showed a weak to absent correlation for the upper horizons but still a strong correlation for the deeper horizons bc c1 and c2 for the upper horizons the spatial variation strongly resembled that of the measurements this is a strong indication that bioturbation in the course of soil formation due to treefalls influences spatial patterns of horizon depths

phase transition and density of subducted morb crust in the lower mantle abstract phase relations mineral chemistry and density of a natural mid oceanic ridge basalt morb composition were investigated up to 134 gpa and 2300 k by a combination of in situ x ray diffraction measurements and chemical analyses using transmission electron microscope tem results demonstrate that the morb composition consists of mgsio 3 rich perovskite stishovite casio 3 perovskite and cafe 2 o 4 type al phase in the upper part of the lower mantle the most abundant mineral of mgsio 3 rich perovskite undergoes phase transition to a cairo 3 type post perovskite phase above 110 gpa and 2500 k post perovskite phase is similar in composition to perovskite except considerably high na 2 o content stishovite transforms to cacl 2 type sio 2 phase above 62 gpa and 2000 k and further to pbo 2 type phase above 110 gpa pbo 2 type sio 2 phase includes large amount of al 2 o 3 which significantly expands its stability relative to cacl 2 type phase phase transition of casio 3 perovskite from tetragonal to cubic was also observed with increasing temperature cafe 2 o 4 type al phase is stable to the bottom of the mantle the density of morb crust was calculated using volume data combining with measured chemical compositions and calculated mineral proportions the former morb crust is denser than the average lower mantle at all depths greater than 720 km contrary to earlier predictions the subducted basaltic crust may have accumulated at the base of the mantle

whole mantle sh velocity model constrained by waveform inversion based on three dimensional born kernels summary a whole mantle sh velocity model is obtained by using a unique data set and techniques body and surface waveforms including major and multi orbit phases are used as a data set and are inverted by using 3 d born kernels the resultant model sh18ce reveals the different natures of the two major upwelling systems the strong low velocity anomalies beneath africa extend for more than 1000 km from the core mantle boundary cmb whereas those beneath the pacific are restricted to 300 400 km from the cmb the results also show the variable natures of stagnant slabs on the 670 discontinuity around japan the depths of the strongest high velocity anomalies within the stagnant slabs are different region by region which is consistent with the detailed delay time tomography model in this area

processes responsible for the development of a pit and mound microrelief abstract hummocky ground is a conspicuous feature of some cultivated pastures in the mountain forests of the alps in the german scientific literature this pit and mound microrelief is termed buckelwiese literally hummocky meadow and is commonly interpreted as a fossil late glacial relief of cryogenic origin this paper suggests an alternative hypothesis namely that relief formation was initiated by the uprooting of trees during storms in the rootstock pits karst processes gradually amplified the initial relief this alternative hypothesis is tested in a buckelwiesen area of the northern limestone alps where pit to mound vertical relief amounts to 52 cm and mounds are 250 510 cm long and 170 270 cm wide and the density of pits and mounds is 400 ha 1 field investigations included a ground survey using a tacheometer and the excavation of a trench to check the internal structure of one pit mound couple the trench was subsequently used to estimate solution rates in the subsurface material of pits and mounds based on the results of the field measurements and two radiocarbon dates from the test site the paper concludes that in the study area a treethrow event occurred between 1120 and 1280 ad subsequently the pits created by the uprooted trees were deepened by limestone solution at a rate of 77 2 mm 1000 years the reconstructed formation history of the microrelief of the study area is consistent with a holocene origin with rates of limestone dissolution as measured in the field and with the morphometry of the features themselves

elasticity of ferropericlase and seismic heterogeneity in the earth s lower mantle deciphering the origin of seismic heterogeneity has been one of the major challenges in understanding the geochemistry and geodynamics of the deep mantle fully anisotropic elastic properties of constituent minerals at relevant pressure temperature conditions of the lower mantle can be used to calculate seismic heterogeneity parameters in order to better understand chemically and thermally induced seismic heterogeneities in this study the single crystal elastic properties of ferropericlase mg0 94fe0 06 o were measured using brillouin spectroscopy and x ray diffraction at conditions up to 50 gpa and 900 k the velocity density results were modeled using third order finite strain theory and thermoelastic equations along a representative geotherm to investigate high pressure temperature and compositional effects on the seismic heterogeneity parameters our results demonstrate that from 660 to 2000 km compressional wave anisotropy of ferropericlase increased from 4 to 9 7 while shear wave anisotropy increased from 9 to as high as 22 5 the thermally induced lateral heterogeneity ratio rs p lnvs lnvp of ferropericlase was calculated to be 1 48 at ambient pressure but decreased to 1 43 at 40 gpa along a representative geotherm the rs p of a simplified pyrolite model consisting of 80 bridgmanite and 20 ferropericlase was approximately 1 5 consistent with seismic models at depths from 670 to 1500 km but showed an increased mismatch at lower mantle depths below 1500 km this discrepancy below mid lower mantle could be due to either a contribution from chemically induced heterogeneity or the effects of the fe spin transition in the deeper parts of the earth s lower mantle

