estimation of rock physics properties from seismic attributes part 2 applications abstractthe estimation of quantitative rock physics properties is of great importance for reservoir characterization and monitoring in co2 storage or enhanced oil recovery as an example we have combined the high resolution results of full waveform inversion fwi methods with rock physics inversion because we consider a generic and dynamic rock physics model our method is applicable to most kinds of rocks for a wide range of frequencies the first step allows determination of viscoelastic effective properties i e quantitative seismic attributes whereas the rock physics inversion estimates rock physics properties porosity solid frame moduli fluid phase properties or saturation this two step workflow is applied to time lapse synthetic and field cases the sensitivity tests that we had previously carried out showed that it can be crucial to use multiparameter inputs to accurately recover fluid saturations and fluid properties however due to the limited data availability and difficulties in get

denudation rates and a topography driven rainfall threshold in northern chile multiple cosmogenic nuclide data and sediment yield budgets abstract the quantification of geomorphic process rates on the outcrop and the orogen scale is important to describe accurately the interaction between the relative effects of erosion tectonics and climate on landscape evolution we report single and paired cosmogenic nuclide 10 be 26 al and 21 ne derived erosion rates and exposure ages on hillslope interfluves from the tectonically active western central andes that show a distinct spatial variation a positive correlation of erosion rates with elevation and present day rainfall rates is observed erosion rates at lower altitudes the hyperarid coastal cordillera and the western escarpment with the northern part of the atacama desert are extremely low and of the order of 10 100 cm my nominal exposure ages 1 6 my in contrast erosion rates at higher altitudes the semiarid western cordillera range up to 4600 cm my nominal exposure ages 0 02 0 1 my this latter average long term bedrock erosion rate record suggested to be coupled to an orographically controlled pattern of rainfall is also reflected in the pattern of denudation rates derived from a short term decadal record of limited sediment yield data specifically denudation rates calculated from sediment flux data are of a similar order of magnitude as erosion rates deduced from long lived cosmogenic nuclides from bedrock hillslope interfluves of the western cordillera nevertheless the production and the supply of sediment from the western andean slope are very limited analysis of multiple cosmogenic nuclides allows simultaneous determination of erosion rates and exposure ages but also reveals complex exposure histories of non bedrock samples such as boulders or amalgamated clast samples notably this study shows that saturation of nuclides usually assumed in studies where only a single nuclide is analyzed is rather the exception than the rule as revealed by erosion island plots constant erosion that started much later than the formation age of the rocks or episodic erosion by spalling can partially explain non steady state concentrations and more complicated exposure scenarios furthermore the use of multiple nuclides with different half lives allowed us to infer that no significant variations in long term erosion rates have occurred and that at the western escarpment erosion rates have been low and constant for most of the late neogene nevertheless the time intervals necessary to reach steady state concentrations for cosmogenic nuclides can be quite different from those needed for landscapes to reach steady state

seismic imaging of complex onshore structures by 2d elastic frequency domain full waveform inversion quantitative imaging of the elastic properties of the subsurface at depth is essential for civil engineering applications and oil and gas reservoir characterization a realistic synthetic example provides for an assessment of the potential and limits of 2d elastic full waveform inversionfwiof wide aperture seismic data for recovering high resolution p and s wave velocity models of complex onshore structures fwi of land data is challengingbecauseoftheincreasednonlinearityintroducedbyfreesurface effects such as the propagation of surface waves in the heterogeneous near surface moreover the short wavelengths of the shear wavefield require an accurate s wave velocity starting modeliflowfrequenciesareunavailableinthedata weevaluated different multiscale strategies with the aim of mitigating the nonlinearities massively parallel full waveform inversion was implemented in the frequency domain the numerical optimization relies on a limited memory quasi newton algorithm that outperforms the more classic preconditioned conjugate gradient algorithm the forward problem is based upon a discontinuous galerkin dg method on triangular mesh which allows accuratemodelingoffree surfaceeffects sequentialinversionsofincreasingfrequenciesdefinethemostnaturallevelofhierarchyin multiscale imaging in the case of land data involving surface waves the regularization introduced by hierarchical frequency inversions is not enough for adequate convergence of the inversion a second level of hierarchy implemented with complexvalued frequencies is necessary and provides convergence of the inversion toward acceptable p and s wave velocity models amongthepossiblestrategiesforsamplingfrequenciesintheinversion successive inversions of slightly overlapping frequency groups is the most reliable when compared to the more standard sequential inversion of single frequencies this suggests that simultaneous inversion of multiple frequencies is critical when consideringcomplexwavephenomena

