sources of spatial complexity in two coastal plain soil landscapes abstract the spatial pattern of soils and soil properties in soil landscapes is considered here as a function of 1 systematic variation along catenas or associated with spatial patterns of soil forming factors and 2 local pseudo random variations associated with local disturbances or small unobserved variations in soil forming factors the problem is approached at two study sites in the u s atlantic coastal plain using algebraic graph theory and the spectral radius of the soil adjacency matrix as a measure of complexity the matrix is constructed based on the observed spatial contiguity of soil taxa and soil factor sequences sfs are defined for each site based on systematic soil variation associated with variations in parent material topography sandy surface thicknesses and secondary podzolization the spectral radii of the networks described by the adjacency graphs are compared to those associated with the maximum for a graph of the same size and the maximum associated with control entirely by variations in soil forming factors at the clayroot study site which is entirely cropland complexity of the adjacency matrix is less than the maximum that could be accounted for by the four identified sfs due to redundant information in the sfs the littlefield site by contrast has a spectral radius greater than here where about half the site is forested the contingent variation is likely associated with effects of individual trees on soil morphology the utility of the adjacency analysis is in identifying whether soil heterogeneity is likely associated with sfs or with contingent factors not captured in sfs

soil endemism and its relation to soil formation theory abstract in this paper the concept of soil endemism is elucidated endemic soils are restricted to a particular geographic area based on a unique combination of soil forming factors that may operate from the landscape to the eco region scale to validate that soils are endemic soil bodies occurring on different continents but having a similar combination of soil forming factors were compared using national soil survey characterization data a key finding is that similar soil families occur within a given climate class koppen trewartha system and vegetation type bailey s eco region division reinforcing the former concept of zonal soils in a second test soil series were compared within a soil family from randomly selected benchmark soil series using the state soil geographic statsgo database and evaluated in terms of the soil forming factors contributing to endemism this analysis showed that soil endemism is locally influenced by parent material e g volcanic ash clay secondary silica and topography e g closed basins i e intrazonal soils soils lacking a well developed profile because of youth of parent material or peculiar conditions of parent material or relief azonal soils do not show endemism therefore zonal and intrazonal soils generally are endemic and azonal soils tend to be non endemic the concept of endemism is important for detecting rare unique or endangered soils

aspherical structure of the core mantle boundary from pkp travel times maps of aspherical structure in the vicinity of the core mantle boundary have been constructed from a tomographic analysis of p df and p ab travel times in the distance range 150 180 these maps reveal long wavelength features not previously detected by mantle tomography the peak to peak amplitude of these features is on the order of 1 s in vertical travel time too large to be explained by conventional thermal boundary layer models or dynamically supported topography on the core mantle boundary we hypothesize the existence of one or more chemical boundary layers whose large scale accumulations on the surface of the core may in some ways be analogous to continents at the earth s surface

shear wave travel time amplitude and waveform analysis for earthquakes in the kurile slab constraints on deep slab structure and mantle heterogeneity shear wave travel times amplitudes and broadband waveforms from 16 events in the kurile slab are analyzed to place further constraints on the seismic velocity heterogeneity associated with the subducted oceanic lithosphere several previous studies have proposed that the kurile slab penetrates into the lower mantle with little deformation other than a steepening of the dip angle while other studies suggest that strong slab deformations occur with perhaps negligible lower mantle penetration in an effort to detect any deep slab effects we compare anomaly patterns covering a 60 azimuthal range straddling the strike of the slab for events in three different depth intervals 500 km 350 500 km and 100 200 km s and scs pulse broadening is used as a measure of waveform complexity complexity of broadband shear waves does not vary systematically across our azimuthal range as the propagation direction changes with respect to the postulated lower mantle slab model for this region strong residual sphere travel time variations are found for shear waves from events at all depths however these variations do not display the depth dependence apparent in previous p wave analysis that has been interpreted as requiring a change in slab geometry and lower mantle penetration the same s wave residual pattern is apparent in ss depth phases and is well predicted by a recent model of shear velocity structure beneath north america a combination of deep mantle and near receiver aspherical structure can explain most of our observed shear wave travel time patterns with only a minor source depth dependent component remaining after correction individual amplitude and travel time measurements are poorly correlated however scs s amplitude ratios and scs s differential times are significantly correlated consistent with geometric focussing and defocussing effects somewhere along the raypaths the travel time behavior suggests that the responsible velocity heterogeneity is not located near the source the absence of a strong deep slab effect on the shear waves indicates that deep slab heterogeneity is less pronounced for shear waves than expected on the basis of existing p wave models derived from travel time residual sphere analysis various interpretations include estimates of vs t and compositional effects previously used to predict shear velocity structure of the deep kurile slab are in error with actual lower mantle slab anomalies being much weaker than proposed the kurile slab is so distorted in the lower mantle that no source depth dependent trends are produced for our limited focal sphere coverage or the kurile slab does not penetrate into the lower mantle

seismicity patterns in the himalayan plate boundary and identification of the areas of high seismic potential abstract space time distribution of earthquakes along the himalayan plate boundary has been investigated with a view to discerning fluctuations in seismicity rates associated with great earthquakes the possibilities of epicentre migration and gaps in seismic activity data from 1800 to 1976 were considered this study shows that all great earthquakes m 8 0 were preceded by seismically quiescent periods of at least 19 years furthermore earthquake quiescence has also been recognised to follow the great earthquakes three possible trends of migration of epicentres of great earthquakes have been recognised 1 1 the first trend starts from the 1905 kangra earthquake the epicentres of subsequent earthquakes migrating eastwards along the plate boundary 2 2 the second trend of migration starts from the great nepal earthquake of 1833 associated with eastward migration 3 3 the third trend commences from the great assam earthquake of 1897 and shows a westward migration of earthquake epicentres the middle section of the himalayan convergent plate boundary 80 e to 90 e in general displays a relatively low level of seismicity as compared to the adjacent sections a remarkable decrease in seismicity following the year 1970 has been observed along a section of the himalaya which lies to the east of the rupture zone of the great 1905 kangra earthquake since 1970 the seismicity rate has also dropped in the region lying in between the rupture zones of the great assam earthquakes of 1897 and 1950 as has earlier been reported by khattri and wyss 1978 such decreases in the level of seismicity along active plate boundaries have been demonstrated to be indicative of building up of stresses leading to future great earthquakes mogi 1969 mccann et al 1979

constraints on the kurile slab from shear wave residual sphere analysis we analyze residual spheres for teleseismic s wave arrival times from 10 intermediate and deep focus earthquakes in the kurile subduction zone long period wwssn and csn recordings of transverse component s and scs arrivals provide good azimuthal coverage for each event with arrival time estimates that compare well with short period observations in order to isolate the near source structure substantial lower mantle and receiver path effects are suppressed both by using empirical station path statics derived from s ss scs and sscs arrivals for a total of 28 northwestern pacific events and by constructing differential residual spheres ray tracing through three dimensional aspherical shear velocity models supports the inferred large magnitude of the deep mantle and near receiver effects although existing models do not appear to provide accurate corrections the events are relocated in the prem structure and a modest spatial smoothing of the residuals is applied the resulting residual spheres are modeled using a finite difference travel time method that accounts for three dimensional ray path perturbations our starting models are derived from slab structures determined by previous p wave residual sphere analyses we explore the compatibility of the p and s wave observations to constrain the vs vp velocity ratio of the slab and to test whether the s wave arrival times place additional constraints on the slab geometry the modeling supports the previous results favoring penetration of the kurile slab to at least 800 km depth for most of the length of the arc with some evidence that the northern portion of the slab broadens by as much as a factor of 3 upon entering the lower mantle the preferred slab shear velocity models have relatively low 2 3 shear velocity contrasts below 670 km depth which can be accounted for by slab temperature reductions of 300 400

