empirical relationships among seismic velocity effective pressure porosity and clay content in sandstone we use a multivariate analysis to investigate the influence of effective pressure pe porosity and clay content c on the compressional velocity vp and shear velocity vs of sandstones laboratory measurements on water saturated samples of 64 different sandstones provide a large data set that was analyzed statistically for each sample relationships between effective pressure and vp and vs have been determined all samples were well fit by relationships that have an exponential increase in velocity at low pe tapering to a linear increase with pe for pe greater than 0 2 kbar there are differences in the pressure dependences of velocity for different rocks particularly at very low pressures however the differences cannot be attributed to or c for the combined set of measurements from all samples the best fitting formulations are vp 5 77 6 94 1 73c 0 446 pe e 16 7pe and vs 3 70 4 94 1 57c 0 361 pe e 16 7pe while this is admittedly a very simplified parameterization it is remarkable how well

morphology and filling of incised submarine valleys on the continental shelf near the mouth of the fly river gulf of papua 1 much historical perspective about terrestrial and marine processes can be obtained from examination of fluvial valleys formed during lower sea level on surfaces that are now continental shelves the continental shelf near the mouth of the fly river gulf of papua has three incised valleys which were not extensively modified or filled during the holocene transgression multibeam mapping of the valleys documents their morphology seismic profiling reveals stratigraphy of sediment fill and coring within and near the valleys suggests mechanisms of filling kiwai valley is deep 20 50 m relief narrow 1 km wide steep sided and meandering due to river flows that caused its excavation through competent sedimentary deposits purutu valley is shallow 10 20 m relief and broad 2 km wide umuda valley is widest 14 km and has multiple channels with variable incision depths suggesting more extensive fluvial activity than the other two valleys valley filling has occurred in several ways reflecting valley morphology and location relative to the present river mouth kiwai and umuda valleys reveal three stages of infill 1 hemipelagic sedimentation at distal sites 2 gravity driven flows spreading down the valley and 3 subsequent clinoform progradation that completely fills the valley purutu valley fill is dominated by clinoform progradation clinoform progradation in umuda valley is driven by intense sediment reworking on the surrounding topset regions and its large width allows progradation from the sides as well as down its axis most shelf valleys around the world were filled long ago and available techniques have severe limitations for documenting the details of morphology and the mechanisms of filling the shelf valleys described in this paper provide a unique perspective to terrestrial and marine processes before during and after the holocene transgression

dual simulations of fluid flow and seismic wave propagation in a fractured network effects of pore pressure on seismic signature summary fluid flow in the earth s crust plays an important role in a number of geological processes in relatively tight rock formations such flow is usually controlled by open macrofractures with significant implications for ground water flow and hydrocarbon reservoir management the movement of fluids in the fractured media will result in changes in the pore pressure and consequently will cause changes to the effective stress traction and elastic properties the main purpose of this study is to numerically examine the effect of pore pressure changes on seismic wave propagation i e the effects of pore pressures on amplitude arrival time frequency content this is achieved by using dual simulations of fluid flow and seismic propagation in a common 2 d fracture network note that the dual simulations are performed separately as the coupled simulations of fluid flow and seismic wave propagations in such fracture network is not possible because the timescales of fluid flow and wave propagation are considerably different typically fluid flows in hours whereas wave propagation in seconds the flow simulation updates the pore pressure at consecutive time steps and thus the elastic properties of the rock for the seismic modelling in other words during each time step of the flow simulations we compute the elastic response corresponding to the pore pressure distribution the relationship between pore pressure and fractures is linked via an empirical relationship given by schoenberg and the elastic response of fractures is computed using the equivalent medium theory described by hudson and liu therefore we can evaluate the possibility of inferring the changes of fluid properties directly from seismic data our results indicate that p waves are not as sensitive to pore pressure changes as s and coda or scattered waves the increase in pore pressure causes a shift of the energy towards lower frequencies as shown from the spectrum as a result of scattering attenuation another important observation is that the fluid effects on the wavefield vary significantly with the source receiver direction that is the azimuth relative to the fracture orientation these results have significant implications for the characterization of naturally fractured reservoirs using seismic methods and may impact on experimental design to infer such attributes in a real reservoir situation particularly in acquiring time lapse seismic data

sensitivity of time lapse seismic to reservoir stress path the change in reservoir pore pressure due to the production of hydrocarbons leads to anisotropic changes in the stress field acting on the reservoir reservoir stress path is defined as the ratio of the change in effective horizontal stress to the change in effective vertical stress from the initial reservoir conditions and strongly influences the depletion induced compaction behaviour of the reservoir seismic velocities in sandstones vary with stress due to the presence of stress sensitive regions within the rock such as grain boundaries microcracks fractures etc since the response of any microcracks and grain boundaries to a change in stress depends on their orientation relative to the principal stress axes elastic wave velocities are sensitive to reservoir stress path the vertical p and s wave velocities the small offset p and sv wave normal moveout nmo velocities and the p wave amplitude versus offset avo are sensitive to different combinations of vertical and horizontal stress the relationships between these quantities and the change in stress can be calibrated using a repeat seismic sonic log checkshot or vertical seismic profile vsp at the location of a well at which the change in reservoir pressure has been measured alternatively the variation of velocity with azimuth and distance from the borehole obtained by dipole radial profiling can be used having calibrated these relationships the theory allows the reservoir stress path to be monitored using time lapse seismic by combining changes in the vertical p wave impedance changes in the p wave nmo and avo behaviour and changes in the s wave impedance

relating shear sonic anisotropy directions to stress in deviated wells we develop a model that relates the polarization direction of a dipole sonic fast shear wave propagating along the borehole hereafter called fsa to the relative deviatoric stress tensor for arbitrary well orientations we first define stress quantities or subsidiary principal stress relevant for sonic dipole shear characterized sufficiently far away into the formation to be unaffected by borehole stress concentration next we show analytically for wells oriented within principal stress planes and numerically for wells outside principal stress planes that the stress induced fsa coincides with the maximum normal stress direction orthogonal to the borehole maximum subsidiary principal stress using a nonlinear elastic model for isotropic unstressed background media and plane wave solutions this model is independent of stress sensitivity parameters this result is a consequence of first the direct relationship between the stressellipsoid factor and the shear stiffness difference ratio r 2