long offset time lapse seismic tested on the valhall lofs data conventional time lapse seismic has been less successful for stiff rock reservoir monitoring such as carbonates this is mainly because of the negligible time lapse changes in the seismic properties therefore we propose to use long offset time lapse seismic as an alternative method to estimate small velocity changes more specifically we monitor the maximum amplitude offset that is beyond critical offset the properties of the maximum amplitude offset are similar to critical offset except that they appear for longer offsets and are frequency dependent increased frequency reduces the gap between this offset and the critical offset we find that the maximum amplitude offset is a function of overburden and reservoir velocity and practically independent of density this method requires a velocity increase across the interface that is to be analyzed this criterion usually is satisfied for stiff rock reservoirs also by long offset acquisition we mean typically 1 to 2 km beyond the critical offset for

el nino southern oscillation events recorded in the stratigraphy of the tropical quelccaya ice cap peru snow accumulation measured during 1982 1983 on the quelccaya ice cap peru was 70 percent of the average from 1975 through 1983 inspection of 19 years 1964 through 1983 of accumulation measured near the summit of quelccaya reveals a substantial decrease 30 percent in association with the last five el nino southern oscillation enso occurrences in the equatorial pacific the enso phenomenon is now recognized as a global event arising from large scale interactions between the ocean and the atmosphere understanding this extreme event with the goal of prediction requires a record of past occurrences the quelccaya ice cap which contains 1500 years of annually accumulated ice layers may provide a long and detailed record of the most extreme enso events

reconstructing ancient topography through erosion modelling one of the main aims of geomorphology is to understand how geomorphic processes change topography over long time scales over the last decades several landscape evolution models have been developed in order to study this question however evaluation of such models has often been very limited due to the lack of necessary field data in this study we present a topography based hillslope erosion and deposition model that is based on the watem sedem model structure and works on a millennial time scale soil erosion transport and deposition are calculated using slope and unit contributing area the topography is iteratively rejuvenated by taking into account modelled erosion and deposition rates thereby simulating topographic development backwards in time a first attempt has been made to spatially evaluate the model using detailed estimates for historical soil erosion and sediment deposition volumes obtained from an augering campaign in a small catchment in the belgian loess belt the results show that the model can simulate realistic soil redistribution patterns however further research is necessary in order to deal with artificial flaws that cause routing problems and significantly influence results common problems and issues related to this type of backward modelling are also discussed

cloud and surface textural features in polar regions the study examines the textural signatures of clouds ice covered mountains solid and broken sea ice and floes and open water the textural features are computed from sum and difference histogram and gray level difference vector statistics defined at various pixel displacement distances derived from landsat multispectral scanner data polar cloudiness snow covered mountainous regions solid sea ice glaciers and open water have distinguishable texture features this suggests that textural measures can be successfully applied to the detection of clouds over snow covered mountains an ability of considerable importance for the modeling of snow melt runoff however broken stratocumulus cloud decks and thin cirrus over broken sea ice remain difficult to distinguish texturally it is concluded that even with high spatial resolution imagery it may not be possible to distinguish broken stratocumulus and thin clouds from sea ice in the marginal ice zone using the visible channel textural features alone

importance of slope gradient and contributing area for optimal prediction of the initiation and trajectory of ephemeral gullies abstract ephemeral gully erosion rates are controlled by various factors out of which topography plays an important role this study investigates the possibility to predict the location of ephemeral gullies using two topographic attributes only i e local slope gradient s and upslope contributing area per unit length of contour a s an inverse relationship between s and a s in which the relative importance of the area exponent was varied was evaluated as to its performance in predicting the location of ephemeral gullies for three intensively cultivated catchments in the belgian loess belt this model is easily applicable as it only uses information on topography which can be derived from a digital elevation model and land use predicted locations of ephemeral gullies were confronted with the locations recorded over 5 years of field observations for all catchments a high relative area exponent relative to the slope exponent was required to yield good results the optimal relative area exponent ranged from 0 7 to 1 5 however the quality of the prediction did not vary significantly when changing the exponent within this range an average relative area exponent of ca 1 is appropriate for all three study areas and may therefore be proposed for similar areas under similar conditions a striking discrepancy was found between the high relative area exponent required to predict optimally the trajectory of the gullies and the low relative area exponent 0 2 required to identify the spots in the landscape where ephemeral gullies begin this indicates that spots in the landscape where gullies start are more controlled by slope gradient while the presence of concavities control the trajectory of the gullies until the slope gradient is too low and sediment deposition starts no relationship was found between the frequency of the occurrence of ephemeral gullies and the percentage of predicted gully pixels for each frequency class this indicates that frequently occurring gullies at the same location are not easier to predict than accidental gullies