divergent evolution and the spatial structure of soil landscape variability abstract the spatial structure of soil variability at the landscape scale was examined on adjacent geomorphic surfaces dating from 80 to 200 ka in eastern north carolina the purpose was to determine whether there is evidence at broader scales distances of 102 104 m for the divergent evolution observed in the field at very detailed scales distances of 100 102 m the state probability function spf which measures spatial dependence for categorical environmental data along a transect was applied to soil series mapped at a 1 24 000 scale the older talbot terrace and younger pamlico terrace surfaces showed distinctly different patterns of spatial variability the range of spatial dependence was shorter on the older surface about 200 vs 300 m and the spf was higher at any given distance indicating more variability the spf for the pamlico surface also indicates a periodicity related to fluvial dissection of the landscape which is not readily detectable on the talbot transect despite its greater degree of dissection the results confirm earlier field studies which suggest that pedogenesis is marked by divergence whereby differences in initial conditions or local perturbations persist and increase to produce a more variable soil cover

seismic tomography in boreholes summary synthetic seismic tomographic data sets for cross hole and hole to surface arrays are computed and inverted inversion imaging is performed through an iterative projection solution to a matrix equation the orientation as well as the position of an anomaly relative to the source and recorder arrays affects both the rate of convergence of the solution and the resolution obtained data density and distribution determine the physical validity of the image obtained at convergence borehole tomography is apparently a viable method for imaging inter hole structure

large artificial water reservoirs in the vicinity of the himalayan foothills and reservoir induced seismicity there are 11 large reservoirs exceeding a capacity of 1 km3 and or the height of the dam being 100 m or more in the vicinity of the himalayan foothills nine of these have been fully impounded only a couple of these reservoirs are adequately instrumented for seismic surveillance while the rest have inadequate instrumentation however there is no incidence of reservoir induced seismicity reported from any of these nine sites nonoccurrence of induced earthquakes is comprehended primarily due to the thrust fault environment generally prevalent in the himalayan foothills which is not conducive for reservoir induced seismicity nevertheless a few normal and strike slip faults oblique and parallel to the general trend of the himalayas have been reported where reservoir induced seismicity could occur all of these dams are located in a highly seismic area where earthquakes of magnitude exceeding 7 have occurred in their vicinity in the past normally occurring earthquakes therefore pose a much more severe threat to himalayan reservoirs than do reservoir induced seismicity

focal depths and fault plane solutions of earthquakes and active tectonics of the himalaya synthetic seismograms were compared with long period body waves for nine earthquakes with epicenters in the himalayan arc to determine depths of foci and to improve fault plane solutions focal depths are shallow 10 20 km inferred slip vectors are locally perpendicular to the mountain range they plunge very gently about 10 deg in the eastern sections of the range and more steeply about 25 deg in western sections assuming india to be a rigid plate the radially oriented slip vectors imply that southern tibet extends at about half the rate of underthrusting in the himalaya and therefore probably at about 5 10 mm yr the shallow depths and gentle dips of the fault planes at least for the events in the eastern half of the range are consistent with coherent underthrusting of the indian plate beneath at least the lesser himalaya the steeper dips of fault planes in the western part of the arc might reflect deformation of the overriding thrust plate or simply a steepening of the main underthrusting zone beneath the greater himalaya

fault plane solutions of earthquakes and active tectonics of the tibetan plateau and its margins summary fault plane solutions of earthquakes within and on the margins of the tibetan plateau show diverse styles of faulting and deformation with thrust faulting and crustal shortening normal to the margins of the plateau and with normal and strike slip faulting resulting in roughly east west crustal extension within the plateau the direction of overthrusting of the himalaya onto the indian shield is radially outward varying from southwest in the western himalaya to south southeast in the east assuming that the indian shield behaves rigidly this requires a west northwest divergence of western tibet from southeastern tibet at a rate of 18 9 mm yr 1 comparable with the rate of convergence at the himalaya fault plane solutions of earthquakes in the southern portion of the tibet plateau consistently show large components of normal faulting on roughly north striking planes and corroborate such extension within the high plateau where elevations exceed 5000 m normal and strike slip faulting occur so that an overall east southeast west northwest extension of the region at about 10 mm yr 1 is partitioned into roughly equal parts of crustal thinning and north northeast south southwest crustal shortening about 5 mm yr 1 in general strike slip faulting characterizes solutions for earthquakes within eastern tibet where mean elevations drop below 4500 5000 m but the orientations of the strike slip faults vary across the region in central tibet left lateral slip occurs on planes trending roughly northeast but for earthquakes farther east the orientations of that plane become progressively east west and then southeast this variation in orientation implies a rotation of material along curved left lateral shear zones thus the eastward extrusion of tibet appears to be facilitated not only by rapid left lateral shear but also by large clockwise rotations of the material in eastern tibet the rate of eastward extrusion of material in eastern tibet relative to the tarim basin to its north is roughly 30 40 mm yr 1 fault plane solutions of earthquakes in the northern and eastern margins of tibet show large components of thrust faulting with the p axes oriented radially outward from the plateau and approximately perpendicular to the regional topographic contours of the plateau the orientation of this crustal shortening is northeast southwest on the northeastern margin east west on the eastern margin and northwest southeast in the longmenshan on the southeastern margin thus at least some of the extrusion of eastern tibet out of india s northward path into asia is absorbed by crustal shortening on the margins of the plateau the variation from normal faulting in the high tibetan plateau where elevations exceed 5000 m to dominantly strike slip faulting farther east where elevations are lower and then to thrust faulting on the margins of the plateau where elevations drop below 3000 m surely results at least in part from a decrease in the value of the vertical stress the magnitude of the east west compressive stress need not vary across the plateau

seismotectonics of the himalayan collision zone geometry of the underthrusting indian plate beneath the himalaya fault plane solutions and well determined focal depths of medium sized earthquakes topography and landsat imagery in conjunction with seismicity maps cross sections and available geological information are used to investigate the present tectonics of the himalayan continental collision zone most of the accurately located epicenters of events along the himalayan arc 78 e 95 e that occurred between 1961 and 1981 are concentrated in a narrow zone about 50 km wide lying between the northerly dipping main boundary mbt and main central mct thrusts most of these events are located just south of the mct though the epicenters of the events are in general well located their depths as determined by teleseismic travel time data are very unreliable events with accurately determined depths obtained from identification of surface reflected phases define a simple planar zone from about 10 km and 20 km depth with an apparent dip of about 15 this result is all the more remarkable considering that the events used were located along about an 1800 km length of the himalyan arc except for one all available focal mechanisms of events within this zone indicate shallow 30 north dipping thrusts this shallow north dipping zone apparently defines a part of the detachment that separates the underthrusting indian plate from the lesser himalayan crustal block the spatial extent and the geometry of this interplate thrust zone strongly indicate that the mbt and nearby subsidiary surface and blind thrusts rather than the mct are currently the most active structures of the himalayan arc we suggest that the great himalayan earthquakes m 8 occur along the same detachment surface as defined by the thrust type medium sized events events located to the south of the mbt and beneath the ganges foredeep show normal faulting with t axes perpendicular to the himalayan trend the above results suggest that the indian continental plate is underthrusting the himalayan crustal blocks in a relatively coherent and simple geometry and that this geometry is not much different from that observed along oceanic subduction zones the november 19 1980 earthquake that occurred near the mct near 88 5 e shows a predominantly strike slip focal mechanism one of the nodal planes of this mechanism is transverse to the himalayan structural grain and moreover this plane has a trend similar to that of the recently mapped yadong gulu rift in the tethyan himalaya and in southern tibet just northeast of the earthquake we interpret this predominantly left lateral strike slip mechanism to indicate a possible genetic relationship between transverse structural features in the underthrusting indian plate the kishangang basement fault and the upper himalayan blocks and tibet