understanding of elastic anisotropy of shale under triaxial loading porosity deformation approach abstracttheoretical models for the description of stress dependencies for anisotropic rocks are important for building velocity models and the interpretation of seismic data with respect to stress lithology and pore content especially important is the accurate description of the change of anisotropy due to applied anisotropic stress by means of a quantitative model to aid the interpretation the porosity deformation approach pda originally introduced as the piezosensitivity theory describes stress induced changes of elastic properties without any knowledge about the geometry and orientation of the microcracks we have developed a formulation of the theory for a transverse isotropic rock which was loaded parallel to the bedding plane and we found that it can be described theoretically as an orthorhombic rock we also found out how properties that described the velocity change due to hydrostatic loading can be used to predict elastic anisotropy under additional axial loading the number of free para

crustal stress determination from boreholes and rock cores fundamental principles abstract obtaining quantitative information on the state of stress in the crust can only be accomplished by accessing the zone of interest by drilling the borehole cavity however disrupts the virgin stress state by concentrating stresses in predictable patterns with a number of consequences at sufficiently low stress magnitudes the concentrated stresses amplify the elastic anisotropy azimuthally around the borehole because the elastic properties of most rocks depend nonlinearly on stress at higher levels the stresses damage then fracture the rock near the wellbore wall or within a growing core stub indeed almost all of the borehole techniques indirectly measure stress through these manifestations of the concentrated stresses this contribution reviews at a fundamental level the concentration of stresses by the borehole the effects on the materials in the borehole s vicinity and how these are used to infer stress states stress concentrations applied to rocks which are generally nonlinear elastic materials induce both radial and azimuthal variations in elastic wave speeds near the borehole that can be used to infer stress directions from advanced acoustic logging methods hydraulic fractures initiate propagate and remain propped open by measured pressures that can be interpreted with knowledge of the stress concentrations to obtain quantitative stress magnitudes at higher stress levels the rock fails producing borehole breakouts or drilling induced tensile fractures both of which are indicative of stress directions and can be used to constrain stress magnitudes similarly the various styles of drilling induced core fractures indicate both stress directions and the faulting environment encountered unfortunately no method currently allows for complete determination of the stress tensor using a number of different but complementary techniques is necessary to best constrain in situ stress states

predicting stress induced velocity anisotropy in rocks a simple transformation using measured isotropic vp and vs versus hydrostatic pressure is presented for predicting stress induced seismic velocity anisotropy in rocks the compliant crack like portions of the pore space are characterized by generalized compressional and shear compliances that are estimated from the isotropic vp and vs the physical assumption that the compliant porosity is crack like means that the pressure dependence of the generalized compliances is governed primarily by normal tractions resolved across cracks and defects this allows the measured pressure dependence to be mapped from the hydrostatic stress state to any applied nonhydrostatic stress predicted p and s wave velocities agree reasonably well with uniaxial stress data for barre granite and massillon sandstone while it is mechanically similar to methods based on idealized ellipsoidal cracks the approach is relatively independent of any assumed crack geometry and is not limited to small crack densities

elastic piezosensitivity of porous and fractured rocks understanding the stress dependencies of seismic velocities is important for interpreting a variety of seismic data ranging from amplitude versus offset avo and velocity analysis to overpressure prediction and 4d seismic monitoring of reservoirs sometimes rather complex forms of these dependencies based on specific models of porous space geometry are used for example spherical contacts models duffy and mindlin 1957 merkel et al 2001 duffy merkel 2001 and crack contacts models gangi and carlson 1996 carcione and tinivella 2001 have been used in different studies gangi96 however usually the pore pressure velocity dependence along with the velocity dependence on the confining pressure are phenomenologically described by the following simple relationship zimmerman et al 1986 eberhart phillips et al 1989 freund 1992 jones 1992 prasad and manghnani 1997 khaksar et al 1999 carcione and tinivella 2001 kirstetter and macbeth 2001

an analytic model for the stress induced anisotropy of dry rocks one of the main causes of azimuthal anisotropy in sedimentary rocks is anisotropy of tectonic stresses in the earth s crust we have developed an analytic model for seismic anisotropy caused by the application of a small anisotropic stress we first considered an isotropic linearly elastic medium porous or nonporous permeated by a distribution of discontinuities with random isotropic orientation such as randomly oriented compliant grain contacts or cracks the geometry of individual discontinuities is not specified instead their behavior is defined by a ratio b of the normal to tangential excess compliances when this isotropic rock is subjected to a small compressive stress isotropic or anisotropic the number of cracks along a particular plane is reduced in proportion to the normal stress traction acting on that plane this effect is modeled using the sayers kachanov noninteractive approximation the model predicts that such anisotropic crack closure yields elliptical anisotropy regardless of

modeling elastic anisotropy resulting from the application of triaxial stress abstractelastic wave velocities in rocks vary with stress due to the presence of discontinuities and microcracks within the rock we analytically derived a model to account for stress dependency of seismic velocities when a rock is subjected to triaxial stresses we first considered a linearly isotropic elastic medium permeated by a distribution of cracks with random orientations the geometry of cracks is not specified instead their behavior is defined by a ratio b of their normal to tangential excess compliances when this isotropic rock is subjected to triaxial stresses cracks tend to close depending on their orientation with respect to the applied stresses for small stresses the model predicts ellipsoidal anisotropy and expresses the ratios of thomsen s parameters in the three orthogonal planes of symmetry as a function of the compliance and poisson s ratios it also establishes relationships between anisotropy parameters and stress ratios deriving the model for larger stresses shows that su

static and dynamic pressure sensitivity anisotropy of a calcareous shale optimizing the productivity of nonconventional low permeability shale reservoirs requires detailed knowledge of the mechanical properties of such materials these rocks elastic anisotropy is acknowledged but usually ignored due to difficulties in obtaining such information here we study in detail the dynamic and static elastic properties of a suite of calcareous mudstones from the nonconventional duvernay reservoir of alberta canada the complete set of transversely isotropic elastic constants is obtained from strategically oriented ultrasonic transducers to confining pressures of 90 mpa wave speed anisotropies of up to 35 are observed at even the highest confining pressures furthermore the stress sensitivity of the wave speeds and hence moduli is itself highly dependent on direction with speeds taken perpendicular to the bedding plane being highly nonlinearly dependent on pressure whereas those along the bedding plane show unexpectedly nearly no pressure dependence these observations are in qualitative agreement with the preferentially oriented porosity and minerals seen in scanning electron microscope images these results may be significant to the interpretation of sonic logs and azimuthal amplitude versus offset for principal stress directions for the concentration of stress within such formations and for estimation of static engineering moduli from sonic log wave speeds