breakage or uprooting how tree death type affects hillslope processes in old growth temperate forests abstract tree breakage and uprooting are two possible scenarios of tree death that have differing effects on hillslope processes in this study we aimed to i reveal the long term structure of the biomechanical effects of trees bets in relation to their radial growth and tree death types in four old growth temperate forests in four different elevation settings with an altitudinal gradient of 152 1105 m a s l ii quantify affected areas and soil volumes associated with the studied bets in reserves and iii derive a general model of the role of bets in hillslope processes in central european temperate forests we analyzed the individual dynamics of circa 55 000 trees in an area of 161 ha within four old growth forests over 3 4 decades basal tree censuses established in all sites in the 1970s and repeated tree censuses in the 1990s and 2000s provided detailed information about the radial growth of each tree of dbh 10 cm as well as about types of tree death we focused on the quantification of i surviving still living trees ii new recruits iii standing dead trees iv uprooted trees and v broken trees frequencies of phenomena were related to affected areas and volumes of soil using individual statistical models the elevation contrasts were a significant factor in the structure of bets differences between sites increased from frequencies of events through affected areas to volumes of soil associated with bets an average 2 7 m3 ha 1 year 1 was associated with all bets of the living and dying trees in lowlands while there was an average of 7 8 m3 ha 1 year 1 in the highest mountain site differences were caused mainly by the effects of dying trees bets associated with dead trees were 7 8 times larger in the mountains effects of dying trees and particularly treethrows represented about 70 of all bets at both mountain sites while it was 58 at the highland site and only 32 at the lowland site our results show a more significant role of bets in hillslope processes including slope denudation in the mountains we would expect a significant decrease of the biogeomorphic effect of trees in managed forests but with a greater relative effect in mountains

comment on mixing by time dependent convection by u christensen commentaire et reponse concernant l article de u christensen earth planet sci lett 95 382 394 1989

seismic evidence for small scale heterogeneity throughout the earth s mantle details in the amplitude structure of short period precursors to the seismic core phase pkp can be used to constrain the depth extent of mantle scattering the simplest model consistent with the observations invokes small 8 km weak r m s velocity perturbations of 1 random heterogeneities uniformly distributed throughout the mantle the data do not support previously proposed models that place an increase in the concentration of scattering sites near the base of the mantle and instead place an upper limit on the amplitude of any short wavelength topography at the core mantle boundary

subparallel dipping heterogeneities in the mid lower mantle 1 data from western u s short period seismic networks show anomalous later phases which we interpret as s to p converted waves from heterogeneities in the mid lower mantle depths of 1000 1850 km northeast of the mariana subduction zone the geometry of the objects is mapped by a two step approach 1 computing the s to p scattering likelihood with the arrival time slowness and azimuth of the later arrivals measured by array techniques relative to direct p waves and 2 by direct use of the waveforms using semblance at least three subparallel objects are detected in the lower mantle study region with the dips of 30 to 40 southward and with a lateral extent larger than 500 km by 300 km the elastic properties associated with the heterogeneous objects appear to change within several kilometers considering their high efficiency at converting short period waves wavelengths of 5 10 km previous seismic tomography studies have not predicted significant velocity anomalies around the heterogeneities this is probably because they are below the resolution limit of present methods the three major heterogeneities are separated from each other nearly 300 km vertically and significant anomalies seem absent between each object nevertheless semblance cross sections with a finer grid size 0 1 0 1 10 km of the clearest intermediate object at 1400 1600 km show a hint that the object is not a single interface but is actually composed of double interfaces nearly 50 km apart purely thermal anomalies of kilometers scale must be transient features in the mantle and thus are highly unlikely to be the cause of the heterogeneities they should rather represent either sharp chemical variations in major element composition or sharp changes in preferred orientations of anisotropic lattice of the lower mantle minerals thermal anomalies however may be superimposed on such variations because of heat generation either by concentrated radioactive nuclei or by viscous shear heating due to deformations a plausible tectonic interpretation of these dipping objects is that they represent remnants of subducted lithospheric plates which preceded the current subduction of the pacific plate although we cannot make conclusive arguments on what the mechanism of creating such heterogeneities from these observations alone we suggest that they may represent stretched thinned and duplexed rocks within chaotic mantle flows