effects of earthquake mislocation on estimates of velocity structure abstract recently there have been several attempts at imaging slab structure using teleseismically observed travel times these times are a function of both event location and velocity structure teleseismically determined epicenters of subduction zone earthquakes which can occasionally be checked by comparison with accurately determined epicenters using local seismographs are systematically incorrect by as much as 40 km observed travel time residuals are calculated with respect to this incorrect location theoretical residuals on the other hand are usually calculated by initiating ray tracing at the teleseismically determined hypocenter in comparing the theoretical and observed times we make two errors first ray tracing should be initiated at the true location of the earthquake not at the location determined from teleseismic observations obviously this can rarely be done but fortunately this source of error produces only subtle differences in the theoretical residuals the second much more significant error results from the fact that the observed residuals are calculated with respect to a location that differs from the actual source whereas the theoretical residuals are calculated with respect to the same location used to initiate ray tracing this inconsistent handling of event locations produces profound differences in residuals which unless accounted for in the velocity determination could result in velocity estimates that are severely biased to demonstrate this we analyze travel time residuals from a small thrust earthquake in the central aleutians which produced impulsive teleseismic arrivals times from the local adak array provide tight constraints on its absolute location the isc location which is constrained primarily by teleseismic times is 40 km north of the local array location we compute residuals from the observed arrival times with respect to the local array and the teleseismic locations the residual distribution computed at the local array location is dominated by large average of 2 s negative residuals to the north as expected for a high velocity slab dipping to the north on the other hand the residual distribution computed at the teleseismic location has negative residuals averaging less than 0 5 s to the north and larger amplitude negative residuals to the south theoretical times are calculated by initiating ray tracing within a thermal model of the aleutian slab at the local array location when theoretical residuals are calculated with respect to the location used to initiate ray tracing these times agree well with observed times at the local array location the correlation coefficient is 0 84 however the correlation between these synthetic times and observed times at the teleseismic location drops to 0 04 this latter comparison is often used in the literature and can lead to biased estimates of velocity structure the former comparison is only possible when absolute event locations are known we suggest a technique to correct for this bias the procedure of calculating travel time residuals with respect to the hypocenter determined by least squares minimization of the residuals is equivalent to applying a specific high pass linear filter to the residuals mapped on the unit focal sphere in nearly all teleseismic problems this filter has been applied to the data to make a self consistent analysis we should also apply this filter to the synthetic times the correlation between filtered data and filtered synthetic for the aleutian event is 0 51

earthquake source parameters and stress distribution in the adak island region of the central aleutian islands alaska source parameters have been systematically determined for all earthquakes with mw 5 that occurred between 172 w and 179 w longitude in the adak island region of the central aleutian islands during 1977 march 1987 we relocate the events using a plate velocity model developed for the region and use two alternative methods of depth determination the first method uses arrival times of direct and prominent reflected phases primarily pwp the second method uses broadband p wave displacement seismograms in an inversion for source depth the analysis of these events provides a well constrained data set for the study of stress release along an active subduction zone three earthquakes which occurred seaward of the trench axis are located just below the crust mantle interface and show extension nearly perpendicular to the trench axis seven events occurred in the wadati benioff zone sixty four events are located in the main thrust zone and except for five unusual events are characterized by thrust mechanisms with one nodal plane dipping north at a shallow angle in cross section the thrust zone appears as a thin 10 15 km thickness interplate region which extends from 15 to 50 km depth a 10 15 average discrepancy between observed slip vector azimuths and the predicted relative motion direction between the pacific and north american plates exists for these events the observed slip vectors are oriented more normal to the trench than is predicted by plate motions five earthquakes which occurred as aftershocks to the may 7 1986 earthquake mw 8 0 in the crust of the overriding plate have strike slip mechanisms consistent with right lateral motion on arc parallel fault planes observations of slip vectors along the whole aleutian arc show a similar trend to that observed in the adak island region the largest differences 30 between observed and predicted slip azimuths occur around 175 e we propose a model of plate interaction in which a portion of the along arc motion occurs along a weak strike slip shear zone in the upper plate near the volcanic line the slip azimuths in the main thrust zone fit this model well if the amount of transcurrent slip occurring in the upper plate is 60 of the arc parallel relative plate motion a consequence of the model is along arc extension of the overriding plate between the accretionary wedge and the volcanic line especially in the western part of the aleutian arc calculations based on a tectonic model by geist et al 1988 for the formation of arc summit basins through block rotation and translation suggest that along arc extension has been significant since late miocene or early pliocene

travel times and station corrections for p waves at teleseismic distances approximately 3300 shallow focus earthquakes and 1000 seismic stations have been used in a study of p wave travel times and station residuals including azimuthal effects the events were selected from a catalog containing 160 000 earthquakes and those having uniform distance and azimuthal coverage were systematically relocated and used to refine p wave travel times and station corrections station corrections are provided for 994 seismic stations the station corrections involve three terms the static effect and two cosine terms with appropriate phase shifts they exhibit general consistency over broad geographic areas and where coverage is dense often show abrupt changes from one geological province to another the cos 2 terms appear to be due to upper mantle anisotropy and they correlate with the stress direction in the crust

p and s wave travel time inversions for subducting slab under the island arcs of the northwest pacific we have observed slablike high p and s velocity anomalies around the wadati benioff zone under island arcs of the northwest pacific through travel time tomographic inversions nineteen years of international seismological centre travel time residuals for events and stations in this large region are used analyses of resolution and noise show that the images are generally well resolved the images illustrate that slab anomalies are continuous along strike in most parts of the upper mantle of the region and become contorted and generally broadened with depth near the bottom of the upper mantle fingering of the slabs including segmenting and spreading is indicated the fast anomalies associated with the japan izu bonin and mariana subduction zones tend to flatten to subhorizontal at depth while downward spreading may occur under parts of the mariana and kurile arcs the fast anomalies below 700 km are not in the shape of a single coherent sheet the principal compressional axes of focal mechanisms in the region consistently follow the downdip direction of the high velocity slab even when it bends to subhorizontal at depth the depth at which compression begins to dominate the downdip stress regime in the slab apparently depends on bending of the slab and its dip slab fingering and intense deep seismicity probably are the consequence of the slab encountering a barrier of some form around the 670 km discontinuity