microcrack induced elastic wave anisotropy of brittle rocks the failure of brittle rocks during compression is preceded by the formation growth and coalescence of microcracks elastic wave velocities are reduced in the presence of open microcracks and fractures and may therefore be used to monitor the progressive damage of the rock in general these microcracks are not randomly oriented and the rock displays an elastic anisotropy the elastic anisotropy due to cracks can be expressed in terms of a second rank and fourth rank crack density tensor for open cracks the contribution of the fourth rank crack density tensor to the elastic wave velocities is small these results are compared with recent measurements of the ultrasonic compressional and shear wave velocities for propagation parallel and perpendicular to an increasing axial stress applied at constant confining stress to berea sandstone inversion of the velocity measurements indicates that the microcracks propagate parallel to the maximum compressive stress in agreement with current rock mechanics theory a reasonable fit to the data is obtained using only the second rank crack density tensor even though at high confining stress the cracks are expected to be in partial contact along their length this is consistent with the model of elastic wave propagation in a medium containing partially contacting fractures published by white however measurements of off axis wave velocities are required to fully quantify the contribution of the fourth rank crack density tensor

stress induced seismic azimuthal anisotropy sand shale content and depth trends offshore north west australia abstractseismic azimuthal anisotropy is apparent when p wave velocities vary with source receiver azimuth and downward propagating s waves split into two quasi s waves polarized in orthogonal directions not accounting for these effects can degrade seismic image quality and result in erroneous amplitude analysis and geologic interpretations there are currently no physical models available to describe how azimuthal anisotropy induced by differential horizontal stress varies with sand shale lithology and depth we develop a model that does so in unconsolidated sand shale sequences offshore north west australia our method naturally introduces two new concepts critical anisotropy and anisotropic depth limit critical anisotropy is the maximum amount of azimuthal anisotropy expected to be observed at the shallowest sediment burial depth where the confining pressure and sediment compaction are minimal the anisotropic depth limit is the maximum depth where the stress induced azimuthal anisotropy is ex

frequency dependence of anisotropy in fluid saturated rocks part ii stress induced anisotropy case a major cause of attenuation in fluid saturated media is the local fluid flow or squirt flow induced by a passing wave between pores of different shapes and sizes several squirt flow models have been derived for isotropic media for anisotropic media however most of the existing squirt flow models only provide the low and high frequency limits of the saturated elastic properties we develop a new squirt flow model to account for the frequency dependence of elastic properties and thus gain some insight into velocity dispersion and attenuation in anisotropic media in a companion paper we focused on media containing aligned compliant pores embedded in an isotropic background matrix in this paper we investigate the case for which anisotropy results from the presence of cracks with an ellipsoidal distribution of orientations due to the application of anisotropic stress the low and high frequency limits of the predicted fluid saturated elastic properties are respectively consistent with gassmann theory and mukerji mavko squirt flow model in the most important case of liquid saturation analytical expressions are derived for elastic properties and thomsen anisotropy parameters the main observations drawn from this model are as follows crack closure perpendicular to the applied stress leads to an increase in seismic velocities as a function of stress in the direction of applied stress and a decrease in squirt flow induced dispersion and attenuation in this direction the anisotropy of squirt flow dispersion engenders a decrease in the degree of anisotropy with frequency the stress induced anisotropy remains elliptical even in saturated media for all frequency ranges

compressibility of porous rocks four compressibilities are defined for porous rock relating changes in the bulk and pore volumes to changes in the pore and confining pressures using a micromechanical theory based on classical linear elasticity three relations are found between these compressibilities two of these relations are verified experimentally for berea and bandera sandstone bounds are derived for these compressibilities involving only the porosity and the elastic moduli of the rock forming minerals for the strains to be unique functions of the stresses the compressibilities must be functions only of the difference between the confining and pore pressures this dependence is verified for berea bandera and boise sandstone while the strains cannot be expressed as functions of an effective stress regardless of how it is defined the elastic volumetric behavior of porous rocks can be studied through tests conducted at zero pore pressure

geological causes and geomorphological precursors of the tsaoling landslide triggered by the 1999 chi chi earthquake taiwan the tsaoling landslide one of the largest landslide areas in taiwan has been affected by catastrophic events triggered by rain or earthquakes six times since 1862 these landslides including that caused by the 1999 earthquake have essentially not been reactivated old slides but were sequential new ones that developed upslope retrogressively the landslide area is underlain by pliocene sandstone and shale to form a dip slope with a bedding plane dipping uniformly at 14 the slip surface of the 1999 landslide was smooth and planar parallel to the bedding plane with a slightly stepped profile it formed within thinly alternated beds of fine sandstone and shale with ripple lamination or in a shale bed the shale is weathered by slaking and probably by sulfuric acid which is inferred to be one of the major causes of the intermittent retrogressive development of the landslides the weathering was likely accelerated by the removal of overlying beds during earlier landslides in 1941 and 1942 the top margin of the 1999 landslide in plan view coincided with a v shaped scarplet which can be clearly recognized on aerial photographs taken before the landslide this geomorphological feature indicates that this landslide had already moved slightly before its 1999 occurrence providing precursory evidences

a seismologically consistent expression for the total area and volume of earthquake triggered landsliding we present a new seismologically consistent expression for the total area and volume of populations of earthquake triggered landslides this model builds on a set of scaling relationships between key parameters such as landslide spatial density seismic ground acceleration fault length earthquake source depth and seismic moment to assess the model we have assembled and normalized a catalog of landslide inventories for 40 shallow continental earthquakes low landscape steepness causes systematic overprediction of the total area and volume of landslides when this effect is accounted for the model predicts the total landslide volume of 63 of 40 cases to within a factor 2 of the volume estimated from observations r2 0 76 the prediction of total landslide area is also sensitive to the landscape steepness but less so than the total volume and it appears to be sensitive to controls on the landslide size frequency distribution and possibly the shaking duration some outliers are likely associated with exceptionally strong rock mass in the epicentral area while others may be related to seismic source complexities ignored by the model however the close match between prediction and estimate for about two thirds of cases in our database suggests that rock mass strength is similar in many cases and that our simple seismic model is often adequate despite the variety of lithologies and tectonic settings covered this makes our expression suitable for integration into landscape evolution models and application to the anticipation or rapid assessment of secondary hazards associated with earthquakes