an analysis of large scale variations in small scale mantle heterogeneity using global seismographic network recordings of precursors to pkp high frequency precursors to the core phase pkp are caused by scattering off heterogeneities in the lowermost mantle and d regions and they provide a unique window into the small scale structure of the deep earth we study lower mantle scattering by analyzing 412 high quality pkp precursor records at ranges between 120 and 137 5 as obtained from the global seismic networks during the last 10 years to examine regional variations in scattering strength we compare individual records with the globally averaged pkp precursor stack of hedlin et al 1997 we identify strong differences in apparent scattering strength among specific source receiver paths inversion of these data for scattering source regions is complicated by ambiguity between source and receiver side scattering and the sparse and uneven data coverage synthetic tests however suggest that inversions with applied smoothness constraints can resolve large scale differences in scattering strength over significant parts of the lower mantle we use a conjugate gradient method based on an approximation to rayleigh born scattering theory to image differences in the average strength of scattering within the lowermost 1000 km of the mantle our results indicate particularly strong scattering beneath central africa parts of north america and just north of india whereas weaker scattering is seen beneath south and central america eastern europe and indonesia some regions of strong scattering correlate roughly with large scale anomalies revealed by seismic tomography including the african plume and the tethys trench these correlations are tentative rather than definitive because bootstrap resampling tests show that many details in our model are not reliably resolved and the network data alone do not permit complete resolution of the source receiver ambiguity in all areas further progress in this area will require integration of available network recordings with data collected by regional networks and arrays and consideration of the phase velocity of the precursors as well as their temporal variations

absorption band q model for the earth body wave surface wave and normal mode data are used to place constraints on the frequency dependence of q in the mantle with a simple absorption band model it is possible to satisfy the shear sensitive data over a broad frequency range the quality factor qs is proportional to in the band and to and 1 at higher and lower frequencies respectively as appropriate for a relaxation mechanism with a spectrum of relaxation times the parameters of the band are q min 80 0 15 and width 5 decades the center of the band varies from 101 seconds in the upper mantle to 1 6 103 seconds in the lower mantle the shift of the band with depth is consistent with the expected effects of temperature pressure and stress high qs regions of the mantle are attributed to a shift of the absorption band to longer periods to satisfy the gravest fundamental spheroidal modes and the scs data the absorption band must shift back into the short period seismic band at the base of the mantle this may be due to a high temperature gradient or high shear stresses a preliminary attempt is also made to specify bulk dissipation in the mantle and core specific features of the absorption band model are low q in the body wave band at both the top and the base of the mantle low q for long period body waves in the outer core an inner core qs that increases with period and low qp qs at short periods in the middle mantle the short period qs increases rapidly at 400 km and is relatively constant from this depth to 2400 km the deformational q of the earth at a period of 14 months is predicted to be 463

compositional vs thermal buoyancy and the evolution of subducted lithosphere we formulate 2 d cartesian finite element models that explore the fate of compositionally defined lithosphere as it encounters a viscosity increase at the boundary between the upper and lower mantle subducted lithosphere is represented as a cold stiff layered composite of denser eclogite underlain by more buoyant harzburgite slabs impinging on a lower mantle 30 and 100 times more viscous than the upper mantle thicken and fold strongly as they penetrate the lower mantle approximately a factor of two thickening occurs via pure shear just above the discontinuity with additional enhancement due to folding by over a factor of two no separation of the individual slab components occurs at the discontinuity and direct comparison with models in which compositional buoyancy is explicitly ignored indicates that slab evolution is largely controlled by the thermal buoyancy these results are at odds with hypotheses about slab evolution in which the compositional buoyancy contributions lead to component separation and the formation of slab megaliths or a compositionally layered upper mantle