3 dimensional structure of the indian ocean inferred from long period surface waves to improve the lateral resolution of the first global 3 dimensional models of seismic wave velocities regional studies have to be undertaken the dispersion of rayleigh waves along 86 paths across the indian ocean and surrounding regions is investigated in the period range 40 300 s the regionalization of group velocity according to the age of the sea floor shows an increase of velocity with age up to 150 s only similar to the results in the pacific ocean but here this relationship vanishes more quickly at long period therefore the correlation of the deep structure with surface tectonics seems to be shallower in the indian ocean than in the pacific ocean a tomographic method is applied to compute the geographical distributions of group velocity and azimuthal anisotropy and then the 3 d structure of s wave velocity horizontal wavelengths of 2000 km for velocity and 3000 km for azimuthal anisotropy distribution can be resolved except for the central part of the south east indian ridge which displays high velocities at all depths the inversion corroborates a good correlation between lithospheric structure down to 120 km and surface tectonics low velocities along the central and southeast indian ridges velocity increasing with the age of the sea floor high velocities under african indian and australian shields at greater depths the low velocity zones under the gulf of aden and the western part of the southeast indian ridges hold but the low velocity anomaly of the central indian ridge is offset eastward the low velocity anomalies suggest uprising material and complex plate boundary

whole mantle p wave travel time tomography abstract a method of tomographic inversion to obtain three dimensional velocity perturbations in the earth s whole mantle has been developed and applied to more than two million p wave arrival time data reported by international seismology center isc the model is parameterized with 32 768 blocks the divisions in latitude longitude and radius are 32 64 and 16 respectively horizontal cell size is 5 6 5 6 the layer thicknesses vary with depth 29 km just below the surface and 334 km just above the core mantle boundary starting from a spherically symmetric earth model we obtained a three dimensional model using the following iterative procedures first we relocated all the events second we backprojected the residual into the whole mantle third we refined the spherically symmetric earth model the solutions have been converged in five iterations we adopted the following techniques in the backprojection procedure the first order smoothness was introduced as a damping which makes the solution independent of the starting model and its apparent fluctuation minimal the basic equations for delay times and smoothness are solved using the conjugate gradient method an iterative method which guarantees the convergence of solution into the exact least squares solution the weight on the smoothness i e the damping factor was objectively determined by a simplified cross validation technique the final solution was obtained as an average of the ten solutions each of which was derived from one tenth of the total data set the reliability of the solution is examined in two ways 1 mapping the resolution given by the reconstruction of checkerboard patterns and 2 mapping the variance given from the gaussian noise input this is the first result which delineates the whole mantle structure with its reliability mapping the longest wavelength anomalies of the lower mantle are similar to those of previous studies by dziewonski 1984 and hager and clayton 1989 however the shorter wavelength patterns have many discrepancies the fast anomalies of the uppermost mantle beneath the shield and the slow anomalies beneath the active tectonic regions are clearly seen we also revealed the l 2 pattern at the transition zone reported by the previous surface wave and free oscillation studies the most striking feature is that of the fast anomalies lying along the extension of the large subducting plate up to depths of about 1000 km or more the resolving powers in these regions are generally good

the trade off between volumetric and topographic structure for seismic traveltimes 660 km topography and mantle structure summary synthetic body wave traveltime inversion experiments were performed to evaluate the effect of unmodelled 660km discontinuity topography on the inference of aspherical volumetric mantle structure synthetic residuals were computed for s waves refracted through a 660 km discontinuity with topography we employed a spherical harmonic parametrization for lateral variations of the topography of the 660 km discontinuity and the mantle velocity structure the radial dependence of the velocity structure in the mantle was parametrized in two ways smooth chebyshev polynomial functions and uniform shells the results of both para metrizations show that significant smearing of the input topographic signal appears in the models of volumetric mantle structure inferred from the synthetic data solving for higher order radial structure with the smooth chebyshev functions reduces the smearing but resolution is limited to the half wavelength of the radial basis functions more of the input synthetic residual variance is absorbed into the solution for volumetric structure by solving for higher order radial structure with smooth polynomials or with thinner shells directly below 660km depth however fundamental differences between the kernels for volumetric and topographic structure restrict recovery of the input signal to approximately 80 per cent this work points to the possible value of relating volumetric and topographic structure when inverting seismic observations this may be addressed by incorporating geodynamic modelling and mineral physics results into the modelling of seismic observations

seismic structure of the deep kurile subduction zone three dimensional modeling of p wave travel time residuals was performed to investigate the deep slab related velocity structure within the kurile subduction zone travel times of p waves from earthquakes at all depths within the kurile subduction zone to world wide standard seismograph network and canadian stations were measured instead of analyzing the travel time residuals of a single event relative travel time residuals of p waves to common stations have been analyzed and used in this study to isolate near source contributions from the total travel time residuals the effect of uncertainties in long wavelength heterogeneity far from the source in the lower mantle and the effect of uncertainties in the reference earth model have been significantly reduced by analyzing relative travel time residuals the effect of uncertainties in station corrections are eliminated by relative travel time residuals our measured p wave travel time data clearly indicate that high velocity anomalies exist in the lower mantle beneath the kurile subduction zone but they do not appear to be caused by simple slab continuation into the lower mantle the travel time modeling was accomplished using a fully three dimensional finite difference technique for wave propagation within the source region the modeling results show that high velocity anomalies extend several hundred kilometers into the lower mantle but they appear to be very complicated a large number of models consisting of simple slab continuation into the lower mantle were tested and the results show that none ofthese models was able to produce synthetics which match the observed p wave travel time data the slab related velocity anomalies in the upper mantle of the kurile subduction zone are generally consistent with the seismicity the high velocity anomalies in the lower mantle below the kurile subduction zone are broad and geometrically change from the southern to the northern kuriles below the southern kuriles the high velocity anomalies appear to be subhorizontal however beneath the central kuriles there are broad about 600 km wide high velocity anomalies on the continental side of the slab which extend several hundred kilometers into the lower mantle the high velocity anomalies found below the northern kuriles are broad and on both the continental and the ocean side of the slab and extend several hundred kilometers into the lower mantle

soil geomorphic classification soil taxonomy and effects on soil richness assessments the study of pedodiversity and soil richness depends on the notion of soils as discrete entities soil classifications are often criticized in this regard because they depend in part on arbitrary or subjective criteria in this study soils were categorized on the basis of the presence or absence of six lithological and morphological characteristics richness vs area relationships and the general pattern of soil variability and diversity were then compared to analyses of pedodiversity based on soil taxonomy the study area consists of sixteen 0 13 ha plots on forested sideslopes of the ouachita mountains arkansas with a minimum of 20 classified soil pits per plot an ad hoc classification was developed from the standpoint of soil geomorphology and studies of the coevolution of soils and landscapes and based on the regional environmental framework soils were classified based on 1 underlying geology shale sandstone bedrock or transported sandstone rock fragments and on the presence or absence of 2 texture contrast subsoils 3 eluvial horizons 4 surface and or subsurface stone lines or zones 5 lithological contrasts between soil and underlying geology and 6 redoximorphic features the soil geomorphic classification sgc yielded 40 different soil types out of 288 possible different combinations of the criteria compared to 19 different series or taxadjuncts identified by standard soil classification however 21 of the sgc soil types had only one or two representatives individual plots contained five to 11 different sgc soil types with extensive local variability a standard power function relationship between soil richness s and area or number of samples a provided the best fit for most plots s ca b the exponent b was slightly higher than for the taxonomy based analysis but in general the analyses lead to similar conclusions with respect to the relationship between richness and area and the relative importance of local within plot versus regional between plot variability results support the view that soils can be viewed and treated as discrete entities that richness assessments are not necessarily extremely sensitive to the classification used and that highly localized variability may be critical to pedodiversity the suggested criteria for identifying discrete soil types are given based on qualitative morphological differences and state factor relations contiguity and connectivity

soil redistribution and pedologic transformations in coastal plain croplands in agricultural basins of the southeastern coastal plain there are typically large disparities between upland soil erosion and sediment delivered to streams this suggests that colluvial storage and redistribution of eroded soil within croplands is occurring and or that processes other than fluvial erosion are at work this study used soil morphology and stratigraphy as an indicator of erosion and deposition processes in a watershed at littlefield north carolina soil stratigraphy and morphology reflect the ways in which mass fluxes associated with cultivation transform the local soils fluvial aeolian and tillage processes were all found to be active in the redistribution of soil the soil transformations are of five general types first erosion and compaction in the cultivated area as a whole result in the thinning of arenic and grossarenic paleudults and paleaquults to form arenic typic and aquic paleudults and paleaquults second redistribution of surficial material within the fields results in transitions between arenic and typic or aquic subgroups as loamy sand a and e horizons are truncated or accreted third aeolian deposition at forested field boundaries leads to the formation of compound soils with podzolized features fourth sandy rill fan deposits at slope bases create cumulic soils distinct from the loamy sands of the source area or the darker finer terrace soils buried by the fan deposits finally tillage and fluvial deposition in upland depressions results in the gradual burial of rains poorly drained typic paleaquults soils results confirm the importance of upland sediment storage and redistribution and the role of tillage and aeolian processes as well as fluvial processes in the region copyright 1999 john wiley sons ltd