a decade of tomography over the past 10 years ray based postmigration grid tomography has become the standard model building tool for seismic depth imaging while the basics of the method have remained unchanged since the late 1990s the problems it solves have changed dramatically this evolution has been driven by exploration demands and enabled by computer power there are three main areas of change first standard model resolution has increased from a few thousand meters to a few hundred meters this order of magnitude improvement may be attributed to both high quality complex residual moveout data picked as densely as 25 m to 50 m vertically and horizontally and to a strategy of working down from long wavelength to short wavelength solutions second more and more seismic data sets are being acquired along multiple azimuths for improved illumination and multiple suppression high resolution velocity tomography must solve for all azimuths simultaneously to prevent short wavelength velocity heterogeneity from being mistaken for azimuthal anisotropy third there has been a shift from predominantly isotropic to predominantly anisotropic models both vti and tti with four component data anisotropic grid tomography can be used to build models that tie pz and ps images in depth

seismic anisotropy of fractured rock a simple method for including the effects of geologically realistic fractures on the seismic propagation through fractured rocks can be obtained by writing the effective compliance tensor of the fractured rock as the sum of the compliance tensor of the unfractured background rock and the compliance tensors for each set of parallel fractures or aligned fractures the compliance tensor of each fracture set is derivable from a second rank fracture compliance tensor for a rotationally symmetric set of fractures the fracture compliance tensor depends on only two fracture compliances one controlling fracture compliance normal the other tangential to the plane of the fractures the stiffness tensor which is more useful in the consideration of elastic wave propagation through rocks can then be obtained by inversion the components of the excess fracture compliance tensor represent the maximum amount of information that can be obtained from seismic data if the background rock is isotropic and the normal a

motion of the south bismarck plate papua new guinea the absolute motion of the south bismarck plate was first estimated by tregoning et al 1998 from three site velocities estimated from global positioning system gps observations we report an improved estimate of the euler vector for this plate using site velocities derived from new gps data which include the velocity of a site located 25 km from the pole of rotation the gps velocities of madang witu jacquinot bay and finschafen can be modelled to within 3 mm yr using a single pole of rotation located at 6 75 s 147 98 e with a clockwise rotation rate of 8 11 my the known tectonic features and available geophysical data surrounding the south bismarck plate can also be explained by a rotation of the south bismarck plate about this pole

landslide inventory maps new tools for an old problem landslides are present in all continents and play an important role in the evolution of landscapes they also represent a serious hazard in many areas of the world despite their importance we estimate that landslide maps cover less than 1 of the slopes in the landmasses and systematic information on the type abundance and distribution of landslides is lacking preparing landslide maps is important to document the extent of landslide phenomena in a region to investigate the distribution types pattern recurrence and statistics of slope failures to determine landslide susceptibility hazard vulnerability and risk and to study the evolution of landscapes dominated by mass wasting processes conventional methods for the production of landslide maps rely chiefly on the visual interpretation of stereoscopic aerial photography aided by field surveys these methods are time consuming and resource intensive new and emerging techniques based on satellite airborne and terrestrial remote sensing technologies promise to facilitate the production of landslide maps reducing the time and resources required for their compilation and systematic update in this work we first outline the principles for landslide mapping and we review the conventional methods for the preparation of landslide maps including geomorphological event seasonal and multi temporal inventories next we examine recent and new technologies for landslide mapping considering i the exploitation of very high resolution digital elevation models to analyze surface morphology ii the visual interpretation and semi automatic analysis of different types of satellite images including panchromatic multispectral and synthetic aperture radar images and iii tools that facilitate landslide field mapping next we discuss the advantages and the limitations of the new remote sensing data and technology for the production of geomorphological event seasonal and multi temporal inventory maps we conclude by arguing that the new tools will help to improve the quality of landslide maps with positive effects on all derivative products and analyses including erosion studies and landscape modeling susceptibility and hazard assessments and risk evaluations

unsupervised classification of scattering behavior using radar polarimetry data the use of an imaging radar polarimeter data for unsupervised classification of scattering behavior is described by comparing the polarization properties of each pixel in an image to that of simple classes of scattering such as even number of reflections odd number of reflections and diffuse scattering for example when this algorithm is applied to data acquired over the san francisco bay area in california it classifies scattering by the ocean as being similar to that predicted by the class of odd number of reflections scattering by the urban area as being similar to that predicted by the class of even number of reflections and scattering by the golden gate park as being similar to that predicted by the diffuse scattering class it also classifies the scattering by a lighthouse in the ocean and boats on the ocean surface as being similar to that predicted by the even number of reflections class making it easy to identify these objects against the background of the surrounding ocean

gps and seismological constraints on active tectonics and arc continent collision in papua new guinea implications for mechanics of microplate rotations in a plate boundary zone 1 the island of new guinea is located within the deforming zone between the pacific and australian plates that converge obliquely at 110 mm yr new guinea has been fragmented into a complex array of microplates some of which rotate rapidly about nearby vertical axes we present velocities from a network of 38 global positioning system gps sites spanning much of the nation of papua new guinea png the gps derived velocities are used to explain the kinematics of major tectonic blocks in the region and the nature of strain accumulation on major faults in png we simultaneously invert gps velocities earthquake slip vectors on faults and transform orientations in the woodlark basin for the poles of rotation of the tectonic blocks and the degree of elastic strain accumulation on faults in the region the data are best explained by six distinct tectonic blocks the australian pacific south bismarck north bismarck and woodlark plates and a previously unrecognized new guinea highlands block significant portions of the ramu markham fault appear to be locked which has implications for seismic hazard determination in the markham valley region we also propose that rapid clockwise rotation of the south bismarck plate is controlled by edge forces initiated by the collision between the finisterre arc and the new guinea highlands