the micro scale simulation of maturation outline of a new technique and its potential applications a micro analytical technique has been developed for artifically maturing sedimentary organic matter and then quantifying the major components generated during this process in a single analytical step such a capability is well suited for examining the compositional relationships between kerogens and petroleums determining reaction kinetics and making precursor product mass balances according to this technique simulations are made using sealed glass capillary tubes heated here for three days at 300 c 330 c and 350 c pyrolysis products are then released directly into a combined thermovaporisation pyrolysis gc instrument and the major components of the entire c1 yto c35 range can be quantified in a single step using gas chromatography alkene yields are very low and pyrolysates are oil like this is exemplified by the fact that then c9 c19 alkane distribution range of simulated whole petroleum chromatograms from originally immaturegloeocapsamorpha typz alginite a resembles that seen in crude oils generated from this same kerogen type in nature sealed tube experiments usingbotryococcus type alginite a generated a high wax pyrolysate the relative abundance ofn alkanes in the c2 c32 range of many kerogen pyrolysates does not appear to change significantly despite an approximately fifteen fold difference inn alkane yield between the 300 c and 350 c experiments kerogens which are paraffinic oil prone and whose pyrolysates are very rich inn alkanes might therefore generate petroleums in nature with a fixed wet gas c2 c4 to oil c5 ratio alginite b in a greenland shale is much more thermally labile than eitherbotryococcus type alginite a orgloeocapsamorpha type alginite a the mass balance capabilities of the technique have been tested using alum shale kerogen two gas chromatograms were obtained one for the free compounds generated during simulation and one for the high temperature pyrolysate of the kerogen residue for each heating experiment precursor product relationships were qualitatively assessed and dead carbon formation was quantified in this exercise

lower mantle scattering profiles and fabric below pacific subduction zones abstract the earth s mantle is compositionally evolving principally through the process of mid ocean ridge basalt production 95 by lithospheric area but also by way of arc magmatism 5 and continental growth reymer a schubert g 1984 phanerozoic addition rate to the continental crust and crustal growth tectonics 3 63 77 rowley d b 2002 rate of plate creation and destruction 180 ma to present geol soc am bull 114 927 933 convection eventually must mix these products back into the mantle but the details of the mixing process are unknown we report here new observational data documenting the location of differentiated material in the present day lower mantle and scattering power profiles with depth small scale 10 km objects which efficiently scatter short period s waves are present in the mantle lying below the pacific ocean rim at depths between 1100 and 1800 km we also observe a reduction in scattering power with depth indicating that the objects represent bodies richer in differentiated basalt than the surrounding mantle the scattering objects appear to be deformed to various degrees and usually form clusters separated from each other by a distance of 100 to 200 km the clusters probably represent folds of the order of 100 km probably corresponding to early stage of mixing process because the scattering power does not increase with depth neither does a permanent barrier to flow exist in the mid mantle nor does the intrinsic density of basalt prevent re entrainment into mantle flow from the bottom of the mantle

soil creep the driving factors evidence and significance for biogeomorphic and pedogenic domains and systems a critical literature review abstract soil and regolith creep have been analyzed for at least the last 140 years using many methodological configurations and temporal and spatial scales the general concept of creeping soil and its mechanism first proposed by w m davis and g k gilbert at the end of the 19th century evolved since the 1940s towards theoretical models and precise short and long term field measurements this fruitful epoch continued with results enhanced at the turn of the 20th century by the application of new research methods e g radiometry and a redefinition of the term soil creep to encompass the sum of stochastic shallow subsurface and near surface processes causing net downslope movement of soil or regolith simultaneously another possibility of creep detection was noticed in dendrochronology and since the 1970s in the formally defined discipline of dendrogeomorphology indirect evaluations of creep activity were performed based on tree ring analyses of bent trees this method found many followers but was also heavily criticized as imprecise and lacking in evidence of which kind of tree trunk curvature e g pistol butt like deformation s shape curvature could be ascribed to creep movement from the beginning soil creep was associated with the activity of living organisms on hillslopes however this aspect of creep studies has never been fully developed in spite of the solid foundations and directions of potential studies pointed out by charles darwin at the end of the 19th century in this paper we focus on the historical context of soil creep studies and highlight forest ecosystems as probably the most active environment of biogenic creep mainly due to tree uprooting and other biomechanical effects of living and dead trees root channel infilling tree root mounding etc that are a factors in biotransport in the final sections the position of biogenic creep in the structure of biogeomorphic systems is discussed in relation to such important conceptual frameworks as the biogeomorphic ecosystem biogeomorphic feedback window and ecosystem engineering we also describe several hypotheses that should be carefully tested in the future and propose several research methods that have the ability to further our knowledge about soil creep radiometry laser scanning and soil micromorphology