pedodiversity and global soil patterns at coarse scales with discussion several algorithms for analyzing the diversity of the world pedosphere are reviewed and employed special emphasis has been laid on indices based on the theory of information we study the diversity and distribution of major soil groups by continents and climatic zones on the basis of data compiled by the fao at the scale i 5 000 ooo major soil group distribution model relationships on a world level seem to follow more equitable patterns than those established for biocenoses and soil patterns at fine scales at a continental level the pedosphere s diversity is characterized by similarities rather than differences differences in diversity by climatic zones are more marked evenness pielou s index and diversity shannon s index tend to be greater in the climatic zones of intermediate latitudes than in circumequatorial and circumboreal latitudes the climatic zones closest to the poles could be the planet s most uniform soil patterns at small scales mountain areas in general achieve the highest pedorichness and lowest values of diversity global soil pattern distribution was also analyzed using multivariate techniques at a continental level it is possible for the structure of the global pedosphere to be determined by the continent s geological tectonic and climatic histories soil patterns of different climatic zones are linked in a very well defined latitudinal gradient

how deep can we see the high velocity anomalies beneath the japan islands high velocity anomalies are found in the lower mantle beneath the japan islands and their vicinity through an analysis of detailed three dimensional p wave velocity structure based on a tomographic inversion of isc data beneath the sea of japan the high velocity anomalies in the lower mantle are slab like and appear to extend below the deep focus earthquakes of the high velocity pacific slab descending from the japan trench this slab like high velocity body extending into the lower mantle steepens below a depth of 500 600 km resolution analyses confirms the existence of a slab like high velocity region in the lower mantle though the depth extent is not well resolved on the other hand the pacific slab descending from the izu bonin trench seems to be fingering that is high velocity anomalies are penetrating into the lower mantle beneath latitude 26 n and not penetrating but horizontally bending in the deeper portion of the upper mantle around 29 n

three dimensional velocity models of focal zones and refinement of hypocenter parameters we develop an iterative procedure to calculate three dimensional p wave velocity fields by earthquake observations in areas of dense seismicity we describe the principal features of the algorithm considering the stability of the experimental data and of the derived velocity fields as well as problems of averaging results results are presented for the kuril kamchatka seismic zone

simultaneous travel time inversion for earthquake location and subduction zone structure in the central aleutian islands a combined location and velocity inversion technique is applied to travel time data from 151 well recorded central aleutian earthquakes the data include p and s wave arrivals at stations of a local network and p pp and sp wave arrivals at teleseismic stations after correction for crustal structure at the reflection points the depth phases pp and sp provide important constraints on subduction zone structure not ordinarily resolved by other types of data the structure is assumed to vary only across the arc and in depth it is parameterized with cubic splines by specifying the velocity at each point of a gridded arc cross section to avoid ray tracing it is assumed that the velocity part of the problem is linear preliminary results show that deep earthquakes apparently occur within a narrow downdip zone near the upper surface of the descending slab in contrast with previous studies which have located them within the presumably stronger and colder inner core of the slab a slab thickness of 80 100 km and a downdip length of about 400 km well below the deepest seismic activity are indicated the slab is characterized by seismic velocities as much as 11 higher than the surrounding mantle in its upper portions and 4 6 higher at depth a sharp velocity gradient and lower velocities occur directly beneath the volcanic arc near the top of the slab the slab anomaly appears to spread out and fall off very slowly with depth these are probably not real effects but consequences of the omission of three dimensional ray tracing

travel times from earthquakes near southern kuril and their implications for the fate of subducted lithosphere abstract analysis of travel time residuals from deep and intermediate focus earthquakes along the kuril kamchatka arc has been a major impetus in advancing the hypothesis of deep slab penetration the interpretation of travel times however has been controversial the quality of arrivals reported in bulletins has also been debated using both digital and analog seismograms we precisely measured approximately 400 arrival times of teleseismic p phases for seven earthquakes most of which occurred since 1987 near southern kuril travel times from many of these events have not been analyzed by other researchers including a unique pair of shallow and deep focus earthquakes beneath the island of sakhalin in general differences between our precisely measured p arrivals and those reported by the international seismological center isc are within 0 4 s although isolated large differences do exist at common stations large differences in travel time residuals up to 1 5 s are observed between one of the deepest earthquakes in northern kuril and a deep focus event beneath the island of sakhalin located some 150 km farther west of the well defined wadati benioff zone in southern kuril significantly faster travel times up to 1 2 s or more are also observed along north northeast and south southwest azimuths for the deep focus event in northern kuril than for a shallow focus earthquake west of the sakhalin island where the effect of subducted lithosphere should be minimal in both cases the observed differential residuals between earthquakes in northern and southern portions of the arc are too large to be caused by epicenter mislocation since differential travel time residuals largely reflect differences in near source structure seismic wave speeds below depths of approximately 650 km seem to vary along this arc the magnitude of slab like anomalies in the lower mantle beneath sakhalin is probably two to three times smaller than that in northern kuril kamchatka if the pattern of travel time anomalies observed for deep focus earthquakes in northern kuril kamchatka is caused by coherent subducted slab in the lower mantle wholesale slab penetration into the lower mantle probably did not occur beneath the sakhalin there also appears to be a correlation between the state of strain within subducted lithosphere in the upper mantle and the extent of slab penetration into the lower mantle along southern kuril a net down dip extensional strain is observed within the slab at intermediate depths and persists to an unusual depth of approximately 450 km on the other hand in the northern kuril kamchatka down dip compressional strain dominates at all depths in the subducted lithosphere

the fate of descending slabs oceanic lithosphere the stiff plate formed by the cooling of chemically diffcrentiated material that rises and mclts under mid ocean ridges and spreads laterally in the process called sea floor spreading has an ephemeral residence at the surface of the earth typically within 100 200 ma densi fication of the old oceanic lithosphere leads to a dynamic instability causing it to sink into the interior descending as a layered slab with highly anom alous thermal and chemical characteristics relative to the surrounding ambient mantle the slab heats as it sinks but the warming is sluggish slow to overcome the effect of more than 100 ma of cooling at the surface and the negative buoyancy of the slab continues to drive its descent increasing pressure and temperature with depth drive various chemical reactions in the slab including expulsion of water and other volatiles accumulated at the surface and destabilization of associated hydrous phases suites of mineralogical phase transformations occur within the slab s crustal and depleted mantle components because the slab has been processed through the melting zone at the ridge partially hydrated and cooled significantly the phase equilibria within the slab differ from those of the surrounding mantle near 400 km depth an exothermic phase transformation occurs with mg fe 2si04 olivine in the slab converting to the high pressure modified j spinel structure the spinel transition helps to drive the slab onward although a central core of metastable olivine may persist to greater depths with eventual transformational faulting