seasonal landslide mapping and estimation of landslide mobilization rates using aerial and satellite images abstract we tested the possibility of using digital color aerial ortho photographs and monoscopic panchromatic satellite images of comparable spatial and radiometric resolution to map recent landslides in italy and to update existing measures of landslide mobilization in a 90 km 2 area in umbria central apennines rainfall resulted in abundant landslides in the period from september 2004 to june 2005 analysis of the rainfall record determined the approximate dates of landslide occurrence and revealed that the slope failures occurred in response to moderately wet rainfall periods the slope failures occurred primarily in cultivated terrain and left subtle morphological and land cover signatures making the recognition and mapping of the individual landslides problematic despite the difficulty with the identification of the landslides without the use of stereoscopic visualization visual analysis of the aerial and satellite images allowed mapping 457 new landslides ranging in area 3 0 10 1 a l 4 m 2 for a total landslide area a lt 6 92 10 5 m 2 to identify the landslides the investigators adopted the interpretation criteria commonly used to identify and map landslides on aerial photography the result confirms that monoscopic very high resolution images taken by airborne and satellite sensors can be used to prepare landslide maps even where slope failures are difficult to detect provided the imagery has sufficient geometric and radiometric resolutions the different dates of the aerial march 2005 and the satellite june july 2005 images allowed the temporal segmentation of the landslide information and studying the statistics of landslide area and volume for different periods compared to pre existing information on the abundance and size of the landslides in the area the inventory obtained by studying the aerial and satellite images proved more complete the new mapping showed 145 more landslides and 85 more landslide area than a pre existing reconnaissance inventory as a result of the improved mapping the rate of landslide mobilization for the 2004 2005 landslide season was determined to be l 27 1 mm year 1 30 higher than a previous estimate for the same period this seasonal rate of landslide mobilization is significantly larger than the long term regional erosion rate in the central apennines the accelerated rate is attributed to agricultural practices that favor slope instability

recognition of large scale deep seated landslides in forest areas of taiwan using high resolution topography abstract large deep seated landslides can be reactivated during intense events and they can evolve into destructive failures they are generally difficult to recognize in the field especially when they develop in densely forested areas a detailed and constantly updated inventory map of such phenomena and the recognition of their topographic signatures is absolutely a key tool for landslide risk mitigation the aim of this work is to test in forested areas the performance of the new automatic and objective methodology developed by tarolli et al 2012 for geomorphic features extraction landslide crowns from high resolution topography lidar derived digital terrain models dtms the methodology is based on the detection of landslides through the use of thresholds obtained by the statistical analysis of variability of landform curvature the study was conducted in a high risk area located in the central south taiwan where an accurate field survey on landsliding processes and a high quality set of airborne laser scanner elevation data are available the area has been chosen because some of the deep seated landslides are located near human infrastructures and their reactivation is highly dangerous thanks to lidar s capability to detect the bare ground elevation data in forested areas it was possible to recognize in detail landslide features also in remote regions difficult to access the results if compared with the previous work of tarolli et al 2012 mainly focused on shallow landslides and in a not forested area indicate that for deep seated landslides where the crowns are more evident and they are present at large scale the tested methodology performs better higher quality index the method can be used to interactively assist the interpreter user on the task of deep seated landslide hazard mapping and risk assessment planning of such regions

ground displacements around the fault of the september 20th 1999 chi chi taiwan earthquake ground displacements in the meizoseismal area of the september 20 1999 chi chi earthquake are derived from accelerograms at 39 stations on the hanging wall side a maximum horizontal nw directed motion of 8 meters and a vertical rise of 3 7 meters are found near the northern end of the n s trending surface trace of the fault on the footwall side and next to the fault a maximum horizontal motion of 1 3 meters and a maximum downward vertical motion of 1 meter are observed the displacement field describes the source as a thrust fault with left lateral motion the displacements increase from south to north along the fault and so does the left lateral component of the fault motion from about 10 to 60 of the total horizontal displacement the recorded motions especially ground velocities and accelerations are noticeably stronger on the hanging wall side than on the footwall side

sensitivity of elastic wave velocities to stress changes in sandstones the drilling of wells and production of hydrocarbons lead to changes in the stresses acting on the reservoir and surrounding rocks and these changes in stress may lead to problems such as wellbore instability sanding loss of permeability reservoir compaction casing deformation surface subsidence etc elastic wave velocities in sandstones are sensitive to changes in stress due to the presence of grain boundaries and microcracks within the rock this paper shows how changes in elastic wave velocities can be used to monitor the changes in stress that occur and a method for predicting the velocity changes due to a given change in stress is illustrated using the example of a borehole drilled into a sandstone reservoir

seismic and geological controls on earthquake induced landslide size abstract landslide size controls the destructive power of landslides and is related to the frequency of occurrence with larger landslides being less frequent than smaller ones for this reason the analysis of landslide size is essential for landslide hazard assessment we analyse six earthquake induced landslide inventories with earthquake magnitude ranging between 6 6 and 7 9 mw papua new guinea 1993 chichi 1999 northridge 1994 niigata chuetsu 2004 iwate miyagi nairiku 2008 wenchuan 2008 for each inventory we developed magnitude frequency curves to analyse the size distribution of landslides as a function of ground motion distance from the seismic source both fault trace and epicentre local relief and lithology for three earthquakes we observed a clear relationship between the landslide size and ground motion with larger landslides associated with higher ground motion we investigate different possible causes for such observation and propose that the main mechanical reason is that stronger shaking induces higher stresses that may overcome the strength which increases with depth triggering larger landslides we also show that landslide size decreases with distance from the fault trace whereas this trend is not clear for distance from the epicentre local relief does not seem a first order control on landslide size for the earthquake induced landslides considered here some lithologies do influence landslide size but we were unable to identify a general behaviour for different lithologies