pattern and rate of erosion inferred from inca agricultural terraces in arid southern peru abstract earthworks of assumed age and their initial and current morphologies provide an ideal basis for developing and testing models for long term landform erosion inca agricultural terraces abandoned at 1532 a d in the drylands of southern peru may be used to document morphological changes since the abandonment the objective of this research is to determine the erosion pattern and process to estimate the erosion rate the development of rills and channels on the inca agricultural terraces is evidence for erosion by wash processes on slopes where the anchoring effect of vegetation is absent and loose material is available for removal the pattern and amount of erosion from 1532 2005 a d is estimated by comparing elevation models of the observed morphology and reconstructed models of the original morphology of the inca terraces the results show that in areas of sediment accumulation surface elevation increased up to 0 5 m elevation lowering on the terrace treads was 0 7 m at maximum and a temporally and spatially averaged lowering rate was 0 094 mm yr 1 this gives insights about how the rate of erosion occurs on currently disturbed lands in arid environments where soil resources are scarce and lands are prone to desertification

on the role of reflections refractions and diving waves in full waveform inversion full waveform inversion suffers from local minima due to a lack of low frequencies in data a reflector below the zone of interest may however help in recovering the long wavelength components of a velocity perturbation as demonstrated in a paper by mora with the born approximation for a perturbation in a reference model consisting in two homogeneous isotropic acoustic half spaces and the assumption of infinitely large apertures available in the data analytic expressions can be found that describe the spatial spectrum of the recorded seismic signal as a function of the spatial spectrum of the inhomogeneity diving waves can be included if the deeper part of the homogeneous model is replaced by one that has a vertical velocity gradient we study this spectrum in more detail by separately considering scattering of direct reflected and head waves as well as singly and multiply reflected diving waves for a gradient model taking the reflection coefficient of the deeper reflector into account we obtain sensitivity estimates for each wavetype although the head waves have a relatively small contribution to the reconstruction of the velocity perturbation compared to the other waves they contain reliable long wavelength information that can be beneficial for full waveform inversion if the deeper part has a constant positive velocity gradient with depth all the energy eventually returns to the source receiver line given a sufficiently large acquisition aperture this will improve the sensitivity of the scattered reflected and refracted wavefields to perturbations in the background model the same happens for a zero velocity gradient but with a very high impedance contrast between the two half spaces which results in a large reflection coefficient

application of seismic full waveform inversion to monitor co2 injection modelling and a real data example from the ketzin site germany seismic monitoring of an injected carbon dioxide co2 distribution at depth is an important issue in the geological storage of co2 to help monitor changes in the subsurface during co2 injection a series of 2d seismic surveys were acquired within the framework of the co2sink and co2man projects at ketzin germany at different stages of the injection process here we investigate using seismic full waveform inversion as a qualitative tool for time lapse seismic monitoring given the constraints of the limited maximum offsets of the 2d seismic data prior to applying the inversion to the real data we first made a number of benchmark tests on synthetic data using a similar geometry as in the real data results from the synthetic benchmark tests show that it is difficult to recover the true value of the velocity anomaly due to the injection but that it is possible to qualitatively locate the distribution of the injected co2 after the synthetic studies we applied seismic full waveform inversion on the real time lapse data from the ketzin site along with conventional time lapse processing both methods show a similar qualitative distribution of the injected co2 and agree well with expectations based upon more extensive 3d time lapse monitoring in the area

the little ice age as recorded in the stratigraphy of the tropical quelccaya ice cap the analyses of two ice cores from a southern tropical ice cap provide a record of climatic conditions over 1000 years for a region where other proxy records are nearly absent annual variations in visible dust layers oxygen isotopes microparticle concentrations conductivity and identification of the historical a d 1600 huaynaputina ash permit accurate dating and time scale verification the fact that the little ice age about a d 1500 to 1900 stands out as a significant climatic event in the oxygen isotope and electrical conductivity records confirms the worldwide character of this event

cloud cover analysis with arctic advanced very high resolution radiometer data 2 classification with spectral and textural measures the variation in cloud amount over polar ice sheets sea ice and ocean surfaces can have important effects on planetary albedo gradients and on surface energy exchanges so that monitoring of polar cloud cover is crucial to studies of climate change the spectral and textural characteristics of polar clouds and surfaces for a 7 day summer series of advanced very high resolution radiometer avhrr data in two arctic locations are examined and the results used in the development of a cloud classification procedure for polar satellite data since spatial coherence and texture sensitivity tests indicate that a joint spectral textural analysis based on the same cell size is inappropriate cloud detection with avhrr data and surface identification with passive microwave data are first done on the pixel level as detailed in part 1 key and barry 1989 next cloud patterns within 250 km sup 2 regions are described then the spectral and local textural characteristics of cloud patterns in the image are determined and each cloud pixel is classified by statistical methods results indicate that both spectral and textural features can be utilized in the classification of cloudy pixels although spectral features are most useful for the discrimination between cloud classes this methodologymore provides a basis for future objective automated mapping of cloud types and amount over snow and ice covered surfaces less