subduction zone calibration and teleseismic relocation of thrust zone events in the central aleutian islands abstract teleseismically determined epicenters for thrust zone earthquakes in the central aleutian islands are systematically mislocated by about 40 km to the north relative to local network solutions we attribute the mislocation to travel time anomalies produced by the higher p wave velocity in the subducting slab these travel time anomalies can be estimated by seismic ray tracing through a thermally modeled velocity structure for the slab observed teleseismic station residuals and slab travel time anomalies computed from local network hypocenters plotted as a function of event distance to the center of curvature of the island arc show good agreement this distance versus residual relationship can be used to validate the local network hypocenters and to constrain the length of subducting lithosphere computed slab source corrections when incorporated in a standard location program reduce teleseismic mislocations to 20 km the addition of empirical station corrections reduces the mislocation to about 10 to 15 km depth and origin time estimates can be further improved through use of better station corrections a local station within 2 and depth phases

seismic constraints on the morphology of deep slabs residual sphere images from deep earthquakes not only detect the presence of slab associated velocity anomalies but also lend insight into the flow and deformation of lithosphere subducted into the lower mantle we have compared travel times from deep events in the kuril and mariana arcs with the seismic velocity anomalies implied by kinematical models that thicken the slab perpendicular to its plane by reducing the vertical velocity of the flow with depth we assume that the details of the deformation whether the slab buckles imbricates fragments etc are averaged out along the ray paths and hence our models constrain the scale not the mode of slab thickening the deep event travel times are best fit by undeformed models but the ability of the residual sphere method to resolve slab thickness is limited by ray bending effects although the mariana times are consistent with advective thickening factors of 5 or more factors larger than 3 are ruled out by the kuril data for all models examined the data require that slab material extends to depths of 900 1000 km global tomographic models and regional studies which delineate high velocity anomalies in the lower mantle beneath zones of cenozoic subduction are consistent with our results as is recent work on pulse distortion by slab gradients comparison of observed and predicted rates of seismic moment release suggests that if substantial advective thickening does occur it is largely aseismic

nonequilibrium regolith thickness in the ouachita mountains abstract interpretations of regolith and soil thickness in the context of landscape evolution are typically based on the notion that thickness is controlled by the interaction of weathering rates and erosion and tuned to topography on sideslopes of the ouachita mountains arkansas however there is a high degree of local spatial variability that is largely unrelated to topography this indicates nonequilibrium in the sense that there is no evidence of a balance between rates of weathering and removal as is postulated in some conceptual models in geomorphology and pedology johnson s soil thickness model is applied as an alternative to interpret local variations in regolith thickness at the study sites regolith thickness is not generally related to slope curvature elevation or pedogenic development in the solum this indicates that variability in thickness is related chiefly to processes and controls acting in the lower regolith below the solum the primary controls of variability are local lithol

rock fragment distributions and regolith evolution in the ouachita mountains arkansas usa rock fragments in the regolith are a persistent property that reflects the combined influences of geologic controls erosion deposition bioturbation and weathering the distribution of rock fragments in regoliths of the ouachita mountains arkansas shows that sandstone fragments are common in all layers even if sandstone is absent in parent material shale and sandstone fragments are produced at the bedrock weathering front but the shale weathers rapidly and intact fragments are rare in the solum sandstone is weathered from ridgetop outcrops and transported downslope some of these fragments are moved downward by faunalturbation and by transport into pits associated with rotting tree stumps upward movement by treethrow is common resulting in a net concentration of rocks near the surface however the highest fragment concentrations are in the lower regolith indicating active production at the weathering front the regolith is a dynamic feature reflecting the influences of vertical and horizontal processes of active weathering at the bedrock interface and of surficial sediment movements the role of trees in redistributing rock fragments suggests that significant regolith mixing occurs over time scales associated with forest vegetation communities and that forest soils have likely been extensively mixed within holocene and historic time copyright 2005 john wiley sons ltd

is land use change a cause of loss of pedodiversity the case of the mazzarrone study area sicily abstract anthropogenic soils created ex novo by land use change in large scale farming are from a pedogenetic point of view catastrophic events that bring the soils to time zero and change the natural pattern of the soilscape remarkably in some cases the quantitative aspects of pedodiversity of a soilscape in south east sicily where some types of soils in recent decades have suffered a consistent reduction due to the transformations by large scale farming are considered the evolution of pedodiversity over a 53 year period 1955 to 2008 is examined using a dedicated statistical method and a space time model based on markov analysis and cellular automata in order to predict the evolution of the soilscape pattern in the next 42 years i e until 2050 soil subgroups using the usda soil taxonomy and a classification proposal were considered and the following indices were used richness shannon s diversity index simpson diversity index modified simpson s diversity index shannon s evenness index simpson s evenness index and modified simpson s evenness index these indices measured over time show quantitatively a decrease in pedodiversity that highlights the effect of the human intervention in modifying the natural order of the soilscape

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

mapping the lower mantle determination of lateral heterogeneity in p velocity up to degree and order 6 the data from the international seismological centre bulletins for the years 1964 1979 are used to derive a three dimensional model of lateral variations of the p velocity in the lower mantle unlike previous studies in which such perturbations were represented by a blocklike parameterization we seek the solution in the form r k 0k l 0l m 0l k r kalm cos m kblm sin m plm cos some 500 000 travel time residuals for teleseismic distances from 5000 earthquakes are used in an iterative procedure to derive the coefficients a and b the maximum k and l used are 4 and 6 respectively in each iteration in addition to solving for the three dimensional structure we also relocate all the earthquakes perturb the average travel time curve and determine station corrections for over 1000 stations particular attention is given to the problem of weighting the individual observations in order to avoid as much as possible the bias due to the uneven distribution of sources and receivers the resulting model shows a high level of perturbations just below the 670 km discontinuity and just above the core mantle boundary where the maximum perturbations reach 1 1 5 of the average velocity even for this highly smoothed model at a depth of 2000 km the rms perturbations are some 3 to 4 times lower than at either of the two boundaries the model predicts well the large scale pattern of observed travel time residuals for various source regions except for the distinct effects of the subduction zones the most striking large scale three dimensional feature of the model is a ring of high velocities circumscribing the pacific basin within a depth range from 1000 km to the core mantle boundary if the proportionality between perturbations in the velocity and temperature is assumed the derived pattern of anomalies could be consistent with a two boundary layer model of convection in the lower mantle some caution however should be exercised in interpreting the results near the 670 km discontinuity where the resolving power of our data set is limited by the lack of adequate control of the upper mantle structure at the same time a significant global increase in the level of perturbations in the lowermost mantle is established beyond question the results of dziewonski et al 1977 on the correlation between the equivalent geoid and the observed geoid for the angular order numbers 2 and 3 is confirmed but there is no significant correlation for degrees from 4 to 6 these calculations are made for the rigid earth richards and hager this issue show that introduction of finite viscosity can change the sign of a geoid anomaly in addition recent studies of lateral variations in the shear velocity reveal the presence of large scale anomalies in the upper mantle thus while the inferences made here with respect to the origin of the gravest orders of the geopotential field are not conclusive they point the way in which results from seismology can be used to address some of the basic questions of geodynamics