data fusion technique using wavelet transform and taguchi methods for automatic landslide detection from airborne laser scanning data and quickbird satellite imagery landslide mapping is indispensable for efficient land use management and planning landslide inventory maps must be produced for various purposes such as to record the landslide magnitude in an area and to examine the distribution types and forms of slope failures the use of this information enables the study of landslide susceptibility hazard and risk as well as of the evolution of landscapes affected by landslides in tropical countries precipitation during the monsoon season triggers hundreds of landslides in mountainous regions the preparation of a landslide inventory in such regions is a challenging task because of rapid vegetation growth thus enhancing the proficiency of landslide mapping using remote sensing skills is a vital task various techniques have been examined by researchers this study uses a robust data fusion technique that integrates high resolution airborne laser scanning data lidar with high resolution quickbird satellite imagery 2 6 m spatial resolution to identify landslide locations in bukit antarabangsa ulu klang malaysia this idea is applied for the first time to identify landslide locations in an urban environment in tropical areas a wavelet transform technique was employed to achieve data fusion between lidar and quickbird imagery an object oriented classification method was used to differentiate the landslide locations from other land use covers the taguchi technique was employed to optimize the segmentation parameters whereas the rule based technique was used for object based classification in addition to assess the impact of fusion in classification and landslide analysis the rule based classification method was also applied on original quickbird data which have not been fused landslide locations were detected and the confusion matrix was used to examine the proficiency and reliability of the results the achieved overall accuracy and kappa coefficient were 90 06 and 0 84 respectively for fused data moreover the acquired producer and user accuracies for landslide class were 95 86 and 95 32 respectively results of the accuracy assessment for quickbird data before fusion showed 65 65 and 0 59 for overall accuracy and kappa coefficient respectively it revealed that fusion made a significant improvement in classification results the direction of mass movement was recognized by overlaying the final landslide classification map with lidar derived slope and aspect factors results from the tested site in a hilly area showed that the proposed method is easy to implement accurate and appropriate for landslide mapping in a tropical country such as malaysia

regional patterns of earthquake triggered landslides and their relation to ground motion 1 we have documented patterns of landsliding associated with large earthquakes on three thrust faults the northridge earthquake in california chi chi earthquake in taiwan and two earthquakes on the ramu markham fault bounding the finisterre mountains of papua new guinea in each case landslide densities are shown to be greatest in the area of strongest ground acceleration and to decay with distance from the epicenter in california and taiwan the density of co seismic landslides is linearly and highly correlated with both the vertical and horizontal components of measured peak ground acceleration based on this observation we derive an expression for the spatial variation of landslide density analogous with regional seismic attenuation laws in its general form this expression applies to our three examples and we determine best fit values for individual cases our findings open a window on the construction of shake maps from geomorphic observations for earthquakes in non instrumented regions

topographic fingerprints of bedrock landslides bedrock landslides in mountainous regions may be triggered by either storms or earthquakes the dominant mechanism in a region affects both landscape evolution and landslide hazard we describe a simple observational test to distinguish between storm and earthquake triggers based on a probabilistic measure of hillslope morphology in areas that are dominated by storm triggered landslides steep topographic slopes are concentrated on the lowermost parts of the hillslopes storm triggers act primarily on the hillslope toes and landslides preferentially remove material from those locations giving rise to inner gorges areas where most landslides are earthquake triggered have more uniform spatial distributions of steep topographic slopes because coseismic shaking causes failures at both ridge crests and hillslope toes earthquake triggered landslides lead to planar hillslopes and rare or absent inner gorges

effects of fracture intersections on seismic dispersion theoretical predictions versus numerical simulations abstract the detection and characterisation of domains of intersecting fractures are important goals in several disciplines of current interest including exploration and production of unconventional reservoirs nuclear waste storage co2 sequestration and groundwater hydrology among others the objective of this study is to propose a theoretical framework for quantifying the effects of fracture intersections on the frequency dependent elastic properties of fluid saturated porous and fractured rocks three characteristic frequency regimes for fluid pressure communication are identified in the low frequency limit fractures are in full pressure communication with the embedding porous matrix and with other fractures conversely in the high frequency limit fractures are hydraulically isolated from the matrix and from other fractures at intermediate frequencies fractures are hydraulically isolated from the matrix porosity but can be in hydraulic communication with each other depending on whether fracture sets are intersecting for each frequency regime the effective stiffness coefficients are derived using the linear slip theory and anisotropic gassmann equations explicit mathematical expressions for the two characteristic frequencies that separate the three frequency regimes are also determined theoretical predictions are then applied to two synthetic 2d samples each containing two orthogonal fracture sets one with and another without intersections the resulting stiffness coefficients thomsen style anisotropy parameters and the transition frequencies show good agreement with corresponding numerical simulations the theoretical results are applicable not only to 2d but also to 3d fracture systems and are amenable to being employed in inversion schemes designed to characterise fracture systems

semi automatic recognition and mapping of rainfall induced shallow landslides using optical satellite images abstract we present a method for the semi automatic recognition and mapping of recent rainfall induced shallow landslides the method exploits vhr panchromatic and hr multispectral satellite images and was tested in a 9 4 km2 area in sicily italy where on 1 october 2009 a high intensity rainfall event caused shallow landslides soil erosion and inundation pre event and post event images of the study area taken by the quickbird satellite and information on the location and type of landslides obtained in the field and through the interpretation of post event aerial photographs were used to construct and validate a set of terrain classification models the models classify each image element pixel based on the probability that the pixel contains or does not contain a new rainfall induced landslide to construct and validate the models a procedure in five steps was adopted first the pre event and the post event images were pan sharpened ortho rectified co registered and corrected for atmospheric disturbance next variables describing changes between the pre event and the post event images attributed to landslide occurrence were selected next three classification models were calibrated in a training area using different multivariate statistical techniques the calibrated models were then applied in a validation area using the same set of independent variables and the same statistical techniques lastly combined terrain classification models were prepared for the training and the validation areas the performances of the models were evaluated using four fold plots and receiver operating characteristic curves the method proved capable of detecting and mapping the new rainfall induced landslides in the study area we expect the method to be capable of detecting analogous shallow landslides caused by similar rainfall or different e g earthquake triggers provided that the event slope failures leave discernable features captured by the post event satellite images and that the terrain information and satellite images are of adequate quality the proposed method can facilitate the rapid production of accurate landslide event inventory maps and we expect that it will improve our ability to map landslides consistently over large areas application of the method will advance our ability to evaluate landslide hazards and will foster our understanding of the evolution of landscapes shaped by mass wasting processes

observation of shear wave splitting in the multicomponent node data from atlantis field gulf of mexico in 2005 a multicomponent ocean bottom node data set was collected by bp and bhp billiton in the atlantis field in the gulf ofmexico our results are based on data from a few sparse nodes with millions of shots that were analysed as common receiver azimuthal gathers a first order look at p wave arrivals on a common receiver gather at a constant offset reveals variation of p wave arrival time as a function of azimuth indicating the presence of azimuthal anisotropy at the top few layers this prompted us to investigate shear arrivals on the horizontal component data after preliminary processing including a static correction the data were optimally rotated to radial r and transverse t components the r component shows azimuthal variation of traveltime indicating variation of velocity with azimuth the corresponding t component shows azimuthal variation of amplitude and phase polarity reversal the observed shear wave s wave splitting previously observed azimuthal p wave velocity variation and azimuthal p wave amplitude variation all indicate the occurrence of anisotropy in the shallow just below the seafloor subsea sediment in the area from the radial component azimuthal gather we analysed the pp and ps wave amplitude variation for the first few layers and determined corresponding anisotropy parameter and vp vs values since fracture at this depth is not likely to occur we attribute the observed azimuthal anisotropy to the presence of microcracks and grain boundary orientation due to stress the evidence of anisotropy is ubiquitous in this data set and thus it argues strongly in favour of considering anisotropy in depth imaging for obtaining realistic subsurface images at the least