largest explosive eruption in historical times in the andes at huaynaputina volcano a d 1600 southern peru the largest explosive eruption volcanic explosivity index of 6 in historical times in the andes took place in a d 1600 at huaynaputina volcano in southern peru according to chronicles the eruption began on february 19 with a plinian phase and lasted until march 6 repeated tephra falls pyroclastic flows and surges devastated an area 70 40 km2 west of the vent and affected all of southern peru and earthquakes shook the city of arequipa 75 km away eight deposits totaling 10 2 13 1 km3 in bulk volume are attributed to this eruption 1 a widespread 8 1 km3 pumice fall deposit 2 channeled ignimbrites 1 6 2 km3 with 3 ground surge and ash cloud surge deposits 4 widespread co ignimbrite ash layers 5 base surge deposits 6 unconfined ash flow deposits 7 crystal rich deposits and 8 late ash fall and surge deposits disruption of a hydrothermal system and hydromagmatic interactions are thought to have fueled the large volume explosive eruption although the event triggered no caldera collapse ring fractures that cut the vent area point to the onset of a funnel type caldera collapse

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

the effect of spatial resolution upon texture based cloud field classifications the previous cloud classification investigations in parts 1 3 of this study have been conducted using 1 16 km landsat multispectral scanner mss imagery however for global monitoring much lower spatial resolutions of the order of 1 8 km generally are used the present study examines the loss of cloud classification accuracy as a function of spatial resolution by degrading the imagery through progressive averaging textural measures are computed using the gray level difference vector approach significant improvement in cloud classification accuracy can be obtained using 1 2 km spatial resolution data rather than the current 1 km resolution data available today from avhrr and goes cirrus classification accuracy is especially compromised as the spatial resolution is degraded however the use of texture measures defined at the combination of pixel separations d 1 4 improves classification accuracies by several percent even for 1 km spatial resolution data cirrus accuracy is significantly improved by use of multiple distance features classification accuracies using 1 8 km spatial resolution data are similar to those obtained using the full spatial resolution features the implications are that there are no advantages to be gained in cloud classification accuracies by using even higher spatial resolutions available from landsat thematic mapper or spot imagery finally it is found that multiple resolution imagery can be used to improve classification accuracy indeed the global rather than the local aspects of texture appear to be most important to the classifier

sea bed diffractions and their impact on 4d seismic data a sea bed reflection is used to estimate changes in water layer velocities between timelapse seismic surveys such corrections are crucial in order to obtain high quality 4d seismic data this might be a challenge in areas where rough sea bed topography creates sea bed diffractions that interfere with the sea bed reflection as in several of the northern fields in the norwegian sea these diffractions and diffracted multiples are difficult to attenuate during data processing and become a source of noise in time lapse data in this work we study how cross correlation analysis of time lapse seismic data at a sea bed reflection may be perturbed by the presence of diffractions the seabed topography from the norne field is used in 2d finite difference modelling to explain some of the observed variation in a water layer time shift in field data we find that a rough sea bed and the diffracted energy it induces cause residual noise on the 4d data the variation to the water layer time shift increases with sea bed complexity and is amplified by interaction with other sources of non repeatability like water column variations mis positioning and strength of the ice scours creating the diffracted energy time shift variations with mis positioning and velocity changes between the surveys seem to best explain the observed variation in the time shift for time lapse seismic field data from norne

full waveform inversion in the time lapse mode applied to co2 storage at sleipner carbon capture and storage is a viable greenhouse gas mitigation technology and the sleipner co2 sequestration site in the north sea is an excellent example storage of co2 at the sleipner site requires monitoring over large areas which can successfully be accomplished with time lapse seismic imaging one of the main goals of co2 storage monitoring is to be able to estimate the volume of the stored co2 in the reservoir this requires a parametrization of the subsurface as exact as possible here we use elastic 2d time domain full waveform inversion in a time lapse manner to obtain a p wave velocity constrain directly in the depth domain for a base line survey in 1994 and two post injection surveys in 1999 and 2006 by relating velocity change to free co2 saturation using a rock physics model we find that at the considered location the aquifer may have been fully saturated in some places in 1999 and 2006