global scale p wave tomography optimized for prediction of teleseismic and regional travel times for middle east events 1 data set development 1 we extend the bayesloc seismic multiple event location algorithm for application to global arrival time data sets bayesloc is a formulation of the joint probability distribution spanning multiple event location parameters including hypocenters travel time corrections pick precision and phase labels stochastic priors may be used to constrain any of the bayesloc parameters markov chain monte carlo sampling is used to draw samples from the joint probability distribution and the posteriori samples are summarized to infer conventional location parameters such as the hypocenter the first application of the broad area bayesloc algorithm is to a data set consisting of all well recorded events in the middle east and the most well recorded events with 5 spatial sampling globally this sampling strategy is designed to provide the ray coverage needed to determine lithospheric scale p wave velocity structure in the middle east using the complementary ray geometry provided by regional subhorizontal and teleseismic subvertical raypaths and to determine a consistent albeit lower resolution image of global mantle structure the data set consists of 5401 events and 878 535 p pn pp sp and pcp arrivals recorded at 4606 stations relocated epicenters are an average of 16 km from bulletin locations the data set included events that are known to an accuracy of 1 km a k a gt1 based on nonseismic information the average distance between gt1 epicenters and our relocated epicenters is 5 6 km for arrivals labeled p pn and pcp 92 90 and 96 are properly labeled with probability 0 9 respectively incorrect phase labels are found to be erroneous at rates of 0 6 0 2 1 6 and 2 5 for p pn pcp and depth phases pp and sp respectively labels found to be incorrect but not erroneous were reassigned to another phase label p and pn residual standard deviation with respect to ak135 travel times are dramatically reduced from 3 45 s to 1 01 s the differences between travel time residuals for nearly reciprocal raypaths are significantly reduced from the input event locations suggesting that bayesloc relocation improves data set consistency the reciprocity tests suggest that the dominant contribution to travel time residuals calculated from information provided in global bulletins is location and picks errors not travel time prediction errors due to 3 d structure modeling the whole multiple event system results in accurate locations and an internally consistent data set that is ideal for tomography and other travel time calibration studies simmons et al 2011 companion paper use the bayesloc processed data set to develop a 3 d tomographic image which further reduces residual standard deviation to 0 50 s

on the possibility of reservoir induced seismicity in the garhwal himalaya chander r 1991 on the possibility of reservoir induced seismicity in the garhwal himalaya eng geol 30 393 399 it is argued from a brief review of available evidence that the possibility of reservoir induced seismicity ris in the himalaya as a whole cannot be ruled out at the present time on the other hand a review of recent local investigations of small earthquakes mb less than 5 and teleseismic investigations of moderate earthquakes mb between 5 and 6 mainly occurring in the garhwal segment of the alpide himalayan seismic belt provides evidence that ris in the region can be anticipated while their epicentral belts coincide geographically the estimated focal depths of small and moderate earthquakes of the garhwal himalaya are in the ranges of 0 14 and 10 20 km respectively small earthquakes occur by reactivation of strike slip and reverse faults and moderate earthquakes occur on thrust faults elsewhere in the world ris has been observed most often in the crust at the depths where small earthquakes have been observed in the garhwal himalaya in addition ris has been experienced during the impoundment of reservoirs in strike slip and reverse fault environments while theoretical analyses indicate that if suitably located in relation to the reservoir even a thrust fault may be destabilised by impoundment

application of the jhd technique to the loma prieta california mainshock aftershock sequence and implications for earthquake location relocation of the loma prieta mainshock aftershock sequence using the jhd technique places the events an average of 1 km to the southwest of the locations determined by other authors the new locations show a concentration of seismic activity in the wedge between the san andreas and sargent faults furthermore there seems to be little seismic activity to the east of the sargent fault these features of the seismicity are not observed in other published locations determined using similar data sets a depth cross section perpendicular to the sargent fault near its intersection with the san andreas fault shows two clusters of events along a line segment between 3 and 10 km that dips to the ne and that intersects the main sw dipping plane these clusters may correspond to secondary faults postulated by other authors the jhd station corrections vary between 0 6 and 0 6 sec and indicate the presence of large velocity variations across and along the san andreas fault these corrections are very close to the weighted average of the station residuals obtained when the events are located singly the locations obtained with a single event location program and using the average residuals as station corrections give locations almost coincident with the jhd locations this high similarity of locations is very unusual and is interpreted as the result of quasi random lateral velocity variations in the loma prieta area to estimate the effect of these variations on the location of events synthetic travel times were computed for a realistic although preliminary three dimensional 3d velocity model these synthetic data were then treated as the actual data the corresponding results show that the jhd technique is able to locate events with an average error of 0 5 km in epicenter depths on the other hand are consistently deeper by about 1 km in addition the station corrections are close to the observed corrections additional tests with synthetic data also show that the observed station corrections suggest velocity variations of up to 40 in the top 3 km of the crust although these variations may seem extremely large they are within the range of variation found by other authors and most importantly are required by the observations

investigation of deep slab structure using long period s waves travel times and amplitudes of long period sh scsh ssh and sscsh phases from several deep focus earthquakes in the northwest pacific are analyzed for evidence of lithospheric slab penetration into the lower mantle inclusion of amplitude observations in the analysis provides constraints on lateral velocity gradients present in the deep slabs which are not resolvable using travel times alone travel time and amplitude residual spheres are presented for two deep focus events with good azimuthal coverage but while interesting patterns are present quantitative analysis is precluded by the lack of accurate methods for calculating synthetic long period seismograms for three dimensional slab models therefore we focus our analysis on a two dimensional approximation to the downdip geometry of the kurile and japan slabs which allows comparison of a much larger data set with accurate two dimensional synthetics as well as the use of ss and sscs travel time and amplitude patterns as empirical corrections for deep mantle structure while the limited azimuth range required for this approximation reduces the diagnostic capability of the data it also increases our confidence that the corrected data are most sensitive to the near source region the ss and sscs observations indicate that the downdip shear wave travel time pattern previously attributed to a deep slab extension is primarily caused by broad scale lower mantle heterogeneity once corrected for this structure the s wave observations do not support a simple undeformed slab steepening in dip and penetrating deep into the lower mantle beneath the kurile and japan islands as proposed by jordan 1977 and creager and jordan 1984 1986 rather the observations support shorter and or broader slab models man those previously hypothesized models which can probably be reconciled with p wave data further analysis of the complete three dimensional patterns will be required for more precise resolution of the penetration depths of these slabs if indeed any deep slab heterogeneity is actually seismically detectable

selection of a taxonomic level for soil mapping using diversity and map purity indices a case study from an iranian arid region abstract there is a growing demand for digital soil maps for environmental planning modeling and management if mapped soil classes are taken from a hierarchical taxonomic system a question arises which taxonomic level is most appropriate to be depicted on the map with a given sample size available environmental covariates and the strength of predictive relations between covariates and the soil classes pedodiversity the study and measurement of soil diversity can be considered as a framework to analyze spatial patterns depicted on soil maps this paper discusses the selection of the taxonomic level for soil mapping in an arid region in southeast iran on the basis of 1 the purity of a digital soil class map derived from an artificial neural network ann prediction method using environmental covariates and 2 pedodiversity indices of these soil maps the prediction of soil classes and the calculation of diversity indices were carried out for taxonomic categories of order suborder great group and subgroup using the feed forward back propagation algorithm three layer anns with input hidden and output layers were trained for soil class prediction at each category level in most predictions the combined use of terrain attributes and geomorphic surfaces provided the best results when the taxonomic level changed from order to subgroup the purity decreased whereas the values of the diversity indices increased the highest purity and lowest diversity are observed at the order level indicating a good quality map in terms of its purity but reflecting only little soil diversity thus with a low usage potential on the other hand soil maps at the level of subgroup illustrate high diversity and low purity so that the predicted map units are highly uncertain this map is also inappropriate for users we introduced an index combining the diversity and purity which indicated that the best taxonomic level for soil mapping in the study area is the great group with both high diversity and purity