polarimetric synthetic aperture radar study of the tsaoling landslide generated by the 1999 chi chi earthquake taiwan 1 we employ l band airborne synthetic aperture radar sar polarimetry to detect surface changes produced by the tsaoling landslide the largest slope failure triggered by the september 1999 chi chi earthquake in central taiwan imaging polarimeters provide a complete description of the scattering properties of radar target materials resurfacing of forested hillslopes by landslides alters scattering mechanisms from those dominated by backscatter from trees to mechanisms associated with scatter from rough bare surfaces scattering mechanism information on a per pixel basis is extracted by decomposing matrices formed as the outer product of the complex scattering vector measured for each resolution cell we classify surface cover type and thereby identify the extent of the landslide using such polarimetric parameters as scattering entropy anisotropy and pedestal height derived from the eigenvalues of the decomposition as well as the weighted average scattering mechanism derived from the eigenvectors we address the utility of full polarimetry versus dual polarimetry for landslide mapping purposes and show that fully polarimetric sar is necessary for distinguishing water surfaces of varying roughness from the bare surfaces created by landsliding we show that scattering entropy and average scattering mechanism for example can be used to identify the tsaoling landslide source run out area and impounded lakes as proficiently as maps obtained using satellite optical sensors such as landsat and the indian research satellite however the operational advantages of radar over optical sensing techniques namely its day night all weather data acquisition capability suggest that sar polarimetry could play a leading role in the rapid assessment of landslide disasters

a three component scattering model for polarimetric sar data an approach has been developed that involves the fit of a combination of three simple scattering mechanisms to polarimetric sar observations the mechanisms are canopy scatter from a cloud of randomly oriented dipoles evenor double bounce scatter from a pair of orthogonal surfaces with different dielectric constants and bragg scatter from a moderately rough surface this composite scattering model is used to describe the polarimetric backscatter from naturally occurring scatterers the model is shown to describe the behavior of polarimetric backscatter from tropical rain forests quite well by applying it to data from nasa jet propulsion laboratory s jpls airborne polarimetric synthetic aperture radar airsar system the model fit allows clear discrimination between flooded and nonflooded forest and between forested and deforested areas for example the model is also shown to be usable as a predictive tool to estimate the effects of forest inundation and disturbance on the fully polarimetric radar signature an advantage of this model fit approach is that the scattering contributions from the three basic scattering mechanisms can be estimated for clusters of pixels in polarimetric sar images furthermore it is shown that the contributions of the three scattering mechanisms to the hh hv and vv backscatter can be calculated from the model fit finally this model fit approach is justified as a simplification of more complicated scattering models which require many inputs to solve the forward scattering problem

nonlinear rock physics model for estimation of 3d subsurface stress in anisotropic formations theory and laboratory verification we develop a rock physics model based on nonlinear elasticity that describes the dependence of the effective stiffness tensor as a function of a 3d stress field in intrinsically anisotropic formations this model predicts the seismic velocity of both p and s waves in any direction for an arbitrary 3d stress state therefore the model overcomes the limitations of existing empirical velocity stress models that link p wave velocity in isotropic rocks to uniaxial or hydrostatic stress to validate this model we analyze ultrasonic velocity measurements on stressed anisotropic samples of shale and sandstone with only three nonlinear constants we are able to predict the stress dependence of all five elastic medium parameters comprising the transversely isotropic stiffness tensor we also show that the horizontal stress affects vertical s wave velocity with the same order of magnitude as vertical stress does we develop a weakanisotropy approximation that directly links commonly measured anisotropic thomsen parameters to the principal stresses each thomsen parameter is simply a sum of corresponding background intrinsic anisotropy and stressinduced contribution the stress induced part is controlled by the difference between horizontal and vertical stresses and coefficients depending on nonlinear constants thus isotropic rock stays isotropic under varying but hydrostatic load whereas transversely isotropic rock retains the same values of dimensionless thomsen parameters only unequal horizontal and vertical stresses alter anisotropy since thomsen parameters conveniently describe seismic signatures such as normal moveout velocities and amplitudevariation with offset gradients this approximation is suitable for designing new methods for the estimation of 3d subsurface stress from multicomponent seismic data

squirt flow in fully saturated rocks we estimate velocity frequency dispersion and attenuation in fully saturated rocks by employing the squirt flow mechanism of solid fluid interaction in this model pore fluid is squeezed from thin soft cracks into the surrounding large pores information about the compliance of these soft cracks at low confining pressures is extracted from high pressure velocity data the frequency dependence of squirt induced pressure in the soft cracks is linked with the porosity and permeability of the soft pore space and the characteristic squirt flow length these unknown parameters are combined into one expression that is assumed to be a fundamental rock property that does not depend on frequency the appropriate value of this expression for a given rock can be found by matching our theoretical predictions with the experimental measurements of attenuation or velocity the low frequency velocity limits as given by our model are identical to those predicted by gassmann s formula the high frequency limits may sign

in situ identification of high vertical stress areas in an underground coal mine panel using seismic refraction tomography abstract because high stress anomalies can induce dynamic failures in the underground panels of coal mines the identification of high stress areas is critically important for mining safety we have identified areas of high vertical stress of an in situ longwall panel with seismic refraction tomography and interpreted our results using rock physics models constrained by core measurements since p and s velocities in rocks are stress sensitive mapping of them can provide useful information to identify areas of potential high stress we have inverted p and s velocities of main roof of an in situ panel with refraction tomography and converted them into vertical stress estimates using a calibration function from core measurements those estimates are classified into three groups high medium and low respectively identified zones of high vertical stress show qualitative agreement with monitored in panel microseismic data zones derived from p waves give a more plausible assessment than s waves we also discuss the link between high vertical stress areas and in panel faults because of the impact of the regional stress field and previously mined out voids the existing fault zone affects the redistribution of vertical stress in the underground panel