searching for seismic scattering off mantle interfaces between 800 km and 2000 km depth 1 we systematically examined seismic data from deep earthquakes in the western and northwestern pacific tonga fiji and south america for signs of sharp gradients in seismic properties that could represent either a mineralogical phase change or the boundary between geochemical reservoirs in the earth s lower mantle this involved the stacking of short period vertical component teleseismic waveforms from the dense pacific northwest seismic network and searching for evidence of s to p conversions at sharp mantle structures between 800 and 2000 km depth with these data we estimate we should be able to detect seismic discontinuities with vs 2 transition width 20 km and limited local topography using data from over 45 earthquakes we found no evidence of a horizontal global discontinuity neither near 920 km nor near 1700 km beneath the four convergent margins studied here consistent with previous results we detected a deep structure with topography near 1600 km beneath the marianas region because we observed the signal over a large geographical region beneath the marianas 10 n to 20 n it is likely a coherent local structural and not a point source the absence of such a structure beneath the northwest pacific the tonga fiji region or south america argues against a global feature near 1600 km depth however the lack of convincing and consistent scattering suggests that no composition boundary or thermal boundary layer exists between 800 to 2000 km depth beneath the convergent zones studied that has vs 2 locally limited topography and a transition interval 20 km

constraining the geometries of small scale heterogeneities a case study from the mariana region a new array based method for seismic waveform data is developed to detect small scale heterogeneities in the mantle and constrain their possible locations and sizes detecting small scale heterogeneities using scattered waves has been challenging because scattered phases usually suffer from low signal to noise ratios and determining the shapes of such heterogeneities is even more difficult because of isochronal artifacts in the proposed method the problem of the low signal to noise ratio is addressed by adopting dual bootstrap stacking which can detect weak signals even with a limited number of seismic traces as well as by ensuring reproducibility among multiple events the locations of detected scatterers and their sizes and shapes are then estimated using a new kind of hierarchical cluster analysis that could minimize the effect of isochronal artifacts the new method is applied to a previously analyzed data set of mariana earthquakes to facilitate a comparison with conventional methods in the mid to lower mantle beneath the mariana trench region a total of 39 scatterers are identified via s to p scattering with their potential volumes ranging from 8 104 to 1 106 km3

deterministic chaos and historical geomorphology a review and look forward the study of nonlinear dynamics in geomorphology has been dominated by analytical techniques derived largely from other fields ultimately however confronting nonlinear complexity requires problematizing from within a geomorphological context this paper focuses on deterministic chaos the major classes of techniques for detecting chaos in geomorphic systems are reviewed while the long time series most amenable to traditional methods of chaos detection are only occasionally available to geomorphologists there are methods for detecting chaos in spatial data including qualitative and categorical data many of these are similar to or are adaptations of familiar techniques for partitioning within and between unit variation and for identifying elementary uniform landscape units the manifestations of chaos in landforms and landscapes take the form of divergent vs convergent evolution increasing vs decreasing irregularity disproportionality vs proportionality of response to perturbations or initial variations and the lack of geographical consistency or commonality of response these also serve as criteria for distinguishing between achievement of a new steady state and unstable divergence in interpreting geomorphic changes study of nonlinear dynamics in earth science need not be dominated by theoreticians and modellers as complex nonlinear behaviors can be identified and diagnosed using the types of data observations and methods typically available to geomorphologists even more important is the need to further inform the study of nonlinear dynamics on the basis of field based geomorphology

high temperature anomalies oceanward of subducting slabs at the 410 km discontinuity abstract our p wave whole mantle tomography revealed a low velocity region oceanward of the northern honshu slab of the pacific plate at depths around the 410 km seismic discontinuity resolution tests and scrutiny of the traveltime residuals for the ray paths passing through the low velocity region indicate that this anomaly is a resolvable feature and not an artifact due to the strong slab anomalies the existence of the slow anomalies is also supported by the analysis of the p wave records from the j array a large aperture seismic array in japan for a bonin earthquake the p arrivals to northern honshu at epicentral distances of 13 20 are strongly triplicated because of the 410 km discontinuity the later arrivals along the retrograde branch where ray paths pass through the low velocity region are anomalously slow comparison of the observed and synthetic waveforms indicates not only slow anomalies but also depression of the 410 km discontinuity this depression represents the direct evidence for the low velocity zone of primarily thermal origin an excess temperature of 200 k and the associated fractional melt of less than 1 can explain both the results of the tomographic and waveform analyses