monitoring a shallow subsurface gas flow by time lapse refraction analysis studying time lapse time shifts for refracted events is a complementary method to conventional 4d analysis especially for detecting changes in relatively shallow subsurface layers we find that this method has potential by studying data associated with an old underground blowout we find consistent time shifts of up to 4 ms when comparing a base survey that was acquired before the underground blowout with a monitor survey acquired 20 months after the blowout these time shifts are interpreted as caused by shallow gas migration the 4d refraction time shifts are estimated by a standard windowed crosscorrelation technique observed time shifts are compared with a simple synthetic modeling to find the possible property and location of the anomaly the synthetic result was qualitatively matched with real data we believe that more quantitative matches can obtained when the method is combined with full waveform inversions time lapse refraction analysis has some clear limitations for instance the presence of refracted events which requires a positive velocity contrast for the interface to be studied another limitation is that for deeper events the signal from shallower refractions and noise associated with the water layer will distort the 4d time shifts however we found that these results demonstrate the potential of refraction time shifts as a complementary 4d analysis technique we believe that the method has a significant potential for quantitative 4d interpretation

a 38 000 year record of floods and debris flows in the ilo region of southern peru and its relation to el nino events and great earthquakes abstract previous work throughout the ilo region of south coastal peru has documented the existence of flood and debris flow deposits produced by two el nino events evidently much more severe than any in recent history these two events have been dated to ca ad 1300 1400 and ad 1607 08 the late pleistocene to holocene record of older sedimentary deposits in this region is dominated by flood and debris flow deposits of similar scale these older deposits have been described and dated from three coastal alluvial fan sites these deposits which are as old as 38 200 years are dominated by massive debris flow deposits several tens of cm thick typically composed of cobble and boulder sized clasts in a matrix of silty sand with characteristics indicating generation by heavy rainfall in an arid environment twenty two radiocarbon dates and a single infrared stimulated luminescence date show that particularly severe el nino events occurred throughout the late pleistocene and two of three divisions of the holocene with significantly different frequencies the period of greatest activity was during the early holocene when at least six such events took place during a period of ca 3600 years beginning near the end of the younger dryas ca 12 000 years ago one of these events produced a debris flow that may have caused abandonment of the paleo indian site at quebrada tacahuay one of the oldest on the andean coast no severe events took place during the middle holocene between ca 8400 and 5300 years ago when a wide variety of other paleoclimate proxy records indicate that the el nino southern oscillation regime was particularly weak since ca 5300 years ago four of these severe events have taken place the late pleistocene sequence is constrained by only two dates which indicate that at least ten severe events took place between ca 38 200 and 12 900 years ago mechanisms probably responsible for generating these large scale deposits include 1 mega ninos that produced anomalously heavy rainfall along most or all of the central andean coast 2 el ninos that occurred shortly after great earthquakes that produced large amounts of sediment or 3 el ninos that produced anomalously heavy local rainfall the existence of these large scale deposits in the ilo region implies a level of hazard much higher than indicated by the historical record alone

the surface topography of large ice masses from landsat imagery les images de landsat mss de l antarctique et du svalbard ont ete comparees a des mesures altimetriques effectuees a partir d avion

sensitivity analysis and application of time lapse full waveform inversion synthetic testing and field data example from the north sea norway time lapse refraction can provide complementary seismic solutions for monitoring subtle subsurface changes that are challenging for conventional p wave reflection methods the utilization of refraction time lapse has lagged behind in the past partly due to the lack of robust techniques that allow extracting easy to interpret reservoir information however with the recent emergence of the full waveform inversion technique as a more standard tool we find it to be a promising platform for incorporating head waves and diving waves into the time lapse framework here we investigate the sensitivity of 2d acoustic time domain full waveform inversion for monitoring a shallow weak velocity change 30 m s or 1 6 the sensitivity tests are designed to address questions related to the feasibility and accuracy of full waveform inversion results for monitoring the field case of an underground gas blowout that occurred in the north sea the blowout caused the gas to migrate both vertically and horizontally into several shallow sand layers some of the shallow gas anomalies were not clearly detected by conventional 4d reflection methods i e time shifts and amplitude difference due to low 4d signal to noise ratio and weak velocity change on the other hand full waveform inversion sensitivity analysis showed that it is possible to detect the weak velocity change with the non optimal seismic input detectability was qualitative with variable degrees of accuracy depending on different inversion parameters we inverted the real 2d seismic data from the north sea with a greater emphasis on refracted and diving waves energy i e most of the reflected energy was removed for the shallow zone of interest after removing traces with offset less than 300 m the full waveform inversion results provided more superior detectability compared with the conventional 4d stacked reflection difference method for a weak shallow gas anomaly 320 m deep