investigation of borehole cross dipole flexural dispersion crossover through numerical modeling crossover of the dispersion of flexural waves recorded in borehole cross dipole measurements is interpreted as an indicator of stress induced anisotropy around a circular borehole in formations that are isotropic in the absence of stresses we have investigated different factors that influence flexural wave dispersion through numerical modeling we determined that for a circular borehole surrounded by an isotropic formation that is subjected to an anisotropic stress field the dipole flexural dispersion crossover is detectable only when the formation is very compliant this might happen only in the shallow subsurface or in zones having high pore pressure however we found that dipole dispersion crossover can also result from the combined effect of formation intrinsic anisotropy and borehole elongation we found that a small elongation on the wellbore and very weak intrinsic anisotropy can result in a resolvable crossover in flexural dispersion that might be erroneously interpreted as borehole stress induced anisotropy a thorough and correct interpretation of flexural dispersion crossover thus has to take into account the effects of stress induced and intrinsic anisotropy and borehole cross sectional geometry

rotations in the actively colliding finisterre arc terrane paleomagnetic constraints on plio pleistocene evolution of the south bismarck microplate northeastern papua new guinea abstract we report paleomagnetic results from 12 plio pleistocene localities in the actively colliding finisterre arc terrane of northeastern papua new guinea png calcareous hemipelagic cover rocks possess a stable syn collisional remagnetization indicating a clockwise rotation of the colliding terrane through about 40 in post miocene time a decrease in paleomagnetic declination anomalies as a function of along strike distance in the finisterre arc terrane analyzed by our preferred model of a linear remagnetization and a migrating euler pole suggests an average rotation rate of 8 ma 1 in good agreement with the instantaneous rate from global positioning system geodesy thus we propose that this rotation results from a coherent rigid body rotation of the finisterre terrane rather than from sequential docking of independently colliding blocks of the terrane moreover we conclude that these paleomagnetic declinations result mainly from south bismarck plate motion and not decoupled rotation of the crustal terrane independent of the underlying lithosphere we examine models of a syn collisional remagnetization with both fixed and migrating euler poles of south bismarck australia plate relative motion and suggest that the euler pole describing south bismarck plate motion has migrated southwestward to its present location on the collision suture in response to the propagating collision this plate kinematic model agrees with the variability in depth of the seismogenic slab beneath the collision zone our best fit model of pole migration describes south bismarck australia relative motion producing a highly oblique collision in its early stages with the finisterre arc terrane converging along a left lateral ramu markham suture gradually changing to the nearly orthogonal convergence observed today

effects of borehole stress concentration on elastic wave velocities in sandstones the stress redistribution that occurs in the vicinity of a borehole may lead to damage or failure of the rock if the vertical stress is a principal stress the principal stresses at the wall of a vertical well are the hoop radial and vertical stresses the hoop stress varies with position around the wellbore and takes its maximum compressive value at the azimuth of the far field minimum horizontal stress this may lead to compressive failure at this azimuth if the compressive strength of the rock is exceeded recent developments in sonic logging allow the variation in elastic wave velocities with radius and azimuth around a borehole to be characterized since elastic wave velocities in sandstones are sensitive to changes in stress owing to the presence of stress sensitive grain boundaries within the rock this allows the changes in stress to be monitored an expansion of the elastic compliance of the grain boundaries to first order in stress shows that a radially polarized vertically propagating shear wave is more sensitive to radial stress than to hoop stress close to the wellbore however large changes in stress occur and any nonlinearity in the variation in compliance of the grain boundaries as a function of stress becomes important this nonlinearity increases the sensitivity to the wellbore pressure and can cause significant reductions in the velocity of compressional and shear waves in the vicinity of the wellbore

use of s wave anisotropy to quantify the onset of stress induced microfracturing abstractmicrofracturing and induced elastic anisotropy impart changes on body wave velocities with implications to seismic and wellbore testing methods and interpretation we have conducted simultaneous triaxial stress tests and ultrasonic wave propagation monitoring to quantify s wave anisotropy and microfracture development in berea sandstone and silurian dolomite the onset of stress induced microfracturing is detected at the beginning of appreciable s wave anisotropy called the s wave crossover swx the swx and subsequent increases in s wave anisotropy evidence microstructural damage development well before quasistatic indicators such as the volumetric strain point of positive dilatancy ppd and yield failure in all samples x ray microtomography confirmed fracture development and allowed for geometric assessment of fracture orientation stresses at the swx and ppd are compared with peak axial stress to understand linkages between damage and ultimate rock strength in berea sandstone the swx occ

geologic cause of seismic anisotropy a case study from offshore western australia velocity model building with a good understanding of anisotropy is one of the important elements in a prestack depth migration psdm project during a recently conducted psdm project we observed that 1 the application of negative delta epsilon is necessary to achieve reasonable depthing and gather flatness and 2 azimuthal variation in gather flatness exists in the interval where negative delta epsilon are necessary a geologic explanation of these interesting observations was necessary to justify the velocity model building result investigation of stress magnitude orientation and theoretical anisotropy of unconsolidated sandstone under nonhydrostatic stress revealed that these observations can be explained by stress induced anisotropy this concept may be applicable to other fields and the existence of azimuthal anisotropy and value of anisotropy parameters can be roughly estimated by the method described

mid crustal detachment and ramp faulting in the markham valley papua new guinea earthquakes and geodetic evidence reveal the presence of a low angle mid crustal detachment fault beneath the finisterre range that connects to a steep ramp surfacing near the ramu markham valley of papua new guinea waveforms of three large m w 6 3 to 6 9 thrust earthquakes that occurred in october 1993 beneath the finisterre range 10 to 30 km north of the valley reveal 15 north dipping thrusts at about 20 km depth global positioning system measurements show up to 20 cm of coseismic slip occurred across the valley requiring that the active fault extend to within a few hundred meters of the earth9s surface beneath the markham valley together these data imply that a gently north dipping thrust fault in the middle or lower crust beneath the finisterre range steepens and shallows southward forming a ramp fault beneath the north side of the markham valley waveforms indicate that both the ramp and detachment fault were active during at least one of the earthquakes while the seismic potential of mid crustal detachments elsewhere is debated in papua new guinea the detachment fault shows the capability of producing large earthquakes