mapping the tonga slab we applied residual sphere analysis to 25 intermediate and deep focus earthquakes in the tonga subduction zone and mapped variations in slab strike and dip depth extent and deep lateral advection at all latitudes along the arc as in the northwest pacific travel time data from intermediate and deep focus events are well modeled by simple thermal slab structures and a thermal coefficient of velocity p t of 0 5 0 2 m s k i e peak velocity perturbations of about 3 7 in all regions where the seismicity extends to depths of 600 km or more the shortest thermal slab models that cannot be rejected at the 90 confidence level reach depths of 750 km northern tonga to 850 km southern tonga these models however require a value of p t 1 5 m s k 3 times the value suggested by laboratory studies if the magnitude of p t is constrained to be less than 1 0 m s k the minimum penetration depth varies from 800 km to 900 km the travel time data are equally consistent with slab structures that deform at the base of the upper mantle thickening by a factor of 3 and models that contain no advective thickening inferred slab structure varies considerably throughout the subduction zone and the nearly ubiquitous match between the observed seismicity and detailed undulations in slab strike and dip is evidence that residual spheres do reflect near source heterogeneity travel times in southern tonga 21 5 s 27 s are consistent with and in some cases require slab models that bend to a steeper dip at depth this phenomenon is also observed in parts of the northwest pacific but is not required in central 19 s 21 5 s and northern 13 s 19 s tonga the residual spheres of both intermediate and deep focus events suggest a sharp bend in slab strike at 25 s this feature coincides with a kink in strike observed at all depths in the seismicity and occurs at the intersection of the trench and the louisville ridge northern tonga is the locus of considerable complexity in deep slab structure seismicity strain rate and travel time data are consistent with although they do not uniquely require a slab structure in northern tonga which curves sharply to the west at the base of the upper mantle but which strikes to the north at shallower depths and in the lower mantle the contorted segment would have begun subducting roughly 10 m y ago during a major plate reorganization in northernmost tonga a decrease in the maximum depth of seismicity and inferred slab structure provides evidence for southward shear of deep material relative to the shallow slab compared to data from the northwest pacific where travel time observations also suggest slab penetration below the deepest earthquakes tonga seismicity and residual spheres show more complexity at depth and may indicate more deformation internal to the slab these observations argue against convective models which are rigorously stratified at 650 km depth but they are consistent with a discontinuity in mantle properties such as an increase in viscosity or a small percent variation in chemistry if it merely resists and deforms the descending slabs without acting as a complete barrier to flow

toward a theory of island pedogeography testing the driving forces for pedological assemblages in archipelagos of different origins abstract the theory of island biogeography has been based on biodiversity studies and used as a powerful predictive tool currently pedogeography does not have a similar theoretical construct although island biodiversity and biological assemblages have been topics of widespread interest in biogeography ecology and conservation biology soil scientists have conducted few studies of pedodiversity and pedological assemblages in archipelagos several studies have demonstrated that pedodiversity and biodiversity patterns have striking similarities in very disparate environments and at different scales thus it is possible to test for a similar construct of island pedogeography we analyze similarities and differences in the pedosphere for three archipelagos with different origins i oceanic intra plate chains islands hawaiian islands ii oceanic intra plate cluster islands canary islands iii non marine land bridge islands with volcanism associated with plate boundary conditions aegean islands and iv as a comparison islands in a nonplate boundary setting the british isles in the canary islands we also compiled selected biological physiographical geological and climatic data for further analysis of pedodiversity climatic diversity geodiversity and biodiversity our pedogeographic analysis of the three archipelagos indicates archipelagos of varying origins contain different soil assemblages with plate tectonics as the main driving force the similarities between pedodiversity and biodiversity are more remarkable than the differences we tested the hypothesis that soil taxa distributions on island chains can be modelled as a power function similar to the species area relationship sar proposed by mcarthur and wilson for archipelagos the sar functional relationship has been widely corroborated in other biodiversity studies the same patterns were obtained for pedodiversity and biodiversity in the british isles and after that in the aegean archipelago in this study we show similar results in the canary islands furthermore in the canary archipelago a strong relationship exists between pedodiversity biodiversity climate diversity habitat heterogeneity and relief for the hawaii archipelago we did not obtain a statistically significant relationship because soil inventories are not published for the smallest islands and islets however hawaii does have a chronosequence from the older to the younger land units overall the dynamics of the underlying plate tectonic hot spots seems to be the major driving force affecting the various diversity types based on these results we suggest a theoretical proposal of island pedogeography consistent and similar to the theory of island biogeography in view that the latter one also predicts the pedodiversity of soil assemblages in archipelagos this study illustrates several possibilities for further research in soil geography

seismicity and the state of stress from investigations of local earthquakes in the kumaon himalaya abstract results of investigations of local earthquakes in the region of the main central thrust mct in the kumaon himalaya between and adjacent to the valleys of the bhagirathi and yamuna rivers are presented records of over 250 earthquakes were analysed and the following facts emerged 1 1 earthquakes in the himalayas occur in specific areas and belts one such belt has been identified in the region under investigation hypocentral estimates being more reliable for earthquakes occurring in the middle segment approximately 70 km long of this belt crossing the yamuna river between the villages of barkot and syanachatti 2 2 all but a few epicentres in this middle segment lie to the southwest of the surface trace of the mct in a zone with a width of 10 30 km 3 3 most of the earthquakes in this segment occur at depths of less than 10 km below the ground surface the maximum estimated depth being 32 km using observations of first motion for a composite focal mechanism solution the nodal planes were observed to be near vertical and the compression axis near horizontal and normal to the local strike of the seismic belt and of the mct we conclude that although the main central thrust itself is not seismically active in this region there is considerable activity immediately to the southwest of it furthermore the mode of faulting as inferred from the records of these earthquakes is strike slip

the geometry of aleutian subduction three dimensional seismic imaging we constrain the subduction geometry of the aleutian slab by the distribution of seismicity recorded at local seismic networks and by a teleseismic p wave residual sphere analysis of 11 earthquakes and one nuclear explosion the source depth and mechanism of each earthquake are determined by modeling teleseismically recorded long period p and sh waveforms we construct theoretical residual spheres by tracing rays through three dimensional thermal models of the subducting slab assuming a pressure independent thermal coefficient of velocity vp t rays are initiated at the estimated source depths and at epicenters whose relative locations are consistent with those obtained from the observed travel times after correction for slab effects for each event we determine the values of slab strike and dip that provide the best match to the observations average values of 67 confidence intervals determined by an f test are 5 in dip and 10 in strike strike varies along the arc by 60 for all but one of the modeled events the estimated orientation of the slab s aseismic extension agrees to within two standard deviations of that derived from seismicity distributions assuming a constant dip a slab penetration depth of 600 km fits the central aleutian events best this is at least 300 km below the deepest earthquakes slabs terminating above 400 km or below 1000 km provide significantly worse fits though there is a trade off between vp t and penetration depth the best fitting value of vp t using a 600 km deep slab is 0 5 0 1 ms 1 k 1 this is consistent with both ultrasonic laboratory measurements and values obtained for deeper earthquakes in several other subduction zones vp t estimated from shallow thrust events is 20 50 larger than that for intermediate focus events suggesting that a simple thermal model with constant vp t under predicts the velocity anomalies shallower than 100 km depth the fact that a 600 km deep slab provides better fits than a 1000 km deep slab implies that the downdip p rays exit the slab near a depth 600 km a slab bend to either a shallower or steeper dip would satisfy the p times hand picked pcp travel times are most consistent with the slab bending to a 20 steeper dip before plunging into the lower mantle in the western aleutians the relative plate motion becomes transform seismicity ceases at less than 100 km depth and volcanism is no longer active we image a slab like high seismic velocity zone apparently associated with the along arc lateral transport of cold subducted lithosphere from the east an earthquake whose location is known from local observations is analyzed in detail the velocity structure inferred using this location is nearly identical to that obtained using our scheme of annihilating location information from both theoretical and observed times a severe bias would result however from the commonly used procedure of analyzing travel times computed with respect to an incorrect event location such as that of the isc